i
LIBRARY
FACULTY OF FORESTRY
UNIVERSITY OF TORONTO
(13).
PLANT INDICATORS
THE RELATION OF PLANT COMMUNITIES
TO PROCESS AND PRACTICE
BT
FREDERIC E. CLEMENTS
PUBUSHED BT THE CaBNEGIE INSTITUTION OF WaSBINGTON
Washington, 1920
CARNEGIE INSTITUTION OF WASHINGTON
Publication No. 290
PRESS OF GIBSON BBOTHERS, INC.
WASHINGTON, D. C.
II
PREFACE.
The present book is intended to be a companion volume to "Plant Succes-
sion." The latter was planned to contain several chapters on the applications
of ecology, but these were omitted on account of the lack of space. Chief
among these was the consideration of succession as the primary basis for a
system of indicator plants, and this has been made the theme of the present
treatise. For the sake of clearness, it has been necessary to give a concise
account of the climax communities of the region concerned. The original
plan included a brief summary of the priseres and subseres of the various
cUmaxes, but the limitations of space have precluded this. The same reason
has made it desirable to deal with principles and examples in the three fields
of practice, rather than to attempt a complete account of the host of climax
and serai communities which serve as indicators. The general principles and
specific indicators have been tested repeatedly during the field work of the
past five years, and the treatment has profited from the fact that a special
inquiry into indicator relations throughout the West was made during the
season of 1918.
It is beheved that succession and indicators constitute the most essential
and useful form into which the results of research can be put for practical use.
They are the fundamental responses of plant and community to the conditions
in control, and hence contain their judgment as to the fitness of the environ-
ment in which they grow or are to be grown. Such responses require transla-
tion into familiar terms, and for this purpose the quantitative analysis of
habitats and responses by means of instruments and phytometers is indis-
pensable. Moreover, habitat and response vary not only with the develop-
ment of the community, but also in accordance with the phases of the climatic
cycle. The importance of the latter can hardly be overestimated, and it seems
certain that the climatic cycle must be accorded a unique position in all future
research and practice.
The indicator method will naturally have its greatest usefulness in new or
partly settled regions. While the results given apply only to western North
America, and to the western United States particularly, the principles and
methods are of universal application. They should be of especial value on
other continents where there is still a distinct frontier. Australia, South
Africa, and South America should furnish fertile soil for indicator investigations
and applications, while large portions of Asia and northern Africa should
possess almost equal promise for this work. Even in Europe and in other
thickly settled regions, indicator studies will have much value, and this will be
true everywhere that natural or semi-natural vegetation is found. Indeed,
it is probable that indicator methods in some form will come to be applied to
all cultural vegetation with the advance of quantitative ecology and the dis-
appearance of the artificial barrier between science and practice.
The author is under especial obligation to Dr. H. L. Shantz for many
helpful suggestions arising from the reading of the manuscript. Grateful
m
IV PREFACE.
acknowledgment is made of the indispensable help given by Dr. Edith Clem-
ents, who has assisted throughout the field work, made the larger number of
the photographs, and read the manuscript. The latter has also been read by
Dr. H. M. Hall and Dr. J. E. Weaver, to whom acknowledgment is given.
The author is indebted to Dr. Frances Long and Miss Rena Huber, who have
aided in many ways in the preparation of the manuscript and the illustrations.
I*rints for several of the forest illustrations have been furnished by Dr. G. E.
Nichols and Mr. C. G. Bates, and the graphs have been drawn by Professor
F. C. Kelton, to whom due acknowledgment is made.
Frederic E. Clements.
Tucson, Arizona, April 1919.
CONTENTS.
PAGE.
I. Concept and Histobt.
The practical aspect 3
The scientific aspect 3
HISTORICAL.
Agricultural Indicators.
Hilgard. 1860 5
Chamberlin, 1877 5
Merriam, 1898 6
Hilgard, 1906 8
Clements, 1910 9
Shantz, 1911 10
Kearney, Briggs, Shantz, McLane, and
Piemeisel, 1914 11
Shantz and Piemeisel, 1917 12
Shantz and Aldous, 1917 13
Weaver, 1919 13
Forest Indicators.
Cajander, 1909 14
Clements, 1910 14
Pearson. 1913-1914 15
Zon, 1915 16
Hole and Singh, 1916 16
Korstian, 1917 17
Grazing Indicators.
Smith, 1899 19
Bentley. 1902 20
Griffiths, 1901, 1904, 1907, 1910, 1915.... 21
Sampson, 1908, 1909, 1913, 1914 22
Jardine, 1908, 1909, 1910, 1913 23
Wooton, 1915, 1916 23
Jardine and Hurtt. 1917 24
Jardine and Anderson, 1919 24
Sarvis, 1919 25
Chresard and Water Requirement Studies.
Significance 26
The chresard 26
Gain, 1895 26
Kihlmann, 1890 27
Briggs and Shantz, 1912 27
The water requirement 28
CONCEPT.
General 28
Animals as indicators 29
Plant and community 29
Sequences 30
Direct and indirect sequences 31
Direction of indication 32
Scope 32
Materials 33
Basing studies 34
II. Bases and Cbiteria.
BASES AND UETHOD8 OF DETBBMINATION.
Fundamental relations 35
The Physical Basis.
Direct and indirect factors 36
Controlling and limiting factors 36
Chmatic and edaphic factors 37
Climates and habitats 38
Variation of climate and habitat 39
Inversion of factors 40
Measurement of habitats 42
The Physiological Basis.
Kinds of response 43
Effect of habit 43
Individuality in response 44
Effect of extreme conditions 44
Phytometera 46
The AssocicUioncd Basis.
Nature of association 47
Dominants 47
Equivalence of dominants 48
Absence of dominants 49
Subdominants 50
Secondary species 51
Plant and animal association 51
The Successional Basis.
Scope 51
Sequence of indicators 52
Major successions as indicators 53
The Experimental Basis.
Nature 53
Essentials 54
INDICATOB CRrrEBIA.
Nature and kinds of criteria 55
Species and genera 65
Life-Forms.
History 57
Pound and Clements, 1898-1900 57
Raunkiaer, 1905 58
Warming. 1908 69
Drude. 1913 60
Comparison of the systems 62
Vegetation-forms 62
Indicator significance of vegetation-forms 63
Habitat-Forms.
Concept and history 64
Warming's system 64
Modifications of Warming's system 65
Indicator value 66
Ecads 67
VI
CONTENTS.
PAGE.
II. Babes and Cbitbbia — Continued.
INDICATOR CBITERIA — OODtlDUed.
Growth-Formt.
N»tuw 68
Kinds 69
Indicator rdations 69
Standard plants for growth correlations . . 70
Competition-forms 71
Communitiet aa Indicators.
Value 72
Kinda of communities 72
Community structures 73
Altemes 73
Layers 74
Aspects 75
III. Kinds of Indicators.
Basis of distinction 76
factor indicators.
Basis and kinds 76
Quantitative sequences 77
Climatic and edaphic indicators 77
Water indicators 78
light indicators 79
Temperature indicators 81
Indicators of solutes 83
Saline indicators 83
Lime indicators 84
Aeration indicators 85
Indicators of factor-complexes 88
Soil indicators 88
Slope-exposiire indicators 88
Altitude indicators 89
Oiganism indicators 90
process indicators.
Nature 91
Kinds 91
Fire indicators 92
Lumbering indicators 93
Cultivation indicators 93
GrazinfE indicators 94
Indicators of irrigation and drainage 95
Construction indicators 96
Physiographic indicators 97
Climatic indicators 97
practice indicators.
Nature and kinds 98
PALKIC INDICATORS.
Paleo-ecology 99
Nature of paleic indicators 100
Kinds 101
Paleic indicators of climates and cycles. . . 103
Paleic indicators of succession 103
Plant indicatois of animals 104
Animal indicators of plants 104
rV. CuMAX Formations of Western
North America.
Nature 105
Tests of a climax 105
Stnieture and development 106
PAOB.
IV. Climax Formations of Western
North America — Continued.
Societies 107
Names of climax communities 109
Serai communities 109
Indicator significance of climax formations 111
Significance of succession Ill
Indicator value of disturbed areas 112
Summary of the climax formations 113
THE GRASSLAND CUMAX.
Stipa-Bouteltnia Formation.
General relations 114
Unity of the grassland 116
Correlation with climate 116
Use of weather records 116
Relationship of associations 118
Floristic relations 119
Ecological relations 120
Subdominants 120
Developmental relations 121
THE TRUE PRAIRIE.
Stipa-Koeleria Association.
Extent 121
Factor relations 123
Sequence of dominants 123
Sodetiea.
Nature 125
Control of dominants 125
Relation to consociation 126
Origin 126
Mixed societies 127
Aspects 127
Zones and alternes 128
Studies of prairie societies. 129
Clans.
Vernal clans 131
Estival clans 131
Serotinal clans 131
THE SUBCLIMAX PRAIRIE.
Andropogon Assodes.
Nature 131
Range 132
Factor relations 133
Sequence 133
Grouping 134
Societies and Clans.
THE MIXED PRAIRIE.
Stipa-BordeUma Association.
Nature 135
Effect of grazing and climatic cycles 135
Range 136
Grouping 137
Sequence of dominants 138
Societies of the Mixed Prairie.
Prevernal societies 139
Vernal societies 139
Estival societies 139
Serotinal societies 139
CONTENTS.
vn
PAOB.
IV. Clibiax Formations of Westebn
North America — Continued.
THE SHORT-GRASS PLAINS.
BulbUis-BouUloua Aaaociation.
Nature 139
Range 140
Grouping of dominants 141
Factor relations 142
Sequence of dominants 142
Societiea.
Prevernal societies 143
Vernal societies 143
Estival societies 143
Serotinal societies 144
Clans.
Prevernal clans 144
Vernal clans 144
Estival clans 144
Serotinal clans 144
THB DESERT PLAINS.
Ariatida^Bouteloiui Association.
Nature 144
Range 145
Rank of dominants 146
Grouping of dominants 146
Sequence of dominants 147
Societies.
Vernal societies 148
Estival societies 148
Serotinal societies 149
Clans.
THE BUNCH-ORA88 PRAIRIE.
Agropyrum-Stipa Association.
Nature 149
Range 149
Factor relations and sequence 151
Societies.
Prevernal societies 152
Vernal societies 152
Estival societies 152
Serotinal societies 152
Clans.
Prevernal clans 152
Vernal clans 152
Estival clans 152
Serotinal clans 152
THE SAGEBRUSH CLDCAX.
Atriplex-Artemisia Formation.
Nature 152
Unity of the formation 163
Range 154
Subclimax sagebrush 155
Associations 156
PAGE.
IV. Climax Formations of Western
North America — Continued.
THE BASIN SAGEBRUSH.
Atriplex-Artemisia Association.
Range 166
Rank and grouping 167
Correlations 168
Successional sequence 169
Societies.
Grass communities appearing as societies . 1 60
Vernal societies 160
Estival societies 160
Serotinal societies 160
THE COASTAL SAGEBRUSH.
ScUvior-Artemisia Association.
Range 160
THE DESERT SCRUB CLIMAX.
Larrea-Prosopis Formation.
Nature 162
Range 163
Unity of the formation 163
Structure of the formation 165
Summary of Dominants.
Associations 166
Relation to other formations 167
THE EASTERN DESERT SCRUB.
Larrea-Flourensia Association.
Correlations and sequence 168
Societies.
THE WESTERN DESERT SCRUB.
Larrea-Franseria Association.
Nature 170
Extent 171
Structure 172
Groupings 172
Factor relations 173
Successional relations 174
Root relations 176
Societies and Clans.
THE CHAPARRAL CLIMAX.
Quercus-Ceanothus Formation.
Nature 177
Unity of the chaparral formation 178
Climatic relations 178
Origin and succession 179
Range and extent 180
Structure of the formation 181
Grouping of dominants , 181
Associations 183
THE PETRAN CHAPARRAL.
Cercoearpus-Quereus Assoeiaiion.
Nature and extent 183
Contacts 184
Groupings 185
Equivalence of dominants 186
VIII
CONTENTS.
PAGE.
IV. ChOLkX Formations or Western
I North America — Ck)ntinued.
THB PSTBAN CHAPARRAL — Continued.
Societies.
Venial societies 187
Estival societies 187
Serotinal societies 187
THE 8UBCLIMAX CHAPARRAL.
Rhu»-Querciu Aasociea.
Nature 187
Elzfent and contacts 188
Groupings 189
Relations of the dominants 189
(Societies.
THE COASTAL CHAPARRAL.
Adenostoma-Ceanothua AssocicUion.
Nature and extent 190
Groupings 191
Factor and serai relations 192
Societies.
Prevemal societies 193
Vernal societies 193
Estival societies 193
THE WOODLAND CLUIAX.
Pinus-Juniperua Formation.
Nature 193
Range and extent 194
Unity of the formation 195
Structure of the formation 196
Contacts 197
THE PINON-CBDAB WOODLAND.
Pimis-Juniperus Association.
Nature and extent 197
Societies.
Shade societies 199
THE OAK-CEDAB WOODLAND.
Quercus-Juniperus AasocicUion.
Nature and extent 200
Factor relations 201
Societies.
Shade societies 202
THE PINE-OAK WOODLAND.
Pinus-Quercus Aaaociation.
Nature and extent 202
THE MONTANE FOREST CLIMAX.
Pinus-Pseudotsxiga Formation.
Nature 205
Extent 205
Unity of the formation. 205
Rdationship and contacts 206
Associations 207
PAGE.
IV. Climax Formations of Western
North America — Continued.
THE PETRAN MONTANE FOREST.
Pinua-Paeudotauga Aaaociation.
Extent 207
Groupings 208
Factor relations 209
Serai relations 209
Sodetiea aAd Ckma.
THE SIBRRAN MONTANE FOREST.
Pinua Aaaociation.
Extent 211
Groupings 212
Factor and sersd relations 212
Societies.
Shrubs 213
Herbs 214
THE COAST FOREST CLIBIAX.
Thuja-Tsuga Formation.
Nature 214
Extent 214
Unity 215
Relationship and contacts 215
Associations 216
THE CEDAR-HEMLOCK FOREST.
Thuja-Tauga Aaaociation.
Nature and extent 217
Groupings 217
Factor and serai relations 218
Sodetiea.
Shrubs 219
Herbs 219
THE LARCH-PINE FOREST.
Larix-Pinua Aaaociation.
Nature and extent 219
Groupings 220
Factor and serai relations 220
Societies.
THE SUBALPINE FOREST CLIMAX.
PiceorAbies Formation.
Nature 222
Extent 222
Unity 222
Relationship and contacts 223
Associations 224
THB PETRAN 8CBALPINB FOREST.
Picea-Abies AssociaHor*.
Extent 224
Groupings 225
Factor and serai relations 225
Societies.
CONTENTS.
IX
PAGE.
IV. Climax Formations of Western
North America — Continued.
THE SIERRAN SUBALPINE FOREST.
Pinua-Tsuga Association.
Extent 226
Groupings 227
Factor and serai relations 228
Societies.
THE ALPINE MEADOW CLIMAX.
Carex-Poa Formation.
Nature 228
Extent 229
Unity 229
Relationship and contacts 230
Associations 231
THE PETRAN ALPINE MEADOW.
Carex-Poa Association.
Extent 232
Dominants.
Groupings 232
Factor and serai relations 233
Societies.
Vernal societies 234
Estival societies 234
THE SIERRAN ALPINE MEADOW.
Carex-Agrostis Association.
Extent 234
Dominants.
Groupings 235
Factor and serai relations 235
Societies.
V. Agbictjlttjral Indicators.
General relations 237
LAND CLASSIFICATION.
Nature 237
Relation to practices 238
Proposed bases of classification 238
The indicator method of land classification 240
Use of climax indicators 240
Soil indicators 241
Sbantz's results 242
A SYSTEM OF LAND CLASSIFICATION.
Bases 245
Classification and use 245
Methods 246
PAGE.
V. Agricultural Indicators — Continued.
CLIMATIC CYCLES.
Nature 247
The 11-year cycle 247
Evidences 248
Periods of drought 250
Recurrence of drought periods 251
Significance of the sun-spot cycle 252
Prediction of drought periods 253
Utilization of cycles 254
farming indicators.
Types of farming 255
Relation of types of farming to indicators 255
Edaphic indicators of types of farming. . . 256
CROP indicators.
Nature and kinds 257
Climatic indicators of the types of crops. . 258
Climatic indicators of kinds of crops 259
Climatic indicators of varieties 259
Life zones and crop zones 260
Edaphic indicators of crops and methods . . 26 1
Indicators of native or ruderal forage
crops 262
agricultural PRACTICE AND CLIMATIC
CYCLES.
Cycles of production 262
The excess-deficit balance 264
Anticipation of cycles 266
VI. Grazing Indicators.
Kinds of grazing 270
GRAZING TYPES.
Kinds of grazing indicators 271
Significance of climax types 272
Formations as indicators 273
Associations as indicators 273
Consociations as indicators 274
Local grazing types 275
Savannah as an indicator 276
Kinds of savannah 278
Savannah in relation to fire and grazing . . . 279
Significance of serai types 279
Prisere communities as indicators 280
Subsere communities as indicators 282
Fire indicators and grazing 283
CARRYING CAPACITT.
Nature and significance 284
Determining factors 284
Relation to communities and dominants. . 285
Nutrition content 286
Relation to climatic cycles 292
Relation to rodents 293
Relation to herd and management. 293
Measurement of carrying capacity 294
Present and potential carrying capacity. . 295
CONTENTS.
N«I«M.
PAOB.
VI. Obauiio Ixdioatobs — Continued.
OTKMoiunxa.
205
297
Indkaton of OTVfinnns 297
SoflfatiwMiiKlkttton 298
Hdftfurutw M indioaton 299
CMd M indioaton 300
BbrabaMindkMton 300
Ammi^u as indioaton 301
Ptairto and plains indieatora 302
DMirt plaint indieatora 302
DuiMili t' *— prairie indicators 303
Great Basin indieatora 304
Orecirasinc in the past 304
Sucweasion and cycles 307
Relation of tall-grasses and short-grasses . 308
Overgraiing cycles 309
RANGE IMPROVEMENT.
Hiatory
AvrequiBtea
IhwiiiMil faetors.
Pkoperatoeking..
Rotation graxing.
310
311
312
312
314
Rodent eradication 316
Eradication of poisonous plants 317
Eradication of weeds and cacti 319
Eradication of brush 320
Manipulation of the range 321
Plant introduction on the range 322
Pnrequisites for seeding and planting .... 324
New investigations 326
Forage development 327
Water development 328
Herd management 329
EaaENTIALS OP A ORAZINO POLICT.
A proi>er land system 330
Esbentials 330
PAOB.
VI. Grazing Indicators — Continued.
ESSENTIALS OP A ORAZINO POLICT — Continued.
The Kent grazing bill 331
Classification and range surveys 334
Production cycles 334
Ranch management surveys 335
VII. Forest Indicators.
Nature 336
Kinds of indieatora 336
PORBST types.
Bases 337
Comparison of views 342
Forest sites 343
Succession as a basis 344
Significance 345
climatic and edaphic indicators.
Climatic indieatora 345
Edaphic indicators 348
Water-content indicators 348
Light indicators 349
Site indicators 349
Growth as an indicator 360
Burn indieatora 353
Grazing indieatora 355
Cycle indieatora 367
PLANTING indicators.
Kinds 357
Prerequisites for planting and sowing .... 358
Use of climatic cycles 359
Reforestation indieatora 369
Afforestation indieatora 362
Bibliography 364
Index 375
LIST OF ILLUSTRATIONS.
PLATES.
PAGE.
Plate A. Quadrat-bisect in the half-
gravel slide, Alpine Laboratory,
Colorado 32
Plate I.
A. Short-grass (Bouteloua gracilis) on
hard land, Colorado Springs,
Colorado 10
B. Wire-grass (Aristida purpurea) on
short-grass land, Walsenburg,
Colorado 10
Plate 2.
A. Spirostachys occidentalis in salt
marsh, Bakersfield, California . . 12
B. Shadscale (Atriplex confertifolia) in-
dicating saline land, Rock Springs,
Wyoming 12
Plate 3.
A. Lodgepole forest (Pinus contorta) in-
dicating fire. Long's Peak, Colo- 14
rado
B, Aspen woodland (Populus tremu-
loides) arising from root-sprouting
due to fire. Long's Peak 14
Plate 4.
A. Protected pasture in Aristida-Boute-
loua association, Santa Rita
Range Reserve, Tucson, Arizona 22
B. Fenced quadrat in rotation pasture,
Bouteloua eriopoda consociation,
Jornada Range Reserve, Las Cru-
ces, New Mexico 22
Plate 5.
A. Dominant Agropymm glaucum and
subdominant Tradescantia vir-
gjniana in mixed prairie.Winner,
South Dakota 30
B. Agropymm glaucimi in roadway, in
sagebnish, indicating the rela-
tion of water-content to com-
petition. Red Desert, Wyoming . . 30
Plate 6.
A. Lowland mesquite (Prosopis juli-
flora) at 2,500 feet in the San
Pedro Valley, Arizona 40
B. Foothill mesquite meeting oak at
4,600 feet, Patagonia Mountains,
Arizona 40
Plate 7.
A. Phytometer station in grassland at
6,000 feet, Colorado Springs,
Colorado 46
B. Battery of oats, gravel-slide btation,
Minnehaha, Colorado 46
C. Battery of oats, brook-bank station,
Minnehaha, 46
Plate 8.
A. Anogra albicaulia as a serai dominant
in a fallow field, Agate, Nebraska 48
B. Stipa comata as a climax dominant of
the mixed prairie, Chadron,
Nebraska 48
Plate 9.
A. PentstemoD gracilis as a climax sub-
dominant in mixed prairie, Gor-
don, Nebraska . .* 60
Plate 9 — Continued. page.
B. Pedicularia crenulata as a serai sub-
donunant in a Juncus-Carez
swamp, Laramie, Wyoming 50
Plate 10.
A. Stages of a hydrosere from floating
plants to forest. Pike's Peak,
Colorado 52
B. Stages of a burn subsere from the
pioneer annuals to the chaparral
climax, San Luis Rey, California 62
Plate 11.
A. Normal Campanula rotundifolia at
8,300 feet, and alpine ecad at
14,100 feet. Pike's Peak, Colorado 68
B. Shade ecad and normal Gentiana
amarella at 8,300 feet and alpine
ecad at 13,000 feet. Pike's Peak. 68
C. Alpine ecad, normal form and shade
ecad of Androsace septentrionalis.
Pike's Peak 68
Plate 12.
A. Alternation of sagebrush on southerly
slopes and Douglas fir on north-
erly ones. King's Ranch, Colo-
rado 74
B. Layers of Impatiens, Helianthus and
Acalypha in oak-hickory forest.
Weeping Water, Nebraska 74
Plate 13.
A. Typha altemes indicating pools in a
salt-marsh, Goshen, California. 78
B. Jimiperus indicating seepage lines in
hills of Mancos shale. Cedar,
Colorado 78
Plate 14.
A. Fragaria and Thalictrum, indicators
of medium shade in montane for-
est, Minnehaha, Colorado 80
B. Mertensia sibirica, indicator of deep
shade in montane forest, Long's
Peak, Colorado 80
Plate 16.
A. Hordetmi plain and Dondia hum-
mocks indicating differences in
salt-content, Great Salt Lake,
Utah 84
B. Commimities of Phleimi-Equisetum
and of Juncus-Heleocharis mark-
ing differences in water-oontent
and aeration, Sapinero, Colorado . 84
Plate 16.
A. Andropogon hallii indicating stable
sandy soil in sandhills. Agate,
Nebraska 88
B. Altemes of sagebrush and aspen-
Douglas fir forest indicating
various slope-exposures. King's
Ranch, Colorado 88
Plate 17.
A. Alpine fir (Abies laaiooarpa) at timber
line, showing the dwarfing eflfect
of high altitudes. Long's Peak,
Colorado 90
B. An alpine dwarf, Rydbergia grandi-
flora. Pike's Peak. Colorado 90
ni
ILLUSTRATIONS.
PAOB.
Plats 1&
A. CarMM rtr"*^* abowinc awto of
cildedfli«lnr(CoUpt««ebnmi(l«)
Tueaon. Arisona 00
B. Datoa ■pino— dying >e a reault of the
work of kancaroo-rata (Dipodo-
mya dewrti), Glamio, California 90
Platb 19.
A. Aapeo indioating an early fire, and
aagebniah altemea, a recent one,
Strawbony Can>-on, Utah 92
B. Artemiiia frUtida indicating an old
fallow field. Warbonnet Canyon,
Pine Ridge. Nebraska 92
Plat* 20.
A. Opuntia comanchica indicating over-
grased pastures, Sonora, Texas. 96
B. Euphorbia ni.irRinata marking road-
ways, Walscnburg, Colorado ... 96
Plate 21.
A. Stipa Andropogon association, Lin-
coln. Nebraska 120
B. Stipa spartea consociation, Halsey,
Nebraska 120
C. Andropogon scoparius consociation.
Medora, North Dakota 120
PLATB22.
A. Koderia cristata and Andropogon
■copaiius association. Agate. Ne-
braska 124
B. Erigeron ramosus society, Lincoln,
Nebraska 124
C. Detail of society of Paoralea tenui-
folia and Erigeron ramosus. Lin-
coln. Nebraska 124
Plat* 23.
A. Association of Andropogon furcatus.
nutans, soopariua and Bouteloua
racemoea. Peru, Nebraska 132
B. Society of Silphium laciniatum in
Andropogon-Agropyrum associa-
tion. Salina. Kansas. 132
Platb 24.
A. Stipa comata consociation. Pine
Ridge. South Dakota 136
B. Agropyrum glaucum consociation,
Winner. South Dakota 136
C. Detail of aaaodation of Stipa comata.
Sporoboluscryptandrusand Bou-
teloua gracilis. Colorado Springs.
Colorado 136
Platb 25.
A. Agropynun glaucum and Bouteloua
gracilis aaaodation, Vermpjo Park,
New Mexico 138
B. Detail of AKropyrum-Bulhilia asso-
ciation. Winner, South Dakota. . 138
C. Polygala alba society in Bouteloua
consociation. Interior. South
Dakota 138
Plate 26.
A. Bouteloua-Bulbilis association, with
Bubclimax of Andropogon scopa-
rius and Bouteloua racemosa on
butte, Stratford, Texas 140
B. Dense sod of BulbilLs and Bouteloua,
Goodwell, Oklahoma 140
PAGE.
Plate 26 — Continued.
C. Open sod of Bouteloua. Dumas,
Texas 140
Plate 27.
A. Muhlenbergia gracillima and Boute-
loua gracilis. Manitou. Colorado. 142
p. Detail of Bouteloua KracilLs, Ver-
mejo Park, New Mexico 142
C. Hilaria janiesii on a saline plain.
Delta, Colorado 142
Plate 28.
A. Bouteloua-Hilaria association. Em-
pire Valley, Arizona 144
B. Bouteloua rothrockii and Aristida
divaricata, Santa Rita Reserve,
Tucson, Arizona 144
C. Bouteloua racemosa consociation.
Oracle, Arizona 144
Plate 29.
A. Bouteloua- Aristida association.
Sweetwater. Texas 146
B. Bouteloua gracilis, Scleropogon brevi-
folius and Hilaria mutica (valley).
B. eriopoda, gracilis, racemosa
(hills). Van Horn. Texas 146
C. Bouteloua gracilis, hirsuta. eriopoda,
and Aristida divaricata, Jornada
Reserve, Las Crucea, New Mex-
ico 146
Plate 30.
A. Agropyrum-Festuca association,
The Dalles, Oregon 150
B. Agropyrum consociation. MisBoula,
Montana 150
C. Agropyrum consociation on "scab"
land. John Day Valley, Oregon. 150
Plate 31.
A. Stipa setigera consociation in track-
way, Fresno, California 150
B. Avena fatua consocies, with relicts of
Stipa setigera and eminens. Rose
Canyon, San Diego, California. . 150
Plate 32.
A. Artemisia tridentata consociation,
Henefer. Utah 154
B. Artemisia tridentata consociation,
Garland, Colorado 154
C. Artemisia arbuscula consociation,
Evanston, Wyoming 154
Plate 33.
A. Subclimax sagebrush in bad-land val-
leys. Hat Creek, Nebraska 158
B. Altemes of Artemisia and Kochia,
Strevell, Idaho 156
C. Sarcobatus, Chrysothamnas, Atri-
plex and Artemisia, Vale, Oregon 156
Plate 34.
A. Atriplex confertifolia consociation.
Delta, Colorado 158
B. Atriplex corrugata consociation,
Thompson, Utah 168
C. Atriplex lentiformis consociation.
Salton Sea. California 158
Plate 35.
A. Contact of Basin sagebrush with
Coastal sagebrush and chaparral,
Campo. California 160
ILLUSTRATIONS.
XIII
PAQB.
Plate 35 — Continued.
B. Artemisia califomica, Salvia melli-
fera and ErioKonum faaciculatum
sasociation, Elainore, California. 160
C. Coastal saRebrush with Adenoatoma
in ravines, Temecula, California. 160
Plate 36.
A. Larrea consociation, Stockton,
Texas 168
B. Larrea-Flourensia association, Pecos,
Texas 168
C. Larrea plain. Sierra Blanca, Texas. 168
9 LATE 37.
A. Larrea consociation, Tucson, Ari-
»ona 170
B. ProBopis consociation, San Pedro
Valley, Arizona 170
C. Parkinsonia torreyana and Acacia
greggii, Tucson, Arizonia 170
Plate 38.
A. Larrea and Franseria dumosa, Ajo,
Arizona 172
B. Larrea, Prosopis and Hilaria rigida,
Ajo, Arizona 172
C. Encelia farinosa on lava ridge, Ajo,
Arizona 172
Plate 39.
A. Cereus-Encelia on lava ridge with
Larrea below, Tucson, Arizona. 174
B. Parkinsonia microphylla and Cereus
giganteus on foothills of Tucson
mountains 174
C. Fouquiera splendens consociation,
Santa Rita Reserve 174
Plate 40.
A. Fouquiera subclimax in Larrea plain,
Tucson, Arizona 176
B. Opimtia fulgida consociation, San
Pedro Valley, Arizona 176
C. Opuntia discata, fulgida and spino-
sior, Tucson, Arizona 176
Plate 41.
A. Quercus-Rhus-Cercocarpus associa-
tion. Manitou, Colorado 182
B. Detail of sfime, Quercus and Rhus in
foreground, Cercocarpus behind,
Manitou, Colorado 182
C. Cercocarpus parvifolius consociation.
Chugwater, Wyoming 182
Plate 42.
A. Quercus-Cercocarpus-Fallugia chap-
arral, Milford, Utah 184
B. Same showing contact with sage-
brush, Cercocarpus Icdifolius in
foreground, Milford, Utah 184
Plate 43.
A. Rhus glabra consocies, Peru, Nebras-
ka , 188
B. Quercus virens and undulata, Ed-
wards Plateau, Sonora, Texas.. 188
Plate 44.
A. Chaparral hills and sagebnish val-
ley. Pine Valley, California 190
B. Adenoetoma-Ceanothus association,
Descanso, California 190
Plate 45.
A. Pinus-Jimipenu association. Grand
Canyon, Arixona 198
PAOB.
Plate 45 — Continued.
B. Detail of pifion-eedar woodland,
Delta, Colorado 198
Plate 46.
A. Quercus-Juniperus association, Santa
Rita mountains, Arizona 200
B. Quercus arizonica consociation, Santa
Rita mountains 200
Plate 47.
A. Pinus-Quercus association, Chico,
California 202
B. Quercus douglasii consociation. Red
Bluff, California 202
Plate 48.
A. Pinus ponderosa consociation. Flag-
staff, Arizona 206
B. Pinus ponderosa consociation. Bend,
Oregon 206
C. Pinus ponderosa consociation. Black
Hills, South Dakota 206
Plate 49.
A. Pseudotsuga mucronata consocia-
tion, Alpine Laboratory, Pike's
Peak 210
B. Detail of Pseudotsuga-Abies forest,
Cameron's Cone, Pike's Peak . . 210
Plate 50.
A. Pinus ponderosa-lambertiana asso-
ciation. Prospect, Oregon 212
B. Pinus, Libocedrus, Abies, and Pseu-
dotsuga, Yosemite National Park,
California 212
Plate 51.
A. Pseudotsuga, Thuja, and Tsuga. Rai-
nier National Park, Washington. 216
B. Sequoia sempervirens consociation,
Muir Woods, Mount Tamalpais,
California 216
Plate 52.
A. Pseudotsuga, Tsuga, and Pinus mon-
ticola, Carson, Washington 220
B. Pseudotsuga, Pinus monticola, Larix,
and Thuja, Priest River, Idaho. . 220
Plate 53.
A. Picea-Abies association at Monarch
Pass, Salida, Colorado 224
B. Picea-Abies association on Uncom-
pahgre Plateau, Colorado 224
C. Picea-Pinus aristata at timber-line.
King's Cone. Pike'is Peak 224
Plate 54.
A. Tsuga lyallii consociation. Crater
Lake, Oregon 226
B. Abies magnifica consociation. Glacier
Point, Yosemite National Park,
California 226
Plate 55.
A. Carex-Poa asaociBtion, King's Cone,
Pike's Peak 228
B. Carex consociation. Campanula so-
ciety. Pike's Peak 228
Plate 56.
A. Polygonum bistorta society. Pike's
Peak 232
B. Campanula rotundifolia society,
Pike's Peak 232
C. Mertensia alpina society. Pike's
Peak 232
MV
ILLUSTRATIONS.
PAOB.
Plats 67.
A. Cam>Acro«tk aatoeUtioo, Mount
Bainkr. WMbiactoo 234
B. LapiBiM Tnlwaifaw and ValeriuiA
ritnhnwh tooltty. Mount Rainier 234
Plats ft&
A. AbandoBod farm. Wood, South Da-
koU 238
B. Flald ol eom and midan graai during
the drou^t of 1917. Glendive.
Montana 238
Plats W
A True prairie indicating agricultural
land. Lincoln, Nebraska 240
B. Oak chaparral indicating gracing
land. Sonora. Texas 240
C. Aajmn, spruce and pine indicating
forest land. Minnehaha, Colorado 240
Plats 60.
A. Artemisia filifolia indicating sandy
soil. Canadian River, Texas 242
B. Grama and buffalo-grass on hard-
land. Goodwell, Oklahoma 242
C. Atriplez nuttallii indicating non-
agricultural saline land, Thomp-
■on. Utah 242
Plats 61.
A. Tall valley sagebrush indicating a
deep soU for irrigation, Garland,
Colorado 256
B. A legume, Lupinua plattenais, indi-
cating a rich moist soil, Monroe
Canyon. Pine Ridge, Nebraska. . 256
C. BaBet Stipa and Balsamorhisa in
■■cebrush, indicating a bunch-
grass climate for dry-farming.
Hagerman. Idaho 256
Plats 62.
A. Mixed prairie (Stipa oomata) indi-
cating dry-farming. Scenic, South ^
Dakoto 25^
B. Tall-grass (Andropogon scopariua)
indicating humid farming, Madi- ^
•on. Nebraska 2Si
C. Bunch-grass prairie (Agropyrum-
Festuca) indicating dry-farming
with winter rainfall.The Dalles.
Oregon 258
Plats 03.
A. Ruderal crop of Russian thistle, Sal-
sola, in a field of feterita, Tulia,
Texas 268
B. Ruderal crop of horseweed, Erigeron
canadensis, in a fallow field. Good-
well, Oklahoma 262
Plats 64.
A. Grass type, Andropogon-Bulbilis-
Boateloua. Smoky Hill River,
Hays. Kansas 272
B. Weed type. Erigecon, Geranium, etc.,
in aspen forest. Pike's Peak. Col-
orado 272
C. Browse tsrpe, Artemisia tridentata,
Beolah. Oregon 272
PAOS.
Plats 65.
A. Savannah of desert scrub, Flourensia-
Larrea-Prosopis, and desert plains
grasses, Bouteloua gracilis, erio-
poda and racemosa. Van Horn,
Texas 276
B. Bum park in subalpine forest, Un-
compahgre Plateau, Colorado . . 276
C. Bum park of Wyethia and Artemisia
in chaparral, Logan, Utah 276
Plate 66.
A. . Grass park of Elymus and Agropyrum
arising from sagebrush, Boise,
Idaho 278
B. Sagebrush dying out as a result of
competition with Agropyrum,
Craig, Colorado 278
Plate 67.
A. Serai stages in sandhills, the sub-
climax grasses Andropogon and
Calamovilf a. Agate, Nebraska . . . 280
B. Serai stages in bad lands, Atriplex
corrugata, nuttallii, and conferti-
folia the chief dominants, Cisco,
Utah 280
Plate 68.
A. Bromus tectorum marking a bum in
sagebmsh, Boise, Idaho 282
B. B}rodium cicutarium indicating
trampling in desert plains grass-
land, Oracle, Arizona 282
Plate 69.
A. Tobosa "swag," Hilaria and Sclero-
pogon subclimax to desert plains
grassland. Las Cruces, New Mex-
ico 284
B. Play a in the Bulbilis subclimax stage,
the old shore-line marked by
Euphorbia, Texhoma, Oklahoma. 284
Plate 70.
A. Mixed turf of tall-grass (Agropyrxim)
and short-grass (Bulbilis), Win-
ner, South Dakota 286
B. Pure turf of short-grass (Bulbilis),
Ardmore, South Dakota 286
Plate 71.
A. Bouteloua-Aristida association in
1917, Santa Rita Reserve, Tuc-
son, Arizona 292
B. The same area in 1918 after serious
drought and overgrazing by cat-
tle and rodents 292
Plate 72.
A. Denuded area about a kangaroo-rat
mound in grassland, Santa Rita
Reserve, Tucson, Arizona 294
B. General denudation by kangaroo-
rats in desert scrub, Ajo, Arizona. 294
Plats 73.
A. Reiict Bouteloua and Aristida indi-
cating former grass cover in des-
ert scrub, Tucson, Arizona 296
B. Relict Stipa and Balsamorhiza indi-
cating replacement of grassland
by sagebrush, Hagerman, Mon-
tana 296
ILLUSTRATIONS.
XV
PAGE.
Plat* 74.
A. Aristida purpurea and divarioata in-
dicating moderate overgraiing on
Bulbilis plains, Texhoma, Okla-
homa 298
B. An annual, Lepidiumalysaoides, indi-
cating complete overgraring in a
pasture. Fountain, Colorado 298
Plate 75.
A. Grindelia indicating overgraiing in
original Stipa bunch-grass prairie,
Williams, California 300
B. Vemonia indicating overgraiing in
short-grass plains, Stratford,
Texas 300
Plate 76.
A. Gutierreiia and Aristida in short-
grass plains, Albuquerque, New
Mexico 300
B. Yucca and Aristida in mixed prairie,
Hays, Kansas 300
Plate 77.
A. Opimtia polyacantha indicating over-
grazing in mixed prairie, Guern-
sey, Colorado 302
B. Prosopis and Calliandra indicating
overgrazing in desert plains, Santa
Rita Reserve, Tucson, Arizona. 302
Plate 78.
A. A summer annual. Euphorbia mar-
ginata, indicating complete over-
grazing in a pasture. Fountain,
Colorado 304
B. A winter annual, Eschscholtzia mexi-
cana, indicating both overgrazing
of grasses'andj'grazing capacity,
Santa Rita Reserve, Tucson,
Arizona 304
Plate 79.
A. Stipa setigera indicating the original
bunch-grass prairie, Fresno, Cali-
fo""a 306
B. Avena fatua on bunch-grass land.
Rose Canyon, San Diego, Cali-
fornia 306
C. Festuca mjoirus and Bromus hordea-
ceus on bunch-grass land, Com-
ing, California 306
Plate 80.
A. Mixed prairie of Andropogon-Boute-
loua racemosa and BiJbilis-Bou-
teloua gracilis, Wilf»on, Kansas. . 308
B._^The same prairie in an overgrazed
pasture, showing pure short-grass
sod, Wilson, Kansas 308
Plate 81.
A. Isolation transect in Stipa-Bouteloua
pasture, Mandan, North Dakota. 314
B. Isolation transect in Agropyrum-Bul- "^
bilis pasture, Ardmore, South
I>*kota 314
PAOB.
Plate 82.
A. Rodent exclosure, showing combined
effect of cattle and rodents on the
crop of winter annuals, chiefly
poppy (Esch.scholtzia mexicana),
Santa Rita Reserve 316
B. Difference in yield of poppies in ro-
dent exclosure, cattle exclosure,
and pasture, Santa Rita Reserve. 316
Plate 83.
A. Wheat-grass (Agropyrum glauctun)
following sagebrush after clear-
ing, Brookings, Oregon 320
B. Bunch-grass (Agropymm spicatum)
following fire in sagebrush, Boise,
Idaho 320
Plate 84.
A. Mixed grazing type of oak chaparral
and grass, Sonora Grazing Sta-
tion, Edwards Plateau, Texas . . 326
B. Mixed type of tall-grass (AgropjTum)
and short-grass (Bulbilis-Boute-
loua) with relicts of Sarcobatus,
Ardmore Station, South Dakota. 326
Plate 85.
A. Park of Nolina and grass in oak chap-
arral, Sonora Grazing Station,
Edwards Plateau, Texas 328
B. Yucca radiosa in desert plains. Em-
pire Valley, Elgin, Arizona 328
Plate 86.
A. Climax subalpine forest of Abies and
Pinus as a climatic indicator,
Yosemite National Forest, Cali-
fornia 336
B. Consocies of Rudbeckia occidentalis
as an edaphic indicator of clearing
and fire, Utah Experiment Sta-
tion, Ephraim 336
Plate 87,
A. Chamaebatia foliolosa indicating fire
in pine forest, Yosemite National
Park, California 354
B. Ceanothus velutinus indicating fire in
pine forest. Bums, Oregon 354
Plate 88.
A. Anaphalis and Epilobium indicating
a recent bum. Wind River Ex-
periment Station, Washington . . 354
B. Pteris and Rubus indicating fire fol-
lowing one marked by Arbutus,
Prunus, etc., Pseudotsuga forest,
Eugene, Oregon 354
Plate 89.
A. Pine reproduction in a fenced area.
Fort Valley Experiment Station,
Ariiona 356
B. Fenced quadrat showing effect of
grazing upon reproduction. Cliffs,
Ariiona 356
XVI
ILLUSTRATIONS.
Plate 90.
A. Reproduction cycle of Picea engel-
manni, Uncompahgre Plateau,
Colorado 358
B. Extension of Junipcrus into sage-
brush during wet phase of cycle,
Milford, Utah 358
Plate 91.
A. Arbutus indicator of reforestation
sites, Pseudotjiuga f orest.Eugene,
Oregon 360
PAQB.
Plate 91 — Continued.
B. Reproduction of Pseudotsuga from
seed stored in soil, Wind River
Experiment Station, Washington. 360
Plate 92.
A. Salix and Ceanothus indicating plant-
ing site in sandhills, Halsey, Ne-
braska 362
B. Three-year-old plantation of jack
pine (Pinus divaricata) in sand-
hills, Halsey, Nebraska 362
C. Jack pines 10 years after transplant-
ing, Halsey, Nebraska 362
TEXT-FIGURES.
PAGE.
1. Zones of a fairy ring due to Agaricus
tabularis: A and C, during a moist
period; B, during a dry period. . . 11
2. Diagram of the climax and serai com-
munities of the formation 73
3. Monthly and total rainfall in the
grassland climax 117
4. Map showing the percentage of annual
precipitation between April 1 and
September 30 119
5. Monthly and total rainfall in the
Basin sagebrush association 153
6. Monthly and total rainfall in the desert
scrub climax 164
7. Monthly and total rainfall in the
chaparral climax 179
8. Monthly and total rainfall in the
woodland climax 195
9. Monthly and total rainfall in the
montane forest 206
10. Monthly and total rainfall in the
Coastal forest 215
11. Monthly and total rainfall in the
Petran subalpine forest 223
12. Monthly and total rainfall for the
alpine meadow climax, sununit
of Pike's Peak. 14,100 feet 233
13. The 11-year cycle during the last 250
years, as shown by the yellow
pine and Sequoia 248
PAGE.
14. Double and triple sun-spot cycle in
yellow pine from 1700 to 1900
A. D 250
15. 2-year cycle in a sequoia 263
16. Graph of total and seasonal rainfall at
Williston, North Dakota 264
17. Graph of total and seasonal rainfall at
Cheyenne, Wyoming 265
18. Graph of total and seasonal rainfall at
Akron, Colorado 266
19. Graph of total and seasonal rainfall at
Amarillo, Texas 267
20. Cycles of rainfall in the Ohio Valley,
and in Illinois 269
21. Cycles in the yield of corn and in the
rainfall of its critical period of
growth 269
22. Pastures for the intensive study of
carrying capacity and rotation
grazing, Mandan, North Dakota. 313
23. Isolation transect for measuring cyclic
changes in yield under protection
and under grazing 314
24. Arrangement of corrals, sheds and
scales, Mandan, North Dakota . . 315
25. Indicators of planting sites in the vari-
ous zones, Utah Experiment Sta-
tion, Ephraim 361
PLANT INDICATORS
THE RELATION OF PLANT COMMUNITIES
TO PROCESS AND PRACTICE
By Frederic E. Clements
I. CONCEPT AND HISTORY.
The practical aspect. — Every plant is a measure of the conditions under which
it grows. To this extent it is an index of soil and climate, and consequently an
indicator of the behavior of other plants and of animals in the same spot. A
vague recognition of the relation between plants and soil must have marked
the very beginnings of agriculture. In a general way it has played its part in
the colonization of new countries and the spread of cultivation into new areas,
but the use of indicator plants in actual practice has remained slight. It is
obviously of greatest importance in newly settled regions. However, it is in
just these regions that experience is lacking and correlation correspondingly
difficult. In fact the pioneer is often misled by his endeavor to transfer the
experience gained in his former home to a new and different region. Differ-
ences of vegetation and climate, and often of soil as well, make a wholly new
complex of relations. As a consequence, the settler is very apt to go astray in
reaching conclusions as to the significance of a particular plant. As the coun-
try becomes more settled, experience accumulates and makes it increasingly
possible to recognize helpful correlations. But this period usually passes too
quickly to establish a procedure before the native plants have disappeared,
except from roadsides, meadows, and pastures. The manner and degree of
utiUzation of natural meadows and pastures are clearly indicated by the
plants in them. Yet it is exceptional that these indicators are recognized and
made use of by the farmer.
The scientific aspect. — On the scientific side, the concept of indicators could
hardly be expected to emerge until plant physiology had made a b^inning.
Looking backward, one discerns something of this idea in the studies of vege-
tational changes by King (1685:950), Degner (1729), Buffon (1742:234, 237),
and Biberg (1749 : 6, 27) .^ It is likewise suggested in the description of stations
by Linn6 (1751:265) and especially by Hedenberg (1754:73). The basic
correlations were made definite by De Luc (1806: Plant Succession, 10) in his
studies of succession in peat-bogs and by Schouw (1823: 157, 166) in the clas-
sification of plants by habitats. The idea is more or less in evidence in the
long series of observations and discussions relating to the chemical theory of
the influence of soils. The chief proponents of the chemical theory were Unger
(1836), Sendtner (1854), Naegeli (1865), FUche and Grandeau (1873), Bonnier
(1879), Contejean (1881), Hilgard (1888, 1906), and Schimper (1898, 1903).
The founder of the physical theory was Thurmann (1849), though his views
necessarily placed his results in more or less harmony with the water-content
classification of Schouw. The century-old controversy over the chemical
theory has centered around the question of the importance of Ume in the soil.
While the broadening of ecological research has thrown this question more and
more into the background, there is still anything but unanimity of opinion
concerning it. While it is felt that the problem can be solved only by more
comprehensive and thoroughgoing experimentation than it has yet received,
*Cf. Plant Succession, 1916:8-10; Development and Structure of Vegetation, 1904:12.
4 CONCEPT AND HISTORY.
the several divergent views are later considered briefly for the sake of a clearer
appreciation of existing opinion. Finally, the many studies of foresters upon
the tolerance of trees to shade had large elements of indicator value, but these
were never brought together into a system.
Studies of the relation of plants to soil were based upon the response of the
individual or species. The first serious attempt to organize these into a sys-
tem of indicator plants was made by Hilgard (1860, 1906). In a similarly
virgin region, Bessey (1891, 1901) also recognized the indicator value of native
plants, and especially vegetation for the proper development of agriculture.
His ideas of the practical value of vegetational studies stimulated the develop-
ment of ecology as recorded in the " Phytogeography of Nebraska" (Pound
and Clements, 1898, 1900) and the " Development and Structure of Vegetation"
(Clements 1904:1). In the latter the need of quantitative studies of habitat
and community and the importance of succession were first emphasized, and
these were made the basis of a definite quantitative system in " Research Meth-
ods in Ecology" (Clements, 1905). As a consequence, the way was prepared
for the use by Shantz (1911) of the plant community as an indicator with
particular reference to succession. In another direction, E. S. Clements (1905)
made a searching investigation of the relation of leaf structure to different
factors and habitats and laid the foundation for the use of habitat-forms and
ecads as indicators.
The development of the idea that plants are indicators of climate is more
difficult to trace. Tournefort (1717) probably furnished the first recorded
instance of the idea, when he pointed out that the slopes of Mount Ararat
showed many species of southern Europe, while still higher appeared a flora
similar to that of Sweden, and on the summit grew arctic plants such as those
of Lapland. Perhaps the most important studies of climatic zones of vegeta-
tion were those of Humboldt and Bonpland (1805:37), Kabsch (1855:303),
KSppen (1884:215), Drude (1887:3), and Schimper (1898, 1903:209). In
none of these is there a distinct recognition of the indicator concept. This is
likewise true of the formulation of life zones and crop zones on the North
American continent by Merriam (1898). His applications of the indicator
idea are so numerous and definite, however, that he must be given the credit
for organizing the first system of climatic indicators. As to the soil, Hilgard
is to be regarded as the pioneer in recognizing the great possibilities of systems
of indicators and applying this on an adequate scale, and Shantz as the inves-
tigator who has placed the whole matter upon an adequate scientific basis.
HISTORICAL.
In a general account of the important steps in the spread of the indicator
concept, it appears best to deal only with those studies in which the concept is
either evident or actually stated. Even with these the details are reserved for
discussion under the various climaxes or apphcations. There are numerous
books and papers on plant-geography, forestry, and agriculture, which have
some general relation to the idea. Most of these have contributed nothing
tangible or important and for the most part are ignored. A few are considered
or mentioned in the proper special sections. Entire justice might demand
consideration of the work of Bonnier, Fliche and Grandeau, and Contejean at
this point, but for many reasons it has proved undesirable to treat these in
HISTORICAL. O
detail. The following accounts are of these researches in which the term
indicator is actually employed or in which the use of instrument, quadrat, or
sucessional methods gives them distinct indicator objectives.
AGRICULTURAL INDICATORS.
Hilgard, 1860. — The following excerpt will serve to show that Hilgard was
the first investigator to recognize clearly the importance of indicators in soil
studies and to make actual use of them in determining the agricultural possi-
bilities of new lands. A further account of his views and results is given on
a later page.
"Judging of land by its natural vegetation. The distinction just men-
tioned, so far from being of merely theoretical value, is one of the highest
practical importance. Agriculturists are accustomed to judge of the quaUty
of lands by the natural vegetation which they find upon it; and they rarely
direct their attention to anything but the forest trees. Yet these are, for the
most part, indicative rather of what, in the agricultural sense is termed the
subsoil, than that of the surface stratum usually turned by the plow, in the
shallow tillage prevaiUng at present, which may be of a totally different
character.
"As a general thing, the forest growth when considered not only with regard
to the kind (species), but also to the form and size of the trees, is a very safe
guide in judging of the quahty of land, and the systematic study of the subject
in connection with analyses of soils, promises results of a highly practical
importance, which it is intended to communicate more fully in a future report.
But this criterion may not infrequently lead to grave mistakes unless a proper
examination of the soil and subsoil be made at the same time.
"These examples may suffice to show that while in the forest trees we possess
trustworthy guides to a knowledge of the character of the material in which
their roots are buried, it is quite essential to determine at the same time, by
inspection, that it is the arable soil itself, and not merely the subsoil, which is
thus characterized ; and we should especially make sure that the smaller plants,
viz, the shrubs and perennials, corroborate the evidence of the trees. Annuals
are less reliable in their indications because their development is to a greater
extent influenced by the accidental circumstances of the seasons."
Chamberlin, 1877. — Chamberlin shares with Hilgard the honor of being a
pioneer in the use of native plants to indicate the agricultural possibihties of
a region (1877 : 176). He deserves especial credit for being the first to recog-
nize that the community was a better indicator than the species, and for classi-
fying the vegetation of Wisconsin into communities with more or less definite
indicator value. Several of ChamberUn's associates on the Geological Survey
of Wisconsin made more or less use of his system of indicators (Woo'ster, 1882:
146; King, 1882: 614; Irving, 1880: 89), though it unfortunately appears to
have remained unknown to botanists, and consequently led to no further work
in this field.
"The most reliable natural indications of the agricultural capabiUties of a
district are to be found in its native vegetation. The natural flora may be
regarded as the result of nature's experiments in crop raising through the
thousands of years that have elapsed since the region became covered with
vegetation. If we set aside the inherent nature of the several plants, the
native vegetation may be regarded as a natural correlation of the combined
agricultural influences of soil, climate, topography, drainage and underlying
6 CONCEPT AND HISTORY.
fonnations and their effect upon it. To determine the exact character of each
ol these agencies independently is a work of no little difficulty; and then to
oompare and combine their respective influences upon vegetation presents
yvy great additional difficulty. But the experiments of nature furnish us in
the native flora a practical correlation of them. The native vegetation there-
fore merita careful consideration, none the less so because it is rapidly disap-
pearing, and a record of it will be valuable historically.
"It is rare in nature that a single plant occupies exclusively any considerable
territory, and in this respect there is an important difference between nature's
methods and those of man. The former raises mixed crops, the latter chiefly
simple ones. But in nature, the mingling of plants is not miscellaneous or
fortuitous. They are not indiscriminately intermixed with each other without
reg^urd to their fitness to be companions, but occur in groups or communities,
the members of which are adapted to each other and their common surround-
ings. It becomes then a question of much interest and of high practical
importance to ascertain, within the region under consideration, what are the
natural groupings of plants, and then what areas are occupied by the several
groups, after which a comparison with the soils, geological formations, surface
configuration, drainage and climatic influences, can not fail to be productive
of valuable results.
"The following natural groups are usually well marked, though of course
they merge into each other where there is a gradual transition from the condi-
tions favorable for one group to those advantageous to another. In some
instances it is unquestionably true that other circumstances than natural
adaptability control the association of these plants, and an effort has been
made in the study of the region, to discern these cases and eliminate them
from the results, so that the groups that are given here are beUeved to be
natural associations of plants. Their distribution is held to show in what
localities conditions pecuUarly advantageous to them occur, and hence advan-
tageous to those cultivated plants that require similar conditions."
The author has used both class and group as synonyms of community, but
the latter term is substituted in the following list for the sake of clearness:
A. Uplaod vegetation. B. Marsh veKetation.
(J) Herbaoeous. 10. Grass and sedge community.
1. Prairie community. 11. Heath community.
(2) Arboreous. 12. Tamarac community.
2. Oak community. 13. Arbor vitae community.
3. Oak and maple community. 14. Spruce community.
4. Maple commimity. C. Communities intermediate between
5. Maple and beech community. upland and marsh.
6. Hardwood and conifer community. 15. Black ash community.
7. Pine community. 16. Yellow birch community.
a. Limeatone ledge community.
0. Comprdiensive community.
Meiriam, 1898. — In "Life Zones and Crop Zones," Merriam summarized the
experiential evidence as to the cUmatic indications for crop plants. This was
arranged in relation to seven life zones based theoretically upon temperature,
but determined for the most part by the distribution of native plants and
animals. As a pioneer attempt to organize a vast field, it deserves great credit,
even though later studies have rendered his zonal classification of secondary
value. The author's understanding of the nature and scope of climatic indi-
cators is best shown by the foUowirig excerpts:
"For ten years the Biological Survey has had small parties in the field
traversing the public domain for the purpose of studying the geographic dis-
HISTORICAL. 7
tribution of our native land animals and plants, and mapping the boundaries
of the areas they inhabit. The present report is intended to explain the rela-
tions of this work to practical agriculture and to show the results thus far
attained.
"It was early learned that North America is divisible into seven transconti-
nental belts or life zones and a much larger number of minor areas or faunas,
each characterized by particular associations of animals and plants. It was
then suspected that these same zones and areas, up to the northern Umit of
profitable agriculture, are adapted to the needs of particular kinds or varieties
of cultivated crops, and this has since been fully established. When, there-
fore, the natural Ufe zones and areas, seemingly of interest only to the natur-
alist, were found to be natural crop belts and areas, they became at once of the
highest importance to the agriculturist. A map showing their position and
boundaries accompanies this report, and Usts of the more important crops of
each belt and its principal subdivisions are here for the first time pubUshed.
The matter relating to the native animals and plants has been reduced to a
fragmentary outUne for the reason that this branch of the subject is of com-
paratively little interest to the farmer and fruit-grower." (p. 7.)
"The Biological Survey aims to define and map the natural agricultural
belts of the United States, to ascertain what products of the soil can and what
can not be grown successfully in each, to guide the farmer in the intelligent
introduction of foreign crops, and to point out his friends and enemies among
the native birds and mammals, thereby helping him to utilize the beneficial
and ward off the harmful kinds." (p. 9.)
"The farmers of the United States spend vast sums of money each year in
trying to find out whether a particular fruit, vegetable, or cereal will or will not
thuive in localities where it has not been tested. Most of these experiments
result in disappointment and pecuniary loss. It makes Httle difference
whether the crop experimented with comes from the remotest parts of the
earth or from a neighboring State, the result is essentially the same, for the
main cost is the labor of cultivation and the use of the land. If the crop
happens to be one that requires a period of years for the test, the loss from its
failure is proportionately great.
"The cause of failure in the great majority of cases is climatic unfitness.
The quantity, distribution or interrelation of heat and moisture may be at
fault. Thus, while the total quantity of heat may be adequate, the moisture
may be inadequate, or the moisture may be adequate and the heat inadequate,
or the quantities of heat and moisture may be too great or too small with
respect to one another or to the time of year, and so on. What the farmer
wants to know is how to tell in advance whether the climatic conditions on his
own farm are fit or unfit for the particular crop he has in view, and what crops
he can raise with reasonable certainty. It requires no argimient to show that
the answers to these questions would be worth in the aggregate hundreds of
thousands of dollars yearly to the American farmer. The Biological Survey
aims to furnish these an.swers."
Life-zone surveys upon the basis laid down by Merriam have been made by
Bailey for Texas (1905) and New Mexico (1913), and by Gary for Colorado
(1911) and Wyoming (1917). Bobbins (1917) has made a somewhat similar
study of the zonal relations in Colorado with reference to plants alone. Hall
and Grinnell (1919:37) have recently published comprehensive lists of plants
and animals which are regarded as "life-zone indicators" for California. As
with Merriam's life zones, these are floristic and faunistic in character and
hence do not necessarily correspond with community indicators.
8 CONCEPT AND HISTORY.
Hllgardy 1906. — In summarizing his soil studies of more than 50 years, Hil-
gard fotmulated more fully and definitely his ideas of the indicator value of
native vegetation. This account makes it clear that to Hilgard must be given
the great credit of being the first to adequately realize the significance of indi-
eatore and to urge their inclusion in a basic agricultural method.
"The importance of the natural relations of each soil to vegetation is obvi-
ous, both from the theoretical and from the practical viewpoint. From the
former, it is clear that the native vegetation represents, within the climatic
limits of the regional flora, the result of a secular process of adaptation of
plants to climates and soils, by natural selection and the survival of the fittest.
The natural floras and silvas are thus the expression of secular, or rather
millenial experience, which if rightly interpreted must convey to the cultivator
of the soil the same information that otherwise he must acquire by long and
costly personal experience.
"The general correctness of this axiom is almost self-evident; it is explicitly
rec(^mz^ in the universal practice of settlers in new regions of selecting lands
in accordance with the forest growth thereon ; it is even legally recognized by
the valuation of lands upon the same basis for purposes of assessment, as is
practiced in a number of States.
"The accuracy with which experienced farmers judge of the quality of tim-
bered lands by their forest growth has justly excited the wonder and envy of
agricultural investigators, whose researches, based upon incomplete theoretical
assumptions, failed to convey to them any such practical insight. It was
doubtless this state of the case that led a distinguished writer on agriculture
to remark, nearly half a century ago, that he 'would rather trust an old farmer
for his judgment of land than the best chemist alive.'
"It is certainly true that mere physico-chemical analyses, unassisted by
other data, will frequently lead to a wholly erroneous estimate of a soil's
agricultural value, when applied to cultivated lands. But the matter assumes
a very different aspect when, with the natural vegetation and the correspond-
ing cultural experience as guides, we seek for the factors upon which the
observed natural selection of plants depends, by the physical and chemical
examination of the respective soils. It is further obvious that these factors
being once known, we shall be justified in applying them to those cases in
which the guiding mark of vegetation is absent, as the result of causes that
have not materially altered the natural condition of the soil. (p. xix.)
"It was from this standpoint that the writer originally undertook, in 1857,
the detailed study of the physical and chemical composition of soils. It
aeemed to him ' incredible ' that the well-defined and practically so important
distinctions based on natural vegetation, everywhere recognized and contin-
ually acted upon by farmers and settlers, should not be traceable to definite
physical and chemical differences in the respective lands, by competent,
comprehensively trained scientific observers, whose field of vision should be
broad enough to embrace concurrently the several points of view — geological,
physical, chemical, and botanical — that must be conjointly considered in
forming one's judgment of land. Such trained observers should not merely do
as well as the 'untutored farmer,' but a great.deal better." (p. 315.)
This attitude toward plants and vegetation as indicators prevails through-
out the book, and the subject is treated in considerable detail for the first time
in Chapters XXIV to XXVI. These deal respectively with the recognition of
the character of soils from their native vegetation, in Mississippi, and in the
United States and Europe generally, and with the vegetation of saline and
HISTORICAL. 9
alkali lands. While the author ascribes primary importance to the presence
of lime, he does not fail to assign great vaJue to water, especially in the West.
He not only recognizes the indicator value of the presence of a particular
species or group of species, but also takes into account the size, form, and
development of the indicators. Significant tables and lists of indicators are
given on pages 490, 497, 514-516, 518-519, and 536. In so far as these con-
cern the West, they are considered in Chapters V, VI, and VII.
Clements, 1910. — In 1908, the work of the Botanical Survey of Minnesota
was reorganized upon an ecological basis, for the purpose of making a classifica-
tion and use survey of the lands of the State. The objectives of the survey were
defined as follows (Clements, 1910:52):
"The first step in determining the final possibilities of Minnesota in plant
production is to ascertain just what the conditions of soil and climate are from
the standpoint of the plant. This must be determined separately for the two
great groups of lands, those still unoccupied and those now in use. For the
former, a knowledge of soil and climate and of the plant's relation to them is
necessary' to determine what primary crop, grain, forage, or forest is best.
For the farms of the State, the best use is a matter of knowing the soil and cli-
mate differences of regions and fields, and of taking advantage of these in crop
production. For the unoccupied lands of Minnesota, we need a classification
survey to determine the best use of different areas, to prevent the waste of
human effort and happiness involved in trying to secure from the land what it
can not give and yet to insure that the land will reach as quickly as possible
its maximum permanent return. For occupied lands, the study and mapping
of soil and climatic conditions would constitute a use survey of the greatest
value in adjusting plant production to the conditions which control it.
"The chief object of a classification survey is to group the unoccupied lands
of the State as accurately as possible into three great divisions: (1) agricul-
tural land, for crop production; (2) pasture land, for dairying and stock raising;
(3) forest land, for lumbering, water regulation, and recreation parks. Such a
division would be determined primarily by studies of soil and climate, neces-
sarily supplemented by the evidence of native vegetation itself and of such
cultivation as has been tried. The value of classification depends upon its
accuracy, but the study of an area from these three standpoints neglects no
source of evidence, and discloses practically all that can be learned of the
possibilities."
The survey method was based upon the instrumental and quadrat study of
habitats and communities, cultural as well as natural. The main divisions
were vegetation mapping, the determination of indicators, and the study of
succession. Vegetation and physiography were recorded on maps in which
each division of 40 acres was represented by a square decimeter. Quadrat
and transect charts were made of typical communities in each section of the
township, and determinations of physical factors in all charted quadrats.
The indicator work was devoted to the recognition of indicator species and
communities so closely dependent upon water-content, soil, acidity, or light
that they could always be used as indicating a certain set of conditions.
Especial attention was given to the correlation of indicators with crop plants
and with the secondary successions in burns, cutovers, fallow fields, pastures,
roadsides, etc. Four townships were mapped upon this basis in 1912. and a
large number of successional areas from 1913 to 1916. Some of the general
10 CONCEPT AND HISTORY.
rasuHs have already been published (Bergman and Stallard, 1916; Stallard,
1916; Bergman, 1919; Stallard, 1919), while a part of the indicator findings are
disouBBed later (Chapter III).
SbanU, 1911. — ^The study of the natural vegetation of the Great Plains
by Shanti is the classic work on indicator plants. It was the first avowed
investigation of indicators to be based upon the three cardinal points, namely,
instrumentation, succession, and quadrats, and will long serve as the model
for all thorough research in this field. Becaufe of its great importance, the
original should be consulted for the details. Here it must suffice to quote
the author's general principles, (p. 9.)
"Farmers and other persons who have occasion to examine new land in
order to form a judgment of its agricultural value depend largely upon the
natural vegetation, or plant covering, as an indicator of its crop-producing
qualities. But there are many possibilities of error in judging land upon this
basis. Species that are closely related botanically and very similar in appear-
ance may indicate quite different conditions of soil and climate. The popular
names of plants are likely to cause confusion. Thus, the farmer who has
learned in the Great Basin region that 'greasewood' is an indicator of alkali
land and that * sage-brush ' usually grows on land free from alkali, will find if
he moves to southern Arizona or southeastern California that the scrub there
known as 'greasewood' indicates absence of alkali, while the so-called 'sage
bushes' of that region grow on strongly alkali land. Furthermore, there is a
general tendency to depend upon a single plant species as an indicator, while
the investigations set forth in this bulletin show that the composition of the
plant covering as a whole is a much more reUable basis for judging the crop-
producing capabilities of land.
"The chief object of the present paper is to show how these sources of error
may be avoided and how new land may be classified readily and with reasona-
ble accuracy on the basis of its natural vegetation. This paper is not a report
of a land survey, but rather a discussion of methods which it is believed could
be utilized to advantage in making such a survey, the methods being illus-
trated by application to a Umited territory in the Great Plains area.
"Too much emphasis can not be laid upon certain facts that have been
clearly brought out in the course of these investigations: (1) Correlations
between the natural plant cover and the crop-producing capabilities of land in
a given area can be satisfactorily determined only after careful study of the
different types of vegetation of the area in relation to their physical environ-
ments; (2) such correlations, determined for some particular region, will need
to be modified to a greater or less extent before they can be applied in another
region where the physical conditions are different. When, as a result of suffi-
cient investigation, correlations of this nature are determined for a given area,
it is beUeved that they will afford a basis for classifying the land of that area
more readily and at least as accurately as by any other known method.
"In order to test and perfect the methods here described, it was necessary to
make a detailed study of the vegetation of some particular area in relation to
the physical conditions, checking the observations by the study of such exam-
ples of actual crop production as exist on the different types of land. It was
decided to be^n work in the Great Plains area, for this region contains the
lar^t body of land in the United States having possible agricultural value on
which the native plant covering is still undisturbed. A further advantage is
the comparative uniformity of the climate throughout the area from the
Canadian boundary on the north to the 'Panhandle' of Texas on the south.
The investigations thus far have been made chiefly in a portion of eastern
CLEMENTS
PLATE 1
^1^^
^^r
^^g
grvv-y^Sj^Jl
WR
J^K^SBf-fA
f&
M%M
»'"«r.- •
■Hsi^
ii3SSl
B^Hi
BRp
^K^mfit^
P
mi^iiiS.
&5i&!r'/,v.
w^
K Ad. «.
,ij . '
''' ,/ ^ ',j/f 'y»i^>'••;W-
/ ■.^^■^
.^^ ,v-^-::-:.^^v:.
A. Short-grass {Bouteloria gracilis) on hard land, Colorado Springs, Colorado.
B. Wire-grass {Aristida purpurea) on short-grass land, Walsenburg, Colorado.
HISTORICAL. 11
Colorado, a region which is considered representative because of its central
position and because its climatic conditions are almost as severe as anywhere
in the Great Plains. But enough data have been gathered in other portions of
the Great Plains to make it fairly certain that with comparatively Uttle modi-
fication the correlations shown will hold throughout the area.
"The work so far accomplished has brought out clearly that in this area the
general conditions, whether favorable or unfavorable to crop production, are
indicated by the character of the native plant cover." (plate 1.)
Kearney, Brlggs, Shantz, McLane, and Piemeisel, 1914. — The first quanti-
tative study of plant communities as indicators of alkaline soils was made by
Kearney and his associates in the Tooele Valley of Utah. This was essen-
tially an application of Shantz's methods to a saline ba^in and met with
similarly important results, as the following indicates:
"In the arid portion of the United States the different types of native vege-
tation are often very sharply delimited, the transitions being so abrupt that
they can not be attributed to climatic factors; this has suggested the possi-
bility of correlating the distribution of the vegetation with the physical and
chemical properties of the soil. If such correlations can be made, they may be
utilized in the classification of land with respect to its agricultural capabilities.
"One of the writers has described the correlations which exist in the Great
Plains between the different types of vegetation and the physical characteris-
tics of the corresponding types of land, and has pointed out how the native
growth may be used in that region to determine the suitability of the land for
dry-farming.
"The results obtained in the Great Plains made it desirable to undertake
similar investigations in the Great Basin region. The problems to be solved
were: First, what types of vegetation indicate conditions of soil moisture
favorable or unfavorable to dry farming, and second, what types indicate the
presence or absence of alkali salts in quantities Ukely to injure cultivated crops.
For the purpose of this investigation it was necessary to find a locality where
both dry farming and irrigation farming are practiced, where much of the soil
is still covered with the original native growth, and where some of the soils
contain an excess of alkali salts.
"After a reconnoissance trip through portions of Wyoming, Utah, Idaho,
and Oregon in August, 1911, the Tooele Valley in central Utah was selected for
the following reasons: (1) Several very distinct types of vegetation are found
in a small area, (2) the soils show a great diversity in their moisture conditions
and salt content, (3) the greater part of the area retains its original plant cover,
while examples of crop production, both with and without irrigation, exist on
different types of land.
" Detailed studies of the vegetation of Tooele Valley in relation to the mois-
ture conditions and salt content of the soil were carried on in 1912. The work
was begim near the close of the rainy season (end of May) and was terminated
during the first week of August, when the summer drought had reached its
height. Additional data were obtained during a third visit to the valley in the
latter part of August 1913.
"The distribution of the native vegetation was found to depend in a marked
degree upon the physical and chemical properties of the soils, factors which also
influence crop production. So far as this particular area is concerned, the
vegetation unquestionably can be used with advantage in classifying land with
respect to its agricultural value. To what extent the correlations established
in the Tooele Valley hold good in other parts of the Great Basin region remains
to be determined by future investigation." (p. 365.)
12
CONCEPT AND HISTORY.
The succesaional relations of the dominants have been discussed as well as
graphically illustrated by Shanta (1916:234). The primary succession ex-
hibits two adseres, one from Salicomia and Allenrolfea to Artemisia, and the
other from Allenrolfea through Distichlis and Sporobolns to Chrysothamnus.
These eeral facts give much additional value to the indicator studies of the
Great Basin, especially in establishing the indicator sequence and in imparting
a distinct significance to the various mixed communities, (plate 2.)
ouTtioe (5)
OUTER triMULATEO ZONE (4)
OUTSIDE (5)
WITHERED ZONE (4*)
BARE ZONE (3)
PLANT SURFACE
SOIL SURFACE
Fio. 1. — Zones of a fairy ring due to Agaricua tabularis: A and C, during a moist
period; B, during a dry period. After Shantz and Piemeisel.
Shantz and Piemeisel, 1917. — In their exhaustive study of fairy rings in
the Great Plains, Shantz and Piemeisel (1917:191) have shown the causal
relation between the rings of mushrooms and grasse?^, as well as the indicator
Fignificance of the latter. They distinguish three types of fairy rings, based
upon the effect shown by the vegetation: (1) those in which the vegetation is
killed or badly damaged, caused by Agaricus tabularis (fig. 1) ; (2) those in which
the vegetation is only stimulated, produced usually by species of Calvatia,
Catastoma, Lycoperdon, Marasmius, etc. ; (3) thope in which no effect can be
noted in the native vegetation, due to species of Lepiota. In the Agaricus
rings, the vegetation shows three zones concentric to the central area of normal
shortrgrass sod (1): the inner stimulated zone (2) is a broad one, differing in
botanical compxwition, the more luxuriant growth, and the deeper green color
from the center. The bare zone (3) is narrower and somewhat more irregular,
while the vegetation is either dead or consists of a few very poor perennials or
short-lived annuals. The inner zone is the most prominent feature of the ring
in spring or wet seasons, the bare one in late summer or fall or in dry seasons.
The outer stimulated zone (4) is rather narrow and is made up for most part
of species peculiar to the short-grass sod, though resembling the inner zone
somewhat. The mushrooms occur in the outer zone near the outside edge.
Cv
CLEMENTS
PLATE 2
A. Spirostachys occidentalis in salt marsh, Bakersfield, California.
B. Shadscale {Atriplex conferlifolia) indicating saline land, Rock Springs, Wyoming.
HISTORICAL. 13
In the case of most fairy rings, the fungus produces a temporary stimulating
effect only, and the ring is indicated merely by the increased size, vigor, and
chlorophyll-content of the annuals and the perennial graases.
The stimulation of the grasses and other plants which produced the inner
and outer zones is probably due to the presence in the soil of nitrates and
ammonia salts derived from (1) the reduction of the organic matter of the soil,
(2) the decay of the mushrooms, and (3) the decay of the mycelium. The
bare zone results from the death of the vegetation as a consequence of a lack
of available soil moisture. Water penetrates very slowly into the sod filled
with mycelium when it is once dry. The increased growth in the outer zone
hastens the drying-out of the soil and, once dry, the latter is not wetted by
heavy and continued rain. The vegetation is not noticeably damaged during
growing seasons uniformly wet, but it quickly shows the effect of dry years or
periods of drought. The secondary sere initiated by the fairy rings is essen-
tially Uke that caused by any other disturbance in the short-grass association.
Shantz and Aldous, 1917. — ^In the field instructions for classifying public
lands under the terms of the Stock Raising Homestead Act of 1916, Shantz
and Aldous have made the most comprehensive use of indicators for the pur-
pose of land classification. Ninety different types are recognized as indicator
communities and are described briefly, though usually without a statement of
the correlated conditions. Of these, 32 belong to the prairie-plains grassland
climax, 20 to the sagebrush climax, 16 to the desert-scrut) climax, and 9 to
the chaparral. The types are designated by the names of dominants and
subdominants and represent both serai and climax communities. Density,
percentage of grasses and grass-like plants, and height of shrubs are also made
use of for minor indications, while overgrazed areas are given especial atten-
tion. A key to correlation conditions and crop-producing capabilities was
filed with the Geological Survey and is used by it in the interpretation of
the types.
Weaver, 1919.— While the work of Shantz (1911), Weaver (1915), Sampson
(1914, 1917), and of Cannon (1911, 1913, 1917), Markle (1917), and others
had laid the basis for the consideration of root systems in connection with
indicator values, the first special and comprehensive study of the indicator
significance of roots was made by Weaver in 1918. This investigation derives
its importance not only from the thoroughness of the methods, but especially
also from the large number of species concerned, the wide range of the com-
munities, and the consistency of the instrumental results. Approximately 160
species were investigated, involving the examination of about 1,150 individual
plants. These were largely grasses and grassland herbs, but they included
shrubs, undershrubs, weeds, and forest herbs as well. The communities
represented were the prairies of Nebraska and the Palouse region of the North-
west, the short-grass plains and the sandhills subcUmax of Colorado, the gravel-
slide and half-gravel-slide associes, and the forest climax of the Pike's Peak
region. In practically all these, readings were made of water-content, humid-
ity, temperature, and light, and in critical ones of transpiration as well. In
showing the community relations of competing root systems use was made of
the quadrat-bisect (plate a; cf. Weaver, 1919, for plate 26a). Many of the
detailed results have been utilized in the discussion of particular indicators
in Chapters IV and VI.
14 CONCEPT AND HISTORY.
FOREST INDICATORS.
A general idea of indicator plants has existed in forestry for nearly a century,
and it is strange that the forester was not the first to formulate a system of
indicators. His nearest approach to this is found in the tables of tolerance
(Graves and Zon, 1911 : 20). The fact that the forester's attention was
fixed primarily upon reproduction and Httle or not at all upon the shrubs
and herbe of the forest floor probably explains the long absence of any definite
recognition of indicators. In forestry as elsewhere, but even to a greater
degree, a system of indicator plants and communities was impossible before
the »i8e of instruments and quadrats and the application of successional prin-
ciples. As is shown later, however, forestry already possesses a large amount
of indicator material which only needs to be organized upon a systematic basis.
Practically all site studio? have much and some of them great indicator value.
However, the researches directed primarily toward this have been few, and it
is necessary here to consider only the following:
Cajander, 1909. — Cajander (1909; Zon, 1914 : 119) has made an interest-
ing endeavor to recognize forest types on the basis of the living ground-cover
as indicators of the soil conditions. He classified the forests of Germany,
composed largely of spruce, fir, beech, and oak, into three types:
1. Oxalis type (forests with a layer society of Oxalis acetosella).
2. MyrtiUtis type (forests with a layer society of MyrtiUus nigra).
3. Calluna heath type (forests with a layer society of CaUuna trulgaris).
The Oxalis type characterizes the best soiU and comprises nearly all the
dominant trees. It is further divided into four subtypes , marked by Impa-
tiens-Asperula, Aspenda, Oxalis, and Oxalis-Myrtillus respectively. As Zon
points out, the dominant species of trees are assumed to play no part in deter-
mining the type. The author also dismisses the effect of light as of no impor-
tance. This appears to be quite unwarranted, as no measurements seem to
have been made of light, as is apparently true of the other factors as well, and
consequently the correlation between communities and conditions is super-
latively general. Little or no attention is paid to the successional sequence
of dominants or subdominants, and here again the real indicator values are
overlooked or lost. Zon further points out that the author's own statements
are contradictory, in that he states in one place that the layer societies indicate
the physical conditions independent of the tree species, while in another the
trees are said to determine the character of the herbaceous vegetation beneath
them. While Cajander has erred in assigm'ng greater importance to the sub-
dominant herbs and low shrubs than to the dominant trees, his use of the
forest societies as indicators is sound, and will serve to correct the usual prac-
tice of foresters who have neglected the undergrowth.
Clements, 1910. — The investigation of the lodgepole-burn forests of
northern Colorado in 1907-1908 was essentially a study of fire indicators,
herbaceous as well as woody. Its real importance in this connection lay in the
fact that it wa* the first study of forests made on the complete basis of instru-
ments, quadrats, and succession. It was pointed out that lodgepole pine and
aspen are practically universal indicators of fire and not of mineral soil or other
conditions, at least for the Rocky Mountains. Agrostis hiemalis, Chamaene-
rium angustifolium and Vaccinium oreophUum were recognized as the chief
CLEMENTS
PLATE 3
A. Lotlgtpole forest {I'inua coiUorta) mdiculmt; lire, Long s Peak, Colonulo.
B. Aspen woodland (Popuius tremuhides) arising from root-sprouting due to fire, Long's
Peak.
HISTORICAL. 15
pioneers of the burn subsere, together with the mosses Bryum argenteum and
Funaria hygrometrica. Several other species are almost equally good indi-
cators of burns, especially when abundant. These are Rubus slrigosus, Carex
rossiiy Arnica cordifolia, Achillea lanulosa, and Anaphalis margaritacea. The
water and light factors for the six dominant trees were measured and the
successional sequence thus obtained exhibits the indicator value of each
species, (plate 3.)
A successional study was made of the so-called natural parks of Colorado
in 1910 for the purpase of determining their indicator significance as to refor-
estation, both natural and artificial. The conclusion was reached that all
such grassland areas in forested regions are but serai stages leading to a forest
climax. The majority of them are due to repeated burns or the slow filling
of lakes, with the result that they persist as apparent climaxes for several
hundred 5^ears. Their origin is readily disclosed by the indicators in tiiem, a&
is also tnie of the rate of development.
Pearson, 1913-1914. — In discussing the proper basis for the classification
of forest lands into types, Pearson (1913 : 79) has reached the following
conclusions :
"The only scientific basis for such a classification is that of potential pro-
ductiveness, considering both agricultural and forest crops. The productive
value may be ascertained in two ways : The first measures directly, as far as
possible, all physical factors on the site and gauges the productive capacity by
the measure in which the sum of these factors meets the requirements of various
crops. The second method uses characteristic forms of vegetation on the
ground as an indicator of the physical conditions present, and upon this basis
ascertains the adaptability of the site for different crops. The obvious objec-
tion to the first method is the need of climatological data and soil analyses on
each site to be classified; and owing to the diversity of sites in our forest
regions, together with the almost complete absence of climatological records in
many sections, the collection of the needed data would involve an expense
which, at this stage of our advancement in forestry, would be almost pro-
hibitive. The second method requires a thorough preUminary investigation
in each region to be covered, in order to secure a working knowledge for the
actual land classification, and obviously reliable results can only be obtained
by the employment of trained men. This method is the simpler and probably
the more reliable of the two, and it is considered entirely applicable to the
needs of the forester."
A general indicator relation is established between the five forest types and
the agricultural possibilities of the Coconino National Forest in northern
Arizona. The same author (1914 : 249) has employed seedlings of Douglas
fir as indicators of the conditions for planting in aspen and in open situa-
tions at 8,700 feet on the south slope of the San Francisco Mountains.
The seedUngs were planted in two plots in the aspen and two in the opening
each spring of the 3-year period, and instrumental readings were made of
water-content, evaporation, wind, and temperature. The aspen uniformly
gave a larger survival of seedlings than the opening, the percentage varying
from 7 to 13. The critical factor in this wa& evaporation, which was 50 to
90 per cent higher in the open than under the aspen. The author further
points out that the results indicate that yellow pine, because of its lower
5i/
16 CONCEPT AND HISTORY.
moisture requirements and greater demands for light, will probably prove
more suitable than Douglas fir for openings' within the natural range of the
former. A later study has dealt with the correlation of height-growth with
pndpitation, but this is considered under growth-forms in Chapter II.
Zon, 1915. — At the suggestion of the writer, a conference was held at
the Utah Forest Experiment Station in 1915 to discuss the feasibility of a
system of indicators for silvics and grazing, and especially the indicator value
of shrubby and herbaceous species and communities, with particular reference
to succession. The conference consisted of Mr. Zon, chief of silvics, Mr.
Jardine, inspector of grazing, Dr. Sampson, director of the station. Dr. E. S.
Clements, and the writer. There was general agreement upon the value of
indicators as a basis for the experhnental regeneration of forest and grassland.
As an outcome, Mr. Zon drew up a preliminary outline of the indicator sig-
nificance of the important dominants of the various zones and represented
this graphically in a schematic transect (fig. 25). This appears to have been
the first definite organization of the indicaEbrexperience of the Forest Service
in silvical work. Its proposals as to indicators are considered in Chapter VII.
A similar conference on indicators and succession was held at the station in
1917. It was attended by Professor Toumey, Professor Pool, Dr. E. S.
Clements, Dr. Sampson, Mr. Korstian, Mr. Baker, Mr. Weil, and other mem-
bers of the staff, together with the writer. Particular attention was given to
serai indicators of grazing burns, erosion and slides, as well as to climatic
indicators in the chaparral belt. Some of the conclusions are to be found in
the discussion of indicator papers in Chapter VII, as well as in the body of the
text itself.
Hole and Singh, 1916. — In studying the reproduction of sal (5^orea ro6t*sto)
in the forests of India, Hole and Singh have made a quantitative study of the
water and light factors which control germination and ecesis. Their work is
especially noteworthy in that experimental quadrats have been employed for
the analysis of different sites (p. 48), and that a detailed study was made of
soil aeration as a critical factor. The general indicator results are given in
the following excerpts :
"Broadly speaking three principal soil types may be distinguished in these
areas, and these are characterized by different types of vegetation, as follows:
A. Containing a large percentage of sand and a relatively small percentage of the
finer particles of silt. The soil is also frequently shallow, with gravel and
boulders below, and is therefore essentially dry.
Dry miscellaneous forest with Acacia catechu and Dalbergia sissoo prominent, or
grassland with Saccharum munja dominant.
B. Sal forest or grassland, well aerated deep loam with Saccharum narenga (often
mixed with Anthistiria gigantea arundiruicea) dominant.
C. Badly aerated deep loam. This differs from (B) either in containing more clay
and silt, in being actually denser with less p>ore space per cubic foot, or in
having the water-table nearer the surface.
Moist miscellaneous forest with Butea frondosa, Stereospermum srutveolens, Ter-
minalia, Cedrela toona and others, or grassland with Erianthus ravennae
(often mixed with Anthistiria gigantea villosa) dominant.
"One of these types is unsuitable for the growth of sal, inasmuch as the
water-content of the soil falls rapidly to the death-limit after the close of the
rainy season, while another type is unsuitable on account of bad soil-aeration
which leads to a low percentage of germination, a high percentage of deaths
HISTORICAL. 17
during the rains, and a superficial root system. The latter point is of great
importance, inasmuch as it leads to the roots being situated in those layers of
soil the water-content of which is reduced to the death-limit in the dry
season. It will thus be seen that the results obtained go far to explain the
natural distribution of sal, and also indicate those grasslands and forestless
areas in which afforestation with sal offers the greatest chance of success.
Finally, it has been shown that, owing chiefly to the heavy shade, the aeration
of the superficial soil layers in dense sal forest is commonly below the death-
limit for several weeks during the rains and that this factor is responsible (1)
for the holocaust of sal seedlings which takes place during the rains in shady
forests in years of heavy rainfall and (2) for the development of a superficial root
system which, in the hot season when the sal sheds its leaves and the forest
canopy thins out, leads to widespread damage from drought among those
plants which survive the rains. Opening of the cover and temporary removal
of the humus are obvious expedients by means of which the soil-aeration can be
improved. Firing would also in some cases probably be beneficial in this
respect." (p. 38.)
" It will be seen that the management of any particular sal forest to a great
extent depends on the fact whether the seedlings in it suffer chiefly from
drought or from bad soil-aeration and therefore the determination of this point
is of primary importance. Observations regarding the season when the seed-
lings chiefly die and the dryness of the soil at the time naturally indicate to a
great extent which factor is primarily concerned. In addition to this, how-
ever, the work which has been carried out at Dehra during the last few years
has shown that the dominant grasses on an area are, as a rule, excellent indi-
cators of the soil conditions. Thus in northern India, where Saccharum
narenga and Anthistiria gigantea arundinacea tend to be dominant, the soil
moisture and aeration are as a rule suitable for the best development of sal and
sal forests of the moist type prevail. In shady forest in such localities, the
seedlings suffer chiefly from bad soil-aeration and the most efficient remedy
consists in opening the cover and exposing the soil. On the other hand, such
grasses as Saccharum munja, S. spontaneum, Eragrostis cynosuroides, Imperata
arundinacea, Vetiveria zizanoides, Andropogon contortus, and Ischcemum angus-
tifolium usually indicate a soil too dry or too dense for the best sal development,
and such forests as occur are of the dry sal type. The recognition of the domi-
nant grasses in the sal tracts therefore is a matter of considerable practical
importance, and a subsequent paper will deal in more detail with the grasses
of the sal tracts, in their capacity as soil indicators." (p. 83.)
Korstian, 1917. — In a study of permanent quadrats on the Datil National
Forest of New Mexico, Korstian (1917:267) gives the increment data for
Pinus ponderosa on sites I and II, and points out that the growth of a domi-
nant tree is the best indication of the quality of forest sites. The differences
in the native vegetation on the two sites were so great as to suggest its cor-
relation with tree-growth and its use as an indicator of forest sites. A large
number of list quadrats were employed, but the lack of previous successional
studies makes their accurate interpretation difficult and probably explains in
part the conclusion that
"In studying the indicator significance of the native vegetation it is neces-
sary to go directly to the individual species instead of attempting to stop at
the association, society, or community.
"The writer believes that the native vegetation found on deforested areas
may be considered as a criterion of the latent potentialities of the site for forest
production provided the vegetation has not been too seriously or too recently
18 CONCEPT AND HISTORY.
disturbed and that the more important phases of the successional series are
properly understood.
"The fundamental study of forest planting sites logically resolves itself into
three categories: (1) The empirical establishment of plantations and the
obeervation and study of their survival and subsequent development; (2) the
measurement and study of the most important physical factors of the site,
such as the available soil moisture or growth water and evaporation; and (3)
the indicator significance of the native vegetation occurring on the sites, imply-
ing a very careful correlation of all three phases.
"It is readily conceivable that site studies of this character will be of the
utmost value in explaining the presence or absence of tree growth on certain
areas, in the judicious selection of the proper species and sites in the reforesta-
tion of much of the denuded forest land of the United States, and in establish-
ing a working basis for the classification of forest lands. Only after considering
the relative agricultural and forest productivity of the land on a combined
scientific and economic basis, can a positive conclusion be reached that its
greatest utility Ues in its use for forestry or for agricultural purposes."
V GRAZING INDICATORS.
Grazing has been recognized as a distinct field for investigation for scarcely
more than a decade. Complete recognition of grazing as a subject for experi-
ment should perhaps be dated from the establishment of the Utah Forest
Experiment Station for grazing in 1912. Three more or less marked steps in
advance had preceded this and had made it inevitable. The first was a
general study of the West with reference to the species, distribution, and value
of the native grasses and forage plants. The stimulus for this seems to have
been the work of Bessey in Nebraska, as indicated by the publication of many
reports dealing with grasses and forage plants from 1886 to 1907. Webber
(1890), Smith (1890), and Williams were associated with Bessey in some
of this work and the last two later carried on extensive grassland studies
over the Great Plains and the Rocky Mountain region (Smith, 1898; Williams,
1897, 1898). Similar studies were made by Shear and Clements in 1896, by
Rydberg and Shear in 1897, by Pammel in 1897, Nelson in 1898, and others (cf .
Shear, 1901). The second step was perhaps the most significant, inasmuch as
it introduced the quantitative study of grazing areas by means of the quadrat,
and provided an exact method of measuring carrying capacity and deter-
mining the degree of overgrazing or the amount of regeneration. This work
was begun by Griffiths and Thornber in 1901 and enlarged in 1903 on what is
now the Santa Rita Grazing Reserve of the Forest Service. It has been
carried on continuously since that time by Griffiths, Wooton, Thornber, Hurtt,
and Hensel in turn, and now constitutes the classic field for grazing study
anywhere in the world. It has yielded publications of primary importance
by Griffiths (1901, 1904, 1907, 1910), Thornber (1910), and Wooton (1916).
Somewhat similar lines of experiment were begun by Coville and Sampson in
1907 in the Wallowa National Forest in northeastern Oregon. The results
are recorded in a series of reports of unusual significance, namely, Sampson
(1908, 1909, 1913, 1917) and Jardine (1908).
The third period of rapid development in grazing studies began with the
organization of grazing reconnaissance in the six districts of the Forest Service
in 1911. During the past seven years reconnoissances have been made on
practically all of the National Forests, and the grazing upon these has been
HISTORICAL. 19
administered upon the basis of a definite carrying capacity. The result has
been to favor regeneration to such an extent that most of the ranges have
recovered their normal carrying capacity to a large degree. With the exten-
sive work in reconnoissance went the establishment of permanent quadrats,
especially in the Coconino, Targhee and Deerlodge National Forests. Those
on the Coconino especially have been actively studied (plate 89, b), and have
already yielded results of much value (Hill, 1917).
The most signal advance has been marked by the organization of a grazing
experiment station of the Forest Service at Ephraim, Utah, in 1912. This
has been followed by the estabUshment of experimental pastures for grazing
at Mandan (North Dakota), and Ardmore (South Dakota), by the Ofl&ce of
Dry Land Agriculture of the U. S. Department of Agriculture. Somewhat
earlier than this, in 1908, Marsh had begun experimental work in Colorado on
poisonous plants, and this is now carried on at a special experiment station
at Salina, Utah, on the Fishlake National Forest. In 1914, the Jornada Grazing
Reserve was established near Las Cruces, and this, like the Santa Rita Reserve,
is essentially a grazing experiment station in the open range country. It
seems inevitable that the organization of grazing reserves and experiment
stations will proceed rapidly until they are found in all the important grazing
types of the country, as well as in each State, including the South. An account
is given in Chapter VI of the inauguration of a comprehensive system of grazing
investigations throughout the West during 1917-1919.
Practically none of the grazing studies abstracted in the following pages
was intended to deal with indicator plants. In spite of this fact, however,
they all contribute more or less definitely to the understanding of grazing
indicators, because of the simple and direct relation grassland dominants and
subdominants have to grazing. In addition, the abstracts furnish a fairly
complete outline of the progress of grazing investigations during the past
twenty years.
Smith, 1899. — The first clear recognition of grazing as a fundamental
field for investigation was accorded by Smith in his study of grazing problems
in the Southwest. His paper is a mine of valuable suggestions, and fore-
shadows a large number of the later experiments. The author has a distinct
idea of gracing indicators and of succession, as the following excerpts show:
"Before the ranges were overgrazed the grasses of the red prairies were
largely bluestems or sage grasses (Andropogor^ , often as high as a horse's back.
After pasturing and subsequent to the trampling and hardening of the soil,
the dog grasses or needle grasses (Aristida) took the whole country. After
further overstocking and trampling, the needle grasses were driven out and the
mesquite grasses {Hilaria and Bulbilis) became the most prominent species.
The occurrence of any one of these as the dominant or most conspicuous grass
is to some extent an index of the state of the land and of what stage in over-
stocking and deterioration has been reached.
" There is often a succession of dominant grasses in nature through natural
causes, but never to so marked an extent as on the cattle ranges during the
process of deterioration from overgrazing. Thus, the grasses in any given val-
ley are liable to change in a long series of years through destruction by wood
Uce, prairie dogs, by fires, unusually early or late frosts, or by failure on the
part of the plant to ripen seed. This latter contingency frequently occurs in
the case of the big bluestems and the feather sedge, and probably with some
20 CONCEPT AND HISTORY.
others of the Andropogon species. The curly mesquite will stand almost any
amount of drought, trampling, and hard usage, but is easily killed and rotted
out during a wet cold winter. The drought-resistant needle grass is frequently
destroyed by wood lice over considerable areas. This usually happens in the
spring on burned areas after hght local showers. Finally, the entire seed crop
may be destroyed by early autumn fires. Thus it is seen that through some
one of many natural causes a species of grass may be all but exterminated and
its place taJcen by others, often of less value.
"On overstocked land there is uniformly an alternation of needle grass and
mesquite at short intervals, unless the overstocking is carried too far, when
these perennials give way to annuals and worthless weeds. The carrying
capacity then depends almost absolutely on the proper distribution of rainfall
through the growing season in order to bring this transient vegetation to its
fullest maturity." (p. 28.)
The text is divided into the following heads: (1) investigation of carrying
capacity, (2) destruction of grasses by anim.al pests, (3) deterioration through
increase of weeds, (4) renewing the cattle ranges, (5) rest versus alternation
of pastures, (6) additional aids to range improvement, (7) grazing regions in
Texas and New Mexico, (8) relation of land laws to range improvement, and
(9) benefits of improving the ranges. The most significant part of the report
is that which has to do with the regeneration of the range by means of rotation
pastures. Experimental sections were selected at Abilene and Channing,
Texas, representing prairie and plains respectively.^ On these the following
experimental pastures and areas were established (p. 20; Bentley, 1902 : 15).
Pasture No. 1 (80 acres) : No treatment except to keep all stock off until June 1 of each
year, pasturing the balance of the season.
Pasture No. 2 (80 acres) : To be cut with a disk harrow, and stock to be kept off until June 1
of each year, pasturing the balance of the season.
Pastures Nos. 3 and 4 (40 acres each) : To be grazed alternately, the stock to be changed
from one pasture to the other every two weeks, thus allowing the grasses a short
period for recovery after each grazing.
Pasture No. 5 (80 acres) : No treatment except pasturing until June 1 and keeping stock
off the balance of the season.
Pasture No. 6 (80 acres) : No treatment except to keep stock off during the first season.
Pasture No. 7 (80 acres) : To be harrowed with an ordinary straight-toothed harrow and
stock kept off during the first season.
Pasture No. 8 (80 acres) : To be disked and stock kept off during the first season.
Pasture No. 9 (70 acres): Reserved for special experiments, viz, to determine (1) whether
or not seeds of a number of wild and cultivated varieties of grasses and forage
plants, exclusive of the grasses, could be sown directly in the sod with satisfactory
results. (2) Whether the roots of certain sod and pasture grasses could be trans-
planted to the bare spots and a good stand secured in that way. (3) Whether the
stand (rf grass could be improved by opening furrows across the pasture, in which
the grass seeds blown over the ground by the winds could be arrested and the
stand ol grass be improved.
Bentley, 1902. — The preceding experiments, though initiated by Smith,
were carried out by Bentley from 1898 to 1901. His results are of great value
as the first outcome of actual and successful experimentation in improving
the range. At the beginning the maximum carrying capacity of the area was
determined to be 16 acres per head, or 1 : 16. During the first year, the
carrying capacity was estimated to have increased to 1 : 8, or 100 per cent.
'No reomxl Menu to have been made of the experimenta at Channing, and it is assu med these
««« Muty diMontuiTied.
HISTORICAL. 21
Unfortunately, no detailed report was made on the different pastures, and it
was impossible to tell whether rotation or disking and harrowing was of the
greater value in securing these results. At the end of the second year, a
further improvement of 30 to 50 per cent was noted in the disked pastures.
By the close of the three-year period, while the whole area had improved more
than 100 per cent, the greatest improvement was noted in the pastures which
had been disked and harrowed. Two minor experiments of much practical
interest were also carried out successfully. The one consisted of plowing
furrows 12 feet apart over 10 acres of pasture 9. The many fruits caught in
the furrows germinated readily and grew vigorously because of the increased
water-content. The latter also benefited the grasses between the furrows.
The other test involved the transplanting of grass mats and bunches for the
purpose of covering bare areas in prairie-dog towns and other denuded areas.
1 he results are of especial significance and are further discussed in Chapter VI.
Griffiths, 1901, 1904, 1907, 1910, 1915.— Griffiths's work upon the grazing
ranges of southern Arizona from 1903 to 1910 is entitled to great credit as the
earUest consistent study of range production. The quadrat method was
employed more or less, and some attention was paid to physical factors and
incidentally to changes of population. The objects of the investigation were
(1) to demonstrate that run-down and overstocked ranges will recover under
proper treatment, (2) to ascertain how long a time is necessary to get appreci-
able and complete recovery, and what methods of management will produce
such results, (3) to carry on reseeding and introduction experiments in the hope
of increasing the total quantity of feed, (4) to measure as accurately as possible
the carrjang capacity of a known representative area. The report of 1915 on
the native pasture grasses of the United States contains a large amount of
valuable material with direct bearing upon grazing indicators (plate 4, a).
The general results of the investigations are shown by the following sum-
mary (1910:24):
"The lands under consideration appear to regain their original productivity
in approximately three years of complete protection.
"Evidence thus far secured seems to indicate that the best lands in the
vicinity will improve under stocking at the rate of one bovine animal to 20
acres. The poorer lands take a correspondingly larger acreage for each ani-
mal. The areas that will carry one head to 20 acres are very limited.
"Brush and timber are encroaching upon the grasslands, due, it is believed,
to protection from fires.
"A ground cover is not a factor below an altitude of about 3,500 feet.
"Although the maximum yield of forage may be reached in about three
years of protection, improvements in quality of forage will probably go on
longer through the continued supplanting of annual plants by perennials of
greater value.
"Thus far alfilerilla is the only introduced plant which has succeeded and
this only in the most favored situations. It does not appear to thrive in com-
petition with the native perennial grasses at those altitudes where the latter
are not grazed.
"None of the other 200 lots of seed sown has given any promise of success
except those of three or four native species. These give beneficial results, but
the cost is high.
"Results seem to be secured much more rapidly through proper protection
from overgrazing than by any other method."
22 CONCEPT AND HISTORY.
Sampson, 1908, 1909, 1913, 1914.— The series of reports by Sampson on
revegetation in the Wallowa National Forest constitute a contribution of the
first inip>ortance to the science of grazing. They likewise furnish a large
amount of experimental data as to grazing indicators in the montane and
Bubalpine zones. The general results (1914:146) are applicable to a wide
range of grasslands and are summarized below. They not only take into
account the need of thoroughgoing and extensive studies of quadrats, factors,
and succession, but they also consider in detail the ecological requirements of
the various species.
"(1) Normally the spring growth of forage plants begins in the Hudsonian
■one about June 25. For each 1,000 feet decrease in elevation this period
comes approximately 7 days earlier.
"(2) In the Wallowa Mountains the flower stalks are produced approxi-
mately between July 15 and August 10, while the seed matures between
August 15 and September 1.
" (3) Even junder the most favorable conditions the viability of the seed on
summer ranges is relatively low.
" (4) Removal of the herbage year after year during the early part of the grow-
ing season weakens the plants, delays the resumption of growth, advances the
time of maturity, and decreases the seed production and the fertility of the seed.
"(5) Grazing after seed-maturity in no way interferes with flower-stalk
production. As much fertile seed is produced as where the vegetation is pro-
tected from grazing during the whole of the year.
" (6) Germination of the seed and establishment of seedlings depend largely
upon the thoroughness with which the seed is planted. In the case of practi-
cally all perennial forage species, the soil must be stirred after the seed is
dropped if there is to be permanent reproduction.
" (7) Even after a fertile seed crop has been planted there is a relatively
heavy loss of seedlings as a result of soil heaving. After the first season, how-
ever, the loss due to climatic conditions is negligible.
" (8) When 3 years old, perennial plants usually produce flower-stalks and
mature fertile seed.
" (9) Under the practice of year-long or season-long grazing, both the growth
of the plants and seed production are seriously interfered with. A range so
used, when stocked to its full capacity, finally becomes denuded.
" (10) Year-long protection of the range favors plant growth and seed pro-
duction, but does not insure the planting of the seed. Moreover, it is imprac-
ticable because of the entire loss of the forage crop and the fire danger resulting
from the accumulation of inflammable material.
"(11) Deferred grazing insures the planting of the seed crop and the per-
manent establishment of seedling plants without sacrificing the season's
forage or establishing a fire hazard.
"(12) Deferred grazing can be applied wherever the vegetation remains
palatable after seed maturity and produces a seed crop, provided ample water
faciUties for stock exist or may be developed.
" (13) The proportion of the ranges which should be set aside for deferred
grazing is determined by the time of the year the seed matures. In the
Wallowa Mountains, one-fifth of the summer grazing season remains after the
seed has ripened, and hence one-fifth of each range allotment may be grazed
after that date.
" (14) The distribution of water and the extent of overgrazing will chiefly
determine the area upon which grazing should first be deferred.
CLEMENTS
PLATE 4
A. l'roUc(«'(i pjisture in A rUl ida-JJoukloua a-ssocialioii, riautu Rita Range Reserve, Tucson,
Arizona.
B. Fenced quadrat in rotation pasture, Bouteloua eriopoda consociation, Jornada Range
Reserve, Las Cruces, New Mexico.
HISTORICAL.
23
" (15) After the first area selected has been revegetated, it may be grazed
at the usual time and another area set aside for deferred grazing.
"This plan of rotation from one area to another should be continued, even
after the entire range has been revegetated, in order to maintain the vigor of
the forage plants and to allow the production of an occasional seed crop."
Jardine, 1908, 1909, 1910, 1913.— Jardine has made a careful study of the
relation of coyote-proof pastures to carrying capacity, and finds that the
latter is nearly 100 per cent greater than under the usual method of herding
in large bands. This is due to the fact that the sheep graze much more
openly and do much less trailing, with the result that the vegetation is trampled
very much less (1908:31, 1909:38).
1 he estabhshment of grazing reconnoissances on the six forest districts and
the organization of a method by Jardine in 1911 marked the beginning of an
adequate system of grazing on the National Forests. This work has yielded
a large number of facts of importance in connection with grazing indicators.
Although it has never been published, its value is such as to warrant a brief
abstract of it here. The main object of the reconnoissance was to secure a
map classifying all the land of each National Forest into grazing types, and
the location of each type, its carrying capacity and nature, whether winter,
smnmer, or year-long range. The field notes dealt with the dominant species
of each type, the density of ground cover expre^ed in tenths, the degree of
utilization, and the presence of poisonous plants and range-destroying animals.
Of most interest to the student of indicator plants is the system of types and
subtypes which is outlined below. As quadrats gradually came into use in
connection with reconnoissance, the latter is now intensive to some degree in
its methods.
Type 1. Open grassland other than meadow
and secondary meadow.
Subtypes: bimch-grass, grama grass.
Type 2. Meadows.
Subtypes : wet meadow, dry or secondary
meadow.
Type 3. Weed.
TVpe 4. Browse.
Type 5. Sagebrush.
grasses,
Type 6. Timber, with a cover of
weeds, and browse.
SubtjTpes: pine-grass, weeds, browse.
Type 7. Waste range.
Subtypes: waste timber, waste brush
Type 8. Barren land.
Type 9. Woodland.
Type 10. Aspen.
Wooton, 1915, 1916. — In his discussion of the factors affecting range man-
agement in New Mexico, Wooton (1915:20, 23) has touched incidentally upon
grazing indicators. The bulletin on the carrying capacity of ranges in southern
Arizona (1916) continues the studies carried on by Grifl&ths from 1903 to
1910. Five associations are recognized, and an interesting account is given
of the secondary succession following plowing in the crowfoot-grama and the
six-weeks grass communities. Of especial interest is the account of carrying
capacity as determined by cut-quadrats, and by actual grazing tests in the
various pastures. The conclusions are grouped under the following heads :
Recovery. — The revegetation above 3,200 feet had become marked in about
three years after fencing. This improvement has continued, but more and
more ^owly each year, indicating that the normal condition is being reached.
Below 3,200 feet, the rate of recovery has been slower and hence it should
24 CONCEPT AND HISTORY.
continue for a longer period. Three years of complete protection gave about
three-f curt lis of complete recovery for the crowfoot-grama consociation with
an annual rainfall of 15 to 18 inches. After 11 years the grazed areas are but
partially recovered, though their carrying capacity has increased about 30
percent.
Reteeding. — Practically all attempts to introduce new species of forage
plants or to increase the abundance of endemic species beyond the normalhave
failed. Alfilaria and some aggressive annuals have given promise, but in the
course of a few years the native perennials have crowded them out.
Carrying capacUy. — This has been determined by means of cut-quadrats,
hay-cutting, mapping the communities, and by grazing tests of the best part of
the reserve. For the latter, the carrying capacity is 14 acres per head, while
it is 20 acres for the whole reserve. One of the pastures stocked on the basis
of 58 acres per head was not noticeably different in condition from adjacent
land protected for 1 1 years, thus indicating a utilization below 50 per cent.
Jardine and Ilurtt, 1917. — In the account of the results obtained on the
Jornada Grazing Reserve from 1912 to 1917, Jardine and Hurtt have em-
bodied the essentials of the first complete grazing system based upon actual
experimental study of the herd as well as of the range. As a consequence, it
serves as an excellent model for all ranches large enough to permit the rotation
system of pastures and to warrant the segregation of herds by ages and classes.
Taken in conjunction with the more intensive grazing experiments such as
have been carried on by Sarvis (1919) at Mandan, it furnishes a complete
experimental method of range studies. It is especially important in demon-
strating how much experimental work and resulting improvement of range
and herd can be carried on even under existing economic conditions on well-
managed ranches (plate 4, b).
The authors' most important conclusions are as follows:
The grama-grass range has improved at least 50 per cent in three years,
compared with adjoining unfenced range grazed yearlong. This has been
secured by reducing the number of stock during the main growing season from
July to October to about half the average number the area will carry for the
year, by refraining from overstocking during the other eight months and by
better distribution of watering places. The range thus lightly grazed during
the growing season has apparently improved as much as similar range pro-
tected during the whole year. Where the whole of a range unit is grama,
about one-third should be reserved in rotation for light grazing during the
growing season for two successive years.
Fairly efficient utilization of the range is secured by watering places with a
2.5 mile grazing radius. When the distance is greater than this, serious over-
grazing or actual denudation occurs around the well or tank, while the remote
areas are but partially utilized. The carrying capacity of the grama grass is
20 to 30 acres, of the tobosa grass 38 to 45 acres, and of the mountain range
60 acres. This is based upon carrying stock through the average year in good
condition, and feeding the poorer stock concentrates to eliminate loss from
starvation at critical periods.
Jardine and Anderson, 1919. — In an account of range management on the
National Forests, Jardine and Anderson (1919: 17) have discussed briefly the
general indicators of overgrazing:
HISTORICAL. 25
"Overgrazing for an extended period will leave 'earmarks,' which usually
will be recognized. To recognize current overgrazing at the time of examina-
tion on a range previously not overgrazed is difficult and yet important in
order to make timely adjustment. The following obvious earmarks are the
most rehable indicators of overgrazing prior to the year of examination:
" The predominance of weeds and grasses such as knotweed (Polygonum spp.),
tarweed (Madia spp.), mustard (Sophia incisa), annual brome grasses (Bromus
hordeaceus, brizaeformis, tectorum), and fescues (Festuca megalura, micro-
stachys, confusa), with a dense stand of such species and lack of variety in
species. This condition is a severe stage of overgrazing such as occurs around
sheep bedding grounds which have been used for long periods each year for
several years in succession.
" The predominance of plants which have Utile or no value for any class of stock,
such as sneezeweed (Dugaldia hoopesii), niggerhead (Rudbeckia ocddentalis),
yellowweed (Senecio eremophilus) , snakeweed (Gutierrezia sarothrae) and gum-
weed (Grindelia squarrosa). These and similar plants frequently occur in
abundance over large areas of range and indicate that the range needs careful
management to give better forage plants a chance to grow.
" The presence of dead and partly dead stumps of shrubs, such as snowberry
(Symphoricarpos oreophilus), currant (Ribes spp.), willow (Salix spp.), service
berry (Amelanchier spp.), birch-leaf mahogany (Cercocarpu^ montanus), and
Gambel oak (Quercus gambellii). This condition usually indicates that the
most palatable grasses and weeds have been overgrazed. There may be some
exceptions to this, as in the case of drawfed willows on ranges where grasses
predominate above timber line. Sheep sometimes kill the willows before the
grasses are overgrazed.
^^ Noticeable damage to tree reproduction, especially to western yellow-pine
(Pinus ponderosa) reproduction on sheep range and aspen (Populus tremu-
loides) reproduction on cattle range. Lack of aspen reproduction on a weed
sheep range indicates overgrazing, provided the natural conditions are favor-
able to aspen reproduction. On a sheep range where grass predominates
severe injury to western yellow-pine or aspen reproduction may indicate that
the range is not well suited to sheep.
"The earmarks described are, perhaps, more typical of overgrazed sheep
range than of overgrazed cattle range, but the general appearance of the two
does, not differ greatly when overgrazing reaches a stage to be recognized by
one or more of these earmarks. The main differences are in the species of
plants indicating the overgrazing. Weeds eaten by sheep are often found in
abundance on overgrazed cattle range; coarse grasses palatable to cattle are
often abundant on overgrazed sheep range. This fact has given rise to the
use of the term 'class overgrazing.' "
Sarvis, 1919. — ^The first adequate intensive experiments in grazing have
been carried on by Sarvis (1919) at Mandan, North Dakota, since 1916, and
at Ardmore, South Dakota, since 1918. These have dealt primarily with
carrying capacity and rotation grazing, though a number of related problems
have been taken into account, such as rate of growth, effect of mowing, etc.
The experiments are based upon actual grazing tests to determine the present
carrying capacity of a particular type and the optimum utilization resulting
from rotation At Mandan, for example, the carrying capacity tests comprise
four fields of 30, 50, 70 and 100 acres respectively, each grazed by 10 animals
of the same age and class. These are weighed at frequent intervals and the
carrying capacity expressed in terms of pounds gained in weight. There are
26 CONCEPT AND HISTORY.
three rotation pastures to permit grazing during one-third of the growing
aeaaon— fipnng, summer, and fall respectively. The behavior of the community
under the different degrees and kinds of grazing is measured by means of an
unusually complete system of chart- and cut-quadrats. The details of the
method are discussed in Chapter VI.
CHRESARD AND WATER REQUIREMENT STUDIES.
SIgnifleanee. — While practically all studies of the chresard or available
water in soils have been made without definite reference to indicator plants,
it is clear that they have a direct bearing upon the latter. This is Ukewise
true of researches upon water requirements, especially those that relate to
controlling physical factors. Since the value of an indicator depends upon the
exactness of its correlation with direct factors, and especially water, it is often
totally misleading to relate it to obvious or superficial facts. For this reason
a scientific s)rstem of indicators has but recently become possible. It was a
distinct step in advance to connect species with the total water-content or
holard. But this gives trustworthy results only for the same soil. To obtain
exact results it has become necessary to determine the water-withholding power
of different soils and the water-using capacity of different plants. It has like-
wise proved imperative to take into account the salt-content and air-content
of the soil solution. In the further analysis of indicators, it proves desirable
to utilize their form, growth, and abundance for more minute and exact values.
Hence a knowledge of the growth requirements, which are largely water
requirements, has come to be highly significant.
Much work has been done upon the chresard of different soils and plants,
and a still larger amount upon water requirements. Most of the former is
American, and has been done in the West. As a result, it has a direct bearing
upon the problem under consideration here. Of the great mass of water
requirement data only a few deal with native or non-cultivated species, and
are pertinent to the present discussion. For these reasons a concise account
is given of the progress of the chresard concept.
The chresard. — The earliest studies of the water-content non-available to
plants were incidental and failed to recognize the fundamental importance of
the distinction.
Sachs (1859, 1865 : 173) found that a young tobacco plant began to wilt in
a mixture of sand and beech mold at 12.3 per cent and that the chresard for
this soil was 33.7 per cent. A second plant in clay wilted at 8 per cent, with
a chresard of 44.1 per cent, while for a third the echard in sand was 1.5 per
cent and the chresard 19.3 per cent. Heinrich (1874) determined the echard
of barley in peat as 47.7 per cent and of rye as 53.4 per cent. In calcareous
soil com wilted at 8.6 per cent and broad beans at 12.7 per cent. Mayer
(1875) observed that pea plants wilted at 33.3 per cent in sawdust, 4.7 per
cent in marl, and 1.3 per cent in sand, while Liebenberg found that beans
wilted in loam at 10 per cent, in marl at 6.9 per cent, and in coarse sand at
1.2 per cent.
Gain, 1895. — Gain (1895 : 73) has studied the behavior of three mesophytes
in six different soils, with the results indicated in the table below. The echard
varies less than 50 per cent for these species in any one of the first three soils.
HISTORICAL.
27
but the variation rises as high as 60 to 130 per cent in the last three. Part of
this may be due to a larger error in determining the low echard. The author
concludes that species not only wilt at different points, but also that this varies
for different stages of the development of the same species.
Soila.
Erigeron
canadensis.
Phaaeolua vulgaria.
Lupinus albus.
Echard.
Echard.
Echard.
I.
II.
I.
II.
I.
II.
Heath aoil..
Clay
Humua
T.ime soil . . .
Garden soil .
Sand
p.et.
9.26
7.73
6.80
4.19
2.30
0.45
p.et.
9.40
7.78
6.83
4.25
2.40
0.48
p. ct.
10.73
9.73
6.10
2.94
1.79
0.33
p.et.
10.60
9.58
5.92
2.90
1.88
0.35
p.d.
10.90
11.60
6.86
6.15
2.82
0.76
p.et.
11.10
11.36
6.95
6.23
2.91
0.76
Klhlmann (1890 : 105) was probably the first to perceive the ecological
significance of the echard, in connection with his studies of water relations in
the frozen bogs of Lapland. However, Schimper first recognized the universal
application of the concept and formulated it definitely as follows (1898 : 3;
1903:2):
"It is necessary to distinguish between physical and physiological dryness
and wetness; the physiological water-content alone is important for plant-life
and hence for plant-geography."
Neither Kihlmann nor Schimper appears to have made actual determina-
tions of the physiological water-content. Clements (Pound and Clements,
1900: 167; Clements, 1904:23; 1905:30; 1907: 13; 1916) developed methods
for determining the echard and chresard in the field as well as under control.
These were applied to various habitats in the prairie and woodland regions of
Nebraska, and on Pike's Peak in Colorado. The general results were in accord
with those of the earUer investigators, Sachs, Gain, and others, with respect to
the variation of the echard with different species as well as with different soils.
This led to a comprehensive investigation by Hedgcock (1902) of the echard
and chresard of some 130 species under control, and 25 in the field. These were
largely native and ruderal species, though a number of cultivated ones were
included also. The great majority were mesophytes, though they ranged from
xerophytic grasses, such as Boxdehua gracilis, to such hydrophytes as Sagittaria
and Potamogeion. The author reaches the general conclusion that " the abiUty
of plants to take water from the soil varies in an ascending scale from hydro-
phytes through mesophytes to xerophytes."
Briggs and Shantz, 1912. — The most complete and thoroughgoing investiga-
tion of the echard has been made by Briggs and Shantz in connection with
crop-plants for the Great Plains. Their methods and results are perhaps too
well known to require comment, but it seems desirable to touch the latter
briefly for the sake of comparison. The term wilting coefficient is employed
for non-available water or echard, but it is an exact synonym of these. The
determinations of the echard for various soils are in essential accord with those
28 CONCEPT AND HISTORY.
of all other investigators, the values ranging from 1 per cent to 16 per cent,
or in the heaviest clays to 30 per cent. But a striking departure from all
previous results occurs with respect to echard for different species. While
Heinrich, Gain, Clements, and Hedgcock found differences between species
in the same soil represented by a ratio of 1 to 1.5 or 1 to 2, or even more in the
case of hydrophytes, the greatest ratio found by Briggs and Shantz was 1 to
1.1. The thorouglmess of their work seems to leave little question of the
soundness of the conclusion "that the differences exhibited by crop plants in
their abiUty to reduce the mositure content of the soil before wilting occurs
are so slight as to be without practical significance in the selection of crops for
semi-arid regions." The issue must still be regarded as open with reference
-to material differences in the echard of native species, and this can only be
settled by further research. Recent studies by Dosdall (1919) have shown
that Equisetum differs greatly from Helianthus and Phaseolus in its ability to
draw water from the soil, as was likewise demonstrated by growing them side
by side in the same spots. In seeking to harmonize the discordant results of
qualified investigators, it has become more and more probable that types of
echard must be recognized.
Water requirement. — In summing up the results of their own researches, as
well as those obtained by many earlier observers, Briggs and Shantz (1913 :
1:46; 2:88) reach the following conclusions:
Experiments upon the effect of water-content on the water requirement
show that the latter increases as a rule when the water-content approaches
either extreme.
A reduction in water requirement generally accompanies an increase in the
nutrient-content, while a higher water requirement may result from a defi-
ciency in the amount of a particular nutrient.
The type of soil affects the water requirement only though the water or
the solutes it contains.
The water requirement increases with the dryness of the air, and is pro-
foundly affected by climatic conditions.
The water requirement varies greatly for different species and varieties. In
Colorado, it was found to be approximately 1,000 for alfalfa, 700 for sweet
clover, and 300 for millet and sorghum. The grains ranged from 369 for corn
to 507 for wheat and 724 for rye.
The greatest value of water requirement work for indicator studies is in
connection with the phytometric analysis of climates and habitats. So far as
the water relation is concerned, the values obtained by means of phytometers
can be expressed in terms of water-loss per unit area or rate of growth, or in
the water requirement in terms of dry weight or seed production. For crop
plants, the latter are the most important, but for native species all four values
must be taken into account, in addition to photosynthetic efficiency.
CONCEPT.
General. — Every plant is an indicator. This is an inevitable conclusion
from the fact that each plant is the product of the conditions under which it
grows, and is thereby a measure of these conditions. As a consequence, any
response made by a plant furnishes a clue to the factors at work upon it.
While this general principle seems to be of universal significance, its applica-
tion is far from simple. This is because the most direct responses are physio-
CONCEPT. 29
logical and for the most part can be determined only by experiment. Such
complex physiological processes as growth and reproduction are exceptions
inasmuch as they are subject to direct observation. Consequently they are
among the most valuable of indicator evidences. Structural responses are
the most visible of all, but their exact use is the most difficult since they stand
at the end of the process initiated by the causative factors. Structure also
possesses a well-known inertia, as a result of which it may register the impact
of factors but partially or slightly. Moreover, the adaptation to the habitat
may be made in the tissues of the leaf without affecting the gross features to
an appreciable degree. A plant may show the most exact response to chang-
ing conditions by the behavior of chlorenchyma or stomata, and yet reveal
no sign of this in its outward appearance (E. S. Clements, 1905).
The interpretation of indicators is profoundly affected also by the double
complex of factors and plants. The species of a community do not always
register the same response, nor do they respond to any one factor in the same
degree. The habitat itself is still largely a puzzle, and it is often difficult to
assign well-marked effects to definite causes. The behavior of individuals,
though manifestly of less importance, is not without its difficulties. It is^
impossible to tell at present whether the varying behavior of individuals of 1
the same species is due to individuality or to minute differences in the habitat. 1
Hence, the problem of indicator values is chiefly one of analyzing the factor- I
complex, the habitat, and of relating the functional and structural responses 1
of both the plant and community to it. This then makes possible the accurate /
emplojTnent of indicators in practical operations. ^
Animals as indicators. — Since their response is direct, plants are the best
indicators of physical processes and factors. They are by no means unique
in this respect. Animals likewise show direct responses to physical conditions
and to this extent serve as indicators of them. For a number of reasons they
are inferior to plants, however. The chief reason is that their significance is
subordinate to that of plants because the latter as food-supply usually con-
stitute the controlhng factor. In other words, animals are as a rule indicators
of plants more directly than of physical conditions. Their mobiUty makes
the control of a particular habitat or set of conditions less absolute, especially
with land animals. With the exception of insects, land animals are much less
abundant than plants, and the indications of an animal conmaunity are much
less complete and definite. Finally, our knowledge of the ecology of animals is
much less than that of plants, especially with reference to factor control and
succession. In spite of all this, however, animals do have great indicator
value, second only to that of plants. While the time has not yet come for an
adequate treatment of them in this connection, they are taken into account
at various points in the text. Indeed, any other course would be illogical in
view of the conviction that the complete response to habitat is the biome, or
community of both plants and animals.
Plant and community. — It has already been suggested that the individual,
the species, and the community are all involved in the indicator concept.
Each of these has its own value, while all of them must be taken into account
sooner or later. Up to the present, the species has almost monopohzed the
r61e, though the work of Shantz (1911) in particular has emphasized the impor-
tance of the community as an indicator. In constructing a complete scale of
30 CONCEPT AND HISTORY.
indicator values, the individual will play a necessary part. Its indications
are more minute and subject to greater error. While further quantitative
work will increase the accuracy and usefulness of individual indicators, at
present they are distinctly secondary. In fact this will probably always be
their relative position, inasmuch as they will serve to refine the major indica-
tions of species and communities. The question of species and community
values is much simpler than appears at first. It is not a matter of employing
one to the exclusior^ of the other, but of taking advantage of their complemen-
tary relation. There can be no doubt that the community is a more reliable
indicator than any single species of it. This is a necessary consequence of
the essential harmony of the important species as to physiological response
and factor control. The community not only affords a better norm for the
major indications, but it is likewise, so to speak, more finely graduated and
hence more sensitive, owing to the fact that no two of its dominants or sub-
dominants are exactly equivalent. It is also a better indicator of the whole
habitat, since it levels the variations from one point to another.
The indicator value of a species depends primarily upon its r61e in the com-
munity. A secondary or subordinate species may be of little or no practical
value, in spite of the general rule. It merely accompanies the major species,
or as a subordinate accepts the conditions made by them, thus indicating minor
differences. It assumes practical value only in case of the destruction of the
dominants, as often happens in overgrazing and in deforestation. Even here
the real meaning of a secondary species is due to the fact of its association with
more important indicators. The significant species are the dominants and
subdominants which give character to definite communities. With these the
species and community values approach closely or merge completely. In fact
such species give their typical indication only where dominant. Their inci-
dental or scattered occurences may have meaning, but it is not the normal
one. In the present stage of our problem, then, attention should be focussed
upon the dominants and subdominants of the climaxes and their various seres.
When these have been correlated on the one hand with their efficient factors
and on the other with practical processes in agriculture, grazing, and forestry,
it will become evident whether an analysis of secondary species is profitable.
The dominant may well be regarded as the real basis of indicator study, so
conmianding is its r6le in the processes of vegetation (plate 5, a).
Sequences. — Every indicator owes its value to its position in a cause-and-
effect sequence. With this, however, must always be associated correspon-
dence with another cause-and-effect sequence. The value of the compass-
plant, Silphium ladniatum, as an indicator of corn production rests not merely
upon its preference for relatively moist rich soils, but also upon an experiential
knowledge at least of the production capacity of such soils. Up to the present,
our knowledge of indicators rests chiefly upon the basis of experience. In
emphasizing the point that this alone is usually inaccurate and insufficient,
there is no intention of failing to give it proper recognition. It is an essential
and often the critical part of indicator research, but its true value can be
obtained only by correlation with the other steps of the process. As a conse-
quence, it makes Uttle difference whether the approach has been through
experience or investigation. Both must be taken into account before the
CLEMENTS.
PLATE 5
A. Dommiiut A ;ir„ /,,/,. .,,1 and subdominant Tradescanlia vimininmi in mixed
prairie, Winner, i^ouih Dakota.
B. Agropyrum glaucum in roadway in sagebrush, indicating the relation of water-content to
competition, Red Desert, Wyoming.
CONCEPT. 31
exact meaning of any indicator is secured. For the future it is clear that
much time will be saved by a method of investigation which replaces more or
less vague experience by actual investigation.
Direct and indirect sequences. — As is shown later, plants may indicate con-
ditions, processes, or uses. The simplest of these is the first, the most prac-
tical is the last. The plant may indicate a particular soil or climate, or some
limiting or controlling factor in either. This would seem to be axiomatic, but
it is well known that grassland, which is typically a climatic indicator, often
occupies extensive areas in forest climates. Thus, the presence of a plant,
even when dominant, is only suggestive of its meaning. It is necessary to
correlate it with the existing factors and, better still, to check this correlation
by experimental planting, or an actual tracing of the successional development.
Indicators of processes usually require a double correlation, namely, that of
the plant with the controlling factor, and that of the factor with the causal
process, such as erosion, disturbance, fire, etc. Thus, in the Red Desert of
Wyoming, roads through the sagebrush are marked by vigorous growths of
Agropyrum. The latter is here a clear indicator of disturbance. From its
usual position in adjacent lowlands, it is presumably an indicator of increased
water-content as well. Actual instrumental study alone can determine the
exact relation between the disturbance and the water-content, and between
the water-content and the presence of Agropyrum. The indicator sequence
is further complicated by the question whether the increased water-content is
due to disturbance directly, to the elimination of competition, or to both. As
a matter of fact, however, the field study of Agropyrum and Artemisia under
a wide variety of conditions and in different successional relations indicates that
disturbance acts through competition upon water-content (plate 5, b; plate
a; cf. Weaver, 1919, for plate 26 a).
In the case of use or practice indicators, the sequence differs in accordance
with the nature of the crop. When the crop is a natural one as in grazing,
the sequence is simple and direct. This is especially true of grazing in which
the value of the range is determined directly by actual experiential or experi-
mental grazing tests, which establish the indicator value of each species. With
overgrazing, the sequence is similar to that found in process indicators.
Trampling disturbs the soil and destroys the less resistant plants. Both
effects tend to increase the water-content of the soil and to give the advantage
to such plants as Gutierrezia and Artemisia frigida (Clements, 1897 : 968;
Shantz, 1911 :65). This relation is clearly recognizable in the field from the
fact that Gutierrezia, for example, is characteristic of depressions, alluvial fans,
roadways and other disturbed areas. In the case of forests, plants may serve
directly as indicators of water or light values, or indirectly of disturbance such
as limibering or fire, and of such practices as reforestation and afforestation.
In these processes the crop is partly or wholly artificial, and the indicator
sequence is essentially the same as for crop plants. This involves the corre-
lation of indicator and crop plants with their respective habitats, and the close
correspondence of the controlling factors in the latter. With forage and grain
crops, the sequence is more complex, partly because the species concerned ar
not native, but largely because the physical conditions are unnatural as well
as controlled. As a corisequence, while factor correlation and indicator corre-
spondence are still important, the chief part must be taken by experiment and
32 CONCEPT AND HISTORY.
experience extending over a period of years. It is desirable if not essential
that this period be 12 to 15 years, in order to cover the range of conditions
from the wet phase to the dry phase of a climatic cycle. This is particularly
true in the use of indicators for land classification, in which grazing, forestation,
and crop production must all be taken into account.
Direction of indication. — The increasing attention paid to plants as indicators
during the past decade has largely arisen from practical considerations. While
this is highly desirable, it must be recognized that indicators have also a wide
range of scientific application. Moreover, the more important and certain
practical values are made possible only through the ecological study of indi-
cators. It is in the ecological sense that every plant is an indicator. The
indicators of actual practice will be obtained by the selection of those which
are the most distinctive and dependable. Thus, while the indicators for graz-
ing, forestry, agriculture, and land classification will be established by more
and more exact study, many indicators will find their chief use in ecology and
related fields, which must lay the foundation for the scientific agrici^lture and
forestry of the future.
For these reasons, it is necessary to recognize that every dominant can be
used as an indicator of past and future as well as of present conditions. This
is due, of course, to the fact that every dominant or subdominant has a definite
position in succession. As a consequence, it is an indicator not only of the
plants which precede and follow it, but also of the soil conditions in which they
grow. At the same time the definite existence of a climatic cycle makes it
possible to relate growth and successional movements to climatic changes,
both past and future, and to extend the application of indicators correspond-
ingly. On the one hand, this enables us to greatly broaden and definitize the
use of plants as indicators of soil, climate, and vegetational movements in the
geological past; on the other, it permits us to look ahead and anticipate the
changes due to climatic cycles and the development and movements of vegeta-
tion and habitat.
Scope. — ^A complete understanding of the broad significance of indicator
studies must rest upon a recognition of the aims and methods of modern
ecology. In the early characterization of this field (Clements, 1905 : 1) it
was emphasized that ecology is the central and vital part of botany and that
all the questions of botanical science lead sooner or later to the two ultimate
facts, plant and habitat. These statements appear even truer to-day in the
light of the progress made during the past twelve years. The one essential
ampUfication is the inclusion of zoology, due to the growing conviction that
the real unit of response to the habitat is the biological community. Further-
more, it is desirable to place all possible emphasis upon the fact that ecology
must fix its attention upon habitat and conmiunity in their natural relation.
Finally, there must be the clearest recognition of the fact that the plant or
animal must be the final arbiter in ecology, except of course in the vast field
of human ecology. Fascinating and valuable as they are, instruments and
quadrats are useful only in so far as they tell us what the plant, animal, or
community is doing. The most complete records of climate, for example,
have no merit in themselves. They acquire value only as the plant or animal
discloses by its responses the factors or quantities which are effective or con-
trolling.
PLATE A
CONCEPT. 33
The threefold basis of ecology is factor, function, and form (Clements, 1907:
1). As a consequence, every ecological fact has its indicator significance,
and it becomes possible to determine these just as rapidly as factor correlar
tions are made. The chief objective for the student of indicators is the cause-
and-effect relation, and his chief task to show how effects may be used as signs
' of their causes. In a sense, the use of indicators reverses ecological procedure
inasmuch as it leads from effects to causes. Sooner or later it involves a more
or less complete system of reading all the evidence afforded by the responses
of plants and animals, whether as individuals or communities.
With respect to its application, the scope of indicator work is far-reaching.
It not only furnishes a basic method in ecology, and especially in succession,
but it is also equally applicable in paleo-ecology. Because it gives us the
judgment of the plant upon the physical factors of the habitat, it is indispens-
able to studies of soil and chmate in so far as they have to do with vegetation.
For the same reason, it is invaluable in land classification, and to the great
plant industries, agriculture, grazing, and forestry. While this is truest of
new regions, it holds to some degree for older agricultural commimities as well.
It applies with especial force to the great imoccupied or poorly utilized inte-
riors of other continents, such as South America, Africa, Asia, and Australia,
and is not without meaning for large stretches in Europe. In short, wher-
ever plants grow, in field, forest, grassland, or desert, indicator results are
always of some, and usually of paramount, importance.
In their relations to succession and to climatic cycles, plants exhibit some
of the most important indicator values. These involve quantitative relations
of abundance and growth which in conjunction with factor determinations
. will give to ecology an accuracy and certainty more and more approaching
those of the physical sciences. As a consequence, it will become increasingly
possible to definitize ecological processes and principles, and to use them as a
basis for accurately forecasting the behavior of plants under changed condi-
tions. Such prophecy is possible at present in any region where an adequate
study of succession has been made. Its scope will be extended and its proba-
bility increased in just the proportion that instrumental, quadrat, and devel-
opmental studies of vegetation become the rule.
Materials. — As has been suggested earlier, while every study of the actual
relation between habitat and plant is a possible source of indicator materials,
only those are of real value which are based upon instrumental, quadrat, or
Buccessional investigations. The permanent foundation of indicator research
must be laid by those studies which employ all three methods. For these
reasons the published sources of indicator material are relatively few and
recent. They are largely American and are confined almost wholly to the
period since 1900. In fact, adequate ecological studies having indicator values
as their avowed objective are all subsequent to 1910, and are largely due to the
appearance of Shantz's paper on the indicator value of natural vegetation
in 1911. As a consequence, the present treatise is of necessity based primarily
upon the investigations of the author during the past 20 years and of Shanta
for the last decade or more. While these have had indicator plants as a
definite objective only since 1908, the preceding 10 years of instrument, quad-
rat, and succession work were an intrinsic part of the investigation.
34 CONCEPT AND HISTORY.
Basing studies. — Initial studies of grassland were made in Nebraska from
1893 to 1898. These included a journey along the Missouri and Niobrara
Rivers during the summer of 1893, one to the plains and foothills in 1897, and
to the Black Hills in 1898. The first ecological expedition to Colorado was
made in 1896, at which time a provisional outline of the plant communities
was drawn up. Beginning with 1899, all the summers were devoted to inves-
tigations in Colorado until 1913, with the exception of that of 1911, which was
spent abroad. During the spring and fall from 1899 to 1907, studies in prairies
and woodland in eastern Nebraska were carried on with the aid of advanced
classes. The six summers from 1913 to 1918, inclusive, have been devoted to
vegetation studies throughout the West, with especial emphasis upon succes-
sion, indicator plants, and climatic cycles. From 1912 to 1917, the work of the
Botanical Survey of Minnesota was directed along similar lines.
The use of quadrats was begun in 1897 and the instrumental analysis of
habitats in 1898. The principles of succession were formulated into a working
system for the field in 1898 (Clements, 1904: 5), while studies of the echard
and chresard were first made in 1900. The fundamental importance of the
distinction between climax and serai communities was recognized in 1913,
and the significance of climatic cycles in 1914. The two most recent advances
which extend the use of indicators are the organization of the field of paleo-
ecology in connection with the study of Badlands in 1915-16 and the formu-
lation in 1916 of the concept of the biome as the basic biotic unit.
Shantz (1906) began the ecological study of Colorado vegetation in 1903 on
the basis of instrumental, quadrat, and successional methods. This led to
the direct study of indicator plants on the Great Plains (1911) and in the
Great Basin (1914). Out of this grew the extensive series of water require-
ment studies, as well as of transpiration, made by Briggs and Shantz between
1912 and 1916. During the same period much attention was paid to western
vegetation, and this was crystallized in the list of indicator types for land-
classification (Shantz and Aldous, 1917) and a map of the climax communities
of the United States (Zon and Shantz, 1919). The text accompanying the
map contains much information relating to the indicator value of the different
vegetation types.
II. BASES AND CRITERIA.
BASES AND METHODS OF DETERMINATION.
Fundamental relations. — Plants serve as indicators by virtue of their
response to conditions about them. Every plant response has some signifi-
cance, the kind and degree of which must be subjects of exact determination in
each case. Some responses are obvious, others less evident, while still others
are invisible though demonstrable. All these, however, must be referred to the
habitat for the decision as to their meaning and their possible use as indicators.
It is clear that the causal relation of the habitat to the plant is the primary
basis of plant indicators. Each response is the effect of some factor or factor-
complex acting as a cause, and is consequently the indication of this factor.
Tiie chief task of the investigator is the measurement of responses, and their
correlation with measured factors.
In deciding upon possible bases for an indicator method, physiological
responses and physical causes must be given the place of first importance.
As further consequences of these must be considered the responses shown in
the development and structure of communities, i. e., the basic facts of associa-
tion and succession. The method of obtaining the facts in these four great
fields will continue to be both empirical and experimental. Experiment will
steadily increase in amount and value, but the result will be to refine and direct
observation and not wholly to displace it. In fact, the more completely
experiment is taken into the field, the more readily will observation reveal
the meaning of the innumerable natural experiments brought about by changes
of habitat and of climate. In this there is no intention of minimizing the
crucial value of experimentation, but rather to widen its scope so that all
experiments can be taken into account. This is especially important when
one recalls the slow advance in experimentation under natural conditions and
the insignificant area covered by it. The possibilities of this method have
been strikingly shown for many years at the Alpine Laboratory, where numer-
ous examples of natural transplanting in fragmented habitats verify and
extend the results of a relatively small number of artificial transplantings.
Similar results are to be obtained from natural experiments on a wider scale.
The value of Bouteloua gracilis as an indicator of climate was graphically
shown in the bad-land levels at Glendive, Montana, in 1917. The drying culms
of the current year were just half as tall as those of 1916 which still persisted
in the same mat. The rainfall for the two years was 26 and 12 inches, respec-
tively. Thus the inevitable adjustment of the short-grass cover to decreased
rainfall and water-content furnished results hardly to be surpassed by the
most carefully checked experiment.
In indicator work, as in all adequate investigation, by far the best method
is that which uses all sources of information and does not emphasize one to
the neglect of others. While the very nature of indicators insures proper
consideration of habitat and plant, the study of each species must be accom-
panied by that of its associational and successional relations, and all four of
these objectives must be reached by the combined use of observation and
experiment, in which each must be utiUzed to the fullest capacity consistent
with accurate results.
35
36 BASES AND CRITERIA.
THE PHYSICAL BASIS.
Direct and indirect factors. — An adequate understanding of the habitat as
the cause of plant responses which serve as indicators must rest upon two
facts. The first of these is that the habitat is a complex, in which each factor
acts upon other factors and is in turn acted upon by them. The second is
that some of these factors are direct causes of plant response, while others
can affect the plant only through them. Water, light, solutes, and soil-air
are direct factors of the first importance because of their variation from habitat
to habitat. Other direct factors, such as carbon dioxid, oxygen, and gravity,
are negligible because of their constancy. Temperature is both direct and
indirect, but its indirect action through the water relation is usually the most
tangible. Wind, pressure, slope, exposure, soil texture, etc., are all indirect,
acting for the most part through water-content or humidity, or through tem-
perature upon these.
Too much importance can not be given this distinction between direct
and indirect factors. The indicator value of every plant depends upon it
absolutely. A plant can only indicate a direct factor. But by the correla-
tion of the latter with factors which are modifying it, the indicator response
of the plant may be related to these. Thus, dwarfed herbs usually indicate
a lack of water. In alpine regions this lack is largely caused by excessive
transpiration and evaporation due to low pressure. As a consequence, dwarfs
are typical indicators of high altitudes and hence of alpine climates. By other
correlations of direct factors with causative processes, such as disturbance,
erosion, cultivation, etc., plants come likewise to be used as process or prac-
tice indicators. The true basis of all plant indicators is to be found in the
responses made to direct factors, especially water, light, solutes, and soil-
air. These once established, it becomes a simple matter to connect indica-
tors with any correlated factor or process.
Controlling and limiting factors. — ^It is evident that the factor in immediate
control of the behavior of plant or community must be a direct one. But the
latter may be profoundly affected by another factor in which the actual con-
trol may be said to reside. For example, montane timber-lines are often
determined by water, but the availability of the water-content is decided
by frost and its sufficiency by the wind. As indicated above, the immediate
control and hence the immediate indication must be sought among the few
direct factors, while the final control and indication will be found among the
indirect factors which exert a critical effect.
All the direct factors of the habitat play a part in the responses of the plant,
but only those which vary widely in quantity leave a distinct impress upon it.
This is necessarily true, since such constant factors as carbon dioxid, oxygen,
and gravity produce fairly uniform responses, and consequently do not differ-
entiate species or communities. In the case of each individual plant or species,
its distinctive features are due to one of the variable direct factors. In prac-
tically all cases at least one of these will be deficient, with the result that it
becomes the limiting factor in the plant's development. This term is used in
an ecological sense and not in the physiological one employed by Blackman
(1905) and others. As a result the search for indicator correlations among
the four direct factors narrows itself to the one or two which are deficient.
Some of these factors regularly bear an inverse relation to each other and all
THE PHYSICAL BASIS 37
of them often show such a relation. Thus an abundance of water means a
lack of oxygen, and a deficit of water a strong soil solution. Habitats deficient
in light rarely show a lack of water or nutrients, though the oxygen-content of
the soil may be low also. In practically all herbaceous communities, light
is usually at the maximum, and the limiting factor must be sought in the soil.
Hence, a careful scrutiny of many habitats narrows the search for limiting
factors to a single one, and it is then possible to proceed at once with the
quantitative correlation of factor and indicator.
It must also be recognized that some factors Umit plant response in conse-
quence of an excess. This is true to some extent of solutes and water, but
not of Ught or oxygen in nature. Even with the former, while the excess
definitely limits or at least characterizes the plant's activity, the corresponding
deficit of water in saline soils and of oxygen in wet ones or in ponds also plays
a significant r6le. For water and solutes, it is probably more accurate to say
that the extremes, either excess or deficiency, act as limits. While there are
statements to the efifect that full sunlight is directly injurious to many species,
there is Uttle or no conclusive evidence. This feeling has been based largely
upon Bonnier's work with alpine dwarfing, which has not been confirmed by
similar studies in the Rocky Mountains.
After eliminating the large groups of species which owe their indicator
character to the limiting action of water, solutes, oxygen, or shade, there
remains a much larger group of sun mesophytes which bear no such distinctive
impress. In a mesophytic habitat the four factors are present in a more or
less balanced optimum. No one exists in marked deficiency or excess. Yet
it has been demonstrated experimentally that a moderate increase in any
one of the factors* will be reflected in an increase of growth. Each factor in
reahty exerts a circumscribed limiting action as an outcome of competition
between the plants. The various effects, however, are so moderate and so well-
balanced that it is practically impossible to separate them. While water is
usually paramount and light often the least important factor in the competi-
tion between sun mesophytes, all four factors show a limiting action in at least
a small degree. In spite of its apparent lack of a distinctive impress, a meso-
phyte is as much the product of its habitat as the well-marked hydrophyte or
halophyte, and serves equally well as an indicator.
Climatic and edaphlc factors. — The factors of climate and soil are so intri-
cately interwoven in the habitat as to discourage analysis. For many reasons
it is better to ignore such a distinction as of httle or no significance to the
plant and to fix the attention upon the cause-and-effect relation of one factor
to another, quite independently of its location. This will reveal clearly two
basic facts, namely, that the habitat is a unit and that the action of this unit
is focussed upon plant and community by one or two limiting factors. The
relation of the plant to water makes it evident that the distinction is merely
one of classification which has no real significance to the plant. Water-
content as a direct factor resident in the soil is directly or indirectly the result
of precipitation, a climatic factor, and is profoundly affected by humidity, a
climatic factor which it also influences. Its availability is determined by
soil-texture, solutes, and oxygen, all soil factors, and by temperature, which
belongs to both soil and air, though in origin it is climatic. The baffling nature
of the distinction has been well shown by Raunkiaer (Plant Succession, 1916:6).
38 BASES AND CRITERIA.
In one sense, however, the distinction may possess some value. This is with
reference to the factors which give character to the great areas marked by
cUmaxes, in contrast to locaUzed ones occupied by successional stages. It
is more or less convenient to refer to such areas as climatic or edaphic, if
it is recognized that the one denotes a permanent condition over a wide region
and the other a relatively transitory stage in a restricted area.
Moreover, the grouping of factors as physical and biotic appears to have
little value beyond that of mere classification. Furthermore, it does not con-
duce to clear thinking to use the same causal terms for the physical conditions
which control plants and animals, and for the plants and animals themselves.
With the growing recognition of the community as consisting of both plants
and animals, the true nature of biotic factors will become evident, and they
will be recognized as reactions.
Climates and habitats. — If one accepts the developmental basis for the study
of vegetation, he must also admit the same process in habitats. Habitat and
community develop reciprocally from extreme conditions to the final climax
controlled by the climate. At this point climate and habitat become merged
and are coextensive with the major community, the climax formation. In
this connection, however, it is necessary to discard our ordinary ideas of climate
and to accept the plant's view of what constitutes a climate. The fact has
been appreciated by Wojeikov especially, in his work on the climate of beech
(1910). The great grassland climax of North America lends particular
emphasis to the difference between climates as determined by plants and by
man. In the human sense the climate of southern Saskatchewan is very
different from that of northern Arizona, chiefly because of temperature, yet
Bouteloua gracilis is an important grass in both places and the grassland
formation is characteristic of both regions. Likewise the Palouse district of
Washington and Idaho with its winter rainfall seems wholly different from
the bunch-grass hills of Utah and the prairies of Nebraska; but if the vegeta-
tion be taken as the indicator of climate, all three are essentially the same,
since they are characterized by prairie associations (Weaver, 1914, 1917).
The acceptance of the climax climate as the major or climax habitat enables
us to estabUsh a perfect correlation between habitat and vegetation. The
climax habitat will show divisions corresponding to the association, and each
association habitat will exhibit subdivisions in agreement with the consocia-
tions. This is practically axiomatic, since each community is the product of
the factor complex of its habitat. The habitat of one association must neces-
sarily differ from that of another to the degree that one association does from
the other. The subordinate communities of a formation, viz, societies and
clans, also have their minor habitats, though these are less clearly marked, as
would be expected. The structure of the climax climate or habitat corre-
sponds closely if not exactly with that of the climax formation. It may be
best illustrated by the grassland climax with its five associations, namely, the
true prairie, mixed prairie, bunch-grass prairie, the short-grass plains, and
desert plains. While all of these fall in the same climax climate, each one
marks a corresponding division of it, or a subclimate. In the case of the true
prairie, there are five dominants or consociations, Stipa spartea, S. comata,
Agropyrum glaucum, Koeleria cristata, and Andropogon scoparius, no two of
them exactly equivalent as to habitat. Their requirements approach each
THE PHYSICAL BASIS. 39
other so closely, however, that they occupy the same sublicmate, in which they
mix or separate in accordance with local variations. An interesting regional
separation occurs with the two species of Stipa, as well as in the case of
Agropyrum. Stipa spartea marks the eastern portions of the true prairies
and S. comata the western; Agropyrum glaucum is typically associated with
Stipa comata, while A. spicatum is best developed in the Northwest, especially
in the Palouse. The essential point is that each consociation or mixture of
two or more marks a subdivision of the association habitat, and is the indicator
of it. Similar though minor habitat divisions are indicated by such character-
istic societies as those of Glycyrhiza lepidota, Amorpha canescens, Psoralea
argophylla, P. tenuiflora, Petalostemon Candidas, and P. purpureus, the water
relations of which are essentially in the order given here. In the eastern
prairies, where water is abundant, several of these may occur together more or
less constantly, but farther west each tends to form a distinct society, and to
indicate a corresponding water-content. The differences are slighter than in
the case of consociations, and hence society habitats do not necessarily fall
in the habitat of a particular consociation. This is probably to be explained
partly also by the action of climatic cycles. For example, the wet phase would
favor the local extension of Psoralea argophylla and Petalostemon candidus for
a few years, while during the dry phase the less mesophytic Psoralea tenuiflora
and Petalostemon purpureus would have the advantage.
Since the habitat, like the formation, shows development in the course of
succession, it exhibits developmental divisions and subdivisions. Each of
these necessarily has its own indicator community, namely, the associes, con-
socies, and socies. The habitats which correspond to these have a time as
well as a space relation. If the best-known succession, the hydrosere, be
taken as an example, these two relations are shown in the familiar zones of
lakes and ponds. Each plant zone or associes from the center of submerged
plants to the surrounding climax of forest or prairie indicates a major develop-
mental habitat, e.g., the habitat of the floating aquatics, of the reed-swamp
the sedge-swamp, etc.* Each of these associal habitats is subdivided into the
habitats of consocies indicated in the reed-swamp, for example, by Scirpus,
Typha, and Phragmites, respectively. Within the latter may be minor habitats
characterized by such socies as Sagittaria, Alisma, Heleocharis, etc. As a
result every region is a complex of climax and developmental habitats of vary-
ing rank and extent, each controlling a plant community which serves as the
indicator of it.
Variation of climate and habitat. — While many reasons make it desirable if
not necessary to regard each habitat as a unit, it should be clearly recognized
that it varies from place to place and from year to year. The seasonal varia-
tions are more or less of the same character and they are marked by their own
indicators in the form of the seasonal societies. A grassland climate is char-
acteristically different from a forest climate by virtue of its product, the
grassland climax. This has its explanation in the average difference between
'Pearsall (1917 : 78) has recently recognixed three associes of submerged plants, namely, (1)
linear-leaved associes of iVaias, etc.; (2) Potamogeton associes; (3) NUeUa associes. This is in
full accord with our growing knowledge of vegetational development, which must result in the
general acceptance of more rather than fewer units (Clements, 1916 : 132). However, the latter
must be based upon quantitative studies and checked by extensive scrutiny of other vegetations
if the results are not to be mere personal judgments, leading to the condition in which taxonomy
finds itself to-day.
40 BASES AND CRITERIA.
the controlling factors of the two during a term of years, but this difference
is often less than that shown by the grassland climate in the dry and wet
phases of the same climatic cycle. The rainfall of the wet phase if continued
for a century or two under natural conditions would turn the prairie into
forest, that of the driest period would under the same conditions convert it
into desert. Similarly the distribution of rainfall is so erratic that two con-
tiguous locaUties may show striking differences amounting to the success or
failure of a particular crop. Progressive changes of rainfall, temperature, and
evaporation occur with increasing altitude, latitude, and longitude. Further,
each climate shades imperceptibly into the next, often through wide stretches.
These are all elementary facts and the climatologist might well say that they
are taken account of in the ordinary way of determining means or normals.
As a matter of climatology this is true, but from the standpoint of indicator
vegetation it is not. It is a simple matter to trace the line of 20 inches of
rainfall, or of the 60 per cent ratio of rainfall to evaporation and to assume
that it marks the line between prairies and plains. Such an assumption
reverses the proper procedure, in which the associations themselves must be
permitted to indicate their respective climates. When this has been done
and the limits of the various communities established, it will be possible to
determine the correlated factors.
The real importance of climatic variations within a chmax habitat lies in
the fact that the correlations of vegetation and climate must be studied on
the spot year by year. No single station can be typical of the whole habitat,
and no year of the whole cycle. Yet for each station and for each year the
indicator evidences of the vegetation should correspond closely if not exactly
with the controlling factors. As a result, the study of representative localities
for each year throughout a climatic cycle should disclose the range of fluctua-
tion in both cUmax habitat and vegetation, and establish all the indicator
values of the latter upon a secure basis.
The minute study of habitats reveals differences which are reflected in the
behavior of plant and community, and hence cause the latter to serve as
indicators. It is probable that every square foot of a habitat differs in some
degree from every other one. Moreover, when the reactions of competing
plants are taken into account, the differences are often more minute. In
natural studies of competition made in Colorado and in Cahfornia, as well as
in competition cultures, differences of height and flowering have been found
for each inch or two. Corresponding differences of density are of even more
frequent occurence in herbaceous communities. These indications have been
checked by factor determinations only in a few cases as yet, but there can be
little question that many more habitats show the most minute differences,
each with the corresponding indication in terms of density, height, reproduc-
tion, etc. In short, the indicator correlation of plants and habitats exemplifies
a universal principle which applies from the relation between climax formation
and habitat through units of diminishing rank to the relation between the
individual plant and its miniature habitat.
Inversion of factors. — One of the early puzzles encountered in indicator
studies, especially in connection with succession, was the occurrence of the
same dominant in adjacent but diverse areas. This was first noted for Andro-
pogon scopariiLS and Calamovilfa longifolia in sandhill and badland regions.
These were found in rough areas and in blowouts on the one hand and in
CLEMENTS
PLATE 6
A. Lowland me^quite (Prosojnsjuliflora) at 2,500 feet in the San Pedro Valley, Arizona.
B. Foothill mesquite meeting oak at 4,50Ofeet, Patagonia Mountains, Arizona.
THE PHYSICAL BASIS. 41
meadows on the other. While the serai relations were very different, the
relation to water was much the same. On the broken or sandy ridges the
soil was porous and the competition relatively small, due largely to the bunch
habit, while in the moist meadows the grasses grew in a sod, the competition
for water was keen, and the amount for each plant correspondingly limited.
A similar inversion in hilly and mountainous regions has since been found for
the majority of grass dominants, as well as for an increasing mmiber of shrubs.
The breaking-down of the Miocene rim of the Bad Lands of Nebraska and
South Dakota yields a talus in which Rhus, Ribes, Symphoricarpus, Rosa, and
other shrubs occur, all of which form dense thickets in the valley several hun-
dred feet below. Chrysothamnus, Artemisia, and Atriplex grow far up the
walls and buttes of bad lands, and are found again as dominants in the
ravines and draws. In the Southwest the desert scrub consists of two major
dominants, Prosopis and Larrea. While they are often mixed in the
vast stretch over which they occur, Prosopis is typical of the valley and
washes. The valley plains and bajadas are characterized by a zone of Larrea,
above which lie Aristida-Bouteloua grasslands wherever broad sloping plains
occur. In these Prosopis again occurs as a consequence of increasing rainfall,
at an elevation of 1,000 to 2,000 feet above its position in the desert (plate 6).
Similar inversions occur in mountain regions, either as a consequence of
air-drainage or of exposure, or often indeed of both. In the case of exposure,
the general relations are obvious, though the relative importance of water
and temperature is usually uncertain. It seems probable that both are
directly concerned, and that water plays the primary r61e, except in mountain
regions characterized by a very short growing season .and minimum night
temperatures (cf. Shantz, 1906:25; Shreve, 1915:64; Weaver, 1917:44). The
effect of temperature inversions was pointed out by Kemer (1876 : 1) and
Beck (1886 : 3) in Europe and has been studied by MacDougal (1900) and
Shreve (1912 : 110; 1914 : 197; 1915 : 82). The latter's conclusions are as
follows (1914 : 115):
"The influence of cold-air drainage might be expected to affect both the
upward limitation of lowland species and the downward occurrence of mon-
tane species. As a matter of fact the downward limitation of the forest and
chaparral vegetation of the desert mountain ranges is due to the operation of
the factors of soil and atmospheric aridity, and not to the chimenal factors.
The limitation of the upward distribution of desert species appears to be
attributable to chimenal factors, as the writer has shown for Carnegiea
gigantea. The writer has observed that a number of the most conspicuous
desert species range to much higher altitudes on ridges and the higher slopes of
canyons than they do in the bottoms and lower slopes of canyons. Samples
indicate that there is no essential difference between the soil moisture of ridges
and the bottoms of canyons during the driest portions of the year. Neither is
there any evidence that desert species would fail to survive in the canyon bot-
toms if they were somewhat higher in soil-moisture content. An explanation
of the absence of desert species from canyon bottoms and their occurrence at
higher elevations on ridges must be sought in some operation of the chimenal
factors rather than in the factors of soil and atmospheric moisture. An
analysis of the operation of the chimenal factors will be sure to discover that
cold-air drainage plays an important r61e in determining not only the lowness
of the mininaum, but also the still more important features of the duration of
low temperature conditions."
42 BASES AND CRITERIA.
Measurement of habitats — The importance of correlating indicator plant
or community with the controlling factors of the habitat has already been
emphasized. While the standard method of doing this has been by means
of physical instnmients, a number of attempts have been made to utilize
plants themselves for this purpose. While the work of Bonnier (1890 : 514),
in which he made reciprocal plantings of alpine and lowland plants, was essen-
tially of this nature, he seems to have had no thought of using plants as instru-
ments. The first conscious endeavor to do this was perhaps in 1906, when
potometers of several different species were used with recording instruments
to determine the effect of pressure on transpiration at different altitudes on
Pike's Peak (Clements, 1907 : 287; 1916 : 439). Sampson and Allen (1909:
45) employed sun and shade forms in different habitats at the Alpine Labora-
tory to determine transpiration in various light intensities, while standard-
ized plants of Helianthus annuus were utilized in habitat measurements con-
ducted by the Botanical Survey in Minnesota in 1909. During 1912-1913,
Pearson (1914 : 249) grew seedlings of Pseudotsuga beneath aspen and in open-
ings to determine the better habitat for planting operations, and the method
has since had a limited application by foresters. The most comprehensive
use of the planting method has been made by Hole and Singh (1916 : 48; cf.
Chapter III), who established experimental quadrats in the sal forests of
India to measure the role of shade and aeration in reproduction.
McLean (1917 : 129; cf. Livingston and McLean, 1916) employed soy beans
to measure general climatic conditions by means of growth at two stations in
Maryland. The three main criteria used in determining growth were leaf
area, stem height, and dry weight of tops, all of which showed the Easton region
to be nearly 2.5 times as efficient as the Oakland one. A definite correlation
was established for temperature, but not for water, owing to auto-irrigation
of the plants. Weaver and Thiel (1917 : 46) measured the transpiration rela-
tion by means of bur-oak seedlings in three habitats, prairie, hazel-scrub, and
oak forest, near Minneapolis. Similar measurements were made with maple
and elm seedlings in scrub and prairie at Lincoln. Further experiments were
made with sun and shade forms of the same species, and with sun and shade
branches of the same plant. The species employed were Acer saccharinum,
UlmtiS americana, Fraxinus lanceolata, Rosa arkansana, Prunus serotina, and
Acer negundo. The general results showed a transpiration 2 to 3 times greater
in prairie than in scrub and 6 to 10 times greater than in the Typha swamp.
Evap>oration was regularly greater than transpiration, and no constant rela-
tion was found between the two, as would be expected. Sampson (1919 :4)
has recently made a comprehensive use of Pisum arvense, Triticum durum,
and Bromv^ marginatum as standard plants in measuring the differences of
the climax zones of the Wasatch Mountains in central Utah (cf. Chapter VII).
The use of plants to measure light intensities has as yet received almost no
attention in spite of its great promise. This correlation has been made from
the standpoint of adaptation by E. S. Clements (1908 : 83); when combined
with growth and gross form, as in later studies, this method is simple
and of great value. Even more significant is the use of standard plants for
measuring light intensity and quahty by means of the photosynthate produced
in imit areas. Preliminary work of this nature has been carried out by Clem-
THE PHYSIOLOGICAL BASIS. 43
ents and Long (Clements, 1918:29; 1919; cf. Long, 1919) in the habitats at
the Alpine Laboratory, and the chemical procedure has been refined to furnish
a basic method of universal application. The use of plants as instruments for
habitat analysis is further discussed on a later page.
THE PHYSIOLOGICAL BASIS.
Kinds of response. — With rare exceptions a physical factor produces a func-
tional response. Such responses are the most direct and the most accurate
measures of the habitat, and hence would serve as nearly perfect indicators
were it not for their being invisible. Fortunately, functional responses when
marked regularly bring about structural changes which are visible. This is
especially true of growth which, as the middleman between function and form,
has the advantage of being direct as well as visible. Growth, like structure,
has the further merit of showing quaUtative as well as quantitative differences
and thus serves as an obvious record of abnormal response. From the stand-
point of indicators, it is desirable to take all three kinds of response — function,
growth, and structure — into account and to assign toeach its proper value. The
relative value is indicated by the sequence of the three as successive effects of
controlling factors as causes. The rapidity and accuracy of the response
decreases with the distance from the impinging factors, while the readiness of
its recognition correspondingly increases. As a consequence, indicator values
have so far been based largely upon species and form. The importance of
growth has later been recognized and it is but recently that function has been
taken into account. In the further investigation of plants as habitat measures
and indicators, it is essential to determine the functional responses first, as the
most direct and quantitative. These should then be correlated with growth
measures and the latter with structural adaptations. When this has once
been done, either structure or growth can be used as ready and accurate meas-
ures, without resorting each time to the experimental analysis involved in
functional measurements. As a matter of practical application, however, it is
probable that growth and reproduction will serve as the best indicators of
conditions for crop plants since the habitat is more or less controlled. In the
case of forest and grassland, where the factors are essentially natural, a further
analysis by means of functional determinations seems desirable if not imperative.
Effect of habit — There are three reasons for the superiority of function over
form for indicator correlations. The first is that considerable adjustments to
factors can occur without affecting structure at all, the demands being fully
met by functional responses. Another is that there is almost always a lag
between function and structure, by which the effects of a factor appear in the
latter only after a time or in diminished degree. These reasons are relatively
unimportant compared with the r61e of habit, however, and the second is
perhaps only a consequence of the latter. While there has been little experi-
mental study of habit as such, there are many suggestions of its importance in
modifying or reducing response, especially in structure. This influence of
habit is well known to foresters and agriculturists in connection with the
germination of seeds from different regions and the behavior of their seedlings.
It has also been shown in the case of alpine species transplanted to lower levels
in that some retain the dwarf habit and others do not (Bonnier, 1890), and
44 BASES AND CRITERIA.
for Bubalpine trees, some of which change their form and not their seasonal
phenomena, while others reverse this behavior (Engler, 1912 : 3). The
response of herbaceous species grown in two or more habitats is equally signifi-
cant. Some are so responsive or plastic that both form and structure show
practically perfect adjustment to each habitat in the first generation. Others
modify the form and not the anatomy, and still others the interior of the leaf
but not its form. There are all degrees of completeness of response to the
stable plant, in which form and structure change little, and all the adjustment
must be secured through function (E. S. Clements, 1905: 93).
As a consequence, the indicator value of any species can not be known until
its functional response has been measured and correlated with the structural.
This does not mean that the constant occurrence of a species in certain condi-
tions can not be turned to practical account, but it does suggest the wisdom of
regarding such correlation as tentative until the functional indication has been
determined. The latter will also solve the puzzles presented by communities
in which very different Ufe-forms, such as evergreen and deciduous trees,
appear to flourish on equal terms. The most striking case of the masking of
the real response by habit is seen in such leafless rush-forms as Sdrpiis locus-
tris and Eguisetum, in which it is now proved that the functional response is
that of a hydrophyte (Sampson and Allen, 1909 :49; Dosdall, 1919).
Individuality in response. — Indicator values center about the species. Uni-
formity of behavior imder uniform conditions and clear-cut adjustment when
these are changed are the essentials of a good indicator. For these reasons it
is important to deal chiefly with species which are represented by many indi-
viduals, such as dominants and subdominants, and hence to use the community
as the basis for indicators. This makes it necessary to determine the range of
individual response in function and growth as well as in structure. In devel-
oping the use of standard plants as instruments, this matter is of the first
importance. While the question of standardization will alv/ays enter, it will
be convenient to use those species in which the individuality of functional
response is shght. In the use of indicators, the range of individual behavior
is a less important consideration than the knowledge of the range.
Sampson and Allen (1909 : 37) have studied the individual behavior of four
montane species as to transpiration and reached the following conclusion :
"Only shght variations occur, not usually exceeding 3 mg. per square centi-
meter for a period of 12 hours. Therefore, it may be concluded that plants of
the same species grown in the same habitat when tested under the same
physical conditions show but shght variation in transpiration per unit of
surface exposed."
Effect of extreme conditions. — The significance of extreme conditions for
response and the relation to indicator values is shown by the case of xerophytes
and halophytes. While the latter are now known to be merely xerophytes of a
somewhat special type, they were long thought to constitute a distinct class.
This is still true in a measure of those species which tolerate salts directly
injurious, but it is well known that the majority owe their impress to physio-
logical dryness due to the abundance of salts. But, while halophytes are
indicators of arid conditions, it is a special type of aridity, and the indication
must not be assumed to mean just what it does in ordinary soils.
THE PHYSIOLOGICAL BASIS. 45
A somewhat similar case is afforded by the evergreen shrubs. In spite of the
work of Kihlmann (1890 : 88, 105), it has been generally assumed that the
evergreen shrubs of bogs, such as Chamaedaphne, Andromeda, Vacdnium,
Ledum, etc., were xerophytes essentially similar in water relations to evergreen
shrubs of arid clhnates. Recently the experiments of Gates (1914 : 445) have
confirmed the conclusions of Kihlmann that while they are xerophytic, it is in
response to physiological dryness in winter, and that they do not indicate
aridity in such habitats during the summer. In fact, the summer indications
are rather those of deficient aeration.
When growth is considered, the response of the same species to different
extremes of one factor or another is often very similar. E. S. Clements
(1905:93) has found in control experiments with Chamaenerium, Aquilegia,
and Anemone that extremes of any factor which are not optimimi for the species
tend to dwarf plants growing in them. The general principle has been formu-
lated as follows by Clements (1905 : 105) :
"When a stimulus approaches either the maximum or minimum for the
species concerned response becomes abnormal. The resulting modifications
approach each other and in some respects at least become similar. Such
effects are found chiefly in growth, but they occur to some degree in structure
also. It is imperative that they be recognized in nature as well as in field and
control experiment, since they directly affect the ratio between response and
stimulus."
This applies with especial force to the recognition of indicators, since their
value depends primarily upon the close correspondence between response and
the causative factor.
Phy tometers. — The best indicator of the nature of a habitat and of its practical
utihzation is the particular plant or community concerned. This is axiomatic,
but it needs emphasis in connection with the experimental study of indicators.
Such study may be made by means of physical instruments, standard plants, or
the plants to be grown as a natural or artificial crop. The former is the simplest
of the three, the latter the most effective. The use of standard plants com-
bines the advantages of both to a large degree, and seems destined to undergo
extensive development during the next few years. The refinement of method
will lead to an increasingly wider range of possible standard plants, until it
includes a large number of the species of greatest importance in agriculture,
forestry, and grazing. Out of these will emerge a few species of broad powers
of adjustment and adaptation which can be used as measures over great areas,
such as between the associations of a climax formation or even between climax
habitats themselves. A number of species of this sort are already clearly
pointed out by their vast ranges and their vigorous growth in different regions.
Of the grasses, Bouteloua gracilis, B. racemosa, Stipa comata, and Andropogon
scoparius are perhaps the most promising, and among shrubs RhiLS trilobata,
Cercocarpus parvifolius, Ceanothus velutinus, and Rubus strigosus. Of the
trees, aspen is the best, with Pinus ponderosa and Pseudotsuga mucronata as the
best of the conifers for the western half of the continent. As general stand-
ards, such weedy herbs as Helianthus annuus, Melilotus aWa, and Brassica
nigra are most useful. The most satisfactory cultivated plants are yet to be
determined, but wheat, corn, and beans have obvious advantages.
46 BASES AND CRITERIA.
Preliminary results justify the feeling that standard plants or phytometers
can be developed with more or less readiness to measure varying amounts of
the direct factors, water, light, temperature, soil-air, and solutes. Such func-
tional responses as transpiration and photosynthesis furnish the most accurate
measurements, but growth responses are also of the greatest value, especially
where factor-complexes are to be measured. Determinations based upon
responses in form and structure are also distinctly valuable. Because of the
longer time involved, they do not permit of such complete control, and their
correlation is less exact. In all of these, the error due to individual behavior
must be checked out by careful selection of individuals and by using a number
suflSciently large to yield a mode and to permit the elimination of those which
depart widely. In addition it has proved increasingly desirable to use a
battery of two or more species as phytometers, since this increases the number
and accuracy of the results quite out of proportion to the extra labor involved.
The first application of the phytometer method was made by Clements and
Weaver (Clements, 1918 :288; 1919) at Pike's Peak in 1918 and 1919. The plants
used were sunflower, beans, oats, wheat, sweet clover, and raspberry, Rubus
strigosus. These were grown in sealed containers, with plants in open pots as
checks on the conditions for favorable growth in the former. The normal
number of pots for each species was 3 to 5, but this was often reduced by mis-
haps. Three series were grown during the summer, the period varying from
28 to 45 days. The habitats measured were those of the short-grass associa-
tion at 6,000 feet, the half-gravel associes, the gravel-slide associes, and the
Pseudotsuga consociation at 8,500 feet, and the Picea engelmanni consocia-
tion at 9,000 feet. Stations were visited each week for the purpose of making
weighings and of reading the various recording instruments. The responses
primarily considered were transpiration and growth, though photosynthesis
was measured also. These showed marked differences with reference to alti-
tude, degree of shade, and seasonal factors. The relative values were the same
for the native Rvhus as for the cultivated plants, and the complete results seem
to leave no question of the paramount importance of plants for the quantita-
tive study of habitats and communities (plate 7).
The use of several dominants in a phytometer battery amounts almost to
employing a plant community as a measure, and suggests the possibility of
utiUzing portions of actual communities in this way. The simplest way of
doing this at present is by means of permanent quadrats which are visited each
month or each year and growth actually recorded by height or volume meas-
ures or by weight. Since many communities containing both dominants and
subdominants, such as Stipa with Amorpha canescens, Psoralea tenuiflora, and
Brauneria pallida, occur throughout the area of most climaxes, a series of
quadrats containing essentially the same population can be established through
a wide range of conditions. Locally, where diverse habitats are found within
short distances, as in the case of zones about ponds and of dynamic areas, it is
not difficult to transfer soil-blocks of the same community to several different
habitats and to follow their behavior in terms of the growth and abundance of
the species concerned. Such communities afford the best possible measure of
the serai habitats and reactions typical of succession, especially when recip-
rocal transfers are made between two contiguous or successive stages.
CLEMENTS
PLATE?
A. Phytomcter station in grassland at 6,(XX) feet, Colorado Springs, Colorado.
B. Battery of oats, gravel-slide station, Minnehaha, Colorado.
C. Battery of oats, brook-bank station, Minnehaha.
BASES AND METHODS OF DETERMINATION. 47
THE ASSOCIATIONAL BASIS.
Nature of association — ^The association of two or more species in a community
is due to one or two of the following three reasons: (1) general similarity of
functional response to controUing factors; (2) dependence upon the reactions
of the dominants modifying these factors; (3) dependence upon the autophytes
as hosts or matrices. The last two reasons also explain as a rule the presence
of the animals of a community as well. Hence it is obvious why one species of
a community should indicate the actual or probable presence of the others
regularly associated with it, and likewise the corresponding factors. This
principle is susceptible of extended application, but it is nowhere more striking
than in the case of relict herbs of a former forest. Though axiomatic, it must
be used with some care, since no two species are exactly alike in response and
indication, and since successional factors often enter to cause confusion.
The occurrence of a dominant indicates not only the presence or possibility
of its associated dominants, but also that of the related subdominants, second-
ary species, hysterophytes, and animals. This is as axiomatic as it is patent in
the case of an actual community in the field. This relation becomes of real
indicator significance where the community is partially or largely destroyed,
when it is rapidly changing, or is but incompletely known, especially in the case
of fossil vegetation. A subordinate species likewise indicates other subordi-
nate species as well as the controlling dominants, except in those plants which
occur in two or more associations or formations, as well as in different serai
stages. Even hysterophytes have, a distinct indicator value when they are
restricted to particular hosts. Moreover, it is clear that the associational rela-
tion signifies that animals may often be indicators of plants, as well as plants
of animals.
Dominants. — A dominant is the most important of all indicators. This is due
to several reasons. The first of these is that it receives the full impact of the
habitat, usually throughout the growing period. The second reason is that it
reacts upon the controlling factors, and thus modifies the response of its asso-
ciates. It also marks the progress of succession and consequently is bound up
in a sequence of dominants, with the result that it affords both developmental
as well as associational indications. In addition, it shows great abundance
over extensive areas and occupies a wide range. In fact, its very dominance
is the sign of its success under the conditions where it controls. However, it
is necessary to recognize that a dominant species is not always dominant, and
that its control may be local and developmental in parts of its range, while it is
extensive and cfimax in the main portion. Bouteloua gracilis is one of the most
exclusive of climax dominants in its typical area, the short-grass association of
the Great Plains, but it becomes a co-dominant or merely a successional one in
the related associations of the grassland formation, and on the edge of adjacent
climaxes, such as the chaparral and the sagebrush. In the Stipa-Koeleria
prairies it is subclimax on the ridges and drier slopes, while in the Aristida-
Bouteloua desert plains it is usually subclimax also, but in the valley plains and
swales it is truly climax. In all three associations it possesses indicator value
as a dominant, but this value is different in each one, both as to its associates
and the relative conditions. Near the edge of its range it loses its dominance
and becomes merely a subordinate member of the community with a greatly
modified or restricted significance.
48 BASES AND CRITERIA.
The distinction between the dominance and the mere presence of a species is
vital, from the standpoint of the structure of vegetation as well as from that of
indicators. It is this which makes catalogues, lists of species, and general
descriptions of the flora of a region of little value to the ecologist. In fact, such
materials are trustworthy only in associations already known, where they are
superseded. This is exemplified by a number of grass dominants. Bouteloua
gracilis is found from Manitoba to Wisconsin and Mississippi, west to Texas,
central Mexico, and California, and northward to Alberta and Saskatchewan.
It occurs as the characteristic climax dominant of the short-grass association
only in eastern Colorado, southwestern Nebraska, western Kansas and Okla-
homa, northeastern Arizona, northern and eastern New Mexico, and in the
Panhandle and Staked Plains of Texas. Usually with Bulbilis, it is more or
less regularly associated with Stipa and Agropyrum from northwestern
Nebraska and northern Wyoming through the Dakotas and Montana, into
Saskatchewan. Altogether it is a climax dominant over perhaps a quarter
of its range and a serai dominant over another quarter. Stipa comata is a
climax dominant to-day only in Nebraska, northern Colorado, Wyoming, the
Dakotas, Montana, and Saskatchewan, though it ranges from the latter to
Nebraska, New Mexico, California, and northward to Alaska. As a conse-
quence, the vegetational and indicator importance of any dominant species can
be determined only by field studies of its abundance and r61e. Maps and con-
clusions based upon the distributional area alone are both misleading and
erroneous (plate 8.)
Equivalence of dominants. — ^The dominants of a formation owe their associa-
tion to the generally similar responses which they make to the climax habitat.
This fact is further attested by the identity of life-forms and, to a small degree
as yet, by actual measurement of the controlling factor. As the sum of similar
responses, the formation is thus the largest and most distinctive of all indicator
communities. Within the formation the dominants fall into associations by
virtue of still closer similarity in response. Thus Stipa, Agropyrum, and
Koeleria constitute the climax prairies. By their height and general turf
habit they indicate a rainfall of 20 to 30 inches. Bouteloua gracilis and Bul-
hilis dactyhndes form the short-grass plains. Their short stature and mat habit
are responsive to a smaller rainfall of 12 to 22 inches, which in effect is much
reduced by evaporation. The Aristidas and Boutelouas of the desert plains
from Arizona to western Texas are somewhat taller, but their bunch habit is
an index of a smaller water efficiency, largely the result of excessive evaporation.
This relation is further indicated by the presence of Bouteloua gracilis in the
moister valleys, and by the fact that Stipa and Agropyrum regularly mix with
the short-grasses as indicated above, but have never yet been found mixed
with the species of Aristida and Bouteloua characteristic of the desert plains.
So far as our present knowledge goes, dominants of the same association or of
the same associes are never exactly equivalent. Actually, they may seem to
be since the annual variations of the climatic cycle are often much greater than
the difference in conditions. Even here, however, they tend to maintain their
position or abundance, relative to the controlling factor. As a consequence,
each consociation has its own indicator value, which, so far as its presence is
concerned, necessarily varies somewhat from wet to dry phases of the cycle,
but is checked by corresponding variations in growth, reproduction, and abun-
CLEMENTS
K?
PLATE 8
A. Anogra alhicaub's as a serai dominant in a fallow field, Agato, X(>l)i;uska.
B. Stipa comata as a climax dominant of the mixed prairie, Chadron, Nebraska.
THE ASSOCIATIONAL BASIS. 49
dance. Thus, Stipa spartea and Agropyrum glaucum show climatic diflferences
from S. comata and A. spicatum, while Stipa comata and Agropyrum glaucum
occur together over thousands of square miles, but are differentiated by water
relations determined by soil and slope. The actual physical differences in equiva-
lence are slight, and hence the dominants of an association tend to mix or to
alternate intimately instead of being pure over wide areas. However, this is
necessarily truer of an association with several to many dominants than of one
with but a few (cf. Zon, 1914 : 124).
Each dominant will grow in a fairly wide range of conditions, but will thrive
only in a much narrower range. The field optimum for each is not a single
point but an area. The areas of the dominants of the same association or
associes overlap to such an extent that they coincide except at the extremes.
If the ranges of normal adjustment of Stipa comata and Agropyrum glaucum be
represented in each case by a rectangle, the two rectangles will coincide for
three-fourths of their lengths approximately. This indicates the degree of
equivalence, the projections of each rectangle representing the actual difference
in water-response for each species. This overlapping has its real counterpart
in communities where the dominants are zoned. The mixed area between two
zones represents the range of factors for which the two dominants are equiva-
lent, and the pure zone on either side indicates the range peculiar to each.
There is no necessary correspondence between the width of the zones and the
mixed area, and the range of factor coincidence for the two dominants, owing
to the varying rate at which such a factor as depth of water or amount of
water-content may change. In the lakes of Nebraska, the two successive
dominants, Scirpus and Typha, occupy the same depths from a few inches to
several feet. Over most of this range they are mixed or alternating, but
beyond 4 to 5 feet Typha drops out, while Scirpus may persist to a depth of
6 to 7 feet. Except where shores slope rapidly, the mixed zone is many times
wider than the zone of pure Scirpus.
In this connection it should be recognized that dominants show a wider
margin between the normal range and better conditions than between it and
worse conditions. In other words, a species is quickly and definitely Umited
by unfavorable factors, while those generally favorable to growth exert little
limiting effect, the real effect being due to competition. This is the obvious
explanation of the number of dominants and the abundance of species in sunny
well-watered habitats, such as prairies, open woods, alpine meadows, etc., and
their paucity in deserts and saline wastes. In short, abundance is itself an
indicator, whether it concerns the individuals of one species or the species of a
community.
Absence of dominants. — The absence of a dominant from its particular com-
munity is often of indicator significance. A dominant may be lacking as a
result of several different causes. Its absence may be due to unfavorable
controlling factors, to very uniform conditions, to competition, destruction, or
to the failure of invasion for any reason. In all of these cases except the last,
absence has a definite indicator value, though it is practically always supple-
mentary to the presence of its associates. This is perhaps its chief value, in
that it enables us to check the positive indications obtained from presence.
Absence due to unfavorable conditions or to competition is the rule. Uni-
fonmty of conditions, however, is a more frequent cause than has generally
60 BASES AND CRITERIA.
been recogniaed. This is well illustrated by shallow lakes in the sandhills of
Nebraska, where the depth is so uniform that Scirpus is the sole dominant in
spite of the fact that neighboring lakes show Typha, Zizania, and Phragmites.
Abeenoeaa a result of destruction is usually difficult to determine and yet is of the
greatest indicator importance. The grassy parks of the Uncompahgre Plateau
in Colorado are so extensive and appear so permanent that their real signifi-
cance, as well as that of the absence of the trees, was finally determined only
by the discovery of burned wood deep in the soil. Similarly, much evidence
has been found to show that the absence of Stipa or Agropyrum over wide
stretches of the Great Plains reveals overgrazing of a type that has never been
suspected. Thus, while absence is necessarily correlated with the presence of the
related dominants in order to be usable , it does furnish indications of much value .
Subdominants. — Subdominants are species which exert a minor contro
within the area controlled by one or more of the dominants of an association or
associes. They are the successful competitors among the species which accept
the conditions imposed by the dominants. As a rule they differ from the latter
in life-form, and their competition is largely mutual rather than with the domi-
nants. This is obviously the case in forests where the subdominants form
layers. In grassland, where light controls in a minor degree alone, the layer-
ing is in the soil, but with a somewhat similar result that the dominants use the
water before it reaches the deep-rooted herbs. In prairie and meadow, there
is often enough water for both, a condition favored by the fact that subdomi-
nants reach their maximum at different times during the season, and hence
cause the characteristic seasonal aspects. During dry phases of the climatic
cycle, however, there is direct competition between dominants and subdomi-
nants, but usually at the expense of the latter.
Within the limitations set by the dominants, subdominants follow the same
general principles as to indicator values. This applies to their association in a
community, either climax oi>«eral, their equivalence, their dominance as com-
pared with mere presence, and to their absence. They diverge, however, in
exhibiting a seasonal sequence in many associations, by which they appear to
escape too intense competition with each other. Prairies purple with Astra-
gcdus crassicarpus in April and May are covered with Amorpha, Psoralea,
Petalostemon and Erigeron in June and July, and these in turn yield to golden
rods, asters, and blazing stars in August and September. To a large extent
these successive societies occupy the sa ne ground and would seriously compete
with each other were it not for the fact that the maximum demands of Astra-
galus, for example, are over before those of Psoralea and Erigeron begin.
Societies thus have a time as well as a space value as indicators. While the
subdominants of the same aspect are equivalent to a large degree, those of the
three aspects, spring, summer, and autumn, differ in being progressively more
xerophytic, owing to the seasonal relations of rainfall and evaporation.
Societies are not only most numerous and best-developed during the early
summer because of optimum conditions, but they likewise reach a maximum in
those communities with optimum conditions, such as prairie and forest. In
the short-grass plains they are greatly reduced, and in desert they are relatively
few, except in the spring. This exception covers those deserts with two rainy
seasons in which the socies of winter and summer annuals are possible only
because of a relative excess of moisture near the surface at these times (plate 9).
CLEMENTS
PLATE 9
A. PenUtemon gracilis as a climax subdominant in mixed prairie, Gordon, Nebraska.
B. Pedicularis crenulala as a serai subdominant in a Juncua-Carex swamp, I^iraniie,
Wyoming.
THE SUCCESSIONAL BASIS. 51
Secondary species. — This is here used as an inclusive term to comprise all the
autonomous species of a community outside of dominants and subdominants.
Their subordinate importance has caused them to receive relatively little
attention, but their correlation with habitat factors has gone far enough to
show that they all possess indicator value to some degree. In a sense, this is
thrice removed from the habitat, since in climax conmiunities in particular the
conditions to which secondary species respond have been modified by the
dominants and then by the subdominants. Secondary species either make
minor communities such as clans, c. g., Antennaria dioeca, Meriolix aerruUUa,
Anemone caroliniana, Delphinium carolinianum, etc., or they occur^as scattered
individuals in society or consociation. When they form more or less extensive
clans which recur throughout an association, their indicator value approxi-
mates that of a subdominant. In fact, it must be recognized that some of the
niost important clans might well be regarded as societies. Or to put it more
clearly, some subdominants vary sufficiently in abundance and control from
place to place and year to year that they may form societies at one place or time,
and clans at another. Apart from these, clans and scattered species have
their chief importance in revealing minor differences of habitat within the con-
sociation or society. They are often due to small disturbances and to succes-
sion in minute areas, and derive their indicator significance from this fact.
It is probable that the careful study of secondary species will disclose some
indicators of much sensitiveness and usefulness.
Plant and animal association. — It is desirable for many reasons to consider
animals an intrinsic part of the community as a biological unit. The great
value of this is that it insures an adequate and correlated treatment of both
plants and animals. It does not change in the least the basic relations between
physical factors, plants, and animals, upon which their mutual indicator sig-
nificance depends. Just as the plant indicates the factors and processes to
which it responds, so does the animal serve as an indicator of the plant or
community which furnishes it food, shelter, or building materials. The
animal also indicates physical factors in so far as they affect it directly. The
plant, however, has a double indicator relation by virtue of its response to
factors on the one hand and of its control of animals on the other. Since
animals are mobile for the most part, the control and the indications afforded
by plants are necessarily less definite and exact. While the study of animal
communities has gone far enough to provide a qualitative basis for plants and
animals as reciprocal indicators, there has been no conscious endeavor to
investigate this relation as yet. This is not true of paleontology, however, in
which such causal relations as that between grassland and grazing animals
have been much used. Even here an adequate and comprehensive system
must await a fuller development of indicator values in present-day communi-
ties. A preliminary attempt at such a system in both ecology and paleo-
ecology is made in Chapter III.
THE SUCCESSIONAL BASIS.
Scope. — Since the nature of the habitat and the character of the population
are constantly changing in all serai areas, succession is of profound importance
in connection with indicators. While the basic rule that plants respond to the
controlling factors holds for developmental as well as climax communities, the
indicators change as the succession advances. Each stage of the succession is
marked by factors which act upon species which react in turn. Hence the
52 BASES AND CRITERIA.
indicator relations change more or less slowly but inevitably from one stage to
the next. While the developmental areas of a formation are usually less in
aggregate extent than those occupied by the climax stage, they are so numerous
and various as to demand constant attention. The relative permanence of an
indicator relation dep)ends wholly upon whether it is determined by develop-
mental or climax conditions. Since the use of any area for cropping, foresta-
tion, or grazing either demands or effects constant changes in it, succession is
the basis of all utilization of communities or dominants as indicators. This is
especially true in the case of land classification, as Shantz has shown (19 11 : 18),
and it applies also to all engineering and construction operations in which the
soil is disturbed or new habitats produced.
Sequence of indicators. — Succession has been defined and analyzed as the
development of a complex organism, the climax community or formation
(Clements, 1905 : 199; 1916 : 3). It is a chain of causally related functions or
processes. Development begins at certain definite points, pursues a regular
course, and ends in the final or mature stage, the climax. As a result, each
serai dominant or community has indicator values beyond those arising from
the basic relation between plant and habitat. Each stage is the outcome of
those that precede and the precursor of those that follow until the climax is
reached. It indicates not merely the existing conditions, but it also points
backward through successively remote stages to the beginning of the sere, and
forward through those which lead up to the climax. Since the development of
the habitat proceeds step by step with that of the formation, each stage is an
indicator of earlier and later habitats as well as communities. Succession,
moreover, is always progressive, and makes it possible to forecast not only the
direction of development but something of the rate as well. It depends
primarily upon the production of new, denuded, or disturbed habitats, and thus
serves as an indicator of the many processes, physiographic, biotic, etc., which
initiate new habitats or denude existing ones.
The several indicator values of a serai conmiunity depend primarily upon
the climax and the sere to which it belongs. The climax determines the domi-
nants and subdominants from which the stages are drawn, indicates the climate
in general control of the habitat changes, and constitutes the final stage toward
which all the successions are moving. It is in itself an indicator of succession,
since it permits the prediction of the general course of development that
results from any disturbance in it. The division of seres into primary and
secondary rests upon the double basis of habitat and development, and explains
why each sere has indicator significance in itself. The primary sere or prisere
indicates an extreme condition of origin, such as water or rock, slow reaction
on the part of the earlier communities especially, and hence a large number of
successive communities. The secondary sere or subsere begins on actual soil
in which the conditions are not extreme, requires less reaction, exhibits few
stages as a rule and runs its course to the climax with much rapidity. All
seres, but primary ones in particular, are distinguished upon the basis of the
climax and the water relations of the initial area. The great majority of seres
are mesotropic, that is, they progress to a mesophytic climax. In desert regions
they are xerotropic and in the tropics may be hydrotropic (Whitford, 1906).
Their indicator meaning varies accordingly, but it is even more subject to the
water-content of the initial area. Seres are termed hydrarch (Cooper, 1912:
198) when they originate in water or wet areas, and xerarch when the initial
CLEMENTS
PLATE 10
A. StaJ^cs ol a hydrosere from floating plants to forest, Tike's Peak, Colorado.
B. Stages of a burn subsere from the pioneer annuals to the chaparral climax, Stin Luis
Rey, California.
THE EXPERIMENTAL BASIS. 53
condition is xerophytic or at least considerably drier than the climax. The
nature and indicator value of hydroseres differ in accordance with their
origin in lakes and swamps, or in bogs or other poorly aerated wet soils
(oxy seres). Similarly, the indicator values of xeroseres vary with their origin
upon rock, dune-sand, or in saline areas (plate 10).
Major successions as indicators. — The seres or unit successions discussed
above are themselves parts or stages of greater successions. The cosere is a
series of two or more unit successions in the same spot, and is best illustrated
by those peat bogs in which the remains of the various stages and seres are
accumulated in sequence and in position. In addition to the indications
furnished by each sere, the cosere always indicates one or more striking changes
of condition. When it exists over a wide area or recurs in the same relation in
several regions, it is an indicator of climatic change. An effective change of
climate is denoted by the occurrence of the peat formed by water-plants as the
layer above that which records the presence of the climax or subcUmax trees.
Such coseres have been industriously studied by European investigators,
Steenstrup, Blytt, Lewis, and others (Plant Succession, 378), and their cUmatic
correlations estabUshed with much certainty. The record of a cosere is well
preserved in water and especially in peat-bogs, but the more or less fragmen-
tary records furnished by burns, dunes, moraines, and volcanic deposits are
often of great value. This is especially true of the deposits of periods of great
volcanic activity, such as the Miocene, as found in Yellowstone Park and the
John Day Basin (Plant Succession, 367).
Major changes of climate are accompanied by the shifting of chmaxes as
well as by the succession of seres in the same spot. The differentiation of
climates during the Paleophytic and Mesophytic eras led to corresponding
differentiation of vegetation with characteristic zones grouped around centers
of deficiency or excess. These zones were clearly marked out by the middle of
the Cenophytic era, since which time the major effects of climate have been
recorded in their shifting. It seems highly probable that the climatic cycles
which produced and characterized the glacial period were accompanied by
marked shifting of climax zones and that the close of the period left the primary
zones of continents and mountains much as they are to-day. Such zones are
the most striking and important of all climatic indicators, and their significance
has been appreciated and investigated for more than a century. Perhaps even
more important is the fact that such a series of shiftings or zones is a succes-
sional process by which it becomes possible to predict the general effect of any
climatic cycle. This relation has already been developed to some extent
(Plant Succession, 347, 364) and is further discussed in connection with paleo-
ecology (Chapter III). The greatest climatic changes of geological times are
thought to be indicated by the evolution of the great land-floras and their
differentiation into climax vegetations. Thus, the entire course of the devel-
opment of the earth's vegetation, which is called the geosere, is divided into
eossres corresponding to the three great eras, and each eosere then exhibits
clisere shifting in response to lesser cycles. The use of zones as indicator
criteria is discussed in the next section.
THE EXPERIMENTAL BASIS.
Nature. — Indicators derive their importance chiefly from their practical
applications. For all practical purposes, indicator values must finally be
determined by experiment. The degree of their usefulness will depend mostly
54 BASES AND CRITERIA.
upon the kind and thoroughness of the experimental test. The planting of a
trial crop by a settler will give some idea of the indicator meaning of the native
vegetation that has been removed. In such a case the evidence is slight and
its value tentative. If the planting is repeated for several years or is extended
to other farms or localities, its value increases accordingly. As this is the
usual course for a crop in a new region, it is obvious that ordinary agricultural
practice must suggest indicator correlations with crop plants. This is well
known to be the case, but the actual utilization of indicators by farmers seems
always to have been inconsiderable. This is largely due to a lack of knowledge
of native plants, especially in a new region, but also to the fact that this
knowledge was needed most in selecting land and choosing crops, at a time
when it was still to be acquired. Thus, while the aggregate experience of a
neighborhood might possess real value, there has rarely been any method of
formulating it and making it effective.
The extension of experiment stations and substations throughout the West
initiated the period of scientific study of agricultural problems. The investi-
gations were directed chiefly to the selection of the best varieties for different
regions and soils and to the improvement of yields. Unfortunately, the bota-
nist was not interested in the problems of field crops and the agronomist was
little or not at all concerned with native vegetation. The result was that a
great mass of experimental data remained unavailable because it lacked corre-
lation. It was possible to give this only through ecological studies, and then
only after quantitative methods had been devised for the analysis of habitat
and conununity. As a consequence, exact and purposeful studies on indica-
tors date from the present decade for each of the three great fields, agriculture
(Shantz, 1911), forestry (Clements, 1910), and grazing (Clements, 1916 : 102;
1917 : 303; 1918 : 296; 1919). In spite of this late beginning, the recognition
and utilization of indicators are destined to undergo rapid development. This is
especially true of forestry and grazing, owing to the fact that the corresponding
experiment stations and reserves are organized upon the basis of exact ecology.
Essentials. — It has already been insisted that experiment affords the only
decisive test of an indicator. A single experiment may do this if properly
checked, but repetition is regularly necessary to cover the range of conditions
in space and in time. The experiment itself must be made with the fullest
knowledge of the factors concerned as well as the vegetation to be correlated.
As already pointed out, this involves quadrat study of the community and its
successional relations, and instrumental study of the habitat and its variation
through the climatic cycle. The thoroughgoing appUcation of this method
makes it possible to take advantage of countless natural happenings to convert
them into experiments. The number of such possibilities furnished by denu-
dation, lumbering, fire, cultivation, grazing, etc., is countless. If adequately
utilized, they will not only greatly reduce the number of set experiments
necessary, but will also make the latter possible on a scale otherwise out of the
question. The natural experiment has the advantage in economy of time and
effort, and in repetition of examples. The checked experiment permits of a
definite choice as to time and place, and allows greater control. It is the essen-
tial task of experimental ecology to combine these into a complete method,
which will give quantitative results throughout the field of ecology as well as in
connection with indicators. This is one of the primary objects of the present
treatment, though the indicator relations are necessarily given first place.
BASES AND METHODS OF DETERMINATION. 55
INDICATOR CRITERIA.
Nature and kinds of criteria. — Every response of the plant or community
furnishes criteria for its use as an indicator. These are most serviceable when
they are visible, but demonstrable functional responses may be even more
valuable, though invisible. The evidence as to functional responses in natural
habitats is still very limited, and will be considered in the next chapter under
the factors concerned. Here the discussion is confined chiefly to the criteria
afforded by form and structure, with which growth is included. The develop-
ment of the community is also considered along with its structure for the same
obvious reasons
Criteria may first be divided into two kinds in accordance with their relation
to the individual plant or to the plant community. Individual criteria are
phylogenetic when they have to do with species and genera, and ecological
when they relate to life-forms and habitat-forms. It is probable that these
are all ecological responses, and that species and genera are more remote in
origin and hence their ecologic significance less evident. Life-forms are less
remote and their dependence upon the habitat more evident, while habitat-
forms are mostly of more recent origin and their relation to the habitat obvi-
ous. This view seems to be supported by the fact that it has proved impossible
to make a system of life-forms which is not based in part upon taxonomic
forms and in part upon habitat-forms. All of these criteria permit still finer
analysis, as species into varieties and forms, and habitat-forms into those pro-
duced by local or minute habitats. The experimental study of species and
life-forms is still too slight for such a procedure, and it is possible as yet with
only a small nmnber of habitat-forms. The consideration of indicator criteria
is based upon the following divisions: (1) species and genera; (2) Ufe-forms;
(3) habitat-forms; (4) growth-forms; (5) communities.
Species and genera. — Quite apart from the life-forms and habitat-forms
which they exhibit, species and genera, and to some extent families also, have
an indicator value dependent upon their systematic position. The latter is
determined primarily by the responses recorded in the reproductive structures
at a time relatively remote. Their indicator meaning is consequently often
obscure, and this obscurity is increased by a complete lack of experimental
knowledge as to the factors which originate reproductive characters. Thus,
while many species and genera show correlations with habitat or climate, this
is chiefly on the side of vegetative responses, such as the relation of the Nym-
phaeaceae to bodies of water. They often exhibit, however, a valuable indirect
correlation with climate due to origin and migration. This is the basis of
floristic studies such as those of Sendtner (1856), Drude (1890), and others, and
of the more exact floristic methods of Jaccard (1901-1914) and Raunkiaer
(1905-1916). The value of these must remain statistical and general until
they are related to successional movements and to measured physical factors.
Species and genera acquire their chief significance by virtue of the ecological
values involved in phylogenetic relationship. This is obviously true of all
genera which are largely or wholly consistent as to life-form, and it holds to a
considerable degree for all others. Habitat, successional, and indicator values
are concerned in this, and the genus thus becomes a sign of a more or less
definite ecological complex of responses. This is hkewise true of species in the
general sense employed by Limi6 and Gray. A genus consists of several to
56 BASES AND CRITERIA.
many species because of the diverging evolution of an original stock under the
more or less direct control of changing habitats. A species shows a similar
evolution of forms, distinguishable from each other but mutually related to each
other by descent, as are the species of a genus. For the ecologist, the relation-
ship of such forms to the parent species is fully as important and even more
significant than their recognition. It is imperative for his purposes that this
relationship to the species be shown by the name as the latter shows that of
species to the genus. This demands the use of trinominals, which is in accord
with the general practice of ornithologists and mammalogists, but contrary to
that of many systematic botanists. The one disadvantage of the trinomial is
length, but this is readily obviated by using merely the initials of the specific
name, e. g., Achillea m. lanuhsa, Ranunculus f. reptans, Galium h. sdas (Clem-
ents, 1908:263; Clements and Clements, 1913). This has long been the
well-known practice of mammalogy and ornithology, e. g., Citellus t. parvus,
Lepus c. melanotis, Cyanocitta s. frontalis, Buteo h. calurus, etc. This or a similar
method is inevitable if systematic biology is to aid and not hinder the develop-
ment of ecologj' and the closely related practical sciences of agriculture, horti-
culture, forestry, plant pathology, economic zoology, etc. Three reasons would
appear to lead irresistibly to this result. The field worker must deal with units
which are recognizable in the field with a fair exercise of patience and keenness.
He must carry in mind the names and characteristics of a large number of
species, and he can do this only by relating them to each other. There is a very
definite limit to the capacity of the average memory, and this limit is greatly
overstepped by a system which trebles the total number of species in a region
and substitutes for a clearly marked genus like Astragalus 17 genera recogniz-
able with difficulty by the systematist and practically impossible for others.
Finally, while the ecologist is willing to go even farther than the systematist
in recognizing minor differences, providing these are based upon statistical
field studies and experiment and not upon herbarium specimens, the practical
scientist is concerned primarily with real species rather than the many varieties
and forms into which some of them fall. At least, when the need for a closer
knowledge arises in a particular case, it is infinitely easier and more helpful to
deal with the variations of a well-recognized species than with a dozen binom-
ials, none of which to him have the slightest relation to each other.
If taxonomy is to be helpful to anyone but taxonomers, it must clearly do
several things. It must recognize the field as the only adequate place for
determining new forms, and must commit itself unreservedly to the methods
of statistical and experimental study. It must restrict the use of the binomial
to species in the Linnean and Grayian sense and employ the abbreviated
trinomial for all segregates of such species, except in the rare cases where a
coordinate species has been overlooked. It must realize that the splitting of
genera only places so many stumbling-blocks in the way of all non-systematists,
and makes them still more unsympathetic with such methods. Finally, it must
recognize that a manual which can be used with success only by the syste-
matist fails signally in its purpose, and be wilUng to construct keys and descrip-
tions primarily for foresters, agronomists, grazing ecologists, and others whose
knowledge of taxonomy is slight. Upon such a basis, species and genera will
not only have vastly greater usefulness, but greater significance also to the
ecologist, and he will be encouraged to do his share by handling them with
greater accuracy and certainty.
CRITERIA.
57
LIFE-FORMS.
History. — ^The concept of the life-form was first formulated by Humboldt
(1805 : 218), who used the term vegetation-form. Under various names,
the concept has since been employed by many plant geographers and ecolo-
gists, and several have proposed more or less complete systems of classifica-
tion. Grisebach (1872), like Humboldt, based vegetation-forms upon physi-
ognomy, and both systems have in consequence little more than historical
value to-day. Warming (1884) and Reiter (1885) contributed many of the
essentials of the modern systems, but these probably owe more to Drude
(1890, 1896) than to anyone else. Krause proposed a classification in 1890
and Pound and Clements (1898) modified that of Drude somewhat in applying
it to American vegetation. For this reason it is proposed to treat the latter
here in detail, as well as the more recent systems of Raunkiaer (1903-1907),
Warming (1908-1909) and Drude (1913). It will readily be seen that all of
these have much in common, though this is not obvious in Raunkiaer's
classification, which is based mainly upon adaptation for overwintering. All
of them are founded more or less upon the two principles enunciated by Drude,
namely, (1) the r61e played by a particular species in vegetation and (2) its
life-history under the conditions prevailing in its habitat, with especial
reference to duration, protection, and propagation. In the following discus-
sion life-form is used as the general term to include vegetation-forms, habitat-
forms, growth-forms, etc.
Pound and Clements, 1898-1900. — ^As indicated above, the system employed
by Pound and Clements in the " Phytogeography of Nebraska" (1898 : 45;
1900 : 95; cf. Clements, 1902 : 616) was essentially the earlier system of
Drude (1896) modified to fit the vegetation of a prairie State. It possessed
some intrinsic interest in that the entire flora of the State was passed in review
from the standpoint of the various groups, and with reference to the general
conditions of the different habitats (1900 : 95-312). Vegetation-forms were
arranged in 7 main groups, which were divided into 34 minor ones. This sys-
tem was used by Clements and Clements in " Herbaria Formationum Colora-
densium" in 1902 and "Cri^togamae Formationum Coloradensium " in 1906.
I. Woody plants.
1. Trees.
2. Shrubs.
3. Underehrubs.
4. Climbers and twiners.
II. Half shrubs.
5. Half shrubs.
III. Pleiocyclic herbs (perennials).
6. Rosettes.
7. Mats.
8. Succulents.
9. Creepers and climbers.
Turf-builders
10. Sod-formers.
11. Bunch-grasses.
Rhiiomaia.
12. Rootstock plants.
13. Bulb and tuber plants.
14. Ferns.
IV. Hapaxanthous herbs.
15. Dicychc herbs (biennials).
16. MonocycUc herbs (annuals).
V. Water plants.
17. Floating plants.
18. Submerged plants.
19. Amphibious plants.
VI. Hysterophjles.
20. Saprophytes.
21. Parasites.
VII. Thallophytes.
22. Mosses.
23. Liverworts.
24. Foliaceous lichens.
25. Fruticulose lichens.
26. Crustaceous lichens.
Fungi.
27. Geophilous fungi.
28. Xylophilous fungi.
29. Biopbilous fungi.
30. Sathrophilous fungi.
31. Hydrophilous fungi.
32. Entomophilous fungi.
Algae.
33. Filamentous algae.
34. Coenobioid algae.
58 BASES AND CRITERIA.
Raunkiaer, 1905. — The system of Raunkiaer (1905 : 347) seems on the
surface to differ radically from all others. This is due to the fact that the
winter protection of buds is assigned the first rank and the growth-form
during the vegetative season is regarded as secondary. The apparent differ-
ence is increased by the use of new terms based upon the degree of bud pro-
tection. As a matter of fact, Raunkiaer's system, like the others discussed
here, takes account of both summer and winter conditions, and its difference
is more a matter of arrangement and terminology than of essentials. For
example, the group of phanerophytes corresponds essentially to woody plants,
crjrptophytes constitute the bulk of pleiocyclic herbs, and therophytes are
annuals, while the subdivisions practically all have their equivalents in the
other systems. The hemicryptophytes are far from satisfactory as a group,
because of their similarity to helophytes on the one hand (p. 420) and thero-
phytes on the other (p. 423) . By the omission of cryptogams, the classification
avoids confusion with systematic types and presents an attractively con-
sistent character, increased by a consistent terminology. While the terms
are well-chosen and properly constructed, their length will preclude their
common use, except perhaps in the case of the five major groups:
I. Phanerophytes (bud-shoots aerial):
1. Herbaceous phanerophytes.
2. Evergreen megaphanerophytes (above 30 m.) without bud-scales.
3. Evergreen mesophanerophytes (8 to 30 m.) without bud-scales.
4. Evergreen microphaneroph5rtes (2 to 8 m.) without bud-scales.
5. Evergreen nanophanerophytes (below 2 m.) without bud-scales.
6. Epiphytic phanerophytes.
7. Evergreen megaphanerophytes with bud-scales.
8. Evergreen mesophanerophytes with bud-scales.
9. Evergreen microphanerophytes with bud-scales.
10. Evergreen nanophanerophytes with bud-scales.
11. Phanerophytes with succulent stem.
12. Deciduous megaphanerophytes with bud-scales.
13. Deciduous mesophanerophytes with bud-scales.
14. Deciduous microphanerophytes with bud-scales.
15. Deciduous nanophanerophytes with bud-scales.
II. Chamaephytes (bud-shoots protected by snow or fallen leaves);
16. Suffrutescent chamaephjiies: many Labiatae.
17. Passive decumbent chamaephtyes: species of Sedum, Saxifraga.
18. Active chamaephyt€«: Linnaea, Empetrum.
19. Cushion plants: Azorella, Raoulia.
III. Hemicryptophytes (bud-shoots at the soil level) :
20. Protohemicryptophytes.
A, Plants without creeping offshoots: Linaria, Verbena, Medicago.
B. Plants with creeping offshoots, stolons, or rhizomes: Urtica, Saponaria.
21. Subrosette plants.
A. Plants without creeping offshoots: Caltha, Geum.
B. Plants with creeping offshoots: Ranunculus reptans.
22. Rosette plants.
A. Plants without offshoots: Primula, Taraxacum, Carex.
B. Plants with offshoots: Hieracium, Petasites.
Plants with monopodial rosette.
I. Monopodium with leaves but no scales.
A. Aerial leaf and flower shoots: Trifolium pratense.
B. Aerial shoots flower-bearing only.
a. Without creeping offshoots: Plantago major.
h. With creeping offshoots: Fragaria, Trifolium repens.
II. Monopodium with both leaves and scales.
A. Without creeping offshoots: Anemone hepatica.
B. With creeping offshoots: Convallaria majaUs.
III. Monopodium with scales alone: Sedum rhodiola.
LIFE-FORMS. 59
IV. Cryptophytes (bud-shoots buried in the soil) :
Greophjrtes:
23. Rhizome geophytes: Polygonatum.
24. Tuber geophytes: Cyclamen.
25. Tuberous root geophjiies: Orchis.
26. Bulb geophytes: Allium, Lilium.
27. Root-bud geophytes: Cirsium arvense, Moneses.
28. Helophytes: Typha, Scirpus, Equisetum, Sagittaria.
29. Hydrophytes: Nymphaea, Zostera, Hippuris, Potamogeton.
V. Therophytes (3); annuals: GaUum aparine, Thlaspi arvense.
Warming, 1908. — ^Warming (1909 : 5) has based his outline of growth-
forms upon the following principles:
"Just as species are th§ units in systematic botany, so are growth-forms the
units in oecological botany. It is therefore of some practical importance to
test the possibility of founding and naming a limited number of growth-forms
upi*n true oecological principles. It can not be sufficiently insisted that the
greatest advance not only in biology in its wider sense, but also in oecological
phytogeography, will be the oecological interpretation of the various growth-
forms: From this ultimate goal we are yet far distant.
"It is an intricate task to arrange the growth-forms of plants in a genetic
system, because they exhibit an overwhelming diversity of forms and are
connected by the most gradual intermediate stages, also because it is difficult
to discover guiding principles that are really natural. Nor is it an easy task
to find short and appropriate names for the different types. Genetic rela-
tionships and purely morphological or anatomical characters such as the vena-
tion and shape of leaves, the order of succession of shoots, monopodial and
sympodial branching, are of very slight oecological or of no physiognomic
significance. Oecological and physiological features, particularly the adapta-
tion of the nutritive organs in form, structure, and biology, to climate and sub-
stratum, or medium, are of paramount importance. Cases are not wanting, how-
ever, in which oecological grouping runs parallel with systematic classification.
"In the case of the polycarpic plants it is necessary to consider, first, their
adaptation to climate, and in particular the season imfavorable to plant life;
secondly, the vegetative season ; and finally the conditions prevailing in regard to
the soil, which Schimper terms edap/itc conditions. Of greatest importance is —
" 1. Duration of the vegetative shoot: Lignified axes of trees, shrubs, and under-
shrubs; perennial herbaceous shoots; herbaceous shoots deciduous after a
short period.
"And closely associated with this is —
"2. Length and direction of the internodes: Whether the shoots have short
internodes (rosette-shoots) or long internodes, and whether the latter are
erect (orthotropous) or prostrate and creeping (plagiotropous).
" 3. Posiiion of the renewal buds during the unfavorable season high up in the
air, near the soil, under the surface of the soil, or buried in the soil (geophilous).
"Of less importance is —
" 4. Structure of the renewal -buds or of buds in general.
" 5. Size of the plant is of some moment, not only because in the struggle for
existence the taller plants are enabled to establish a supremacy more easily,
but also because they are more exposed to the inclemency of climate; shrubs
reach greater altitudes and latitudes than trees, while dwarf shrubs and
herbs extend even further than shrubs.
"7. The adaptation of the assimilatory shoot to the conditions of transpiration.
"8. The capacity for social life is of great importance in the struggle between
species and consequently in the composition and physiognomy of the plant-
60
BASES AND CRITERIA.
community. This capacity is due in some cases to the prolific production of
seed, but usually to more vigorous vegetative multiplication by means of
travehng shoots, or shoots given off from the root. And this latter is to some
extent determined by the soil (moist or wet soil, loose sandy soil, etc.) "
Warmmg divides growth-forms into six classes and subdivides this into
subclasses and types as follows:
6. All other autonomous land-plants — cont.
11. Polycarpic p]&nts— continued.
(6) Rosette-plants — continued.
(7) Grass-rosettes: grasses, sedges,
Eriocaulaceae.
(8) Musa-form: gigantic tropical
herbs (banana).
(9) Tuft-trees.
1. Trunks without second-
ary growth; leaves large and
divided: tree-ferns, palms,
cycads.
2. Trunks with secondary growth;
leaves undivided, linear;
Yucca, Dracaena.
3. Strelitzia-form.
(c) Creeping plants.
(1) Herbs: Lycopodium clavatum,
Menyanthes.
(2) Dwarf shrubs: Arctostaphylus
uva-ursi, Linnaea.
(3) Jungerraannia-form.
(rf) Land-plants with long, erect, long-
lived shoots.
(1) Cushion-plants: Silene acauUs,
Azorella.
(2) Undershrubs:
1. Labiate type: Salvia, Thymus,
Artemisia.
2. Acanthus type: Acanthaceae.
3. Rhizome-undershrubs: Vac-
cinium myrtillus.
4. Cane-undershrubs: Rubus
idaeus.
5. Soft-stemmed plants: Araceae.
6. Cactus-form: Cactaceae, Sta-
pelia.
7. Woody plants with long-lived
lignified stems, canopy-trees,
shrubs, dwarf shrubs.
1. Heterotrophic growth-forms: holopara-
sites and holosaprophytes.
2. Aquatic growth-forms.
3. Muscoid growth-forms.
4. Lichenoid growth-forms.
5. Lianoid growth-forms.
6. All other autonomous land-plants.
I. Monocarpic herbs.
(o). Aestival annual plants.
(6). Hibernal annual plants,
(c). Biennial-perennial herbs.
II. Polycarpic plants,
(a) Renascent herbs.
(1) Herbs with multicipital rhizomes:
Silene inflata.
(2) Mat-geophytes.
a. With stem-tubers: Crocus.
6. With root-tubers: Ophrydeae.
c. With bulbs : LiUaceae.
d. With perennial tuberous stem:
Cyclamen.
(3) Rhizome-geophytes.
a. On loose soil of dunes: Ammo-
phila, Carex.
6. On loose humus soil in forests:
Polygonatum, Anemone nemo-
rosa.
c. On mud in water or swamp:
Phragmites, Hippuris.
(6) Rosette-plants.
(1) Leaves sessile, elongated: Plan-
tago, TaraxaciUB.
(2) Leaves long-stalked, broad: Ane-
mone, Hepatica.
(3) Leaves succulent: Crassulaceae.
(4) With runners: Fragaria, Poten-
tilla anserina.
(5) Flowers on leafy shoots: Alche-
milla, Geum.
(6) Flowers on leafless shoots:
Primula.
Drude, 1913. — In broadening his earlier classification into a universal
system oif life-forms, Drude (1913 : 29) has applied the following criteria:
1. The basic form (tree, shrub, annual or perennial herb), by the organization of which for
a long period of years, or for a single season of growth, each plant maintains its
own place. The method of propagation is an essential part of this basic form.
2. The form and duration of the leaves.
3. The protective devices of leaf- and flower-shoots during the period of rest.
4. Position and structure of the organs of absorption.
5. Flowering and fruiting in relation to reproduction as a single or recurrent process.
LIFE-FORMS.
61
On this basis, Drude makes three great divisions in which he recognizes
55 types and many subtypes.
1. Aerophytes (woody plants, perennial and
annual herbs).
1 . Monocotyl tuft-trees : Sabal, Yucca.
2. Monocotyl palm shrubs and limes:
Bactris, Calamus.
3. Dwarf palms: Nipa.
4. Tree-ferns and cycads: Cyathea,
Cycas.
5. Needle-leaved woody plants.
6. Dicotyl trees.
7. Dicotyl shrubs and bushes.
8. Dicotyl woody lianes.
9. Mangrove-form.
10. Lobelia-form.
11. Tree-grasses: Bambusa.
12. Smilaceous bushes and hanes:
Smilax, Ruscus.
13. Leafless dicotyl rushwood and
thorn bushes: Casuarina, Ephe-
dra, Spartium.
14. Few-leaved columnar woody plants :
Adenium, Tumboa.
15. Stemmed evergreen rosette succu-
lents: Agave, Sempervivum.
16. Dicotyl stem succulents : Cactaceae.
17. Dicotyl dwarf shrubs: Calluna,
Artemisia, Drj'as.
18. Woody parasites: Loranthus.
19. Monocotyl giant herbs: Musa,
BromeUa.
20. Monocotyl root-climbers: Mons-
tera.
21. Rosette ferns and cycads: Aspid-
ium.
22. Tuber-stemmed epiphytes: Bulbo-
phyllum, Myrmecodia.
23. Perennial and renascent grasses:
Andropogon, Poa, Carex.
24. Sedges and rushes with suppressed
leaves: Juncus, Scirpus.
25. Erect half-shrubs: Ruta.
26. Half-shrubs with creeping stems
or offshoots: Linnaea.
27. Dicotyl cushion-plants: Raoulia,
Silene acaulis.
28. Succulent cushion-plants: Aloe,
Mesembryanthemum.
29. Biennial and perennial rosettes:
Pulsatilla, Verbascum.
30. Renascent and annual climbers:
Dioscorea, Ipomoea.
31. Renascent multicipital herbs: Peu-
cedanum, Galium.
32. Geophilous rootstock plants: Iris,
Circaea, Equi^etum.
I. Aerophytes (woody plants, perennial and
annual herbs) — continued.
33. Geophilous tuber plants: Orchis,
Cyclamen.
34. Geophilous bulb plants: Allium,
Oxalis.
35. Monocotyl therophytes : Eragrostis.
36. Dicotyl therophytes :Chenopoiium.
37. Dicotyl short-hved herbs: Koenigia.
38. Saprophytic and parasitic herbs:
Corallorhiza, Monotropa,
Cuscuta.
II. Water plants:
39. Amphibious slime-rooted plants
with aerial leaves: Sagittaria,
Nelumbo, Marsilea.Equisetum.
40. Amphibious free-swimming plants
with aerial leaves: Pistia, Eich-
homia.
41. Amphibious plants rooting on
stones: Podostemaceae.
42. Hydrophytes with rooting axis and
immersed leaves: Isoetes, Zos-
tera. Lobelia.
43. Hydrophytes with rooting axis and
floating leaves: Potamogeton,
Nymphaea.
44. Free-swimming hydrophytes:
Lemna, Utricularia, Azolla.
III. Life forms of mosses and thallophytes:
A. Aerophytes:
45. Terrestrial cushion-mosses: Leuco-
bryum.
46. Terrestrial tall-stemmed mosses:
Polytrichum.
47. Terrestrial and epiphytic mat-
mosses: Hypnimi, FruUania.
48a. Petrophilous creeping mosses,
chiefly hverworts: Marchantia,
Jungermannia.
486. Petrophilous mat- and cushion-
mosses: Georgia, Andreaea.
B. Hygrophytes and hydrophytes:
49. Bog mosses: Sphagnum.
50a. Streaming mosses: FontinaUs.
506. Forming mats in water: Aneura,
Scapania.
51. Epiphytic lichens : Usnea.
52. Fruticose and fohose Uchens on
rocks and earth: Cetraria, Um-
bilicaria, Cladonia.
53. Crustose lichens: Lecanora.
54. Forms of marine algae, green algae,
bluegreen algae, etc.
55. Forms of saprophitic and para-
sitic fungi.
62 BASES AND CRITERIA.
Comparison of the systems. — ^The three systems of Raunkiaer, Warming,
and Drude differ greatly as to manner of classification, but they are in much
greater harmony as to the essential basis. Drude, however, constantly uses
taxonomic criteria, though he is very far indeed from consistent, separating
monocotyls, dicotyls, and ferns sometimes into distinct types, sometimes into
8ubt>'pes, and then frequently uniting two of them or all three into the same
type or subtype. Raunkiaer ignores taxonomy altogether and Wanning
practically does the same, with the exception of the thallophytic forms, in
which taxonomic form and Ufe-form are more or less identical. The treatment
of aquatics, in which the impress of the habitat is marked, is very different in
the three cases. Raunkiaer makes helophytes and hydrophytes two types of
cryptophytes, coordinate with geophytes. Warming treats aquatic plants
as one of his six main divisions, though he considers them under ecological
classes or habitat-forms (136), while Drude makes water plants one of his two
great divisions of flowering plants and recognizes three amphibious and three
aquatic types. Raunkiaer uses bud-position as the primary criterion for his
five main groups (all flowering plants and ferns). Warming employs sys-
tematic criteria for two of his six divisions, ecologic for three, and physiologic
for one. Land-plants are divided upon the nature of the life-period into
monocarpic and polycarpic. Drude's first division is ecologic for aerophytes,
and water-plants, and systematic for mosses and thallophytes. In all three
systems the types and subtypes are frequently the same, except that Drude
usually divides the same type or subtype upon the basis of taxonomy.
The systems of Raunkiaer and Drude are the most imlike, while Warming's
occupies an intermediate position. Raunkiaer's classification is much the
most compact and consistent, probably because he has adhered to one cri-
terion throughout. Because of this, and because he has given definite names
to practically every type, it is also much more usable. In fact, its great merit
lies in the possibility of using it as a sort of climatic index, while the other
two systems merely classify a great mass of plants in the usual static fashion.
As Warming points out, Raunkiaer's system has one disadvantage in that it
fails to take account of the growing season response (1906 : 6) and hence
applies to the flora and not to the vegetation of a region or country.
Vegetation-forms. — For our purpose, much the most useful and consistent
view of life-forms is obtained from a single point of view, that of vegetation.
The development and structure of vegetation are chiefly a matter of dominants
and subdominants, and it is the fife-forms shown by these which are of
paramount importance. Hence it becomes desirable to speak of them as
vegetation-forms, as Drude did originally, following Grisebach and Humboldt.
For practical purposes, it is undesirable to make a complete classification of
vegetation-forms and the latter is carried only so far as the demands of indi-
cator vegetation warrant.
The dominance of a species depends upon the perfection of its methods of
increa.se on the one hand, and upon the success of its vegetative shoots in
competition on the other. While the latter is partly a matter of length of
shoot and rate of growth, it is chiefly one of carrying the shoots of one season
over to the next. A wholly consistent and usable system is possible upon the
basis of these three processes. It avoids the complexities and uncertain cor-
VEGETATION-FORMS. 63
relations introduced by taxonomy and permits a consistent treatment of
habitat-forms with their more evident factor correlations. It contains the
essentials of the systems discussed above, inasmuch as Drude states that
the basic life-forms are trees, shrubs, perennial and annual herbs, Warm-
ing divides his group of land-plants into monocarpic and polycarpic, while
Raunkiaer's largest groups, phanerophytes, cryptophytes, and therophytes,
practically correspond to woody plants, perennial and annual herbs. In
giving more or less equal value to the life-period, method of over-wintering,
and conservation of shoots and success in competition, it appears desirable to
recognize four coordinate groups, viz, annuals, biennials, herbaceous peren-
nials, and woody perennials, characterized as follows:
1. Annuala: Passing the winter or dry season in seed or spore form alone; no propagation
or accumulation of aerial shoots; living one year.
2. Biennials: Passing one unfavorable season in the seed or spore form, and the next as a
propagiile; no accumulation of aerial shoots; Uving two or parts of two years.
3. Herbaceous perennials: Passing each unfavorable season in both seed or spore and
prof>agule form; no accumulation of aerial shoots; living several to many years,
4. Woody perennials: Passing each unfavorable season as seeds or spores, and aerial shoots
or masses, often with propagule forms also, especially when injured; Uving many
seasons as a rule.
E^ch of these divisions is thoroughgoing and all forms of annual habit are
placed in the first group, whether flowering plants, mosses, or fungi, just as
perennials are placed in their respective group regardless of their systematic
position or habitat-form. The varying nature of the four groups makes it
obviously impossible to employ the same criterion for the division into types.
For annuals and biennials, the fonn of the aerial plant body is probably of first
importance and the size next, while for woody plants height is perhaps most
decisive, leaf-character next, and form last. While perennial herbs usually
show the most marked differences in the propagules, the form of the aerial
shoot is often even more distinctive, and both criteria must be employed as
occasion warrants. The final result is a simple compact system, closely
resembling the earlier one of Drude (1896; Pound and Clements, 1900)
and different but little in essence from that of Raunkiaer. For the
study of indicators only the major divisions appear to be of value at present,
and these alone are given in the outline.
1. Annuals. 6. Cushion-herbs. Woody perennials.
2. Biennials. 7. Mat-herbs. 11. Half shrubs.
Herbaceous perennials: 8. Rosette-herbe. 12. Bushes.
3. Sod-graasee. 9. Carpet-herbs. 13. Succulents.
4. Bunch-graaeee. 10. Succulents. 14. Shrubs.
5. Bush-herbs. 15. Trees.
Indicator significance of vegetation-forms.— It is obvious that the vegeta-
tion-forms of climax dominants are indicators of climate. This has long been
recognized as the basis for the climatic zones of continents and mountains.
The same principle applies to climax formations generally; and these are
accordingly taken as indicators of the major climates of the globe (Clements,
1916). This close correlation between the major vegetation-forms and climate
as expressed in progressively favorable conditions of temperature and moisture
is paralleled by the succession of vegetation-forms in the development of a
64 BASES AND CRITERIA.
climax. In the development of a sere, extreme conditions as to water yield
to those more and more favorable to growth, and this change is accompanied
by a sequence of dominants belonging to successively higher vegetation-forms.
In short, the more striking indicator values of succession are afforded by the
changes from one vegetation-form to another, just as those next in importance
are marked by the change from one associes to another of the same form.
Moreover, while the exact significance of any species can be known only by
determining its functional response to the factors of its habitat, its general
meaning is indicated by the vegetation-form to which it belongs.
Raunkiaer (1905, 1908; Smith, 1913: 16) has employed his system of vege-
tation-forms to determine the climatic relations of a particular flora. He
establishes a hypothetical normal spectrum for the whole earth by selecting
1,000 representative species, of which 400 were carefully analyzed. The bio-
logical or phyto-climatic spectrum of a particular region is obtained by finding
the percentage of species belonging to each life-form. Raunkiaer's method
adds interest and detail to the long-accepted relations between climate ahd
flora. It can not be applied to vegetation and hence it has no real indicator
value, as is shown by the author's own statements (1905 : 433) :
"If we consider the flora of Denmark, it is characterized from the botano-
climatic viewpoint by its hemicryptophytes and not by its phanerophytes, for,
however important may be the role played by the forests in the vegetation of
Denmark, the small number of species of phanerophytes is significant of the
conditions offered by this region: The species of phanerophytes represent but
6 to 7 per cent of those living in Denmark, while the henriicryptophytes con-
stitute nearly a half of all the species.
"But from the standpoint of the formation, the phanerophytes, or trees,
dominate by their size wherever one finds them. In spite of the inferiority in
number of the species of phanerophytes to those of hemicryptophytes or
crj-ptophytes, our forests belong to the phanerophytic formations because the
phanerophytes they contain dominate the other components of the forests."
HABITAT-FORMS.
Concept and history. — In addition to the taxonomic form and vegetation-
form, species exhibit a form which is much more distinctly related to the
habitat. These usually bear the clear impress of the latter and hence are
called habitat-forms. The fuller recognition of their basic importance by
Warming (1895, 1896 : 116) was largely responsible for the rapid development
of ecology during the last two decades. Unlike taxonomic forms and vegeta-
tion-forms, their value is primarily ecological and not floristic, and they are of
correspondingly greater importance as indicators. Their significance lies in the
fact that they bear the primary impress of the controlling or limiting factor,
and thus serve as direct indicators of the critical factors of the habitat. They
are the essential basis of all indicator values, and must be regarded as the
main objective in all such studies.
Warming's system. — Warming (1896 : 116) was the first to adequately
organize the four universally known groups of habitat-forms, namely, hydro-
phytes, xerophytes, halophytes, and mesophytes (cf. Clements, 1904 : 20).
Pound and Clements (1898: 94; 1900 : 169), feeling the need of recognizing
light as well as water, divided mesophytes primarily upon the basis of light
HABITAT-FORMS. 65
and combined halophytes with xerophytes, thus establishing the following
six groups: hydrophytes, mesophytes, hylophyt«s, poophytes, aletophytes,
and xerophytes. This division of mesophytes retained some idea of life-forms,
and it was later dropped (1902 : 166; 1907 : 183) for the consistent light
grouping of mesophytes into heliophyta, sciophyta, and scotophyta, correspond-
ing essentially to Schouw's classification into sun, shade, and darkness plants
(1823 : 166). A detailed classification of habitat-forms was made by Clements
(1902 : 5-14), in which light, solutes, aeration, and other factors were taken
into account, but with water-content as the primary basis. The 64 sub-
divisions were largely successional and physiographic; and this number can
be greatly reduced if factors alone are considered. This is essentially what
Warming has done in his most recent grouping of formations (1909 : 136),
which also represents much the best classification of habitat-forms up to the
present. His system is as follows:
A. The soil (in the widest sense) is very wet, and the abiuidant water is available to the
plant; the formations are therefore more or less hydrophilous:
Class 1. Hydrophs^tes (of formations in water).
Class 2. Helophytes (of formations in marsh).
B. The soil is physiologically dry, i.e., contains water which is available to the plant only
to a slight extent; the formations are therefore composed essentially of xerophi-
lous species:
Class 3. Oxylophytes (of formations on sour (acid) soil).
Class 4. Psychrophytes (of formations on cold soil).
Class o. Halophjrtes (of formations on saline soil).
C. The soil is physically dry, and its shght power of retaining water determines the vege-
tation, the chmate being of secondary import; the formations are therefore likewise
xerophilous:
Class 6. Lithophytes (of formations on rocks).
Class 7. Psammophytes (of formations on sand and gravel).
Class 8. Chersophytes (of formations on waste land).
D. The climate is very dry and decides the character of the vegetation; the properties of
the soil are dominated by climate; the formations are also xerophilous:
Class 9. Eremophytes (of formations on desert and steppe).
Class 10. Psilophytes (of formations on savannah).
Class 11. Sclerophyllous formations (bush and forest).
E. The soil is physiologically or physically dry:
Class 12. Coniferous formations (forest).
F. Soil and climate favor the development of mesophilous formations:
Class 13. Mesophji,es.
Modifications of Warming's system. — In making use of habitat-forms as
indicators in North American vegetation, a few modifications of the above
groups are desirable. These are perhaps further warranted by some advance
in ecological knowledge in the ten years since Warming made the following
statement concerning habitat-forms (1909 : 133) :
"When endeavoring to arrange all land-plants, omitting marsh-plants, into
comprehensive groups, we meet with first some communities that are evidently
influenced in the main by the physical and chemical characters of the soU
which determine the amount of water therein; secondly, other conmiunities
in which extreme climatic conditions and fluctuations, seasonal distribution of
rain and the like, decide the amount of water in soil and character of vegeta-
tion. In accordance with these facts, land-plants may be ranged into groups,
though in a very uncertain manner. The prevailing vagueness in this group
66 BASES AND CRITERIA.
ing is due to the fact that oecology is only in its infancy, and that very few
detailed investigations of plant-communities have been conducted, the pub-
lished descriptions of vegetation being nearly always one-sided and floristic,
as well as very incomplete and unsatisfactory from an oecological stand-
point."
The terms employed are those suggested by Clements (1902 : 5) and
adopted by Warming for most of his divisions:
I. Hydrophytes: Chresard maximum to very high, the soil being water or'covered with
water; climate usually moist.
1. Emophytes: Entire plant submerged; no transpiration or fimctional stomata.
2. Plotophytes: Plant floating, at least the leaves; transpiration and fimctional
stomata on upper surface of leaves at least.
3. Helophytes: Amphibious, rooted in water or mud; transpiration high and stomata
on both surfaces, the stem often fimctioning as a leaf.
II. Mesophytes: Chresard medium, soil moist; climate moist; transpiration high to
medium.
4. Heliophytes: Sun-plants, growing in sunUght or light stronger than 0.10.
5. Sciophytes: Shade-plants, growing in light less than 0.10.
III. Xerophytes: Chresard low, soil physically or physiologically dry, climate usually dry,
or various; transpiration low.
A. Soil physiologically dry, climate various:
6. Halophjrtes: Chresard low, due to an excess of soil salts.
7. Psychrophytes: Chresard low, due to cold soil or to ice.
8. Oxyphytes: Chresard low, due to lack of oxygen in the soil.
B. Soil physically dry, climate various:
9. Lithophytes: Chresard low, due to a rock matrix.
10. Psammophytes : Chresard low, due to sandy or gravelly soil.
11. Chersophytes: Chresard low, due to a rock substratum.
C. Climate dry and soil physically dry in consequence:
12. Eremophytes: desert plants, chresard low or lacking much of the year.
13. Psilophytes: grassland plants (prairie, plains, stepi}es), chresard low some of the
year.
14. Drymophytes: bushes, shrubs, and small trees, mostly sclerophyll scrub, chaparral,
and woodland; chresard low or discontinuous.
The changes from Warming's system lie in the subdivision of hydrophytes
and mesophytes, well-recognized distinctions which Warming himself makes
use of (18, 165), in the distribution of conifers among helophytes, mesophytes,
psammophytes, and drymophytes, in the line drawn between desert and
grassland plants, and in treating the bush-shrub form as primary and the
division into sclerophyll and deciduous types as secondary.
Indicator value. — Habitat-forms are the most satisfactory of all indicator-
forms. This is chiefly because of their obvious response to the controlling
factors which the forester, grazing expert, and others must deal with. This is
partly also because they mark out a definite area in which these factors pre-
vail. For all practical purposes in a particular region, habitat-forms con-
stitute the ground-work of an indicator system. This is evident when it is
realized that the fourteen groups comprise all dominants and thus each
habitat-form has a conmiunity value as well. When reinforced by vegetation-
forms in so far as their significance for climate is known, and by ecads and
growth-forms for the more recent or the minor effects of physical factors,
habitat-forms afford a nearly complete system of indicators for the practical
application of biology. It is still necessary to interpret some of them with
ECADS. 67
greater accuracy sind certainty. This will come about from the quantitative
study of their physiologic response, permitting the closer correlation of form
and function, as well as by the increasing use of standard plants as even more
accurate indicators.
Habitat-forms can be used to give a general statistical expression to the
climatic or physiographic conditions of a region, and thus permit comparisons,
much as Raunkiaer has used vegetation-forms. Their paramount value Ues
in their positive indication of definite local conditions on the basis of known
correlation with measured factors. It should be noted that the mesophytes
and the last three groups of xerophytes represent climax habitats and com-
munities, while the hydrophytes and the first six groups of xerophytes charac-
terize developmental stages. This is a natural outcome of the fact that the
climate is controlling as to soil conditions in the former, while the climatic
control is much reduced or is none at all for the latter. The general correla-
tion of climax habitat-forms and their most important representatives with
physical factors is given in Chapter IV, in so far as quantitative results are
available.
In a recent paper, Raunkiaer (1916 : 225; cf. Fuller and Bakke, 1918 : 25)
has sought to express the general relation of plants to climate by a series of
leaf classes based upon size. Of the latter, he recognizes six kinds as fol-
lows : leptophyll, 25 sq. mm. ; nanophyll, 9 X 25 sq. nun. ; microphyU, 9* X 25
sq. mm. ; mesophyll, 9^ X 25 sq. mm. ; macrophyll, 9* X 25 sq. mm. ; megaphyll.
While this classification wlQ serve a useful purpose in drawing the attention
of ecologists to such relations, it seems quite too subjective for final accep-
tance. This seems obvious from the author's difficulties as to compound and
lobed leaves, and especially from the following statement (1. c, 29) :
"Originally I multiphed by 10, but the resulting limits between the 'size-
classes' did not seem as natural as when 9 was used. It is easy in the final
analyses to separate the single classes into the groups of small, medium, and
large."
Thus, while there can be little question that leaf-size often serves as an
indicator of climate or habitat in some degree, it must be refined by means of
leaf-number, thickness, structure, outline, and texture, and checked by quan-
titative studies of factors (cf. E. S. Clements, 1905 : 91).
Ecads. — An ecad is produced by direct and demonstrable adaptation to
a habitat. It is a habitat-form in the making. The habitat-form, while
capable of modification within certain hmits, has recorded the impress of a
particular habitat for so long that its general character is fixed and trans-
mitted. An ecad, though it may show just as striking adaptation, is a recent
product, and its character is not yet fixed and transmissible. The difference
between the two is solely one of inheritance, and it seems probable that ecads
become fixed and pass over into habitat-forms after a long residence in the
same habitat. This is indicated by the behavior of alpine dwarfs, some of
which retain their form when moved to lower altitudes or shifted to wetter
alpine situations, while others at once change in response to the new condi-
tions. The former have attained the stabiUty of habitat-forms, the latter are
ecads.
68 BASES AND CRITERIA.
Because of its plastic nature, the ecad is a more exact and sensitive indicator
than the habitat-form. Its structural change corresponds more nearly to the
functional response and can be regarded as a measure of the latter to a con-
siderable degree. Its growth as well as its fonn is often characteristic, and its
indicator value can be based upon both. One unique advantage of the ecad
is that it is produced in abundance in nature, wherever habitats touch, espe-
cially where they recur constantly, as in mountain regions. A plastic species
found in two or more habitats regularly shows an ecad corresponding to each.
Similar results are readily obtained by transplanting such species to several
different habitats. Ecads produced under definite quantities of water and
light may be grown under control (Clements, 1905 : 157; 1919) and used for
comparison with the natural ones (E. S. Clements, 1905) (plate 11).
Ecads have been classified and named with reference to habitats, as hylo-
coins, psilocolus, etc. (Clements, 1902 : 17; 1904 : 329). It seems much better
to group and designate them with reference to the controlling factor (Clements,
1908 : 263), as water ecads, light ecads, etc. Thus the general classification
of ecads would necessarily correspond closely to that of habitat-forms, except
in xerophytes, where the groups would be fewer. Such a classification would
be of little value, however, since it is the relationship of the ecad to a particu-
lar species which is significant, as well as the number and kind of ecads actually
occurring. A floating species, such as Sparganium angustifolium, forms both
submerged and amphibious ecads, while Nymphaea polysepala has been seen
to produce only amphibious ones. A plastic helophyte, such as Ranunculus
sceleratus, or a mesophyte, such as Achillea millefolium, may give rise to
several ecads. The same species may produce both water and light ecads,
though as a rule wide a range of adaptation to the one factor is accompanied
by a narrow range for the other. Under control it has been possible to produce
ten distinct water ecads of Ranunculus, but beyond this point differences have
'to do chiefly with amount of growth rather than with structure. For the
present, it is sufficient to recognize the controlling factor by designating ecads
as hydrads, xerads, sciads, heliads, halads, etc., and to leave the question of
a more exact terminology for the future. The importance of ecads in indicator
work is so great that their recognition can no longer be neglected.
GROWTH-FORMS.
Nature. — ^While it is assumed that all plant forms are referable to the
immediate or remote action of the habitat, this correlation is least certain for
taxonomic forms. Its certainty increases progressively through life-forms
and habitat-forms to reach a maximum in growth-forms. While Warming in
particular has used this term in place of life-form and vegetation-form, the
latter have the preference, both by priority and significance. But growth-
form is such a desirable term for the immediate quantitative response made
by a plant to different habitats or conditions that its retention in this sense
seems well-warranted. As the direct visible response of the plant to physical
factors, growth affords a more delicate scale of measurements even than the
ecad. In fact, the latter is only a growth-form in which adaptation as shown
by a qualitative change of form or structure is more striking than the quanti-
tative difference in amount of growth. In the case of dwarfing, both changes
usually occur together, and the growth-foim differs from the ecad only in
6^
CLEMENTS
PLATE 11
A. Normal (Unnfanuld rotundijolia at 8,300 feet, and alpine ecatl at 14,100 feet, Pike's
Peak, Colorado.
B. Shade ecad and normal Geniiana amarella at 8,300 feet and alpine ecad at 13,000 feet,
Pike's Peak.
C. Alpine ecad, normal form and shade ecad of Androsace scptenlriona'.is, Pike's Peak.
GROWTH-FORMS. 69
being the product of the conditions presented by a single season. If these
continue, the growth-form persists and becomes an ecad characteristic of the
particular habitat. Thus, while the two forms may be measures of the same
conditions, the one is an indicator of the annual variation, the other of the
normal condition of the habitat. From the ecological side, it appears that
growth-forms may become ecads, ecads become habitat-forms, and these
finally fixed as vegetation-forms.
Kinds. — Every direct factor exerts an influence upon growth and produces
corresponding growth-forms. Such factors are water, light, temperature, and
aeration, and possibly certain solutes. Since all of these are concerned in the
growth of each plant, it is possible to assign a particular one as the cause of
any growth-form only when it is the controlUng or limiting factor. In the
majority of cases, the limiting action is evident, as with water in arid and
serai-arid habitats or dry seasons, light in forests and thicket, temperature in
high altitudes or latitudes or cold seasons, and aeration in wet areas or seasons.
Maximum growth results when all four factors are at the optimum for a par-
ticular species. An apparent exception is afforded by the behavior of many
species in moderate shade, but their height is usually offset by their slender-
ness, and the mass growth and dry weight are usually less than in the sun.
With the optimum growth as the basis, it becomes possible to distinguish
growth-forms due to the extremes of each factor, as well as to correlate differ-
ent amounts of growth with known quantities of the limiting factor. In the
case of water, growth is decreased by both an excess and deficit as a rule, but
the former seems to operate through reduced aeration and lowered tempera-
ture. Similarly, growth is diminished by both high and low temperatures,
but high temperatures act chiefly through the water relation. It is doubtful
whether full sunshine as light ever inhibits growth, since photosynthetic
activity decreases with any material reduction in light intensity. While
many species are taller and more branched in moderate shade, it appears that
mass growth is at a minimum and often becomes completely impossible with
the increasing density of forest or thicket.
As a consequence of the above, it is most practical to distinguish four types
of growth-forms, based upon the lack of the direct limiting factors, namely,
those due to insufficient water, to insufficient heat, to shade, and to poor
aeration. Since growth is primarily quantitative, each species will exhibit a
series of forms from the optimum to the minimum, corresponding to each
effective degree of change in the limiting factor. This relation Ues at the base
of ecological response and can only be determined experimentally. Two
factors may act together in producing a growth-form, as in the case of alpine
dwarfs due to drouth and low temperature. One factor may serve to empha-
size another, as where the drouth of a desert is reinforced by an excess of salts
in the soil, or it may decrease or counteract the effect of another, as is true of
shade in arid regions. Finally, all four factors may be concerned causally in
an effect produced directly by one of them. This is apparently the case in the
death of sal seedlings in tropical forests, as shown by Hole and Singh (Chap. III).
The immediate cause is poor aeration, due to the acciunulation of soil-water as
a consequence of lower temperature resulting from shade.
Indicator relations. — The growth of a species varies from one year to the
next, and from one habitat to another. It often differs also in different por-
70 BASES AND CRITERIA.
tions of the same habitat. In an area which is uniform physically, individuals
frequently show striking variations due to competition. These four relations
sum up the indicator values of growth-forms as they occur in nature and hence
serve as the basis of all correlations. While they are well-known, little
quantitative work has yet been done with them. This has been due to the
time necessary to organize quantitative studies and methods out-of-doors and
to focus these upon growth as the most basic of visible responses. Pearson
(1918) has made measurements of the annual growth in height of yellow-pine
seedlings for a period of six years and has found a close correlation with
spring rainfall. Sarvis (1919) has clipped and weighed the growth on perma-
nent grass quadrats at intervals of ten days and has made a general correla-
tion with seasonal factors. Since species vary greatly in rate and amount of
growth, it is desirable to select those most responsive to the habitat.
It is impossible to say as yet what type of growth is most readily correlated
with seasonal variations or habitat differences. Theoretically, it seems that
total growth as indicated by the dry weight of mature plants would furnish
the best correlation (cf. Pearson, 1918; Frothingham, 1919; Sarvis, 1919).
Actually, however, vegetative growth and reproductive growth make different
demands, and are often antagonistic to each other. This is true to a large
degree of the height-growth and width-growth of woody plants. The determi-
nation of dry weight is a practical impossibility for trees except when young,
and the indicator correlation must be with growth directly. At present it
is only possible to say that for the first 100 to 150 years height-growth offers the
better correlation, and after this period growth in diameter reflects conditions
more accurately. Mitchell (1918 : 23) has shown in the case of incense cedar
(Ldbocedrus decurrens) that the mean height-growth for the first 100 years was
65 feet, for the second century 28 feet, for the third 12 feet, and for the fourth
6 feet. The width-growth was 13 inches, 14 inches, 9 inches, and 5 inches for
the same periods. Thus practically 60 per cent of the height-growth was
made in the first century, and but 31 per cent of the width-growth, while the
height-growth of the fourth century was but 5 per cent in contrast to a width-
growth of 12 per cent. The correlation of reproductive growth and especially
of seed-production with seasonal or habitat conditions is known only to the
extent that it tends to rise with less favorable conditions as to water up to a
certain point, as shown by alpine and arid regions. For most woody plants
it is little or none in youth, and it increases steadily up to maturity. In the
case of crop plants, it seems clear that the correlation with dry weight offers a
satisfactory basis for comparison, though even here greater accuracy can be
expected from the separate correlation of vegetative and reproductive growth
with the controlling factors in the two periods.
Standard plants for growth correlations. — Because of the control possible as
well as the opportunity for measuring functional responses, standard plants
offer much the best method of establishing growth correlations. The value
of the method increases as the standard plant approaches the one to be
indicated in character, and reaches a maximum when the latter is itself
employed as a standard, as in the use of yellow pine, Douglas fir, etc., in forest
investigations. The employment of phytometers in this form is the most
basic of all quantitative methods and is destined to play the paramount r61e
in all exact studies of conmiunities and habitats in the future.
GROWTH-FORMS. 71
Competition-forms. — ^The amount of a particular factor available for any
species or individual is either determined by the habitat alone or by com-
petition. In the great majority of cases, the major limits are fixed by the
habitat, and within these competition determines the amounts available for
each plant. Indeed, this is probably true of all communities except those
initial ones in which the individuals are widely scattered. In nearly all cases,
then, a growth-form is due partly to the nature of the habitat and partly to
the modification of this by competition. The part played by each can be
determined only by actual experiment or by the comparison of individuals
growing in the same habitat but in areas with and without competition.
Fortunately, such areas are of sufficient frequence in nature to reveal the
normal growth-form of the habitat as well as the growth-form due to com-
petition. A study of the chaparral and strand communities of southern
California (Clements and Clements, 1916) disclosed an unusually large number
of such competition-forms, especially among the annuals, as would be expected.
While competition-forms are probably just as frequent among perennials,
they are often much less striking.
As competition may occur in all degrees in accordance with the number
and density of individuals, so there may be a complete series of forms from
the normal to the extreme in which the plant never develops beyond the
seedling stage before it dies. Under somewhat less severe competition, plants
develop stems and leaves but fail to form flowers and fruit. In the next
degree, reproduction occurs, but the flowers are single or few, while beyond
this are more and more perfectly developed forms until the optimum for the
habitat is reached. Each form is an index to some degree of competition, but
its exact indicator value is more difiicult to determine. This is due largely to
the fact that competition has as yet received but Httle attention, especially
on the experimental side. The view advanced by Clements (1904 : 166;
1905 : 310; 1907 : 251; 1916 : 72) that competition is purely physical seems
to be confirmed by recent experiments. While it is perhaps unnecessary to
rigidly exclude metaphor in connection with competition, it should be recog-
nized that the experimental results so far obtained show that plants do not
compete for "room." Competition has to do only with the direct factors of
the habitat. Water and Ught are the factors universally concerned, though
soil-air, nutrients, and heat must also be taken into account in particular
habitats. In addition, there is often more or less decisive competition between
the flowers of a community for pollination agents. Furthermore, the course of
competition may be determined by a deleterious substance, especially a solute,
which handicaps one species more than another. Such a handicapping influ-
ence is even more frequently represented by biotic agents, parasitic plants,
rodents, grazing animals, etc.
The competition-forms commonly met with are due to competition for
water or light, or for both together. There has been no experimental study
of competition for soil-air or for nutrients, and it is impossible to assert at
present that plants do compete for heat. Studies of germination under differ-
ent densities of seeding suggest such competition for seedlings at least. No
adequate study of competition-forms has been made, and hence it is impossible
to relate them to definite quantities of water or Ught. In fact, it seems
increasingly probable that the forms resulting from intense competition are
72 BASES AND CRITERIA.
due to a lack of both factors, though in different degree. As a consequence,
competiiion-forms can at present be used directly only as indicators of the
general degree of competition. In connection with the habitat-forms or ecad,
they have an indirect value in making it possible to distinguish in indicators
the direct effect of the habitat as contrasted with the added effect of com-
petition.
COMMUNITIES AS INDICATORS.
^'alue. — The community as an indicator is a complex of all the preceding
values. It derives its primary significance from the dominants, chiefly
through their Ufe-forms and ecological requirements. It includes the mean-
ings of the less significant subdominants, and those of the much less important
secondary species. In short, it is a complete scale upon which all the indica-
tions of the habitat are written. These values can be obtained only by
analysis, however, and the latter leads at once to the study of dominants and
subdominants, both climax and serai. The general principles of the latter
have already been outlined under the sections on associational and succes-
sional bases. This leaves for consideration the various types of communities
and the functions and structures they exhibit.
Kinds of communities. — ^With reference to association alone, three kinds of
communities may be distinguished, viz, consocial,^ associal, and mixed. The
first consists of a single dominant, the second of two or more belonging to the
same association or serai stage, and the third of dominants from different
associations or associes. The basic indicator value of these is determined by
whether they are climax or serai. The consocial community affords the most
definite indication, while the associal type has the advantage of checking the
indications of one dominant by those of the related ones. This is even truer
in the case of mictia, but the indications are necessarily somewhat confused
here, since one set of dominants is disappearing and the other increasing in
number and importance. In this connection it is desirable to emphasize the
fact that serai and climax communities furnish not only indications of existing
factors and possibilities, but also of past and future ones. Each serai stage
indicates the preceding stage and its habitat. The climax forecasts the con-
sequences of any primary or secondary disturbance in it, and foreshadows the
effects of climatic changes. As a result, both serve as invaluable indicators
of the course and outcome of all possible human practices in them, and lend
themselves to methods of scientific prophecy which can hardly be surpassed.
A similar relation exists between consocial and associal communities. Wherever
a consocies or consociation is found, the related dominants have occurred or
can occur, at least with the slightest modification of the habitat. Thus, the
indicator analysis of a community involves not only the measurement of
existing conditions, but especially also a study of the linkage with the other
communities of the sere or the climax. For indicator research, as in all
serious ecological studies, any investigation which fails to take full account of
successional and climax relations is inadequate, and at best can only lead to
half-truths.
^This term is here used to refer to the community marked by a single dominant, whether con-
■odes or oonsodation, and associal in a similar sense. Both terms are also used to refer definitely
to ooDSodes and aasodes respectively, but the context is usually decisive.
COMMUNITIES AS INDICATORS. 73
The basic correlations of communities may be illustrated by the following
diagram (fig. 2.) :
CuuAX Formation.
society - consociation - association - ecotone - association - consociation - society
1 I. . .
Bocies - consociea - associes - subclimax - associes - consocies - socies
mictium.
mictium.
1
I
associes.
associes.
t.
,
88800166.
associes.
!
I
associes.
1
associes.
1 .
associes.
1
colony.
1
t
associes.
family.
1
associes.
(Prisere) associes. associes. (Subsere)
colony.
t
family.
Fia. 2. — Diagram of the climax and serai communities of the formation.
Community structures. — In addition to the units themselves, associal and
consocial communities show general structural features, such as zones, alternes,
layers, and aspects. These are due primarily to the grouping or appearance
of the subordinate communities with reference to a particular factor or factor-
complex, and are of the greatest indicator value. The well-known zonation
of the hydrosere in and about ponds is the best example of this. Each zone
not only marks the general factor limits for its proper community, but also a
distinctive step in the decrease of water-content and the increase of soil-air
from the extreme conditions in the center. Such a series actually shows on
the ground the " before-and-after " correlation of each stage typical of succession.
Serai zones may be formed by consocies or associes; in their fullest expression
the major zones are marked by associes within which occur minor zones con-
stituted by the consocies in the order of their requirements. The zones of
high mountains are essentially similar, though they have to do with climax
associations and consociations. The same zonal structure recurs universally,
wherever climax or serai communities are grouped about a center of excess or
deficiency of some factor or group of factors. Zonation is sometimes obscured,
especially in the dense vegetation of prairies (Plant Succession, 133), but
it is rarely altogether absent, except in initial communities.
Alternes. — Alternes are due to the interruption of zonation through any
cause whatsoever (Clements, 1916 : 115), but they are especially typical
where disturbed or other successional areas are found. They are frequent
74 BASES AND CRITERIA.
in climax areas wherever inequalities of surface structure and so forth occur.
The term alternation is applied to two types of structure, one in which the
same dominant or subdominant recurs from place to place, the other in which
two or more alternate over the same area. The first kind is usually serai, the
second is typical of associes or associations, and also of socies and societies.
Recurring alternes are clear-cut indicators of the same set of conditions, and
are of the greatest value. Striking examples are found in the burn alternes
of aspen or lodgepole in the Rocky Mountains. Alternating dominants or
subdominants are Ukewise indicators of their respective habitats. As indi-
cators, they are naturally less sharply set off from the related dominants,
but this is compensated by the evidence afforded of the degree of their equiv-
alence (plate 12, a).
Layers. — Layers are best known in forests and the term has usually been
restricted to the subordinate communities in them (Hult, 1881; Clements,
1916 : 15). With the increasing study of root-systems and their competitive
relations, it seems desirable to recognize root-layers as well as shoot-layers.
Our knowledge of the former is still rudimentary, but it is possible that they
are more general and significant than the well-known layers of woody com-
munities. It is almost axiomatic that a layer of either type will have a double
indicator value. It indicates the general equivalence with reference to the
controlling factor of all the important species in it. Conversely, it denotes
the dissimilarity of the adjacent layers and marks a certain stage in the
progressive modification of the controlling factor from its point of maximum.
Layers also serve to indicate the course of serai development, in that they are
generally absent during the initial stages. They appear during the medial
stages and usually reach a maximum in the subclimax or climax, often dis-
appearing in woody communities as they become mature. As a consequence,
the presence of several layers indicates more or less optimum conditions as to
water or Ught or both (plate 12, b).
Root-layers are regularly determined by water-content, though soil-air
and perhaps solutes also must sometimes be taken into account. In saline
soils they are due to differences in the salt-content acting through its effect
upon water-content, except where the salts are chemically injurious. As to
water-content, root layers may be a response to the physical distribution as
determined by penetration and evaporation, or to the ecological consequences
of competition. In the great majority of soils, both causes play a part (cf.
Cannon, 1911; Weaver, 1919). Many communities show a striking correla-
tion between the demands of the shoot and the root-position. This is often
expressed in the corresponding development of root and shoot as well. It is
best exemplified in the desert scrub, in which the tall shrubs are most deeply
rooted, the undershrubs 'ess deeply, the perennial herbs still less deeply, while
the low annuals of the rainy season are rooted only in the first few inches.
The obvious relation of shoot-layers is to light, though water-content and
humidity must sometimes be taken into account also. The best development
of layers is found in well-lighted forests with a Ught intensity between 0.1 and
0.02. The midsummer values are rarely conclusive, however, as the layers
tend to develop in the order of increasing height, with the result that each
layer receives the maximum during its period of major activity. Each layer
thus has two indicator values, one when it is uppermost and another when it
CLEMENTS
•7t.'''
PLATE 12
A. Alternation of sagebrush on southerly slopes, and Douglas fir on northerly ones, King's
Ranch, Colorado.
B, Layers of Impatiens, Helianthus, and Acalypha in oak-hickory forest, Weeping Water,
Nebraska.
COMMUNITIES AS INDICATORS. 75
has been overtopped by the later layers. This naturally does not hold for the
primary layer of trees or shrubs and for the highest layer of herbs which
develops last. The practical value of shoot-layers as indicators is in con-
nection with the natural reproduction of forests and the selection exerted by
light upon the tree seedlings of a mixed forest, especially of conifers.
Aspects. — The character of a conmiunity changes with the season. This
is best shown in prairie where the characteristic subdominants reach their
maximum at different times, producing three or even four aspects, viz, pre-
vemal, vernal, estival, and serotinal (Pound and Clements, 1900 : 140).
Similar aspects occur in the herbaceous layers of forests. The mmiber
decreases with the altitude and latitude, so that arctic and alpine regions
usually show but two, spring and summer. The indicator significance of
aspects is partly a matter of the societies which characterize them,^ but they
have a seasonal value as well. This lies in recording the advance of the season
and in permitting the determination of departures from the normal rate.
The correlation of this with the behavior of crop-plants and with all processes
which deal with the renewal or rate of growth each year should have con-
siderable practical value. Phenological lists suggest these values, but are too
general and unrelated as a rule to be of much service (Lamb, 1915).
III. KINDS OF INDICATORS.
Basis of distinction. — Each plant or community serves as the immediate
indicator of a factor or group of factors. As a consequence, it may also be
employed to indicate the process or agency which causes or modifies the
particular factor, as well as that in which the factor or habitat is involved.
When the process is one set up or controlled by man, the plant likewise becomes
an indicator of practice, and gives direct service in land classification, agri-
culture, grazing, and forestry. The relations of the plant or community to
process and practice are direct corollaries of the basic principle that each is
the best possible measure of the conditions under which it grows. Such
measures merely require correlation with a particular process or practice to
be of immediate service. This is the inevitable sequence, whether indicator
values are the result of actual experience or the outcome of scientific investi-
gation. In the latter case, the correlation is merely more detailed or more
definite. Thus, while they all spring from, the basic relation of plant or com-
munity to habitat, it appears desirable to distinguish indicators with respect
to the use made of them. On this basis, they may be recognized as factor
indicators, process indicators, or practice indicators. Furthermore, the
development of the field of paleo-ecologj' makes it desirable to extend the
application of indicator principles to the geological past. The sequence of
indications is essentially identical, but the results must be inferred from
present-day investigations, and hence it is desirable to speak of paleic indi-
cators in this connection.
FACTOR INDICATORS.
Basis and kinds. — Every habitat is a complex in which the factors are
almost inextricably interwoven. Each factor influences every other factor,
and is in turn affected by it. This relation should never be lost sight of, since
it is essential to the proper understanding of every factor indicator. Never-
theless, some factors are of such paramount importance in the habitat-
complex that it is desirable to relate the plants to them directly. This is
particularly true of the direct factors, water, light, temperature, solutes, and
soil-oxygen. The indirect factors, soil, slope, exposure, wind, and altitude,
can act only through these, but they too may be connected with plants as
indicators, whenever they exercise a compelling effect upon a direct factor.
Each factor leaves a distinct impress upon a plant or community in propor-
tion to its intensity and the plant's habitual requirements. The plant becomes
an indicator of a particular factor to the more or less complete exclusion of
others only when the factor exercises the paramount limiting effect. This is
regularly the case when it is present in marked excess or deficiency, and hence
a factor indicator usually denotes one extreme or the other, or a tendency
toward it. Even in such cases, some at least of the other factors are con-
cerned in producing the particular intensity of the limiting factor or are
themselves affected by it. Consequently, each factor indicator not only
denotes the controlling or limiting factor, but also a sequence of factors related
to it either as causes or effects. A hydrophyte indicates deficient aeration as
well as excessive water-content, while a xerophyte as a rule marks high tem-
peratures and low humidity as well as low water-content. In some instances,
76
FACTOR INDICATORS. 77
two or more factors appear to be equally important, and the plant indicates
all of them. An excellent example of this is seen in alpine plants, where tem-
perature, water-content, and humidity are of almost equal importance, and
wind and pressure of much significance. The situation may be taken to
represent the factor-complex, and such plants may be said to indicate high
altitudes.
Quantitative sequences. — It has already been pointed out that practically
every species has an optimum habitat, in which it exhibits its typical indicator
value. Outside the optimum or habitual habitat, it has a narrow range in the
direction of less favorable conditions for it, and a wider range in that of more
favorable conditions. The mere presence of a species or even of a community
can not be taken as evidence of its normal indicator value. Its actual value
can be determined only by reference to the normal habitat as well as to the
plants associated with it. It is this which makes dominance of the first
importance in arriving at indicator results. A plant is dominant only within
the range of essentially optimum conditions, and its control decreases in both
directions, but most rapidly toward less favorable ones. The behavior of the
individual plants is in close accord with these changes in abundance. The
sp)ecies has its most typical form where it is dominant, and changes in size and
form usually furnish clear indications of departures from the optimum habitat
toward either extreme. Subdominance follows the same rules and has similar
values, though these are less striking than in the case of the dominants. In
the tall-grass prairies, the societies often approximate the value of dominants,
but in woodland and forest they are always strictly subordinate, and their
indications serve only for a minute analysis of the general conditions of the
forest.
In the present condition of quantitative studies, serai and topographic
sequences must furnish the chief source of the indicator values of dominants
and subdominants. This will probably always be true to a large degree, but
the rapid growth of quantitative methods will afford a more detailed basis,
and one which can be understood in terms of factors as well as of plants. In
this connection, it must be recognized that a floristic census has slight value,
and that accurate results can be obtained only by the use of exact methods
which have dominance and sequence as their chief objectives. The floristic
outlook upon vegetation is a survival of the early days of distributional
plant-geography, and it must steadily decrease in importance as ecology
becomes truly quantitative in method and result.
Climatic and edaphic indicators. — Every factor plays a part in the develop-
ment of a community as well as in the control of its final condition. In the
developmental habitats the local conditions, especially those of the soil, are
paramount, while in climax ones the general climatic factors are controlUng.
The local or edaphic conditions find their expression in the serai dominants
and subdominants, and the communities which they constitute. The wide-
spread climatic conditions are reflected in the climax formation, associations,
and societies. As a consequence, it frequently becomes desirable to speak of
climatic and edaphic mdicators. Certain factors, such as water and tem-
perature, will be represented by both chmatic and edaphic indicators. Others,
such as light, solutes, soil oxygen, are primarily edaphic, while still others,
such as wind and pressure, may be either local or general. In the use of these
78 KINDS OF INDICATORS.
terms for indicators, it must be clearly understood that the reference is to the
nature and size of the area concerned, and not to the position of the factor
in the soil or the air. In the sense employed here, climatic and edaphic indi-
cators are synonymous with climax and serai ones, respectively, though the
emphasis in the former case is upon the factors rather than the process of
development.
^^'ate^ indicators. — ^A detailed account of our present knowledge of the
indicators of each factor is impossible within the limits of the present treat-
ment. It must suffice to point out here the general relations of each factor to
its plant and community indicators and to consider the most important and
best understood of the latter in the chapters which have to do with climaxes
and with practice indicators. The broader correlations of water and its
indicators have already been touched upon in Chapter II, and the following
brief statement is intended primarily to emphasize some of the basic points
involved and to suggest probable lines of advance in future work.
Water use will undoubtedly become the primary basis for interpreting the
water-relations of plants, when the use of phytometric methods becomes
general. Expressed in terms of transpiration per unit area and per gram of
dry matter produced, this will furnish the first exact basis for the classifica-
tion of plants on the basis of water. The application of such methods to
native species will be a slow matter, however, especially under field conditions.
Consequently, the indicator value of native plants for water must still rest
largely upon determinations of water-content, hiunidity, evaporation, and the
transpiration of standard plants, supplemented to some degree by studies
of the form, structure, and growth of the plants themselves. Thus it becomes
particularly important to refine the concept of water-content, since this
exerts the basic control in water relations, and to render its expressions more
definite and comparable (plate 13).
The general value of the echard for the various kinds of soils is now so well
known that determinations of the holard are helpful in refining the values
gained from sequences. This is particularly true when a single uniform soil
is concerned, though even here account must be taken of differences at the
various levels. The importance of the echard at the critical period has
obscured the fact that it is the chresard which represents the amount of water
available for the work of the plant, and that a very large number, if not the
majority of species, probably never reach the echard during their lifetime.
The water-response of such plants, and hence their indicator value, is con-
cerned with the chresard. In the case of xerophytes and xeroid plants, includ-
ing the crop plants of arid regions, the echard may be reached more than once
during the growing season, or the plant may remain at that point for a con-
siderable portion of the year. When the latter occurs, the plant bears a dis-
tinctive xerophytic impress, the intensity of which is apparently correlated
with the length of the period of deficiency. The difficulty of making echard
determinations in the field is such that in practice it is much more satisfactory
to obtain this indirectly by means of the moisture-equivalent method of
Briggs and Shantz (1912 : 56), and to express the seasonal chresard graphi-
cally, as has been done by Weaver (1917).
The lack of agreement between the results of the earher investigators and
those of Briggs and Shantz may be due in part to the more exact physical
methods of the latter. So far as native plants are concerned, however, there
CLEMENTS
PLATE 13
A. Typha alteraes indicating pools in a salt-marsh, Goshen, California.
B. Juniperus indicating seepage lines in hills of Mancos shale, Cedar, Colorado.
^
FACTOR INDICATORS. 79
seems to be no question that they vary considerably in their ability to obtain V
water from the same soil. This is obviously to be explained in part by the
fact that the roots are not at the same level, and hence not in the same soil.
But there are many cases in which certain species wilt before others, where the
roots are interwoven in the same soil. As already mentioned, Dosdall (1919)
has found that Equisetum arvense regularly wilts before Helianthus annuus
and Phaseolus vulgaris when their roots are at the same depth in uniform soil.
This agrees with results obtained in the field at the Alpine Laboratory with
uniform gravelly soils, and indicates a considerable difference in the absorbing
power of native species. This may be due to striking differences in the rate
of transpiration or of the osmotic pressure of the root-hairs, or it may arise
from differences in the extent and growth of the roots themselves. As Shull
(1916 : 27) has suggested, it would appear less under moderate and uniform
conditions, and it seems likewise that it would be less in evidence with crop
plants and weeds which grow in fairly uniform root environments. It seems
clear that this point must receive further investigation. Meanwhile, it is
necessary to recognize that species of the same local group and habitat do
wilt at different points, whatever the various causes may be.
In the endeavor to definitize the significance of water indicators, the primary
division into hydrophytes, mesophytes, and xerophytes will still have value.
In addition to the subdivision which Warming has already made of them,
they will require still further analysis. This will become possible only with
more exact study of the controlling factors, and especially of the actual water
use. In fact, the precise meaning of any particular indicator will depend
wholly upon the latter, and this will involve a readjustment of the relations
of the main groups. Meanwhile, a keen appreciation of the need for more
exact methods should not be allowed to obscure the fact that indicators of
great practical value can still be made available by our present methods of
ecological observation and instrumentation.
Light indicators. — In spite of the fact that small differences in Ught values
are more readily detected by observation than with water-content, the
recognition and use of plants as indicators of different light intensities are
matters of recent development. The forester has long understood the general
importance of light in the forest, and his tables of tolerance are an indirect
recognition of indicator values. As long as he was chiefly interested in sil-
viculture, however, tolerance was a matter of relative growth in the same or
similar situations. The development of silvics as a phase of ecology directed
attention more to the factors of the habitat, and led to the use of photometers
for measuring light intensity. This has made possible the correlation of tables
of tolerance with measured intensities and the use of the dominants con-
cerned as direct indicators. Such work has merely been begim, however, and
much quantitative study will be required before the general values of tables
of tolerance can be made exact. Measurements of light intensity have been
largely confined to forests, but it is clear that light values have considerable
importance in other communities as well. This is especially true in wood-
land, scrub, and savannah, but it holds also for grassland, particularly the
tall-grass prairies.
Two facts must be taken into account in correlating light indicators with
measures of Ught intensity. One of these is the effect of variations in the
80 KINDS OF INDICATORS.
composition or quality of the light. There can be no question that white light
is modified in passing through the leaves of the forest canopy, the red and
blue being absorbed to a larger degree than the green and yellow. In the case
of conifers practically no light passes through the needles, and the light
beneath them is white light, which has passed through the openings between
the needles. In the case of broad-leaved forests, the amount of light entering
between the leaves decreases with increasing density of the canopy, and that
modified by transmission through the leaves becomes correspondingly more
important. In all forests studied by the writer, the light has been essentially
normal in composition, but there seems no good reason for questioning the
results of Knuchel (1914; 1915: 90) in beech forests especially. Even here,
however, his tables and diagram show a somewhat uniform reduction in the
different parts of the spectrum. Moreover, several facts indicate that the
actual differences in quality in a beech forest are probably of little importance.
Photosynthesis takes place almost wholly in the red and blue, which are more
or less reduced. Furthermore, this function employs but a small part of the
incident light, and a very serious disturbance of the normal composition
would be necessary to affect it. Finally, reduction in intensity seems to have
much greater influence than the change in quality. Forests of Picea engel-
manni suppress the undergrowth even more completely than those of beech,
in spite of the fact that the composition of the light is practically normal
(plate 14).
The significance of light indicators is also complicated by the influence of
other factors. As already stated, this is the rule for all factors, but it is more
marked in the case of hght than of water. This is partly because light affects
fewer functions directly, and partly because the modifying influence of water
upon tolerance has been too much ignored (Plant Succession, 93). It is per-
fectly clear that the intimate interaction of water and light in competition,
especially in forests, makes it necessary to take them both into account in
determining tolerance as well as indicator values. This is true to a much
smaller extent of nutrients and temperature, but these would have some
influence wherever they tend to become limiting factors. Furthermore, there
can be little question that light is usually the controlling factor in tolerance
wherever the canopy is closed and that water plays a decisive part only when
the light intensity is higher and evaporation and competition consequently
greater. However, actual experimental studies of the respective rdles of the
two factors, such as those of Fricke (1904), are needed for the various forest
communities and the different groupings of dominants within them.
Tolerance has dealt almost wholly with the light relations of forest domi-
nants (Zon and Graves, 1910). The latter are among the simplest and most
direct of all light indicators, since they constitute actual experiments in plant-
ing, natural or otherwise. As indicators they have the same unique value as
crop plants and, so far as practice is concerned, make the use of less direct
indicators and of instrmnents more or less superfluous. In many cases,
however, seedlings of a particular dominant or of all the related ones are absent
from the forest floor, or the forest itself may be represented only by the
undergrowth or certain elements of it. In such cases, the subdominant shrubs
and herbs must be employed as indicators. The latter in particular are often
more sensitive than the trees themselves and hence furnish a more exact scale
CLEMENTS
PLATE 14
A. Fragaria and Thaliclrum, indicators oi medium shade in montane forest, Minnehaha,
Colorado.
B. Mertensia sibirica, indicator of deep shade in montane forest, Long's Peak, Colorado.
FACTOR INDICATORS. 81
of indications. The widespread occurrence of certain herbaceous societies
throughout one or more forest associations, or even formations, affords a
striking opportunity for correlating the Ught relations for dominants asso-
ciated under varj-ing conditions as to other factors. The perennial herbs are
of especial importance in this connection, as the effects of differing Ught
intensities are clearly reflected in a variety of ways, in density, form, height,
flowering, etc.
In deflnitizing the use of light indicators, it will be necessary to resort more
and more to quantitative measurements of responses and factors. The most
important responses in this connection are photosynthesis and growth. Both
of these have certain values, and they will be more and more employed in
combination, as complete and accurate results become necessary. At present,
however, the determination of photosjTithesis and its correlation with light
is a much simpler and more exact process. As a consequence, the best deter-
mination of indicator values for Ught will continue to be initiated by close
observation of general correspondences, which are first tested by means of
measurements of intensity and then by studies of photosynthate production.
It is probable, indeed, that this will give the real Ught indication without
recourse to growth responses, but the latter wiU prove necessary to obtain the
fuU indicator value for practical purposes.
Temperature indicators. — Temperature produces no clear-cut response in
structure or grouping, and hence its indicators are not readily recognized by
observation alone, as in the case of water and Ught. The most obvious response
to it is growth, but this is affected so profoundly by other factors in nature
that a primary correlation with temperature is always difficult and usually
impossible. As a consequence of their striking distributional correlation with
latitude and altitude, a number of endeavors have been made to classify
plants with reference to temperature. The most suggestive are the classi-
fications of A. de CandoUe (1874) and Drude (1913 : 154). Both of these are
based upon general climatic features, and take some account of water as well
as temperature. While they have more or less interest, their ecological value
is sUght, owing to the almost complete lack of experimental and quantitative
bases. Moreover, the usefulness of the groups is further reduced by such
terms as "Etesial-Poikilotherme-Psychrochimenen."
The most notable attempt to correlate flora and fauna with temperature is
that of Merriam (1890, 1894, 1898). The laws of temperature control of the
geographic distribution of plants and animals are stated by him as foUows :
"The northward distribution of terrestrial animals and plants is governed
by the sum of the positive temperatures for the entire season of growth and
reproduction, and the southward distribution is governed by the mean tem-
perature of a brief period during the hottest part of the year."
His well-known sj'stem of Ufe-zones was established upon the basis afforded
by these hypotheses. As indicated by his discussion of the Arctic, Hudsonian,
and Canadian zones (1898 : 54), the Ufe-zones appear to be actuaUy based
upon the outstanding vegetation zones of the continent, with temperature
control as a more or less correlated principle. While Merriam's system has
been of undoubted service in studies of floristics, its ecological value rests upon
the extent to which it has followed the natural vegetation zones and climaxes,
and upon the correlation of these with crops. It can not be regarded as fur-
82 KINDS OF INDICATORS.
nishing adequate proof of the paramount control of temperature in so far as
plants are concerned at least. It p)ossesses the disadvantages of every system
erected upon a single factor, and emphasizes the basic truth that studies of
causes must be grounded upon experiment, and not merely upon field observa-
tions and meteorologic data.
While there can be little or no question that every species has a climatic
maximum and minimum of temperature, this is known experimentally for
none of them. What is ordinarily observed in nature is, broadly speaking,
an optimum to which the plant is more or less confined by the action of com-
petition, water, and other factors. Theories of temperature control have
generally failed to realize the unique importance of the period of germination
and seedUng establishment in determining the range and dominance of a
particular species. There is sufficient experimental evidence in the case of a
few dominants to suggest that many if not all of them can be extended beyond
their present northern and southern, as well as their altitudinal limits, by the
proper control of local conditions during the period of early ecesis. Moreover,
when the part played by water in many of the effects supposed to be caused
by temperature is adequately understood, it will be recognized that many of
the so-called temperature responses must be ascribed to the combined action
of the two.
In accordance with the rule, the impress of temperature should be most
pronounced in climates where it is most extreme. These are arctic and alpine
regions, and the tropics and subtropics. However, the influence of water is
also pronounced in the first two, and over much of the other two. The dwarf
shrubs and perennial herbs of alpine and arctic regions have long been regarded
as undouVjted responses to short seasons and low temperatures. But in the
ease of some alpine plants at least, it is certain that dwarfing is due as much
or more to water than to temperature (Clements, 1907). It appears highly
probable that this is true of the dwarfing of trees at timber-line also. In the
latter case, the non-availability of the water-content is caused by freezing,
and the dwarfing might well be regarded as due to both the direct and indirect
action of temperature. A similar relation exists in tropical and subtropical
deserts, where the actual impress is largely due to water. The latter is pro-
foundly influenced by temperature, which appears to be in control of dis-
tribution to considerable degree, especially in the case of succulents (Shreve,
1911, 1914).
If some weight be assigned to the indirect action of temperature, a con-
siderable number of species may be regarded as temperature indicators.
These are primarily alpine and arctic plants, and the succulents of hot desert
regions. The trees and shrubs of the boreal tree limit and of timber-line on
mountains are similar indicators, and this is true to some degree of those trees
which become shrubs as they extend downward into the deserts of the South-
west. The absence of certain life-forms and species as a consequence of frost
also constitutes a temperature indication of great importance. As a conse-
quence of the gradual change of temperature with latitude and altitude,
climax communities serve as the best of temperature indicators. They com-
bine the responses of both life-form and species on such a large scale that there
can be Uttle question of the paramount control of temperature where its
extremes are concerned. Between the latter, climax dominants and com-
FACTOR INDICATORS. 83
munities must be regarded as primarily related to water, and hence treated as
indicators of it. While these doubtless have relations to temperature which
are susceptible of measurement, they are subordinate, and in our present
incomplete knowledge can not be regarded as indications of it.
Indicators of solutes.— The term solute is used here to indicate any sub-
stance dissolved in the holard. It may be solid or gaseous, or even Uquid.
The best-known solutes are the mineral salts found in the soil, of which some
are nutrients, others more or less inactive, and some actually deleterious to
the plant. Of the gases dissolved in the holard, oxygen and carbon dioxid
are the most important, but oxygen is the only one which bears a clear rela-
tion to indicator plants. In addition, there are the debatable toxic exudates
and soil toxins, the existence of which is in doubt or the relation to the plant
uncertain. Livingston, who has devoted much attention to this subject
(1918 : 93), states:
"Evidence that agricultural plants do actually excrete toxic substances into
the soil is not very strong in any of this work, however. As to the manner in
which these poison substances arise in the soil, no definite statements can yet
be made, but they are surely not excreted as such from plant roots. There
is physiological evidence, however, that such substances are given off by living
roots when the latter are practically deprived of oxygen."
In so far as indicator plants are concerned, the effects ascribed to toxins
are much better explained on the basis of an inadequate supply of oxygen.
The ordinary' nutrient salts of the soil rarely leave a distinctive impress
upon plants, owing to lack of concentration. When the concentration reaches
a point where absorption is interfered with, the plant makes a definite physio-
logical and structural response to the saline or alkaline conditions. The
relation to lime and magnesia is less clear and the indicator impress less
marked. In the case of deficient aeration, the response is clear, but its expres-
sion is often limited to physiological and histological features. Since all
solutes act through water or in conjunction with it, their effects are often
obscured by the^ responses to it. This is particularly true of saline indicators,
which are merely xerophytes of a more or less peculiar type.
Saline indicators. — ^The term saline is preferred as the general term for all
soil conditions in which soil salts occur in excess or a deleterious alkaline salt
is present. In the West it is practically synonymous with the word alkali,
and the two are employed interchangeably. Saline indicators are typical of
sea-shores the world over, but their most striking development is found in the
arid basins of the interior of continents, such as the Great Basin of North
America. Practically all the work with them has been done in such regions,
where the limits set by alkali to agricultural development are of the greatest
importance. The outstanding studies in this field are those of Hilgard (1906)
and Kearney (1914), and their respective associates. The work of Hilgard
touched a large portion of the West, but dealt especially with California; that
of Kearney and his associates was confined to the Tooele Valley in Utah, but
it is applicable to the major part of the Great Basin. Both dealt specifically
with the tolerance of the important dominants, but the work in Utah was
much more intensive, treating the plant communities in detail, and measuring
the water-content and salt-content at different depths and in a wide variety
84
KINDS OF INDICATORS.
of conditions. The indicator values of this classic study were completed by
Shants (Clements, 1916 : 233), who brought out the successional relations of
the various conmiunities (plate 15, a).
Plants indicate alkali by their presence or absence. The positive indicators
are the halophytes, which bear a distinctive xerophytic impress, caused pri-
marily by the decreased chresard in the presence of an excess of salts. When
the relation is chiefly one of concentration, the condition is known as "white
alkali." This is due to the presence of sodium chloride, sodium sulphate,
calcium sulphate, or other salts which possess no directly injurious action.
Sodium carbonate produces "black alkali," which is directly deleterious to
the plant, probably through corrosion of the tissues. The latter renders the
Boil. useless agriculturally, while the former does not, except when present to
an excessive degree. Since the three sodium salts often occur together, the
plants of alkaU soils serve chiefly as indicators of the total concentration, and
the significance of the "black alkali" can be determined only by chemical
analysis or crop test. Hilgard (1906 : 535) regards the following species as
indicators of irreclaimable land when they occur as dominants, unless the
land is underdrained to remove the excess of salts: Sporoholus airoides, Dis-
iichlis spicata, Spirostachys ocddentaliSfSalicomiaspp., Dondiatorreyana, D.
suffnitescens, Sarcobatus vermiculatus, Frankenia grandifolia campestris, and
Cressa truxiUensis. In the Tooele Valley the crop-producing power of saline
lands have been smnmarized by Kearney et al. (1914 : 414) in the following:
Community indicators of crop production in saline lands.
Type of vegetation.
Is land capable of crop-production —
Without irrigation.
With irrigation.
Artemisia tridentata ....
Kochia vestita
Yes
Yes.
Yes; if alkali can be re-
moved.
Yes; after alkali is re-
moved.
Yes ; after alkali is removed.
Possibly; with drainage.
No.
Precariously in years of rainfall above
the normal
Atriplex coofertifolia ....
Saroobatus-Atriplex
Sporobolus-Distichlis ....
Spirostachys-Salicornia . .
Precariously ; conditions rather more
favorable than on Kochia land ....
No
Probably not
No
Lime indicators. — The original plan of giving a concise but complete
account of the various views as to the effect of lime in native vegetation has
necessarily been abandoned by reason of the limitations of space. Conse-
quently, it must suflBce to point out that the former views of the calciphily or
calciphoby of various species are untenable, and that the effects usually
ascribed to lime are either due to a complex of factors or to its indirect action.
Schimper (1903 : 94) has presented the best summary of the arguments which
support the assumption that lime is a factor of primary importance, but even
his account reveals the many weaknesses of the theory. The latter are clearly
brought out in the following statement :
"External conditions, however, change with the area. In one area, the
silica-form, in another the lime-form, is better adapted to local conditions,
whilst in a third area both forms may be able to maintain themselves in the
struggle for existence. Accordingly, one and the same species is calciphobous in
the first area, calciphilous in the second, and indifferent in the third." (p. 104.)
CLEMENTS
PLATE 16
A. HonhumiHAm :ui I Uondta liumniutk.s uuli.-aling dilTen-uces in =iaU-conlcnt. Great 8jilt Lake. Utah.
""• "^'^rSiri^^in^rt'SS^^^^^^^^ "' Ju....Hel.ocfu.ri. marking differeneos in water^ontent
FACTOR INDICATORS. 85
One by one the " calciphile " and "calciphobe" species have been found or
grown in the opposite conditions, until practically no obligate species remain.
The present situation is well-expressed by Wanning (1S09 : 58) :
" Recently it has been definitely established that the amount of lime in itself,
in so far as it does not operate physically, can not be the cause of differences in
the flora, for not only can calcicolous plants be cultivated in soil that is poor
in lime, but silicolous plants, and even bog-mosses, which are regarded as pre-
eminently calciphobous, can grow vigorously in pure Ume-water if the aqueous
solution be otherwise poor in dissolved salts. It has been overlooked that
nearly all lime soils are rich in soluble mineral substances, and this wealth
excludes plants belonging to poorer soils ; beyond this the important physical
characters of calcareous soil, compared with granite soil, come into play."
The century-old controversy over the significance of lime has been as
unscientific as it has been useless. No ecologist questions the influence of
both the chemical and physical properties of the soil, though there can still be
much opportunity for disagreement as to their respective importance, where
observation is the method relied upon. The general employment of quanti-
tative methods and experiments in the fields would long ago have assigned to
lime its proper position. Naegeli (1865) was perhaps the first to point out that
the response to lime was largely a matter of competition, and the validity of
this explanation has been greatly increased by cultures showing the facultative
nature of "calciphile" and "calciphobe" plants. His conclusions were based
upon observational studies, however, and, like all such work, can only suggest
working hypotheses for critical field experiment. The following statement
(Clements, 1913 : 76) seems still an adequate summing-up of the lime problem:
"To one skeptical as to the influence of lime, the results of the Excursion
were most interesting. One could not fail to be impressed with the abundant
evidences of the distributional significance of lime, while he was struck by the
fact that scarcely a single 'calciphilous' or 'calciphobous' plant could prove a
clear title to the term, physiologically. It is useless to add a single line to the
Uterary solution of this hoary problem, but the British experience serves to
emphasize the conviction that nothing but physiological and competition
studies in the field can hope to lead to a final solution."
In the western United States lime has nowhere been found to be a direct
factor of importance. Neither observation nor experiment has disclosed any
definite correlation with it, and hence no plants have been found which can be
regarded as hme indicators. The plants of wet soils which have been con-
sidered to indicate the absence of lime are dealt with in the next section.
Aeration indicators. — ^The effects of wet and acid soils upon plant behavior
have long constituted a puzzling problem. The leading r61e in such habitats
as marshes and bogs has been assigned to various factors, such as acids, bog
toxins, toxic exudates, the absence of lime, and the lack of oxygen. Probably
all of these are more or less concerned in the problem, with the exception of
the supposed exudates, but the view held here is that the lack of oxygen is the
cause, and the other conditions, consequences, or concomitants (Clements,
1916 : 90). The presence of acids and bog toxins is regarded as the direct
result of the activity of the roots and bog flora under deficient aeration (cf.
Stoklasa and Ernest, 1909 : 55; Livingston, 1918 : 95). The absence of lime
is apparently a concomitant of acid production, since the addition of lime to an
86 KINDS or INDICATORS.
acid soil either neutralizes the acid or affects the colloidal relations in such
fashion as to make the soil agriculturally productive. It is significant, how-
ever, that Ume is not the only substance that has this effect, since it is also
produced by other materials which improve aeration. An acid soil is regarded
as unfavorable to plant growth primarily because of the deficit in oxygen, and
consequently because of the poor development of the micro-organisms that
reconvert organic nitrogen into available form (plate 15, b).
The current assumption that bog water contains acids or toxins which are
in themselves unfavorable to absorption seems disproved by the experiments
of Bergman (1919). This investigator submerged pots containing plants of
Phaseolus in bog water and tap water respectively until the tops were covered.
In both the leaves wilted and turned yellow within 3 days. Both the bog
water and tap water were then oxygenated night and morning, and by the
following day the leaves had regained their normal turgor, and remained so for
several days while oxygen was supplied. Similar results were obtained with
Geranium and Impatiens. With the former, bubbling carbon dioxid through
the water containing turgid plants produced wilting on the second day, and
led to final chlorosis and fall of the leaves. When pots of Impatiens were
submerged in water with and without Philotria, the ones remained turgid,
while the others wilted within 3 days. Plants of Coleus and Fuchsia were
grown in ordinary pots and in submerged ones, and the root pressure was
found to be two or three times as great in the former. When the plants in the
submerged pots were aerated by bubbling air, or by placing Philotria or
Spirogyra in the water, the root pressure was nearly as great and as well
maintained as in the normal conditions. Hydroid species, such as Salix sp.,
Cyperus altemifolius, and Ranuncuhis sceleratus, grew about equally well in
bog water and tap water, whether aerated or not.
The studies of Hole and Singh (1914 : 10) upon aeration in forest soils
indicate that the lack of oxygen is a factor of greater importance and wider
extent than has been supposed. The general summary of their results is as
foUows (101) :
"1. The present experiments have confirmed the results previously ob-
tained regarding the very injurious effect of bad aeration on the growth of Sal
seedlings in the local forest soil.
" 2. When water is long held in contact with this soil, which is the case under
conditions of bad aeration, it becomes heavily charged with carbon dioxid and
impoverished as regards its supply of oxygen.
" 3. The bad growth of Sal seedlings in this soil is correlated with an accumu-
lation of carbon dioxid in the soil-solution and a low oxygen content, and this
possibly explains the evil effects of bad aeration. Further work however is
required to prove this and also to decide the relative importance of carbon
dioxid and oxygen, respectively.
" 4. Liming this soil, immediately before sowing, has an injurious effect upon
Sal seedlings, and, during the rains, soil which has been thus limed appears to
contain more carbon dioxid and less oxygen than the unlimed soil. It seems
possible that this may be due to accelerated bacterial activity.
"5. As carbon dioxid is rapidly dissipated and a deficiency of oxygen made
good under the ordinary conditions of water cultures, it is not easy to prove
the effect of varying quantities of these gases on plants grown in cultures. For
the same reason, artificial aeration of such cultures may not show any bene-
ficial result.
FACTOR INDICATORS. 87
"6. As Sal seedlings can be successfully grown in water cultures, the injuri-
ous effect of bad aeration is not due to water as such. This probably explains
the fact that Sal can grow on the banks of the rivers or even of stagnant lakes,
in which the water is kept well aerated by exposure to the air or by the pres-
ence of green aquatic plants."
The significance of aeration in field soils has been emphasized by Howard
(1913 :7, 10):
"Important results have been obtained relating to water-logging and drain-
age, and it is suggested that these matters are of far greater importance than is
generally supposed. Even partial water-logging has been shown to reduce the
wheat crop 50 per cent. It is possible that the so-called indigo disease is the
consequence of water-logging and a want of cultivation in a wet season, and
that the best way of dealing with the situation is by improved drainage and
by a more thorough aeration of the soil. I believe the damage done to land in
Bihar by water-logging during the monsoon is not even dimly realized. Land
can be harmed by water-logging when water does not lie on the surface for long
periods and when water-logging would not even be suspected."
Plants may indicate good or bad aeration. The former are naturally of
Uttle importance as aeration indicators, since their impress is due to some
other factor or factor-complex. Aeration indicators proper are correlated
with a deficiency of soil-oxygen, and are naturally confined to wet soils and
water, owing to the inverse relation existing between the amount of water and
of oxygen. They may be conveniently arranged in four groups, based upon
the kind of response to deficient aeration. In the first two, the species have
developed adaptations which enable them to live so successfully in swamps
and bogs that the habit is now obligate for the majority of them. The species
of swamps regularly possess a special aerating system of air-passages and
diaphragms, often supplemented by superficial roots and a marked movement
of the transpiration stream. Such indicators are found typically in Equi-
setum, J uncus, Heleocharis, Scirpus, Alisma, Sagittaria, Sparganium, etc.
Air-passages also occur in some bog-plants, but they are Uttle or not at all
developed in the shrubby species, such as Vacdnium, Ledum, Andromeda,
Kalmia, Empetrum, etc. In most of these, the aeration devices are subordi-
nate to those designed to conserve the water-supply during drought, especially
in winter (Gat^s, 1914). Coville (1911, 1913) has emphasized the importance
of good aeration for the successful culture of the blueberry, pointing out that
this is secured in nature by the superficial roots as well as by their position in
hummocks. It is probable also that mycorhiza plays an important r6le, partly
in increasing the available nitrogen, and partly also perhaps in directly com-
pensating for the deficit in oxygen.
The other two groups of aeration indicators consist of plants which grow
normally in well-aerated soil. Hence they lack special adaptations for aera-
tion, and consequently serve to indicate a lack of oxygen by their growth or
distribution. Those which are somewhat tolerant of water-logged and poorly
aerated soils respond to reduced oxygen content by decreased growth and
reproduction. Intolerant species drop out, and their reduced number or
absence serves as an indicator of conditions. Field studies of aeration or
acidity have been few in the region concerned here. The most important is
that of Sampson (1912 : 51) in the Wallowa Mountains of northeastern Oregon.
88 KINDS OF INDICATORS.
Indicators of factor-complexes. — While indicators are concerned most imme-
diately with direct factors, they are also definitely related to the indirect ones.
Since the water-content is profoundly influenced by the nature of the soil,
water indicators often serve as indicators of soil also. In practice, the charac-
ter of the soil is more readily recognized than the amount of water in it, and
the indicators of good soil represent not merely an adequate water-content
and air-content, but a proper supply of nutrients as well. Slope or exposure
and altitude are similar factor-complexes, in which the relation of the indicator
to the complex is often clearer than it is to any one of the factors in it. In
all of these, however, it is understood that the correlation is with one or two
limiting factors, which are controlled or modified by soil, exposure, or alti-
tude (plate 16, a).
Soil indicators. — Since the soil is the seat of water-content, salts, oxygen,
and acids, as well as of nimiberless organisms, it may be related to the indi-
cators of any of these. This is the case in ordinary practice, and plants are
spoken of as indicators of moist soil, alkaline or acid soil, as the case may be.
In the stricter sense, indicators refer to the soil as defined by its physical
properties, though this necessarily includes water-content. On this basis,
plants may be indicators of sand, clay, loam, or humus soils. When their
gi'owth and distribution are taken into account, they may serve to indicate
even finer divisions of each of these types. In such cases, however, local
variations in water-content are often more potent than soil texture, and
correlation with one does not necessarily mean correlation with the other.
Since the physical character of the soil is of primary importance in determin-
ing the echard, soil indicators may be used to distinguish high and low echard.
The plants of clay and humus soils are indicators of the one, those of gravelly
and sandy soils of the other. In humid regions this distinction is of Uttle
importance, except possibly in relation to drainage, but in arid climates or
during seasons of drought it is frequently a vital matter. This has been
emphasized by Shantz (1911 : 87) in his indicator studies in eastern Colorado:
" Many of the older settlers in eastern Colorado have moved from short-grass
onto wire-grass land, or even bunch-grass land, where they claim there is much
less hkelihood of crop failure ; but the newcomer in the region or the speculator
almost invariably chooses the hard or short-grass land because it is darker in
color, and looks more Uke the soil he has been accustomed to farm successfully
in the East."
Slope-exposure indicators. — While slope and exposure are regarded as
distinct topographic features, they are so intimately combined on every
hill and mountain that their separation is undesirable, so far as indicators are
concerned at least. Both modify the direct factors, water-content, humidity,
light, and temperature, and through them nearly all other factors of the
habitat. Exposure is of the most immediate importance, as it determines the
exposition toward the sun or away from it, but is itself determined in large
measure by the angle of slope. Exposure directly affects the temperature and
humidity, and through them the water-content, and consequently the nutrients
and aeration. A northerly exposure also reduces the amount of direct sunhght,
but this is perhaps felt only in transpiration. An increase in the angle of slope
has a marked effect in increasing the runoff and correspondingly reducing the
CLEMENTS
PLATE 16
A. Atuirojiogon hallii indicating stable sjindy soil in sandhills, Agate, Nebraska.
B. ^'^^'■"^j^f ^^K^^'^'^sh and aspcn-Douglas fir forest indicating various slope-exposures, King's Ranch,
FACTOR INDICATORS. 89
water-content. Perhaps its most significant effect lies in emphasizing the
effects of exposure toward or away from the sun. Together the two increase
temperature and evaporation, and decrease humidity and water-content on
all southerly exposures, while they have just the opposite effect on northerly
ones. In arid regions, the effects upon plants are often most pronounced.
Succession moves much more rapidly and the climax is reached much sooner
on the north side, with the result that the communities often differ greatly
on the north and south slopes of the same hill. Growth usually begins earlier
on south slopes, but the plants are taller anU denser on north ones. The
indicator differences deal with the presence or absence of various species and
the corresponding communities, and with the growth and abundance of the
individuals. Such indications are related primarily to water-content and
evaporation, though temperature plays a direct r61e of some consequence
(plate 16, b).
Alternation in vegetation is largely a matter of slope-exposure (Clements,
1904 : 165; 1905 : 285; 1907 : 289). Much attention has been given to the
alternation of dominants and subdominants on different slopes in the rolling
prairies of Nebraska and the mountains of Colorado. Shantz (1906 : 25)
has shown the variation in temperature and light intensity during the day for
different slopes in the short-grass association at Colorado Springs. Weaver
(1917 : 43; 1919) has made a detailed study of the evaporation, water-content,
and temperatures of northeast and southwest slopes in the Palouse region of
Washington and adjacent Idaho. All the factors agree in showing that the
southerly slopes are much more xerophytic, and readily explain the absence
of a large number of species, or their greater abundance on the northerly slopes.
Spalding (1909 : 43) studied the occurrence of species on two opposite slopes
in the desert scrub at Tucson. He found that they had 15 perennial species
in common, while the northeast slope had 24 not found on the southwest,
and the latter 9 not present on the other. Shreve (1915 : 97, 61) has given a
detailed account of the differences in the vegetation of the Santa Catalina
Mountains due to slope-exposure, and in the factors concerned.
Altitude indicators. — Altitude is not so much an edaphic factor-complex as
the expression of a specialized cUmate, of which elevation above the sea-level
is the remote cause. This expression occurs in some degree at all altitudes,
but its accumulation becomes most striking at the higher ones and especially
above timber-line. Because of the close relation between altitude and latitude,
the actual level of a particular effect, such as timber-line, varies from sea-level
at the northern tree-limit to 12,000 feet or more in the southern Rocky
Mountains. As is well known, the direct effect of increased elevation is seen
in reduced pressure and a correspondingly rarefied atmosphere, which is the
primary cause of most of the changes. The factor most affected is tempera-
ture, the rays passing readily through the rarer air during the day, while for
the same reason radiation is very rapid at night. As a consequence, the soil
and the air inmiediately above it may become very warm on a sunny day and
then drop to freezing at night. On Pike's Peak the surface of the soil may
show a temperature of 140** F., while in the air 5 feet above, the temperature
is but 70° F. Probably still more important is the shortness of the growing
season. The frostless season is nearly 5 months long at Colorado Springs
(6,000 feet), while on the top of Pike's Peak (14,100 feet) frost occurs fre-
90 KINDS OF INDICATORS.
quently throughout the summer. The light changes Uttle in quality or inten-
sity with the altitude in the Rocky Mountain region generally, though this may
be due to low humidity. The relative humidity increases, but evaporation
and transpiration are greater at higher elevations, owing to reduced pressure,
wind, etc. The annual precipitation rises steadily with altitude, and an increas-
ing amount of it occurs as snow. The -excessive snowfall of subalpine and
alpine regions accounts for many of their characteristic features and explains
the generally high water-content. Winds are usually prevailing and force-
ful, and have both a direct And indirect effect in the dwarfing of trees at
timber-line. The indicator values associated with high altitudes are primarily
due to temperature or water, or usually to both acting together. With the
exception of the wind and snow forms of trees and shrubs, all alpine and sub-
alpine indicators are related to these factors in the region concerned.
The sharp changes of climate with altitude produces a corresponding
sequence of climaxes, which serve as the most outstanding of indicators.
These are considered in more or less detail in the following chapter. In addi-
tion, the majority of montane and alpine species have rather definite lower
and upper limits, and may be used as indicators of altitude, though a cor-
rection is necessary for those of wide range in latitude. Cockerell (1906 : 861)
has made an analysis of the alpine species of Colorado, based upon Rydberg's
Flora of Colorado (1906), which brings out their altitudinal relations clearly,
and makes it possible to use many of them as altitude indicators for the
central Rocky Mountains (plate 17).
Organism indicators. — The many basic relations between plants and
animals make it clear why the plants often serve as definite indicators of
animals. Animals may also act as indicators of plants, but to a less degree
and in a less definite manner. In addition, plants regularly serve as indicators
of such other plants as bear a distinct nutritional relation to them. This is
particularly true of the fungi and bacteria, of which one of the most striking
indicator relations, the fairy ring, has already been discussed (p. 12). The
use of plants as indicators of animals is based upon the relation of food,
shelter, disturbance, or pollination. In all of these the indications may be very
definite, a certain plant or commimity denoting a particular animal, but as a
rule the relation is necessarily more general. In some cases, moreover, the
relation may be concomitant rather than causal, as in the case of the alpine
conies and marmots, where the control seems to be rather one of climate than
of the alpine plants upon which they feed. Furthermore, the indicator rela-
tion varies from region to region with the range of local occurrence of the
species concerned. A striking example of this occurs in the relation of the
kangaroo rat (Dipodomys deserti) to the shrubs about which it makes its
mounds. In the savannahs of the desert plains it occupies every clump of
Celtis pallida as its first choice. In the usual desert mixtures of Larrea and
Prosopis where Celtis is absent, the preference is almost exclusively for
Prosopia, but when the latter is lacking or has been destroyed by the rats,
the mounds are made about Larrea. In portions of the Colorado Desert,
mounds of remarkable size are built about Dalea spinosa, and both Prosopis
and Larrea are practically ignored. Throughout the desert scrub, one or the
other of these four genera will be the indicator, depending upon their grouping.
CLEMENTS
PLATE 17
A. Alpine fir (Abiea lasiocarpa) ut timber line, showing the dwarfing effect
of high altitudes, Long's Peak, Colorado.
B. An alpine dwarf {Rydbergia grandiflora) , Pike's Peak, Colorado.
CLEMENTS
PLATE 18
e .
A. Cereus giganleus showing nests of gilded flicker {Colaptes chrysoides) Tucson, Arizona.
B. Dalea spinosa dying as a result of the work of kangaroo-rats (Dipwiomys deserti), Glamis^
California.
i
PROCESS INDICATORS. 91
Food and shelter relations are naturally often combined in the same com-
munity. When they are found in the same species, the indicator value of the
latter is distinctive. This is not infrequent for mammals and birds, as in the
case of Neotoma and Yucca or Opuntia in their respective communities, but it
is best seen in the case of insects. The classic example is afforded by Yucca and
Pronuba, but Xyloscopa, Megachile, and other genera of pollinators furnish
similar instances, while the host-plants of gall-producing insects exhibit a
like relation. Such examples are naturally rare among birds, but a close rela-
tion exists in some cases. Taylor (1912 : 414) has called attention to this in
the case of Artemisia tridentata and the sage-thrasher, Oreoscoptes montanus,
and it occurs also between the cylindric opuntias and the cactus wren, Heleo-
dytes brunneicapillv^, as well as between the giant cactus, Cereus giganteus,
and the gilded flicker, Colaptes chrysaides (plate 18).
The indicator relations between plants and animals arising out of the
disturbances caused by the latter are nmnerous, and play a large part in the
study of secondary succession. Among the striking examples are ant-hills,
rodent burrows, prairie-dog towns, and beaver dams. The indicators of this
type are considered further in the section on paleic indicators.
PROCESS INDICATORS.
Nature. — Process indicators comprise those plants and communities which
indicate definite processes in the habitat. Such processes may be natural,
as when they are topographic or climatic, or artificial, when they are the result
of disturbances due to man. Such a distinction is convenient rather than
essential, since there is no real difference in the overgrazing due to a herd of
bison and that caused by a herd of cattle, or in distiu-bances of the soil pro-
duced by primitive or civiHzed man. The latter, however, does cause dis-
turbances in vastly greater number and on a much greater scale, with the
result that the majority of process indicators ordinarily encountered are
related to his activities. While the two have much in common, the more
vital distinction is based upon the nature of the area, and the vegetational
development which results (Plant Succession, 33, 60). Primary areas are
represented by water-bodies, rock, dune-sand, etc., in which extreme condi-
tions prevail, and a long line of development occurs. Secondary areas are due
to disturbance by man or animals, or to superficial erosion or deposition.
The conditions are usually much less extreme for the initial invaders, and the
development is correspondingly short and simple. Both are alike, however,
in that the successional development progresses by more or less well-marked
stages, in which there is a definite relation between the dominants and the
factors. Each stage or associes thus serves as a conununity indicator of the
conditions of the habitat, each consocies as an indicator of smaller habitat
differences, and each socies of still finer differences.
Kinds. — Process indicators are grouped primarily upon the nature of the
process itself. They are all indicators of the successional process in vegeta-
tion, and hence this relation is taken for granted. The great majority of them
are concerned with unit successions or seres related to physiographic pro-
cesses or disturbances, but many of them have to do with climatic processes
or cycles, as found in potential succession, and in coseres and cUseres. Hence
it is desirable to distinguish the indicators of primary processes, such as
92 KINDS OP INDICATORS.
eliniatie tuul physiop-aphic cycles, and those of secondary processes such as
Buperficiftl disturbances which result in denudation merely, whether produced
by man or other agencies. The major secondary processes are fire, lumbering,
cultivation, grazing, engineering op)erations which involve cutting or filling,
iirigation, drainage, and superficial erosion and deposition due to natural
agencies. These are all aUke in that they initiate secondary seres, but they
differ sufficiently in detail to be characterized by more or less distinctive
indicators. This is so true of some that it is possible to distinguish different
kinds of cultivation, grazing, etc., by means of their indicators.
Process indicators serve not only to denote the kind of process, as well as
certain variations in it, but they can also be used to approximate the time of
origin and the rate of movement. This is the natural outcome of the sequence
of stages in sere and habitat which marks succession. Moreover, they possess
the further advantage peculiar to all successional dominants of indicating
conmiunities and conditions which have preceded, as well as those which are
to follow, including the final climax. As already indicated, this is often of the
greatest practical value in enabling one to restore an earlier condition or com-
munity, to hasten a later one, or to hold the succession in the stage desired.
Accurate determinations of the rate of progress can be made only by the use
of permanent quadrats, but it can often be closely approximated, in woody
communities especially, by ascertaining the age of the dominants in relation
to the life-history.
Fire indicators. — While fire has some points in conmion with other agencies
which cause denudation, it differs especially in its action upon the surface
soil and in the more or less complete destruction of plants and germules, as
well as in the fact that the soil is not actually disturbed. These differences are
reflected in the large number of indicators either pecuUar to it or more typical
of it than of other processes. Certain vegetation-forms appear to owe their
character or at least their dominance to fire. This is particularly true of
scrub, where the form and consequently the dominance are due to the root-
sprouts produced after fire. This relation is practically universal in the
Coastal chaparral, and explains the greater massiveness of this association in
comparison with the other scrub conmiunities. It is general in the Petran
chaparral and the desert scrub, and is poorly developed only in the Basin
sagebrush. The response to fire is typical of the subclimax chaparral in Cali-
fornia and Oregon, as well as of that which occurs in the prairies of the Middle
West. The bush or scrub type is a characteristic fire indicator in forest ch-
maxes the world over, and throughout the northern hemisphere it often con-
sists of the same genera and even species (plate 19, a).
Fire has played a similar r6le in making certain genera and species of trees
almost universal indicators of its action. The best known examples are
foimd in Populiis and Betxda. Poptdus tremuUndes and Betula papyrifera are
the characteristic indicators of fire in forest communities throughout boreal
North America, as well as in many mountain regions. They owe this to their
ability to form root-sprouts, and the trees often or regularly consist of several
stems in consequence. In the Old W^orld, corresponding species of the same
genera play a similar part. A second striking group of indicators is found
among the conifers, and especially the pines. The latter are characterized
by cones which may remain closed upon the branches for many years, but open
CLEMENTS
c
PLATE 19
A. A^pen indicating an early fire, and sagebrush altemcs, a recent one, Strawberry
Canj'on, Utah.
B. Artemisia frigida indicating an old fallow field, Warbonnet Canyon, Pine Ridge,
Nebraska.
PROCESS INDICATORS. 93
readily after fire, thus furnishing a large number of seeds for immediate ecesis.
Three important species of this type occur in western North America, namely,
lodgepole pine, Pinus contorta, jack pine, P. divaricata, and knobcone pine,
P. attenuata. These are all typical fire trees, and form subchmaxes of great
extent and duration in areas frequently swept by fire (Clements, 1910). In
the Coast forest, Larix ocddentalis and Pseudotsuga mucronata likewise owe
their dominance in large measure to fire, though for reasons partly connected
with their intolerance.
Among herbaceous plants the number of fire indicators is legion. A large
number of these are annuals and biennials, but some of the most widespread
are perennials, such as Epilohium spicatum and Pteris aguilina. They are not
restricted to flowering plants, but are represented by Pyronema confluens
among the fungi, Marchantia polymorpha among the liverworts, and Bryum
argepteum and Funaria hygrometrica among the mosses. The most typical
fire-grass is Agrostis hiemalis, while among the composites, Anaphalis mar-
garitacea, Achillea millefolium, Arnica cordifolia, Erigeron acris, and species
of Carduus, Senedo, and Solidago are especially important. In severe burns,
the germules may be largely destroyed, and the resulting subsere shows
distinct stages of which Agrostis hiemalis is the first community and Epilo-
hium the second. Very often, however, the dominants of the various stages
appear during the first two years, and the successional movement consists
chiefly of the successive dominance of annuals, biennials, perennials, bushes,
and trees, as they replace or overtop each other. Many of the herbs and
bushes persist as layers if the shade permits, suggesting that they were origi-
nally derived from s^ch. In most cases, their continued persistence as societies
is connected with occasional ground fires. In such instances, the evidence
furnished by their presence can be checked by means of fire-scars, the age of
burned seedlings, and the presence of charcoal in the soil.
Lumbering indicators. — As a general rule, the indicators of lumbering
operations are of much less importance than those of fire. This is due to the
fact that the direct evidence afforded by stumps and reUct trees is altogether
conclusive, and that furnished by the herbs and shrubs is superfluous. In
spite of this, there are not infrequent cases where the clearing has been so
complete that the usual woody reUcts are absent. Many of these are com-
plicated by fire or cultivation, and some by both. However, in the midst of
virgin forest, clearings occur in which the evidence as to the agent must be
sought from the species in possession. In all clearings due to the ax, whether
the direct evidence is still available or not, many of the dominants are the
same as in burns. The chief difference in the two communities lies in the
greater selection exerted by fire, with the result that the dominants are fewer
in number and more controlling. For the same region, the major dominants
are the same for both, particularly where fire has followed lumbering, as has
been the rule.
Cultivation indicators. — As suggested previously, these might well be called
indexes rather than indicators, since they are the consequence of cultivation
instead of an indication of its possibility. The number of such indicators is
very large and they vary from one clhnax to another in accordance with the
flora. Many of them are introduced weeds, but the majority are subruderal
species derived from the adjacent vegetation. The relative importance of
94 KINDS OF INDICATORS.
the two elements varies greatly, but the introduced species decrease rapidly
in number toward the interior as well as upward into mountain ranges. For
a number of reasons, the prairies and plains exhibit the largest number of
cultivation indicators, but they occur in all cUmaxes with the exception of the
alpine meadow.
Especial attention has been paid to the subsere originating in fallow and
abandoned fields, and on timber claims throughout the grassland climax.
In the more arid portions of this vast region, there have been several waves
of settlement, coinciding more or less closely with the wet phases of the sun-
spot cycle. These waves have receded during the drought phases of the
early seventies, the early nineties, and of 1916-1918. However, the recession
has been less each time, owing largely to better methods of tillage and to the
diversification of crops. In the drought of 1893-1895, the Niobrara region of
northeastern Nebraska was nearly depopulated, where to-day there exists
an assured agricultural practice. As a consequence, also, the belt of abandoned
fields and farms has moved westward, and the indicators have changed to
correspond. Many of them occur over much of the region, however, and these
are still those of greatest importance and almost universal occurrence. A large
number are annuals, and the pioneers are all annual or biennial. As is typical
of weeds and subruderals, they occur in dense stands of a single dominant, or
a mixture of but two or three major dominants (plate 19, b).
The widespread dominants of the fallow fields of the prairies and plains are
Salsola and Helianthus, the latter represented by H. annuiLS in the eastern
portion, and H. petiolaris in the western. Both genera occur from Montana
to Texas, but are more abundant southward. Erigeron canadensis is perhaps
next in importance in fields, while Grindelia, Gutierrezia, and Artemisia
frigida, though abundant, are of still greater importance in pastures. Core-
opaia tinctoria and Polygonum pennsylvanicum are typical of moister fields in
the eastern half, while Anogra aUncaulis, Oenothera rhombipetala, Eriogonum
annuum, and Cycloloma platyphyllum characterize fallow areas with more or
less sandy soil, especially in the West. Other indicators of common occurrence
are Euphorbia marginata, E. geyeri, Ambrosia artemisifolia, Iva xanthifolia,
Chenopodium aUmm, Panicum capillare, Era^rostis pedinacea, Cenchrus
tribuloides, etc. A similar wealth of indicators of fallow or abandoned fields
is found in Cahfornia. Eschscholtzia calif ornica is by far the most striking of
these, though it is less widely distributed than Amsinckia intermedia, Ere-
tnocarpus setigerus, Sisymbrium altissimum, Rhaphanus sativus, Brassica
nigra, Bromus maximus, etc.
Grazing indicators. — Like the species which indicate cultivation, grazing
Indicators mark disturbance in varying degree. It is likewise necessary to
distinguish such indicators or indexes from those which denote the kind of
grazing possible or desirable, and the carrying capacity as measured by number
of animals. The latter are among the most direct of practice indicators, and
might well be taken for granted, if their value did not change critically from
one community to another, or in different portions of the same community.
There is much less difference in the nutritive value of the ordinary grass
dominants, for example, than in their palatability, but the latter varies
greatly with the choice possible.
PROCESS INDICATORS. 95
A considerable number of cultivation indicators are also indicators of over-
grazing. This is explained by their common relation to disturbance. In the
case of cultivation, the disturbance is much greater and usually operates in a
shorter time. The disturbance produced by overgrazing is gradual and
accumulative, and requires several years or more to attain definite expression.
In the case of breaking and tiUing in a new region on the plains, the original
vegetation is completely or mostly destroyed, and a distinct subsere beginning
with annuals is initiated. On the other hand, overgrazing changes the com-
petition relations between the dominants as its primary effect, and the actual
disturbance of the soil is usually secondary. The grasses and herbs that are
not eaten gradually secure an advantage over the others, and correspondingly
increase in dominance or importance. In most cases, they are already present
in the community, but where they are not, their invasion from roadsides or
other disturbed places into the trampled soil is a simple matter. There are
in consequence two general types of indicators of overgrazing, i. e., those due
primarily to the fact that they are not eaten, and those which invade because
of disturbance. There is naturally no hard-and-fast line between them, as is
shown in the detailed discussion in Chapter VI (plat€ 20, a).
As a consequence of the difference in the successional process, the indicators
of overgrazing resemble those of old fallow fields, and there are instances in
which careful scrutiny is needed to distinguish the initial cause. However,
when trampling has destroyed the control of the dominants and greatly dis-
turbed the surface soil, as happens frequently in sandy areas, a subsere begin-
ning with annuals results. Throughout the grassland climax, there occur
three overgrazing indicators which outrank all others in importance. These
are Gutierrezia sarothrae, Aristida purpurea, and Artemisia frigida. There are
many others of great significance, especially among the species of Grindelia,
Opuntia, Psoralea, Petalostemon, Verbena, Vernonia, Euphorbia, Carduus,
Solidago, etc., which are discussed in Chapter VI.
Indicators of irrigation and drainage. — ^These are related in that they are
connected primarily with a decisive disturbance in the water relations, though
they are more or less opposite in nature. Plants which register the effects of
irrigation are numerous, and are to be found along every irrigation ditch and
field. Those which indicate the possibiUty or desirability of irrigation are less
definite and have received much less attention. Many of them are of great
importance in denoting good soils of sufficient depth, e. g., Artemisia, Prosopis,
etc., or sufficiently free from alkali, e. g., Artemisia, Atriplex canescens, etc.
The disturbance of the soil in constructing irrigation canals and ditches,
coupled with the abundant water supply, has permitted the development of
a large and varied plant population along them. This is composed largely of
the weeds of cultivated fields and roadsides, but it also contains many sub-
ruderals developed from the natural communities. Macbride (1916) has made
an interesting study of the successional changes which occur under irrigation,
and his results serve to indicate the general indicator value of the dominants.
Plant communities serve as excellent indicators of the need of drainage,
as well as of its progress and success. The need for drainage is clearly indi-
cated by the presence of any one of the stages of the hydrosere or oxysere.
The latter also indicates the necessity of liming the soil, or employing some
other method of securing aeration and neutraUzation. Drainage hastens the
96 KINDS OF INDICATORS.
movement and reaction of the succession in swamps and bogs, and the later
aeral stages clearly indicate when the successive points have been reached
at which the area can be used for grazing, forestation, or crop production.
However, in extensive drainage operations, the areas concerned are put into
conmiission so rapidly that the natural communities are destroyed.
Construction indicators. — Practically all engineering and other construction
operations in nature disturb the soil, often in a most striking fashion. The
most common and important are the building of roads and the construction
of railways and canals. The construction of buildings and similar operations
belong in the same category, but the effects are usually masked by the sub-
sequent activities of man. The general relation of engineering operations to
succession and hence to indicators is best exemplified in the case of a railway
cut and fill. In addition to the cut and the corresponding fill, there is often a
dump of new earth on each side of the cut. These three secondary areas for
succession have much in common, but the loose soil of the dump and the fill
is invaded much more rapidly than the firm soil of the sloping sides of the
cut. This difference is even more striking when the track runs through a
level stretch and the bed is built up from soil scraped out from both sides.
The moist depressions are readily invaded by the more mobile or vigorous
species of the original community. The bed is not only more xerophytic, but
also is disturbed from time to time. Moreover, invasion proceeds along it
more readily than into it across the depressions which separate it from the
native community. As a consequence, the bed remains more or less permanently
in the early stages of succession, which consist of annual and perennial weeds,
some of which are derived from the native population. The depressions, on
the other hand, pass more or less rapidly through the usual stages to the climax,
unless the sere is kept in the subclimax by burning or cutting. Their indicators
are often of the most exceptional value in regions where the native vegetation
has been greatly modified or largely destroyed (plate 20, b) .
Roads resemble railways in their general relation to succession and indi-
cators. This is particularly true of highways in which cutting and filling,
though less extensive, are as frequent as in the case of railroads. Roadsides
usually show a typical zonation from the bare trackway to the natural com-
munity on either side (Clements, 1897 : 968). The sequence of zones sum-
marizes the successional movement, and the latter is shown in especial detail
when there are many parallel roads of different ages (Shantz, 1917 : 19).
In addition to indicating the disturbance caused by roads, plants may be used
as indicators in connection with road-building and even in traveling. The
correlation between certain communities and good roads is as striking as it is
gratifying, and in actual travel it is often a matter of much importance to be
able to determine the character of the road from the vegetation which stretches
for many miles ahead. During the constant field travel of the past five sum-
mers, many communities have been recognized to have some value for road
construction as well as travel, but there are a few of the greatest importance
and the widest extent. Throughout the mixed prairies, Stipa generally indi-
cates good upland roads, Agropyrum, poor lowland ones, while the presence
of short-grass on the hills and ridges usually means a road made rough by the
matted roots of Carex. In the sagebrush climax, sagebrush, Artemisia tri-
derUata, indicates excellent natural roads, Atriplex confertifolia, much poorer
I
CLEMENTS
PLA1E20
A. Opunlia conianchUa iiulicatiiig overj^razed pastures, Sonora, Texas.
B. Euphorbia niarginata marking roadways, Walsenburg, Colorado.
PROCESS INDICATORS. 97
ones, and Atriplex nuttallii and A. corrugata, very poor ones. Throughout the
desert scrub, Larrea is an index of good roads, Prosopis of poorer ones, and the
saline subclimax of the very poorest, except where the presence of sand makes
some improvement.
Physiographic indicators. — Plant communities owe their significance as
indicators of physiography or physiographic processes to the influence of the
latter upon the direct factors, especially water and solutes. It is clear that the
indicators of factor-complexes, such as slope-exposure and altitude, have a
distinct physiographic correlation also. However, the basic relation between
physiography and indicators is through such processes as erosion and deposi-
tion which directly control the soil and its water-content. Since physio-
graphic processes are the universal causes of primary bare areas, their indi-
cators occur in successional communities that mark the progressive change of
the area from the initial condition to one of relative stabiUty. As has been
emphasized elsewhere (Plant Succession, 35), causes other than physiography
may produce similar bare areas and initiate the same sere, the successional
movement being due to the reaction of the conmiunities alone, or to this and
physiographic processes working together. In the great majority of primary
areas, however, physiographic causes or processes are so important or con-
trolling that the serai indicators are readily correlated with them and their
changes.
The most outstanding and best-known series of indicator communities of
physiographic processes is that of ponds and lakes. In these, physiography
is normally the initial cause of the body of water, and deposition the process
which controls or promotes the serai movement. The primary stages of the
process are marked by the well-known associes of submerged plants, floating
plants, reed-swamp, and grassland, or scrub. Pearsall (1917 : 189) has
recently pointed out that still other associes should be recognized, and these
would serve as indicators of somewhat smaller changes. Finally, each con-
socies indicates a more or less definite set of conditions within the associal
stage. The succession in dunes, sandhills, and blowouts is almost equally
well known. In these the physiographic processes are very active, and the
indicators of the different degrees of reaction or stabilization well-marked
(Cowles, 1899; Gleason, 1907; Pool, 1914). The indicators of sandhills, and
of river and coastal dunes have received much attention during the studies
of the past five years. The dominants and serai communities are identical or
similar throughout the West, except along the Pacific Coast, where a very
different flora is concerned. During the same period, a special study has been
made of succession in Bad Lands, and this has permitted the correlation of a
large number of indicators with erosion and deposition, and the resulting
differences in water-content and salt-content. Similar though less extensive
investigations have been made of the indicators of saline bolsons and playas,
and of the geyser and mud-volcano areas of Yellowstone Park. Finally, the
serai indicators of cliffs, rock-fields, and gravel-slides have been worked out for
the central Rocky Mountains in particular (Clements, 1905 : 270; 1916 : 225).
Climatic indicators. — The value of climax communities as climatic indicators
has already been emphasized. Formation, association, consociation, and
society are correlated with different cUmates or cUmatic subdivisions, and
98 KINDS OF INDICATORS.
their general values as indicators are pointed out in the succeeding chapter.
In addition to this, plants and communities have striking significance as
indicators of climatic cycles and hence may become of great value in deter-
mining the proper practices in production for the arid and semi-arid regions of
the West. The existence of such cycles has been demonstrated beyond a
doubt by the work of Douglass (1909, 1914), Arctowski (1912), Huntington
(1914), Kapteyn (1914), and Clements (1916). The relation of climatic cycles
to succession and hence to indicators has been discussed at some length in
"Plant Succession," and an extensive study of the relation of the 11-year
cycle to grazing and dry-farming has been made during the drought of 1916-1918
(Clements, 1917, 1918). A complete summary of the relations between cycles
of rainfall, sun-spots, and tree-growth has recently been made by Douglass
(1919).
Trees and shrubs are the best indicators of minor climatic cycles by virtue
of the annual record of growth in rings. It is also probable that height-growth
furnishes a correlated record, but little study has as yet been made of the
cyclic nature of the latter. It has been found that the height-growth and the
reproduction of dominant grasses and half shrubs, such as Bouteloua, Agro-
pyrum, Gxitierreziay and Isocoma, show a close correspondence with the rain-
fall of the dry and wet phases of the sun-spot cycle. It is, moreover, a matter
of general experience that the carrying capacity of the western ranges varies
100 per cent or more from wet periods to times of drought. Even more
striking variations in the yield of field crops are shown for similar periods
(Ball and Rothgeb, 1918 : 49). Since wet phases usually offer the best con-
ditions for germination and growth, and drought periods the poorest, the
ecesis of dominants often affords striking indications of climatic phases. This
is especially well seen in the ecotone between two adjacent communities such
as grassland and scrub, woodland and sagebrush, or forest and grassland. In
the majority of cases so far investigated in which a woody dominant is extend-
ing into another community of smaller water requirements, the annual rings
indicate its establishment during the wet phase of the cycle.
The general significance of climatic cycles and of cycle indicators in practice
is discussed in the next section. Their fundamental value in paleo-ecology
is dealt with under paleic indicators at the close of the chapter.
PRACTICE INDICATORS.
Nature. — Practice indicators are those plants or communities which point
out the possibility or desirability of a particular practice. This is the original
as well as the general use of the word "indicator," and there are good reasons
for restricting it to this sense, and designating the so-called indicators of
factors and processes as "indexes." However, two cogent reasons have
caused the word indicator to be retained in the general as well as the special
sense. The first of these is the impossibility of drawing a line between actual
practices, as in agriculture, and the combination of human practice and
natural process in forestry and grazing. The second is that the value of an
indicator for practice rests upon the factor or process which it denotes.
Furthermore, the term indicator has become so generally understood that it
would be unfortunate to restrict its meaning, though it has been found con-
venient to employ "index" as a partial synonym.
PALEIC INDICATORS. 99
Kinds. — The basic practices concerned in a system of indicators are agri-
culture, grazing, and forestry. The primary consideration, however, is which
of these is possible or most desirable in a particular area or region. Since
successful agriculture brings the largest returns per unit area, the first question
is whether the land is agricultural. If not, the next question deals with its
value for forestry or grazing, or for a combination of the two. The methods
employed in reaching a decision as to the most desirable of the three practices
constitute land classification, which in a new region at least is to be regarded
as a practice prerequisite to the others. It is preeminently dependent upon
plant indicators, as is shown by the first serious endeavor to classify the lands
of the western United States upon anything approaching a scientific basis
(Shantz and Aldous, 1917). It is obvious that similar methods, refined by
quantitative methods and increasing experience, must sooner or later be used
in all the new regions of the world where maximum economic returns are
desired.
In addition to distinguishing areas as primarily agricultural, grazing, or
forest land, practice indicators serve also to indicate particular types of
agriculture, grazing, or forestry, as well as to suggest the crop of the greatest
promise. Thus, in the case of agriculture, indicators may be used to denote
the greater feasibility of humid, dry, or irrigation farming, or the importance
of combining grazing with dry-farming. Where grazing is concerned, the type
of vegetation not only determines whether cattle, sheep, or goats are prefer-
able, or a combination of two or three possible, but it also indicates whether
the introduction of other dominants is possible or desirable. In similar
fashion, indicators may be employed to determine the possibility of afforesta-
tion or reforestation, as well as the most promising dominants for any particu-
lar region. Finally, practice indicators have more or less value for reclama-
tion projects and other engineering operations, especially road-building, and
they are of the first importance for indicating the course and intensity of
climatic cycles and the modifications of current practice which they demand.
Because of their direct economic importance, a chapter is devoted to the
indicators of each of the great basic practices, agriculture, grazing, and
forestry, respectively. Land classification is considered in the following
chapter in connection with agriculture, and the relation of cUmatic cycles to
optimum production is discussed in connection with each type of practice.
PALEIC INDICATORS.
Paleo-ecology. — ^The significance of paleic indicators rests upon the con-
viction that ecologic processes were essentially the same during the geological
past as they are to-day (Clements, 1916 : 279; 1918 : 369). It is assumed
that the vegetation of the globe was differentiated into climax formations
corresponding to the primary climates. Such formations possessed a develop-
ment and structure strictly comparable with that of present-day climaxes.
They were divisible into associations, consociations, and societies, and they
exhibited primary and secondary seres wherever bare areas occurred. The
control of the direct factors, water, light, temperature, etc., must have been
just as to-day, and this is equally true of their modification by physiographic •
processes and climatic changes, as well as by the competition and reaction of
plant com^munities. Then, as now, the latter furnished food and shelter to the
100 KINDS OP INDICATORS.
Und animals, and these modified plant and conmiunity as a result of various
kinds of distrubance. The conception of the biome, or biotic social unit,
aeems even clearer for past periods than for the present, owing to the lack of
confusing detail, especially in the remoter eras. Finally, there is positive
evidence of the minor climatic cycles, such as the 11-year sun-spot cycle, in
the rings of fossil trees, and of greater cycles in the coseres of peat-bogs.
Paleo-ecologj' is characterized, moreover, by great changes of flora and vege-
tation such as are unknown for ecology to-day. These are expressed in great
successions, such as the cUsere and eosere, which correspond with the grand
deformational cycles.
Nature of paleic indicators. — While all the types of indicators now recog-
nized must have existed in the past, especially if the Recent period is included,
paleic indicators show one essential difference. This lies in the fact that com-
munities were but rarely fossilized, and that the community itself must be
inferred often from the merest fragments of its total population. Fortunately,
the conception of the community as a complex organism with characteristic
parts and processes furnishes an adequate method of interpretation. The
great majority of species not only play a definite r6le in the climax or in its
development as a dominant, subdominant, or concomitant, but each species
also bears distinct relations to other species. When its r61e is interpreted in
the light of its vegetation-form and habitat-form, it can be placed in the
vegetation with something of the certainty possible in existing communities.
As a consequence, the indicator values which have been taken for granted in
all the preceding discussion, namely, the indication of other species, or even a
whole conmiunity or sere by a single dominant or subdominant, play a para-
mount part in paleo-ecology. The smallest fragment of a fossil may thus be-
come an indicator of the greatest significance, providing only that its generic
identification be certain. In the case of plants at least, even this is not
absolutely necessary if the vegetation-form or habitat-form be sufficiently
distinctive to determine its habitat, and consequent position in climax or sere.
The methods of interpretation employed in paleo-ecology have been dis-
cussed in "Plant Succession" (p. 280), and smnmarized in a later paper
(1918 : 371). Because of its importance for the understanding of paleic
indicators, this summary is quoted in full:
"The methods by which the ecological results of to-day can be carried back
into the past have been briefly discussed in 'Plant Succession' and it will
suffice to pass them in review here. For the most part these are methods with
which the paleontologist is already familiar, since they have to do primarily
with the translation of facts from the present to the past. The foremost is the
method of causal sequence, already mentioned, with its basic relation of habitat,
Klant, and animal. This is well illustrated by the occurrence of Siipa in the
liocene of Florissant, which indicates not merely the existence of prairie, but
also, of course, a grassland climate and a grazing population. A similar but
even more fundamental sequence begins with deformation and passes through
gradation, climate, and vegetation to exhibit its final effects in the fauna. The
method of phylogeny which has been the most serviceable of taxonomic tools is
likewise of great value in the reconstruction of the life-forms and conmiunities
of the past. It shares with the method of succession the credit of permitting
us to give more and more detail to the bold outlines of past vegetations and
vegetation movements. The method of succession is based on the great strides
PALEIC INDICATORS. 101
made by the developmental study of vegetation during the last twenty years.
When successional studies become the rule in zoo-ecology as well, there will
seem to be no Umit to the increasing perfection of detail in picturing the rise
and fall of past populations and conmiunities. In the case of vegetation, this
method has already gone so far as to bring conviction that all the essential
features of successional processes and climax communities as seen to-day
already existed in the past.
"As indispensable corollaries of the methods of phylogeny and succession
are inferences from distribution in space and in time, and from association.
The former enables us to close many a gap in the fossil record and to fill in the
areas outlined by the known distribution of dominants. Inference from asso-
ciation, for example, aided by phylogeny, makes it all but certain that swamps
of reed-grass, bulrushes, and cattails existed as far back as the Cretaceous,
though Phragmites is the only one of the three dominants recorded for that
period. The most recent is the method of cycles, which gives promise of becom-
ing one of the most important. It is perhaps too soon to insist that cyclic
processes are universal in time and in space; but the great mass of evidence
from geology and climatology is matched by an increasing body of facts from
biological succession."
Kinds. — ^The indicator values of a fossil plant or animal clearly depend
upon the accuracy of its identification and stratigraphic position. With
reference to the former, its generic position, together with the vegetation-
form and habitat-form, is of paramount importance, partly because speciflc
determinations are often very uncertain among plants at least, and partly
because the majority of genera are uniform as to the ecological type of their
constituent species. While definite stratigraphic allocation is necessary for
finer analysis, the assignment of a plant to a particular era or period has much
value, owing to the fact that many dominant genera persist throughout most
or all of an era. The indicator value also depends greatly upon whether the
plants were fossilized in position and hence in their conmiunity relations, or
whether they have been scattered and carried to points more or less remote
from their home. The distinction between the corresponding deposits, termed
sta-ses and strates, is discussed at some length in "Plant Succession" (291).
Here it wtII suffice to point out that the water stase as exempUfied in peat-
bogs has nearly the complete indicator values of an existing sere, while those
of the much more universal strate are usually incomplete and subject to
interpretation.
It is evident that fossil plants, and animals also to a lesser degree, may
serve as indicators of factors, processes, or practices, in essentially the same
way that existing species do. Practice indicators are naturally connected
with the presence of man, and hence are restricted to the Pleistocene and
Recent periods. Grazing must have been the earliest of these, perhaps reach-
ing back into the late Pleistocene, but agriculture was relatively well-advanced
by the time of the Lake-dwellers, and construction, as well as a crude sort of
forest utilization, was at least begun. Moreover, it must be recognized that,
while grazing took on some new features as herds came under the control of
man, it must have existed as a natural process throughout the Tertiary at
least. In the case of fire, this agency must have begun its modifying influence
upon vegetation as early as the Paleozoic, but its effect must have greatly
increased with the differentiation of deciduous forest and grassland in early
102 KINDS OF INDICATORS.
Tertiary times. It could hardly have become a universal process until the
pastoral phase became general, and its greatest extension has doubtless taken
place during the last 1,000 years. The primary processes involved in physio-
graphic and climatic changes must have had much the same indicators as
to-day, allowing for the differences in flora during the various eras. While
such changes seem much greater and more frequent during the geological
past than to-day, this is almost certainly the result of a short perspective.
With respect to factor indicators, the plant genera concerned during the
Cenozoic era were largely those which characterize marked differences in
water, light, and temperature to-day, and this was particularly true after the
Miocene. During the earlier eras, the genera were mostly different, but the
vegetation- and habitat-forms the same.
The fragmentary nature of the fossil record makes it necessary to emphasize
certain existing indicator relations, as well as to employ some not needed in act-
ual vegetation. These are derived from the methods of interpretation already
discussed. The use of indicators based upon the successional sequence is
much the same, except that a single dominant or stage must often serve to
denote the presence of the entire sere. Even this is not so different from
conditions to-day, since there are many swamps in arid regions especially
in which the reed-swamp associes is represented by Sdrpus or Typha alone.
The method of causal sequence furnishes many of the most striking and sig-
nificant of paleic indicators. Habitat, plant, and animal are linked together
in a fundamental cause-and-effect relation, in which each one serves as an
indicator of the other. The importance of the plant in this relation has
been emphasized elsewhere. It may be said to have a double indicator
value, since it indicates the habitat directly by its response, and the animal
directly by virtue of the control exerted through food and shelter. Thus,
while there are numerous examples of definite relations between habitat and
land animals, most of these take the plant community for granted. The
indicators of cycles comprise both those derived from succession and from
causal sequence. In fact, they are the indicators of the grand successions
recorded in the clisere and eosere, and consist chiefly of shifting formations
and floras. Fossil genera and families often possess great indicator values
which arise from their phyletic relationships. While phylogeny must long
remain a field for varied opinions, certain great lines of relationship receive
increasing recognition, and can be employed with corresponding certainty.
Thus, while Juncus is not recorded until the Eocene, the presence of both
Carex and Phragmites in the Cretaceous makes it all but certain that the more
primitive Juncus was already in existence. In connection with phylogeny
and succession, plants may indicate distribution in space and in time as well
as the presence of associated dominants (Plant Succession, 352).
Since the field of indicators has been developed wholly with reference to
plants and with particular application to agriculture, the importance of
reciprocal indicators has not been recognized. However, in paleo-ecology
where the body of definite facts is relatively small, it is of the greatest aid to
secure all possible indications from every fact, and to check these by the
indications of related facts. Fossil plants and animals constitute the best of
reciprocal indicators, but topography and cUmate are often of great service
also. When all four can be employed as indicators in a particular period or
PALEIC INDICATORS. 103
region, it is possible to reconstruct the biome in much detail and with the
greatest possible certainty. For example, the geologic evidences of arid
climates at different periods must be regarded as more or less tentative until
confirmed by plant or animal indicators of aridity. When both occur, as in
the Miocene, the chain of evidence is complete. It then becomes possible
with the aid of the indicator relations discussed here to present a fairly
detailed and complete picture of the structure and development of the biotic
climaxes of the past. The general features of this have already been done for
animftla by Osborn (1910), and much progress has been made in doing this for
the associated plants and animals of the Bad Land horizons of the West.
Paleic indicators of climates and cycles. — The evidences of past cUmates
and cUmatic changes have been summarized from the geologic, botanic, and
zooic aspects (Plant Succession, 313). Since plants are the most immediately
responsive to cUmatic influences and constitute the best indicators, they are
chiefly considered here. The grand climates of geologic time are indicated by
corresponding great floras and faunas, which have served as the basis for the
division into eras. During each of the latter, climatic differentiation in both
space and in time has been faithfully reflected in the vegetation, and the com-
bined effect of cUmate and vegetation in the fauna. It seems highly probable
that a considerable differentiation of climates and climaxes took place during
the Paleophytic era, and that this was increased during the Mesophytic era
to become the most outstanding feature of the biosphere during the Ceno-
phytic. Thus, while each era is indicated by a particular climax flora, it also
exhibits climax formations as indicators of more or less distinct climates, just
as is the case to-day. While the grand deformation cycles which produced
the eras were marked by a changed flora and fauna, the major deformation
cycles and grand sun-spot cycles are thought to correspond with shiftings of
cUmate and vegetation, such as are indicated for the Pleistocene. These have
to do with climaxes as indicators, and it seems a fair assumption that the
series of climaxes found in the Pleistocene shiftings likewise occurred in some
degree in the earUer cliseres of the Mesophytic and Paleophytic eras. The
constitution of the cUmaxes during the various eras and their relation to
climatic cycles is discussed in some detail in "Plant Succession" (356, 406,
419) and need not be repeated here.
Paleic indicators of succession. — Apart from the great successional move-
ments involved in the change of floras and the shifting of cUmaxes, there must
have been innumerable examples of seres and coseres in every era. Primary
areas of erosion and deposition were probably more abundant than to-day,
and primary succession must have been the rule, though secondary seres were
not unknown. Coseres resulting in the formation of coal or peat have occurred
repeatedly from the Paleophytic to modern times, while in periods of great
volcanic activity, such as the Miocene, they were produced by deposits of
volcanic dust. While each era possessed its particular flora, all the Ufe-
forms were represented. Thus, while the genera typical of the various serai
stages during the Paleophytic and Mesophytic are practically all different
from those of the Cenophytic and to-day, the vegetation-forms and habitat-
forms are the same or nearly so. With reference to the genera which con-
stituted the serai dominants and hence served as indicators of habitats and of
succession, the hfe-forms have been discussed in "Plant Succession" (pp. 354,
104 KINDS OF INDICATORS.
405, 420). Throughout the major portion of the Cenophytic, the serai genera
as well as the life-forms were essentially the same as those of to-day, and their
indicator value is readily inferred from existing conditions.
Plant indicators of animals. — The general indicator relations of fossil
plants and animals have long been recognized and utiUzed by paleontologists,
but chiefly on the animal side. The correlation between the app)earance of a
dominant angiospermous flora and the evolution of mammals is the most
outstanding example of this, but the rise of the cursorial ungulates in response
to an expanding grassland climax is hardly less striking. Such correlations
must be superlatively general before the Cenophytic, though the existing
relations between serai and climax communities and the great groups of
animals must have had analogies at least during the Mesophytic era. Since
the larger animals were all totally different, and the dominant genera of
plants practically all different likewise, the use of plant and animal indicators
as a basic method in paleo-ecology must be confined chiefly to the Cenophytic
era for the present. Here, however, it seems to offer great possibilities, some
of which must wait upon the further study of communities as biotic units
with development and structure. The indicator value of plants in this con-
nection is limited only by our knowledge of existing correlations with animals.
This is due to the fact that a large number of modern genera of plants have
existed since the Cretaceous. The evolution of animals has been much more
rapid, and the number of existing genera of mammals, for example, which
reach back to the Eocene is very small. However, among the rodents and
ungulates, where plant correlations are most important, nearly half the families
contain both modern and fossil genera. With respect to the birds and insects,
our knowledge is much less complete, but it appears highly probable that
many existing families and orders had arisen at least by the Tertiary. As a
consequence, it becomes possible to scan the rapidly growing list of plant
indicators, and to extend their correlations as far into the past as the recorded
existence of the genera or related genera permits.
Animal indicators of plants. — ^The reciprocal relation of plants and animals
as indicators, whether as communities or species, greatly extends the use of
indicators in geological times. In many horizons, animals have been pre-
served to a much larger degree than plants, while in some, plant remains are
entirely lacking. Fossil animals are especially significant in the reconstruc-
tion of upland life, since the cursorial forms of the uplands were preserved in
fairly large number, while the record of the associated plants is exceedingly
fragmentary. Moreover, animals may serve to indicate the presence of
plants in regions or in periods where they are not yet actually found. Outside
of the insects, there are few extinct animals in which there is an indicator
correlation with a single species of plant. On the other hand, the correlation
of herbivores with plant conununities, both climax and serai, is practically
universal, and they serve to indicate with a high degree of probability the
development and extension of sedgeland and grassland from the Cretaceous
to the Pliocene. The general correlation of browsing ungulates with forest
and scrub, of the earlier types of grazing animals with sedgeland and meadow,
and of the highly specialized upland types with the cUmax grassland of
xerophytic grasses (Osbom, 1910 : 9, 237) is fundamental, and has been used
to furnish the basis for the treatment of the development and structure of
the biotic communities in the Bad Lands of the West.
IV. CLIMAX FORMATIONS OF WESTERN NORTH AMERICA.
Nature. — The vegetation of a continent falls into a number of major
divisions or units. These are known as plant formations, and are regarded as
complex but definite organic entities with a characteristic development and
structure (Plant Succession, 124). They are the product of climate and are
controlled by it. Each formation is the highest expression of vegetation
possible under its particular climate, and hence it is also termed a climax.
As here understood, the formation and climax are identical, and the terms
are essentially synonymous. For the sake of emphasis as well as of conven-
ience, however, the two are used together. Hence the same unit may be
referred to as a cUmax, a formation, or a climax formation. Since it exhibits
a development as well as structure, it is further necessary to recognize that the
successional areas in the great grassland formation, for example, are an inte-
gral part of the climax, however much they may differ from it. Whatever
seems inconsistent in this is apparent and not real, since it is a matter of
conmion knowledge that the same organism may appear in two or more
unlike forms, such as the seedling and adult plant, or the larva, chrysalis,
and butterfly.
Climaxes owe their character to the controlling species or dominants which
make them up. These climax dominants belong to the same vegetation-
form, which represents the highest type possible under the prevailing climate.
In grassland the climax dominants are all grasses or sedges, in forest they
are trees, in chaparral, shrubs, and so forth. The exceptions to this rule all
seem to be merely apparent. They are well illustrated by the so-called
savannah in which the trees or shrubs are more noticeable than the grasses,
but the latter are in actual control of the habitat. Moreover, in the prairies
the dominant grasses may be concealed for much or all of the growing season
by tall herbs, such as Psoralea, Amorpha, and Solidago. These are called
subdominants and characterize minor communities subject to the control of
the grasses. In addition to the climax dominants are the other species which
mark particular stages in the development of the climax. These are develop-
mental dominants, and are usually termed successional or serai because of
their role in the succession or sere which reestablishes the climax on a bare
area.
Tests of a climax. — Each climax is regarded as the direct and complete
expression of its climate. The climate is the cause, the climax the efifect. So
close is this relation that the climax must be regarded as the final test of a
climate. From the standpoint of vegetation at least, climates are to be recog-
nized and delimited only by means of climaxes, and i^ot the reverse. No
matter how complete his equipment of meteorological instruments, the ecologist
must learn to subordinate his determination of climate to that of the plant if
his results are to be reliable and usable. The paramount importance of forma-
tions in indicating climates makes their objective recognition of the first
importance. In the search for criteria which would permit an objective and
consistent basis for formations, several guiding principles have become evi-
dent. The first of these is that the climax dominants must all belong to the
same great vegetation-form, since this indicates a similar response to climate.
105
106 CLIMAX FORMATIONS OF WESTERN NORTH AMERICA.
The second is that one or more of the dominant species must range throughout
the fonnation as a dominant to a larger or smaller degree. The importance
of this lies in the fact that while no two dominants are exactly alike, those of
the same formation are so nearly equivalent that the presence of one indicates
the possibility of others. This is well illustrated by the behavior of Botiteloua
ffracilis, which ranges as a dominant from the Missouri River to California
and from Saskatchewan to Mexico. While the climate of this vast stretch
varies greatly in physical or in human terms, the conclusion is unavoidable
that the extensive areas covered with Bouteloua have the same or a similar
grassland climate. This obviously permits the application to vegetation of
the . principle that things equal to the same thing are equal to each other.
This approximate equivalence of dominants receives its best proof in the
grassland formation, in which the mixed prairie shows Bouteloua gracilis in
intimate mixtures with Stipa, Agropyrum, BuUdlis, Carex, or Koeleria. The
third criterion is that the majority of the dominant genera extend through-
out the formation, though represented by different species. This is well
exemplified by the chaparral climax, in which Quercus, Prunus, Rhus, Cer-
cocarpus, and Ceanothu^ are found in the several associations. A corollary
of this is that most of the subdominants likewise belong to the same genera,
as, for example. Astragalus, Erigeron, Psoralea, Petalostemon, Solidago, Erio-
gonum, and Artemisia in the grassland associations. The fourth criterion is
developmental or successional and has several aspects. It is seen in the
behavior of such subclimax dominants as Aristida purpurea, which charac-
terizes certain types of disturbed areas in all the grassland associations, and
later yields to the cUmax dominants of each. It is equally well shown by
Andropogon scoparius and Bouteloua racemosa, which are subclimax in rough
areas as well as in meadows to the final dominants of the four most extensive
grassland associations. Finally, the degree of equivalence of dominants is
indicated by their mingling but is checked by their successional alternation.
The position of Andropogon in meadows, Agropyrum and Stipa on slopes,
BuUnlis and Bouieloua on the crests of the rolling prairies, is not only signifi-
cant of their physiological and successional relations, but also of their as-
sociational positions. Andropogon furcaius and scoparius are typical of the
subclimax prairie of the Mississippi Valley, Stipaand Agropyrumoitheclimax
prairies, and Bulbilis and Bouteloua of the still drier plains.
Structure and development. — By far the greater portion of a climatic region
is occupied by the climax characteristic of it. But all through it occur areas
of varying size in which new or denuded soils are available for colonization and
the development of the climax as a consequence of succession (Plant Succes-
sion, 3). As a result, every formation shows subdivisions or communities of
two sorts, namely, cUmax, and successional or serai. Initial serai communi-
ties, such as the colonies of water-plants in ponds and streams and of Uchens
and mosses on cliffs and boulders, are readily distinguished from climax ones.
As succession proceeds, however, the communities more and more nearly
approach the climax in appearance. In the last analysis, they can be dis-
tinguished only by the fact that each stage slowly yields to the next until the
climax is reached, when the succession stops. In many cases where the dis-
turbance due to fire, grazing, or cultivation is continuous or periodic, the sub-
1
GENERAL RELATIONS. 107
climax may persist for a long period and appear to be a true climax. In the
great majority of cases, however, the successional movement though slow is
constant, and there can be no question of the climax, especially when the
permanent quadrat is employed to reveal changes.
Each climax formation falls readily into two or more major subdivisions
known as associations. Toward their edges these blend into each other more
or less, making a transition area or ecotone. The latter is broad in the case of
relatively level regions, and narrow in that of the climax zones of mountain
ranges. The associations have one or more dominants in common, or at least
belonging to the same genus, and there is a certain degree of similarity as to
subdominants also. Each association consists of several dominants as a rule,
though there may sometimes be as many as eight or ten or more, as in scrub
and chaparral. Each dominant constitutes a consociation. It may occur
alone, though as a rule it mixes and alternates with the other dominants of
the same association. This is the direct outcome of the similar requirements
of the dominants, and hence it is a guiding principle that two or more con-
sociations are regularly associated in the larger unit. This is emphatically
true of the associations covering a large area and possessing a rich flora, such
as prairie, chaparral, and forest. It is less striking in desert associations where
the dominants are often few, but even in the case of sagebrush and desert
scrub an extensive survey indicates that mixing of dominants is the rule.
Since no two consociations are exactly equivalent, there are often large areas
in which a single one occurs, such as the yellow pine in Arizona and the
Douglas fir in Oregon. Such areas are often due as much to migration and
successional factors as to differences in climatic requirements (cf. Zon, 1914 :
124).
As will be seen later, there are more groupings of consociations than are
represented by the associations actually named. This is illustrated most
clearly by the basic association of the grassland climax, the Stipa-Bouteloua
poion. This association is named from the two most characteristic con-
sociations, but it contains several dominants, e. g., Stipa comata, Agropyrum
glaucum, Koeleria cristata, Bouteloua gracilis, BuUrilis dadyloides, Carex
filifolia, and C. stenophylla. It seems clear that a community of Stipa and
Bouteloua, or Agropyrum and Bulbilis, differs in nature and in indicator value
from one containing most or all of these. When detailed mapping of vegeta-
tion is undertaken on a large scale, all of these actual groups will demand
recognition as well as definite names. But for the present, it seems sufl5cient
to give names to the association and to each consociation, while recognizing
that the former will often be represented by groups containing only two or
three of the several dominants.
Societies. — A subdominant is a species which controls an area within that
of a dominant or group of dominants. The actual community formed by a
subdominant is called a society. Its exact nature is best seen in forest or
prairie, where the control of the dominant vegetation-form, tree or grass, is
complete, though at the same time it permits a secondary control by a domi-
nating species of a different vegetation-form. Thus the yellow pine consocia-
tion of Oregon frequently shows a typical layer or society of Purshia tridentata,
the Douglas fir forest of the Rocky Mountains one of Thalidrum fendleri, and
the Stipa apartea prairies, mixed societies of Psoralea, Amorpha, and Petalo-
108 CLIMAX FORMATIONS OF WESTERN NORTH AMERICA.
akmmL Tte lirftirt feature of a society, that of a ccmtit^ within a contitJ,
oAen apiMnatitj pefttar than that of the cozi5ociati<Mi itself in the case ol
grMriand at iBttk, k doe to the difference in vegetation-forms and hence in
fiB^liyiMl raqtanneBlB. A lodely may conceivably belong to the aaae
vesptetioo-lbim aa tiM conaociatkai or aaaociation in which it occiub, bat auch
eaaea are praelieaQjr voBkaamn, Apparent fnamplw! of thie hare all been
readily referred to soeeeaMonal eauaea, aa where a loraKapd area of Hardmm
pAaium occurs in praine, or one of AriaUda pw^iuaa on the plama. The
abMMk iBtfaoabb rab IB that the aocaety belongs to a Tegetalk»4anft of kmcr
requiieMenta than tiiat of the eonaodation. The forest will haive aoaetiea of
shnibe, herbs, mosees, etc., the chaparral of undershrubs, graaaes, and herfaa,
and the prairie of herba principally. In this connection, it is especiaQy
■qtortant to ■■»«■* »gM— ttat aafannahe do not represent tree or shrub aocietiea
ingraadand,butareanineoMiiJetee]qpiaMHonof theDextstagemaw
The degree of control exerted by the society deariy depoidB upcn the M»-
history rdations of the dominant and subdominant concerned. This is larigely
a matter of the heig^it and extent of the shoot, but the root alao i^ays a hatgt
part. In f OTeat the aodeties of varying rank, from dimb to moss or lidien,
are whoDy and obTkariy sobordmate to the trees. In chaparral this is abo
true to a kxge extent, but aodeties of miderahnibe and graases often play a
ii*iMipninw part. As to giiwiiiiil, the societies are frequently much mote
iiWM|a< lawin than the dnminant graasesy and at times thqr appear to be in
aonlroL In audi eaaea the conteol ia seasonaL EaA aoibdaninant reafdiea
a fM^T^Twitm in spring, aommer, or fall, when it seems to *V— »''**^, hot tl«
real rdations are '****'"^"*^ at the other seasons. This tendoicy of ■""*■*■— to
appear daring a partiralar seaaon further eTplains the relation of daniaania
toaabdoasiaantB. Tliej not on^ ■«&» diliBRntdanandafaiyirirtae of their
^FogBtaticMi-ionBa, bat these dBBMods are also made at fiflereut times. Soeie-
tiea eidubft a similar wnawisl rdation in forest and scrub, in which their time
of appearance ia afanoat wiioQy eontroOed by the dcaninanta.. In most
tiM rdatkm is so akfftang tiiat it is posdUe to dkstinggiBii two or more ;
daring a seaaon, nnribed by partienlar societies (Clwnentn, 1905 : 296 ; 1916 :
133). Vntu ti» preeedmg (fiaeoasion, it is dear that varioas kinds hare
alnendy been <fistingaished (dements, 1916 : 132), and it is hi^^ probable
that adfl others win demand reeognition aa the study of vegetation beeomea
■aore detailed and accorate.
llie society is not a aabdnridon of the eonaodation in the aaane way that tfaia
is of the association. The latter condwtw of its conaoriitionB, gronped or
dn^; they oocopy its total area. The consociation does not rvmmi of
andrtiea, bat the latter merely occur in it or throat it to a laiBer or
degree. Thia ia readily aeen to be doe to Jte hmrit dMferenee in
fonna and to the wMwrmal nature of snCiietifa Aa a conseqaenoe, a
aoeiety may oceor not only in two or more (fifterent conanciatinna, bat alao
in two or more aaBodatioos of the same formation, It may extend
leas eoaiiBtnonilly oiver wide Btretdiea, or it may recar aa aoeeesdi
or phydcal taatota drtw iniiie A typical example of thia is i^Mra
whidi occurs in nearly every aaaodation and fonanciatinn of the y bmIbimI
wUe the chisely related aodety of P. sijajrifctlls is restricted to the
lOBma aBMiar coBBBaimities of
GENERAL RELATIONS. 109
wider range, but this is probably to be explained by the assumption that it is
really a subclimax consocies as described below, and persists as an apparent
society well into the climax. In general, however, the climatic and floristic
differences between associations are sufficiently marked to restrict each
society to a particular association.
When a species exhibits a local or restricted subdominance covering a few
square yards or a few acres, it constitutes a clan. It is clear that the differ-
ence between society and clan is merely one of degree. Theoretically, there is a
point at which they are indistinguishable, but practically very few difficult
cases have been encountered. The best examples of clans are species of gre-
garious habit, especially stoloniferous ones, and of low growth. Such clans
are capable of holding ground very tenaciously, and of slowly extending it,
but they are able to make only limited headway against the double control
of dominants and subdominants. Clans are best exemplified by Delphinium
penardi and Erigeron flageUarU in grassland, and by Pirola, Goodyera, Heu-
ehera, etc., m forest.
Names of climax communities. — ^An endeavor has already been made to
de\'ise a system of names for plant communities, in which the names would
be short, significant, and usable, as well as international in character (Clem-
ents 1916 : 127, 129, 133, 137, 138). Some such system will be indispensable
as ecol(^y becomes more and more definite in nature as well as international
in 80oi)e. In the present treatise, which is purposely limited to the western
half of the United States, the technical terms are unnecessary and are used
only as an occasional convenience. Hence, the practice will be to secure the
maximum of definiteness consistent with brevity and clearness by uniformly
distinguishing between associations, consociations, societies, and clans by
means of the one or two most characteristic genera or species. At the same
time, an endeavor is made to furnish a somewhat more asable equivalent in
vernacular terms, in the expectation that these will come into practical use.
Thus the SUpa-Borddoiui poion will be referred to as the Stipa-Botddoua
dimax or formation, or as the grassland climax or formation, and the Stipa-
Koderia affiodation as the Stipa-Koderia prairie or true prairie. The alter-
native terms for the various formations and associations are given in the
summary on page 114.
Serai eommonities. — The limits of space make it impossible to give an ade-
quate account of the basic process of succession as exhibited in the develop-
ment of climax formations, and for this the reader must be referred to "Plant
Suooesflion," especially Chapters I, V, VI, and VII. Here it must suffice to
point out that succession is a universal phenomenon by which bare areas
become colonized by plants and slowly develop through successive stages into
the chmax formation which surrounds them. Bare areas are initially bare,
as in the case of bodies of water, rock ridges, and fields and sand-dunes, or
they are denuded of vegetation by various forces, especially fire, lumbering,
graiiiig, and cultivation. The course of succession is much longer and slower
in the former case than in the latter, but the essential features of development
are the same. Each population or community reacts upon the area or buedjitat
in such a way as to make conditions less extreme and correspondingly more
favorable to species of greater requirements. These enter gradually and
compete successfully with the occupants, finally driving them out or com-
110 CLIMAX FORMATIONS OF WESTERN NORTH AMERICA.
pelling them to take a subordinate role. This dominance of the invaders
marks a new stage in the succession, which persists until its reaction upon the
habitat permits the invasion of new-comers of still greater demands. This
process continues until the climax stage is reached, when no further change
occurs, unless denudation again intervenes to produce a new bare area for
succession.
The course of development in each succession or sere is marked by a series
of stages or communities of progressively higher requirements, determined
largely by the characteristic vegetation-form. While they differ in nature and
composition, they are alike in being more or less temporary as well as in playing
an intrinsic part in the development of the climax. As a consequence, they
are termed developmental, successional, or serai communities, in contrast
with the final and permanent cUmax communities. Apart from this basic
distinction, a serai community exhibits much the same structure as a climax
one. Both are associations of two or more dominants, and exhibit societies
of subdominants. Practically as well as developmentally, however, the dis-
tinction between temporary and serai communities and permanent climax
ones is so important that it has proved desirable to use terms which at once
place each in its proper developmental position. Accordingly, each serai
stage or conmiunity is termed an associes — i. e., it is a temporary or develop-
mental association. Similarly, the community formed by each dominant is
called a consocies and that by each subdominant a socies, corresponding
respectively to consociation and society. In addition, the terms family and
colony are used for initial stages in which dominance is lacking or little
developed. The colony is the community formed by two or more pioneer
species, while the family consists of individuals belonging to a single species.
The colony is regularly characteristic of the initial stages of succession.
An associes consists, like an association, of two or more dominants or con-
socies. The most familiar example is the reed-swamp, which usually com-
prises three consocies, Scirpits Uiaustris, Typha latifolia or T. angustifolia,
and Phragmites communis. In extensive swamps, all of these occur, usually
alternating or sometimes mixed, and in northern regions with a fourth con-
socies, Zizania aquatica. Over much of the West, Scirpus and Typha alone
are found together and in many localized areas only one or the other is present.
Some socies, such as Heleocharis, Sagittaria, and Alismxi, are practically
coextensive with the dominants, though not always to be found in each local
area. Other subdominants are more restricted, and some are more frequently
associated with one consocies than with the other. Other well-marked
associes are Nymphaea-Potamogeton in ponds, Ammophila-Elymus on sand-
dunes, Redfiddia-Muhlenbergia in blow-outs, Spirostachys-Dondia in salt
marshes, Popidus-Betula in bums, and Gutierrezia-Artemisia frigida in dis-
turbed areas.
The designation of serai communities is essentially like that of climax
ones. The associes is distinguished by the use of its two most important
consocies, as the Scirpus-Typha associes or reed-swamp, while consocies and
socies are named from the dominant or subdominant, as the Scirpus con-
socies, Nymphaea consocies, Popvlus tremuloides consocies, Sagittaria socies,
PerUstemon socies, etc. Colonies are like associes in requiring the names of
the two most important species for designation.
GENERAL RELATIONS. Ill
Indicator significance of climax formations. — The formation is the greatest
of all indicators. In its climax form, it not merely indicates but actually
delimits plant climates. In its developmental stages, it sets a definite mark on
each successional habitat, and indicates the rate and degree to which these
approach the final condition. In practical terms, the climax indicates climate,
and its successional stages indicate soil or edaphic conditions. The climax
indicates the range of natural and cultural possibilities of a region, the suc-
cessions point out the possibilities of localized areas and soils. In a particular
locality the climax denotes the general limits of production, and the seres
suggest the ways by which maximum production may be reached. Thus,
while it is necessary to keep the climatic limitations in mind, the concrete
problem in any region is to utilize the indications furnished by the various
successions. In the case of agriculture, the facts derived from succession can
only be indications, since the vegetation is removed. With grazing and
forestry, however, as well as irrigation, reclamation, and many engineering
problems, succession itself becomes an instrument by which the desired
natural crop can be indefinitely maintained, or by which one crop can be sup-
planted by another.
As stated in a former chapter, succession is the universal key to the prac-
tical as well as the technical use of indicators. The stages of a sere are regu-
larly linked together in such a definite and organic process of development
that the presence of one serves as a record of those preceding and as a pre-
diction of those to follow. In every stage lies a record of the past and a
prophecy of the future. In practice, this means that a sere can be held in
any stage desired, that its progress can be retarded or accelerated, or that it
may be destroyed in part or in whole, and a new stage or sere produced.
Succession thus becomes a tool of the greatest utility wherever natural crops
are concerned. Even in agriculture, it has considerable value quite apart
from its indicator significance in meadow and pasture crops and in all those
where weeds are a serious factor. It is hardly necessary to point out that such
a use of succession is possible only through a good understanding of its pro-
cesses. For a complete treatment of this subject, the reader is again referred
to "Plant Succession." Here it must suffice to point out the general types
of succession and to emphasize their indicator significance.
Significance of succession. — Since succession is the development, or usually
the redevelopment of the climax in a particular spot, it is clear that the actual
successions or seres will differ in accordance with the climaxes in which they
occur. In other words, each sere is an integral part of the development of the
climax and its indicator value pertains primarily or wholly to that climax.
As to origin, all seres arise on a bare or on a denuded area. But bare surfaces
differ profoundly in nature and hence in the kind of plant community which
they can support. Some, such as rock and water, present extreme conditions
for plant growth and require a long period of reaction and development before
an actual soil is formed and land communities can thrive upon them. Other
areas, such as fallow fields and burns, have well-developed soils into which
plants can invade immediately. Rock and water are regarded as primary
areas, while burns, fields, etc., are secondary ones. A primary area shows a
primary succession or prisere, characterized by extreme conditions as to water-
content in particular, by a correspondingly slow reaction and soil formation,
112 CUMAX FORMATIONS OF WESTERN NORTH AMERICA.
and by a long series of stages leading very gradually to the climax. Such
priaeres are found in lakes, ponds, and streams, and on rock cliffs, ridges, lava
flows, and cinder cones. They usually occur also in salt marshes and basins,
and in shifting dune-sand, both of which regularly afford extreme conditions
for colonization, in spite of the presence of a soil. A secondary area is one in
which an existing vegetation has been destroyed or removed without destroy-
ing the soil. Its water relations are never extreme, and a large number of
herbs or shrubs can invade in the first few years, often indeed during the first
year. The secondary succession or subsere which results is short, consists of
relatively few stages, and passes rapidly into a climax. Subseres are the most
conspicuous and easily understood of all successions. Since they are largely
due to human disturbance, they are most abundant in settled regions and
hence are of the most immediate practical importance.
The nature of the succession in both priseres and subseres is further deter-
mined by the water relations of the bare areas. This is best illustrated by the
prisere, which may begin in water or on rock. In the first case, the reactions
of the successive communities are chiefly concerned with reducing the amount
of water and increasing the amount of solid material. In the second case just
the reverse is true. The amount of water is increased and the rock is broken
down into actual soil. The one begins with submerged aquatics of the highest
water requirements, the other with the rock lichens of the lowest water
requirements. The former is called a hydrosere, the latter a xerosere. Sub-
seres are similarly divided, since they regularly begin in conditions wetter or
drier than the final climax. It is further desirable, especially for indicator
purposes, to recognize hydroseres in which the lack of oxygen is a critical
factor, and xeroseres in which the abundance of alkali or the instability of the
sand is decisive. For the sake of convenience, these are called respectively
oxysere, halosere, and psammosere (Clements, 1916 : 182).
Indicator value of disturbed areas. — As has already been suggested, the most
usable of all successions are subseres, which occur typically in areas disturbed
by man or as a result of his activities. Even a relatively new country, such
as ours, has been the seat of widespread and almost universal disturbance.
Arable lands have been cleared, broken, cultivated, permitted to lie fallow or
to "go back." Forests have been lumbered, burned, or grazed, while grass-
lands and deserts have been constantly grazed and burned. Even in the most
inaccessible parts of the West it is difficult to find wholly primitive conditions,
even though by comparison most of the vegetation may fairly be called natural.
As a consequence, practically all regions show many areas of disturbance
marked by secondary successions. These furnish an enormous amount of
indicator material, which only needs interpretation in the light of successional
knowledge to be of the greatest practical importance. Every burn, every
clearing, every pasture or open range, each fallow field, irrigation ditch,
roadside, or railway fill or cut, in fact every place of whatever size from a
square foot to a township, in which the soil has been disturbed or removed,
has indicator evidence of value to offer. Indeed, the problem is often to find
primitive areas for determining the original conditions of the vegetation and
thus permitting a proper correlation of the subsere. As long ago as 1898, a
systematic search was made in several counties of eastern Nebraska for
prairie that had never been pastured or mowed. Only an insignificant rocky
GENERAL RELATIONS. 113
triangle of a few yards was discovered. Even areas which were mowed but
unpastured were very rare and of small extent. If it were not for the unin-
tentional protection afforded by fencing railroad right-of-ways, it would often
be impossible to determine the original vegetation of many regions. The
appreciation of this fact has led to the development of a method which has
been of the utmost value during the last five years in reconstructing the
primitive vegetation of regions where it has been greatly modified or almost
entirely displaced. This method has yielded surprising results throughout
grassland, sagebrush, and desert scrub, but its most striking success has been
in the great interior valleys of California, where ruderal grasses have almost
undisputed sway. The constant examination of fenced right-of-ways and
other chance protected areas the past three years has confirmed the theoretical
assumption that this was formerly a vast Stipa association. This determina-
tion of the original cHmax might well seem to be without practical importance,
but It is actually of the greatest value in indicating the proper method and
the objectives in restoring overgrazed areas to their normal productiveness,
as is shown in detail in Chapter VI.
The relation of the subsere to the climax is so definite and organic that,
once established for a single locality, it can be extended to all others where
the subsere occurs. Obviously the reverse is true also, namely, that a particu-
lar climax will exhibit the same subsere wherever similar or identical dis-
turbances occur. This same organic correlation applies Ukewise to the prisere.
The succession in water, on rock, or in sandhills is essentially the same through-
out the vast area of the grassland formation, for example. The relation
between climax and prisere once established, it is possible to predict the
climax from the prisere or the prisere from the climax wherever either is
absent. There is also a close correlation between subsere and prisere, espe-
cially in the later stages, and it is further possible to anticipate the effect of
disturbance in a region where the prisere is present, or to prophesy the course
of the slowly moving prisere from that of the subsere. When it is clearly
recognized that practically all human activities in nature result in disturbed
areas, the correlations between climax, subsere, and prisere will be seen to be
of the greatest practical importance.
Summary of the climax formations. — In presenting a sketch of the climax
formations as a background against which indicator values may stand out
more clearly, the treament is purposely limited to the western half of the
country. This is chiefly for the reason that indicator values are greatest in
newer regions, but partly also because the climax relations are simpler and
hence more certain. For this reason the prairie is the most eastern associa-
tion considered, though this necessarily involves occasional reference to the
deciduous climax. It is also recognized that some of the western climaxes
are not confined to the United States, but occur also in Canada and Mexico.
Our knowledge of vegetation and especially of succession in these countries
is ^ scanty that only occasional reference to them is warranted.
The following outline will serve to show the climax formations and their
associations, and will also serve as a guide to the discussion of each in its
proper sequence. The treatment of each formation and association is neces-
sarily brief, as the primary object is not a detailed account of the vegetation,
but only such as will serve the general purposes of indicator studies. This
114 CUMAX FORMATIONS OF WESTERN NORTH AMERICA.
account is based chiefly upon the special investigations of the last six years,
since these were undertaken for the express purpose of determining the
structure and development of the climaxes and their indicator values. These
have been supplemented by the earlier work from 1896 to 1912, and by the
results of the writer's associates and students.
1. The Grassland Climax: Stipa-Bouteloua Formation.
1. True Prairie: Stipa-Koeleria Association.
2. Subclimax Prairie: Andropogon Associes.
3. Mixed Prairie: Stipa-Bouteloua Association.
4. Short-grass Plains: Bulbilis-Bouteloua Association.
5. Desert Plains: Aristida-Bouteloua Association.
6. Bunch-grass Prairie: Agropyrum-Stipa Association.
2. The Sagebnish Climax: Atriplex- Artemisia Formation.
1. Basin Sagebrush: Atriplex- Artemisia Association.
2. Coastal Sagebrush: Salvia- Artemisia Association.
3. The Desert Scrub Climax: Larrea-Prosopis Formation.
1. Eastern Desert Scrub: Larrea-Flourensia Association.
2. Western Desert Scrub: Larrea-Franseria Association.
4. The Chaparral Climax: Quercus-Ceanothus Formation.
1. Petran Chaparral: Cercocarpus-Quercus Association.
2. Subclimax Chaparral: Rhus-Quercus Associes.
3. Coastal Chaparral: Adenostoma-Ceanothus Association .
5. The Woodland Climax: Pinus-Juniperus Formation.
1. Pifion-cedar Woodland: Pinus-Juniperus Association.
2. Oak-cedar Woodland : Quercus-Juniperus Association.
3. Pine-oak Woodland: Pinus-Quercus Association.
6. The Montane Forest Climax : Pinus-Pseudotsuga Formation.
1. Petran Montane Forest: Pinus-Pseudotsuga Association.
2. Sierran Montane Forest: Pinus Association.
7. The Coast Forest Climax: Thuja-Tsuga Formation.
1. Cedar-hemlock Forest: Thuja-Tsuga Association.
2. Larch-pine Forest: Larix-Pinus Association.
8. The Subalpine Forest Climax: Picea- Abies Formation.
1. Petran Subalpine Forest: Pioea- Abies Association.
2. Sierran Subalpine Forest: Pinus-Tsuga Association.
9. The Alpine Meadow Climax: Carex-Poa Formation.
1. Petran Alpine Meadow: Carex-Poa Association.
2. Sierran Alpine Meadow: Carex-Agrostis Association.
THE GRASSLAND CLIMAX.
STIPA-BOUTELOUA FORMATION.
General relations. — ^The grassland is much the most extensive of all the
western formations. It ranges from central Saskatchewan and Alberta in the
north to the highlands of central Mexico on the south, and in its subclimax
form at least from Illinois on the east to California on the west. From its
great extent geographically and climatically, a question naturally arises as to
its unity. It may at once be said that any division of the vegetation of the
North American continent into major units would include this as one of the
most outstanding. The real question is not so much as io its unity as to
whether it should be called a formation or not. The study of vegetation is
still in such a stage that each ecologist will answer as his experience and
insight make possible. In attempting to arrive at a basic and subjective
concept founded upon development as the only real guide to relationship, it
seemed best to employ the term formation for the major unit of vegetation,
THE GRASSLAND CLIMAX. 115
as iisage was coming to do more and more (Plant Succession, 124), and to use
association for the major subdivision, a relation likewise warranted by usage
as well as by the action of the Brussels Congress. Whatever the final solution
of this matter may be, there would seem to be no doubt that the grassland is a
major unit, coordinate with deciduous forest, sagebrush, chaparral, etc.
When we turn to the internal proof of the unity of the grassland climax,
the evidence is more complete. In the first analysis of the grassland. Pound
and Clements (1898 : 243, 1900 : 347) recognized two prairie formations,
viz, the prairie-grass and buffalo-grass formation, a bunch-grass formation
of the sandhills, and a meadow formation. In the light of successional studies,
the last two are to be regarded as subclimaxes. In a few years (Clements,
1902) it had become clear that the buffalo-grass or BuUnlis-Bouteloua forma-
tion and the prairie-grass or Stipa-Agropyrum formation were the two great
ccnununities of the prairie-plains region. This was essentially the view of
Shantz (1906, 1911) and of Pool (1914). This conception was still main-
tained in "Plant Succession" (180 : cf. note) after many additional years of
successional research. However, the developmental concept of the formation
had broadened its scope and afforded a clearer view of its structure. As
a consequence of a special study of these relations, it became necessary to
abandon the view of two separate grassland formations, and to recognize a
single formation composed of several associations. Meanwhile, it had become
increasingly evident that the Agropyrum spicatum consociation of the North-
west was closely related to the Stipa-Agropyrum prairie (Weaver, 1917 : 40).
This was first suggested by frequently finding the three dominants associated
in the field work of 1914 from Washington to Montana. It was confirmed
in 1917, but the true relationship was obscure until it became certain in
1918 that Stipa setigera and S. eminens were the original bunch-grasses of
California. As a consequence, it proved possible to recognize a fourth grass-
land association, composed of bunch-grasses and characteristic of the Pacific
region of winter precipitation.
Unity of the grassland. — ^The conclusion that the grassland is a single great
climax formation is based in the first place on the fact that the three most
important dominants, Stipa, Agropyrum, and Bouteloua, extend over most
of the area, and one or the other is present in practically every association
of it. This would seem the most conclusive evidence possible, short of actual
vegetation experiments, that the grassland is a climatic vegetation unit.
Equally cogent is the fact that these dominants, together with Carex, Bul-
hilis, and Koeleria, mix and alternate in various groupings throughout the
Stipa-Bouteloua association. Indeed, this association appears so conclusive
as to the general formational equivalence of these seven dominants that it is
regarded as the typical or base association. In addition, the characteristic
societies either extend through several of the associations or are represented
by corresponding communities belonging to the same genus. The relation of
the associations to such subclimax species as Andropogon scoparius, Cala-
nuwilfa longifolia, Aristida purpurea, and Elymv^ sitanion further confirms
the relationship of the dominants. The most obvious difference between the
various associations are exhibited by the tall-grass prairies, Stipa-Koeleria
poium, and the short-grass plains, BuUnlis-Bouteloua poium. Yet these are
closely related, as shown not only by the criteria given above, but also by their
116 CLIMAX FORMATIONS OF WESTERN NORTH AMERICA.
geographical contact. Still more eloquent is the fact that overgrazing favors
BouteUnia and Butbilis at the expense of Stipa and Agropyrum, and thus
frequently converts the base association of Slipa-Bouteloua into a pure short-
grass cover. Concrete evidence of this has been obtained in widely separated
areas and has led to the working hypothesis that a pure short-grass cover is
partly if not largely a response to graaing animals. The evidence for this is
discussed in Chapter VI.
Correlation with climate. — The apparent objection to the view of the grass-
land advanced here is that the climates of Saskatchewan, Nebraska, Arizona,
and CaUfornia, for example, are vastly different, and hence the same climax
can not exist in all of them. This objection is partly met by the fact that it is
impossible to speak of the climate of Arizona or California in particular, since
even from the human viewpoint each shows several climates. The conclusive
answer, however, is that the objection is based upon a definition expressed in
human terms or in physical measures. The everyday conception of cUmate
emphasizes temperature, especially the extremes, and rainfall. It ignores
water relations very largely and in particular the compensating r6le of water-
content. Humanly, the Palouse region of Washington and the prairies of
Kansas possess distinct climates, but in terms of wheat production and grass-
land vegetation they are very similar. Likewise, the winter in Saskatchewan
is long and the summer short, while in Texas just the reverse is true. But the
short growth period of Bovleloua gracilis fits into the short summer of Saskat-
chewan as readily as it does into the early summer of Texas, with the result
that this dominant covers large areas in both.
Examples of this sort can be multiplied almost indefinitely to prove that in
the study of vegetation the plant must be taken as the best if not the only
judge of climate. However sympathetic one may be with the use of physical
factor instruments, he can not afford to minimize the unique importance of
the plant for the analysis of cUmates. To do otherwise is to substitute human
judgment for plant judgment in the plant's own field. Hence, in the correla-
tion of vegetation and climate, it has seemed imperative to determine at the
outset and at first hand just where each formation or association is found.
The next step is to accept the judgment of the formation as final, and to
regard the climatic region as identical with the area of the formation. This
done, it at once becomes possible to correlate cUmate and vegetation by means
of phytometers and permanent quadrats, and to check the correlations in
some degree by means of physical instruments.
Use of weather records. — The tendency to approach the problem by the
use of weather records and floristic reports is almost irresistible, especially
in view of the time and effort involved in obtaining an adequate first-hand
knowledge of climaxes. However, the latter not only seems indispensable,
from the vantage ground of a continuous study of the problem, but its para-
mount importance seems to be shown also by the endeavors to correlate an
unknown vegetation with imperfect records of climate. The most interesting
attempts have been those of Merriam (1898) and Transeau (1905), partly
because they have endeavored to determine the limits of vegetational zones
by means of climatic Unes. In so far as Merriam 's life-zones dealt with natural
vegetation, they are necessarily unsatisfactory, since temperature is far less
critical than water for native species.
THE GRASSLAND CLIMAX.
SUBCLIMAX PRAIRIE TRUE PRAIRIR
117
»
Omaha, V
ebtaaka
80 in.
3
2
Jl
11
Lawrence, Kaniias
87 in.
- - -
6
5
Lincoln,,Nebraaka.
4
28 in.
3
2
1
0
ll
II
Manhattan, Kansaa
31 in. ,
1 1
"MIXED PRAIRIE
BUNCH GRASS PRAIRIE
Bismarck, N.Dak.
17 in.
U
ll
Alliance. Nebraska
16 in.
hi
1
II
K
The Dalles, Oregon
i^
17 in.
2
o
0
lilnl
Fresno, California
10 in.
4
SHORT GRASS PLAINS
DESER
T PLAINS
?
Leroy. Colorado
Amarillo
, Texas
3
2
1
0
Ft.DavJs.
Texas
Oracle, Ai
•izona
2
1
17 in.
21 in.
17 in.
]
7 in.
.ll
ll
-
0
ih
Illl
II
Ill
1
Fio. 3. — Monthly and total rainfall for representative localities in the various
associations of the grassland climax.
As a botanist, Transeau properly emphasized the water relations, employing
the percentages found by dividing the mean annual rainfall by the depth of
evaporation. The unavoidable errors due to the imperfection of the record
(Livingston, 1913 : 272) are so great, however, that his results only served to
emphasize the well-known fact that in North America forest yields to prairie,
prairie to plains, and plains to desert from east to west, as rainfall decreases
and evaporation increases. Probably the author did not intend that his
climatic lines should be taken for the limits of vegetation units, but such an
outcome was unavoidable. In referring to Transeau's work, Waller (1918 : 49,
59) says:
118 CLIMAX FORMATIONS OF WESTERN NORTH AMERICA.
"The map makes an acceptable working basis for outlining the vegetation
of the North American continent and remains still the best climatic chart that
has been published on forest and prairie distribution."
It will suffice to point out that no climatic chart, no matter how accurate,
ean hope to outline the vegetation of North America. The formations and
aasociations can never be outlined except as a result of painstaking recon-
naisance and survey, after which alone will it be possible to determine the
coincidence or correlation of the lines showing climatic factors or ratios. The
very general relation of the 60 per cent line of Transeau to the one-hundredth
meridian and the course of the upper Missouri River has led to the feeling
that this is the most important line climatically and vegetationally in North
America. It would seem that even the existence and location of this line must
be regarded as purely tentative at the present time. As to its vegetational
value, it can be stated unreservedly, after crossing and recrossing it repeatedly
from Saskatchewan to Texas during the past six years, that it does not exist.
While there can be no question of the interest and stimulus to be derived from
"trying on" all sorts of climatic correlations, this is certain to be unfortunate
if it does not lead to the conviction that causal relations between vegetation
and climate can only be discovered after we know exactly where plant com-
munities are and what they are doing. With this must also go a realization
of the fact that climax climates necessarily fall into subclimaxes, that a
climate may vary greatly and inconsistently within itself, that the variations
of one climate during a climatic cycle may be greater than the difference
between contiguous climates, and, finally, that it is the critical phases of a
climate which count most, and not its averages or sums. It must be more
fully understood that the growing season is the critical time for the vast
majority of species, and that some parts of this are more critical than others.
Furthermore, we must make more adequate use of our knowledge that plants
stand better conditions much more complacently than they do worse ones
(fig. 3).
Relationship of associations. — The associations of the formation exhibit
relationships which may be considered from various angles. Geographically,
they are grouped in the Great Plains with a narrow interrupted band stretch-
ing across the north to the Palouse region of Washington, Idaho, and Oregon,
and a broader one at the south, reaching through New Mexico and Arizona
almost to California. Both of these connect the bunch-grass association with
the Great Plains mass. Climatically, the Andropogon subclimax is the wettest,
with a rainfall of 30 to 40 inches, largely as summer rain, and the short-grass
and the bunch-grass associations driest, with 10 to 20 inches. In the hotter
regions, where evaporation is great, such as Texas and California, the eflBciency
of an inch of rainfall is naturally less. These are merely general correlations
which apply to the mass and not to its limits. In view of the ecological
requirements of grasses, the most suggestive correlation is with the line of
70 per cent of the annual precipitation occurring between April 1 and Septem-
ber 30 (fig. 4). With the exception of the winter rainfall region of the Pacific
Coast, the general agreement as to limits is good. There appears to be no
evident correlation as to temperature or altitude, as is well illustrated by the
range of Boutdoua gracilis from Mexico to Saskatchewan, and from 3,000 to
9,000 feet.
THE GRASSLAND CLIMAX.
119
Floristic relations. — The floristic relationship of the associations is evident.
Of the five great dominant genera, Stipa, Agropyrum, Bouteloua, Aristida,
and Koeleria, all occur throughout the formation, though Bouteloua is rare in
the Coast region and Stipa in the southeast. Each of these is represented by
a species of pecuharly wide range, namely, Stipa comata, Agropyrum glaucum,
Bouteloua gracilis , Aristida purpurea, and Koeleria cristata, all of which occur
from Saskatchewan to Texas, California, and British Columbia or Alberta.
With the exception of Koeleria, which is monotypic as well as the least impor-
tant of the five, each genus has one or more corresponding species in different
portions of the area. Thus Stipa comata as a dominant is largely replaced in
KEY
Jnder20^
j 20-40)1
}40-60)f
|«0-80J(
)ver SOf
FiQ. 4. — Map showing the percentage of annual precipitation between April 1 and
September 30. After the U. S. Weather Bureau.
the Missouri Valley by S. spartea and in California by S. setigera and S.
eminens. Agropyrum glaucum yields almost wholly to A. spicatum in Idaho,
Oregon, and Washington. In southern Texas, New Mexico and Arizona, and
in Mexico, Bouteloua gracilis gives way largely to B. eriopoda, B. hirsuta,
B. rothrockii, and B. bromoides, while Aristida purpurea is represented for the
most part by A. divaricata, A. calif omica, and A. arizonica. Of the ten most
important subclimax dominants, such as Andropogon scoparius, Bouteloua
racemosa, Sporobclus airoides, Stipa viridula, etc., all but one or two are found
from Canada to Texas and California.
A similar relationship is shown by the climax subdominants which con-
stitute the societies of the formation, though this is naturally somewhat less
close so far as species are concerned. The most important societies are con-
stituted by about 35 genera, of which practically all range throughout the
formation, though they are naturally little in evidence in the California grass-
land to-day, owing to the intensive cultivation and the almost universal
invasion of ruderal grasses. The number of such societies is 45, represented
by as many species. Most of these are found in each of the associations,
120 CLIMAX FORMATIONS OF WESTERN NORTH AMERICA.
though many of them are more characteristic of some associations than others.
The number of societies common to the whole formation or the major portion
of it is several times greater than the number peculiar to any one association.
The behavior of the subdominants seems fully as significant as that of the
domintmts, when their much greater number and plasticity are taken into
account.
Ecological relations. — ^The ecological relationship is indicated primarily
by the vegetation-form. All of the grass dominants are sod-formers, with the
exception of those of the bunch-grass association. These are all bunch-
grasses, and appear to be correlated with a winter precipitation which is 60
to 80 per cent of the total annual. The dominants of the prairie associations
possess a tall growth-form, usually 2 to 3 feet and often 3 to 5 feet high. As
the name indicates, the short-grass association consists of dominants regularly
1 to 2 feet high. These heights refer to the flowering stems, and the difference
between the tall-grass prairie and short-grass plains is even more striking
when the significant growth relations of the leaves are concerned. The leaves
of the buffalo-grass, Bulbilis dactyloides, are normally within 4 inches of the
soil, and those of grama, Boutelotm gracilis, within 4 to 8 inches. This applies
likewise to Carexfilifolia and Carex stenophylla, which are often very important
constituents of the short-grass association and are sometimes more abundant
than the grasses. On the other hand, the basal leaves of Stipa and Agropyrum
are usually 8 to 15 inches high, and the leafy stems reach a height of 2.5 to 3.5
feet. This difference appears to be primarily one of water-content, more or
less emphasized by grazing. The height and leaf-length of Bouteloua in par-
ticular can be doubled or trebled under irrigation. In nature, the height of
the stems has been found to vary 100 per cent from a wet to a dry year.
Striking as this difference between short-grasses and tall-grasses appears to
be in the Great Plains, it disappears to a large extent in the desert plains of
New Mexico and Arizona, where Bouteloua and Aristida regularly reach
heights of 18 to 40 inches. The general ecological equivalence of the two
forms is also well shown in the Stipa-Bouteloun, association, where Bouteloua
is frequently associated with Stipa as a layer, and Bulbilis with Agropyrum.
As would be expected, the tall-grasses tend to have deep roots and the short-
grasses shallower ones. In both cases this is largely determined by the depth
of available water and by the compactness of the soil (Shantz, 1911 : 40;
Weaver, 1915 : 274; 1917 : 56, 1919).
Subdominants. — The subdominants are practically all long-lived perennial
herbs, in which the shoot and root have solved the problem of successful com-
petition with the grasses. Four fairly well-defined types may be recognized.
Perhaps the commonest is the type with tall bushy stems, such as Psoralea
tenuiflora, Amorpha canescens, Glycyrhiza lepidota, and Carduus undulatus,
which both shade and overtop the grasses in some degree. A second type is
shown by such species as Petalostemon candidus, P. purpureus, Solidago
rigida, Lepachys columnaris, etc., in which several tall strict stems come from
one root. A third is illustrated by Eriogorium annuum, Helianihus rigidus,
and Gilia aggregaia, with a single slender shoot overtopping the grasses. In
the fourth type, the stems form a tuft or mat-like mass, which dominates the
grass shoots; this is seen in Astragalus crassicarpu^, Aragalus lamberti, Arte-
misia frigida, and Opuntia polyacahtha. In Balsamorhiza, Solidago, Carduus,
CLEMENTS
True Prairie
PLATE 21
A. Slipa-Andropogon association, Lincoln, Nebraska.
B. Stipa sjmrtea consociation, Halsoy, Nebraska.
C. Androjmgon scoparius consociation, Medora, North Dakota.
I
THE TRUE PRAIRIE. 121
and Brauneria a somewhat similar result is secured by means of the basal
rosette. The roots of the great majority of these are deep-seated, apparently
for the purpose of escaping the competition of the grass roots in so far as
possible. Most of them place their roots at depths of 5 to 12 feet, and some
penetrate as deeply as 15 to 20 feet.
Developmental relations. — From what has been said of the range of subclimax
dominants, it follows that the several associations are closely related in suc-
cessional development. The consocies and socies belong chiefly to the same
genera, and a large number of species, especially those in water, saline areas,
and Bad Lands, occur throughout. Phylogenetically, the formation shows
evidence of having derived its dominants originally from two distinct Vege-
tations. Stipa, Agropyrum, and Koeleria appear to have come from an
original northern cUmax, which was forced southward during glacial times into
the steppes of Eurasia and the prairies and plains of North America. Bcru-
teloua, Bulbilis, Aristida, and Andropogan are genera of southern origin, which
had probably pushed into the prairies and plains during the Miocene. It
seems likely that the four most vigorous species, B&uteloua gracilis, Aristida
purpurea, BuUnlis dadyloides, and Andropogon scoparius pushed still farther
northward after the Pleistocene, and came to be at home with the tall-grasses
of the northern prairies of the Dakotas, Montana, and Saskatchewan. The
ecological unity of this particular association is emphasized by Carex filifolia
and C. stenophylla, which resemble the short-grasses in life-form, but are
holarctic in origin. To the east of this central matrix was differentiated the
Stipa-Koeleria and to the west the Agropyrum-Stipa association, the one in
response to a moderate rainfall of the summer type, the other to winter pre-
cipitation. Within these there was a further tendency to separate into a
northern Agropyrum area and a southern Stipa one. This was well-marked
in the Pacific region, but it has completely stopped as a consequence of settle-
ment. In the south, a similar differentiation resulted in the Aristida-Bou-
teloua association, which still finds its best expression in Mexico, and the
Andropogon subclimax of the Mississippi Basin.
THE TRUE PRAIRIE.
STIPA-KOELERIA ASSOCIATION.
Elxtent. — The true prairies occupy a distinct belt between the subclimax
and mixed prairies, reaching from Manitoba to Oklahoma. This position as
well as their relationship is shown by the presence of Andropogon scoparius
derived from one and Stipa comata from the other. The ecological relation
is well illustrated in northeastern Nebraska, where Andropogon furcatus and
A. scoparius occupy the meadows and moister slopes, and Stipa comata and
Bouteloua gracilis the drier upper slopes and crests of the Stipa-Koeleria hills.
To the southeast, increasing rainfall enables first Andropogon scoparius and
next A. furcatus to extend over the rolling hills, while to the west and north-
west reduced rainfall causes Stipa comata to dominate and then replace S.
spartea, and permits Bouteloua and BuUnlis to become constant associates of
the prairie grasses (plate 21).
Cultivation has perhaps destroyed this association to a larger extent than
any other conmiunity of the grassland^ and its limits are accordingly difficult
122 CLIMAX FORMATIONS OF WESTERN NORTH AMERICA.
to trace. This difficulty is increased by the breadth of the two ecotones
between the three parallel associations. However, the general limits of the
area may be drawn with some definiteness. The eastern edge runs southward
from Manitoba along the western boundary of Minnesota and then swings
southeastward with the Minnesota Valley, reaching its limit between 92° and
93" W. It stretches across northern and central Iowa in the vicinity of the
ninety-third meridian, and then trends southwestward across northwestern
Missouri and eastern Kansas, where it turns south to the Oklahoma line.
The western boundary begins in Manitoba between the one hundredth and the
one hundred and first meridians and continues more or less due south to near
the Nebraska line, where it turns southeast around the sandhill region, beyond
the ninety-ninth meridian. It then follows this in a general way into northern
and central Kansas, and finally approaches the Oklahoma line in the vicinity
of the ninety-eighth meridian. The association reaches its greatest breadth
of 7** of longitude along the forty-third parallel, and it tapers more or less
irregularly in both directions to a width of I*' to 2" in Manitoba and in Kansas.
CONSOCIATIONS.
SnPA SPARTEA. AgROPYRUM OLAUCIIM.
KOELERIA CRI8TATA. AnDROPOGON SCOPARIUS.
Stipa COMATA.
Each of the 5 species may occur as a pure dominant, though this is excep-
tional for Koeleria. The latter has been found in pure communities covering
several square miles only in the Dakotas, where this condition was also found
by Griffiths (Williams, 1898 : 22). Koeleria is sometimes dominant in
meadows and swales, but it is usually associated with Stipa or Agropyrum.
While it possesses the most extensive range of any of the 5 dominants, it is
generally the least important locally, its abundance rarely being more than
30 per cent and often as low as 10 per cent. Stipa spartea and S. comata are
complementary species which overlap as dominants in northeastern Nebraska
and the central Dakotas. The ecotone between them runs in a general way
along the ninety-ninth meridian, though either occurs locally beyond this line.
In Kansas, Stipa spartea ranges over the eastern half of the State, while S.
comata is reported for only five counties in the extreme west. It is probable,
however, that the consociations are in contact with each other in the central
portion. Both occur as pure communities over large areas in their respective
regions, but they are generally associated with Andropogon scoparius or
Agropyrum glaucum. Stipa spartea is the most typical dominant of the true
prairies, while S. comata belongs primarily to the mixed prairies.
Andropogon scoparius is the normal associate of Stipa spartea and Koeleria
eristata, giving the grass tone to the prairies during late summer and autumn,
as they do in spring and early summer. It is one of the most widespread of
dominants, and plays a climax or serai role in all the grassland associations
except that of the Pacific Coast. It shows two life-forms, appearing as a sod-
grass in the true and subclimax prairies, and as a bunch-grass in the sandhills
and "breaks" of the mixed prairies and the plains. Like Stipa comata,
Agropyrum glaucum is found throughout the West, but its dominance is
local or subcUmax in nature outside of the prairie association. It exerts a
greater control on the habitat than any of its associates, owing largely to its
many and vigorous rootstocks. It is purest on the gumbo plains and rolling
THE TRUE PRAIRIE.
123
hills of south-central South Dakota, where it stretches like fields of wheat as far
as the eye can reach. Like Stipa spartea, it often meets and mixes with Andro-
pogon scoparius or A. furccUus in low prairies or subclimax regions. In such
places, as well as in local areas of higher rainfall, Andropogon furcatus and A.
nutans often become controlling. When this is the case, however, the com-
munity is always to be regarded as subcUmax. It need occasion no surprise
to find extensive outposts of subclimax grassland in the true prairies, if account
be taken of the close requirements of the dominants and the considerable
variation in normal rainfall at places not very distant from each other. Thus
Lincoln and Peru, Nebraska, are less than 60 miles apart, but one has a rain-
fall of 28 inches and is in the true prairies, while the other with a rainfall of 34
inches lies in the subclimax prairie (plate 22, a).
Factor relations. — Koeleria is a bunch-grass, while the other four dominants,
as well as the subchmax Andropogon furcatus, are sod-formers in the prairie.
All of the latter become bunch-grasses with the decreasing rainfall, such as is
characteristic of the sandhill areas to the westward. Their water relations
have been worked out for but a few regions as yet, but enough has been done
to indicate the general requirements. These agree well with the growth-form
and with the successional sequence, as well as with the physiographic relation
where this controls the distribution of water. Studies of water-content in the
Stipa-Koeleria prairies at Belmont, north of Lincoln, from April 22 to May 25,
1901, gave the following results at 5, 10, and 15 inches:
Depth.
Crests.
Upper slopes.
Lower slopes
and ravines.
ina.
6
10
15
p.ct.
12 to 6
15 to 5
12 to 3
p.et.
20 to 6
23 to 10
20to 6
p.ct.
32 to 15
34 to 16
28 to 16
The three levels, which were represented by 7 stations, correspond wnth
BouieUma, Stipa-Koeleria, and Andropogon respectively. Weaver and Thiel
(1917 : 15) foimd the water-content of Stipa-Koeleria prairie near MinneapoUs
to range for the most part between 5 per cent and 15 per cent during the sum-
mers of 1915 and 1816. In the low prairie of Andropogon furcatus and some A .
scoparius, the variation in 1915 was 27 to 45 per cent, and in 1917 chiefly from
20 to 55 per cent. In the Belmont prairies in 1916, the range of soil-mois-
ture in the high prairie was chiefly between 10 per cent and 25 per cent
on the slope, while on the ridge it fell for the most part between 5 per cent and
15 per cent. The high prairie at Minneapohs and Belmont gave an evapora-
tion rate nearly twice as great as that of the low prairie. The evaporation
rate on a ridge of the Behnont prairie was usually 2 to 4 c.c. higher than on
the slope.
Sequence of dominants. — These results confirm the water sequence as indi-
cated by the successional and topographic relations. The subclimax Andro-
pogons have the highest water-content requirement, a fact further attested
by the readiness with which they are invaded by scrub or woodland. Agro-
pyrum follows closely, often being nearly equivalent to Andropogon scoparius.
After it come Koeleria, Stipa spartea, and S. comata in this order, with the
124 CLIMAX FORMATIONS OF WESTERN NORTH AMERICA.
extra-associational Bouteloua gracilis occupying the dry crests. The average
range of water-content for the Andropogons is 25 to 35 per cent, for Agro-
pyrum 20 to 30 per cent, for Stipa spartea and Koeleria 15 to 20 per cent, and
for Stipa comata 10 to 15 per cent. It is clear that these values will vary
greatly from the dry to the wet phase of the climatic cycle, and that their
efficiency will change with the factors controlling evaporation and transpira-
tion.
While extensive quantitative studies will refine these values and will
definitize them for different regions, it seems clear that they will also further
verify the successional sequence indicated above. In applying the latter, it
must be borne in mind that the mixing of two or more of the dominants over a
certain area by no means invalidates the sequence. The requirements of two
successive dominants are more alike than different, and under minor dis-
turbances in the habitat-complex are actually or apparently equivalent, for
a time at least. These differences are modified by climatic fluctuations from
year to year. When variation of slope, exposure, and soil are taken into
account, it is readily understood why pure consociations extending over many
miles are impossible. The largest area of Agropyrum seen was in the valley
of Dog Ear Creek in South Dakota, but whenever the valley rose into hills,
Agropyrum gave way to Stipa comata or Stipa spartea. Likewise, on the rough
hills of the Pine Ridge reservation of South Dakota, Stipa comata appears
like fields of golden grain for miles in every direction, but the lower valleys,
swales, and roadways are characterized by Agropyrum. Stipa spartea shows
a similar behavior on a smaller scale. However pure the community appears,
it is regularly mixed with Koeleria or interrupted by Agropyrum or Andro-
pogon.
The mixing of dominants within an association differs only in degree and
extent from the mixing of dominants at the edge of contiguous associations
or formations. But it would be a serious mistake to assume that the associa-
tions or formations concerned were essentially a unit because of the broad
ecotone that exists between them. There is a complete sequence of dominants
with overlapping ranges in the grassland from Andropogon furcatus on the
east to Bouteloua gracilis on the west. This corresponds with a gradual
decrease of rainfall from 30 to 40 inches to 10 to 15 inches. In spite of the
equalization brought about by physiography, the two species practically never
come in contact with each other as dominants. Between them lies the whole
region of the climax prairies, 200 to 400 miles wide, along which Andropogon
makes a broad ecotone on the east and Bouteloua on the west. A similar situa-
tion exists where grassland comes in contact with the sagebrush or the wood-
land climax. There is often a complete and more or less equal mixture for a width
of several to many miles. From the superficial evidence, the dominants
might well be placed in the same formation, but a study of the successional rela-
tions or a comparison of the ecotone with the formation proper on either side
will at once disclose the real facts. As a rule the careful study of the ecotone
will show that most of it can be referred to one or the other of the two forma-
tions or associations, and that the area of actual equilibrium is relatively
small. In fact, increasing familiarity with vegetation shows that most
transitions are due to disturbance or climatic cycles and are actually a part
of succession.
CLEMENTS
True Prairie
PLArE22
A. Koiieriao rislata-Arulropoyon scoparius association, Agate, Nebraska.
B. Erigeron ramosus society, Lincoln, Nebraska.
C. Detail of society of P&oralea tenuifolia and Erigeron ramosus, Lincoln, Nebraska.
THE TRUE PRAIRIE. 125
SOCIETIES.
Nature. — The societies of the grassland formation are constituted by
perennial herbs which give a distinct impress to large areas of the grass cover.
As already indicated, they show a dominance which is subordinate to that of
the grasses, and hence are termed subdominants. Originally the term was
employed for all conspicuous subdominants of wide range (Clements, 1905).
As the importance of the distinction between climax and developmental
communities became manifest, the society was restricted to the climax, and
the corresponding term socies was used for the successional subdominants.
In the superficial study of an association, subdominants of all sorts will be
found to alternate and mix with each other. All such communities appear to be
societies, until a study of succession reveals the fact that some are relatively
permanent while others are temporary, and many indeed persist for only a
few y?ars. Where disturbance is continuous or recurrent, as in grazing,
temporary societies or socies persist as long as the disturbance lasts, and their
real character can be determined only by protected quadrats or by com-
parison with undisturbed areas. In the majority of such cases, however,
socies can be recognized by the fact that they are composed of species of
annual or biennial habit.
Control of dominants. — The subdominance of a society is necessarily limited
by that of the grass dominants. In grassland, water is the primary limiting
factor, and determines the competition between dominants and subdominants
as well as within the corresponding communities. The fact that the two
belong to distinct vegetation-forms means that they avoid competition in so
far as possible by making different demands and at different times. Theoreti-
cally, the grass dominants should gradually gain the advantage over the sub-
dominants and replace the latter completely. This is especially true of legume
societies, the reaction of which greatly stimulates the growth of grasses. Such
an outcome is frequent in the Bouteloua gracilis, Bulbilis, and Agropyrum
glaucum consociations, wherever the dense turf holds the water in the upper
soil layer. In such cases, the grass roots absorb practically all of it and leave
little or none for the deeper-rooted herbs (Shantz, 1911 : 51; Weaver, 1919 :
51). As a consequence, the number and extent of societies depend primarily
upon rainfall. Where the rainfall is from 25 to 40 inches and the evaporation
correspondingly low, societies will usually be so numerous and luxuriant as to
conceal or at least obscure the dominant grasses during much of the growing
season. As the rainfall decreases and the evaporation increases to the- west-
ward, the dominants will take more and more of the water-content, and the
number and extent of the societies will steadily diminish. The result is that
the true prairies (Stipa-Koeleria association) show the best development of
societies. The wealth of subdominants is partly due also to the fact that
the prairies have been able to draw almost equally upon the eastern and the
western floras. The mixed prairies have the same societies for the most part,
but they are reduced in number and even more in extent and density. This
is due partly to reduced rainfall and partly to the presence of the lower layer
of short-grasses and sedges.
The bunch-grass prairie is much poorer in societies, on account of a low
winter precipitation. The poorest of all is the short-grass plains {Bulbilis-
126 CLIMAX FORMATIONS OF WESTERN NORTH AMERICA.
Bauteloua association). This seems to be related to three interacting causes.
Perhaps the most important is the small amount and the character of the
sunmier rainfall, and the rapidity of evaporation. Coupled with this are the
dense sod and the fine mass of shallow roots which limit penetration largely
to the upper foot or two. A third factor is the extensive grazing which has
supplemented the first two by decreasing the competitive vigor of the sub-
dominants or by actually destroying them. In the desert plains (Aristida-
Bouteloua association), somewhat similar conditions prevail, and societies are
relatively few. This essentia] water relation between the consociations and
the societies is well shown in regions where the rainfall or water-content is
locally increased. The number, extent, and dominance of societies are greatly
augmented in the case of mixed prairies along the Pine Ridge escarpment in
Northern Nebraska, the east edge of the Black Hills, and the Front Range of
the Rocky Mountains in Colorado. This is likewise true in the sandhill
region of central Nebraska, where the chresard or available soil-water is
exceptionally high.
Relation to consociation. — ^While there is no necessary connection between
consociation and society, there is a more or less evident correlation based
upon water requirements and floristics. It must be clearly recognized, how-
ever, that consociations are not divided into societies as associations are into
consociations. The entire area of the association is occupied by its consocia-
tions, in pure altemes or in mixtures, except where succession is in process.
The same area will likewise show societies, but they will mix and alternate, or
replace each other without any clear relation to the consociations. This is
partly due to their large number and partly to the fact that subdominants
are naturally susceptible to variations in the composition, density, and vigor
of the grass communities as well as to local differences in the habitat. For
example, Psoralea tenuiflora is one of the most important of grassland societies.
It is essentially a formational subdominant in that it occurs in all of the asso-
ciations with the probable exception of the bunch-grass prairie. Yet its height
and density, and hence its degree of dominance, differ in practically all of them.
It reaches its best expression in the Stipa spartea consociation, but is usually
replaced in the related Agropyrum and Andropogon consociations by its com-
plementary subdominant, Psoralea argophylla. Of the hundred or more
societies, the majority occur in at least three associations, and usually three
contiguous ones. So closely related are the associations in conditions and
floristics that hardly a single society is known to be restricted to one associa-
tion. The societies of the most Umited extent are those which have been
recently derived from other formations. They naturally occur in the sub-
climax, the desert plains, or in the bunch-grass prairie, since these are the
marginal associations of the grassland.
Origin. — This fact corresponds with a general grouping of societies with
reference to the flora from which they come. The grassland has approximately
100 societies, of which more than 40 are derived from the southwest, and about
30 from the east or southeast. Some of the latter were doubtless from the
south or southeast originally. A few are apparently indigenous and a small
number are Pacific, and hence probably southern also. The large number of
southern elements agrees with the southern derivation of most of the grass-
land dominants. The fact that BovieUma, Aristida, and BuUnlis have pushed
THE TRUE PRAIRIE. 127
SO far north explains why the societies of desert plains, short-grass plains, and
the mixed prairie are so largely southwestern. The more mesophytic eastern
prairie affords a readier area for the invasion of the eastern and southeastern
species from regions of greater rainfall. The result is that the prairies are
largely characterized by eastern elements. This is particularly true of the
spring societies and those of the low prairies, as these are especially meso-
phytic. The summer and particularly the autumn societies are increasingly
xerophytic, and are accordingly largely southwestern and western in origin.
Mixed societies. — Subdominants either alternate or mix with each other in
the grassland fundament. Their large number explains why mixing is the
rule. The degree will vary, however, in the different associations in accord-
ance with the water relations, as well as the wealth of the flora. Mixed
societies are regularly characteristic of the true prairie, less so of the mixed
prairie, and still less so of the short-grass plains, where alternation of pure
societies seems rather more frequent. Mixed societies may consist of 2 to 3
dominants, one of which is controlUng, or of several dominants, of which 2 or
3 may be equally important. The most characteristic society of the rolling
Stipa-Koeleria prairie about Lincoln consists of Psoralea tenuiflora, Amorpha
canescens, Petalostemon candidus, P. purpureus, and Brauneria pallida. At
Mandan, North Dakota, this is represented by Psoralea argophylla, Brau-
neria, and P. candidus, while along the Rawhide Hills, in eastern Wyoming,
Psoralea tenuiflora and P. purpureus form the chief society. In the Pine
Ridge region of northwestern Nebraska and South Dakota, Psoralea occurs
as a pure society, as is frequently the case throughout the Great Plains.
While these subdominants may occur in nearly all possible combinations, the
example given illustrates the uniform tendency to reduction wherever local
factors or climatic conditions decrease the water-content. As a consequence,
the pattern woven by the subdominants upon the grass fundament is a com-
plex one and it can be traced only by a careful study of the interaction of com-
petition and the water-content. When layer societies occur in the grassland,
they are the outcome of competition for light primarily. They are naturally
restricted to the prairies.
.Aspects. — ^The most helpful clue to the structure and grouping of societies
is furnished by the study of seasonal aspects and of alternation. These are
chiefly expressions of the relation to water-content differences as brought about
by season and topography. The success of each subdominant depends upon
the extent to which it avoids competition with others. This has led to the
niultiplication of the number of societies up to the limit set by the water rela-
tions. As a corollary, the number of societies and the degree of mixture are
indicative of the water relations of a particular area or region. Species have
necessarily made use of both methods of avoiding competition, namely,
alternation in time and in space. Alternation in time results in periods of
maximum development termed aspects (Pound and Clements, 1900 : 143,
349; Thornber, 1901 : 57; Shantz, 1906 : 26). Aspects are based primarily
on the flowering j)eriod of the subdominants, upon the assumption that the
total requirements of a plant are greatest at the time of flowering and fruiting.
Moreover, the subdominants are most characteristic at this time, and the
corresponding societies stand out sharply. The number of aspects naturally
depends upon the length of the growing season. At Lincoln, the mean dura-
128 CLIMAX FORMATIONS OF WESTERN NORTH AMERICA.
tion of the latter is 234 days, and it is possible to recognize four aspects, early
spring, spring, summer, and fall. As the season grows shorter, the early
spring and fall aspects merge into the spring and summer respectively. These
two aspects persist even when the season is reduced to two months or less, as
is the case on Pike's Peak (Clements, 1904 : 349).
The early spring or prevernal aspect is largely a matter of temperature and
light, the water-content being high and the demands upon it slight. The
plants are chiefly low mat and rosette plants, which must bloom early to
avoid the overshading produced by later species. The maximum water-
content occurs in the spring and evaporation is lowest then also, though
pronounced fluctuations are of frequent occurrence. As a general result, the
more mesophytic species appear in the spring and the more xerophytic ones
in late summer and autumn. The maximum development occurs during the
sunmier aspect in high prairie, and somewhat later in low prairie, the tempera-
ture necessary for mature growth playing some part in this. In the case of
high prairie the growing season is gradually closed by drought, with low prairie
it is usually terminated by frost. With the passing of each aspect, its principal
species decrease their activity greatly. Accordingly, while the number of
mature plants constantly increases during the summer, the demands for
water and light increase less rapidly, and the supply is conserved at the
requisite level. It is hardly necessary to point out that there are no sharp
distinctions between the various aspects. The one passes gradually into the
next, and the change is not perceptible from day to day. If, however, the
prairie is visited in early April, late in May, in early July and early September,
it will present a wholly different appearance at each time.
Zones and alternes. — The structure of the prairie during a particular aspect
is largely due to alternation and zonation. These are both caused by slight
differences in the requirements of the species concerned. This is best illus-
trated by corresponding species of the same genus, such as Petalostemon pur-
pureas and candidus, Psoralea tenuiflora and argophylla, Solidago missouriensis
and rigida, Artemisia frigida and gnaphalodes, Aster multiflorus and sericeus,
and Liatris punctata, scariosa, and pycnostachya. In each case the first species
is more xeroid than the second, with the consequence that one regularly
occurs above the other in more or less zonal arrangement over the rolling
prairies. In many areas the zones are obscure or interrupted, and the two
species occur in drier and moister areas respectively, or the one will be more
abundant in high prairie and the other in low prairie. This relation is con-
firmed by their successional behavior in that the xeroid species usually shows
a marked tendency to appear just before the climax. Petalostemon and Psor-
alea have been studied as to their water relations in the Lincoln prairies,
where Psoralea argophylla characterizes the valley plains and lowermost
slopes with an average water-content of 25 to 35 per cent, while P. tenuiflora
dominates the slopes and broad middle ridges with a water-content of 15 to
20 per cent. The two touch, but only occasionally overlap or mingle to any
considerable degree. Petalostemon has been more adequately studied. The
sharp ecotone between the two species was carefully traced on two opposite
slopes in 1901, and the water-content limit between them was found to be
13 per cent. In 1917, Loftfield studied the water relations of the two species
under control, and succeeded in modifying plants of P. purpureas in high
*'.
THE TRUE PRAIRIE. 129
water-content so that they could not be distinguished in shoot characters from
those of P. candidus. The three species of Ldatris are especially striking in
their relations. About Lincoln, L. pycnostachya is confined to low prairies and
meadows, L. scariosa takes middle levels and lower slopes, while L. punctata
is found on upper slo()es and crests. As would be expected, this agrees with
the difference in growth-form; L. punctata averages 1 to 2 feet in height, L.
scariosa 2 to 3 feet, and L. pycnostachya 3 to 4 feet. It is also in accord with
their distribution westward. The hydroid L. pycnostachya finds its limit in
the prairies and the intermediate L. scariosa in the mixed prairies, while L.
punctata occurs throughout the plains as well as in the bunch-grass prairies
of the Northwest.
The alternation of unrelated subdominants is often more striking. This
is true of Anemone and Viola in the spring aspect, of Psoralea and Erigeron
in the summer, and of Aster, Solidago, and Vernonia in the fall. The most
conspicuous alternation of this sort is that of Psoralea tenuiflora and Erigeron
ramosu^, owing to the dominance and extent of each, as well as the outstand-
ing difference in color. The areas of each broaden and contract with the wet
and dry phases respectively of the climatic cycle. In the wet year of 1915 the
Erigeron society covered the lower slopes and vales of the Lincoln prairies like
fields of snow, while the upper slopes and edges were marked out in the purple-
green of the Psoralea society. At Weeping Water, where the prairie is largely
subclimax, the grass openings on the oak hills were snow-white with Erigeron,
thus confirming its topographic and cyclic relation to Psoralea in the prairie
region (plate 22, b, c).
Studies of prairie societies. — As an adequate treatment of the prairie
societies is impossible, owing to the limits of space, it must suffice to refer to
the work that has been done upon them and to list them in the general order
of importance under the different aspects. The first attempt to deal with the
structure of the grassland was made by Pound and Clements (1898 : 244;
1900 : 349, 244, 299), who distinguished and characterized the various sub-
dominants, determining their rank largely upon the basis of the quadrat
method. Thornber (1901 : 73, 96, 137) made a thorough analysis of the
structure of a subclimax prairie at Nebraska City, paying especial attention
to the alternation of the principal and secondary species. Harvey (1908 : 81)
has traced the seasonal development of the various societies in the prairies at
Yankton, South Dakota. In a careful study of climaxes and their succes-
sional development in the sandhills of Nebraska, Pool (1914 : 221) has dis-
tinguished the principal and secondary species of the subclimax bunch-grass
prairie. Recently Weaver and Thiel (1917 : 9, 32) have dealt with the aspects
and societies of the prairie at Minneapolis and Lincoln, and Pool, Weaver,
and Jean (1919) with the root relations of dominants and subdominants in
subclimax prairie at Peru, Nebraska, and climax prairie at Lincoln. Natur-
ally, the following lists are based chiefly upon the structural and quantitative
studies made in the Nebraska prairies from 1895 to 1907. They have been
checked and extended throughout the true prairies from North Dakota to
Kansas in the special studies made during the summers of 1913 to 1918. All
of the important societies that occur in the prairies are listed here, though
many of them are found also in other associations.
130 CLIMAX FORMATIONS OF WESTERN NORTH AMERICA.
Frmmnal Soeittitt:
Cans pennaylvanioa.
AntHinaria dioeoa.
A— none patww.
AiMtnone oaroliniana.
Lomatium fooniculaceum.
Draba caroliniana.
Androsaee ocddentalis.
Vtmal Soeietiea:
Astragalus crassicarpus.
Ara$;alu8 lamberti.
Tradcscantia virgiaiana.
Phlox pilosa.
Anemone canadensis.
Fragaria virginiana.
Viola pedatifida.
Viola cucullata.
Baptisia leucophaea.
Callirrhoe alcaeoides.
Vicia americana.
Thalictrum purpurascens.
Ranunculus ovalis.
Zizia aurea.
Anemone cylindrica.
Ekiuisetum arvense.
Comandra umbellata.
Senecio aureus.
SisjTinchum angustifolium.
Lithoepennum linearifolium
Lithoflpermum canescens.
Lithospermum hirtum.
Agoseris cuspidata.
Achillea millefolium.
Hosackia americana.
Viola pedata.
Sieversia ciliata.
Hypoxia hirsuta.
Oxalis stricta.
Castilleia sessiliflora.
Houstonia angustifolia.
Soeietiea of the True Prairie.
BbUvoI Societiet:
Psoralea tenui flora.
Amorpha canescens.
Petalostemon candidus.
Petalostenion purpureus.
Psoralea argophylla.
Erigeron ramosus.
Glycyrhiza lepidota.
Brauneria pallida.
Lepachys columnaris.
Helianthus rigidus.
Dalea laxiflora.
Verbena stricta.
Verbena hastata.
Linum sulcatum.
Equisetum levigatum.
Equisetum hiemale.
Veronica virginica.
Allium mutabile.
Pentstemon grandiflorua.
Euphorbia coroUata.
Coreopsis palmata.
Rosa arkansana.
Lespedeza capitata.
Monarda fiatulosa.
Heliopsis scabra.
Pycnanthemum lanceolatum
Pentstemon gracilis.
Silphium integrifolium.
Steironema ciliatum.
Teucriimi canadense.
Teucrium occidentale.
Amorpha nana.
Callirrhoe involucrata.
Serolinal Societie*:
Solidago rigida.
Aster multiflorus.
Solidago missouriensis.
Solidago spceiosa.
Artemi.sia frigida.
Grindelia squarrosa.
Gutierrezia sarothrae.
Kuhnia glutinosa.
Aster oblongifolius.
Artemisia graphalodes.
Artemisia dracunculoides.
Salvia azurea.
Rudbeckia hirta.
Solidago serotina.
Aster sericeus.
Aster paniculatus.
Aster novae-angliae.
Aster azureus.
Nabalus asper.
Eupatorium altissimum.
Liatris pycnostachya.
Liatris punctata.
Liatris scariosa.
Carduus undulatuB.
Solidago nemoralis.
Solidago canadensis.
Vernonia baldwinii.
Vernonia fasciculata.
Helianthus maximiliani.
Helianthus grosse-serratxia
Silphium laciniatum.
CLANS.
Clans are climax communities of limited area or dominance. They usually
occur as secondary areas in societies, but are occasionally found where the
dominance of grasses is too great to permit the appearance of societies. A
clan may consist of a species which is locally important or conspicuous, but
does not occur generally. The most common type is represented by a gre-
garious species which grows in small patches of a few square yards or a few
rods. Another common type is exemplified by subsparse secondary species
which are more or less frequent throughout the association. Some of these
naturally become so sparse that they no longer give any impression of a com-
munity. Clans are perhaps best regarded as conmiunities of the third degree
of dominance, in which the control is necessarily slight as a consequence of
being subordinated to the primary control of the grass dominants and the
secondary control of the subdominants. Near the edges of an association,
societies of adjoining areas enter in reduced abundance and dominance. As
a result, they have the appearance of clans and would pass for such where a
THE SUBCLIMAX PRAIRIE.
131
single locality is studied. Since the fluctuations of societies are of great
importance for indicator studies as well as for climatic correlation, it seems
clear that they should always be treated as such, with the proper statement
as to their reduced significance. It is perhaps even more necessary to main-
tain the distinction between fragmentary consocies or socies, and clans. A
host of minor disturbances may denude a small spot or displace the dominants
sufficiently to start a minute succession. To the unpracticed eye, the com-
munity will appear as a clan, while it is really a stage in succession. Its real
nature is readily disclosed by comparison with other areas where disturbance
is obvious, or by following its development during a few years.
Because of their subordinate importance, the factor relations of clans have
secured Uttle attention. They are clearly controlled by water relations, as is
shown by their topographic position, and their seasonal appearance. They
are also more or less influenced by light as an outcome of their competition
with the subdominants.
Vernal Clans:
Delphinium penardi.
Oxalis violacea.
Oxalis stricts.
Scutellaria parvula.
Astragalus canadensis.
Specularia perfoliata.
Pentatemon cobaea.
Pentstemon albidus.
Onosmodium molle.
Baptisia leucantha.
Erigeron philadelphicua.
Estival Clans:
Asclepias eyri&ca.
Asclepiaa suUivantii.
Asclepias tuberosa.
Asclepias verticillata pumila.
Lactuca pulchella.
Desmodium illinoense.
Schrankia uncinata.
Desmanthus illinoensis.
Lathyrus omatus.
Acerates viridiflora.
Psoralea esculenta.
Potentilla arguta.
Physalis lanceolata.
Physalis virginiana.
Dalea aurea.
Estival Clans — continued.
Evolvulus argenteua.
Gerardia purpurea.
Gerardia a8x>era.
Cacalia tuberosa.
Lythnim alatum.
Lechea minor.
Ruellia ciliosa.
Triosteum perfoliatum.
Serotinal Clans:
Liatris squarrosa.
Hieracium longipilum.
Gentiana pubemla.
Gentiana andrewsii.
Solidago graminifolia.
THE SUBCLIMAX PRAIRIE.
ANDROPOGON ASSOCIES.
Nature. — East of the Stipa-Koeleria association lies a belt of prairie more or
less interrupted by woodland. In general character the two are very similar,
so much so that at first thought it seems impossible to draw a valid distinction
between them. The difficulty arises from the very gradual increase of rainfall
from 30 to 40 inches and the correspondingly broad transition from the one
to the other. In spite of this, the two communities are at least as different as
the other associations of this formation. The climatic difference of 10 inches
of rainfall is reflected in the close sod and the taller growth-form, both more
typically developed than in any other association of the grassland. The
greatest distinction arises from the fact that the dominants are nearly all
different, though their similarity in requirements is attested by the degree to
which they mingle and alternate. Andropogon is typical of the community to
an almost exclusive degree, but the species often mix with Stipa, Agropyrum,
and Koeleria to such an extent as to make the exact relationship of a particular
area difficult to determine. All of these differences are summed up in the
fact that the Andropogon prairie over most of the region is subclimax in charac-
ter, i. e., it will be replaced by scrub, woodland, or forest wherever cultivation,
132 CUMAX FORMATIONS OF WESTERN NORTH AMERICA.
fire, or grazing does not prevent. Here again much of the broad transition
between the two prairies would probably develop into forest where disturbing
processes are not too great, but the Stipa-Koeleria prairie is a climax associa-
tion through practically its entire area. In a few especially favorable locations
and during the wet phase of the climatic cycle, forest may encroach upon it,
but not to an important degree. -Finally, the societies of the subclimax
prairie differ from those of the climax in containing more eastern species and
fewer western. The majority of the societies, however, are the same for both,
and this is likewise true of their luxuriance and complexity (plate 23) .
Range. — ^The Andropogon associes has never been clearly recognized
before, and in consequence it has received little direct attention. The few
studies have been local ones dealing chiefly with succession in dunes or swamps,
and have consequently emphasized the serai stages more than the climax.
The region lies east of the Missouri River for the most part and has been
visited but little in the course of the special survey of the past six years. As
a consequence, its outlines can be traced only in the most general manner.
The area includes southeastern Nebraska, eastern Kansas, northern Missouri,
eastern Iowa, small areas in southeastern Minnesota and southern Wis-
consin, and more considerable areas in Illinois and Indiana. In addition, it
runs into Oklahoma and Texas, but little is known of the extent covered. As
successional fragments, it is found also in Arkansas and Mississippi, but these
are wholly extra-regional. Similar extensions occur throughout the valleys
of the prairies and well into the plains, but here they are subclimax to the less
mesophytic grass associations. A remarkable development of this sort occurs
in the great sandhill region of Nebraska, where Andropogon is again the domi-
nant genus. Here the important dominants are bunch-grass, as demanded
by the more rigorous water conditions, and the climax is the Stipa-Bouteloua
prairie.
The western limit of the subclimax prairie as known at present is fairly well
indicated by the isohyete of 30 inches, as it runs through Minnesota, Iowa,
Nebraska, and Kansas, and northern Oklahoma. It is impossible to draw the
limits in the east, north, or south, not merely because of lack of knowledge,
but also because its occurrence is more and more local in character and suc-
cessional in nature the farther east one goes.
CONSOCIATIONS.
Andropogon furcattjs. Andropogon saccharoides. Panicum virgatum.
Andropogon nutans. Boutelotja racemosa. Spartina cynosuroides.
Andropogon scoparius. Elymus canadensis.
The Andropogons are by all odds the most important dominants of his
association. They give it the distinctive impress everywhere except in
transition areas. Because of its characteristic alternation as a subclimax
with forest on the one hand and true prairie on the other, it often contains
subdominants from the former and dominants from the latter. In the low
prairies and meadows of Nebraska, Iowa, and Minnesota, practically any of
the above may be found intimately mixed with Stipa spartea, Agropyrum
glavcum or Koeleria cristata (Pound and Clements, 1899, 1900 : 345; Thorn-
ber, 1901 : 66, 86; Weaver and Thiel, 1917 : 11). As a consequence, the
CLEMENTS
Subclimax Prairie
A. Association of Andropogon furcalus, nutans, scoparius and Boukiouu raceiiioMi, Peru,
Nebraska.
B. Society of SUphium laciniatum in Andropogon-Agropyrum association, Sjilina, Kansas.
THE SUBCLIMAX PRAIRIE. 133
dominants of the subclimax run the whole gamut of water-content from wet
meadow to true prairie.
Factor relations. — Because of its ability to grow in saturated soil, Spartina
often serves as the last consocies in the wet meadow stage of the hydrosere.
During most of the summer, the soil in which it grows is usually moist rather
than wet, and this, with its tendency to mix with the other dominants, war-
rants putting it in the subclimax for the present. In the regions with more
rainfall, it is properly to be regarded as a wet-meadow dominant. It clearly
has the highest water requirements of all its associates and is apt to be the
most localized, as well as in the purest stands. The water-content of Spartina
ranges from saturation to about 45 per cent, while that of Elymus and Panicum
is from 60 to 30 per cent. The last two are nearly equivalent, though Elymus
will grow in somewhat moister soil. Andropogon furcatus and A. nutans are
the most mesophytic of the four Andropogons, and are nearly equivalent to
Panicum and Elymus. They form a much more perfect sod than these two,
and as a result are more successful in competition and less susceptible to annual
fluctuations. The normal range of water-content for A. furcatus is 50 to 25
per cent. Andropogon nutans is slightly less mesophytic and A. scoparius
still less so, though all three frequently occur together. The water values of
A. saccharides are unknown, but its constant association with A. scoparius
in Kansas, Oklahoma, and Texas indicates an intermediate position between
this and A. furcatus. Bouteloua racemosa has essentially the same water
requirements as A. scoparius, and the two are regularly mixed, not only in the
subclimax, but in rough places throughout the prairies, plains, and desert
plains. For a more detailed account of the ecological factors, the reader is
referred to Thornber (1901 : 32), Weaver (1919), and Pool, Weaver, and
Jean (1919).
Three other species of grasses occur with such abundance or frequence as
to require notice, though none of them can be properly ranked as dominants.
The most important is Poa pratensis, which displaces the native grasses in
many places where grazing, mowing, or other disturbances have given it the
advantage. In sandy soils, and especially in sandhills, Andropogon hallii is
frequently associated with A. scoparius and occasionally with A. furcatus.
Panicum scoparium is abundant throughout the subclimax and also in the
transition to the true prairies, but it can hardly be regarded as a dominant
because of its low stature. In essence, it is a layer society of the first import-
ance, but it is hardly to be treated as an actual society because of its vegeta-
tion-form. Its broad leaves, however, do give it much the value of a sub-
dominant herb.
Sequence. — ^The factor relations of the dominants are confirmed by their
topographic position and serai sequence. Hundreds of locaUties in boldly
rolling prairies will show the fundamental sequence from wet meadow to crest
of ridge. This is (1) Spartina, (2) Elymus, (3) Panicum virgatum, (4) Andro-
pogon furcatus, (5) A. nutans, (6) A. scoparius, (7) Bouteloua racemosa, with
Poa pratensis appearing almost anywhere between Spartina and A. scoparius
as disturbance permits. In sandy meadows of the sandhill region, disturb-
ance often initiates a subsere in which the early grasses are Eriocoma dts-
pidata, Andropogon hallii, and A. scoparius, followed by A. furcatus, Panicum
134 CLIMAX FORMATIONS OF WESTERN NORTH AMERICA.
virgatum, and Elymtis canadensis, with Spartina in the moister areas (cf.
Pool, 1913 : 298). The growth-forms are in almost perfect accord with the
factor and serai sequence. Spartina, which is both hydroid and the earliest
in appearance, has a growth-form usually 5 to 7 feet and sometimes 8 to 10
feet high. Andropogon furcatus and A. niUans are normally 4 to 6 feet and
occasionally 6 to 8 feet tall, while A. saccharoides is a Uttle shorter. Elymus
canadensis and Panicum virgatum are practically the same height, from 3 to
5 feet. Andropogon scoparius is usually about 3 feet in height and Bouteloua
racemosa generally somewhat less. In size and habit, A. scoparius is the
transition form to the true prairies, in which the dominants are between 2 and
3 feet high. This also explains why it is such a constant associate of Stipa
and Koeleria. The root relations are less distinctive, as would be expected.
Andropogon furcatus and Panicum virgatum are the most deeply rooted, A.
nutans and A. scoparius come next, wliile Elymus canadensis resembles Koeleria
and Stipa in having shallow roots (Weaver, 1919).
Grouping. — The dominants which constitute the greater part of the associa-
tion are A. furcatus, A. nutans, and A. scoparius. Mixed or alternating, they
occupy nine-tenths of the area and form the pattern in which the others play
minor parts, except in localized areas. The actual groupings are best shown
by the records of 33 quadrats charted by Thornber (1901 : 95) in the south-
eastern corner of Nebraska, and ranging from wet meadow to hilltops. Of
6 quadrats in the wet meadow, 4 contained Spartina cynosuroides and 5
Poa prcUensis as dominants. The 5 quadrats in the meadow or low prairie
all contained A. furcatus and A. scoparius; 3 contained A. nutans, and 3
showed Elymus and Panicum. With regard to the number of dominants, 2
quadrats showed all five; 1 showed four, and 2 showed three. A. furcatus and
A. scoparius occurred as dominants in every one of the 22 quadrats on the
slopes and crests, Bouieloua racemosa in 4, Koeleria cristata in 2, Pani-
cum scoparium in 2, and P. virgatum in 1. P. scoparium also occurred in
more or less abundance in 17 other quadrats, B. racemosa in 14, Stipa spartea
in 12, and Koeleria cristata in 9, suggesting the transition to the true prairie.
Southward from Kansas into Texas, similar groupings of the dominants occur,
but A. furcatus is partly or largely replaced by A. saccharoides, while A.
haUii plays a r61e of some importance.
SOCIETIES AND CLANS,
These are all but identical with those found in the Stipa-Koeleriapraine and
it is unnecessary to repeat the listson pages 130 and 131. A few additions might
be made, but these are nearly all invaders from woodland and thicket and do not
properly belong in the prairie. Likewise certain societies derived from the
west or southwest, as Gutierrezia sarothrae, Grindelia squarrosa, and Artemisia
frigida, are Uraited to the western edge or are altogether lacking. An excellent
idea of the societies and clans of the subclimax prairie can be gained from
Thornber's treatment (1901). This author gives a detailed account of aspects
and treats the grouping and behavior of the subdominants on pages 54 to 95.
This is followed by an account of the many quadrats in both list and chart
form (pp. 95 to 136), and a phenological record of practically all the species for
1899-1900 (cf. Gates 1912 : 300, 327).
THE MIXED PRAIRIE. 135
THE MIXED PRAIRIE.
STIPA-BOUTELOUA ASSOCIATION.
Nature. — Since the first recognition of a prairie and a plains formation
(Pound and Clements, 1898 : 244; 1900 : 347) it has been assumed that the
one passed into the other through a broad transition region. In the summer of
1914 it was found that Stipa, Agropyrum, and Koeleria did not begin to yield
to the short-grasses in the central Dakotas and Nebraska and then give way
to the plains formation, as had been generally assumed. On the contrary,
the three prairie dominants continued across the plains and into the foothills
of the mountains of Montana, Wyoming, and Colorado (Clements, 1916 : 180).
It was also found that, while Bouteloua, BulMlis, and the two species of Carex
became increasingly abundant, it was as an under-story in the tall-grasses,
especially Stipa or Agropyrum. Moreover, where Bouteloua occurred as a
pm"e consociation, or with Bulbilis, this was discovered to be the usual result
of overgrazing. This has forced the recognition of a mixed association com-
posed of the dominants of both prairies and plains, but essentially prairie in
its tall-grasses, numerous societies, and successional relations (plate 24).
In order to test this assumption fully, the region has been crossed from east
to west during 1915, 1916, and 1917, and in 1918 it was traversed from Col-
orado to North Dakota on the west and from North Dakota to Kansas on the
east. Especial attention was paid to the community relations of the dominants
and the climatic and topographic correlations, particularly where the associa-
tion touched the prairies and the short-grass plains. As a consequence, the
conclusion has become unavoidable that these northwestern prairies represent
a distinct association. They are not a transition community in structure, as
they exhibit seven dominants in various combinations throughout the area.
Nor are they transitional in position, since the short-grass plains he south of
them, while their major western contact is with the sagebrush formation.
They are primarily prairie in character, since the tall-grasses are codominant
throughout, the root systems are relatively deep-seated, and the numerous
societies are identical or similar in floristic and character to those of the true
prairies. The most significant difference is the practically universal presence
of one or more of the short-grasses or sedges as a lower layer.
The constant association of Stipa or Agropyrum with BotUekma or Bulbilis
throughout the community is shown by the following summary: During
1914 the climax grassland was studied in 88 localities east of the Rocky
Mountains, and tall-grasses and short-grasses were associated as dominants
in 83 of these. In 136 local stations the same grouping was found in all but 12.
During 1915, of 76 locahties visited, 73 showed both types. In 1916, of 65
locaUties, 64 showed Stipa or Agropyrum with Bouteloua. or Bulbilis. In 1917
the number was 61 out of 64, and in 1918 tall-grasses and short-grasses were
associated in 97 out of 100 localities. During the six years, without allowing
for duplicate localities, at least one tall-grass and one short-grass were found
together as dominants in all but 15 of the 393 locahties studied.
EfTect of grazing and climatic cycles.— The study of grazed and protected
areas in 1914 disclosed the fact that Stipa and Agropyrum were much more
readily affected by grazing than the short-grasses, and that Stipa in particular
could be completely eUminated by overgrazing. During the succeeding years
136 CLIMAX FORMATIONS OF WESTERN NORTH AMERICA.
a careful search was made for protected areas, especially along railways, in
regions where Stipa or Agropyrum would be expected. The result was the
discovery of one or both in or near practically all pure Boutelmm or Bulbilis
communities found in the Dakotas, Montana, Wyoming, Nebraska, and
Colorado. Similar results were obtained for both dominants over a large
part of the sagebrush association from Oregon to Colorado, and for Stipa
throughout California. Indeed, what was once the climax association of
Stipa over the interior valleys from San Diego to Mount Shasta is now repre-
sented by widely scattered relicts enabled to persist by chance protection.
It was to be expected that such widespread response to grazing would have
been noticed by other observers, and this has proved to be the case. Williams
(1898 : 54, 55) found that Agropyrum, when too closely grazed, made most of
its growth by underground stems, and very few if any fertile culms were
developed. He also observed that Stipa, when kept closely grazed, seldom
seeded in quantity. Wooton (1912 : 58) says that Stipa pennata neomexicana
and S. comata "are relished by stock and are of especial importance because
they appear at a time when most of the other grasses are dead and dry. Appar-
ently they do not reproduce readily and since they are now rarely allowed to
go to seed, they are probably being gradually exterminated wherever stock
can get at them." The Forest Service bulletin on range grasses (1914 : 175)
states that in parts of northern New Mexico Stipa comata is in danger of exter-
mination because it is so closely grazed in spring and early summer that it is
not given a chance to seed. Wooton and Standley (1915 : 66) make the
following statement about these species: "Both are valuable range grasses;
neither, however, reproduces well, but is soon killed by overstocking and
replaced by needle grasses."
The fact that Stipa and Agropyrum are taller and more conspicuous in wet
seasons suggested the possibility that they were greatly reduced or lacking in
dry years. Throughout the association, however, they proved as abundant
and universal in the dry years, 1916 to 1918, as in the exceedingly wet year of
1915. The only evident response to drought was a marked reduction in height
and in the number of flower stalks, a reduction which affected Bouteloua as
much as Stipa, though hardly as much as Agropyrum. This was further con-
firmed by a scrutiny of reports on grassland in the Great Plains from 1889 to
1915 and by field notes from 1897 to 1918. All of these agreed in showing the
constant association of tall-grasses and short-grasses throughout the region,
not only for the wet phases of the three climatic cycles but for the dry periods
as well. Since the latter included two of the severest drouths recorded, it is
certain that the tall-grasses and short-grasses are regularly codominants of
the association, except where grazing interferes. In connection with the
grazing experiments discussed later, permanent protected quadrats have been
established in representative areas of the association for the purpose of secur-
ing an exact record of the effect of grazing and of protection, as well as of the
dry and wet phases of the climatic cycle (plate 24).
Range. — The mixed prairies occur from central North and South Dakota,
central Nebraska, and northwestern Kansas, throughout Montana and Wyo-
ming to the Rocky Mountains, and southward in Colorado along the foothills
of the Front Range. They extend well north into Saskatchewan and Alberta
CLEMENTS
Mixed Prairie
A. Sli/.a comala consociation, Pine Ridge, South Dakota.
B. Agropyrum glaucum consociation, Winner, South Dakota.
C. Detail of association of Slipa comala, Sporobolus cryplandrus, and Bouteloua gracilis, Colorado Sprinirs.
Colorado.
THE MIXED PRAIRIE. 137
and are known to have covered much of northern New Mexico before the
period of intensive overgrazing. On the east, the association is found in more
or less typical form at Medicine Hat in Saskatchewan, Minot and Mandan
in North Dakota, Winner in South Dakota, and Long Pine and McCook in
Nebraska. Along the west, it occurs from near Calgary, Alberta, southward
to Lewiston and Billings, Montana, Douglas and Laramie, Wyoming, and
Colorado Springs and Trinidad, Colorado. Beyond the eastern limit, B&u-
teloua and BuUnlis merely persist as alternes in xerophytic situations in the
midst of the prairie.
CONSOCIATIONS.
SnPA coMATA. Stipa vimdula. Carex fiufoua.
Aqroptrum olaucum. Boitteloua obacius. Carex stenophtlla.
koeleria cri8tata. bulbilis dacttloides.
The distinctive feature of the association is the intimate mixing of the tall-
grasses and short-grasses. This is the direct consequence of their relative
heights, the short-grasses regularly occurring as a layer beneath the tall ones.
The persistence of this relation is explained by the fact that the roots of both
types work at much the same level, and there is little opix)rt unity for one to
get more water than the other. Moreover, while the tall-grasses shade the
others more or less, this is offset by their greater handicap from grazing. The
constant mixture is conclusive testimony to the sufficiency of the rainfall and
to the close equivalence of the two types of dominants. If the water relations
and root penetration were such as Shantz (1911 : 32) has found in the short-
grass plains at Akron, the tall-grasses would soon give way to short-grasses,
especially during the dry phase. This has nowhere been found to be the case,
and the vast area over which they live together not only speaks eloquently
of their associational equivalence under the particular subclimate, but is also
a compelling argument for the unity of the formation.
Grouping. — At the edge of the association, the dominants tend to become
pure and hence to alternate instead of mingling in layers. This is to be
expected in the southwest, where it passes into the short-grass association,
and on the west, where there is a broad transition to the sagebrush formation,
since both of these mark drier climates in which the competition for water is
necessarily keener. Any one of the dominants may appear as a pure con-
sociation over limited areas in such regions. Bouteloua and BtdbiUs show
this tendency chiefly on the southwest, and Stipa, Agropyrum, and Carex
JUifolia on the west. Nearly everj- possible combination of dominants occurs
within the association, but certain ones are the rule. In eastern Wyoming,
in Montana and western North Dakota, the ruling group is Stipa-Agropyrum-
Bauieloua or Siipa-BouteUma. In the moister region south and east of the
Black Hills and through South Dakota to the Missouri River, Agropyrum-
Bulhilis-Stipa-Boutelouo is the tj-pical mixture. The essential basis of this
is formed by Agropyrum and BuWilis, and hence either of the other two may
be lacking. Stipa in particular is much more general than appears to be the
case in summer and autumn after it has been grazed down. Carex filifolia
or C. stenophylla appears commonly in nearly all the groups but usually in
reduced abundance. This is also true of Koeleria in less degree. Other fre-
quent groups are Stipa-Koeleria-Bouteloua, Stipa-Carex-Bouteloua, SHpa-
Bulbilis-Bouteloua, and Agropyrum-BulbiliS'Bouteloua. Combinations of four
138 CLIMAX FORMATIONS OF WESTERN NORIH AMERICA.
or five dominants are often found over large stretches also. The most common
are Stipa-Agropyrum-Bouteloua-Bulhilis and Agropyrum-SHpa-Koeleria-Bou-
teloua-Carex. Stipa viridula, as a sod-former, is the typical dominant of
broad swales and shallow valleys. It is more or less subclimax in habit and
hence is usually associated with Agropyrum.
Sequence of dominants. — ^The factor correlations of the dominants have
received little attention. For the present it must suffice to infer them from
the topographic and successional relations, and to check this by reference to
the behavior of the tall-grasses in the prairie and the short-grasses on the
plains. This establishes a fairly definite and practical sequence, though it
is impossible to assign accurate values to the correlations with water-content,
evaporation, and light. In addition to succession and topography, range,
growth-form, and subclimax dominants, such as Andropogon, Calamovilfa,
and BoiUelaua racemosa, are all in agreement in indicating that Stipa viridula
and Agropyrum are the most mesophytic and Bouteloua the most xerophytic.
The actual sequence is (1) Stipa viridula, (2) Agropyrum, (3) Koeleria, (4)
Stipa comaia, (5) BuUnlis, (6) Carex stenophylla, (7) C. filifolia, and (8) Bou-
telona gracilis. While the rainfall is 5 to 10 inches less and the evaporation
rate correspondingly greater than in the prairies, the water-content is but
little lower, owing chiefly to the lessened transpiration resulting from a
smaller population and a shorter season. This appears to be confirmed by the
deep roots, even of the short-grasses, indicating a fairly adequate water-
supply. It is the similarity of the root behavior which explains the close
equivalence of the seven dominants, as shown by the fact that four or more
frequently occur in the most intimate mixture and that practically every one
has been found with each of the others. This also explains why pure consoci-
ations are rare (plate 25).
While the existence of the Stipa-BouUloua association has not been recog-
nized before, it is now clear that the bunch-grass formation and the grass
formation of high prairies and plains of Pound and Clements (1898; 1900:
354, 380-386) are essentially this association. Even at that time the close
similarity with the true prairies was clearly recognized, as the following shows:
"The foothill grass formation has much in common with the prairie forma-
tion of region II. As one looks at the high rolling prairies in region IV cov-
ered with Stipa comata, from a distance the carpet of Stipa, variegated with
the profusely flowering astragali, lupines, and psoraleas which abound in it,
appears to be a piece out of the famiUar prairie of the eastern portion of the
State."
This similarity is further emphasized by the fact that the societies are
largely the same, as shown by the following list.
SOCIETIES OF THE MIXED PRAIRIE.
By far the major number of subdominants is the same for the Stipa-Koeleria
and the Stipa-BouteUma associations. This would be expected from the
dominance of tall-grasses in both, indicating a deep penetration of water and
roots and hence a favorable soil for deep-rooted herbs. The mixed prairies
naturally lack such societies as Phlox pilosa, Baptisia leucophaea, Anemone
canadensis, etc., which are typically eastern, and they have added a few from
the west. The chief difference lies in the fact that the societies are less lux-
CLEMENTS
Mixed Prairie
A. Agropyrum glaucum-Bouleloua gracilis association, Vermejo Park, New Mexico.
B. Detail of Agropyrum-BuUrilis association, Winner, South Dakota.
C. Polygala alba society in Bouteloua consociation, Interior, South Dakota.
THE SHORT-GRASS PLAINS.
139
uriant and less mixed, and the growth-form is smaller as a rule. It is also
significant that most of the societies are found in the eastern half with a rain-
fall above rather than below 15 inches. In the western portion the societies
are better developed in the valleys and along the lower slopes, and are much
reduced in number and dominance on the upland.
Prevemal Societies.
Carcx pennsylvanica.
Antennaria dioeca.
Anemone patens.
Leucocrinum montanum.
Androsace occidentalis.
Draba oaroliniana.
Vernal Societies.
Astragalus crassicarpus.
Aragalus lamberti.
Erysimum asperum.
Fragaria virginiana.
Viola pedatifida.
Comandra lunbellata.
Vicia americana.
Anemone cylindrica.
Sieversia ciliata.
Achillea millefolium.
Hosackia americana.
Sophora sericea.
Senecio aureus.
Sisyrinchium augustifolium.
Lithospermum linearifolium.
Castilleia sessiliflora.
Astragalus drummondii.
Krynitzkia virgata.
Agoseris cuspidata.
Estival Societies:
Psoralea tenuiflora.
Petalostemon candidus.
Petalostemon purpureus.
Amorpha canescens.
Psoralea argophylla.
Brauneria pallida.
Glycyrhiza lepidota.
Lepachys coltimnaris.
Erigeron ramosus.
Tradescantia virginiana,,
Polygala alba.
. Lupinus ornatua.
Astragalus bisulcatus.
Astragalus adsiugens.
Estival Societies — continued.
Delphinium menzieaii.
Yucca glauca.
Helianthus rigidus.
Monarda citriodora.
Malvaatrum coccineum.
Erigeron pumilus.
Rosa arkansana.
Hymenopappus tenuifolius.
Opuntia mesacantha.
Opuntia polyacantha.
Dalea laxiflora.
Meriolix serrulata.
Linum rigidum.
Phlox dougla-sii.
Pentstemon grandiflorus.
Pentstemon gracilis.
Aster ericoides.
Gaura coccinea.
Astragalus moUissimus.
Gilia pungens.
Gilia aggregata.
Verbena stricta.
Verbena hastata.
Lygodesmia juncea.
Hedeoma drummondii.
Steironema ciliatum.
Castilleia Integra.
Rudbeckia hirta.
Haplopappus spinulosus.
Psoralea cuspidata.
Balsamorhiza sagittata.
Serotinal Clans:
Solidago rigida.
Solidago missouriensis.
Aster multiflorus.
Artemisia frigida.
Artemisia cana.
Grindelia squarrosa.
Gutierrezia sarothrae.
Senecio douglasii.
Artemisia filifolia.
Serotinal Societies — continued.
Liatris punctata.
Chrysopsis villosa.
Carduus undulatus.
Artemisia dracunculoides.
Artemisia gnaphalodes.
Artemisia canadensis.
Kuhnia glutinosa.
Eriogonum annuum.
Thelesperma gracile.
Thelesperma trifidum.
Eriogonum microthecum.
Eriogonum alatum.
Solidago speciosa.
Liatris scariosa.
Liatris pycnostachya.
Gymnolomia multiflora.
Vernal Clans:
Delphinium penardi.
Pentstemon albidus
Specularia perfoliata.
Oxalis stricta.
Oxalis violacea.
Viola nuttallii.
Estival Clans:
Asclepias speciosa.
Asclepias verticillata pumila.
Lactuca pulchella.
Lathyrus ornatus.
Psoralea esculenta.
Potentilla pennsylvanica.
Evolvulus argenteus.
Dalea aurea.
Cactus viviparus.
Acerates viridi flora.
Allionia linearis.
Gerardia aspera.
Verbena bipinnatiflda.
Serotinal Clans:
Solidago graminifolia.
Liatris squarrosa.
THE SHORT-GRASS PLAINS.
BULBILIS-BOUTELOUA ASSOCIATION.
Nature. — The short-grass plains owe their distinctive impress to grama and
buffalo-grass. These are sod-formers with dense root systems. As Shantz has
shown at Akron (1911 : 33), the water below 12 inches is non-available for
much of the growing season, with the result that the roots are usually con-
fined to the first foot of soil.^ A further consequence is that the short-grasses
mature in July. Thus, the soil beneath a short-grass cover is often without
available water below 18 inches, and the water-content in the upper foot is
low after mid-summer. As a consequence, the deeper-rooted tall-grasses and
subdominant herbs are practically excluded and the typical short-grass cover
is very uniform and monotonous as a result.
'Cf, Weaver, 1919, 1920.
140 CLIMAX FORMATIONS OF WESTERN NORTH AMERICA.
Shants (1. c, 62) has traced the succession in sandhills and in secondary
areas, and finds that the depth of water penetration is the decisive factor
In sandy soils, the deep-rooted Andropogons are dominant and with them
occur many deep-rooted perennial herbs, such as Psoralea tenuiflora, Arte-
misia filifolia, and Ipomoea leptophylla. With the entrance of Aristida pur-
purea and the Boutelouas, the water is used chiefly in the 1 to 2 foot layer,
and the deeper species gradually die. out. As the Bouteloua sod becomes
denser, Aristida and its associates disappear, and the short-grass climax is
established. When the cover is destroyed by cultivation or overgrazing, the
water penetrates more deeply, permitting the entrance of Aristida, Gutier-
rezia, Grindelia, Artemisia frigida, and other deeper-rooted species. With
the return of the gramas, the depth of penetration decreases and the invaders
are displaced. Shantz (1917 : 19) has lately shown that the secondary suc-
cession in abandoned roads is due to the same cause, though Bulhilis largely
takes the place of Bouteloua in effecting the return to the climax (plate 26).
Range. — The short-grass association ranges from southwestern Nebraska
and the western half of Kansas through eastern Colorado into northwestern
Texas, northern New Mexico, and Arizona. It is also developed to some
extent in southeastern Utah and southwestern Colorado. The chief dominant
throughout is Bouteloua gracilis. In the eastern part its usual associate is
Bidbilis dadyloides; in the western part it is Muhlenhergia gradllima or
Hilaria jamesii. In sandhill and foothill areas, it is often associated with
Bouteloua hirsuia. The chief contacts of the short-grass plains are with the
other associations of the grassland formation. On the north, in Colorado and
Nebraska, they meet the mixed prairies, in Kansas the subclimax prairie,
and in west-central Texas, central New Mexico, and Arizona the desert
plains. On the west this community comes in contact with the sagebrush
association of the Great Basin, while throughout the Southwest generally
it is frequent in park-like savannahs of pine and pinon-cedar.
As already indicated, nearly pure communities of Bouteloua gracilis occur
well outside the area outlined above. All of these appear to have resulted
from the elimination of the tall-grasses by overgrazing. It is an open question
what part grazing has played in the short-grass association proper. There is
considerable evidence to show that Stipa and Agropyrum were more abundant
formerly, but whether they were sufficiently so to rank as codominants is
uncertain. It is possible that a detailed survey of the short-grass region will
settle this point, but it is more probable that an adequate idea of the original
vegetation will be obtained only from the fenced quadrats established in con-
nection with the grazing investigations. At any event, it is practically certain
that grazing, especially in connection with the former annual movement of
cattle from the south to the north, has played an effective part in maintain-
ing the characteristic short-grass cover.
CONSOCIATIONS.
Bouteloua gracilis. Muhlenberqia qraciluma.
bulbius dacttloioes. hilaria jamesii.
Bouteloua hibsuta.
BouieUma gracilis is regarded as the chief consociation. It is almost uni-
versally present throughout the association, though it varies considerably
in abundance. It not only occurs mixed with each of the others and some-
CLEMENTS
Short-grass Plains
PLATE 26
^
.^^^P^4* fllMJJUl^WWCr. .AJ^A
A. Bouleloua-Bulbilis association, with subchmax of Andropogon scoparius avuX Bouleloua
racemosa on butte, Stratford, Texas.
B. Dense sod of Bulbilis and Bouleloua, Goodwell, Oklahoma.
C. Open sod of Bouleloua, Dumas, Texas.
THE SHORT-GRASS PLAINS. 141
times with two of them, but also as a pure dominant over large areas. Btd-
hilis stands next to Bouiehua in importance, and the two, singly or together,
constitute the fundament of the association. Bidbilis is largely restricted to
the eastern part of the area, while Muhlenbergia and Hilaria are found chiefly
in the western. This results in a differentiation into two halves, an eastern,
consisting almost wholly of Bauteloua and BttUnlis, &nd a western, made up of
BouUloua with Muhlenbergia or Hilaria. The former is typical of western
Kansas and Oklahoma and the Panhandle of Texas; the latter is found in
southern Colorado and the northern half of New Mexico and Arizona.
Any one of the five dominants may appear as a pure community, but this
is rare for Muhlenbergia and infrequent for Bouteloua hirsuta. Hilaria often
dominates extensive areas in New Mexico and Arizona, and in the Great
Basin where the sagebrush and short-grass are in contact. In the latter,
especially, it is more or less subclimax in nature and mixes with Bouteloua
gracilis as the climax is approached. Bouteloua hirsuia is characteristic of
sandy areas and rough gravel or hmestone hills, and is most abundant in
sandhills. While it is an important dominant in the desert plains association,
it is secondary on the plains proper, and is often to be regarded as subclimax.
Muhlenbergia is a fairly constant associate of Bouteloua gracilis in Colorado,
New Mexico, and Arizona. It has been found in pure stands of considerable
extent only in the latter. It bears much the same relation to Bouteloua that
BvXbilis does, and hence rarely occurs with the latter.
The southern Great Plains are characterized by Bouteloua gracilis and
Bidbilis dactyloides in varying relations. As a rule they are associated, but
either may occur as a pure dominant. They may meet on nearly equal terms
or may exhibit varying degrees of relative abundance. In the eastern portion
of the association Bulbilis is usually controlling and Bouteloua secondary,
though this relation is often reversed on the Staked Plains of Texas and New
Mexico. From Colorado southward, Bouteloua is generally controlling and
Bulbilis secondary. Where Bulbilis is predominant the sod is dense and the
grama grass is scattered through it more or less abundantly. Grama typically
forms an open sod, even where it is dominant, but the persistent sod habit
of the buffalo-grass causes the latter to appear in compact mats a few feet
to several yards or more in diameter. The open grama turf dotted with mats
of Bulbilis is so characteristic over much of the Great Plains that it was sup-
posed to be the rule. In the smnmer of 1918, however, buffalo-grass was
found to be either controlling, and sometimes pure, or to meet grama on
equal terms throughout southwestern Kansas and western Oklahoma. This
is in accordance with the water relations, as discussed below.
Grouping of dominants. — The groupings of short-grasses are relatively few
and simple. Bouteloua graciUa is normally present in all of them and usually
as the predominant species. Most of the groups consist of two dominants
only, for example, BouteUma-BuMlis, BuMlis-Bouteloua, BmUel&ua-Hilaria,
BouieUma-Muhlenbergia, and Bouteloua gracilis-B. hirsuta. Bouteloua gracilis
also occurs with B. hirsuta and Muhlenbergia, and with Hilaria and Muhlen-
bergia. On the plains of Oklahoma and Texas, Bouteloua racemosa is a fre-
quent associate of BuJbilis-Bouteloua and sometimes appears to be a codomi-
nant. North and northeast of the associational area Bouteloua and Bulbilis
become constituents of the mixed prairie, forming a layer beneath Stipa and
142 CLIMAX FORMATIONS OF WESTERN NORTH AMERICA.
Agropyrum. In central Kansas they play a similar part, but usually occur
with Andropogon. Toward the southern limits of the area, Bulhilis mixes with
Hilaria cenchroides, H. muiici, and Aristida purpurea in Texas, and Bouteloua
gracilis with B. eriopoda and A. purpurea in New Mexico and Arizona.
When Bouteloua and Bulhilis meet the tall-grasses, both or either may
become dominant as a result of overgrazing. There is increasing if not con-
clusive proof that overgrazing is the cause of the pure areas of short-grass
found in the mixed prairie from Saskatchewan to Kansas, and sometimes
covering many square miles. The study of this problem has also led to the
plausible assumption that the widespread but erroneous belief in the dis-
appearance of the buffalo-grass ia likewise due to the changed conditions
following settlement. The disappearance of the enormous herds of buffalo
gave the tall-grasses a chance to reappear and to conceal the short-grasses
beneath them. At least, it is undeniable that buffalo-grass and grama still
grow abundantly in many places where they were said to have disappeared
in the late sixties and early seventies. This also explains the frequent state-
ment that the bluestems and other tall-grasses entered the Middle West, or
at least became much more abundant, after settlement began. A detailed
discussion of this point may be found in Chapter VI.
Factor relations. — ^While the factor relations of the dominants have received
almost no attention quantitatively, the habitat of the association has been
studied by both Shantz and Weaver. The former (1911 : 32; 1906 : 28)
found the average chresard from June 7 to September 27 at a depth of 0 to 6
inches to be 4.8 per cent, at 6 to 12 inches 2.7 per cent, at 12 to 18 inches
1.25 per cent, at 18 to 24 inches 0.56 per cent, and at 24 to 30 inches 0.23 per
cent. He also dealt with the distribution of the rainfall, and the relation of
runoff, penetration, and evaporation to water-content. Weaver (1919) has
measured the water relations on the plains at Colorado Springs, but it is
probable that this area belongs to the mixed prairie rather than to the short-
grass community. Briggs and Belz (1911) have made a thorough digest of
rainfall and evaporation records for the West, which has much significance for
the climatic relations of these contiguous associations. A study of their figures
makes it clear why grassland goes little beyond the isohyete of 20 inches at
the Canadian boundary, but extends to that of 25 inches in central Texas
(fig. 3). The change from mixed prairie to short-grass plains, moreover, is
in accord with the evaporation values for the respective regions. Over the
northern Great Plains, these values are 30 to 39 inches, and over the southern
they are 52 to 62 inches.
Sequence of dominants. — The evidence drawn from both the habitat and
from succession indicates that Bouteloua is the most and Bulhilis the least
xerophytic of the dominants. This agrees essentially with their general dis-
tribution, in that Bulhilis becomes more controlling to the east with increasing
rainfall, or to the north with decreasing evaporation. As already noted,
Bouteloua forms the matrix over most of the south-central Great Plains, and
Bulhilis makes dense mats in depressions of all sorts, abandoned roadways,
dry pools, playas, etc. The topographic evidence is fully confirmed by the
successional, as Shantz has shown in the case of old roadways (1917 : 19),
and is especially well exhibited in the playa subsere. While the playa is a
CLEMENTS
Short-grass Plains
A. Muhlenhcrgia gracillima and lioxddoua gracilis, Manitou, Colorado.
B. Detail of Bouteloua gracilis, Vermejo Park, New Mexico.
C. Hilaria jamesii on a saline plain, Delta, Colorado.
THE SHORT-GRASS PLAINS. 143
pond, it is bordered by a zone of hydroid ruderals and subruderals, followed
by a broad band of pure buffalo-grass, the whole ^t in a matrix of grama. In
the fall or in years of drought the pond dries to a bed of mud or moist soil,
over which the ruderals extend, followed by the slower invasion of BuUnlis.
When drought, cultivation, or drainage leads to the final drying-up of the
playa, the buffalo-grass sooner or later takes entire possession. It is invaded
at the same time by grama along the upper edge, but the ordinary drainage
into the depression keeps the center more or less permanently in the BuUnlis
stage.
The other dominants are also subclimax to Bouteloua gracilis, and hence,
in an arid climate, are somewhat more mesophytic. The equivalence of
Muhlenbergia is very close to that of BouteUma gracilis, while that of B. hirsuta
is less so. Even in the latter instance, the difference in requirements must be
regarded as slight, since the two are often associated. As in all such cases,
however, it must be borne in mind that the mixing is due rather to the ability
of B. gracilis to invade slightly better conditions than that of B. hirsuta to
enter slightly poorer ones. While Hilaria jamesii is clearly subclimax, its
factor relations are somewhat obscured by its more or less halophytic nature
(plate 27).
SOCIETIES.
The density of the sod and the effect of the superficial roots upon water
penetration explain the relatively small number of societies and the general
lack of conspicuous or distinctive character. These factors naturally owe their
effectiveness to the low rainfall, the average over much of the area being from
10 to 15 inches, and to the high evaporation. As a consequence, while many
of the subdominants of the other associations occur in the short-grass plains,
they attain a relatively feeble expression, and then only where the dominants
have been more or less disturbed. It is not at all infrequent to find a Bou-
teloua plain stretching in all directions without a single conspicuous society to
relieve the monotony. Wherever the soil becomes somewhat sandy or the
rainfall greater, the water penetration increases correspondingly, and societies
become more prominent. As a consequence, the actual number of subdomi-
nants throughout the association is much greater than their diminished
importance or extent would indicate. There are fewer mixed societies, and
both the growth-form and abundance of particular subdominants are reduced.
Prevemal Socid,iet: Eatival Societies: Estival Societies — continued.
Leucocrinum montanum. Psoralea tenuiflora. Astragalus bisulcatus.
Anemone patens. Petalostenion candidua. Ipomoea leptophylla.
Townsendia exscapa. Petalostemon purpureus. Gaura coccinea.
Vemcd Societies: Lepachys columnaris. Erigeron pumilus.
Senecio aureus. Malvastrum coccineum. Linum rigidum.
Astrasalus drummondii. Opuntia polyacantha. Dalea laxiflora.
Anmalus lamberti. Opuntia mesacantha. Meriolix semilata.
Euphorbia robusta. t „^:^.,^ „,„„«♦„,.= Artemisia canadensis.
o L . Lupinus argenteus. * x- n • u j
Sopbora sencca. q,, , ., Actmella nchardsonu.
Pentstemon unilateralis. 1 helesperma gracUe. Haplopappus spinulosus.
Pentstemon coeruleus. Carduus plattensis. Hedeoma drummondu.
Arenaria fendleri. Helianthus pumUus. Lepachys tageies.
Erysimum asperum. Chrysopsis villosa. Gymnolomia multiflora.
Lithospcrmum linearifolium. Polygala alba. Aster bigelovii.
Krynitzkia virgata. Zinnia grandiflora. Aster tanacetifolia.
144 CLIMAX FORMATIONS OF WESTERN NORTH AMERICA.
Fretmmid Clana: Eatital Clans:
Art«mW* frickla. • Cympoterus acaulis. Lathyrus ornatus.
Outierreiia SMothne. Phellopterua montanus. Aater ericoides
ftiMdo dousUiU. Vernal Clan,: Asclepias v. puimla.
Orinddia «,uam>8a. EriReron flagellaris. Cactus viviparua.
CarduUS UndulatUS. Lanmila t^Tuna v^u vivipaiuo.
Am^u«a dracunculoidcs. irnnarfaToeca. ^t""'"« "««'^^"''-
8ohd««o misaouriensis. EriReron canus. ^alea aurea.
Uatna punctata. Pentatemon jameaii. PotenUlla pennaylvamca.
Aat«r multiflorua. Phyaalia'lobata. Allionia linearis.
Kuhnia glutinoaa. Allium cernuum. Serolinal Clan:
Vernonia baldwinii. Aatragalua lotiflorua. Eriogonum jamesii.
THE DESERT PLAINS.
ARISTIDA-BOUTEIX)UA ASSOCIATION.
Nature. — The grassland of the Southwest derives its character primarily
from Aristida and BouteUma. In general appearance it closely resembles the
short-grass plains, but the grasses are taller, more numerous, and the group-
ings more varied. The sod-forming habit is much less developed. It is absent
in Aristida and in Bouteloua rothrockii. While it is more or less evident in
Bouteloua eriopoda, B. hirsuta, and B. bromoides, the sod has no continuity, but
is broken into many small mats. Although this condition obtains in some
parts of the short-grass plains, the sod is much more complete as a rule. No
single species of this association possesses the importance shown by Bouteloua
gracilis in the short-grass region . Probably Bouteloua eriopoda is to be regarded
as the most dominant species of this genus, and A. purpurea, in its several
forms, of Aristida.
The close relationship between the two associations is shown by the long
contact from Texas through New Mexico and Arizona and by their similar
appearance. They are also alike in their successional relation to such sub-
climax dominants as Andropogon scoparius, A. saccharoides, and Bouteloua
racemosa. Their chief relationship, however, lies in the fact that certain
dominants occur in both, although usually with different values. These are
Bouteloua gracilis, B. hirsuta, Aristida purpurea, and Bulhilis dactyloides.
B. gracilis may be more or less subclimax in nature and restricted to mountain
valleys or it may be intimately mixed with B. eriopoda, hirsuta or racemosa.
B. hirsuta is one of the important dominants, usually with B. bromoides or
Hilaria cenchroides on foothills and on mountain slopes. Bulhilis usually
occurs only in small scattered patches, except in Texas, where it meets Hilaria
cenchroides, Bouteloua eriopoda, or Aristida purpurea on more or less equal
terms. Aristida purpurea changes from subclimax to a climax dominant,
especially important in Texas and New Mexico. The similarity as to societies
and clans is less than that between the prairies and plains, but this is due
chiefly to the proximity to the original center of the flora. However, as the
lists show, there is much agreement as to the genera concerned (plate 28).
The desert plains are in close contact with but one other association of the
grassland formation, namely, the short-grass plains. It is probable that there
was formerly a second contact, with the Stipa bunch-grass prairie of California,
but to-day there is a wide gap between, bridged to a certain extent by Hilaria
jamesii H. rigida and Boutelona gracilis. The contact mentioned is from
Snyder and Big Springs in the Staked Plains of Texas to Roswell and Socorro
CLEMENTS
Desert Plains
PLATE 28
h^b&y-i
A. lioutcloua-Ililaria association, Empire \alk'y. Arizona.
B. Bouteloua rothrockii and Arislida divaricata, Santa Rita Reserve, Tucson, Arizona.
C. BouUlotta racemom consociation, Oracle, Arizona.
THE DESERT PLAINS. 145
in New Mexico and to Prescott in Arizona. It was perhaps much broader
at one time, as Bouteloua eriopoda still occurs in some abundance about
Albuquerque and from Adamana to Winslow in Arizona.
Range. — ^The desert plains association extends from Snyder and Sweetwater
in Texas on the northeast through the southern two-fifths of New Mexico
into southeastern and south-central Arizona. In Texas and New Mexico, it
is the typical community of the regions indicated, with saUne associes in the
lower valleys and the mesquite along the benches and upper levels. From
southwestern New Mexico through southern Arizona, it occupies a broad
belt several to many miles wide around the major mountain chains, and
covers the broad intermountain plateaus. Its general range in altitude is
from 3,400 to 5,500 feet.
The association sweeps southward through Chihuahua, Sonora, and
Durango into the high tablelands of central Mexico. It has received no
ecological study beyond a few miles south of the boundary, and its nature and
extent in Mexico must be inferred from floristic and grazing sources. The
inference seems clear that Mexico is the real center of the desert plains grass-
land and that it is richer in dominants and more varied in structure there than
in the United States. This is confirmed by the fact that the best expression
of the community is found in southern Arizona near the border. The extent
of this grassland in Mexico is probably much greater than in this country,
but nothing definite is known about it.
The name "desert plains" is thought to indicate the nature and location
of the association. As to the kind of grassland and topography, "plains" is
clearly the best term to be applied. This conclusion is emphasized by the
relationship with the short-grass plains. In addition, this is not only the
characteristic grassland of the desert region of the Southwest, but it is also
in direct contact with the desert all along its lower edge. A further reason is
found in the fact that there exists a broad transition region between the
scrub desert and the Aristida-Bouteloua grassland. Indeed, Larrea or Proso-
pis is scattered over so much of the latter that it has often been regarded as
mesquite rather than grassland. Finally, relict patches of Bouteloua roth-
rockii, Aristida divaricata, or Muhlenhergia porteri have been found in various
protected places iu the desert, at altitudes as low as 2,400 feet, especially at
Tucson. These indicate that the desert grassland once extended well down
into the scrub desert, and that it was replaced by scrub as a consequence of
overgrazing. The significance of these relict areas is confirmed in some degree
by the statements of stockmen to the efifect that the desert was formerly well-
grassed.
CONSOCIATIONS.
Bouteloua eriopoda. Bouteloua gracius. Aristida caufornica.
Bouteloua rothrockii. Bouteloua racemosa. Aristida arizonica.
Bouteloua bromoides. Aristida divaricata. Hilaria cenchroides.
Bouteloua hirsuta. Aristida purpurea. Muhlenbergia porteri.
All of these may form pure consociations, but Bouteloua eriopoda and
Aristida purpurea are the only ones known to do so for long stretches. Both
are dominant over the northern and lower areas, particularly in New Mexico
and Texas. In these they mix somewhat, but as a rule either one is much more
important than the other wherever they occur together. The others rarely
146 CLIMAX FORMATIONS OF WESTERN NORTH AMERICA.
form pure communities more than a few acres or at least a few miles in extent.
Bouteloua rothrochii might be regarded as an exception to this, for while usually
mixed with Aristida, it covers areas of several to many miles as a practically
pure dominant. The most frequent groupings are those in which Bouteloua
and Aristida occur together, probably because grazing favors the latter at the,
expense of the former.
^Rank of dominants — The general rarik of the dominants and some of their
subclimax associates is indicated by the following table of occurrences in
trans-Pecos Texas, southern New Mexico, and Arizona:
Bouteloua eriopoda 56
Bouteloua gracilis 40
Bouteloua racemosa 35
Bouteloua hirsuta 23
Bouteloua rothrockii 16
Bouteloua bromoides 8
Aristida divaricata 28
Aristida purpurea 20
Aristida californica 4
Aristida arizonica 2
Hilaria cenchroides 10
Mublenbergia porteri 9
Hilaria mutica 33
Scleropogon brevif olius 23
Andropogon saccharoides ... 16
Sporobolus flexuosus 11
The abundance of a dominant is not necessarily in accord with its frequence.
As a result, Bouteloua racemosa is less important than its occurrence indicates,
while B. rothrockii, B. bromoides, and Aristida californica are much more
frequent. It is these species, moreover, which appear to be among the most
characteristic of the grasslands of northern Mexico. The last four dominants
of the list are all really subclimax, with the probable exception of Sporobolus
flexuosus. This is particularly true of Hilaria and Scleropogon, which are
typical of "swags" and other valley-hke depressions throughout the Larrea-
FUmrensia scrub. Both occur so frequently with Bouteloua, and especially
B. eriopoda and B. hirsuta, that they can not be ignored in a treatment of the
desert plains. This HilarichScleropogon subclimax covers thousands of square
miles from the Pecos River to central Arizona.
Grouping of dominants. — ^While all the dominants range more or less
throughout the association, with the exception of Bouteloua rothrockii and
Aristida californica, they vary greatly in importance and grouping in the three
States. This depends upon the altitude and the distance from the center in
Mexico. In Texas Aristida purpurea, in various forms, is the chief dominant
at the lower levels; toward its northern limit it is much mixed with Bulbilis
and Bouteloua gracilis as a lower layer. Hilaria cenchroides, B. eriopoda, A.
divaricata, and Muhlenbergia porteri occur more or less frequently with it.
In the mountain ranges of western Texas, from the Davis and Guadalupe
Mountains to the Sierra Blanca, Bouteloua gracilis, B. eriopoda, and B.
ra,cemosa are the climax dominants, with which Aristida and Muhlenbergia
occur more or less abundantly. Between these ranges lie extensive bolsons
or bolson-like valleys, characterized in the center by Hilaria-Scleropogon
swags in a more or less open scrub desert. The grama grasses extend far down
the gradual slopes of the bolson, and mix with the subclimax grasses over a
wide zone (plate 29).
The chief dominant in New Mexico is Bouteloua eriopoda, often much mixed
with Aristida purpurea, as in the valley of the Pecos. They occur abundantly
on the marl hills north of Albuquerque with B. gracilis and Muhlenbergia
graciUima, and to a smaller degree in northern Arizona. All of the evidence
available indicates that this is the northern edge of the ecotone and that the
CLEMENTS
Desert Plains
A. Bouteloua-Arulida association, Sweetwater, Texas.
B. Boulehua gracilis, Sckropogon brerifolius, and Hilaria mulica valley, B. erinpoda,
gracilis, racenwsa hills, Van Horn, Texas.
C. Bouieloua gracilis, hirsula, eriopoda, and Arislida divaricala, Jornada Reserve, Las
Cruces, New Mexico.
THE DESERT PLAINS. 147
region generally belongs to the short-grass association. The desert plains of
southern and southwestern New Mexico are characterized by Hilaria and
Scleropogon in the subclimax stage, and Bouteloua eriopoda in the climax. In
the Jornada del Muerto the latter is usually associated with SporoholiLS
flexuosus, and with *S. cryptandrus where the soil is somewhat more sandy.
B. racemosa is not infrequent, but it is rarely dominant at this level. On the
slopes of the Organ and San Andreas Mountains at 5,000 to 6,000 feet, the
dominants are Bouteloua hirsuta, B. gracilis, and B. racemosa, with consider-
able Aristida divaricata and little B. eriopoda.
All of the 12 dominants occur abundantly between elevations of 3,500 to
5,500 feet in southern Arizona, and as a consequence the grouping is more
varied and complex than in any other part of the association. Since all the
dominants are present in northern and central Mexico as well, it is practically
certain that the same groupings will be found there. The lowermost com-
munity is typically Bouteloua rothrockii and Aristida divaricata, often with
some A. purpurea and Muhlenhergia porteri. Aristida calif ornica or A.
arizonica may occur as a dominant with either B. rothrockii or B. eriopoda
alone or together. Bouteloua eriopoda and Aristida divaricata are frequently
associated also. Bouteloua bromoides tends to become controlling at 4,000
feet and is often the major dominant for the next 1,000 feet, where its usual
associates are B. racemosa and A. divaricata, with more or less B. hirsuta and
B. eriopoda. This is the typical condition on the upper levels of the Santa
Rita Range Reserve near Tucson. Hilaria cenchroides, Bouteloua hirsuta,
and B. gracilis become abundant at about 4,500 feet and with B. bromoides,
B. racemosa, and more or less Aristida divaricata, constitute the grassland
until it gives way to the Andropogon community of the oak savannah at
5,500 to 6,000 feet. Altogether, nore than 30 different groupings of the
dominants have been found in Arizona; 9 of these consist of two dominants,
12 of three, 8 of four, and 7 of five. These varying combinations furnish
invaluable material for the determination of equivalences.
Sequence of dominants.— No study has yet been made of the habitat rela-
tions of the desert plains grassland, and these must be inferred from the
groupings and the topographic position, as well as the behavior under dis-
turbance. No definite sequence can be suggested without factor measure-
ments for such a large number of closely equivalent dominants, but certain
general relations will serve as a helpful basis for future work. These have to
do with altitude, topography, range, grazing, and succession. The chief
dominants of lower altitudes are naturally those of the greater range northward
in the association. These are Aristida purpurea, Bouteloua eriopoda, A.
divaricata, and B. rothrockii. The most xerophytic of these is B. eriopoda,
which finds its best development in southern New Mexico in a rainfall of 10
to 15 inches, and the least xerophytic, A. purpurea, with a rainfall of 15 to 20
inches in western Texas. At higher altitudes, B. hirsuta, B. bromoides, Hilaria
cenchroides, B. racemosa, and B. gracilis are the dominant species. The first
three mix intimately and probably are to be regarded as the most nearly
equivalent of the many dominants. B. hirsuta is the only one of the three
which ranges far to the northward, where it is a regular associate of B. gracilis
in sandy soils. In the Empire Valley, and probably in the heart of the asso-
148 CLIMAX FORMATIONS OF WESTERN NORTH AMERICA.
ciatioD generally, it is intermediate in requirements between B. gracilis and
B. racemosa, which occupy valleys and north slopes, and B. bromoides and
Hilaria which take upper slopes and tables. It mixes with the former in the
valleys and runs up the slopes to mingle with the latter on equal terms. From
a number of similar transects the sequence as to water relation seems to be
(1) B. racemosa, (2) B. gracilis, (3) B. hirsiUa, (4) B. bromoides, (5) Hilaria
cenchroides. This corresponds well with the successional sequence, so far as
known, and also with the climatic relations.
In the secondary succession due to disturbance, and especially to grazing,
it is apparent that the Aristidas are subcUmax to the Boutelouas as a general
rule. Overgrazing and trampUng tend to destroy the more xerophytic species,
such as B. rothrockii and B, eriopoda, and to permit the entrance of Aristida,
especially A. divaricata. Bouteloua rothrockii and Muhlenbergia porteri are
particularly susceptible to grazing injury and have consequently disappeared
over large areas. Muhlenbergia, in fact, is rarely found at present, except in
the protection of a catclaw or mesquite clump. A similar tendency for
Aristida to replace Bouteloua occurs at the higher altitudes also, but is much
less marked. One would expect disturbance to bring about the replacement
of B. gracilis and B. hirsuta by A. purpurea, as is the case in the short-grass
plains, but no important areas of this sort have been seen. A. divaricata
sometimes plays this role, but much less frequently than at lower levels.
SOCIETIES.
The desert plains have two groupings of subdominants. The most charac-
teristic consists of those found in the heart of the association in southern
Arizona and New Mexico. The second group comprises those found along
the north, where the association meets the short-grass plains. The latter are
those species which constitute the typical societies of the prairies and plains.
While they are largely southwestern in origin, they have had time and oppor-
tunity to migrate throughout the formation east of the Rocky Mountains.
The more characteristic societies appear to be of relatively recent derivation
from the Mexican center, and they are best represented in the region along
the boundary.
The desert plains resemble the short-grass plains in the relatively small
number of societies, and especially of mixed societies. This is readily explained
by the low rainfall over much of the area and the thoroughness with which
the water available is utihzed by the associated dominants of sUghtly different
demands. Wherever the rainfall increases materially, as in the Aristida
consociation of Texas or toward the mountains, the number and complexity
of the societies increase also.
Vernal Societies: E stival Societies: Estival Societies — continued.
Antennaria dioeca. Psoralea tenuiflora. Chrysopsis villosa.
Calliandra eriophylla. Petalostemon purpureus. Eriogonum wriRhtii.
Astragalus bigelovii. Petalostemon candidus. Verbesina eucelioides.
Krameria secundiflora. Dalea laxifiora. Haplopappus gracilis.
Zinnia pumila. Linum rigidum. Yucca radiosa.
Eschscholtizia mexicana. Meriolix serrulata. Yucca baccata.
Malacothriz fendleri. Malvastrum coccineum. Eriogonum polycladum.
Lithospermum linearifolium. Thelesperma gracile. Gaillardia aristata.
PsiloHtrophe cooperi. Hymenopappus filifolius. Lepachys columnaris.
Eriogonum abertianum. Aster tanacetifolius. Plantago elata.
THE BUNCH-GRASS PRAIRIE. 149
Serotinal Socxetiea: Serotinal aocietiea — continued. Ctorw^-continued.
Gutierrezia sarothrae. Artemisia gnaphalodes. Lesquerella fendleri.
Grindelia squarrosa. Carduus undulatua. Lotus mollia.
laocoma hartwegii. Evolvulus argenteus.
Kuhnia rosmarinifolia. Clans: Desmanthufl jamesii.
Vemonia baldwinii. Argemone platyceras. Hofmanseggia stricta.
Liatris punctata. Aster ericoidea.
THE BUNCH-GRASS PRAIRIE.
AGROPYRUM-STIPA ASSOCIATION.
Nature. — The grasslands of the Northwest and of the Pacific coast differ
from those already described in the characteristic bunch-grass habit of the
dominants and in their relation to winter precipitation. The first visit to
them in 1914 led to the suggestion that they were essentially prairies, resem-
bling in many respects the cUmax prairies of the Missouri Valley. The
difference in habit appears greater than it really is, since the prairies of the
great sandhill region of Nebraska are characterized by bunch-grasses also.
This association consists of tall-grasses, which are species of Agropyrum and
Stipa, as in the eastern prairies. Three of the dominants of the latter, Stipa
comata, Agropyrum glaucum, and Koeleria cristata, occur throughout the
bunch-grass prairies, though the latter is the only one of much importance.
Aristida purpurea is likewise important, especially in CaUfornia, while Stipa
tnridula, Elymus sitanion, and Eriocoma aispidata all play a part as subclimax
dominants. Bouteloua gracilis and BuJbilis are the only ones of the great
dominants of the formation that are rare or lacking. The closer relationship
with the prairies shown by the dominants is explained by the fact of a fairly
continuous connection on the north, while the bunch-grass prairies are
separated from the plains by the wide stretch of the Colorado and Mohave
deserts. This fact is further reflected in the societies and clans. In the
Agropyrum consociation, the genera and many of the species of subdominants
are identical with those of the mixed prairie. These generally change south-
ward, and in southern CaUfornia many of the genera and practically all of the
species which form societies are different. However, it is difficult to draw
exact comparisons here, since the rehct areas of Stipa are too small to permit
the original structure to reach full expression.
Range. — ^The bimch-grass prairies find their best expression to-day in the
Palouse region of southeastern Washington and adjacent Idaho. Typical
areas also occur in northern and eastern Oregon, but these are only fragments
of what were once extensive stretches. Cultivation, grazing, and fire have
combined to destroy bunch-grass or to handicap it in competition with the
invading sagebrush. In the form of outposts, this association is found east-
ward in Montana to Helena and Livingston, in western Wyoming from Yellow-
stone Park to the Green River region and southward through northwestern
Colorado and northeastern and northern Utah. Over most of this region, it
occurs on dry rocky hillsides surrounded by sagebrush, indicating that it
formerly covered much larger areas. This is confirmed by the fact that
burning or clearing the sagebrush from an area permits the development of
typical bunch-grass prairie (plate 30).
The southern part of the association is much more fragmentary, so much so
in fact that it has had to be reconstructed from widely scattered relicts. The
150 CLIMAX FORMATIONS OF WESTERN NORTH AMERICA.
Agropyrum and Stipa consociations meet in southern Oregon and northern
California, though here fire, grazing, and the invasion of ruderal grasses have
almost completely destroyed the native grassland. The Stipa consociations
seem formerly to have dominated the interior valley from Bakersfield to
Mount Shasta and from the foothills of the Sierra Nevada and Cascade
Mountains, through and over much of the Coast Range. The successive
invasions of European weedy grasses, the extensive cultivation of the land,
and the repeated burnings which favored chaparral at the expense of grassland,
have operated to practically eUminate the original grasses. A special search
has been made for relict patches of Stipa during the past three years, with
the result that ^uch areas have been found more or less continuously or at
frequent intervals from La Jolla and San Diego northward to Sisson and
Weed. Further information as to the original extent of the Stipa grassland
has been obtained from collections, ranges, the statements of early settlers,
and the accounts of earHer collectors and explorers.
The bunch-grass prairie passes so gradually into the mixed prairie in central
Montana that no line can be drawn between them. This is readily understood
when it is known that Stipa coniata, Koeleria cristata, and Agropyrum glaucum
occur in both, and that a large number of the societies are identical. The
change is marked chiefly by the appearance and increasing importance of
Bouteloua, and the transfer of the major dominance from Agropyrum spicatum
to Stipa comata and Agropyrum glaucum. As already mentioned, there is no
connection between the bunch-grass prairies, and the short-grass and desert
plains in the south. The Colorado and Mohave Deserts have proved an
efifective barrier, which was probably in existence before the Pleistocene. It
thus appears probable that the bunch-grass prairies were derived from the
northeast and spread southward along the Pacific Coast.
CONSOCIATIONS.
Agroptrttm spicatum. Stipa setigera.
PoA tenuifoua. Stipa eminens.
Festuca ovina. Stipa comata.
Koeleria cristata. Elymus sitanion.
The two most important dominants are Agropyrum spicatum and Stipa
setigera. The first is the major and often the exclusive dominant throughout
the Palouse, southward into Oregon and California and eastward into Idaho
and Montana. The second is, or rather was, the great dominant throughout
Cahfornia, and it extends well into Oregon. The others are all secondary to
these in importance. Festuca is the only other one which frequently makes
pure stands, and there is some question as to its true relationship^ It seems
to attain the maximum development at higher elevations, as is true also in the
Rocky Mountains, and to have recently made its way into the bunch-grass
prairies. However this may prove to be, it is impossible to ignore it as a
dominant member of the latter (Weaver, 1917 : 42). In California, Stipa
eminens stands next in importance to S. setigera. It is usually mixed with the
latter, but may constitute a pure community. Elymus sitanion has been
found in pure stands also, but as a rule it is mixed with Stipa setigera or
Agropyrum spicatum. Poa tenuifolia is a fairly constant associate of Agro-
pyrum and Festuca, but is never a pure dominant. This appears to be the
rule also for Koeleria and Stipa comata. They may be expected throughout
CLEMENTS
Bunch-grass Prairie
PLATE 30
/^-o -
A. Agropyrum-Fc&tuca association' The Dalles, Oregon.
B. Agropyrum consociation, Missoula, Montana,
C. Agropyrum consociation' on "scab" land, John Day Valley, Oregon.
o
CLEMENTS
Bunch -grass Prairie
A. Stipa setigera consociation in trackway, Fresno, California.
B. Avena faXua consocies, with relicts of Stipd .aeligera and eminens. Rose Canyon, San
Diego, California.
THE BUNCH-GRASS PRAIRIE. 151
the association, but nowhere in it have they been found in pure communities.
At the present, they are more characteristic of the Agropyrum-Festuca com-
munity.
The role of Agropyrum glaucum in the bunch-grass association is still in
question. As a rule, it is subclimax in lowlands and especially in moist saline
areas. In northern CaUfornia and in Oregon, it often meets Stipa setigera
or Agropyrum spicatum on what appear to be more or less equal terms. In
the Hampton Valley in Central Oregon, the removal of the sagebrush results
in the establishment of an A. glaucum sod instead of the usual bunch-grass
community. In fact, repeated observations in Oregon and Idaho during the
past summer indicate that Agropyrum spicatum frequently loses its bunch
habit under certain conditions, and comes to be almost indistinguishable from
forms of A. glaucum. Through the same region, Elymus condensatus is a
frequent associate of the bunch-grass. It reaches its best development in
saline lowlands, however, and must be regarded normally as a subclimax
dominant. Eriocoma cuspidata and Stipa spedosa likewise occur now and
then with the dominants when the soil is looser or sandy, but they are clearly
subclimax consocies of the xerosere.
Factor relations and sequence. — ^The presence of a prairie of tall-grasses in a
region with 10 to 12 inches of precipitation annually is due to several facts.
Perhaps the most important is the bunch habit, which enables each plant to
draw upon a relatively large area of soil for its water supply. The second is
that 60 to 90 per cent of precipitation comes during winter, with the result
that penetration and conservation of the water are at a maximum. As a
consequence, the root systems are mostly deep-seated, and their efficiency is
high. Along the coast of southern California, moreover, the low precipitation
is offset by the high humidity and reduced evaporation to the extent that
Stipa setigera and S. eminens reach a high development here. The best
expression of bunch-grass prairies to-day occurs in that part of the Palouse
with 15 to 25 inches rainfall (plate 31).
Weaver (1917) has made a careful study of the physical conditions of the
Agropyrum and Festuca consociations in this region, as well as of the root-
systems of the dominants and subdominants. From June to September, at
Colfax, the evaporation in the former averaged 8 to 10 c. c. higher than in the
latter, while the water-content at 10 inches was 5 to 10 per cent lower. Since
the differences between northeast and southwest slopes of the Festuca con-
sociation were 9 to 10 c. c. and 5 to 12 per cent, respectively, it is evident why
the two consociations are frequently mixed. As would be expected from the
behavior in other associations, Koeleria stands close to Festuca in its water
requirements, while Poa is somewhat more xerophytic than Agropyrum.
These relations are confirmed by the successional sequence (Weaver, 1917: 68).
Of the Stipas, Stipa comata is the most mesophytic, followed closely by S.
setigera and this by S. eminens. Elymus sitanion is more xerophytic than
S. setigera and probably slightly more so than S. eminens.
SOCIETIES.
The bunch-grass prairies contain three groups of subdominants: (1) those
derived from the mixed prairie; (2) those characteristic of the Washington-
Idaho center; and (3) those found in central and southern California. The
152 CLIMAX FORMATIONS OF WESTERN NORTH AMERICA.
destruction of (the association over wide stretches and the fact that the
societies have not been made the subject of definite study throughout the
season render the following lists more or less' provisional. It has been espe-
cially difficult to determine the subdominants of the Stipa communities in
California, as the fragmentary areas are almost completely overrun with
annuals. The societies of such grassland areas at present are essentially the
same as for the chaparral (p. 193). The following list for the Agropyrum-
Festuca community of Washington and Idaho has been contributed by Dr.
J. E. Weaver:
Societies of the Agropyrum^Festtica community.
Prevemal Societies:
Carex geyeri.
Erythronium grandiflorum.
Claytonia linearis.
Vernal Societies:
Lupinus wyethii.
Balsamorhiza sagittata.
Leptotaenia multifida.
Phlox speciosa.
Estival Societies:
Wyethia amplexicaulls.
Geranium viBCoaJaaimum.
Astragalus arrectus.
Astragalus coUinus.
Astragalus spaldingii.
Castilleia lutescens.
Helianthella douglasii.
Lupinus leucophyllus.
Lupinus omatus.
Estival Societies — continued.
Lupinus sericeus.
Gaillardia arista ta.
Achillea millefolium.
Galium boreale.
Arnica fulgena.
Serolinal Societies:
Hoorebekia racemosa.
Solidago missouriensis.
Solidago serotina.
Prevemal Clans:
Viola adunca.
Ranunculus glaberrimua.
Fritillaria pudica.
Sisyrinchium grandiflorum.
Vernal Clans:
Synth>Tis rubra.
Collinsia parviilora.
Estival Clans:
Carduus foliosus.
Carduus palousensia.
Potentilla convallaria.
Potentilla blaschkeana.
Sidalcea oregana.
Penstemon confertua.
Agoseris heterophylla.
Agoseris grandiflora.
Eriophyllum lanatum.
Serotinal Clans:
Hieracium scouleri.
Aster fremontii.
Aster levia geyeri.
Erigeron corymboaus.
Carum gardneri.
Gentiana oregana.
THE SAGEBRUSH CLIMAX.
ATRIPLEX-ARTEMISIA FORMATION
Nature. — The sagebrush climax owes its character to the dominance of
low shrubs or bushes, of which Artemisia tridentata is the most important.
It is essentially a scrub desert, in which the dominants seem to have acquired
their distinctive vegetation-form as a rather recent adaptation to the arid
climate itself. In other words, they are shrubby adaptations of herbaceous
families, and not dwarf forms of shrubs or trees, as is true of chaparral and
mesquite. The formation is regarded as composed of 17 dominants, of which
11 belong to the Asteraceae, 4 to the Chenopodiaceae, 1 to the Polygondceae,
and 1 to the Lamiaceae. These families agree in showing a high systematic
development, and doubtless the dominants owe some part of their success to
the highly specialized one-seeded fruit typical of all of them. Their success
is due even more largely to the acquisition of the woody habit in some degree
at least, and especially to the accompanying ability to sprout more or less
readily from the base. As a consequence, the sagebrush dominants are not
only well adapted to their habitat, but they are also particularly well fitted
to invade other habitats, wherever fire or other disturbance has weakened the
hold of the occupants. The result has been a widespread extension of sage-
brush into all of the contiguous formations, the grassland, desert scrub,
chaparral, and woodland, and even into the pine consociation of the montane
forest. These transitions are often very broad, and hence the actual delimita-
tion of the formation on the map is a matter of peculiar difficulty. They also
THE SAGEBRUSH CLIMAX.
153
give the sagebrush a varied aspect, and seem to call in question its value as a
distinct formation, especially in hilly and mountainous country, where it
mixes or alternates constantly with fragments of other climax communities.
As is shown below, however, the great central mass of the community leaves
no doubt as to its format ional unity and rank.
Unity of the formation.— The geographical unity is greater than that of
most other climaxes in that the sagebrush occupies a natural physiographic
unit, the Great Basin. While the most representative species, Artemmo
tridentata, extends far beyond the lunits of the latter, the formation proper
does not. The Great Basin is likewise a climatic unit, and hence naturally
corresponds to its cUmax. It is hemmed in by the high mountains, and con-
tains by far the most extensive area with 5 to 10 inches of rainfall to be found
on the continent. The general rainfall limits are from 5 to 15 inches in the
interior, though to the eastward sagebrush mixes with or yields to grass as the
rainfall rises above 12 inches (fig. 5).
Evanston, Wyo
14 in.
Ill
1
Boise, Idaho
13 in.
Fillmore, U\&b.
15 fn.
u
Fig.
5. — Monthly and total rainfall for representative localities in the Baain sage-
brush association.
With respect to the component species, the unity of the climax is proved by
such widely ranging dominants as Artemisia tridentata, Chrysothamnus
nauseosus, Atriplex confertifolia, A. canescens, Gutierrezia sarothrae, and
Eurotia lanata. Of the 17 dominants, only 4 fail to occur throughout the
central mass of the formation as indicated by the limits of the Great Basin.
As to origin, the formation is characteristically southwestern. The main
body of dominants, which constitute the Atriplex-Artemisia association of the
Great Basin, seem to have moved northward at an early period, perhaps
before the Pleistocene, though they have probably imdergone considerable
differentiation since that time. A more recent lateral development has pro-
duced the Sahia-Artemisia association of southern California and Lower
California. The latter found itself between the chaparral on the one hand
and the rapidly desiccating desert on the other, and has covered but a limited
area in comparison with the main association. Its relationship, however, is
clearly indicated by its frequent contact with Artemisia tridentata, and espe-
cially by its occupying the same position between the desert scrub or grass-
land and the chaparral formations that the Atriplex-Artemisia association
does. The floristic unity of the formation is conclusively indicated by the
154 CLIMAX FORMATIONS OF WESTERN NORTH AMERICA.
fact that Artemisia tridentata haa been found in 314 of the 416 localities where
the community has been studied.
The ecological unity of the climax is due especially to the fact that all of the
17 dominants are half -shrubs or bushes. They range in height from an average
of 3 to 5 feet in Artemisia tridentata, A. calif omica, Chrysothamnus nauseosus,
Atriplex canescens, Eriogonum fasciculatum, and Salvia meUifera, while in
Artemisia trifida, Gutierrezia, and Eurotia the range is 1 to 2 feet. They are
typically deep-rooted, and this, with their bushy habit and perennial woody
stems, accounts for their success in competing with other dominants. For
their region, most of them have a further advantage in being able to endure
a more or less highly saline soil. The close similarity in their nature and
requirements is shown by the fact that they are replaced by such turf-forming
grasses as Agropyrum, BoiUeloua, and Hilaria, wherever conditions permit
the formation of a sod. All of the dominants, without exception, are marked
xerophytes in which transpiration is decreased by reduction of the leaf -surf ace,
a hairy epidermis, or succulence. This similarity in habit is confirmed by their
association. While the sagebrush in particular forms pure stands, mixed
communities are the rule. Of the 416 communities studied, 145 contained
two dominants and 143 contained three; in 44 there were four, in 5 five, and
in 1 six, or a total of 339 mixed communities in contrast with 75 pure ones.
Successionally, the sagebrush climax is perhaps more uniform than any
other formation. This is due to the low rainfall, the high evaporation, and the
rapid drying-out of bodies of water. Since its area is a great intermountain
basin composed of several smaller lake basins, the lakes and ponds are either
saline or they form salt marshes as they dry out. As a consequence, the
typical succession is the halosere, originating in salt marshes, or on the saline
shales and clays, which are especially frequent. In fact, the successional
correlation of the serai and climax dominants is so fundamental that the
development of a local subclimax of Atriplex and Artemisia occurs widely
throughout the Bad Lands of the Great Plains and the prairies, in spite of the
fact that these are several hundred miles from the sagebrush climax proper.
Range. — It is impossible to draw the limits of the sagebrush climax with
accuracy, owing to the extent to which it mixes with contiguous formations.
The general tendency is to use the conspicuous dominants, such as Artemisia
tridentata and A. cana, to outline its area, but these extend far beyond the
limits of the formation proper. Since ecotones are areas in which dominants
meet on more or less equal terms, it follows that the limit of a particular
climax must be drawn at the line where it is still controlling. As a matter of
convenience, a formation is called dominant where it covers three-fourths of
a particular area or region. Outside of this climax mass occur many outposts
of the community as well as of individual dominants, but these are merely
expressions of topographic or climatic diversity in the area of adjoining cli-
maxes. For example, the erosion valleys of the Bad Lands of northwestern
Nebraska are covered with luxuriant sagebrush, but this is really subclimax
to the mixed prairie which ultimately replaces it (plate 32) .
If the limits are set as indicated above, the sagebrush chmax will include
all of Nevada except the southeast, practically all of Utah, Colorado west of
the Continental Divide, central and southwestern Wyoming, a part of south-
western Montana, all of south-central Idaho, Oregon south of the John Day
CLEMENTS
Ba?in Sagebrush
A. Artemima tridenlata consociation, Hencfer, Utah.
B. A. tridenlata consociation, Garland, Colorado.
C. A. arbuhcula consociation, Evanston, Wj'oining.
THE SAGEBRUSH CLIMAX. 155
Valley and east of the Cascades, and California east of the Sierra Nevada.
Disregarding the interruption due to isolated mountain ranges, this consti-
tutes the largest central mass exhibited by any formation west of the prairies
and plains. Tongues of sagebrush stretch out from this mass into eastern
Montana, central Colorado, northern New Mexico, and Arizona, southern
California and Mexico, while climax outposts are found in southeastern
and eastern Washington, and even in southernmost British Columbia. These
are practically all extra-regional, persisting because of peculiar local con-
ditions or because the proper climax has not yet occupied all of its climatic
region.
Subclimax sagebrush. — Much if not all of this marginal portion of the for-
mation is subclimax in nature. This seemsto be true also of long stretches which
are apparently an intrinsic part of the central mass. This relation is obvious
where sagebrush comes in contact with the true woodland climax or with the
montane forest, because of the dominating relation of the trees. It is less clear
in the case of transitions between sagebrush and chaparral or desert scrub,
where the dominants are more nearly of the same size and nature. In such
instances, the mixed conamunity not only seems but actually is a fairly per-
manent community, of which the real climax relationship can only be deter-
mined by prolonged study.
The longest contact of the sagebrush is with grassland. It meets the bunch-
grass prairies in Washington, Oregon, Idaho, Montana, and Utah, the mixed
prairies in Montana, Wyoming, and Colorado, and the short-grass plains in
western Colorado, northern New Mexico and Arizona, and southeastern
Utah. The abiUty of the sagebrush and grassland to live together is shown
not only by the very broad transition between them all along the Une of con-
tact, but also by the fact that such dominants as Agropyrum glaucum and
Stipa comata are found more or less abundantly throughout the climax area
of the formation.
The actual relation between sagebrush and grasses is readily disclosed
wherever sagebrush has been cleared and often also where it has been burned.
When the short subsere which results ends again in sagebrush after a few years,
the area may well be regarded as a part of the sagebrush climax. This can
usually be anticipated by the vigor with which the shrubs form root-sprouts,
as well as by the failure of the grass dominants to appear in abundance during
the first two or three years. If the grasses do develop abundantly during the
first few years and especially the first year, so that they dominate the root-
sprouts of the shrubs, the area is to be regarded as belonging to the grassland.
Examples of this sort have repeatedly been found since 1913 in what appeared
to be typical sagebrush areas. Festuca ovina, Agropyrum glaucum, and A.
spicaium have frequently been found to replace cleared or burned sagebrush in
Oregon. Agropyrum glaucum and Stipa comata have been seen in the same
r6le in many parts of Idaho, northern Utah, and southwestern Wyoming. In
addition, the grass dominants have been found killing out the sagebrush as a
direct result of competition for water. This is not surprising along the
eastern edge in Wyoming where the grasses have a definite climatic advantage,
but it is unexpected in Utah and Nevada, where the advantage is reversed.
Sagebrush has been seen nearly dead or dying as the result of water com-
petition with Agropyrum glaucum, A. spicaium, BoiUeloua gracilis, and Stipa
156 CLIMAX FORMATIONS OF WESTERN NORTH AMERICA.
e&mata. Atriplex canescens shows a similar behavior where Bouteloua forms a
closed sod, and A. conferti folia wherever Hilaria jamesii tends to become domi-
nant. The evidence of the replacement of sagebrush by the grasses during
the dry years of 1917 and 1918, either as a result of fire or clearing, or in conse-
quence of competition, has been so abundant as to indicate that a broad mar-
ginal belt of the climax is really subclimax, or at least tends to become such
during the dry phase of the climatic cycle. This subclimax belt is from 100 to
300 miles wide and extends all along the grassland contact from Oregon to
Montana and from Wyoming to Arizona. If placed under proper treatment,
it is felt that it can again be converted into the original grassland com-
munity. The significance of this for grazing is indicated in Chapter VI.
The conversion of contiguous grassland into sagebrush has undoubtedly
been caused by overgrazing during the past fifty years, aided in a large meas-
ure by repeated fires. This is confirmed not only by evidence of the con-
trolling part formerly played by grasses in regions now covered by sagebrush,
but also by the persistence of the grass covering in areas more or less pro-
tected. This is particularly the case in the John Day Valley of eastern Oregon,
where the original Agropyrum sjncatum is almost completely displaced by
Artemisia tridentata over the range generally, while it persists in its former
dominance on rocky or inaccessible slopes. More recent evidence is afforded
by pastures in which Agropyrum has practically disappeared and weeds
abound, while contiguous protected areas show the pure stand of grass.
Associations. —The sagebrush formation is composed of two communities,
the Atriplex-Artemisia and the Salvia-Artemisia association. When the
climax formation was first recognized, it was supposed that it consisted of a
single association, the Atriplex-Artemisia halium. In attempting to determine
the relation of sagebrush to chaparral in California, it was found that the
community formed by Artemisia califomica, Salvia, and Eriogonum fasd-
cidatum showed a closer relationship to sagebrush than to chaparral. This
was first suggested by its constant position below the true chaparral and by
its more xerophytic nature. Further study showed the frequent contact
with the Artemisia tridentata association and confirmed the evidence afforded
by the similarity of the vegetation-forms with that of the sagebrush, and not
the chaparral. This was further supported by the discovery that the Cali-
fornia association bore the same relation to the Stipa grassland that the Great
Basin association does to the grasslands that touch it. As a consequence,
while the Salvia-Artemisia association is of limited extent in comparison with
the main association, it possesses all the characteristics of a distinct but
related community. It is less conspicuous because it has been more generally
disturbed by fire and overrun by such ruderal grasses as Avena and Bromus.
In protected areas where it retains its original character, it displays a marked
resemblance to some communities of the main association.
THE BASIN SAGEBRUSH.
ATRIPLEX-ARTEMISIA ASSOCIATION.
Bange. — Most of what has been said of the climax formation applies in
particular to this association. It covers the whole of the climax region,
except southern California and Lower California, and its outposts extend
into British Columbia, North Dakota, Kansas, and Mexico, as represented
CLEMENTS
Basin Sagebrush
PLATE 33
A. Subcliiiuix sjigt'brush in baiiland valleys, Hat Crin-k, Nebraska.
B. Altcrnes of Artemisia and Kochia, Strevcll, Idaho.
C. Sarcobatus, Chrysolhamnus, Atriplex and Artemisia, Vale, Oregon.
THE BASIN SAGEBRUSH. 157
by Artemisia tridentata, A. cana, and Gviierrezia. Few other associations of
the West exhibit such a large number of dominants or such a variety of group-
ings. It is also the most xerophytic of all climax associations, with the excep-
tion of the Larrea-Prosopis desert, and is unique in its general halophytic
character. The greatest development of dominants is in the climax mass,
from which they shade out toward the margins, being represented in the out-
post conmiunities by a single species. The haloid dominants are the least
extensive, and the lower non-haloid forms, such as Gviierrezia, have the
widest range. In fact, A. cana, A. trifida, Eurotia lanata, and Gviierrezia
sarothrae are so completely at home in the mixed prairies or short-grass plains
that it has seemed desirable to treat them as societies where they occur in
these associations. Like most of the western associations, the sagebrush has
received little quantitative study as yet, and it is possible to deal only with its
outstanding features and to suggest some of its more obvious correlations.
CONSOCIATIONS.
ABTmaBIA TRIDENTATA. ARTEMISIA CANA. GrATIA SPINOSA.
Atriplex contertifoua. Artemisia arbuscula. Gutierrezia sarothrae.
Chrysothamnus nauseosus. Artemisia trifida. Tetradtmia spinosa.
Chrtsothamntts nsciDiFLORUs. Artemisia riqida. Eurotia lanata.
Atriplex canescens Artemisia spinescens.
The most important as well as characteristic of all the dominants is Arte-
misia tridentata. It is also one of the most widespread, ranging from Saskat-
chewan to Nebraska, Mexico, CaUfomia, and British Columbia. In this
respect it is equaled by Eurotia lanata and Chrysothamnus nauseosus, and
excelled by Gviierrezia sarothrae, which extends eastward to central Kansas.
Atriplex canescens is of nearly as wide range, but it appears to be lacking in
Canada. Atriplex confertifolia and Chrysothamnus viscidiflorus are somewhat
more hmited, as is the case with Grayia spinosa, Artemisia cana, and the
remaining species of Artemisia. Naturally, the range of these as climax
dominants is much more restricted, and is almost wholly confined to the
Great Basin proper (plate 33).
Rank and grouping. — ^The number of dominants in the association is so
large and their equivalences so close that a large number of groupings occur.
In the endeavor to determine the relative importance of the dominants and of
the various mixtures, a simamary has been made for all locahties visited in
the sagebrush association in 1907, 1909, and from 1913 to 1918. The total
number of locahties was 416, including a few duphcated in different years.
The sequence of the various dominants is shown by the following table :
Total number of localities 416
Artemisia tiidentata 314
Atriplex confertifolia 142
Chrysothamnus 140
Atriplex caneecens 66
Grayia spinosa 54
Gutierrezia sarothrae 45
Tetrad j-mia spinosa 37
Eurotia lanata 15
Artemisia spp. (except A. tridentata) . 61
Artemisia tridentata was found 60 times in pure stands stretching over many
miles, often for 20 to 30 miles without interruption. Atriplex confertifolia
was met but 10 times in extensive pure areas, though it is very often found
on hillsides and mountain slopes in pure communities a few miles long. While
the more halophytic and hence subclimax species of Chrysothamr\us make
pure stands, sometimes covering several to many square miles, the climax
158 CLIMAX FORMATIONS OP WESTERN NORTH AMERICA.
ones are regularly found in mixture, or as narrow band-like alternes. Arte-
misia cana has several times been met as a pure zone below A. tridentata,
but it is much more frequent in the mixed prairies. The tendency to form
pure stands of small extent is naturally more marked outside of the climax
area, since the other dominants of similar equivalence are usually lacking.
In spite of the major dominance shown by Artemisia tridentata, the associa-
tion is typically mixed in character. Of -406 instances, pure stands occurred
in but 75, while 331 were mixtures. Two and three dominants are the rule,
the former occurring in 142 cases, the latter in 139. Four dominants were
found in 44 localities, five in 5, and six in 1. The frequency of the most
important groupings is as follows:
Artemisia tridentata-AiripIex confertifo-
lia, alone 24
A. tridentata-A. confertifolia, with other
species 74
A. tridentata-Chrysothamnus na\iseosu8 or
C. viscidiflonis 31
A. tridentata-Chr>*8othamnu8, with others. 79
A. tridentata-Grayia =»= others 41
A.tridentata-A. confertifolia, Grayia=fc others 18
A. tridentata-A. confertifolia, Chrysothamnus
=fc others 23
A. tridentata-Gutierrezia ± others. 30
A. tridentata-A. canescens . . .' 28
A. tridentata-Sarcobatus =*= others 23
A. confertifolia-Grayia =*= others, but no A.
tridentata 10
Correlations. — ^The dominants of the sagebrush association show the most
striking relation to the amount of salt in the soil. While they are essentially
xerophytes, the water relation is so obscured by the presence of salt that the
specific requirements and the successional sequence are most readily indicated
by the latter. Our knowledge of the salt relations of the dominants is due
chiefly to the work of Kearney, Briggs, Shantz, McLane, and Piemeisel
(1914), and of Shantz (Clements, 1916:237). The most saUne of the species
considered here is the subclimax Sarcohatus vermiculaius with a mean of 0.8
per cent. Atriplex confertifolia possesses a mean of 0.5 per cent and Arte-
misia tridentata of 0.04 per cent. Grayia, Tetradymia, Atriplex canescens, and
Artemisia spinescens center about Atriplex confertifolia, while Chrysothamnus
nauseosus, C. viscidiflorus, Eurotia, Gutierrezia, and the several species of
Artemisia resemble the sagebrush more nearly. In spite of the excellent work
which has been done in the salt relations of the dominants of the sagebrush
association, these results do not suffice to explain their varied groupings, nor
are they in full har nony with what seems to be the successional sequence.
When two deep-rooted species, such as Artemisia tridentata and Sarcohatus
vermiculatus are found 23 times in intimate mixture, this relation does not
seem consistent with the mean salt-content for each. This discrepancy appears
even more striking in the case of Artemisia tridentata and Atriplex confertifolia,
which occur intimately associated in 98 localities. This relation is further
complicated by the fact that Artemisia tridentata not only occurs in 278 of the
338 mixed communities, but is also repeatedly associated with every one of
the saline dominants from Sarcohatus to Atriplex canescens. As a consequence,
it seems certain that we are not at the bottom of the salt relation. For a
complete understanding, it will be necessary to determine the root relations
of each dominant alone as well as in mixed stands, and to ascertain the
extremes of salt-content for it in the various mixed communities and at the
different working levels of the roots as well. Here, as everywhere else, the
behavior of the plant or community must be accepted as conclusive as to the
CLEMENTS
Basin Sagebrush
PLATE 34
A. AliipUx cunjiiLijolia consociation, Delta, Colorado.
B. Atriplex corrugata consociation, Thompson, Utah.
C. Atriplex lenliformis consociation, Salton Sea, California.
THE BASIN SAGEBRUSH. 159
equivalence and sequence, and the instrumental results as of secondary
importance. The latter are indispensable but never paramount.
Successional sequence. — A question naturally arises as to the possibility
of succession in a region of such low rainfall and in basins of such high salt-
content. Shantz (1916 : 235) has shown conclusively that succession is a
normal process, even in the most saline areas about Great Salt Lake :
" Two lines of development are initiated by the Allenrolfea association. The
more natural line is brought about largely by the gradual lowering of the
ground-water level. As a result water is less and less supplied from the ground-
water, and more and more from the surface as rain. Allenrolfea, when the
ground-water is not too close, is gradually replaced by Sarcohatus, Suaeda
moquinii may follow Allenrolfea and be replaced in turn by Sarcobatus. As a
rule, SarcobatiLS and Suaeda are mixed, the former being the most important
plant. Sarcohatus, which often forms a pure association in this valley, usually
forms a scattered growth, the interspaces being occupied by Atriplex. This
mixed tissociation finally gives way to pure Atriplex when the ground-water is
no longer within the reach of Sarcobaiv^ roots. The Atriplex association is not
readily replaced in the Tooele Valley. The soil is rather strongly alkaline
and is very slowly leached. No permanent type of vegetation stands between
this and the alkali-avoiding Artemisia in this Valley. Artemisia and Atriplex
are not sharply separated at the ecotone, and, although Artemisia is never
luxuriant along this line, there is no doubt that it is gradually replacing the
Atriplex as the conditions become more favorable for plant growth.
* Kochia, which occurs on land of unusually heavy texture, represents the
most extreme conditions in the Valley in regard to the shortage of water, and
indicates the presence of 0.5 to 1 per cent salt below the first foot. The run-off
in this land is very great, and it is very slowly leached. If a salt flat could be
lifted above the level influenced by ground-water, and slightly leached,
especially in the surface foot, the conditions would be very similar to those in
the larger Kochia areas of the Valley. Since such conditions are not markedly
different from Atriplex land, Atriplex is slowly advancing along the broad
ecotone. In time, Atriplex will probably replace much of the Kochia. The
ecotone between Kochia and Artemisia is very sharp, and a great change occurs
in salt-content and the physical texture of the soil. When water drains over
land of this type, and where unusual leaching occurs, Artemisia enters directly
on Kochia land. This is due to the proximity of the Artemisia and Kochia
areas. A more natural change would be from Kochia to Atriplex, and from
Atriplex to Artemisia.'
This account conforms essentially to the course of the halosere throughout
the sagebrush association. Sarcobatus and Chrysothamnns n. glabratus are the
chief subclimax dominants in saline valleys, though this role is usually taken
by Atriplex corrugata and A. nuttallii over the extensive gumbo plains derived
from such deposits as the Mancos and Steele shales. These are followed by
Tetradymia spinosa and this by Atriplex confertifolia, or by Chrysothamnus
nauseosus. The latter is nexi invaded by Grayia in some regions, and by such
low Artemisias as A. trifida or A. arbuscula in others. In still other areas,
Atriplex confertifolia is followed directly by Artemisia tridentata, often with
more or less Eurotia, Atriplex canescens, Chrysothamnus viscidiflorus, or
Gutierrezia. The general sequence, more or less modified by local conditions,
recurs in hundreds of valleys throughout the association. It not only con-
firms the successional movement, but explains the characteristic mixing
throughout (plate 34).
160 CLIMAX FORMATIONS OF WESTERN NORTH AMERICA.
SOCIETIES.
These are poorly developed in the climax portion generally, but they
become more and more abundant through the marginal subclimax zone leading
to the adjacent formations, particularly the grassland. This is readily
explained by the fact that the sagebrush societies are largely drawn from the
grassland associations, and hence the two groups are similar to a large degree.
The sagebrush likewise contains a number of grasses derived from the various
grass associations. These play a role Essentially similar to that of societies,
though they are properly to be regarded as extra-formational examples of the
particular consociation. The societies peculiar to the sagebrush are largely
constituted by halophytic species which persist from the subclimax. Pure
stands of Artemisia iridentata are to be regarded as the final condition of the
climax. They are characteristically dense and closed, and are often prac-
tically destitute of other species, except for a few plants of such ruderals as
Sisymbrium oltissimum, Lepidium perfoliatum, and Bromus tectorum. The
latter regularly simulate striking societies over large areas, but they are
properly understood as pioneer annuals of a subsere due to fire or grazing, or
usually to both.
Grata Communitiea appearino
aa Societiet:
Agropjrnim spicatum.
Agropjrruni glauctim.
Stipa comata.
Btipa viridula.
Feetuca ovina.
Elymufl condensatus.
Kocleria cristata.
Bouteloua gracilis.
Hilaria jamesii.
Aristida purpurea.
Elymus sitanion.
Erioooma cuspidata.
Vernal Societiea:
Anemone patens.
Antennaria dioeca.
Anemone globosa.
Sieversia ciliata.
Potentilla arguta.
Astragalus flexuosus.
Astragalus dnimmondii.
Astragalus crassicarpus.
Allium cemuum.
Senecio fendleri.
Comandra umbellata.
Vernal Societiea — continued.
Aragalus speciosus.
Aragalus deflexus.
Erysimum parviflorum.
Krynitzkia virgata.
Heucbera par\'ifoUa.
Eatival Societiea:
Balsamorhiza sagittata.
Balsamorhiza deltoidea.
CastUleia miniata.
Achillea millefolium.
Cordylanthus wrightii.
Linum perenne.
Opuntia polyacantha.
Opuntia mesacantha.
Eriogonum umbellatiun.
Calochortus gunnisonii.
Allium cemuum.
Potentilla pennsylvanica.
Potentilla hippiana.
Potentilla gracilis.
Galium boreale.
Erigeron canus.
Erigeron pumilus.
Eriogonum racemosum.
Pentstemon confertua.
Eatival Societiea — continued.
Pentstemon unilateralis.
Pentstemon sti ictus.
Geraniimi caespitosum.
Delphinium scopulorum.
Lupinus argenteus.
Malvastrum coccineum.
Campanula rotundifolia.
Campanula parrj-i.
Gaura coccinea.
Aster bigelovii.
Artemisia canadensis.
Actinella floribunda.
Orthocarpus purpureus albus.
Stanleya pinnata.
Serotinal Societiea:
Artemisia frigida.
Grindelia squarrosa.
Carduus undulatus.
Carduus plattensis.
Wyethia amplexicaulis.
Wyethia arizonica.
Wyethia helianthoides.
Wyethia scabra.
Chaenactis douglasii.
THE COASTAL SAGEBRUSH.
SALVIA-ARTEMISIA ASSOCIATION.
Bange. — The association is limited to the region from northern Lower
California to San Francisco Bay, and from southwestern Nevada to the
Pacific Coast. It is characteristic of the lower foothills, between the Stipa
grassland or the Larrea desert, and the Adenostoma consociation of the
chaparral. It occurs with the latter so much in southern California that
it has been regarded as a particular southern type of chaparral, but it now
seems that this view can no longer be maintained. The first recognition
CLEMENTS
Coastal Sagebrush
PLATE 36 c^
A. Contact of Basin Sagebrush with Coastal sagebrush and chaparral, Campo, California.
B. Artemisia califomica, Salvia niellifera, and Eriogonum fasciculalum association, Elsinore,
California.
C. Coastal sagebrush with Adenoatoma in ravines, Temecula, California.
THE COASTAL SAGEBRUSH. 161
of this as a sagebrush association was made in 1918, and as a consequence it
has received Uttle or no special study. It owes its character to Artemisia
calif ornica as the major dominant. This is a typical sagebrush, resembling
Artemisia JUifolia closely in habit and A. tridentata in climax qualities, espe-
cially when it occurs as a pure consociation.
CONSOCIATIONS.
Artemisia caufornica. Salvia apiana.
Salvia melufera. Eriogonum fasciculatom.
Salvia leucophylla.
The most important consociation is Artemisia califarnica. It not only
occurs in most of the groupings, but it also ranges widely along the Coast
hills as a pure community. Eriogonum fasdculatum is the most frequent as-
sociate of the sagebrush, often with Salvia mellifera. Salvia apiana is restricted
to the southern part of the area, and is more subclimax in nature than the
others. Eriogonum fasdculatum, with the variety polifolium, has much the
widest range, forming extra-associational communities in the Larrea desert,
and the southwestern edge of the main sagebrush association. In southern
California and Lower California, four dominants are frequently associated.
Farther north the community is regularly constituted by Artemisia cali-
f ornica, Eriogonum fasdculatum and Salvia mellifera, or leucophylla. This is
the typical grouping of the association, though any two of the dominants may
occur together in this area. The association shows the usual tendency to
break into pure consociations toward its borders. Along the edge of the desert
it is represented chiefly by Eriogonum fasdculatum, and on the western slopes
of the Coast Range by Artemisia calif ornica (plate 35).
The Coastal sagebrush association is in intimate contact with the Adenos-
toma-Ceanothu^ chaparral and the Larrea desert. In former times it must
have touched the Stipa bunch-grass community along much of the interior
valley, and to-day the two are much mixed in southern California. Through-
out its area, the sagebrush lies just below the Adenostoma consociation of the
chaparral. The ecological requirements of the latter are so nearly equivalent
to those of Salvia and Eriogonum in particular that these often seem an
integral part of the chaparral. All the dominants mix so intimately with
Adenostoma along the ecotone, owing to the characteristically diverse topog-
raphy, that an absolute line of separation is out of the question. This is so
often true of ecotones, however, that it does not affect the vaUdity of the
sagebrush association, as is readily seen when typical areas of the two forma-
tions are compared. This conclusion is supported likewise by a characteristic
difference in the shrub form, and by the systematic relationships, as pointed
out before. Toward the desert the intrusion is even greater and is best
illustrated on the south side of the Mohave, where Eriogonum fasdculatum
is regularly mixed with such desert dominants as Larrea, Salvia carnosa,
Salazaria mexicana, Trictiostema lanatum, and Yucca, as well as frequently
with Artemisia tridentata, Chrysothamnus nauseosus, and Atriplex canescens.
No factor studies have been made in this association and the sequence of
the dominants is a matter of inference. The five species are closely equivalent,
though the topographic and serai relations indicate a definite and constant
sequence. Artemisia calif ornica, Uke A. tridentata, is the most mesophytic
and under static climatic conditions would tend to form a pure climax. Salvia
meUifera and S. lev^xtphylla follow closely in requirements, while Eriogonum
162 CLIMAX FORMATIONS OF WESTERN NORTH AMERICA.
fasdcukUum has a wider range of adjustment, from climax conditions with 15
to 20 inches of rainfall to desert ones at 5 to 10 inches, where it is represented
by Eriogonwn f. polifolium. Salvia apiana seems the least mesophytic and
consequently is more or less subclimax, growing on rocky slopes or in other
more or less disturbed areas.
THE DESERT SCRUB CLIMAX.
LARREA-PROSOPIS FORMATION.
Nature. — The desert scrub, or mesquite, resembles sagebrush and chaparral
in both appearance and character. As the name indicates, it is distinctly the
most xerophytic of the three, reaching its best development in a rainfall of
5 to 12 inches. The dominants are bushy shrubs, 3 to 6 feet high for the most
part. The chief exceptions are Prosopis and Acacia, which often form trunks
and become small trees on flood-plains and in other favorable situations.
Most of the dominants possess the abihty to produce root-sprouts, though to a
smaller degree than the chaparral. To this they doubtless owe the many-
stenmied habit as well as their dominance. With the exception of the typical
dominant, Larrea, most of the species are deciduous, though many are imper-
fectly so and a number have evergreen stems or branches, as in Opuntia,
Parkinsonia, and Koeberlinia. The characteristic feature which distinguishes
the desert scrub most readily from chaparral and sagebrush is its very open
structure. The bushes usually stand 10 to 30 feet apart in t3T)ical situations,
and it is altogether exceptional that the crowns touch each other, even in the
case of the less xerophytic Prosopis and Acadia. The spacing is evidently a
consequence of low rainfall and resultant low water-content, necessitating a
large area for adequate absorption by the roots. As would be expected, this
seems to be correlated with the root habits of the various dominants. The
individuals of Larrea are more widely separated than those of Prosopis, by
reason of a shallow root system as well as a lower chresard. This produces
three results generally typical of the desert scrub, all due to the large intervals
in which more or less water is available superficially. The first is the presence
of tall undershrubs which occupy the intervals in greater or less abundance,
such as Franseria, Isocoma, Parthenium, Gutierrezia, Hilaria, etc. A second
consequence is the development of a characteristic population in the intervals
during the winter rains in February and March. A third result, which has
an important bearing upon the relation of desert scrub to contiguous forma-
tions, especially the grassland, is the readiness with which it forms parks or
savannahs. Such parks are an especial feature of the Southwest, where they
mark the broad transition between the desert scrub and the grassland.
With respect to systematic relationship, the desert scrub is less homogeneous
than chaparral or sagebrush. The three chief dominants belong to as many
different families, Larrea to the Zygophyllaceae, Prosopis to the Mimosaceae,
and Flourensia to the Asteracea^. The Aster aceae and Leguminosae are most
important, and the Rhamnaceae next, while the Liliaceae are represented by
Yucca, the Gnetaceae by Ephedra, the Chenopodiaceae by Atriplex, and the
Poa/xae by a shrubby grass, Hilaria rigida.
This particular type of scrub is known by various names in the different
sections. In Texas it is called chaparral or mesquite, the latter being the
usual name where Prosopis is prominent or predominant. From New Mexico
THE DESERT SCRUB CLIMAX. 163
westward, where Larrea is the chief dominant, the general name is grease-
wood. None of these will serve as a desirable name for the formation as a
whole or for either of its associations. As previously suggested, it seems best
to restrict the use of the word chaparral to the Quercus-Ceanothua climax.
Mesquite is of too limited application in so far as the scrub community is
concerned, being applied only to Prosopia or to Prosopis with some other
related dominant, such as Acacia. The word has the further disadvantage of
being used for a number of grasses, Bouteloua, Bulhilis, and Hilaria, probably
because of their frequent association with the mesquite in grassy parks.
Greasewood is the designation of several shrubs, but the common usage
seems to agree with the scientific in confining the word to Sarcohatus vermi-
culatus. Hence, in seeking a readily usable name for this extensive formation,
it has appeared necessary to employ two words, i. e., desert scrub, the latter
referring to its nature, the former to its typical habitat.
Range. — ^The area characterized by the desert scrub climax is difficult to
delimit for two reasons. It shares with the sagebrush and chaparral forma-
tions the habit of breaking up along the line of contact with grassland or other
scrub communities, and thus forming a broad ecotone of mixed or alternating
conmiunities. In addition, it is especially given to forming parks or savannahs
with grassland, particularly along its northeastern edge and on the bajada
slopes of mountains. This is typical of Prosopis, but it is also true to a large
degree of Yucca and Flourensia, and, to a much smaller one, of Larrea. In
Texas, for example, while the three dominants have not been seen together
east of Ozona and Odessa, Prosopis is a regular feature in the grassland as far
north as Lubbock, and it occurs frequently farther north, finally disappearing
in southwestern Kansas. It also occurs generally, but more or less sparsely,
in the desert plains grassland, from the mountains of western Texas and
southern New Mexico to those of southern and central Arizona, where it is
frequently associated with Yucca radiosa.
If the limits of the formation be determined by the presence of two of the
three dominants in more or less complete control, its area will comprise
southwestern Texas west of Odessa and Ozona, and the southern quarter of
New Mexico. In Arizona the formation is limited to the southern third of the
State, owing to the barrier of the central mountain ranges, and to the north-
western part beyond the Hualpai Mountains and the Grand Canyon. It is
typical in general of southeastern CaUfornia, east of the Laguna, San Jacinto,
San Bernardino and Tehachapi Mountains, and the Antelope Valley. It
occupies the southern portion of Nevada south and west of Caliente and also
the extreme southwestern part of Utah. Its range in Mexico is unknown, but
it is the typical formation of the northern part from the mouth of the Pecos
westward through Lower California (MacDougal, 1904, 1908; Goldman,
1916 : 334, 338). A related community of Prosopis and Acacia extends
eastward along the Rio Grande plain as far as the coast, but too little is known
of it to warrant assigning it definitely to the desert scrub formation.
Unity of the formation. — The geographical unity of the desert scrub is perhaps
greater than that of any other western formation. It constitutes a broad
band 500 to 1,000 miles wide from trans-Pecos Texas to southern California and
and Lower California. This suffers two great interruptions, one due to the Sierra
164 CLIMAX FORMATIONS OF WESTERN NORTH AMERICA.
Madre Mountains, the other to the Gulf of California. Its greatest extension
northward is found in Nevada, while it ranges southward in Mexico through
Chihuahua and Durango. In altitude it reaches its major expression between
1,000 and 3,000 feet, but it occurs from sea-level to 4,000 feet or higher.
With respect to climate, the desert scrub is especially distinct. This is
true of both temperature and rainfall. It has the lowest rainfall, the greatest
evaporation, and the highest mean temperature of all the western climaxes,
though the sagebrush approaches it closely in the matter of rainfall. The
precipitation ranges from 2 to 12 inches, with the major portion of the forma-
tion lying between 5 and 10 inches. The highest rainfall occurs in trans-
Pecos Texas, with 15 inches, and the lowest in the Colorado Desert with 2
inches. There is a general but irregular decrease from east to west, correlated
with changes in the structure of the formation itself (fig. 6).
Kent. Tex
u
13 in.
Mil
1
El Paw>, Texaa
9 m.
Ill.il
II
Tucson, t
\T\
zona
12 in.
I.I
1
Las Vecraa, Nevada
4 in.
I I I I I , I I I I I I
Parker, Arizona
Sin.
Il...-lll.ll
Bagdad, CaliComia.
4 in.
■ I.lll
Fio. 6. — Monthly and total rainfall for representative localities in the associations of
the desert scrub climax.
The floristic unity of the desert scrub is even greater than that of the other
two scrub climaxes. The two most important dominants, Larrea mexicana
and Prosojyis juliflora, occur throughout. This is likewise true of Atriplex
canescens and Fouquiera splendens, though these are probably subcUmax in
character. Acacia, Yucca, and Ephedra extend throughout the area, but the
species change to some degree. Acacia greggii is found from western Texas to
Lower California, while A. constricta ranges nearly as widely. Yucca radiosa
and Y. macrocarpa are present from western Texas through Arizona, but are
largely replaced in California and Lower California by species ecologically
equivalent. While four or five species of Ephedra occur in the formation,
these are essentially similar if not identical in ecological character. Among
the undershrubs, Gutierrezia, Isocoma, Krameria, and Zinnia are distributed
over most of the fonnational area.
The ecological unity of the desert scrub is indicated by the fact that prac-
tically all of the dominants are many-stemmed, bushy shrubs, usually with the
habit of root-sprouting well developed. This is essentially true of Yucca,
especially the most important species, Y. radiosa, in spite of its very different
THE DESERT SCRUB CLIMAX. 165
appearance. Prosopis and Acacia usually constitute exceptions, particularly
when found on flood-plains and in washes. However, on uplands and on
dunes, these too are regularly many-stemmed. As would be expected, the
taller dominants are uniformly deep-rooted, the depth of the roots being
determined largely by that of the soil. Naturally all are intense xerophytes,
in which the chief adaptations are the reduction and loss of leaves and twigs,
the development of evergreen leaves or branches, or of a thick or glutinous
cuticle. The great majority are deciduous, Larrea and Yucca furnishing the
most important exceptions. Nearly all agree hkewise in being somewhat
resistant to alkaU. This is a direct outcome of the prevalence of halophytic
areas in the valleys and bolsons. Many of the most striking playa regions
occur within the area of the formation. The succession on saline soils is
essentially identical from one end of the area to the other. This is true also
of the sand-dune and hummock succession, which is probably the most wide-
spread of all. The third important succession is that of rocky ridges and
slopes. While this shows the same stages in both associations, it is character-
ized by Agave, Yucca, Opuntia, and Dasylirium in the east, and by Fouquiera,
Parkinsonia, Cereus, and Encelia in the west. The close equivalence of these
two subclimaxes is shown by the presence of Fouquiera, Dasylirium, and Yu/xa
radiosa in both.
With respect to its origin, this formation is one of the most homogeneous.
The dominants are all subtropic or Mexican in distribution, with the exception
of Atriplex canescens, while this and Gutierrezia are the only ones that range
far beyond the formational limits to the north. This conforms to its occur-
rence as a broad belt on both sides of the Mexican boundary. The gradual
differentiation of this formational mass has reached a point where it seems
desirable to recognize two associations, the one centering about the Rio
Grande and the other around the Colorado. The reasons for this are dis-
cussed in the following section.
Structure of the formation. — The general abundance of Larrea throughout
the formation gives the impression that the latter contains a single associa-
tion. A scrutiny of the various groupings discloses a nimaber of constant
differences between the eastern and western portions, which warrant the
recognition of two corresponding associations. The statistical evidence from
more than 250 localities is supported by the comparative studies made in
1918, when the formation was examined in its entirety from Texas to Cali-
fornia. In the table on the following page the occurrence of the dominants
and their major groupings are shown for the two associations. The line which
separates them is in general that of the GaUuro and Dragoon ranges in south-
eastern Arizona.
It is evident that Dirrea, Prosopis, and Flourensia far outrank all of the
others in importance, and that Franseria is three times as frequent as Acacia
in the association where they meet, in addition to being much more abundant.
Acacia, Atriplex, Yucca, Ephedra, Fouquiera, and Condalia are all more or less
regular associates of the primary dominants in both associations. While
t3T)ically less abundant, they sometimes equal or exceed them in number.
The division into two associations rests chiefly upon the complete absence of
Flourensia in the one, as a dominant at least, and of Franseria in the other,
166 CLIMAX FORMATIONS OF WESTERN NORTH AMERICA.
and upon the more uniform distribution of Prosopis in the Larrea-Flourensia
type. These differences are reflected in the figures showing the occurrence
of the four groupings. Of the other dominants, Atriplex is more important
in the west, and Yucca and Ephedra in the east, while Fouquiera varies but
little between the two. Parkinsonian Cereus, and Dalea are confined to the
WMtem, and Rhus to the eastern association. Of the undershrubs, Gutier-
retia is much more important in one, and the corresponding genus, Isocoma,
in the other. Hilaria and Enxxlia are confined to the Larrea-Franseria asso-
ciation, Microrhamnus and Parthenium practically to the Larrea-Flourensia,
while Krameria and Zinnia show little difference. All in all, the evidence
supports the recognition of two recently differentiated but fairly distinct
associations.
Summary of dominants.
Larrea-
Flourensia
(Texas-New
Mexico) .
Larrea-
Franseria
(Arizona-
California).
Larrea-
Flourensia
(Texas-New
Mexico).
Larrea-
Franseria
(Arizona-
California).
Total number of
localities
Larrea
168
110
110
97
0
26
75
67
50
30
0
15
31
15
100
82
43
0
35
12
35
0
0
0
31
28
8
3
Fouquiera
Condalia
Rhus
14
16
4
7
9
0
0
0
0
0
7
38
6
5
7
12
8
0
2
0
10
8
8
8
8
1
3
15
6
11
Proaopis
Flourensia
Franaeria
Acacia
Koeberlinia
Microrhamnus. . .
Parkinsonia
Cereus
Larrea-Proaopis . .
Larrea-Flourensia
Flourensia-Prosopis
LarrearFlourenaia-
Prooopis
Larrea-Franseria .
Atriplex
Dalea
Hilaria
Encelia
Parthenium
Gutierrezia
Isocoma
Yucca
Krameria
Zinnia
Ephedra
Associations. — The desert scrub formation consists of two associations,
the Larrea-Flourensia and the Larrea-Franseria. In addition there is the
closely related community of Prosopis and Acacia, typical of the lower valley
of the Rio Grande and probably to be regarded as a subclimax. Besides the
differences in composition already noted, the two associations differ much in
structure. In the Larrea-Flourensia type, the three dominants are of nearly
equal importance, as is shown by their respective frequence, viz, Larrea 110,
Prosopis 110, and Flourensia 97, as well as by that of the four major groupings.
Moreover, the latter show that the dominants are frequently or regularly
mixed on more or less equal terms. Gutierrezia is the characteristic under-
shrub. In the Larrea-Franseria community the ground-tone is given chiefly
by Larrea. The uniform olive-brown color is less broken by Prosopis, except
where the two mix along the line of contact in valleys and draws, or in sandy
soils. Flourensia is altogether lacking. Franseria, though an undershrub,
often ranks next to Larrea in importance, and gives a distinctive impress to
the community. In some places a similar role is taken by Hilaria, and not
infrequently Franseria, Hilaria, and Encelia are to be found mixed or alter-
nating with each other. A further distinction between the two associations
is found in the much greater frequency of Yucca and Ephedra in the Larrea-
THE DESERT SCRUB CLIMAX. 167
Flourensia type. Over much of the area one or both will regularly occur in
abundance with Prosopis or Flourensia, though rarely with Larrea where it
is most typical.
Their relation to the subclimaxes of rocky slopes and ridges marks another
difference between the two associations. In the east the subclimax consists of
Yucca, Agave, Dasylirium, and Fouqaiera chiefly, and this explains why Yucca
radiosa and macrocarpa are such frequent constituents of the scrub below. In
the west Yv^ca is largely confined to the grasslands, and the subcUmax con-
sists primarily of Parkinsonia, Cereus, and Fouqaiera. All of these mix with
Larrea to a considerable extent, and are sometimes found in the heart of the
association, where they are often to be regarded as relicts. Another dis-
tinctive feature of the Larrea-Franseria type is the presence of the cylindric
OpurUias, such as 0. fulgida, 0. spinosior, 0. versicolor, etc. While Opuntia
occurs sparsely in the eastern association, it has nowhere been found in the
abundance which characterizes it in Arizona. Here the species of Opuntia
make important communities on the lower bajada slopes with Larrea or in
the broad washes with Prosopis.
Finally, a unique feature of the Larrea-Franseria scrub is the development
of a more or less continuous cover of winter annuals from January or February
to April. This is the direct consequence of a secondary maximum of rainfall
at this time, and is very similar to what occurs in southern California. This
transitory community of annuals is httle if at all developed in Texas and New
Mexico. Here the rainfall from January to April is less than 15 per cent of
the annual, while in Arizona and southeastern California it is 30 to 60 per
cent of the total. The distribution of the rainfall seems also to explain the
change from one association to the other in eastern Arizona. New Mexico and
western Texas receive 60 to 75 per cent of their annual rainfall between
April 1 and September 30, while the Larrea-Franseria region of Arizona and
CaUfomia receives but 20 to 50 per cent during the same period. Further-
more, the greater tendency of the eastern t3T)e to form savannahs is explained
by the fact that the seasonal distribution of the rainfall is practically the same
as that for grassland.
Relation to other formations. — ^The chief contact of the desert scrub is with
the grassland formation. This is the case in trans-Pecos Texas, New Mexico,
and Arizona, where the contact is with the deSert plains association. This is
especially true of elevated plains and of bajadas with northerly slopes. On
slopes with southerly and westerly exposure or rocky surface the scrub is
usually separated from chaparral or woodland by a broad band of the Yiuxci-
Agave community in the east or one of Parkinsonia-Cereus-Fouqaiera in the
west. The lines of contact are often broad ecotones and, in the case of the
grassland, they regularly develop into parks of scrub and grass several miles
wide along the mountain ranges and hundreds of miles in length over the
southern Great Plains. In Nevada and adjacent Arizona and Utah, the
Larrea scrub yields to the sagebrush formation, and in California it Ues in
touch with the sagebrush or chaparral, or less frequently with woodland. At
the western edge of the Edwards Plateau in Texas, desert scrub meets the
chaparral of oak, and Prosopis becomes the typical shrub of the level valleys
and washes throughout the region.
168 CLIMAX FORMATIONS OP WESTERN NORTH AMERICA.
THE EASTERN DESERT SCRUB.
LARREL\-FLOURENSIA ASSOCIATION.
This community consists primarily of Larrea mexicana, Prosopis juliflora,
and Flourensia cernua, though other species often play a dominant part in it,
as shown by the following table :
DominantA (total nxunber of
localities, 168).
No.
Halfahrub dominants.
No.
Larrea mexicana
110
110
97
31
26
15
15
16
14
7
5
Gutierrezia sarothrae
Microrhamnus ericoides
Zinnia pumila
38
9
7
5
3
T
6
5
1
2
Prosopis juliflora
Flourensia cernua
Yucca radiosa and macrocarpa.
Acacia greggii and constricta . .
Ephedra torreyana
Opuntia chlorotica
Opuntia phaeacantha
Parthenium incanum
Isocoma hartwegii
Atriplex canescens
Condalia lycioides
Fouquiera splendens
Koeberlinia spinosa
Krameria glandulosa
Chryaoma laricifolia
Psilostrophe cooperi
Opuntia arborescens
While any of the shrub dominants may occur alone, this is rarely the case,
even with the three chief species. In the great majority of cases, two of the
latter occur mixed in varying proportions, usually with a smaller quantity
of one of the lesser dominants. This is shown by the occurrence of the four
principal groupings, as follows:
Species.
No.
Species.
No.
Larrea-ProAopis . . .
75
67
Fiourensia-Prosopis
50
30
Larrea-Flourensia
Larrea-Flourensia-ProHopis . . .
Other important groupings are Acacia with Prosopis and Larrea, Atriplex
with Prosopis, and Yucca-Ephedra or either alone with Prosopis, or with
various mixtures of the primary dominants. A layer of undershrubs is more
or less constantly present. Usually this consists of Gutierrezia, less frequently
of Isocoina, Krameria, or Zinnia, or two or three of these may be mixed in
varying degree (plate 36).
This association occupies the levels above the saline valleys and playas to
altitudes of 3,500 to 4,000 feet, where it passes into grassy parks in which the
shrubs are secondary. It occupies trans-Pecos Texas, as well as a considerable
area northeast of the great bend of the Pecos River, adjacent Mexico, southern
New Mexico, and eastern Arizona. Two of the dominants, Prosopis and
Acacia, form an extensive community on the plain of the lower Rio Grande
and extend over much of the Panhandle region as a low open scrub in the
grassy plains.
Correlations and sequence. — The general correlation of the Larrea-Flourensia
scrub is with an annual rainfall varying from 16 inches along the Pecos to
8 inches in south-central and southwestern New Mexico. Over the same
area, the annual evaporation ranges from 40 to 60 inches. The distribution
CLEMENTS
Eastern Desert Scrub
PLATE 36
A. Larrea consociation, Stockton, Texas.
B. Larrea- Flourensia association, Pecos, Texas.
C. Larrea plain, Sierra Blanca, Texas.
THE EASTERN DESERT SCRUB. 169
of the rainfall is peculiar to this general region in that less than a third of the
total usually falls in the first six months, while July, August, and September
receive more than half. On the higher levels near the mountains. May and
June are marked by more rain and the climate there becomes adapted to
grassland. Since relatively high ranges occur at intervals of 50 to 100 miles
from the Davis and Guadalupe Mountains on the east to the Santa Catalina
and Whetstone chains on the west, it is evident why the desert scrub con-
stantly mixes and alternates with grassland throughout the region.
While factor studies of the dominants are lacking, their successional rela-
tions are brought into evidence repeatedly by changes in altitude, topography,
and soil. These have to do chiefly with water-content, but salinity must
frequently be taken into account as well. The basic sequence of the associa-
tion is shown by Prosopis, Flourensia, and Larrea, wherever ridges and valleys
occur. This is especially marked in the valley of the Pecos River from Fort
Stockton and Grandfall to the foothills of the Davis Mountains. The primary
sequence is Prosopis in the middle of the valley, a mixture of Prosopis and
Flourensia, in which Flourensia becomes more and more abundant until
Larrea appears as the slope begins, followed by mixed Flourensia-Larrea,
which becomes pure Larrea on the ridges or Larrea with sparse Flourensia
and Prosopis. More frequently, the valleys are shallower and poorly drained,
with Flourensia in the center, followed by a zone of Flourensia-Larrea on the
slope and of nearly pure Larrea on the ridge. In the case of valley washes,
where the soil is more or less sandy, Prosopis and Larrea exhibit a similar
relation from valley to ridge. This typical relation to water-content is also
found in sandy soils where Prosopis forms hummocks and dunes. As the soil
becomes more stable and the available water decreases, Flourensia enters and
finally Larrea, or where Flourensia is absent, Larrea enters directly. Of the
other dominants. Yucca radiosa and Acacia greggii most nearly resemble
Prosopis in their water use. The former has a wider margin of adjustment to
more xerophytic conditions, and the latter a narrower one. Yucca macrocarpa
is more xerophytic than Y. radiosa and is more often associated with Larrea
as a consequence. Ephedra torreyana makes much the same demands as
Prosopis and Yu^ca radiosa, often occurring in sandy soils with them, as well
as in gumbo valleys with Flourensia. Condalia and Koeherlinia usually occur
sparsely though generally in the harder soils. They have been seen but rarely
in dominant or pure communities, arid such cases were in small closed valleys
or "swags," often with a gypsum soil. Acacia constricta has in general some-
what higher water requirements than Larrea, while Fouquiera approaches
the latter closely in many places. Its preference, however, is for rocky slopes
in which the available water should be higher.
The undershrub dominants are all more xerophytic than the shrubs with
which they are associated. This is indicated by .their lower stature and the
location of their root-systems at a higher level. Gvtierrezia and Isocoma are
nearly equivalent and are regularly associated with Prosopis, or a mixture of
it with Yucca, Atriplex, or Acacia, usually in sandy soil. They are essentially
corresponding species, occasionally occurring together, but found for the most
part in their respective associations. Zinnia and Krameria are typical asso-
ciates of Larrea. Parthenium is found more frequently with Larrea, but
occurs in various mixtures of the three primary dominants.
170 CUM AX rORMATIONS OF WESTERN NORTH AMERICA.
Prosopis is the most tolerant of salinity, though practically all the dominants
possscss tills abiUty in a large measure. Prosopis occurs regularly with
Sporobolus atroide* over great saline flats, especially in the valley of the Pecos.
It is constantly associated with Atriplex canescens on sandy dunes and hum-
mocks throughout. Typical areas of great extent occur from Sierra Blanca
to H Paso along the Rio Grande, and northward through the Jornada del
Muerto and the Tularosa Desert. Prosopis also associates with Atriplex
canescens and A. polycarpa on alkaline plains and occasionaly thrives in saline
meadows of Distichlis spicata. Its ability to withstand high concentrations
is most conclusively shown by its intimate association with Spirostachys
occidentalis and Dondia moguini in the Pecos Valley. Flourensia and Ephedra
are both more halophytic than Larrea as a rule. In the pure gypsum soils of
the Pecos Valley, Larrea is the first shrub to enter in the drier areas, and
Condalia the first in the swales. Both of these are followed by Prosopis, and
this by either Flourensia or Acacia.
The serai sequence of Prosopis, Flourensia, and Larrea is confirmed by their
climatic relations in regions of greater rainfall, such as Texas. In the form of
savannah or forest-hke thicket, Prosopis occurs generally in the western half
of Texas under a rainfall of 20 to 30 inches. Flourensia first appears at about
20 inches, but does not become dominant until a rainfall of 16 inches is
reached. Larrea appears last at a rainfall of about 16 inches, where it quickly
takes rank as a dominant.
Prosopis also differs from Larrea and Flourensia is being a characteristic
dune-former, a habit doubtless related to its more mesophytic nature. Mes-
quite dunes and hummocks are a typical feature of the formation from the
Panhandle of Texas to the Salton Sea. They are due to the ability of Prosopis
to grow faster than the sand accumulates, a property almost whoUj'^ lacking
in both Larrea and Flourensia. It is shared in greater or less degree by
Atriplex canescens. Ephedra torreyana, Yucca radiosa, Artemisia filifolia, and
Dalea scoparia, with the result that one or more of these are usually asso-
ciated with Prosopis in such areas. The much wider range of the mesquite
is due to the fact that its sugary pods are eagerly eaten by animals, which
scatter the well-protected seeds. It suffers some disadvantage in that it is
often browsed by stock, while Flourensia is rarely eaten, and Larrea practically
never. This becomes a marked handicap where the kangaroo rats are abun-
dant, as they make their mounds in mesquite bushes almost exclusively and
feed upon both branches and roots.
SOCIETIES.
No study has yet been made of the seasonal aspects of the eastern desert
scrub and, an adequate treatment of its societies is impossible. Since the
majority are alike for both associations, a fair understanding of them may be
obtained from the list on page 176.
THE WESTERN DESERT SCRUB
LARREA-FRANSERIA ASSOCIATION.
Nature. — ^This association is regarded as the more typical one of the forma-
tion. The evidence of this is found chiefly in the larger number of dominants
and in the more extensive continuous areas Occupied by them. The western
scrub also exhibits much more of the traditional appearance of desert, due
CLEMENTS
Western Desert Scnih
PLATE 37
nc -
A. Jjirrcd consociation, Tucson, Arizona.
B. rrosopis con-ociation, San Pedro Valley, Arizona.
C. Parkinwnin torrcyaria and Acacia greggii, Tucson, Arizona.
THE WESTERN DESERT SCRUB.
171
largely to the abundance of cacti in it. In this respect it resembles closely
the deserts of Mexico, of which it is probably a continuation. At present
it Ukewise differs from the eastern type in general absence of grasses, though
this may be largely the work of animals. While Larrea is still the most typical
dominant, the community shows extensive differentiations in which it is
nearly or entirely lacking. However, it also appears to have a wider range of
adaptation and often becomes a shrub 10 to 15 feet tall in washes. This
seems to be connected with the greater abundance of tall shrubs or low trees,
such as Parkinsonian Olneya, and Dalea. As already indicated, a characteristic
feature is the great development of conmaunities of low winter annuals, the
many species of which cover the ground with a brilUant carpet (plate 37).
Extent. — The eastern hmits of the Larrea-Franseria community are indi-
cated by the Galiuro, Whetstone, and Huachuca Mountains in Arizona. It
extends northward in the valleys of the San Pedro, Gila, Salt, and Verde
Rivers to find its northern Ihnit along the mountains of central Arizona. On
the west the desert scrub occupies the Colorado Desert and reaches into south-
western Utah and southern Nevada, though greatly reduced in number of
dominants. In California it is the climax vegetation of the Mohave Desert
and Death Valley, though much of the area is covered with the halophytic
subclimax of Atriplex and related dominants. West of the Salton Basin
several of the dominants reach the lower slopes of the San Jacinto and Laguna
Mountains. Desert scrub is the most important association throughout
Lower California, while in Mexico proper it occurs as far south as Zacatecas
and San Luis Potosi. The occurrence of both Prosopis and Larrea southward
to Argentina indicates a still greater range for this or some related associa-
tions.
DOMINANTS.
Shrubs:
Larrea mexicana.
Prosopis juliflora.
Acacia constricta.
Parkinsonia microphylla.
Acacia greggii.
Opuntia fulgida.
Opuntia f. mamillata.
Opuntia spinonior.
Parkinsonia torreyana.
Parkinsonia aculeata.
Dalea spinosa.
Olneya tesota.
Cereua gisanteus.
Fouqtiiera splendens.
CeltiB pallida.
Opuntia versicolor.
Opuntia arhuscxila.
Condalia lycioides.
Condalis apathulata.
Simmondflia califomica.
Atriplex canescens.
Shrubs — continued.
Atriplex polycarpa.
Prosopis pubescens.
Yucca radiosa.
Koeberlinia spinosa.
Mimosa biuncifera
Ephedra trifurca.
Ephedra ncvadensis.
Salazaria mexicana.
Dalea emoryi.
Dalea schottii.
Lycium spp.
Cereus thurberi.
Adelia phyllarioides.
Holacantha emoryi.
Canotia holacantha.
Half shrubs:
Franseria dumosa.
Franseria deltoidea.
Itiocoma coronopifolia.
laoooma c. hartwegii.
Halfshrubs — continued.
Isocoma veneta.
Opuntia discata.
Opuntia chlorotioa.
Zinnia piunila.
Hymenoclea salsola.
Calliandra eriophylla.
Chrysoma laricifolia.
Lippia wrightii.
Baccharis wrightii.
Trixis californica.
Opimtia phaeacantha.
Opuntia engelmannii.
Encelia farinosa.
Encelia frut^scens.
Krameria glandulosa.
Hilaria rigida.
Psilostrophe cooperi.
Yucca baccata.
Gutierrezia sarothrae.
Bebbia juncea.
Parthenium incanimi.
In addition to the above, a large number of other shrubs, halfshrubs, and
succulents occur frequently but sparsely, or in occasional clan-like groups.
Others are dominant at higher levels, such as species of Agave, Dasyliriuniy
or at lower ones, Atriplex, Hymenoclea, etc. The relation of all of these is
either actually or potentially successional, or they are of minor importance
and can not be further considered in a brief account.
172 CLIMAX FORMATIONS OF WESTERN NORTH AMERICA.
Structure. — ^The general structure of the desert scrub is clearly revealed
by the color-tones, as seen in a bird's-eye view of one of the great intermoun-
tain valleys. Such a view of the Santa Cruz Valley from the Tucson Moun-
tains shows three clear differentiations of the scrub mass. The long dissected
bajada slopes are olive-green with Parkinsonian Cerens, Fouquiera, and their
associates. The flood-plains of the valley are vivid green with Prosopis and
Acacia, and the central mass on the general level of the plain is bronze with
Larrea. The courses of the streams are hiarked chiefly by Populus, Sapindus,
Frarinus, Juglans, and Celtis, while a nearer view reveals serai communities
of Hymenodea, Baccharis, and Chilopsis in the sandy washes and of Atriplex
and Dondia in saline areas. Finally, there is a striking inversion of the species
of the valleys, by which Prosopis, Acacia greggii, Parkinsonia torreyana,
Olneya tesota, and others are carried up the bajada slopes or up broad canyons
into the zones above.
As a consequence, the general zonation of the regions is as follows: (1) sub-
climaxes of the river-bed and salt-spots; (2) the valley community of Prosopis,
Acacia greggii, and Parkinsonia torreyana; (3) the central mass of the midland
plain, consisting chiefly of Larrea, often with much Acacia constricta; (4) the
community of bajadas and foothills, characterized by Parkinsonia micro-
phylla, Cereus, and Fouquiera; (5) the Prosopis-Acada areas of the canyons
and savannahs of the mountain ranges. The same zonal relations are seen
in miniature throughout the area wherever changes of soil, drainage, or eleva-
tion occur to modify the control of the dominants. As these features recur
constantly, owing to the more or less torrential nature of the rainfall, each
zone is much modified by the mingling or alternation of dominants which
normally grow above or below it. Such alternation is a regular feature of ,
the association and explains the variety and frequence of the groupings as
shown below (plate 38).
Groupings. — A special study has been made of the grouping of the major
dominants over the Tucson plain and the bajadas and foothills of the sur-
rounding ranges. The primary purpose was to throw light upon the degree
of equivalence of the various dominants, based upon Larrea as the final
dominant. It serves also to give a clear idea of the relative importance of the
different species, and the frequence and complexity of the various groupings.
The area covered is about 40 miles in length from the Santa Catalina Moun-
Species.
Larrea mexicana
Prosopis juliflora
Parkinsonia microphylla
Acacia (constricta, greggii) . . .
Cereus giganteus
Fouquiera splendens
Opuntia (fulgida, spinosior,
versicolor)
Olneya tesota
Atriplex (canescena, polycarpa)
Condalia lycioides
Celtis pallida
Simmondsia calif omica
Yucca radiosa
Dom-
Pres-
inant.
ent.
60
8
60
9
41
6
37
5
34
8
22
0
22
20
10
4
7
6
7
3
6
7
6
1
0
6
Species.
Koeberlinia spinosa
Isocoma coronopif olia
Franseria deltoidea.
Encelia farinosa
Zinnia pumila
Krameria glandulosa
Larrea-Prosopis
Larrea or Prosopis with Acacia
Larrea-Parkinsonia
Larrea with Cereus, or Fou-
quiera
Parkinsonia with Cereus, Fou-
quiera or both
Dom-
inant.
0
40
18
6
5
4
35
34
24
15
37
Pres-
ent.
4
4
4
2
1
2
10
7
7
CLEMENTS
Western Desert Scrub
PLATE 38
f^ t^
i
A. Lama and Fratisiria <lunio,sa, Ajo, Arizona.
B. Larrtn, Pronojris and Hilaria rigiiin, Ajo, Arizona.
C Encelia farinosa on lava lid^e, Ajo, Arizona.
THE WESTERN DESERT SCRUB. 173
tains on the north to the Santa Rita on the south, and about 30 miles wide
from the Rincons to the Tucson Range at the west. It was traversed in all
directions and the results are thought to be representative. The total number
of localities considered is 1 10.
The number of dominants in each grouping, irrespective of those of second-
ary importance, varies from 2 to 6, with the following frequency : two domi-
nants, 24; three, 28; four, 38; five, 14; six, 5.
Factor relations. — The wide adaptability of the desert scrub climax is shown
by its occurrence in a region where the rainfall varies from 2 to 16 inches. In
this respect it excels even the sagebrush formation. The desert scrub of Texas
and New Mexico is found in a rainfall of 7 to 16 inches. The western type has
a much wider range. In southeastern Arizona it occurs in a rainfall as high
as 12 to 14 inches, while in the Colorado Desert it is still dominant under a
rainfall of 2 to 3 inches. The evaporation is also much higher in the western
association. From April to September it ranges from 54 inches at Tucson to
71 inches at Calexico, in comparison with 40 to 54 inches in Texas and New
Mexico. The contrast would be even greater if the total annual evaporation
were considered, as should be the case with a community containing so many
evergreen or nearly evergreen dominants. The more xerophytic nature of the
climate is clearly reflected in the greater nmnber of cacti in the Larrea-Fran-
seria scrub, though this probably has a direct relation to winter temperatures
as well (Shreve, 1914 : 194). In so far as the leafy shrubs are concerned, the
lower rainfall and higher evaporation are compensated in large measure by
the distribution of rain during the year. In southeastern Arizona nearly
60 per cent of the rain falls during the period from April 1 to September 30,
and the dominant vegetation is grassland savannah, as already pointed out
for much of the area in southern New Mexico. The percentage of spring and
summer rain decreases rapidly across southern Arizona to become 30 per cent at
Yuma and 20 per cent at Calexico. The latter represents the typical winter
rainfall of California, which finds expression at the lower levels in the charac-
teristic sclerophyll chaparral. Thornber (1910; cf. Spalding, 1909 : 96) has
pointed out the relation of this difference of rainfall in eastern and western
Arizona to the abundance of winter annuals as well as that of grasses. He
also shows that there is a constant difference throughout the year of one-half
to one inch of rainfall between the desert scrub and the desert plains grassland
(1. c, 256).
While a number of quantitative studies have been made of the desert scrub
in the region of Tucson, those of Spalding (1909 : 91) are the only ones which
bear directly upon the comparative factors for different dominants or com-
munities. The curves showing the march of water-content from October 1907
to April 1908 are of the most significance. These are given for the Parkin-
sonia-Fouquiera community of Tumamoc Hill, the Larrea consociation of the
slope, the community of Parkinsonia torreyana and Acacia greggii in a wash,
and the Prosopis consociation of the flood-plain. These are in general agree-
ment with the topographic and successional evidence in that the hill and
flood-plains show the highest water-content and the slope and wash the
lowest. However, it seems certain that the Larrea slope or plain is typically
drier than the wash containing Parkinsonia, Acacia, and Prosopis, in spite of
the figures. This is clearly indicated by the author himself in his discussion
of conditions in the wash (1. c, 14). A comparison of the curves for the hill
174 CLIMAX FORMATIONS OF WESTERN NORTH AMERICA.
and the flood-plain are especially instructive. The former are regularly
higher, due partly to the fact that they were taken on the north slope, but the
two sets are sufficiently alike to furnish a ready explanation of the charac-
teristic inversion by which Prosopis and Acacia greggii in particular occur in
the foothills (plate 39).
Successional relations. — ^No quantitative studies have been made of the
actual or p>otential succession in the desert scrub climax. While the movement
is necessarily slow in a region so arid, there can be no question of the general
occurrence of succession in flood-plains, especially in salt-spots, dunes, and
washes, and in secondary areas. Even in what seem stable areas, the move-
ment toward the Larrea consociation as the final climax dominant is clear.
Spalding (1909 : 16, 30) has noted this tendency on Tumamoc Hill as well as
in the wash, and it can be discovered wherever topographic or biotic factors
produce bare areas or otherwise modify existing ones.
The type of succession is peculiar to desert. Succession is regularly meso-
tropic, I. e., developing in hydrophytic or xerophytic habitats which con-
stantly become more mesophytic to the final climax (Clements, 1916 : 182).
In the desert scrub the seres are all xerotropic, in that the earlier stages are
less xerophytic than the climax. This results in the sere being exceptional in
having a small number of stages and a slow rate of movement. Moreover,
while the topMDgraphic relations of erosion and deposition to the climax plain
are essentially as in ordinary succession, the climax itself is xerophytic. Con-
sequently the Larrea plain is to be regarded as the threefold baseline for
topography, climate, and succession, toward which all the others are tending
slowly but nevertheless surely. In a region where permanent streams and
lakes are all but impossible, the hydrosere is absent or is quickly converted
into a halosere (MacDougal, 1914). The latter begins in a soil more arid than
that of the climax, but its position seems normally to result in a habitat which
is less xerophytic, since Prosopis usually enters before Larrea. Apart from
this, the hill and valley communities are both less xerophytic than the
Larrea plains and hence show similar sequences.
Of the valley dominants, Prosopis is the least xerophytic. This is shown
by its form, which is often that of a tree, capable of forming continuous wood-
lands, and by its association with such mesophytic river-bank species as
Fraxinus, Sapindus, etc. Acaxn,a greggii follows Prosopis closely in its water
requirements, and is followed in turn by Condalia lydoides and Acacia con-
stricta. While their association is much less frequent, Olneya and Parkin-
sonia torreyana appear but little more xerophytic than Prosopis, and this is
likewise true of Dalea spinosa. The three lowland choUas, Opuntia fulgida,
0. f. mamillata, and 0. spinosior have a wide range of equivalence. In general
they are most abundant in the ecotone between Prosopis and Larrea, but
they extend well into both consociations, especially the latter. The three
cacti are often the dominants in Larrea plains on which subaerial processes are
active. Yucca, Ephedra, and Koeberlinia resemble Prosopis more nearly in
their demands, but the latter is often found in the lower Larrea levels also.
Atriplex canescens and A. polycarpa are regularly associated with Prosopis,
perhaps largely because of the ability of the latter to withstand salt.
The dominants of the foothills and the upper bajadas approach Larrea
in requirements, as indicated by the frequence of their association. Here the
CLEMENTS
Western Desert Scrub
PLATE 30
A. Cerens-Eiicelia in hiva ridge with Ldrnn below, Tucs>on, Arizona.
B. Parkinsonia microphylla and Cereus giganleus on foothills of Tucson Mountaias,
C. Fouquiera splendens consociation, Santa Rita Reser\'e.
THE WESTERN DESERT SCRUB. 175
sequence is nore difficult to determine because of the irregular topography
and the confusing effect of temperature. Moreover, the hotter and drier
southerly slopes are younger and less stable than the northerly ones, thus
further complicating the problem. In general, it may be said that Fouquiera
stands nearest Larrea, Cereus comes next, and Parkinsonia microphylla is
last. Though Parkinsonia mixes with Larrea in scores of places, this is largely
due to the wide adaptation of the latter.
The occurrence of the halfshrub dominants is correlated more or less closely
with that of the shrubs, and they exhibit a similar zonation. Isocoma is
habitually associated with Prosojris, but occurs also in the lower Larrea areas.
Opuntia discata is an associate of the cylindric Opuntias and hence has a wide
range. The most typical halfshrub associates of Larrea are Franseria dumosa,
Hilaria rigida, Krameria glandulosa, Zinnia puniila, and Psilostrophe cooperi.
Franseria deltoidea characterizes the Larrea-Parkinsonia ecotone, while
Encelia farinosa is typical of the Parkinsonia-Fouquiera community. Lippia
torightii, Chrysoma laridfolia, Parthenium incanum, and Bebbia juncea are
usually restricted to the latter also. Calliandra eriophylla is typical of the
foothill areas of Prosopis and Acacia and reaches its greatest abundance on the
Prosopis savannahs.
Root relations. — Cannon (1911) has made a comprehensive study of the
roots of desert plants, in which he recognizes three types of root systems. The
generalized tjT)e has the tap-root and laterals both well developed, while of
the two specialized types, one has emphasized the tap-root and the other the
laterals. The dominants with generaUzed root systems are Larrea, Prosopis,
Acacia, Parkinsonia, Fouquiera, Celtis, Lycium, Franseria, and Encelia.
Those with a well-developed tap-root are Condalia, Ephedra, and Koeberlinia.
Practically all the cacti have superficial roots with prominent laterals, though
the arborescent Opuntias approach the generalized type. As would be
expected, the roots of annuals are the most superficial, penetrating the soil
rarely more than 8 inches, and with the maximum development at about 2
nches.
In general, there is a tendency to form three layers of roots in the soil, the
uppermost of annuals, followed closely by the root-layer of the cacti, and a
much broader deep-seated layer composed of tap-root systems, with or without
prominent laterals. The tendency to place roots at different levels minimizes
the direct competition of the dominants, as Cannon has pointed out (1. c, 64).
This is especially effective in the case of the superficially rooted annuals and
cacti. The necessary compensation for the period of seasonal drouth is
secured by drouth evasion in one and drouth resistance in the other. The
wide spread of laterals in many of the dominants explains the characteristic
open spacing of the desert scrub and the bush-like habit. The effect of a
larger water supply is aeen especially on the flood-plain, where Prosopis,
Acacia, and Parkinsonia often become trees, and even Larrea may grow to a
height of 15 feet or more. This is shown even more strikingly along the mar-
gins of roads, where the shrubs become remarkably vigorous as a result of the
increased runoff and the freedom from competition. This effect is universally
exhibited by the halfshrub, Isocoma, in which the plants along the roadside
are often twice as tall as those in the midst of the community. Its response
was especially graphic in 1918, when the roadside plants leafed out fully while
those of the mass were still leafless (plate 40).
176 CLIMAX FORMATIONS OF WESTERN NORTH AMERICA.
SOCIETIES AND CLANS.
The desert scrub possesses an extraordinary wealth of herbaceous species.
The great majority of these are-annuals, owing to the existence of two rainy
seasons separated by periods of drought. There are in consequence two
clear-cut growing seasons which may be regarded for the present as aspects,
though closer study may show that these are themselves divisible into aspects.
The two seasons are winter-spring and summer. Since they depend wholly
upon the incidence of the corresponding rains, the dates of beginning and
closing are extremely variable. After the severe drought of 1917, the first
winter annuals did not appear until March and the seasonal communities
were exceptionally dwarf, sparse, and short-lived. The continuance of the
drought brought about an almost complete failure of the summer annuals and
many of the herbaceous perennials. The occurrence of unusual rains in the
following autumn led to the first appearance of the most important annuals
by the beginning of December, and the ensuing development was exception-
ally complete and vigorous.
Ptrennialt:
Allionia incarnata.
Aster apinosus.
Bahia absinthifolia.
Baileya multiradiata.
Boerhaavia viscosa oligadena.
Delphinium scaposum.
Euphorbia albomarKinata.
Euphorbia capitellata.
Franseria tenuifolia.
Gutierresia microcepbala.
Hoffmannseggia drepano-
carpa.
HofTmannsegfcia jamesii.
HofTmannsegKia stricta.
Pappophorum wrightii.
Pentstenion wrightii.
Philibertella hartwegii heteio-
phylla.
Rumex hymenosepalus.
Betaria composita.
Sida lepidota sagittifolia.
Solanum elaeagnifolitun.
Sphaeralcea cuspidata.
Teucrium cubense.
Triodia mutica.
Triodia pulchella.
Verbena ciliata.
Long-lived Annuals:
Atriplex bracteosa.
Atriplex elegans.
Atriplex texana.
Chenopodium fremontii.
Eriogonum al)ertianum.
Eriogonum deflexum.
Eriogonum trichopodum.
Long-lived Annuals — continued.
Euphorbia preslii.
Helianthus annuus.
Helianthus petiolaris.
Heterotheca subaxillaris.
Lepidium thurberi.
Machaeranthera parvifolia.
Machaeranthera tanacetifolia.
Verbesina encelioides.
Wislizenia refracta.
Summer Annuals:
Amarantus palmeri.
Aristida americaaa.
Bouteloua aristidoides.
Bouteloua polyatachya.
Chloris elegans.
Cladothrix lanuginosa.
Eragrostis neo-mexicana.
Eragrostis pilosa.
Eriochloa punctata.
Kallstroemia brachystylis.
Kallstroemia grandiflora.
Leptochloa viscida.
Panicum hirticaulum.
Pectis papposa.
Pectis prostrata.
Physalis angulata linkiana.
Trianthema portulacaatrum.
Winter Annuals
Actinolepis lanosa.
Amsinckia intermedia.
Amsinckia tessellata.
Astragalus nuttallianus.
Baeria gracilis.
Bowlesia lobata.
Winter Annuals — continued.
Chaenactis stevioidea.
Cryptanthe angustifolia.
Cryptanthe pterocarya.
Daucus pusillus.
Eremiastrum bellidioides.
Eschscholtzia mexicana.
Evax caulescens.
Festuca octoflora.
Cilia filifolia.
Harpagonella palmeri.
Lappula redowakii.
Lepidium lasiocarpum.
Leaquerella gordoni.
Lotus humiatratua.
Lupinus leptophyllua.
Malacothrix glabrata.
Malacothrix aonchoides.
Maivastrum exile.
Mentzelia albicaulis.
Microseris linearifolia.
Monolepis nuttalliana.
Orthocarpus purpuraacens.
Pectocarya linearis.
Pectocarya penicillata.
Phacelia crenulata.
Phacelia distans.
Phalaria caroliniana.
Plagiobothrys arizonicus.
Plantago fastigiata.
Plantago ignota.
Polypogon monspeliensia.
Salvia columbariae.
Sophia inciaa.
Sophia pinnata.
Streptanthus arizonicus.
Thelypodium la.siophyllum.
Veronica peregrina.
The more important herbs of the scrub are grouped in the following list
under four heads, viz, perennials, long-lived annuals, summer annuals, and
winter annuals. The first alone constitute true societies, the annuals repre-
senting the initial stage of a subsere which advances no further because of the
CLEMENTS
Western Desert Scrub
PLATE*
A. Fouquiera subclimax in Larrea plain, Tucson, Arizona.
B. Opuntia fulgida consociation, San Pedro \"allcy, Arizona.
C. Opuntia discata, fulgida, and spinosior, Tucson, Arizona.
THE CHAPARRAL CLIMAX. 177
annually recurrent drought of late spring and early summer. Hence, they are
strictly pioneer socies and families, but by virtue of their annual recurrence
they may well be treated as societies of annuals. In addition to these, there
are the herbaceous communities of dunes, washes, and salt-spots, and of dis-
turbed areas, which are successional in nature. A large number of these serai
annuals are identical with those already mentioned. Finally, there are a num-
ber of perennial grasses, some of which have entered from the desert plains in
contact with the scrub at its upper limit, and others which may be regarded
as relicts of a former savannah condition of certain portions of the desert
scrub. Such are Muhlenbergia porteri, Aristida divaricata, and Bouteloua
rothrockii in particular. The lists given above are contributed by Professor
J. J. Thornber and are based chiefly upon studies in southern Arizona, though
the majority of species extend throughout the association.
THE CHAPARRAL CLIMAX.
QUERCUS-CEANOTHUS FORMATION.
Nature. — The chaparral formation is characterized by low shrubs of the
same vegetation-form and for the most part of similar systematic relationship.
In comparison with forest, it is xeroid in character, but distinctly less so than
sagebrush and desert scrub, which resemble it in physiognomy. It is not
dwarfed woodland, similar to that found at timber-line. It not only lacks
the habit of "elfin" wood, but the characteristic species, with the exception
of those of Quercus, do not belong to tree genera. In fact, there is little more
reason for regarding chaparral as dwarfed forest than for treating sagebrush
or Larrea desert as such. It represents a distinct ecological type, intermediate
in character and requirements between grassland or scrub desert, i. e., sage-
brush and mesquite on the one hand and forest or woodland on the other.
This is supported by its almost universal occurrence in front of forest or
around it wherever it meets grassland or desert. While timber-line scrub has
a general resemblance to chaparral at the first glance, it differs essentially in
habitat, fioristic, and physiognomy, and belongs to a wholly different category.
The term chaparral is in general use throughout the West and Southwest
for scrub or thicket. It is most commonly applied to the mesquite of Texas
and the Adenostoma-Ceanothus association of CaUfornia, and less frequently
to the Quercus-Cercocarpus community of the Rocky Mountains region. In
spite of their general resemblance to chaparral, this term seems never to be
used for sagebrush or for the creosote-bush desert {Larrea consociation).
Naturally, it is in common use in those regions where Spanish influences are
still felt, and it disappears gradually to the northward long before the com-
munity itself has disappeared. In restricting the word to one formation and
in broadening it to cover all the associations of that climax, the thought has
been to follow the major usage and at the same time to definitize it. As a
result, all the associations of this formation from the Missouri Valley to the
Pacific Coast are designated as chaparral on account of the essential eco-
logical unity discussed below. A further refinement has been made in dis-
tinguishing cUmax and subclimax chaparral, both in the East and West. As
indicated later, these are so closely related successionally and have so many
points in common that a distinct term for the subcUmax chaparral seems both
unnecessary and unwise.
178 CLIMAX FORMATIONS OF WESTERN NORTH AMERICA.
Unity of the chaparral formation. — In view of the exceptionally wide range,
the floristic unity of the chaparral is remarkable. The major dominants
belong to 10 genera, namely, Quercus, Ceanothus, Cercocarpus, Rhus, Prunus,
Amelanchier, Symphoricarpus, Rosa, Arctostaphylus, and Shepherdia. With
one or two exceptions, all of these occur as dominants in both associations,
and in the subclimaxes as well. The relationship is even better shown by such
species as Rhus trilohata, Prunus demiesa, Arctostaphylus pungens, Cerco-
carpus parvifolius, and Ceanothus cuneatus, which are dominants in both asso-
ciations. Still other species, such as Amelanchier alnifoUa, Holodiscus dis-
color, Symphoricarpus albus, and Philadelphus gordonianus occur as dominants
in one and are of secondary importance in the other. It is also a striking fact
that of 25 genera which play a considerable part in the formation, all but two
belong to the order Rosales or to the related Acerales and Fagales. This is
reflected in the appearance or physiognomy of the formation. The domi-
nants not only belong to the same vegetation-form, viz, shrubs, but also to
the same general growth-form. Instead of being tall shrubs, as a rule prac-
tically all of them assume the bush-form or produce several ste ns. The
latter is a consequence of the nearly universal habit of forming root-sprouts
to which the chaparral owes much of its success, especially in competition
with grassland. The regular occurrence of several dominants in mixture also
explains the general uniformity in height and habit, which so often gives
chaparral the appearance of a densely woven green carpet.
One evident difference between the Rocky Mountain and the Coastal
chaparral Ues in the fact that the former is deciduous, the latter evergreen or
sclerophyll. This difference is probably to be correlated with winter as the
most xerophytic period for the former and summer for the latter. While this
distinction is characteristic, it is not thorough and must not be given too much
importance. The most representative species of the Rocky Mountain chapar-
ral is Quercus undulata, which exhibits deciduous forms in the north and ever-
green ones in the south. Likewise, Cercocarpus parvifolius is a more northern
deciduous species and C. ledif alius a southerly evergreen one, but in spite of
this, both are found together over the foothills of the Wasatch Mountains
and elsewhere. Moreover, the evergreen Arctostaphylus pungens and Ceano-
thus cuneatus greggii are found from northern Arizona to central Utah in
intimate association with Quercus, Rhus, and Amelanchier. A similar condi-
tion is encountered in California, where most of the chief dominants are ever-
green, but they are often associated with deciduous species, such as Cerco-
carpus parvifolius, Holodiscus discolor, Prunus demissa, and others. As a
consequence, it must be recognized that there is nothing ontradictory in
having deciduous and evergreen dominants in the same ormation and even
in the same association.
Climatic relations. — Geographically, chaparral is a western formation,
reaching its typical development on the foothills of the Rocky Mountans
and its numerous secondary ranges, and on those of the Sierra Nevada, Cas-
cade, and Coast Ranges of the Pacific Slope. This relation is strikingly shown
by its appearance in the Black Hills of South Dakota and the Wildcat Moun-
tains of western Nebraska at a distance of several hundred miles from the
main range. This is naturally to be explained by the climatic relations. As
THE CHAPARRAL CLIMAX.
179
the typical zone between forest and grassland or desert, chaparral has an
intermediate climatic position. It resembles forest in the wide range of rain-
fall conditions in which it occurs, and only a general correlation with the
latter is possible. In the Rocky Mountains the chaparral Ues between 15 and
20 inches of rainfall. In southern California it ranges from 10 to 20 inches,
and in northern CaUfornia and Oregon it occurs on dry slopes under 50 to 60
inches. It seems clear that chaparral is possible in 10 inches of rainfall only
where the proximity of the ocean cuts down evaporation, and at 50 inches only
where insolation greatly increases it. Here, even more than in sagebrush and
grassland, it will be necessary to determine water-content, evaporation, and
especially transpiration relations before adequate correlations can be estab-
lished (fig. 7).
3i 1
Glen Eyrie, Colorado
16 in.
n
1
oli ill
C
Mt.Tamalpais, California
29 111.
n
1
0 .. I I a 1
3
o
Durango, Color
10 in.
■
ado
1
0
1
Or
K
Saata Barbara, California
18in.
0
2
I
0_
1.. .1
3-
0
3oldier Saminit, Utah
11 in.
1
0
1
.lllll
5
San Diesro, California
11 in.
1
q
o
1
n-
I1....1I
Fio. 7. — Monthly and total rainfall for representative localities in the asaociationa of
the chai>arral climax.
Origin and succession.— The chaparral, Uke the grassland and desert scrub,
is largely southwestern iu origin. This would be expected from its general
cUmatic relations as well as from its greater development in the south, and
its uniform shading-out to the northward along both mountain systems.
With the exception of a few genera such as Prunus and Rosa, all of the domi-
nants are either southwestern or have reached their chief development in the
Southwest. Thus, it seems probable that the chaparral has moved north-
ward from an original southern center and has differentiated into two associa-
tions as a consequence of finding ecesis most successful along the two great
mountain axes.
180 CLIMAX FORMATIONS OF WESTERN NORTH AMERICA.
The successional relations of the chaparral are expressed chiefly in the
xerosere and the subsere. The primary succession is found usually on rock
outcrops and especially on talus shdes, and exhibits the same essential stages
in the various regions. The subsere is much the most frequent and important,
especially from the practical side. It is regularly caused by fire, and it is
probable that all chaparral areas, as they exist to-day, have resulted from fire.
This does not mean, however, that all tjhaparral was originally developed in
response to fire. Like grassland, it originated in response to a xeroid climate
and followed the latter in its extension into new regions. Like grassland,
also, it was able to develop its natural dominance after fire much more quickly
than forest could, with the result that fire has constantly increased the area
of chaparral at the expense of the forest. As a consequence, chaparral con-
sists of two distinct types developmentally. The original and most typical is
climax chaparral, corresponding to a climate whose water efficiency is lower
than that demanded by forest. The most recent type is subclimax chaparral,
which occupies a zone of variable width about the climax proper. It is not
only the result of the destruction of the original forest by fire, or clearing and
fire, but also owes its persistence to the periodic recurrence of these disturbing
processes. While it is necessary to trace the process of succession in each
region to determine the nature of the chaparral with complete certainty, the
indicators left by the denuding agent as well as the development itself are
usually sufficient to permit a trustworthy decision. The distinction between
climax and subclimax chaparral is of the first importance in the treatment of
a region, and this matter is further discussed on a later page.
Range and extent. — Chaparral does not dominate great areas, as is the case
with grassland and sagebrush. While it occurs in considerable bodies under
the most favorable conditions, it is generally found in relatively narrow and
often much interrupted belts along the edge of forest formations. Conse-
quently, while the formation has an exceedingly wide range, it posesses rela-
tively little continuity, and hence is little impressive over much of its broad
extent. It is poorly developed along the line of contact between the deciduous
forest and grassland, attains fair expression along the base of the main range
of the Rocky Mountains, becomes massive in the Wasatch Mountains of Utah,
and reaches its fullest expression in California.
As a climax, the chaparral is found from Wyoming and the Black Hills of
South Dakota southward along the Rockies into Texas and Mexico. It
extends across Utah, New Mexico, and Arizona along the mountain ranges.
It is greatly broken up by the mass of the sagebrush and desert scrub fonna-
tions in Nevada and in the Mohave and Colorado Deserts, but it reappears on
the mountain ranges of southern California and the Sierra Nevada. Chaparral
is to-day perhaps the most characteristic association found in California, but
it rapidly loses its importance with increasing rainfall and the consequent
development of forest. In northern California and in Oregon it becomes
limited to the drier slopes more and more and finally becomes a mere subclimax
or completely disappears.
The chaparral dominants belong to 30 genera, the majority of which range
throughout the formation. This is particularly true of Quercus, Cercocarpus,
Ceanothus, Rhtis, Prunus, Amelanchier, Symphoricarpus, Rosa, Opulaster,
Purshia, Ribes, and Cornus. A striking group of genera is limited to the
Southwest or finds its chief development there. This consists of Peraphyllum,
THE CHAPARRAL CLIMAX. 181
Fendlera, Fallugia, Cowania, Coleogyne, Rohinia, and Garrya, all but the last
belonging to the rose order. Of 35 species of dominants more than half range
from Saskatchewan, Manitoba, or the Dakotas to Texas or New Mexico,
thence to Arizona and California on the southwest and to Oregon, Washing-
ton, or British Columbia at the northwest. While only a few are major domi-
nants throughout this wide area, all are sufficiently important to show the
basic unity of the formation and the close relationship of the various associa-
tions, both climax and subcUmax.
Structure of the formation. — The studies of the last six years have revealed
several different regions in which the chaparral type of vegetation reaches
more or less complete expression. These are the Rocky Mountains, the
Pacific Coast, the Southwest, the Northwest, the Missouri Valley, and Texas.
In the last two, as in the moimtains of the Pacific Coast, the chaparral is
subclimax. These conmiunities do not belong to the formation proper and
are considered with it chiefly because of their contiguity and general relation-
ship. They are properly associes of a climax forest. Of the four climax
maxima, two stand out clearly, namely, the Rocky Mountain and Coastal.
The other two have been regarded tentatively as associations during the
course of the field work. In order to determine their real rank as well as the
relationship of the several communities, a summary has been made of all the
groupings of dominants recorded from 1900 to 1918, as well as in 1893, when a
botanical reconnaissance was made along the Missouri and Niobrara Rivers.
The summary comprises approximately 500 locaHties, of which 206 are in
the Rocky Mountain region, 39 in the Northwest, 38 in the Southwest, 45 on
the Pacific Coast, and 164 in the subclimax chaparral of the grassland forma-
tion. The occurrence of the dominants in the five regions is shown in the
table on page 182. No accoimt is taken here of the CaUfornian subclimax,
which is essentially different.
Grouping of dominants.— The unity of the formation is readily seen from
the distribution of the genera especially. The first 7 genera occur in all the
five areas, 5 others occur in three, and 6 are found in two. Three of the
species are present in all five communities, 4 others in four of the areas, 5 in
three, and 9 in two. The differentiation of the maxima is revealed by the
presence of certain genera and species in one area and not in another, as well
as by their frequence. For example, Adenostoma and Quercus dumosa occur
only in the Coast chaparral, while Ceanothus cuneatus and Arclostophyltis
pungens are of the first importance in it alone. Likewise Fallugia, Cowania^
Coleogyne, Rohinia, and Fendlera are limited to the Southwest and the southern
part of the Rocky Mountain association. The differentiation of the subclimax
community is shown by QuerciLS macrocarpa, Symphoricarpus occidentalis,
Rosa arkansana, Elaeagnus argentea, Fraxinus viridis, Prunus americana, and
Rhits glabra, while a less distinct maximum in the Northwest is indicated
by Purshia, OpuUister, Philadelphus, Holodiscus, and Peraphyllum.
The relationship of these five maxima is revealed by the frequence of the
dominants as shown in the table. The italic numbers indicate those which
occur in at least 10 per cent of the total number of localities visited. The
Rocky Mountain chaparral exhibits 12 dominants which occur in 10 or more
localities, and of these 8 are equally important in the Northwest, while but
2 are absent in the latter. The southwestern chaparral has 6 of the 12 most
182 CUMAX FORMATIONS OF WESTERN NORTH AMERICA.
frequent dominants of the Rocky Mountain community. It also shows 6
other important dominants, 5 of which, Cercocarpus ledifolius, FaUugia,
Cotoania, Coleogyne, and Arctostaphylus pungens, are of greater significance
than in the Rocky Mountains, while one, Ceanothus cuneatus greggii, is largely
absent in the latter. A comparison of the subclimax chaparral with the
Rocky Mountain likewise shows a close relationship ; 4 of the chief dominants
of the one are equally important in the other, and all but 2 of the 13 are present
DOMINANTS.
Species.
Rocky
Mountain.
South-
west.
North-
west.
Sub-
climax.
Pacific
Coast.
Total
206
38
39
144
45
Quercus
127
126
1
26
g6
3
49
5
29
11
11
11
11
2
6
6
7
6
1
Quercus undulata
Quercus macrocarpa
Quercus duniosa
Quercus virens
15
2
2
61
63
28
66
■■•■-■■
4
16
Cercocarpus
109
107
2
68
6S
7A
»8
1
10
2?
16
7
13
4
10
4
3
3
6
16
16
11
Cercocarpus parvifolius ....
Cercocarpus ledifolius
Rhus trilobata
Prunus demissa
Amelanchier alnifoUa
Symphoricarpus albus, etc . .
Symphoricarpus occidentalis
Rosa acicularis
2
IS
Ro«a arkansana
Ribea cereum
11
1
5
16
14
5
18
3
2
2
P
6
Ribes aureum
Pn-aphyUum ramosissimum .
Opul aster opulifolius
Holodiscus discolor
Purshia tridentata
1
P»
P
P
P
P
1
10
4
4
11
6
17
8
2
"h
6
Pbiludelphus gordonianus. . .
Robinia neoinexicana
Fallugia paradoxa
3
Cowania mexicana
Coleogyne ramosissima
Adenostoma f asciculatiun . . .
21
26
6
24
6
Ceanothus cuneatus
4
Ceanothus divtiricatus
Arctostaphylus pungens. . . .
Arctostaphylus tomentosa . .
P
6
Shepherdia argentea
Elaeagnus argentea
6
1
16
53
12
21
11
24
Cornus stolonifera
Fraxinu" viridi*'
Rhus glabra
5
3
Prunus americana
'Merely present.
in the Rocky Mountain region. A lesser degree of resemblance is found
between the Coast and the Rocky Mountain chaparral, though their forma-
tional relationship is clear. Of the 6 most typical dominants of the former,
but 1 occurs in the latter, while the most characteristic dominant of the
Rocky Mountains, QiLercus undulata, is completely lacking, unless indeed it
is represented by Q. garryana. On the other hand, the 2 communities possess
8 important dominants in common (plate 41).
CLEMENTS
Petran Chaparral
PLATE 4t
/fr
A. Quercu^-Rhtis-Cercocarpus association, Manitou, Colonido.
B. Detail of same, Qturnm and Rhus in foroRround, Circocarpus behind, Manitou, Colorado.
C. Circffcarpus pamfoliiui consoi.iation, Chugwater, Wyoming.
THE PETRAN CHAPARRAL. 183
Associations. — A careful consideration of the above facts has led to the
conclusion that the chaparral formation consists of but two climax associa-
tions. These are the Petran or Cercocarpus-Quercus association composed
chiefly of Quercus undulata, Cercocarptis parvifolius, Rhus trilobata, Prunus
demissa, Amelanchier alnifolia, Symphoricarpus albus, Peraphyllum, and
Fendlera, and the Coastal or Adenostoma-Ceanothus association, consisting
principally of Adenostoma, Ceanothus cuneatus, Ardostaphylus tomentosa, and
Qiiercus dumosa. The fragmentary chaparral of the Northwest is clearly a
shading-out of the Rocky Mountain association, since the chief difference is
the absence of Quercus undulata^ Cercocarpus parvifolius, and Fendlera in the
former. The chaparral of the Southwest clearly shows its relationship to the
Rocky Mountain association in the abundance of Quercus, Cercocarpus,
Rhu^, Prunus, and Amelanchier. In addition, it possesses two dominants
from the Coastal association, viz, Ardostaphylus pungens and Ceanothus
cuneatus, and exhibits certain genera more or less peculiar to it, such as Fal-
lugin, Cowania, and Coleogyne. The latter, however, are gradually finding
their way into the Rocky Mountain area. As a consequence, this type of
chaparral is perhaps best treated as a transition between the Rocky Mountain
and Coastal associations, but with a much closer relationship as a rule to the
former. In some of the mountains of southern Arizona, however, the chaparral
consists chiefly of Ceanothus and Ardostaphylus, and is clearly an extension
of the Coastal type. In the following discussion, the chaparral of the North-
west and Southwest are considered as more or less differentiated portions of
the Cercocarpus-Quercus association. Because of their general resemblance
to them, the subclimax types are treated with the corresponding climax, the
Rhu^-Prunus community of the Missouri Valley with the Rocky Mountain,
and the Rhus-Ceanothu^ subclimax of the Pacific Coast with the Coastal
association. The oak chaparral of Texas resembles that of the Missouri
Valley in its general relation to the eastern forest, but its dominants are
derived from both the East and West.
THE PETRAN CHAPARRAL.
CERCOCARPUS-QUERCUS ASSOCIATION.
Nature and extent. — The Rocky Mountain or Petran chaparral consists
almost exclusively of deciduous shrubs in more or less intimate mixture. It
ranges in height from 2 to 20 feet, but attains its most characteristic expres-
sion at 5 to 10 feet. Under optimum conditions, it is massive in nature, cover-
ing many square miles with the density of a forest cover. Because of its
intermediate position between forest and other formations and its occurrence
in the diverse topography of foothills, it is much interrupted as a rule. The
total number of dominants is large, and at least several regularly occur in any
one grouping. They agree closely in vegetation-form and in the characteristic
habit of root-sprouting, though some produce sprouts much more readily
than others. In growth habit, they are normally bushy shrubs, though the
range in sijse is considerable. Quercus undulata and Prunus demissa often
become small trees; Rhus trilohala may form a gigantic bush 20 feet high and
25 to 30 feet in diameter, while Cercocarpus parvifolius is usually a slender
erect shrub. It is interesting to note that all the dominants belong to the rose
order, with the exception of Quercus, Rhus, and Symphoricarpus.
184 CLIMAX FORMATIONS OF WESTERN NORTH AMERICA.
The Cercocarpus-Quercus association reaches its best development in
Colorado, northern New Mexico, and eastern Utah. Its extreme limits on the
east are the Black Hills of South Dakota and the Wildcat Mountains of
western Nebraska, and the mountains of western Texas. On the south and
west it runs through southern New Mexico and Arizona, extending more or
less into northern Mexico. It is usually poorly developed in Nevada, and
thence ranges much interrupted through Idaho and eastern Oregon to British
Columbia and Alberta. Chaparral is fairly developed in southern Wyoming,
but is reduced northward to disappear largely in the mountains of central
Montana, where its place is taken chiefly by aspen, or by subclimax chaparral
from the East. Its altitude Umits are of the widest. In Colorado and New
Mexico, the Quercus consociation is found well-developed in dry southern
slopes as high as 9,000 feet, and small outposts exist at somewhat higher alti-
tudes. These, however, are subclimax and will sooner or later yield to mon-
tane forest. The lowest limit is about 4,000 feet, but subcUmax fragments
are frequently found at much lower levels in the Northwest. The association
attains its best development between 5,000 and 8,000 feet and as a climax is
practically restricted to this zone.
Contacts — Along the eastern edge of the Rocky Mountains, the chaparral
is in contact below with the grassland association, touching the mixed prairie
in the north, and the short-grass plains in the south. The ecotone is often
several miles wide, and is usually marked by a striking alternation of the two
associations. On the south and southwest, the contact is usually with the
desert plains, more rarely with desert scrub. In the West, it is typically with
sagebrush, and in the Northwest with sagebrush, or bunch-grass prairie. The
upper contact is with pinon-cedar woodland or with the montane forest,
particularly the more xeroid Pinus ponderosa consociation or the aspen con-
socies. Its relation to woodland is puzzling at first, since it occurs both above
and below the latter. The probable explanation is that climax chaparral
regularly occurs below climax pinon-cedar woodland. The latter is often well
developed as an open subclimax on lower rocky ridges and slopes at altitudes
where it will ultimately be replaced by chaparral or sagebrush. This upper
ecotone is frequently greatly confused in dry rocky country, where one or
more dominants of the sagebrush, chaparral, woodland, and montane forest
may be found in intimate mixture or alternation.
In comparing the rank of the various dominants, it must be borne in mind
that the figures indicate frequence rather than abundance. As a matter of
fact, however, there is so much correlation between the two in the case of
chaparral dominants that the one is a fair indication of the other. This is
especially true of the most massive communities found in the central and
southwestern areas. In these more typical areas, Quercus undulata is by far
the most important dominant, chiefly as the variety gambelii. Cercocarpus
parvifolius is a close second, with Rhus and Prunus approximately half as
important. Amelanchier is secondary to Quercus and Cercocarpus, .but its
frequence must be interpreted in the light of its absence over most of the
eastern slope of the Rocky Mountains, where the other four dominants are
so typical, and its correspondingly greater abundance on the western slope.
It is significant that the four most important dominants are the same for the
first two areas. Prunus demissa loses its rank in the Southwest, but regains
CLEMENTS
A. Quercus-Cercocarpus-Fallugia chaparral, Milford, Utah.
B. Same showing contact with sagebrush, Circocarpus kdifolius in foreground, Milford,
Utah.
THE PETRAN CHAPARRAL.
185
it in the Northwest. In the latter the absence of Quercus and Cercocarpus
and the importance of Purshia suggests a greater differentiation from the
central chaparral mass. However, this seems readily explained by the remote-
ness from the latter and by a less favorable northern climate, which find
expression in the fragmentary character and the sabclimax tendency of the
northwestern chaparral (plate 42).
DOMINANTS.
Central Rocky Mountains (206 localities) :
Quercus undulata 126
Cercocarpus parvifolius 107
Amelanchier alaifolia 74
Rhus trilobata 68
Prunus dcmissa 58
Symphoricarpus albus 23
Peraphyllum ramosissiinuin 24
Fendlera rupicola 18
Holodiscus discolor 15
Purshia tridentata 14
Ribes cereum 11
Ro^a acicularia 10
Philadelphus gordonianus 5
Opulaster opulif oliua 6
Robinia neomexicana 3
Southern Area (38 localities) :
Quercus undulata 26
Cercocarpus parvifolius 16
Rhus trilobata 13
Amelanchier alnifolia 10
Fallugia paradoxa 10
Cercocarpus ledifolius 7
Cowania mexicana 7
Arctostaphylus pungens 6
Prunus demissa 4
Symphoricarpus albus 3
Coleogyne ramosissima 3
Ceanothus cuneatus 3
Northweaiem Area (39 localities) :
Purshia tridentata 17
Prunus demissa 16
Amelanchier alnifolia 16
Rosa acicularia 13
Opulaster opulifolius 11
Symphoricarpus albus 11
Philadelphus gordonianus 8
Holodiscus discolor 5
Rhus trilobata 5
Ribes cereiun 5
Peraphyllum ramosissimum 4
Cercocarpus ledifolius 3
Groupings. — The number of dominants is so large and their equivalence so
close that they occur in the most varied groupings. In any particular locality,
the number of associated dominants is usually 4 or 5, and often 6 or 7 ; 3 is also
a frequent grouping, but communities of 1 or 2 dominants are usually
found only near the limits of the association, where the latter is more or less
fragmentary. While nearly all of the most important dominants do occur in
pure communities, these are usually of limited extent and regularly alternate
with other dominants, except toward the edge of the association as already
noted. The actual groupings are so numerous and varied that a detailed sum-
mary of them possesses little significance. In the central mass, Qitercus, Cer'
cocarpus, Rhus, and Prunus constitute the groundwork in central and eastern
Colorado and New Mexico. In western Colorado and adjacent regions, these
four are still of the first importance, but Amelanchier, Fendlera, PeraphyUum,
and Cercocarpus ledifolius often become equally important. These may mix
with the first four or replace one or more of them. This condition persists
into the Southwest, where Fallu^a and Cowania enter to further compUcate
the grouping, and Arctostaphylus and Ceanothus appear to serve as an indica-
tion of the transition to the Coastal association. In the Northwest, the asso-
ciation is so interrupted and fragmentary that definite groupings are not
obvious. In general, the ground plan seems to be furnished by Amelanchier,
Prunus, Opulaster, Philadelphus, and Symphoricarpus, though with almost
infinite variation in detail. In the drier regions, Amelanchier, Purshia and
PeraphyUum mix and alternate in varying degree.
186 CLIMAX FORMATIONS OF WESTERN NORTH AMERICA.
Equivalence of dominants. — The large number of dominants, their close
equivalance and wide range, and the almost complete absence of quantitative
results make the task of determining their factor relations peculiarly difficult.
This task is further complicated by the ease and intimacy with which the
dominants mix. In spite of this, however, the topographical and successional
relations are sufficiently evident to indicate their general response to physical
factors. Because of the wide range of climatic conditions, this must be done
for each area rather than for the association as a whole. The basic relation is
determined by the five great dominants, Quercus, Cercocarpus, Amelanchier,
Rhus, and Prunus, which have had some factor and successional study in
Colorado and Utah. Since one or more of these is found in practically all the
important groupings, they serve as basing-points for all the other dominants.
Prunus demissa is the most mesophytic of the five dominants, as is shown
by the regular occurrence along streams and in ravines and by its taller habit.
Rhus trilobaia comes next in its water requirements, followed closely by Quer-
cus undulata gambelii. The latter not only stands midway in the series, but
it is also able to adapt itself to a wider range of conditions than the others,
locally at least. This explains its greater frequence in spite of its range being
the most restricted of the five. Qv£rcus undvJata is somewhat more xeroid,
as its evergreen leaves and southern distribution indicate. The two are so
frequently mixed where their ranges overlap that the difference in their
requirements must be slight. Cercocarpus parvifoliv^ and Amelanchier
alnifolia are the most xerophytic and to an almost equal degree. To a large
extent thay are corresponding species, the former being most typical east of
the Continental Divide, the latter west. As a rule, Cercocarpus occupies the
newer or drier areas, though their relative position is sometimes reversed. Of
the remaining dominants, Rohinia neomexicana is somewhat more mesophytic
than the oak, as is shown by its fondness for ravines and valleys. This is
likewise true of Symphoricarpus albus and Rosa adcularis, which often form
a layer in oak thickets especially. Opulaster opulifolius is rather more meso-
phytic than oak and frequently forms a layer in forests of Pseudotsuga which
the oak can not enter. While all of the others occur mixed with Quercus,
this is less true of Purshia tridentata and Ribes cereum, which are to be regarded
as the most xerophytic. Holodiscus and Philadelphus are slightly more
xeroid than oak. Fendlera and Peraphyllum have a wide range of adjustments.
As tall shrubs, they often mix with oak on north exposures and at the base of
slopes, but usually they are nearly equivalent to Amelanchier and Cercocarpus.
As would be expected, the other dominants of the southwestern chaparral
are typically xerophytic. This is indicated by their origin and distribution
as well as by their generally evergreen habit. From the evidence derived from
groupings as well as from the habitat, Cercocarpus ledifolius is nearly equi-
valent to the oak, and Fallugia paradoxa and Cowania mexicana to Cerco-
carpus parvifolius, though all are slightly more xerophytic. Arctostaphylus
pungens and Ceanothus cuneatus are more xerophytic than C. parvifolius, while
Coleogyne seems the most xerophytic of all. It forms pure communities on
shallow soil on rocky cliffs, but since it rarely mixes with the other dominants,
its relative position is uncertain.
The dominants of the northwestern chaparral have already been considered,
but it may be helpful to relate them to each other, since both Quercus and
THE SUBCLIMAX CHAPARRAL.
187
Cercocarpus parvifolius are lacking. Prunus and Rhus are the most meso-
phytic, Purshia the most xerophytic. Amelanchier, Holodiscus, Philadelphus,
and Opulaster are more or less intermediate between these two extremes,
while Cercocarpus ledifoUus, Peraphyllum, and Ribes are nearly equivalent
to Purshia, as is shown by their frequent occurrence as outposts in dense sage-
brush.
SOCIETIES.
From its nature and position, the societies of the mountain chaparral are
largely derived from the climax communities in contact with it. The majority
of these come from the grassland, but a number enter also from sagebrush,
woodland, and even from the montane forest. The societies of the sunny
intervals between the bushes are chiefly those of the ecotone between chaparral
and grassland or sagebrush. As a consequence, it is necessary to list here only
those which grow in the shade of tall clumps or of a more or less continuous
chaparral cover. Some of these have been derived from woodland or forest,
but the majority are shade-forms of grassland and sagebrush subdominants.
A few of them are grasses, Elymus triticoides, Agropyrum caninum, Bromus
ciliaius, Stipa comata, etc., though by far the greater number are herbs. Low
shrubs, such as Symphoricarpus occidentalis, Rosa adcvlaris, Rhv^ radicans,
Pachystigma, and Berheris often form a characteristic layer. Ruderal annuals
are frequent also, perhaps because the denser clumps afford them protection
from grazing.
Vernal Societies:
Anemone patens.
Senecio aureus.
Arenaria fendleri.
Euphorbia montana.
Aragalus lamberti.
Erysimum aspenim.
Pachylophus caespitosus.
Draba aurea.
Pentstemon coenileus.
Arabia holboellii.
Comandra lunbellata.
Mertensia lanceolata.
Scutellaria reidnosa.
Tradescantia virginiana.
Vicia americana.
Erigeron glandulosus.
Litbospermum multiflorum.
Delphinium scopulorum.
Allium reticulatum.
Lappula texana.
Smilacina stellata.
Thalictrum fendleti.
Vernal Societies — continued.
Heuchera parvifolia.
Thermopsis montana.
Estival Societies:
Geraniiun caespitosum.
Chenopodiimi fremontii.
Polygonum convolvxilus.
Polygoniun douglasii.
Calochortus gimnisonii.
Potentilla arguta.
Campantila rotundifolia.
Pentstemon secundiflonis.
Pentstemon barbatus.
Pentstemon unilateralia.
Pentstemon strictus.
Galium boreale.
Erigeron flagellaris.
Gilia aggregata.
Achillea millefolium.
Monarda fistulosa.
Castilleia integra.
Castilleia miniata.
Thelesperma gracile.
Estival Societies — continued
Potentilla gracilis.
Erigeron asper.
Senecio fendleri.
Lupinus pusillus.
Sisymbrium incisum.
Nepeta cataria.
Epilobium paniculatum.
Lactuca pulchella.
Salvia lanceolata.
Bidens tenuisecta.
Erigeron canadensis.
Hedeoma drummondii.
Serotinal Societies:
Artemisia gnaphalodes.
Artemisia frigida.
Brickeliia grandiflora.
Kubnia glutinosa.
Solidago speciosa.
Solidago missouriensis.
Gymnolomia multiflora.
Aster bigelovii.
Mirabilis oxybaphoides.
THE SUBCLIMAX CHAPARRAL.
EHUS^UERCUS ASSOCIES.
Nature. — The subclimax chaparral is a fragmentary community of stream
valleys and bluffs, due to the shading-out of the eastern forest as it meets the
prairies and plains. As a consequence, it is rarely massive, but extends as
narrow belts for hundreds of miles along the upper bluffs of the Missouri and
its main tributaries. Farther west along the lesser streams, it forms the typi-
cal vegetation of the narrow valleys. It is more or less developed in the broken
188 CLIMAX FORMATIONS OF WESTERN NORTH AMERICA.
topc^^phy of the Bad Lands and pine ridges of western Nebraska and the
Dakotas, and it reaches westward into the valleys of the foothills in Colorado
and New Mexico. A similar subclimax occurs in central Texas, where the
oak forest meets the prairies. On the Edwards Plateau the dwarf form of the
live-oak, Qitercus virens, mingles with the shin-oak, Quercus undulata, of the
Rocky Mountains to form what is probably a climax community, closely
related to the Cercocarpus-Quercus association, if not to be regarded as a part
of it (plate 43).
The dominant species are typically shrubs for the most part, but several
important ones are trees which become dwarfed in the more xerophytic condi-
tions of the prairies and plains. This is the case with the bur-oak {QtLercus
macrocarpa) , live-oak (Q. virens), ash {Fraxinus viridis), plum {Prunus ameri-
cana), hawthorn {Crataegus cocdnea), hackberry {Celtis ocddentalis) , box-
elder (Acer negundo), elm (Ulmus americana) , and linden (Tilia americana) .
A large number of the trees which reach the western edge of the deciduous
forest exhibit the same tendency, but they extend little beyond the limits of
the forest proper. The majority of the dominants are bushes or bushy shrubs
from 3 to 10 feet high. They resemble those of the climax in producing root-
sprouts readily and consequently in taking rapid and complete possession
where forest is cleared or subclimax grassland is overgrazed.
Extent and contacts. — Subclimax chaparral appears along the western bor-
der of the deciduous forest and through valleys in the prairies from Manitoba
and Saskatchewan to northern Mexico. It extends westward to the Rocky
Mountains from Montana to Texas, and comes into repeated contact with
mountain chaparral in the upper valleys of the North and South Platte, the
Arkansas, Canadian, and Pecos Rivers. Throughout the eastern edge of this
area, it marks the ecotone between the forest and grassland. It is naturally here
that it finds its best expression, in accordance with the fact that the dominants
are either trees of the forest, or shrubs and bushes which constitute a lower
layer or play the rdle of 'serai dominants. The subclimax occurs generally
throughout the grassland formation in valleys and sandhills where the water-
content is above the normal. It is best developed in the eastern portion of the
prairies and decreases steadily toward the west, persisting only in the larger
valleys, on buttes, or in sandhills. It is everywhere surrounded by grassland,
except where it comes in contact with mountain chaparral, or with the pine
or aspen community in the Black Hills or other outlying montane regions.
DOMINANTS.
Spedes.
Rank.
Species.
Rank.
Symphoricarpua occidentalis .
Prunus demissa
65
63
61
53
47
29
15
16
12
11
Ribes cereum
4
5
28
24
21
16
8
8
3
3
Quercus undulata
Rhus trilobata
Amelanchier alnifolia
Prunus americana
Elaeagnus argentea
Fraxinus viridis
Quercus macrocarpa
Shepherdia argentea
Quercus virens
Ribes aureum
Xanthoxylum americanum . .
Corylus americana
Celtis occidentalis
Rhus glabra
Prunus besseyi
CLEMENTS
Subclimax Chaparral
PLATE 43
A. Rhus glabra consocies, Peru, Nebraska.
B. Quercus virens and undxdata, Edwards Plateau, Sonora, Texas.
THE SUBCLIMAX CHAPARRAL. 189
The relative rank of the dominants is indicated by the figure placed after
each one, indicating the observed frequence. These apply chiefly to the central
and western portions of the area, and are less representative of the eastern and
southeastern edge.
A number of other shrubs and bushes play some part, but most of these are
secondary or incidental. A few will doubtless take their place finally as domi-
nants. They are especially well represented in sandhill areas, such as those of
Nebraska, Kansas, and Oklahoma. The most important of these are Yucca
glauca, Artemisia JUifolia, Ceanothus ovatiLS, Salix humilis, and RhiLS radicans.
Sambucus canadensis and Cephalanthus ocddentalis are more or less hydro-
phytic shrubs which persist with the usual dominants for some time. Comua
asperifolia, C. amomum, and Corylus rostrata are layer dominants which some-
times occur outside the forest, while the shrubby forms of Q. breviloha and
Cerds canadensis, which occur in Texas, are probably to be regarded as true
dominants.
Groupings. — Owing to the fragmentary nature of the conmiunity, many of
the dominants may occur in pure stands. This is most characteristic of the
bushes, such as Symphoncarpus, Rosa, Elaeagnus, Ceanothus, etc., which make
the closest approach to the grasses in their requirements. The shrubs and the
shrub-forms of the trees demand a higher water-content, and this permits the
mixing or intimate alternation of several dominants. Two dominants have
been found associated in 35 cases, three in 26, four in 29, and five, six, or seven
in 45 instances. As a result, the various groupings are too numerous to be
indicated, but the composition of the most common is indicated by the relative
sequence of the first 10 or 12 dominants. In the southern portion, Quercus
virens is the chief species, often with Q. undulata or Q. breviloha and more or
less Celtis, Cerds, Rhus, and Berheris trifoliata.
Relations of the dominants. — The general sequence and factor relations of
many of the dominants have already been indicated. The subclimax chapar-
ral possesses a peculiarly wide range of adjustment, as suggested by the great
variation in the extent and complexity of the communities and the size of the
plants. Moreover, while it finds fair expression as far west as the isohyete of
20 inches, this is usually possible only where the evaporation is low (as toward
the north) or the water-content high (as in sandhills and broken plateaus).
As would be expected from its relation to forest, its best development obtains
between the lines of 30 and 40 inches of rainfall. The explanation of its con-
stant recurrence throughout the grassland climax is found partly in the higher
water-content of valleys, sandhills, and escarpments, and partly in the com-
petition relations between shrubs and grasses. It is highly probable that
shrubs and trees establish themselves in grassland during the wet phase of the
climatic cycle and are then able to persist during the dry phase by virtue of
their deeper root-systems. This appears to be the general explanation of
both tree and scrub savannah (Chap. VI) and the fragments of subclimax
scrub bear a similar relation to the dominance of the grasses. Once estab-
lished, such clumps of shrubs are practically permanent, since they can be
destroyed only by repeated fires or by the hand of man.
While the shrubs modify the air and soil conditions in each thicket, their
growth is still controlled by the climatic factors, more or less affected by the
190 CLIMAX FORMATIONS OF WESTERN NORTH AMERICA.
competition of the grasses. This becomes controlling in the case of both
propagation and reproduction and makes clear why the spread of a particular
clump or the beginning of a new one depends upon the recurrence of wet
phases, in which the upj^er layer of the soil contains more water than the
grasses need. The size and continuity and the height of the shrubs reflect the
water relations with much accuracy and are in close accord with the gradual
decrease of* rainfall to the west. This relation is naturally disturbed or
obscured by fires and grazing, though it is rarely hidden by them. Repeated
fires confine or destroy the shrubs, while grazing reduces the water require-
ments of the grasses and correspondingly increases the growth and spread of
chaparral. This is obviously not true in the case of browsing animals, such as
goats.
SOCIETIES.
The societies of the subclimax chaparral are derived wholly from the forest
or grassland. Practically none of these societies are peculiar to it, though some
of those derived from the grassland are more or less characteristic, owing to
their increased height or abundance in the shade. Among the important
woodland species are Fragaria virginiana, F. vesca, Viola cucullata, Galium
aparine, G. boreale, Aralia nudicaulis, Smiladna stellata, Sanicula marilandica,
Aster levis, Heliopsis scabra, Urtica gracilis, and Elymus virginicus. From the
grassland have entered Poa praiensis, Monarda fistulosa, Vicia americanay
Anemone canadensis, A. cylindrica, Oxalis stricia, Ldthospermum hirtum,
PotentiUa arguta, Teucrium canadense, Lepachys columnaris, Artemisia gna-
phalodes, Solidago canadensis, S. rigida, and others.
THE COASTAL CHAPARRAL.
ADENOSTOMA-CEANOTHUS ASSOCIATION.
Nature and extent. — The Coastal or Pacific chaparral differs from the Petran
in consisting chiefly of evergreen or sclerophyll dominants. One of the four
major dominants, Quercus dumosa, is imperfectly evergreen, and about 20 per
cent of the minor dominants are deciduous. This association is regularly
much more massive and continuous than that of the Rocky Mountains. This
is true, however, only of California, where the chaparral reaches its best
expression, and toward the north and southeast the community is similarly
interrupted. Apart from the fact that the one is typically deciduous and the
other typically evergreen, the two associations resemble each other closely
in the form, height, and general behavior of the dominants and the essential
character of the conMnunity. The Coastal association has been more subject
to fire and its responses to this agency are correspondingly emphasized. It is
also unique in passing gradually into a very similar but distinct subclimax
chaparral typical of the montane zone.
The Coastal association is best developed on the Coast and cross ranges of
middle and southern California and in northern Lower California. Although
reduced in species, it is still an important conmiunity in northern California
and Oregon, but beyond this it is represented by a single species and is very
fragmentary. It extends eastward to the lower slopes of the Sierra Nevada
and thence to southeastern California and adjacent Nevada and Arizona.
Here it is reduced to Ceanothns cuneatus greggii and Ardostaphylus pungens,
CLEMENTS
Coastal Chaparral
A. Cliaj anul hills und 8agel)ru.sh vallry, Pine \allfy, California.
B. Adenoatonia-Ceanothus association, Descanso, California.
THE COASTAL CHAPARRAL. 191
which range to southern Utah, western Colorado, southern New Mexico,
trans-Pecos Texas, and Mexico, where they blend with the Petran association.
The general altitudinal range of this chaparral is from sea-level to 5,000 to
7,000 feet, but the actual Umits vary greatly with the region and the slope.
The normal upper limit is rarely above 5,000 feet (plate 44).
DOMINANTS.
Adenostoma FAScicxji-A'nnn. Abctostaphylus manzanita. Heteromeles arbutifoua.
CEANOTHTTS CUNEATTJS. ARCTOSTAPHTLUS PTJNOENS. DeNDROMECUM RIOIDUM.
ArCTOSTAPHTLUS T0MENT08A. ARCT08TAPHTT.U8 BICOLOR. ErIODICTYXJM CALIFORNICTTM.
QxrERCTTB DUM08A. RhamntjS crocea. Adenostoma SPARSIFOUXJM.
CeaNOTHTB DIVARICATUS. RhaMNUS CALIFORNICA. PrUNTJS lUClFOUA.
CeaNOTHUS 80REDIATU8. RhUS raTEGRIFOLIA. PrUNTJS DEMI8SA.
CEANOTHrS DENTATU8. RhU8 DIVERSILOBA. CercOCARPCB LEDIFOLITJS.
Ceanothtb hir8uti:8. Rhus latjrina. Amelanchier alnifoua.
CeaNOTHUS VERRCC08U8. RhTJ8 OVATA. HoLODI8CX;8 DISCOLOR.
ARCTOSTAPHTLUS OLAUCA. CERCOCARPUS PARVIFOUUS.
This Ust is in essential agreement with the more complete list of Cooper
(1919) for the CaUfomia chaparral. However, a number of species of Umited
range have been omitted. Simmondsia calif arnica is thought to belong more
properly to the desert scrub and the position of Adolphia calif ornica is uncer-
tain. Eriodictyum californicum is the typical dominant in bums and other
disturbed areas, but is included because of its frequence.
More than two-thirds of the dominants Usted are confined to CaUfomia and
Lower California. Of the four major dominants, Ceanothus cuneatus and
Arctostaphylus tomentosa extend to Oregon and British Columbia, respec-
tively, while of those of considerable importance, ArctostaphyliLS jmngens,
Rhamnus californica, R. crocea, Cercocarpus parvifolius, and Amelanchier
alnifolia extend through Arizona into the Petran association, where the last
two become major dominants.
Groupings. — The number of groupings is large and only a few of the most
conmion can be indicated. The four major dominants frequently occur in
pure stands of considerable size, and this is sometimes true of other important
dominants as well. The general rule, however, is a mixture of several species,
usually 5 or more. Adenostoma is the chief dominant from Lake Coimty
southward in California, usually associated with several of the following:
Arctostaphylus tomentosa, A. glauca, Ceanothus cuneatus, Quercus dumosa,
Heteromeles arbuiifolia, Cercocarpus parvifolius, and Rhamnus californica^
several of which may become more important locally than Adenostoma. The
latter drops out beyond Trinity County, and Ceanothus cuneatus and Arc-
tostaphylus tomentosa form the regular groupings as far as northern Oregon,
where the former disappears. Rhus diversiloba occurs with them frequently
and Cercocarpus, Amelanchier, Purshia, Holodiscus, and Philadelphus are
increasingly associated with them to the northward. In the San Gabriel
mountains of southern California, Adenostoma, Quercus dumosa, Ceanothus
divaricatus, Arctostaphylus, and Cercocarpus are the most important domi-
nants, while in the neighboring San Bernardino Range the grouping is prac-
tically the same, but with Cercocarpus much more important (Leiberg, 1900 :
419, 439). On San Jacinto Mountain, Adenostoma fasciculatum and A. sparsi-
folium constitute 50 to 75 per cent of the chaparral below 5,000 feet, with
192 CLIMAX FORMATIONS OP WESTERN NORTH AMERICA.
Ceanothus divaricatus, Quercus dumosa, and Cercocarpus parvifolius as their
most abundant associates, and a dozen or more of less importance (Leiberg,
1900 : 465; Hall, 1902 : 17). Practically the same grouping occurs through
the Laguna and Cuyamaca Mountains to the coast about San Diego. The
chaparral of Lower CaUfornia is composed chiefly of both species of Adenos-
toma, Ardostaphylus glauca and pringlei, Cercocarpus parvifolius, and Ceano-
thus divaricatus (Goldman, 1916 : 330):
Throughout southern California generally, Adenostoma fasciculatum mixes
and alternates at the lower levels and on drier areas with Artemisia cali-
fomica, Salvia mellifera, Salvia apiana, or Eriogonum fasciculatum, the domi-
nants of the Coastal sagebrush association. This is more xerophytic than the
chaparral, and is subclimax to it, a relation which Cooper (1919) has empha-
sized.
Factor and serai relations. — In an intensive study of the habitats of sub-
climax oak forest and the chaparral, Cooper (1919) has reached the following
conclusions:
"As to soil: Humus in the chaparral is very scanty, but in the forest is
abundant — nearly 2 per cent by weight in the surface layer and considerable
to the depth of 1 meter. In water-content there is large difference during the
rainy season, the forest having the greater amount. At this time the surface
layers are most important, since the major part of the absorbing roots are con-
tained therein. It is here, too, that the water-content differences mainly show
themselves; at the depth of 1 meter such being practically negligible. As the
dry season advances, water-content values in both conamunities and at. all
depths converge, and at its culmination they are all very close together and the
correspondence is rendered still more striking by comparison with the wilting
coefl&cient in each case. In brief, there is notable difference in the actual
amount of water available, but at the critical period conditions are about
equally severe in both communities. In water-retaining capacity the only
noteworthy feature is the relatively high value in the surface soil of the forest
community, due to humus. As to soil temperature, the comparative march is
the reverse of water-content; the values are closely similar in the wet season
but widely divergent in the dry, the chaparral being much the higher.
"As to atmospheric factors: Rainfall, cloud, fog, and wind may be dismissed
as inmaaterial to the present local problem. The light impinging upon a leaf
of the foliage canopy is much greater in chaparral than in forest, because of the
fewer obstacles to its transmission, and reflection and diffusion from the
light-colored soil surface. The intensity in the shade is considerably less
beneath the forest canopy, both absolutely and proportionally. The fact that
the shade intensity beneath Ardostaphylus is practically the same as in the
forest indicates that the leaf character is determinative — the sparse needle
foliage versus the broad leaves of the other shrubs and the trees. Tempera-
ture and relative humidity data are unsatisfactory, but their effects relative
to the present purpose are largely included in evaporation. The differences
in this factor, though not strikingly great, are constant throughout the year,
the Adenostoma chaparral being the highest and the Ardostaphylus chaparral
intermediate. This conclusion is drawn from the values obtained at the top of
the vegetation. The rate at the surface of the ground does not show differ-
ences of import to the problem in hand.
"Our conclusion, then, is that the fundamental distinguishing difference
between the two broad-sclerophyll chmaxes — their continuing cause, so to
speak — ^is in the water balance and its variations, whatever the indirect factors
THE WOODLAND CLIMAX.
193
influencing it; that its importance is equally divided between wet and dry
seasons, the greater excess of supply over loss in the forest during the growing
season explaining the size and luxuriance of the plants living there, and the
higher evaporation rate in the chaparral during the dry season, with equally
severe soil-moisture conditions, accounting for the absence of mesophytic
species in that habitat."
SOCIETIES.
The winter rainy season of the Coast region causes a corresponding early
development of societies and necessitates a readjustment of the aspects.
Because of favorable temperatures, societies appear in southern California as
early as January and the first aspect attains its maximum in February or
March. In order to maintain the usual seasonal relations, this is regarded as
the prevernal aspect. It is followed by a late spring or vernal aspect, and this
by one in which summer and autumn relations are more or less combined.
With few exceptions, the societies listed are perennial. Some of them bloom
through more than one aspect, but these are listed in the first one in which
they appear. A large number of annuals occur, especially in southern Cali-
fornia, but these are either members of subsere communities, or they are
desert annuals, most of which have already been given under the desert scrub.
It is practically certain that some of the societies listed below have been
derived from the original Stipa grassland, but the exact determination of these
must await further study.
Prevernal Societies:
Biodiaea capitata.
Brodiaea congesta.
Brodiaea grandiflora.
Brodiaea minor.
Sisyrinchium bellum.
Eriogonum compositum
Eschscholtzia californica.
Delphinium parryi.
Sidalcea malviflora.
Viola pedunculata.
Sanicula bipinnata.
Sanicula bipinnatifida.
Dodecatheon clevelandii.
Castilleia foliolosa.
Wyethia glabra.
Wyethia helenioides.
Vernal Societies:
Calochortus luteus.
Calochortus venustus.
Calochortus splendens.
Vernal Societies — continued.
Hosackia glabra.
Pentstemon heterophyllus.
Pentstemon azureus.
Lupinus formosus.
Lathyrus splendens.
Lathyrus vestitus.
Astragalus crotalariae.
Astragalus leucopsis.
Eriophyllum confertiflorum.
Eriophyllum lanatum.
Phacelia ramosissima.
Castilleia affinis.
Delphinium hesperium.
Gnaphalium bicolor.
Gnaphalium decurrens.
Polygala californica.
Haplopappus linearifolius.
Eriogonum nudum.
Oxalis comiculata.
Agoseris retrorsa.
Agoseris grandiflora.
Vernal Societies — continued.
Hypericum concinnum.
Scrophularia californica.
Convolvulus occidentalis.
Paeonia brownii.
Wyethia angustifolia.
Corethrogyne filaginifolia.
Galium andrewsii.
Lomatium tomentosum.
Estival Societies:
Artemisia heterophylla.
Achillea millefolium.
Solidago californica.
Gutierrezia sarotbrae.
Senecio douglasii.
Zauschneria californica.
Verbena proatrata.
Verbena stricta.
Opuntia engelmannii.
Opuntia basilaris.
THE WOODLAND CLIMAX.
PINUS-JUNIPERUS FORMATION.
Nature. — The woodland formation consists of small trees capable of form-
ing a canopy and hence of constituting a real though low forest. A number of
reasons combine to make it the most difficult of all formations to delimit and
to characterize. The first of these lies in the ability of practically all the
dominants to vary from trees 30 to 50 feet high to shrubs of 10 to 20 feet, and
in some cases to bushes of less than 10 feet. As trees they often give the
194 CLIMAX FORMATIONS OF WESTERN NORTH AMERICA.
appearance of being integral parts of the forest communities in which they
occur, while in the form of shrubs and bushes they are equally at home in
chaparral. The consequence is that the same species may appear as an impor-
tant if not dominant constituent of chaparral, woodland, and forest, and its
proper rdle becomes very difficult of determination. As a community, the
woodland occupies fairly narrow limits of altitude, and hence becomes massive
only on great upland plateaus, such as the Mesa Verde. In general, it occurs
on hillsides and mountain slopes in regions of rough topography. As a con-
sequence, it not only lacks mass and often continuity as well, but it is also
more or less obscured by admixture with dominants from the zones above and
below. This is emphasized by the character of the dominants. Where the
oaks are abundant, they give the woodland the appearance of belonging to
the chaparral, or of constituting an oak savannah, while the pinon and cedar
aline it rather with the forests of yellow pine and fir. However, the chief
source of confusion lies in the ability of all the dominants, but of the cedar^
especially, to invade rocky areas, largely as a result of the readiness with
which their fruits are distributed by rodents and birds. As a consequence,
an open chaparral-like type occurs throughout the West from Texas to Cali-
fornia and from Mexico to Montana. It agrees with the chmax woodland
only in the presence of one or two of the dominants, but differs from it in
habitat, structure, and development. In some regions, it will pass into the
climax, but as a rule it is an anomolous subclimax stage which yields to chap-
arral, sagebrush, or forest.
Typically, the woodland consists of small trees 20 to 40 feet high, belonging
to the three genera, Junipertts, Pinus, and Quercus. While these vary widely
in leaf character, they agree in being evergreen and xerophytic. They form
fairly dense crowns and in favorable situations make a continuous canopy
and a fairly uniform shade. The term woodland was apparently first applied
by the Forest Service, and is used to include all areas in which pifton and cedar
are characteristic. In the present case, woodland is used only for the climax
proper, consisting of cedar, pines, or oaks variously mixed in forests of low
stature. About such climax areas are often much wader ones in which one of
the dominants constitutes a grassland or scrub savannah.
Range and extent. — ^The woodland formation is essentially southwestern
in extent. It finds its best expression as a climax on the high plateaus of the
Colorado Basin, but it occurs from the Davis and Guadalupe Mountains of
western Texas through northern Mexico to Lower California. It extends
northward along the foothills in New Mexico and Colorado to southwestern
Wyoming, and then westward through Utah and Nevada to northern Cali-
fornia. Over by far the greater part of this vast area it forms a more or less
continuous belt along the mountain ranges, broadening out into extensive
forests only where tablelands of median altitude permit. The pifion-cedar
association is much the most extensive as well as the most typical, while the
oak-cedar community is restricted to southwestern Texas, southern New
Mexico and Arizona, and northern Mexico, and the pine-oak to California.
The cedar ranges far beyond the climax region, forming characteristic com-
munities on rocky slopes and escarpments from Scott's Bluff and Pine Ridge
'In view of the divergence in the botanical use of cedar and juniper for various speoiea of
Junipenu, cedar haa been preferred as repreiienting the common usage in the West.
THE WOODLAND CLIMAX.
195
in western Nebraska northward into Saskatchewan and westward to Oregon.
It also occurs frequently with chaparral and scrub on the Edwards Plateau
in Texas.
Unity of the formation. — As has already been indicated, the geographic
unity of the woodland climax is less than in any other western formation.
This is necessarily the case because of its regular occurrence on the lower
levels of mountain ranges and plateaus. As a consequence, it is characteris-
tically fragmentary, though consistent in being generally southern and at
middle altitudes of 7,000 to 8,000 feet. Climatically, it is intermediate between
chaparral and sagebrush on the one hand and the montane forest on the other.
The average rainfall is 15 to 20 inches and the average evaporation about 20
to 25 inches. The summer temperatures are high and the winters moderate
for the most part, though snow lies for some time over most of the climax
regions (fig. 8).
Trinidad, Colorado
17 in.
ill
Grand Canyon, Arix
26 in.
11
1
Ft Huacliuca
Arizona
17 in.
Ill
ll
Redbluff, California
26 in.
Ll...
Fio. 8. — Monthly and total rainfall for representative localities in the associations of
the woodland climax.
Floristically, the woodlands show a high degree of unity. The dominants
all belong to three genera, Pirnis, Juniperus, and Quercus. While the number
of minor species or varieties is large, amounting to 19, the actual species are
but 8. The most important of these are Pinus edvlis, Juniperus califomica,
and J. ocddentalis. These three with their varieties range throughout the
region, and one or the other occurs more or less regularly in each association.
The subdominants are relatively few, but it is significant that Rhus, Ceano-
thus, CercocarpurS, Purshia, etc., are found over the major portion of the forma-
tion.
Ecologically the formation is essentially uniform in its composition, con-
sisting of small trees with evergreen leaves. While the latter are present in
three forms, scale, needle, and broad leaf, it seems clear that these are ecologi-
cally equivalent or nearly so. The constant mixture of cedar and pifion in
the central association leaves no doubt of their essential equivalence, though
the scale-leaved cedar is clearly the more xerophytic. The same is true of the
southern association of cedar, pifion, and oak, and apparently also of the
California association of digger pine and oak. In all of these communities,
the dominants have marked ability to adjust themselves to more xerophytic
conditions by becoming shrubby or by growing in an open stand. A direct
196 CLIMAX FORMATIONS OP WESTERN NORTH AMERICA.
and characteristic consequence of this is the ahnost universal production of
mixed communities, in which grassland, chaparral, or sagebrush play an
important or controUing part. Practically all the dominants are intolerant
of shade, and hence they never constitute a secondary layer in the montane
forest of the zone above.
No special study of the successional relations of woodland has been made as
yet. Throughout the climax area, as well as beyond it, open shrubby woodland
appears relatively early on rocky slopes 'or hills, forming a subchmax to wood-
land proper or to montane forest, or being displaced by scrub or grass as the
habitat develops. The climax woodland may replace grassland, sagebrush,
or chaparral, and may in its turn be displaced by yellow pine or other domi-
nants of the montane forest at the upper edge of its zone.
In origin, the woodland is uniformly southern and largely Mexican. Firms
edvlis and Juniperus monosperma have their centers in Colorado, Utah,
Arizona, and New Mexico, though they extend into Texas and Mexico.
Pinus monophylla and Juniperus utahensis are confined almost wholly to
Utah, Nevada, northeastern Arizona, and eastern California. P. cemhroides
and J. pachyphloea are chiefly Mexican, extending into Arizona, New Mexico,
and western Texas. The oaks are all Mexican, with the exception of Quercus
douglasii and Q. wislizenii, which are almost exclusively CaUfomian. They
range to central Arizona, New Mexico, and western Texas. Juniperus
scopulorum is by far the most widespread of the dominants, as would be
expected from its close relationship to the eastern J. virginiana. It occurs
from central Nebraska to Washington and from British Columbia to the
Mexican boundary, while J. occidentalis ranges from Washington to the border
of southern California. The limits of Pinus sdbiniana lie wholly in Cahfornia,
from near the northern boundary southward to the Tehachapi. Of the 19
species and varieties which comprise the dominants of the formation, prac-
tically all but Juniperus scopulorum and J. occidentalis find their northern
limits below the forty-second parallel, 11 are predominantly Mexican, 4 have
their center on the Colorado plateaus, and 2 are CaUfomian.
The above account indicates clearly the differentiation which has occurred
in the formation. The greatest number of dominants still occurs in the region
of the Mexican boundary. The most uniform development of the formation
is on the Colorado Plateau, while the most specialized area is found in Cali-
fornia, as a natural consequence of the desert and mountain barriers.
Structure of the formation. — The dommants are as follows:
Juniperus californica. Juniperus sabinoides. Quercus emoryi.
Juniperus californica Juniperus virginiana Quercus reticulata.
utahensis.l scopulorum. quercus reticulata
Juniperus occidentalis. Pinus edulis. arizonica.
Juniperus occidentalis Pinus edulis monophylla. Quercus reticulata
monosperma. Pinus edulis quadrifolia. oblongifolia.
Juniperus pachyphloea. Pinus cemhroides. Quercus douglasii.
Juniperus flaccida. Pinus sabiniana. Quercus wisuzenu.
These are grouped in three associations, namely, the Qu£rcus- Juniperus, the
Pinus-Juniperus, and the Pinus-Qu&rcus. The first of these is southern and
^The specific relatioDship of the varieties as understood here is indicated by means of the
trinomial, but the name of the species is omitted in the text for the sake of brevity.
THE PINON-CEDAR WOODLAND. 197
southeastern in position, and is thought to represent the original mass of the
formation. The second is central and typical, while the last is Californian and,
its relationship is less definite. The first two are in contact with each other for
a long distance, but they are readily distinguished by the presence or absence
of Juniperus pachyphloea and the evergreen oaks. The California association
is separated from the other two by the Colorado and Mohave Deserts and the
Sierra Nevada, and the dominants mix but sUghtly. Pinus monophylla and
Juniperus californica are the two species which maintain the contact between
the associations. This contact is in no wise as close or significant as that
between the two eastern associations, but this seems adequately explained
by the barriers mentioned. In other respects especially, the Pinus-Quercua
community appears much more nearly related to the woodland than to any
other climax.
Contacts. — The woodland cUmax occupies the position indicated by its
vegetation-form, viz, the small evergreen tree. This is true both geographi-
cally and successionally, except where one or more dominants occur outside
of the cUmax area. At its lower limit it is regularly in contact with scrub of
some type, usually sagebrush or chaparral, rarely desert scrub. In the region
of the latter, the contact is usually with Prosopis savannah or with the Parkin-
sonia-Cereus scrub, or the oak mass itself shades out into a savannah domi-
nated by Bouieloua and Andropogon. Throughout its central area in the Great
Basin, sagebrush is everywhere in touch with the woodland, though some-
times mixed with chaparral. Along the eastern ranges of the Rocky Moun-
tains and in California, the contact is with chaparral. At the upper edge,
woodland is almost universally in touch with the montane forest, and par-
ticularly the Pinus ponderosa consociation, which is the most xeroid. The
contact may also be with a mixture of Pinus with Pseudotsuga mucronata or
Abies concolor, or with either of the latter consociations alone. This last case
is infrequent, however, and usually occurs where the yellow pine is absent or
unimportant. Successionally, woodland yields to yellow pine forest in the
ecotone between the two cUmaxes, especially during the wet phase of major
sun-spot cycles. Outside of the climax region, where it is represented by cedar
especially, it gives way to the chaparral, sagebrush, or grassland climax with
which it is in contact.
THE PINON-CEDAR WOODLAND.
PINUS-JUNIPERUS ASSOCIATION.
Nature and extent. — ^This association is the most typical and definite of the
three that constitute the woodland cUmax. It usually consists of two domi-
nants, Pinu^ and Juniperus, which are regularly associated. They are similar
in character and requirements, and hence give a much more uniform physiog-
nomy than is found in the other two communities. This type of woodland
occurs most frequently in narrow belts a mile or less to a few miles wide along
the foothills of ranges from the Front Range of the Rocky Mountains to the
eastern slopes of the Sierra Nevada. On the north it ranges from the southern
edge of Idaho and Wyoming to Lower Cahfornia, central Arizona, and New
Mexico. Its most typical expression is found in the center of this great region
on the high plateaus of the Colorado River. In such areas it forms more or
198 CLIMAX FORMATIONS OF WESTERN NORTH AMERICA.
continuous forests many miles in extent. The trees are 20 to 40 feet high
and stand sufficiently close to shade three-fourths or more of the ground.
This results in a sparse though characteristic ground cover. Such extensive
stretches of woodland are typical of the Grand Canyon plateau in northern
Arizona and southern Utah and of the Mesa Verde and Uncompahgre plateaus
in southwestern Colorado. It is on these that the climax association is to be
seen at its best and its extent and importance fully appreciated (plate 45) .
The woodland dominants also occur throughout the range of the associa-
tion as a subclimax community in relatively new areas. They are the distinc-
tive feature of rocky slopes and of cliffs and escarpments at elevations of 5,000
to 8,000 feet over most of the climax area. Single dominants may extend far
beyond the latter as subclimax in sagebrush, chaparral, or grassland. This is
especially true of Juniperus, but it holds for Pinus also in some measure.
Such serai communities are mixed in varying degrees with the dominants of
the climax in which they occur and frequently lead to the assumption that the
woodland dominant is a member of the sagebrush or chaparral. All of the
evidence contradicts this assumption, however, and supports the view that
this is merely the normal response to developmental processes where two
climaxes occupy a broad and greatly interrupted ecotone. The contacts of
this association are essentially those already indicated for the formation,
namely, sagebrush and chaparral below and montane forest above. At its
own level, it touches the Quercus- Juniperus association broadly from Arizona
to Texas, and comes into fragmentary contact with the Pinus-Quercus com-
munity in CaUfomia.
DOMINANTS.
juntperus occtdentali8 monosperma. pintjs edulis.
Juniperus californica utahensis. Pinus edulis monophtlla.
Juniperus virginiana scopulorum.
The most important of the dominants are Pinus edulis and Juniperus
monosperma. They occupy by far the major portion of the climax area, and
are regularly associated. Juniperus scopulorum has much the widest range,
especially northward, but it is usually of secondary importance in the com-
munity. The other four dominants exhibit two interesting and novel correla-
tions. Pinus monophylla and Juniperus utahensis are regular associates in the
western half of the climax, as are P. edulis and J. monosperma in the eastern.
Moreover, they are complementary forms, the latter dominating the associa-
tion through Colorado and most of New Mexico, Arizona, and Utah, the former
in Nevada and California. In western Utah and northwestern Arizona the
ranges of these four dominants overlap.
In this common region, all five dominants may occur together, but this is
rare. The association of the four just mentioned is less so, but it is infrequent
at best. The general rule is that Pinus edulis and J. monosperma, or P.
monophylla and J. utahensis occur together, or that either one of the pifions
is found with both of the cedars. In Colorado and New Mexico at least, it is
not uncommon to find P. edulis associated with both J. monosperma and J.
scopulorum, though usually in the more open and less typical stands. With
the exception of J. scopulorum, all of the dominants frequently occur in pure
stands, but this is usually a consequence of differentiation by altitude.
CLEMENTS
Pifion-cedar Woodland
PLATE 46
A. Pinus-Jvniperus association, Grand Canyon, Arizona.
B. Detail of pifion-cedar woodland. Delta, Colorado.
THE PINON-CEDAR WOODLAND. 199
The groupings of the pifton-cedar woodland have been noted in approxi-
mately a hundred localities throughout the climax area. In the majority of
these, Pinus edulis and Junipems monosperma are the dominants. The pifion
occurs infrequently in pure stands, but this is regularly the case with cedar
at lower altitudes, where the pifion drops out. In such instances, however,
the climax woodland soon disappears and the cedar forms a savannah in sage-
brush or grassland. In addition to the Colorado plateaus already mentioned,
extensive climax areas of pifion-cedar have been studied in Colorado at Gar-
land, Arboles, Mancos, Cortez, Dolores, on the San Miguel plateau, and on
the plateau of Deadman's Cafion south of Cheyenne Mountain. In Utah
similar areas occur at Moab, La Sal, and Bluff.
The pifions make greater demands than the cedars for water though not for
light. In the general absence of quantitative studies, the sequence must be
determined by the consideration of successional relations supplemented by
evidence from growth-forms and distribution. Upon this basis, Pinus edulis
is the least xerophytic, followed by P. monophylla, J. monosperma, and J.
utahensis. J. scopulorum seems to approach P. edulis more nearly, judging
from the fact that it usually makes its best growth in moist canyons. The habit
of P. monophylla and J. utahensis, as well as the nature of the community,
accords with the fact that the western portion of the climax receives several
inches of rain less than the eastern in general. The reduction of the fascicle
to a single leaf in the pifion also suggests the differentiation of this association
into two very closely related communities.
SOCIETIES.
Socio"' ies proper to the woodland are to be expected only where the climax
is more or less extensive. In subclimax areas and especially where the com-
munity is fragmentary or becomes converted into savannah, the herbs and
shrubs of the ground cover are derived from the adjacent or surrounding
climax, sagebrush, chaparral, or grassland. Moreover, the shade of the
typical woodland has reduced the scrub or grassland species which could
adapt themselves to it, just as the more xerophytic habitat has discouraged
invasion from the montane forest. As a consequence, the ground cover is
composed of a sparse community of shade species in the denser woodland,
while the more open areas are occupied by societies more or less conmion to
the adjacent formations. Aspects are little if at all developed in the former,
and no attempt has been made to distinguish them here. Several of the domi-
nants of the chaparral, sagebrush, and grassland have the appearance of
societies, as they are not only constant features, but also take on a habitat-
form more or less peculiar to the shady woodland.
Shade societies.
Chenopodium fremontii. Aster ericoides. Gutierrezia sarothrse.
Draba caroliniana. Malvastrum cocoineum. Senecio fendleri.
Pentatemon linarioides. Gymnolomia multiflora. Astragalus flexuosus.
Sisymbrium incisum. Allium acuminatum. Hymenopappus filifoUus.
Cilia aggregata. Grindelia squarrosa. Eriogonum umbellatum.
Erysimum parviflorum. Pedicularis centranthera. Artemisia discolor.
Pentatemon barbatus. Arabis drummondii. Artemisia frigida.
Pentatemon coeruleua. Chenopodium leptophyllum. Actinella acaulis.
Opuntia mesacantha. Cordylanthus wrightii. Physaria didymooarpa.
Lesquerella argentea. Aster bigelovii. Yucca baccata.
Hedeoma dmmmondii. Cbrysopsia villoaa.
200 CLIMAX FORMATIONS OF WESTERN NORTH AMERICA.
THE OAK-CEDAR WOODLAND.
QUERCUS-JUNIPERUS ASSOCIATION.
Nature and e.vtent. — The oak-cedar association is regarded as the basic or
original community from which the related piiion-cedar and pine-oak woodland
have been differentiated, one to the north and the other to the west. This is
indicated by its position, but especially by its composition. It contains the
three dominant genera and the largest number of species and varieties. It
differs from the northern association in the predominance of oaks. The latter
are important also in the western woodland, but to a less degree, and they
belong to different species. The presence of oaks, pines, and cedars in these
two associations shows the essential equivalence of the broad-leaved and
needle-leaved evergreens as formational dominants. The variable nature of
the deciduous habit is shown by the fact that Quercus douglasii loses its leaves
in the fall or winter, while the other species drop them at different times in the
spring. All of them agree in being essentially sclerophyll in habit (plate 46).
The oak-cedar woodland has its center in southern Arizona and New Mexico
and in northern Mexico. It occurs commonly in the mountain ranges of
trans-Pecos Texas and is found scattered in the canyons and escarpments of
the Staked Plains and the Edwards Plateau. It extends north over the
mountains of the esistern half of Arizona and the western half of New Mexico
to the thirty-fifth parallel, where it yields rather abruptly to the pinon-cedar
association. Pinus cemhroides occurs also in Lower CaUfornia, where it is
associated with P. eduliSy P. monophylla, P. quadrifolia, and Juniperus cali-
fomica, and serves to emphasize the general unity of the formation.
DOMINANTS.
QtJERCUS EMORYI. QtTERCtrS RETICULATA. JuNIPERUS FLACCIDA.
Qtjercus reticulata Juniperus pachyphloea. Juniperus virginiana
ARizoNiCA. Juniperus OCCIDENTAU8 scopulorum.
Quercus reticulata monosperma. Pinus edulis.
oblongifoua. juniperus 8abinoide8. pinus cembroides.
quebcus hypoleuca,
An intermediate mixture of several dominants is characteristic of most of
the associational area, especially the central portion in southern New Mexico
and Arizona, and northern Mexico. The fundament of the latter is formed
chiefly by the oaks, in which cedar and piiion occur in varying abundance.
Pure stands are the exception, particularly in the central mass. They
are more frequent as the areal or altitudinal limits of the association are
approached, owing to the decrease in the number of dominants. At the
edges, communities of single dominants are more or less typical, but they
usually take the savannah form, as in the oaks, or they characterize serai
areas, such as the escarpments covered with Juniperus sabinoides. Near the
margin of the association, there is also a marked tendency for the dominants
to become low and shrubby, and consequently to become confused with the
elements of the chaparral. In the mountains of southern Arizona, the greatly
broken topography produces innumerable fragmentary habitats and causes
a confusing mixture of woodland with desert scrub, chaparral, and even
montane forest (cf. Shreve, 1915 : 31).
The most typical grouping of the oak-cedar woodland is Quercus emoryi,
Q. arizanica, and Q. hypoleuca with Juniperus pachyphloea and Pinus cem-
CLEMENTS
Oak-cedar Woodland
PLATE 48
A. QuercHs-J uniperns a-ssociation, Santa Rita Mountains, Arizona.
B Quercus arizonica consociation, Santa Ilita Mountains.
THE OAK-CEDAR WOODLAND.
201
broides. This is nearly universal in the mountains of southeastern Arizona
and adjacent New Mexico, and doubtless in those of northern Mexico as well.
Quercus ohlongifolia is regularly present in the lowest part of the zone, and a
shrubby form of Q. reticulata in the uppermost portion. To the north and east
Pinus edulis and Juniperus monosperma enter the mixture also. On the
Guadalupe and Davis Mountains of trans-Pecos Texas the grouping is Quercus
arizonica, Q. emoryi, Pinus edulis, Juniperus pachyphloea, J. monosperma,
and J. sabinoides. In the Chisos Range to the south, Pinus cemhroides and
Juniperus flacdda occur as well. East of the Pecos River, the number of
dominants decreases abruptly, and the rough areas of the Staked Plains and the
Edwards Plateau show only Juniperus sabinoides, J. monosperma, Pinus edulis,
and Qi^cus arizonica, single or in varying mixture. Quercus arizonica in par-
ticular becomes reduced to a shrub and mingles with the Uve-oak chaparral.
Factor relations. — The relative requirements of the dominants are shown
by their altitudinal positions. In the mountains of southern Arizona, the
lowest oak is Q. oblongifolia, followed by Q. emoryi, this by Q. arizonica, and
then by Q. hypoleuca. They drop out in about the same order, except that
Q. arizonica is represented at the highest elevations by the shrubby form of
Q. reticulata. Juniperus pachyphloea begins above the lower oaks, while
Pinu^ cemhroides enters still later. Shreve (1915 : 24) places the lower limit
of the woodland or "encinal" zone of the Santa Catalina Mountains at 4,300
feet and the upper at 6,000 to 6,500 feet. Quercus oblongifolia and Q. arizonica
are the first to appear at the lower edge of this zone, followed by Juniperus
pachyphloea. Quercus emoryi and Pinus cemhroides enter at 5,000 feet, and
Q. hypoleuca at 5,600 feet. The cedar and pinon reach their maximum abun-
dance between 5,500 and 6,500 feet. Quercus oblongifolia disappears «.t about
5 200 feet and the typical form of Q. arizonica at 6,500 feet. Quercus emoryi
reached its upper limit at 6,300, while Pinus and Juniperus cease to be domi-
nants between 6,500 and 7,000 feet.
Summer rainfall in inches.
Elevation.
1911.
1912.
1913.
1914.
Average.
3,000 feet
4,000 feet
5,000 feet
6,000 feet
7,000 feet
6.27
9.45
11.97
11.07
15.86
5.61
9.77
8.24
8.68
14.57
6.46
8.59
10.27
8.73
10.62
14.73
19.13
22.68
27.64
7.65
10.63
12.40
8.05
15.21
Average daily evaporation in cubic centimeters for north and south exposures.
Elevation.
May -June.
June.
June-July.
July- Aug.
Aug.-Sept.
S.
N.
S.
N.
S.
N.
S.
N.
S.
N.
3,000 feet
4,000 feet
5,000 feet
6,000 feet
7,000 feet
120.6
84.8
74.2
67.7
72.5
91.2
83.1
68.6
57.6
86.7
81.3
60.8
62.8
55.2
88.4
88.8
47.4
44.3
61.1
67.6
50.9
50.4
46.8
76.5
46.1
43.3
43.3
49.8
64.7
44.2
34.2
37.3
53.5
37.2
33.6
34.1
56.6
42.8
50.8
39.6
39.3
66!o
33.4
28.3
24.0
202 CLIMAX FORMATIONS OF WESTERN NORTH AMERICA
Decrease of temperature toith aUilude.
Elevation.
1914.
Average.
4,000 feet..
5,000 feet. .
6,000 feet. .
7,000 feet..
1.6
8.1
7.6
"14.0
1.9
8.1
9.2
13.7
Shreve {I. c, 46) has made a thorough study of the cUmatic relations of the
Santa CataUna Mountains, and the three preceding tables for the woodland
have been taken from his tables for rainfall (52), evaporation (64), and temper-
ature (75).
SOCIETIES.
The oak-cedar woodland has few distinctive societies. It is in constant or
repeated contact with desert scrub, grassland, chaparral, and montane forest,
and holds practically all its subdominants in common with one or more of
these. Because of its savannah-like contact with the desert plains, the
majority of the societies have been derived from the latter. It is desirable
to consider here only those which occur in the partial or complete shade of the
woodland as a dominant community. The societies vary with the season and
altitude, but a detailed treatment of them is impossible at present.
Solidago speciosa.
Artemisia gnaphalodes.
Monarda citriodora.
Hymenothrix wrightii.
Gaura suffulta.
Desmodium batocaule.
Sporobolus confusus.
Crotolaria lupulina.
Shade Societies.
Gymnolomia multiflora.
Haplopappus gracilis.
Polygala alba.
Comandra umbellata.
Hymenopappus mexicanus.
Cordylanthus wrightii.
Andropogon scoparius.
Bouteloua racemosa.
Muhlenbergia affinis.
Rhus radicans.
Rhus trilobata mollis.
Pteris aquilina.
Pellaea wrightiana.
Cheilanthes fendleri.
THE PINE-OAK WOODLAND.
PINUS-QUERCUS ASSOCIATION.
Nature and extent. — The first suggestion that the community of Pinus
sabiniana and Quercus douglasii, so typical of dry foothill slopes in central
California, constituted a third association of the woodland formation was due
to its general likeness in appearance and position to the oak-cedar woodland.
The probabiUty of this relationship has been greatly increased by the discov-
ery that these two characteristic dominants are associated with pifion and
cedar where their ranges overlap. This is pointed out by Abrams (1910: 317) :
" The Upper Sonoran area on the desert slopes of the mountains is commonly
called the pifion and juniper belts, the two conifers, Pinus monophylla and
Juniperiis calif arnica, being the most characteristic species. Several trees and
shrubs which belong properly to the Intramontane district penetrate through
Tejon Pass and extend in a narrow belt along the western slope of Antelope
Valley. The normal flora of the desert slopes is modified in this section by the
presence of such sp)ecies as Pinus sabiniana and Qu£rcus douglasii."
A further search for groupings of Pinus sabiniana or the associated oaks
with pifion or cedar has disclosed the fact that Coville (1893) had noted these
repeatedly in the southern Sierra Nevada:
CLEMENTS
Pine-oak Woodland
PLATE 47
A. Pinu&'Qucrcus association, Chico, California.
B. Quercus dnvglasii {cntociaticn, Ecd Bluff, Califomia.
THE PINE-OAK WOODLAND. 203
"At about 3,000 feet, the gray-leaf pine (Pinus sahiniana) begins, inter-
mixed with a few Nevada nut pines (P. monophylla)." (8)
"The tree (P. sahiniana) did not form a forest at any point, but grew with
nut pines scattered about in open places or chaparral slopes." (223)
"Juniperus calif omica was found to occur to some extent in both the chap-
arral belt and that of Douglas's oak." (225)
This correlation of the California woodland seems also to furnish the
explanation of the anomaly described by Parish (1903 : 221):
"In the upper end of Antelope Valley, the orographical confusion which
there exists has given rise to a curious phytogeographical anomaly. Here
Pinus sahiniana, Qtieraus douglasii, and Q. vnslizenii, trees characteristic of
the western slope of the Sierra Nevada throughout central California, coming
through Tejon Pass, find themselves on the eastern slope of that range, and
the unusual sight is presented of desert foothills clothed with an almost
unmixed growth of scrub-oaks."
The dominants of the pine-oak woodland correspond somewhat closely
with those of the oak-cedar association. Pinus sahiniana is representative of
the pinons, especially P. cemhroides. Juniperus californica corresponds with
J. pachyphloea, J. monosperma, or J. sahinoides. Quercus douglasii is the
counterpart of Q. reticulata and its varieties, and Q. wislizenii is related to
Q. hypoleuca and perhaps even more closely to Q. emoryi. The two associa-
tions occupy the same relative position with reference to montane forest,
chaparral, desert scrub, and grassland. Both show a preference for rough
topography and dry unstable slopes, and are in consequence much mixed with
chaparral. The oaks of both associations likewise regularly give rise to
savannah where they come in contact with grassland. In both cases the
contact is with associations of the grassland climax, though in the California
the original r61e of Stipa in the savannah is almost completely obscured by the
dominance of the ruderal species of Avena and Bromus (plate 47).
This association is limited to California and Lower California. It extends
from the general region of Mount Shasta southward along the foothills and
mountain slopes to the San Pedro Martir Mountains of Lower California.
In the central part of CaUfornia, it ranges from the Sierra Nevada to the
mountains along the coast, but toward the south it is restricted chiefly to the
San Bernardino, San Jacinto, and Cuyamaca Mountains.
DOMINANTS.
Pinus babiniana. Juniperus californica utahensis. Pinus edulis quadrifoua.
QtJERCus douglasii. Juniperus occidentalis. Pinus cemhroides.
Quercus wislizenii. Pinus edulis monophylla. Yucca arborescens.
Juniperus californica.
The two most typical dominants are Pinus sahiniana and Quercus douglasii,
and these give the character from Mount Shasta southward to the foothills
of Antelope Valley and the Mohave Desert. Quercus wislizenii and Juni-
perus californica are not infrequent associates, but they are less frequent as
codominants. They extend southward into Lower California and hence are
more often associated with the pifions. The latter seem to meet Pinu^ sahin-
iana and Quercus douglasii only in the neighborhood of Tejon Pass and
Tehachapi Pass. South of these points it is often difficult if not impossible to
204 CLIMAX FORMATIONS OF WESTERN NORTH AMERICA.
draw a line between the pine-oak and pifion-cedar woodlands, since Juniperus
lUahensis extends well into California and Pinus monophylla to Lower Cali-
fornia. However, the presence of Quercus vnsUzenii, Juniperus californica,
and Pinus quadrifolia from the San Bernardino or Santa Rosa Mountains to
Lower California, as well as that of P. cemhroides, is regarded as indicating
the pine-oak association.
The community relationship of Yvcca arbor escens is somewhat uncertain,
but its constant association with Juniperus californica along the northern
base of the San Bernardino Mountains from Cajon Pass to Neenach, and to
Hesperia indicates that it is a dominant of the woodland. Like Yucca radiosa
and Y. macrocarpa, it extends downward into the desert scrub, but its life-
form, optimum growth and zone of dominance warrant its inclusion in the
woodland. Merriam (1893 : 341, 354) has noted the occurrence of Yucca
arborescens and Juniperus californica on the mountain ranges south and north
of the Mohave Desert, where they form a distinct belt at 3,500 to 4,000 feet.
Leiberg(1900 : 444-^5, 471) has recorded the composition of several woodland
communities in which Yu,cca occurs on the lower levels of the San Bernardino
Mountains. It is associated with Juniperus californica and Pinus monophylla,
with these and Juniperus ocddentalis, with Pinus monophylla alone or with
P. monophylla and Q. wislizenii also. Parish (1903 : 221) has found Yucca
and Juniperus californica forming an open community along the San Ber-
nardino and Chuckawalla Mountains and from Daggett to Pilot Knob, while
Sudworth (1908 : 201) states that Yu.cca is also associated with juniper,
pifion, and Pinu^ sabiniana. From the nature of its crown, the tree-yucca
forms even more open communities than the other dominants of the woodland,
and hence the consociation is constantly mixed along its lower portion with
dominants from the desert scrub and sagebrush.
Little is known of the factor or successional relations of this conmiunity.
The latter seem in general to correspond with those of the oak-cedar wood-
land. The oaks are the more xerophytic, and Quercus douglasii rather more
than Q. wislizenii, if distribution be regarded as an indication. Their relative
position seems definitely indicated by the frequency with which they form
savannah with grassland at their lower limits. In spite of their occurrence in
rocky subclimax areas, the cedars and pinons appear to be rather more meso-
phytic than Pinus sabiniana. This is suggested by the respective altitudes at
which they reach their greatest dominance, and seems to be certainly true for
Pinu^ cemhroides.
In the rough topography of the foothills, woodland, chaparral, and mon-
tane forest are often much mixed and confused. In spite of this, they appear
as distinct units when differences of slope and successional development are
taken into account. The two oaks and the digger-pine are frequently mixed
with Quercus californica or Q. garryana, which really constitute a subclimax
leading to the montane forest of Pinus ponderosa and Psevdotsuga mucronata.
Where any of the three dominants occur with chaparral, the grouping is usually
successional in character, or it represents an ecotone. In some cases where
the trees are scattered more or less uniformly through a chaparral cover, the
community is to be regarded as a savannah in which the grasses are replaced
by shrubs, and it is probably to be similarly related to the climatic cycle.
THE MONTANE FOREST CLIMAJC. 205
THE MONTANE FOREST CLIMAX.
PINUS-PSEUDOTSUGA FORMATION.
Nature. — ^This climax is an evergreen forest in which the dominants are
exclusively conifers. Broad-leaved deciduous and evergreen species occur in
it, such as Popidus tremvloides, Quercus californica, and Arbutus menziesii,
but they are typically subclimax in character. In contrast with the woodland,
this is a true forest formation. The trees are tall, usually 75 to 150 feet or
more in height at maturity, with massive trunks and dense crowns. In typical
habitats, they grow more or less closely, forming a continuous canopy. The
latter is less dense than in the other two forest formations and the forest nor-
mally exhibits a good development of layers. The number of societies of
shrubs and herbs is large and the aspects are well-marked. The major domi-
nants are few, but they have a wide range and the composition of the forma-
tion is exceptionally uniform. The number of more restricted and of local
dominants is larger, and they serve to give character to the associations. The
most typical as well as the most xeroid of its dominants, Pinus ponderosa,
possesses a striking power of adjustment and often forms savannah, which
extends far into the Great Plains as belts of woodland.
Extent. — ^The montane forest is the most extensive and important of all
the western forest cUmaxes. In its broadest outlines it extends from the
foothills of western Nebraska and South Dakota and the mountains of western
Texas to the Pacific Coast. It reaches from the mountains of central British
Columbia to those of northern Mexico and Lower California. It occurs
throughout the mountain ranges of the Great Basin and on those of the south-
western deserts where the altitude permits. On the east, extensive forests of
Pinus ponderosa cover the Black Hills of South Dakota and a narrow strip
of the same forest follows the canyon of the Niobrara River as far east as the
ninety-ninth meridian. The southeastern limits of the formation are found
in the Guadalupe and Davis Mountains of trans-Pecos Texas. The southern-
most limit is attained by Pinus ponderosa, P. arizonica, and P. chihu^huxina
in the ranges of Sinaloa and Durango.
Unity of the formation. — The occurrence of the three major dominants,
Pinus ponderosa, Pseudotsv^a mucronata, and Abies concolor, from Montana
to Mexico and Colorado to CaUfornia leaves no question of the unity of the
formation. This is further emphasized by the more or less constant presence
of Pinifs contorta, P. flexilis, and P. alhicaulis in both associations. In addi-
tion, Pinus is represented by three species peculiar to each of the two associa-
tions, Picea by one species, and Cupressus by one. There is also a marked
agreement as to the genera of the societies, more than three-fourths of these
being common to both associations. With the major dominants so universal
and controlling, it follows that the ecologic and phylogenetic unity of the for-
mation is equally clear.
Geographically, the formation is typical of the great Cordilleran system
from which it extends out upon the interior plateaus, such as that of the
Colorado, and along the minor ranges and escarpments which front the Rocky
Mountains on the east. Its climatic range rivals that of the grassland in so
far as latitude is concerned. Both formations extend several degrees north-
ward into Canada, and even a greater distance southward into Mexico. But
206 CLIMAX FORMATIONS OF WESTERN NORTH AMERICA.
grassland has a wider extension vertically and hence probably occupies a
broader climatic belt. The vertical range as a climax is often more than 6,000
feet in the Rocky Mountains, and it is usually somewhat more in the Sierras
and Cascades. The corresponding range in rainfall and temperature is enor-
mous, and in either physical or human terms the climax contains several
climates. In the form of the pine consociation, the montane forest often
occurs in a rainfall of 20 inches or less from Colorado to Arizona and the Great
Basin. On the Pacific Coast, it is frequently found in a rainfall of 50 to 60
inches. Moreover, along the central axis of the Rocky Mountains, 50 per cent
or more of the rainfall occurs in the summer, while along the Sierras and Cas-
cades, 70 to 90 per cent of the precipitation falls during the winter. The figures
for temperature are less striking, but still very divergent. There is a differ-
ence of more than 20 degrees in the mean temperatures of the formation in
northern Montana and northern California, and of 60 degrees in the lowest
recorded minimum. In spite of this, the regular association of the three major
dominants throughout the formational area indicates that the cUmate is
essentially a unit from the standpoint of the dominant vegetation (fig. 9) .
Lonff** Peak, Colorado
5
4
3
2
1
0
Fremont
Sta., Colo.
5|
Sp<
4
iarflsh. S.Dak.
5n-
Flagrstaff, Arizona
21 in.
22 in.
22 in.
24 in.
1
-4f '
1
1 .
1
t
1
1
■ 1
1
0
ll
0.
Fio. 9. — Monthly and total rainfall for representative localities in the association of the Petran
montane forest.
Relationship and contacts. — The closest relationship of the montane climax
is with the coast forest. This is best shown in northwestern Montana, north-
em Idaho, and adjacent British Columbia, where the two meet to form a
broad transition. It is further indicated by the fact that Pseudotsuga is the
typical subclimax species of the cedar-hemlock forest. The most important
contact is with the subalpine forest. These touch each other for thousands
of miles along the ranges of the Rocky Mountains and of the Sierra-Cascade
system. They constitute a broad forest zone of fairly uniform physiognomy
and have even been regarded as a single formation. Gray (1878) seems to
have been the first to recognize their distinctness, and a similar view has been
maintained by Merriam (1898) and his followers, obscured somewhat by the
unsuccessful attempt to distinguish two zones, Canadian and Hudsonian, in
the subalpine climax. While the two climaxes are similar in appearance, they
differ fundamentally in composition, climatic and successional relations, and
in origin. The difference between them is clear where they occur in massive
zones, but is more or less hidden in regions of much topographic diversity.
The contacts along the lower edge of the formation are varied. The normal
contact ecologically is with the woodland climax, and this is regularly found
in the southern half of the formational area in which woodland is more or less
CLEMENTS
Petran Montane Forest
PLATE 48 ft
A. /'i«MS/>o7«/<7VAsa consociation, I'lanstafT, Arizona.
H. /^iMits /Jow/^To*;! consociation, Hcnd, Oregon.
C. I'inus poiulcrosa consociation, lilaciv Hills, South Dakota.
THE PETRAN MONTANE FOREST. 207
constant. In the absence of the latter, the pine consociation meets chaparral
in the coast regions and along the slopes of the central Rockies. On the desert
slopes of the Great Basin it is often in touch with sagebrush, especially where
represented by the subclimax lodgepole pine. It may also come in direct
contact with the mixed prairie from Colorado northward, where it passes into
extensive savannahs, characteristic of the isolated ranges and uplands of the
Black Hills and adjacent regions.
Associations. — The general occurrence of Pinus ponderosa, Paeudotsuga
mucronata, and Abies concolor through the montane climax was thought at
first to indicate the presence of a single association. A scrutiny of the list of
codominants reveals a fairly clear differentiation into a Rocky Mountain and
a Sierra-Cascade community. These have three codominants in common,
namely, Pinus contorta, P. flexilis, and P. aUricaulis. The former differs much
in habit and habitat between the two associations, while Pinus flexilis is more
important in the Rocky Mountains and P. aUricaulis in the Coastal region.
Of the remaining 13 codominants, 5 are restricted wholly to the Rocky Moun-
tain conmaunity and 8 to the Sierran. This differentiation is also emphasized
by the variation in habit and size of Pinus ponderosa and Pseudotsuga in the
two regions. This is so pronounced in the case of the pine that the common
form of the Rocky Mountains has generally been treated as a variety or even
as a species, while foresters have regarded the Douglas fir of the Pacific coast
as a distinct variety. A similar differentiation is reflected in the societies of
the forest. More than 75 per cent of the generic subdominants are the same
for both associations, while they have less than 25 per cent of common species.
Finally, the division of the montane climax has its causal justification in the
striking climatic differences between the Rocky Mountain and the Pacific
regions.
The task of finding concise descriptive names for the two associations has
not been simple, owing to the all but universal presence of the major domi-
nants. After much consideration, it seems best to refer to the eastern com-
munity as the pine-fir association, and to the western as the pine association.
When it is desired to emphasize their geographical relation, the Rocky Moun-
tain association is termed Petran, and the Sierra-Cascade one, Sierran.
THE PETRAN MONTANE FOREST.
PINUS-PSEUDOTSUGA ASSOCIATION.
Extent. — The montane forest of the Rocky Mountain region extends from
central Alberta to the Guadalupe and Chisos Mountains of western Texas,
and southward from the mountains of New Mexico and Arizona to Sinaloa
and Durango. At the north its area is relatively narrow and it yields to the
transition association of the Coast forest in the Selkirk Mountains of British
Columbia and in the Kootenai and Coeur d'Alene ranges of northwestern
Montana. It is broadest near the center where it ranges from the Black Hills
of South Dakota and the Pine Ridge and Wild Cat Mountains of Nebraska to
the eastern slopes of the Sierras in Nevada. It apparently finds its south-
western limit in the Charleston Mountains of Nevada and its southern in the
Sierra Madre of Durango and Sinaloa. It is the characteristic forest of the
mountain ranges of this vast region and is the most extensive of all the forest
associations of the West (plate 48).
208 CLIMAX FORMATIONS OF WESTERN NORTH AMERICA.
DOMINANTS.
PiNtJS P0NDEB08A. PiCEA PUNQENS. PiNUS 8TROBIFOHMI8.
pseudotsuoa mucbonata. pinus flbxilis. pinus chihuahuana.
Abies concxjlor. Pinus flexilis albicaulis. Pinus arizonica.
FlNUS contorta.
As already indicated, the first 3 species are to be regarded as the major
dominants of the association by reason of their abundance and wide occur-
rence. The lodgepole pine (Pinus contorta) ranks next in importance. It is
typically the sub'climax dominant of the burn subsere in both the montane and
subalpine forests. However, it is more or less exclusive over such large areas
in the northern Rocky Mountains, and is so relatively permanent owing to
repeated fires that it must be considered with the climax. Picea pungens is
limited to the central Petran regions, and usually occurs in restricted stands
along the lower edge of the zone. More rarely, it forms a mixed forest with
yellow pine and Douglas fir, as in the Pike's Peak region, and in the Blue and
White Mountains of Arizona (Greenamyre, 1913). Pinus flexilis and P.
albicaulis are trees of wide range altitudinally, and hence are found in both the
montane and subalpine climaxes. They are more abundant and relatively
more important at upper elevations near timber-line, and hence are regarded
as belonging primarily to the subalpine forest. Pinus flexilis occurs through-
out the association, while P. albicaulis ranges from the northern edge to Yellow-
stone Park. Pinus strobiformis is a related pine which occurs only in south-
eastern Arizona and adjacent New Mexico, and thence southward into Sonora
and Chihuahua. Pinus chihu^ihuana and P. arizonica are close relatives of
P. ponderosa. They occur with the latter or represent it in southern Arizona
or New Mexico at elevations of 6,000 to 8,000 feet, and extend southward into
the Sierra Madre of Mexico.
Groupings. — The four most important dominants, Pinus ponderosa, P.
contorta, Pseudotsuga, and Abies, regularly occur in pure stands as well as in
mixed communities. This is especially true of the two pines. In the case of
the lodgepole pine, this is a consequence of its ability to occupy burned areas
completely, while with the yellow pine it results from its extension far beyond
the mass of the association. With these two very important exceptions, the
montane forest is largely a mixture or consists of small alternes of the different
species. The minor dominants usually occur intimately mixed with the
major ones, though they too may form pure communities of small size.
In general, Pinus ponderosa, Pseudotsuga, and Abies occur together through-
out the mass of the association. To the northwest, Abies becomes secondary
or is lacking, and the forest consists primarily of yellow pine and Douglas fir,
or of lodgepole pine. Since these are related successionally, one often contains
relicts of the other. In the Wasatch Mountains, Pinus ponderosa is mostly
absent and the forest consists of Pseudotsuga and Abies, while in the desert
ranges, farther west, Pseudotsuga is usually the missing one of the three.
Picea pungens is practically limited to the central area of the association,
represented by Colorado, Utah, northern Arizona, and New Mexico. It is
often in open woodland along streams, but it may be an important member of
the lower portion of the montane zone, mixed with Douglas fir and yellow
pine, or more rarely with Abies concolor. Pinus flexilis occurs with yellow
pine or Douglas fir, or with both on xerophytic ridges and slopes at lower
levels. P. albicaulis has a similar habit, but is much less common in this
association. As already indicated, Pinus strobiformis, P. chihuahuxina, and
THE PETRAN MONTANE FOREST. 209
P. arizonica either occur scattered in the pine consociation or codominant
with it from Arizona southward into Mexico.
Both the yellow pine and the lodgepole pine form pure stands which may
stretch hundreds of miles beyond the main body of the association. The
finest body of yellow pine on the continent is found on the Colorado plateau
of northern Arizona far from the central mass. Similar pure communities but
of less importance occur on the ranges of eastern Wyoming and the Black
Hills. On the mesas of western Colorado and the foothills of central Wyoming,
the Pinus contorta consociation breaks up into masses of varying size, sur-
rounded by sagebrush or grassland in the respective regions. These are out-
posts of the lodgepole forest and are quite different from the savannah type
assumed by yellow pine where conditions favor grassland. Both represent
the same climatic tendency, however, as is shown also by the fact that aspen,
Populus tremuloides, often accompanies them.
Factor relations. — ^The montane forest of the Rocky Mountains has received
more quantitative study than any other community, with the possible excepn
tion of the prairie. This is due to the location in it of the Alpine Laboratory
and the Fremont Forest Experiment Station at Pike's Peak, where factor
studies have been carried on more or less continuously since 1900 and 1910
respectively, and of the Fort Valley Forest Experiment Station near Flagstaff,
Arizona, where observations have been made since 1909. In addition, the
Desert Laboratory has maintained stations in the montane zone of the Santa
CataUna Mountains since 1908. As a consequence, a large mass of factor
data is available, of which but a few general results can be given here.
The rainfall limits for the montane forest are approximately 18 to 20 inches
for the lower margin and 22 to 23 inches for the upper. The great majority
of the records are for the eastern slope, but they agree closely with those for
western Colorado and northern Arizona. The rainfall is somewhat higher in
New Mexico and lower in Montana, but this is obviously compensated by the
evaporation. The savannah form of the pine consociation is found where
precipitation is as low as 15 inches, and lodgepole outposts occur at even lower
limits in western Colorado. The total evaporation for the growing season is
not known, but the relative evaporation is a third greater in the Pseudotsuga
consociation than in that of Picea engelmanni in the lower part of the sub-
alpine forest. The measurement of light values through several summers
has shown that there is no difference in the intensity of the Ught which falls
upon the two forest zones in the Rocky Mountains. There is a constant
difference in air and soil temperature, and in water relations, especially water-
content, the montane forest naturally showing the higher temperatures and
lower rainfall, humidity, and water-content.
Serai relations. — Factor measurements show that Pinus ponderosa is the
most xerophytic of the three major dominants, Pseudotsuga less so, and Abies
somewhat less still. The most mesophytic is Picea pungens. Piniis contorta
is practically as xerophytic as the yellow pine, but it has a wider range of
adaptation. Much the same is true for P. flexilis and P. albicaulis. The
three southern pines resemble Pinus ponderosa in their water requirements.
As to light requirements, the pines are all intolerant. Picea pungens is some-
what more tolerant, Pseudotsuga is moderately tolerant, and Abies endures
still deeper shade. In Colorado the normal Ught intensity for the mature
210 CUMAX FORMATIONS OF WESTERN NORTH AMERICA.
lodgepole consociation was found to be 0.08 to 0.07, while germination was
only fairly good at 0.2 to 0.14 (Clements, 1910 : 40). The values of yellow
pine and limber pine {Pinus flexilis) are not very different, though such
forests are usually more open. Douglas fir is much more tolerant, reproduc-
ing readily in values as low as 0.04, while the mature forest may show intensi-
ties below 0.01.
As would be expected, the serai sequence conforms to the water and light
demands. Pinus ponderosa is everywhere the earliest of the three major
dominants, and is followed by Pseudotsuga, and this a little later by Abies
as a rule (Clements, 1905 : 270). Pinus contorta is the universal subclimax
dominant of bums everywhere from central Colorado northward into Alberta
and British Columbia. In the Rampart Range, about Pike's Peak and south-
ward, its role is taken chiefly by aspen. Picea pungens is generally somewhat
subclimax in moist valleys and canons, while the remaining pines resemble
Pinus ponderosa in their general successional relations (plate 49).
SOCIETIES AND CLANS.
The following lists are for the central Rocky Mountains and are based
chiefly upon studies made in Colorado (Clements, 1904 : 8). Rydberg (1915)
has given comparative lists of the herbaceous flora of the different regions, and
Shreve (1915 : 32, 35) has noted the characteristic species of the pine and fir
forests of the Santa Catalina Mountains of Arizona. The majority of the
genera in the latter are those of the central region, though the species are
largely different. The central and northern areas are seen to resemble each
other closely in the important species, when it is recognized that the transition
region of northwestern Montana and northern Idaho belongs rather to the
Coast forest. Because of the shortness of the season, it is convenient to dis-
tinguish but two aspects, a vernal and an estival.
Societies:
Shrub*—
Acer glabrum.
Betula occidentalis.
Prunua pennaylvanica.
Comus amomum.
Herbs —
Fragaria veaca.
Viola biflora.
Mertensia pratensis.
Besseya plantaginea.
Claru:
Actaea rubra.
Habenaria atricta.
ErigeroQ glandulosua.
Societies:
Thalictrum fendleri.
Galium boreale.
Geranium caespitosum.
Geranium richardsonii.
Caatilleia miniata.
Erigeron asper.
Clans:
Allium cemuum.
Solidago oreophila.
Vernal Aspect.
Opulaater opulifoliua.
Ribes lacustre.
Arctostaphylus uva-ursi.
Heuchera parvifolia.
Pseudocymopterus montanus.
Pentstemon gracilis.
Pentstemon secundiflorua.
Pirola chlorantha.
Smilacina stellata.
Estival Aspect.
Arnica cordifolia.
Gentiana amarella.
Potentilla glandulosa.
Pirola uliginosa.
Saxifraga bronchialia.
Heracleum lanatum.
Pirola secunda.
Androsace septentrionalis.
Jamesia americana.
Rosa acicularis.
Viburnum pauciflorum.
Washingtonia obtuaa.
Aralia nudicaulis.
Atragene alpina.
Viola blanda.
Calypso borealia.
Valeriana silvatica.
Senecio cemuus.
Haplopappus parryi.
Gentiana affinis.
Streptopua amplexifoliua.
Aquilegia coerulea.
Galium triflorum.
Peramium ophioides.
CLEMENTS
Petran Montane Forest
PLATE 49
A. Psewlotsuga mucroiuita consociation, Alpine I^iboratory, Pike's Peak.
B. Detail of Pseudutsuga-Abies forest, Cameron's Cone, Pike's Peak.
THE SIERRAN MONTANE FOREST. 211
THE SIERRAN MONTANE FOREST
PINUS ASSOCIATION.
Extent. — The northern limits of the montane forest of the Pacific coast are
extremely difficult to draw, owing to the fact that Pseudotsuga continues into
the Coast forest as an important dominant and also occurs with Pinus pon-
derosa in both the transition and the Petran montane forest. In general, its
northern limit is regarded as determined by the disappearance of Pinus
lambertiayia, Libocedrus decurrens, and Abies concolor. This forest extends
well into southern Oregon on the Siskiyou and Coast ranges and to central
Oregon along the Cascade Mountains. It is found on the eastern slope of the
Cascades and reaches its eastern Umit in the lake region. In northeastern
California it is present on both slopes of the Sierras, but southward from Lake
Tahoe it is almost confined to the western one. The northern Coast ranges
exhibit this community as far south as Lake County, but it yields to the red-
wood forest along the coast. It is fragmentary in the southern Coast ranges,
but becomes the typical forest at the proper levels in the San Rafael, Sierra
Madre, San Bernardino, San Jacinto, and Cuyamaca Mountains. It reaches
the southern Hmit in the San Pedro Martir Mountains of Lower California.
The range in altitude is exceptionally great. In the Coast ranges of northern
CaUfornia and Oregon the montane forest occurs at altitudes of 1,000 to 3,000
feet, while in the Cascades it is found at 2,000 to 6,000. In the central Sierras
the general elevation is 3,000 to 6,000, but this increases steadily toward the
south and the upper limit reaches 7,000 to 8,000 feet in southern California
and 8,000 to 10,000 feet in Lower California.
DOMINANTS.
Pinus lambertiana. Pintjs ponderosa jEFFREn. Pinus coulteri.
Pinus ponderosa. Pseudotsuga mucronata Sequoia gigantea.
Pseudotsuga mucronata. macrocarpa. Cupressus goveniana.
Abies concolor. Pinus attenuata. Picea breweriana.
Libocedrus decurrens.
The major dominants of the association are Pinus lambertiana, P. ponderosa,
Pseudotsuga mucronata, Abies concolor, and Libocedrus decurrens. All of these
occur from the northern limit of the area in central or southern Oregon to the
San Pedro Martir mountains in Lower California, though the Douglas fir is
represented in southern and Lower California by its variety, Pseudotsuga m.
macrocarpa. In somewhat similar fashion, Pinu^ ponderosa is replaced at
higher levels by P. p. jeffreyi. The remaining species are all of secondary
importance. Pinups attenuata ranges from central Oregon to southern Cali-
fornia, and P. coulteri extends from central to Lower California. Both are
relatively xeroid and subclimax in character. Sequoia gigantea is the most
interesting of the dominants, but it is restricted to scattered groves on the
west slopes of the Sierra Nevada from Placer County to Tulare County. These
are the survivors of what must have been an extensive consociation in later
Tertiary times. Cupressus goveniana occurs sparsely through the Coast
region from Ukiah to Dulzura near San Diego. Picea breweriana is localized
in northwestern California and adjacent Oregon.
Three species of broad-leaved trees occur so frequently in the montane
forest that they require mention. These are Quercus californica, Q. garryana,
and Arbuius menziesii. They are all subclimax in character and occur com-
212 CLIMAX FORMATIONS OF WESTERN NORTH AMERICA.
monly in the edges of the forest or in the more open stands or outposts of
Douglas fir or yellow pine. Quercus califomica and Arbutus extend through
the association to southern CaUfornia, while Q. garryana has its southern limit
in the Santa Cruz Mountains.
Groupings. — The great mass of the association is constituted by the five
major dominants in the most variable proportions. In 50 localities from
Crater Lake to southern California, 4 or usually all 5 of these were found in
more than half the cases. While mixed forest is the rule, Pinus ponderosa
and Pseudotsuga mucronata often occur in extensive pure stands, or they may
be mixed in more or less equal numbers. Abies concolor also occurs pure, but
to a less degree. On the other hand, Pinus lambertiana and Libocedrus prac-
tically always occur in mixture, in which they rarely make more than 15 per
cent of the stand. Sequoia gigantea occasionally is found in pure stands, but
it is usually associated with Pinus lambertiana and Abies concolor, and with the
latter alone at the higher elevations. It is less commonly mixed with yellow
pine and incense cedar, and still less with Douglas fir. Toward the Coast
forest on the north and west, and the Petran montane forest in central Oregon,
the typical members of the conmiunity drop out, leaving only the yellow pine
and Douglas fir, in mixture or in pure forests. At the highest altitudes reached
by the montane forest, Abies concolor and Pmws jeffreyi are the chief domi-
nants, extending more or less into the subalpine forest above. The excepn
tional soUdarity of the association is shown by its composition in the desert
ranges near its southern Umit. Pinus ponderosa, P. lambertiana, Libocedrus
decurrens, Abies concolor, Pseudotsuga macrocarpa, and Pinus coulteri form
the montane forest on the San Jacinto Mountains (Hall, 1902 : 19) and in
the San Pedro Martir Mountains of Lower CaUfornia (Goldman, 1916: 313).
Of the minor dominants, Pinus attenuata is the only one which forms exten-
sive pure forests. It resembles lodgepole pine in making dense growth in
burned areas, and hence is properly subclimax. In the southern half of Cali-
fornia, it occurs frequently with Pinus coulteri in the lower portion of the
forest, where they are associated with P. ponderosa, Pseudotsuga macrocarpa,
and Libocedrus. Pseudotsuga macrocarpa is thought by Sudworth (1908 : 105)
to have occurred formerly in larger pure stands in southern California, but
to-day it ranges widely through the montane zone in small groups or scattered
singly, and extends down into the chaparral formation (plate 50) .
Factor and serai relations. — The montane association grows in a rainfall
of 80 inches in the Coast ranges of northern California. The rainfall decreases
regularly toward the south, until it reaches 20 inches in the montane zone of
the San Jacinto and San Pedro Martir Mountains. No figures are available
for evaporation, but it must be much greater to the southward also. It is
surprising that such great changes in the water relations do not have a marked
effect upon the composition, but the latter is modified chiefly by the substi-
tution of Pseudotsuga macrocarpa for P. mucronata. The height of the domi-
nants and the density of the stand, however, are greatly reduced in the
southern ranges. Even a more striking adjustment to water and temperature
is seen in the upward movement of the zone, from a lower limit of 1,000 feet
or less in the north to 8,000 or 9,000 feet in Lower California.
CLEMENTS
Sierran Montane Forest
A. Pinus pondero&a-lainhcrtiana association, Prospect, Oregon.
B. Pinus, Libocedrus, Abies, and Pseudotsugn, Yosemite National Park, California.
THE SIERRAN MONTANE FOREST.
213
While no factor studies have been recorded for the Sierran montane forest, the
experience of foresters has enabled them to indicate the comparative relations
of the dominants to both water and light. Larsen and Woodbury (1916 : 7)
have shown the soil and water requirements of the major dominants in the
following, in which the order is from more exacting to less exacting. As to
light requirements, the dominants are ranked from the least tolerant to those
most tolerant of shade.
Soil.
Water.
Light.
Pseudotsuga mucroData.
Pinua lambertiana.
Pinus attenuata.
Abies concolor.
Pseudotsuga mucronata.
I*inus ponderosa.
Pinus lambertiana.
Abies concolor.
Pinus jeffreyi.
Libocedrus decurrens.
Libocedrus decurrens.
Pseudotsuga mucronata.
Pinus ponderosa.
Pinus ponderosa.
Pinus lambertiana.
Pinus jeffreyi.
Pinus jeffreyi.
Abies concolor.
Libocedrus decurrens.
The general relation of the dominants to the combined influence of water
and temperature is shown by the order in which they occur with increasing
altitude. The lowermost species are Pinus attenuaia, P. coulteri, and Pseudo-
tsuga macrocarpa, followed by Pinus ponderosa, Pseudotsuga mucronata,
Libocedrus decurrens, P. lambertiana, Abies concolor, and P. jeffreyi. This is
the order of the potential succession (Clements, 1916 : 108). It corresponds
closely with the actual serai sequence of the dominants, when the difference
in the tolerance and zonal position of Libocedrus and Pinus jeffreyi is taken
into account. The first three species are essentially subclimax, Pinus ponde-
rosa is the first and most xerophytic of the true dominants in the lower half
or more of the forest and P. jeffreyi in the upper, and Pseudotsuga is next.
The remaining three differ but little, since the greater tolerance of Libocedrus
is offset by a smaller water requirement.
SOCIETIES.
Shrubs are well developed in the montane zone, but they reach their best
expression in open woodland and in clearings where fire has been active.
They disappear largely or completely in the closed forest stands, in which
herbaceous societies are more or less prominent. Many of the shrubs belong
to the same genera as the dominants of the chaparral and hence form com-
munities with a striking resemblance to the latter. While they ultimately
yield to the montane forest in undisturbed areas, recurrent fires enable them
to occupy the ground as a more or less permanent subclimax. The latter has
usually been included in the general term chaparral, but this view is ecologi-
cally incorrect, as Cooper (1919) has emphasized.
Shrvbt:
Ceanothus cordulatua.
CeanothuB velutinus.
Ceanothus integerrimus.
Ceanothus parviflorus.
Ceanothus prostratus.
Arctostaphylus patula.
Arctostaphylus drupacca.
Castanopsis sempervirens.
Quercua broweri.
Quercus sadleriana.
Quercus chrysolepais vaccini-
folia.
Pasania densiflora echinoides.
Corylus rostrata.
Prunus demissa.
Prunus emarginata.
CastanopsiB ohrysophylla minor. Rhamnus califomica.
Rhamnus purshiana.
Holodiscus discolor.
Amclanchier alnifolia.
Symphoricarpus oreophilus.
Symphoricarpus mollis.
Ribes nevadense.
Rubus parviflorus.
Chamaebetia foliolosa.
Rhus diversiloba.
214 CUMAX FORMATIONS OF WESTERN NORTH AMERICA.
Herba:
Pteris aquilina.
Polystichuni munitum.
Aepidium rigidum.
Pent«t€mon gracilentus.
PentstemoD deustus.
Pentatemon bridgcsii.
Pentotemon labrosus.
Fragaria virginiana.
Washingtonia nuda.
Monardclla odoratissima.
Adenocaulum bicolor.
Lupinus grayi.
Lupinus omatus.
Hoaackia decumbens neva-
densis.
Hydrophyllum occidentale.
Lathynia sulphureus.
Trifolium breweri.
Castilleia parviflora.
Pedicularis semibarbata.
Achillea millefolium.
Erigeron breweri.
MicroBcris nutans.
Hieracium albiflorum.
Senecio lugens.
Crepis occidentalis.
Crepis intermedia.
Chaenactis douglasii.
Antennaria argentea.
Kelloggia galioides.
Phacclia ramosissima.
Draperia aystyla.
Viola lobata.
Pirola picta.
Delphinium decorum.
Silene califomica.
Silene lemmonii.
Erysimum asperum.
Eriogonum umbellatum.
Iris hartwegii.
Corallorhiza multiflora.
Sarcodes sanguinea.
THE COAST FOREST CLIMAX.
THUJA-TSUGA FORMATION.
Nature. — The Coast climax of the Northwest is a coniferous forest of
unrivaled magnificence. The mature trees are very tall, 125 to 200 feet high
and 5 to 15 feet in diameter; or, in the case of Sequoia sempervirens, 300 feet
or more high and 10 to 20 feet in diameter. They form a dense canopy which
makes a deep shade, in which secondary trees find growth all but impossible.
In the mature forest, layers of shrubs and herbs are poorly developed or con-
sist of relatively few species. The layer of duflf and organic soil is deep, and
the conditions within the forest are almost ideal for germination and growth,
except for the low light intensity. The number of major dominants is prac-
tically the same as in the montane forest, with which the Coast climax shows
a closer relationship. The dominants are much more restricted in range,
however, especially from east to west. As a consequence, the cedar-hemlock
forest shows less differentiation, and it might well be regarded as composed
of a single association. The breadth and importance of the transition zone
between it and the montane forest, together with other reasons discussed later,
seem such as to warrant the recognition of two associations.
Extent. — As the name implies, the Coastal climax has its greatest develop-
ment along the Pacific coast. The main body of the formation stretches from
southern British Columbia to northern Cahfornia, but several of the major
dominants extend much farther northward as well as southward. The
northernmost in range is Picea sitchensis, which finds its boreal limit at Cook
Inlet and Kodiak Island, Alaska. Tsuga heterophylla and Chamaecyparis
nootkatensis extend nearly as far, reaching Prince William Sound, while
Thuja plicata is found in southern Alaska and Abies amabilis at the extreme
southern end. The most southerly range is that of Sequoia sempervirens, the
last outposts of which are found in the Santa Cruz and Santa Lucia Mountains
of California. This striking species is practically confined to this State, occur-
ring elsewhere in but few groves just across the Oregon line. Four other
major dominants are found with the redwood to Mendocino, Sonoma, and
Marin Counties. These are Tsuga heterophylla, Thuja plicata, Picea sitchensis,
and Abies grandis. While Pinus monticola, Pseudotsuga mucronata, and other
members of the transition association extend farther south, especially in the
Sierra Nevada, it is as dominants of the subalpine or of the montane forest.
THE COAST FOREST CLIMAX.
215
While the best expression of this formation is along the coast, it extends to
the Cascades and covers their western slopes in typical form. East of the
Cascade Mountains, it passes into a broad transition forest which reaches to
the western slopes of the main range of the Rocky Mountains in northern
Montana and southeastern British Columbia. In the Cascade Mountains
of central Oregon, it is replaced by the montane forest, and becomes more and
more restricted to the coastal belt from this point southward. In similar
manner, it is replaced in central British Columbia by the montane forest,
though the coastal belt remains somewhat broad as a result of the numerous
islands and inlets.
In altitude, the Coast forest extends from the sea-level as far as 3,000 to
6,000 feet in the Coast ranges and the Cascades. On the interior ranges, it
reaches its upper limit at 5,000 feet or lower.
Unity. — The treatment of the Coast climax as a distinct formation is
abundantly justified by the regular association of the major dominants from
Alaska to California and from Washington to Montana. As already indicated,
five of these occur in Alaska, and five also in California, three of these, Tsuga,
Thuja, and Picea, being common to both extremes. The number of dominants
with a wide lateral range is even greater. Those which range from the Coast
to Montana are Tsuga heterophylla, Thuja plicata, Abies grandis, Larix occi-
dentalis, Pinus monticola, Pseudotsuga mucronaia, and Pinus corUorta, while
Picea engelmanni and Pinus ponderosa extend as dominants from the Cas-
cades to Montana. While there is a
Ashford, Wash.
70 in.
'Priest River, Idaho.
30 in.
marked change in the rank of the
dominants as the Cascade Moun-
tains are passed, this is clearly con-
nected with the differentiation of
associations. The ecological char-
acter of the forest remains essen-
tially the same toward the limits
at the east, except where more or
less subclimax dominants, such as
Pinus ponderosa and P. contorta,
become controlUng.
Geographically, the ferest be-
longs to the Coast and tho Colum-
bia Basin. At the higher levels,
the latter, like the former, is a re-
gion of relatively high rainfall and
low evaporation. The tempera-
ture relations are less uniform from east to west at least, but this is reflected
in the mixing of the two climaxes and the differentiation of a transition com-
munity (fig. 10).
Relationship and contacts. — As the last statement indicates, the closest
relationship of the Coast forest is with the montane climax. They resemble
each other much in the size and vigor of the dominants and in the luxuriance
of the forest itself. This is reflected by the important role of Pseudotsuga
mucronata in both and the significant occurrence of closely related Sequoia
Fro. 10. — Monthly and total rainfall for represent-
ative localities in the associations of the Coastal
forest.
216 CLIMAX FORMATIONS OF WESTERN NORTH AMERICA.
consociations in each. Other important species which they have in common
are Pinws Tnonticola, P. ponderosa, and P. contorta, while such subcUmax
species as Arbutus menziesii and Quercus calif ornica occur in both. By far the
most significant fact, however, is the association of 5 coastal dominants with
4 from the montane forest to constitute the transition community.
The chief contact of the Coast climax is with the montane forest. They
are in touch with each other from northern California to central Oregon, and
then as outposts through northeastern Oregon to Idaho and Montana. This
contact continues through British Columbia to the sixtieth parallel. Here the
montane and subalpine forests give way to the boreal forest of Picea mariana,
P. alba, and Pinus divaricata, which covers the interior of Yukon and Alaska
behind the coastal strip of Picea sitchensis and Tsuga heterophylla. On the
mountain ranges of the central area the Coast forest meets the subalpine
climax at altitudes of 5,000 to 7,000 feet. They mingle over a wide mountain
ecotone, and in the transition association, Picea engelmanni and Abies lasio-
carpa form subchmax communities at exceptionally low levels.
Associations. — The chief reasons for recognizing two associations in the
Coast formation have already been touched upon. It may be well to state
them explicitly here, as this involves a readjustment of the current views.
The first and most important of these reasons is the change of dominance
from the western to the eastern portion. Picea sitchensis drops out before the
Cascade Mountains are crossed, while Tsuga and Thuja change from primary
to secondary rank. Pseudotsuga continues to be of the first importance, but
shares this with several other dominants. A second reason of almost equal
significance is that Pinus monticola and Larix occidentalis reach their best
development and maximum dominance in the mountains of northern Idaho
and the adjacent region. The behavior of Picea engelmanni and, to a less
extent, of Abies lasiocarpa in descending from the subalpine forest to play
an important role in valleys and on north slopes, is also significant. Further-
more, the subdominants of the transition forest and its subclimax stages are
largely Rocky Mountain in relationship, especially in Idaho and Montana.
Finally the differences in the vegetation are correlated with a similar differ-
entiation of the climate. Over the region of the coastal community, the rain-
fall ranges generally from 50 to 80 inches, with a maximum in the Olympic
peninsula of more than 100 inches. Over most of the transition forest the
rainfall is only 20 to 35 inches, with a maximum of 40 inches only in the
Bitter Root range. There is Hkewise a marked difference in the annual dis-
tribution for the two regions. In the case of the eastern area, 30 to 60 per
cent of the precipitation occurs between April 1 and September 30, while
in the western but 10 to 30 per cent — i. e., 70 to 90 per cent of the rainfall
takes place during the winter months. The significant difference in tempera-
ture relations is indicated by a mean temperature of 45" to 52° and a minimum
one of 14° to -4° for western Washington, and of 38° to 45° and -25°
to —49° for western Montana.
The two associations may be almost equally well designated on the basis
of location and composition. The latter seems to afford the more clear-cut
and convenient distinction. The western or coastal portion is hence termed
the cedar-hemlock forest or Thuja-Tsuga association and the eastern is called
the larch-pine or Larix-Pinus association.
CLEMENTS
Coast Forest
PLATE 51
A. Pseiulotsuga, Thuja, and Tsuga, Rainier National Park, Washington.
B. Sequoia sempervirena consociation, Muir Woods, Mt. Tamalnais.
THE CEDAR-HEMLOCK FOREST. 217
THE CEX)AR-HEMLOCK FOREST.
THUJA-TSUGA ASSOCIATION.
Nature and extent. — This is much the more massive and continuous of the
two associations. The dominants are fewer and the composition less varied,
though the northern and southern extremes show striking differences from
the central portion. The trees are taller, the canopy denser, and the shrubby
undergrowth often developed to form almost impenetrable thickets. The
most typical expression of the forest is found between the coast and the upper
slopes of the Cascade Mountains from southern British Columbia to northern
Oregon. The long extension to the northward in Alaska shows a more or less
similar ecological character, but becomes reduced practically to two domi-
nants, Picea sitchensis and Tsuga heterophylla. The southward prolongation
into California resembles the main portion in the presence of practically all
its dominants, but this narrow coastal strip is differentiated by the paramount
role of Sequoia sempervirens (plate 51).
DOMINANTS.
TSUQA HETEROPHYLLA. AbIES GRANDIS. AbIES N0BILI8.
Thuja plicata. Sequoia sempervirens. Chamaecyparis nootkatensis.
Picea sitchensis. Abies amabilis. Chamaecyparis lawsoniana.
pseudotsuga mucronata.
Pseudotsuga mucronata is much the most important dominant with respect
to abundance. It is the typical species of burned areas, and hence has more
or less of the nature of a subclimax, particularly in view of its relatively low
tolerance. In addition, it is a major dominant of the montane forest, and for
these reasons it is less characteristic of the association than Tsuga and Thuja.
The essential character is given by Tsuga, Thuja, Picea, and Sequoia, prac-
tically all of which attain their best development along the coast or in low-
lands. Abies grandis is almost equally important in the larch-pine association
and A. amabilis in the subalpine forest. Abies nobilis and Chamaecyparis
nootkatensis also occur to some extent in the subalpine forest. While the
latter ranges to the northern Umits of the formation in Alaska, it drops out
in northern Oregon. Abies nobilis is restricted to western Washington and
Oregon and Chamaecyparis lawsoniana practically to the fog belt from Coos
Bay, Oregon, to Humboldt Bay, California.
Groupings. — The typical grouping of the cedar-hemlock forest is Pseudo-
tsuga, Tsuga, Thuja, and Picea. According to Gannett (1900 : 14:} Pseudotsuga
forms 64 per cent of the standing timber in western Washington, Tsuga 16
per cent. Thuja 14 per cent, and Picea 6 per cent. In western Oregon, the
figures are Pseudotsuga 81 to 85 per cent, Tsuga 6 to 7 per cent, and Thuja
1 to 2 per cent (1899 : 43), excluding the coast region where Picea occurs.
All of the four major dominants may form pure stands, but this is exceptional
for Thuja and frequent for Tsuga and Picea only in the .north. It is more or
less common in the case of Pseudotsuga, though as a rule the other dominants
are scattered through this consociation. Near the coast from British Columbia
to CaUfornia, Douglas fir and Sitka spruce are the chief associates, while in
California Pseudotsuga and Sequoia are most important. According to Sud-
worth (1908 : 147), the redwood is rarely pure, but usually forms 50 to 75
218 CLIMAX FORMATIONS OF WESTERN NORTH AMERICA.
per cent of the stand, with Douglas fir most abundant except in damp places,
and more or less Abies grandis, Tsuga, and Thuja. On river flats along the
coast, scattered Picea, Chamaecyparis lawsoniana, Tsuga, and Abies occur in
it. Abies amabilis and A. nobilis occur more or less commonly through the
groupings of the four major dominants, but usually form only a small fraction
of the stand, as is true also of Chamaecyparis nootkatensis.
Tsuga heterophylla and Picea sitcherms constitute the coastal forest of
Alaska. Sometimes they form pure stands, but they usually occur in mixture,
one or the other being dominant, Picea preferring the vicinity of the coast.
In southern Alaska they are more or less mixed with Thuja plicata, Abies
grandis and A. amabilis, and Chamaecyparis nootkatensis.
Factor and serai relations. — The cedar-hemlock forest occupies a region of
excessive rainfall and frequent or constant fog, with consequent low evapora-
tion. Over much of it the annual rainfall is in excess of 80 inches, the range
being 50 to 120 inches. In the United States 10 to 30 per cent of this falls
during the six winter months, and much the same conditions obtain to Sitka
and beyond. The temperatures are generally equable except at the higher
altitudes. The absolute minimum as far north as Sitka is but — 4°.
Quantitative studies of the water and light relations of the dominants are
still few (cf. Cooper, 1917 : 179), but they are in general agreement with the
topographic and serai relations. The following table of tolerance, based upon
successional relations, agrees fairly well with the conclusions of foresters.
The sequence is from the least to the most tolerant.
Tolerance of Dominants.
Pseudotfiuga mucronata. Abiea amabilis. Picea sitchensis.
Abies nobilis. Sequoia sempervirens. Thuja plicata.
Abies grandis. Chamaecyparis nootkatensis. Tsuga heterophylla.
The last five are unusually close in their tolerance, and the order given here
is not infrequently changed by soil, water, or temperature relations. In a
region of such excessive precipitation, the water relations are less clear and
are much influenced by temperature. The general relation to these com-
bined factors is indicated by the altitudinal range, though this is not in full
accord with that in latitude. The typical fog-belt trees are Picea sitchensis.
Sequoia sempervirens, and Chamaecyparis lawsoniana. These represent the
maximum conditions as to water-content and humidity. They are followed
closely by Thuja plicata, and this by Tsuga heterophylla and Abies grandis.
The abihty of Abies amabilis, A. nobilis, and Chamaecyparis nootkatensis to
endure more xeroid conditions is indicated by the fact that they occur in the
subalpine zone, where the first is frequent at timber-Une. Pseudotsuga is the
most xeroid of all the dominants, a fact in complete accord with its dominance
in bums and its importance in the montane forest.
SOCIETIES.
The development of shrubby societies often reaches a maximum in the
cedar-hemlock forest, though the actual number of species is few. As a con-
sequence, the light at the ground level is greatly reduced, and the herba-
ceous societies as a result are poorly developed.
THE LARCH-PINE FOREST.
219
Shrvba:
Gaultheria shallon.
Berberia nervosa.
Berberis aquifolium.
Vaccinium parvifolium.
Viiccinium macrophyllum
Vaccinium ovatum.
Salix acouleriana.
Acer circinatum.
Acer glabrum.
Cornus nuttallii.
Herbs:
Pteris aquilina.
Epilobium spicatum.
Blechnum spicant.
Polystichum munitum.
Anaphalis marKaritacea.
Adenocaulum bicolor.
Oxalis oregana.
Oxalis pumila.
Fragaria vesca.
Cornus canadensis.
Trientalis latifolia.
Ciintonia uniflora.
Asarum caudatum.
Actaea spicata arguta.
Echinopanax horridum.
Sambucus callicarpa.
Sambucus glauca.
Rubus parviflorus.
Rubus spcctabilis
Ribcs sanguineum.
Ribes bracteosum.
Ribes laxiflonim.
Ribes lacustre.
Pirus diversifolia.
Tiarella trifoliata.
Tellima grandiflora.
Mitella trifida.
Pirola picta.
Aquilegia formosa.
Anemone oregana.
Anemone quinquefolia.
Antennaria raccmosa.
Disporum smithii.
Streptopus roseus.
Washingtonia divaricata.
Vancouveria hexandra.
Viola sempervirens.
Menziesia ferruginea.
Pachystigina myrsinites.
Chimaphila umliellata.
Linnaea borealis.
Spiraea menziesii
Symphoricarpus mollis.
Viburnum ellipticum.
Prunus emarginata.
Rhododendrum ellipticum.
Viola howellii.
Lilium parviflorum.
Lathyrus polyphyllus.
Trillium ovatum.
Smilacina amplexicaulis.
Apocynum androsaemifolium.
Lupinus lepidus.
Lupinus rivularis.
Ranunculus occidentalis.
Ranunculus oreganus.
Calypso borealis.
Moneses uniflora.
Dicentra formosa.
THE LARCH-PINE FOREST.
LARIX-PINUS ASSOCIATION.
Nature and extent. — The transition forest shows much of the general char-
acter of the coastal association, but in a smaller way. The trees are not so
vigorous and the association is less dense and exclusive. Of the four major
dominants of the cedar-hemlock forest, Picea sitchensis has disappeared, Tsuga
and Thuja are greatly reduced in importance as a rule, and Pseudotsuga shares
the control with several equally important species. The canopy is more open
and the undergrowth richer in both species and individuals. There is a wider
range of habitat conditions with the result that the major dominants are more
equal in rank and occur in more clearly differentiated groupings.
This association occupies the eastern slopes of the Cascade Mountains of
Washington and Oregon, below the subalpine zone. It stretches across the
mountains of northern Washington into northern Idaho and northwestern
Montana, reaching its eastern limit on the western slopes of the Continental
Divide. It is found on the Gold and Selkirk Ranges of southeastern British
Columbia and in the Blue and Wallowa Mountains of Oregon and adjacent
Washington, From here it extends eastward through the ranges of Idaho to
the southern portion of the Bitterroot Mountains. To the southeast, as well
as in the interior ranges of British Columbia and northern Washington, it is
often reduced to one or two of the dominants found in the Petran montane
forest, and it then becomes impossible to draw a clear line between the two
formations (plate 52).
DOMINANTS.
LaRIX OCCIDENTAU8.
PiNUS MONTICOLA.
Abies qrandib.
Thuja plicata.
Tsuga heterophylla.
Pseudotsuga mucronata.
PiNUS P0NDER08A.
PlNUS CONTORTA.
PiCEA ENGELMANNI.
220 CLIMAX FORMATIONS OF WESTERN NORTH AMERICA.
The first five species represent the coastal association, the others the mon-
tane forest. Pseudotsuga, however, belongs to both, and Picea engelmanni is
normally a dominant of the subalpine zone. Pinus monticola is also more or
less montane in character, ranging far south into the Sierra Nevada. Like
iMrix occidentalism it reaches its optimum development in northern Idaho and
the adjacent regions, and these two may well be regarded as the most typical
dominants of the transition forest. While Ahies grandis ranges from the
Coast to northwestern Wyoming, it too is more characteristic of the transition
forest, largely perhaps because of the absence of the more tolerant sp)ecies.
Tsuga and Thuja occur generally throughout the region, but are usually of
minor importance. Tsuga drops out jQrst toward the boundaries of the
forest, leaving Ahies and Thuja to represent the final stage of the climax.
Pinus ponderosa, P. contorta, and Picea engelmanni are all of the widest range
and play a part in at least two formations.
Groupings. — The groupings of the dominants of the larch-pine forest are
numerous and complex. The drier areas are generally controlled by Pinus
ponderosa and Pseudotsuga, with more or less P. contorta, Ahies grandis, and
Larix. The moister ones are dominated by Pinus monticola and Larix, with
varying amounts of Thuja, Tsuga, and Picea engelmanni. In the Priest
River region Leiberg (1899:246) gives the abundance of the dominants as
follows: yellow pine zone Pseudotsuga 70 per cent, Pwms 10 per cent, Ahies
15 per cent; white pine zone Pinus monticola 42 per cent, Larix 35 per cent,
Thuja 8 per cent, Picea engelmanni 6 per cent, Tsuga 3 per cent, Ahies 2
per cent. In the Bitterroot Mountains where the western species are im-
portant, the percentages are: Pinus contorta 25, Picea engelmanni 19, Pseu-
dotsuga 14, Pinus monticola 12, Ahies grandis 9, Larix 6, and Thuja 4. Where
the montane element predominates the values are: Pseudotsuga 34, Pinus
ponderosa 21, P. contorta 17, Picea engelmanni 11, Thuja 5, Ahies 4. In the
Flathead region of Montana Larix and Pseudotsuga are often the most im-
portant, with all the other dominants present here and there in some degree.
In the Selkirks Thuja and Picea usually occupy the valleys and Pseudo-
tsuga and Tsuga the slopes, while Pinus monticola, Larix, Pinus contorta, and
P. ponderosa also occur. In eastern Washington Pinus and Pseudotsuga are
controUing, with considerable Larix, Pinus contorta, P. monticola, and a small
amount of Tsu^a and Thuja. The dominants of the Blue Mountains are
Pinus ponderosa, Pseudotsuga, Ahies grandis, Larix, and Pinus contorta.
Factor and serai relations. — The general cUmatic relations of the larch-pine
forest have already been pointed out (p. 216). Larsen (1916: 437) has indi-
cated the general water and Ught relations of the dominants in the following
lists:
Water-content, on wet ground : Picea engelmanni, Tsuga heterophylla, Thuja
plicata.
Water-content, moist or intermediate ground : Pinus monticola, Ahies grandis,
Larix ocddentalis.
Water-content, dry ground : Pinus contorta, Pseudotsuga mucronata, Pinus
ponderosa.
Tolerance : Pinus ponderosa, Larix ocddentalis, Pinus contorta, Pseudotsuga
mucronata, Pinus monticola, Picea engelmanni, Ahies grandis, Tsuga hetero-
phylla, Thuja plicata.
CLEMENTS
Transition Forest
A. Pseudolsuga, Tsuga, and Pintis moniicola, Carson, Washington.
B. Pseudotsuga, Pinus moniicola, Larix, and Thuja, Priest River, Idaho.
THE LARCH-PINE FOREST.
221
The range in altitude is shown by the following list, in which the order is
descending. The first two belong primarily in the subalpine forest.
Abies lasiocarpa.
Picea engelnianni.
Pinus contorta.
Pseudotfiuga mucronata.
Abies grandia
Larix occidentalis.
Thuja plicata.
Pinus monticola.
Tsiiga heterophylla.
Pinus ponderosa.
Weaver (1917: 19) has studied succession in the transition forest near
Moscow, Idaho, and has determined its relation to water-content, evaporation,
and soil temperature. Thuja is the final dominant in this region, Tsnga being
absent. The sequence is as follows : Syniphoricarpus-Opulaster, Pinus-Pseudo-
tsuga, Pinus, Pseudotsuga, Larix-Abies, Larix, Abies, Thuja {Tsuga).
The water-content of the yellow pine community ranged from 5 to 15 per
cent lower than in the Douglas fir-larch, and 20 to 30 per cent below that in
the grand fir-larch, while in the latter it was 10 to 40 per cent lower than in the
final cedar forest. Evaporation in the latter was 2 to 5 c.c. less daily than in
the Pseudotsuga-Larix mictium and 5 to 15 c.c. less in this than in the yellow
pine forest. The soil temperatures decreased with much uniformity from the
pine to the cedar community. The minimum light value for the Pseudotsuga
forest is about 0.02, for the Larix-Abies mictium 0.01 to 0.007, and for the
Thuja forest 0.005 to 0.003.
SOCIETIES.
The number of these depends primarily upon the light intensity. In the less
shady Larix-Abies forest, the number is fairly large and the shrub layer is
well-developed, while the deep shade of the Thuja forest permits but a small
number to persist (Weaver, 1917: 86, 88).
Shrvha:
Chimaphila umbellata.
Lonicera utahensis.
Menziesia ferruginea.
Pachystigma myrsinites.
Herb«:
Actea spicata arguta.
Adenocaulum bicolor.
Anemone quinquefolia.
Arnica cordifoiia.
Asanun caudatum.
Clintonia uniflora.
Shrvba:
Ribes lacustre.
Herbs:
Aconitum columbianum.
Anemone quinquefolia.
Asarum caudatum.
Athyriura cyclosorum,
Circaea pacifica.
LARIX-ABIES COMMUNITY.
Pirua sitchensis.
Ribes viscosissimum.
Ribes lacustre.
Rosa pisocarpa.
Coptia occidentalis.
Disporum majus.
Fragaria vesca.
Linnaea borealis longiflora.
Mitella trifida.
Pirola picta.
THUJA COMMUNITY.
Rubus parviflorua.
Claytonia asarifolia.
Clintonia uniflora.
Coptis occidentalis.
Smilacina amplexicaulis.
Streptopus majus.
Rubus parviflorus.
Sambucus melanocarpa.
Vaccinium macrophyllum.
Streptopus majus.
Thalictrum occidentale.
Tiarella unifoliata.
Smilacina amplexicaulis.
Trillium ovatimi.
Washingtonla divarioata.
Tiarella unifoliata.
Trillium ovatum.
Viola glabella.
Viola orbiculata.
222 CLIMAX FORMATIONS OF WESTERN NORTH AMERICA.
THE SUBALPINE FOREST CLIMAX.
PICEA-ABIES FORMATION.
Nature. — The subalpine climax is the most variable of all the forests in its
ecological character. At its contact with the montane forest, the trees are
often 100 feet high, the canopy is closed, and a typical undergrowth is present.
In the ecotone between the two, the -respective dominants meet on nearly
equal terms to form an apparently homogeneous forest. At higher altitudes the
forest mass becomes more and more open or fragmented and nearer timber-
line is broken up into isolated groves and clumps. The individuals decrease
steadily in stature as the altitude increases and at timber-line they are either
greatly dwarfed or much deformed by the action of wind or snow. It is
exceptional that an actual forest community exists at timber-line when the
latter is due to cUmatic rather than local causes. The subalpine forest may be
bordered by a more or less complete zone of scrub, consisting of willows, birches,
or heaths, at its upper edge, or it may yield directly to alpine sedgeland.
The latter may extend down into the forest for considerable distances
along valleys or on rock or gravel slides, and as a consequence often furnishes
a large part of the undergrowth at the higher altitudes. There is generally a
marked tendency to form pure stands, as a result of the rigorous climatic
selection of species. The number of the latter is especially reduced toward
timber-line, which is often formed for long distances by one or two species.
Extent. — The subalpine forest is found from Alaska and Yukon to Mexico
and Lower California, wherever the altitude is sufficiently great. At the
north it extends somewhat into the plains east of the Rocky Mountains where
it meets the boreal Picea-Abies cUmax. South of the northern portion of
New Mexico and Arizona, and of the Sierra Nevadas, it is fragmentary and
usually represented by but one or two species. Its eastern limit lies along the
crests of the Front ranges in Colorado, and the western is found on the San
Jacinto, San Bernardino, and Sierra Nevada ranges north to the Siskiyous.
In Oregon and Washington, the western limit runs along the Cascades to the
Olympics and the peaks of Vancouver Island, from which it follows the Coast
ranges as far as Cook Inlet in Alaska. The northernmost dominant is PiniLS
contorta, which reaches latitude 64° in Yukon. Between the two great moun-
tain axes on which the subalpine formation attains its major expression, it is
found in reduced form on the higher ranges of the interior, such as the Blue
and Powder River Mountains of Oregon, the Charleston Mountains of Nevada,
and the Panamint and Inyo Ranges of southeastern California.
Unity. — The floristic unity of the subalpine climax is necessarily somewhat
less than that of the montane and coast formation, owing to the many barriers
offered by climate, topography, and vegetation to the species of high altitudes.
In spite of this fact, however, the formation exhibits a high degree of unity.
The two chief dominants, Picea engelmanni and Abies lasiocarpa, occur
throughout the formation, except in California. As a subalpine dominant,
Pinus contorta extends from the mountains of Yukon to the San Pedro Martir
of Lower California, and from the Front Range of Colorado to the Cascades
and the northern Coast ranges. Pinus flexilis and P. aristata also occur
practically throughout the entire formation, though each develops two dis-
THE SUBALPINE FOREST CLIMAX.
223
Lake Moraine
, Colo.
5
4
3
2
1
0
Frances, Colorado
26 in.
26 in.
>
1
1 1
II
II
ll
ll
Fig. 11. — Monthly and total rainfall for represent-
ative localities in the Petran eubalpine forest.
tinct forms which replace e^ch other. The two other most typical dominants
are Tsuga mertensiana and Larix lyallii. These are essentially Coastal in
character, but both occur in the transition area of northern Montana and
Idaho and Larix reaches the Rocky Mountains in southern Alberta. The
other characteristic dominant is Abies magnifica, which is found only in Cali-
fornia and southern Oregon, and may well be regarded as the ecological rep-
resentative of A. lasiocarpa.
The ecological unity of the formation is well shown by the behavior of the
individuals as well as of the community in the upper part of the zone and at
timber-line, as already noted. This is emphasized by its constant relation to
the montane forest below it and the alpine climax above. Geographically,
the formation is consistently one of high mountain ranges and peaks or of
northern ones. The geographic and topographic relations serve to explain
the uniformly boreal cUmate in which it flourishes. This is characterized by a
short growing season, high precipi-
tation, largely in the form of snow,
and wide diurnal and seasonal range
of temperatures. The long winter
is often marked by high winds and
excessive transpiration in relation
to the chresard, and these have a
controlling influence in determin-
ing the timber-line (fig. 11).
Kelationship and contacts. — The subalpine chmax shows some relationship
to three different formations, viz, the boreal forest, the Coast forest, and the
montane forest. Its closest relationship appeals to be with the first, since the
chief dominants in both belong to the two genera, Picea and Abies, and the
species are also more or less related. It seems probable that the boreal forest
represents a Tertiary spruce-balsam climax from which the subalpine forma-
tion was differentiated. The relationship to the Coast forest is shown by the
species of Abies in the latter, and by the presence of Tsuga and Larix in each,
though represented by different species. An additional relation is found in the
fact that Picea engelmanni is common and Abies lasiocarpa not infrequent in
the lower levels of the transition association of the Coast forest. Finally, several
dominants of the latter, such as Abies amabilis, A. nobilis, and Chamaecyparis
nootkatensis occur frequently in the subalpine zone, and the former especially
may often form the timber-Une. The relationship to the montane forest is
shown chiefly by the presence in each of closely related species of Picea and
Abies, though the two genera play a much less important r61e in the montane
zone. Pinus contorta and Populus tremuloides are common to the two zones,
and Abies concolor, Pinus jeffreyi, and Pinus monticola form a broad ecotone
with the subalpine dominants.
The lower contact of the subalpine formation is with the montane forest
in the Rocky Mountains from New Mexico to Alberta and in the ranges of the
interior. This is the case also in the mountains of southern California, the
Sierra Nevada, and the Cascades to northern Oregon. From here to the
Kenai Peninsula in Alaska, and to Idaho and northwestern Montana, the
subalpine forest touches the Coast climax. In northern British Columbia
224 CLIMAX FORMATIONS OF WESTERN NORTH AMERICA.
and Alberta, and in the Yukon, it lies in contact with the boreal forest. The
upper contact is everywhere with the alpine climax when this is present. In
many places the forest becomes so dwarfed and open as to form what is essen-
tially an alpine savannah.
Associations. — The subalpine climax resembles the montane one in its dif-
ferentiation. This is obviously due to the practically complete separation of
the Petran and Sierran axes, except in the north. As a result, the formation
has developed a distinct association along each axis where they are widely
separated and exhibits a transition area in the north, where they are contigu-
ous. Since the transition results from the mingling of two associations of the
same formation, it is undesirable to give a distinct value to it, as was done
with the broad ecotone between the Coast and montane climaxes.
There are three chief reasons for recognizing two associations. The first is
that Picea engelmanni and Abies lasiocarpa are the two major dominants in the
Rocky Mountains, while they have several codominants from Oregon and
Idaho to Alaska and are lacking in California. The second reason is that
Pinus flexilis and P. aristata are typical of the Petran axis, but the former is
replaced in the Northwest and the Sierras by P. aUncauUs, and the latter by
P. balfouriana in California. The third lies in the fact that Tsuga mertensiana,
Larix lyallii, and Abies magnifica are confined to the western association.
Furthermore, the societies of the two associations are composed for the most
part of different species, though the genera are largely identical.
The two associations may be designated as eastern and western simply, as
Petran and Sierran, or by using the names of typical dominants, as the spruce-
balsam and pine-hemlock associations. It seems preferable to use the terms
Petran and Sierran as a rule, since the division is similar to that of the montane
forest. In both cases the word Sierran is used to include the mountain axis
from California to British Columbia.
THE PETRAN SUBALPINE FOREST.
PICEA-ABIES ASSOCIATION.
Extent. — The northern limit of the spruce-balsam forest seems to be in the
inland ranges of southern Yukon, but the contiguity of the two associations
and the boreal forest is such that it is impossible to distinguish their proper
limits with our present knowledge. This association is well-developed in the
Rocky Mountains of British Columbia and Alberta and extends eastward
toward the Lesser Slave Lake. It occurs throughout the main ranges of the
Petran axis from Montana to northern New Mexico and Arizona. It is
found in reduced form on the Charleston Mountains of southern Nevada
and the Panamint Range of southeastern California. It should probably be
assigned to the Blue Mountains of Washington and Oregon also, though Tsuga
mertensiana occurs on one peak. This illustrates the difficulty in drawing a
Umit between the two associations in the Northwest, and at present it must
suffice to assign the spruce-balsam community to the ranges of central Idaho
and southwestern Montana (plate 53).
In altitude, the community ranges from 3,000 to 7,000 feet in the north
to 8,000 to 12,000 feet in Colorado and New Mexico.
CLEMENTS
Petran Subalpine Forest
PLATE 53
A. IHcea-Abies association at Monarch Pass, Salida, Colorado.
B. Picea-Abks association on Unoompahgrc Plateau. Colorado.
C. Picea-Pinus arktata at timber-line, King's Cone, Pike's Peak.
THE PETRAN SUBALPINE FOREST. 225
DOMINANTS.
picea enoelmanni. pinus ari8tata. plnus plexilis albicaulis.
Abies lasiocarpa. Pinus flexilis. Pinus contobta.
Picea engelmanni and Abies lasiocarpa are the two major dominants through
practically the entire area of the association, except for the ranges of the
Great Basin. Pinus contorla has a similar extensive range, but it drops out
in southern Colorado. Pinus flexilis is much less important, though it has the
widest range of all, extending from Alberta to New Mexico, Arizona, and
southeastern CaUfornia. Pinus aUbicaulis belongs chiefly to the Sierran associ-
ation, but is found in the Rocky Mountains from Alberta to northwestern
Wyoming. Pinus aristaia is essentially southern in distribution, occurring
from northern Colorado to northern New Mexico and Arizona and westward
to the Panamint and Inyo Ranges of southeastern CaUfornia.
Groupings. — The basic grouping throughout is that of Picea and Abies
This is varied in the north chiefly by the inclusion of Pinus contorta. Pinus
flexilis and P. aUbicaulis may occur in the community here also, and even
Larix lyallii enters it in Alberta. In northern Colorado the usual grouping
is Picea, Abies, Pinus contorta, and P. flexilis, while in central Colorado and
southward the lodgepole pine drops out and Pinus aristata appears. In the
Pike's Peak region both Pinus contorta and Abies lasiocarpa are absent and
the forest consists of Picea engelmanni for the most part, while Pinus aristata
and P. flexilis become associated with it toward timber-Une. On the desert
ranges of the Southwest, Pinus flexilis and P. aristata alone remain to represent
the subalpine forest. Extensive pure stands are frequent for Picea, Abies,
and Pmits contorta, while the mixed forest of Picea and Abies often covers
great areas without any other dominant except the subclimax Populus tremu-
loides. The last is an important tree throughout the subalpine zone, covering
burned areas everywhere, in the absence of the lodgepole pine especially.
It also resembles the latter in occurring in both zones.
Factor and serai relations. — The precipitation in the central part of the area
ranges from 22 to 40 inches a year, of which the snowfall is 8 to 14 feet. On
interior ranges the rainfall may be somewhat less. The evaporation is much
less than in the montane zone, the reduction often exceeding 25 to 50 per cent.
At the lower limit the growing season is 3 to 4 months long, at the upper barely
2 months. The mean temperatures are 5 to 10 degrees lower than in the
montane forest, and near timber-line frost occurs frequently or regularly during
the summer.
Picea engelmanni is the most mesophytic of the dominants, often growing
at the edges of streams and in bogs. It is followed more or less closely by
Abies lasiocarpa, while all the pines are much more xeroid. Pinus contorta
is the most mesophytic of these, while the remaining species are more or less
similar, P. flexilis usually growing in the driest situations. As to light rela-
tions, Picea is the most tolerant, though Abies often equals it. The pines are
all much less tolerant and do not differ markedly from each other in this
respect. Pinus contorta is the most tolerant, and P. flexilis and P. aristata
the least, though all must be regarded as intolerant.
The water and light relations furnish a clear explanation of the successional
sequence (Clements, 1910: 54). The main body of the forest is composed of
226 CLIMAX FORMATIONS OF WESTERN NORTH AMERICA.
Picea and Abies, the slight handicap of the latter in competition with Picea
being offset by its abiUty to produce new plants by layering. Burn areas are
dominated by lodgepole pine or aspen, or by the two in varying mixture.
The aspen yields to the pine, and this in turn to the spruce and balsam. This
is Ukewise true of Pinus flexilis or P. aristata, where they occur on rocky
ridges or dry slopes in the heart of the association. Wheja the forest becomes
more open or breaks up into groups toward timber-line, the tolerance of the
spruce and balsam loses most of its advantage and the pines persist as per-
manent constituents of the community.
SOCIETIES.
Owing to its position, the subalpine forest has many societies in common
with the montane forest in its lower half and with the alpine meadow in the
upper. The societies are best developed in the central area, and decrease in
numl^er and importance toward both extremes, but especially to the north.
The following list for the Colorado region is fairly representative :
Shrub layer:
Linnaea borealis.
Lonicera involucrata.
Pachystigma myrsiiiites.
Herbs, t emal Societies:
Thalictrum fendleri.
Polemonium pulchellum.
Mertensia polyphylla.
Aquilegia coerulea.
Fragaria vesca.
Draba aurea.
Draba streptocarpa.
Herbs, Eslival Societies:
Sedum stenopetalum.
Solidago humilis.
Arnica cordifolia.
Pedicularia racemosa.
Ribes lacuatre.
Shepherdia canadensis.
Salix nuttallii.
Arabis drummondii.
Aisine baicalensis.
Adoxa moschatellina.
Zygadenus elegans.
Aragallus deflexua.
Ligusticum porteri.
Pirola minor.
Carduus hookerianus.
Castilleia miniata.
Erigeron elatior.
Erigeron salsuginosus.
Vaccinium caespitosum.
Vaccinium myrtilius.
Mitella pentandra.
Mitella trifida.
Parnasaia fimbriata.
Androsace septentrionalis.
Pentstemon glaucus.
Pseudocymopterus montanus.
Gentiana frigida.
Gentiana amarella.
Poa pratensia.
Featuca ovina.
THE SIERRAN SUBALPINE FOREST.
PINUS-TSUGA ASSOCIATION.
Extent. — The subalpine forest reaches its northern limit along the Pacific in
the neighborhood of the sixtieth parallel, stretching west in Alaska from Lynn
Canal to Cook Inlet. It follows the summits of the Coast ranges southward
to southern British Columbia, where it broadens out to the eastward and
comes into contact with the Petran association in Alberta and Montana. It
occurs throughout the mountains of Washington from the Olympics to those
of the northeastern part of the State, but is only slightly developed in the
Blue Mountains. It follows the Cascade Range throughout Oregon into the
Siskiyou and the Sierra Nevada of California. It maintains its characteristic
expression throughout the latter, though Picea and Abies lasiocarpa have dis-
appeared. On the eastern slopes, it sometimes comes into contact with the
Petran association. The subalpine forest is much reduced in the San Ber-
nardino and San Jacinto Mountains ; its most southern outpost is probably in
the San Pedro Martir Range of Lower California (plate 54).
The altitude of the subalpine zone changes greatly from Alaska to southern
CaUfomia. In Alaska it is chiefly at 2,000 to 4,000 feet, in southern British
Columbia at 3,000 to 6,000 feet, and in the Cascades at 5,000 to 8,000; while
in the Sierra Nevada it lies at 7,000 to 10,000, or rarely 12,000 feet.
CLEMENTS
Sierran Subalpine Forest
nfi^ ^'
•^^^r.
A. Tsuga lyaJlii coiisociulion, Crater Lake, Oregon.
B. Abies magnifica consociation, Glacier Point, Yosemite National Park,
THE SIERRAN SUBALPINE FOREST. 227
DOMINANTS.
TSUQA MERTEN8IANA. PiNTJS ARI8TATA BALFOURIANA. AbIES AMABILIS.
PiNUS CONTORTA. PiCEA ENGELAIANNI. AbIES NOBILI8.
PiNUS FLEXILI8 ALBICAULIS. AbIES LASIOCARPA. ChaMAECYPARI8
LaRIX LTALLII. PiNUS FLEXILIS. NOOTKATEN8I8.
Abies magnifica. Pinus monticola.
The characteristic dominants of this association are the first six. The next
three are more typical of the Petran subalpine forest, and the last four of the
Coast forest climax. These differences seem to forehadow a further differ-
entiation of the community, but they may be due largely to the uncompleted
migration of certain species. The two dominants of the greatest extension
are Tsuga and Pinus contorta, the latter more truly cUmax in nature than in
the related association. Tsuga ranges from Cook Inlet to the southern
Sierras and from the Coast to the Bitterroot Range between Idaho and
Montana. Pinus contorta extends from Skagway in Alaska to Lower Cali-
fornia and throughout the greatest width of the association from the coast
to Montana. Pinus albicaulis occurs from southern British Columbia and
adjacent Montana to the Cascades of Washington and Oregon and thence
southward along the Sierra Nevada to the thirty-sixth parallel. Larix lyallii
has a much more restricted distribution ; it is found in Canada only in south-
eastern British Columbia and adjacent Alberta. It is frequent in northwestern
Montana and northern Idaho and occurs throughout the Cascade Mountains
of Washington as well as in those of the northeast, but is found only rarely
in the Cascades of northern Oregon. Abies magnifica, with its variety shas-
tensis, is confined to California and Oregon, extending from Crater Lake
southward in the Sierra Nevada to Kern River, and in the Coast ranges to
Lake county. Pinus balfouriana is found only in California.
Abies lasiocarpa and Picea engelmanni extend from Alaska to southern
Oregon, while Pinus flexilis appears to enter this association only in Alberta
and Montana, the southern Sierras, and the cross ranges from Mount Pinos
to the San Jacinto Mountains. Abies amabilis, A. nobilis, and Chamaecyparis
do not occur south of Oregon, while Pinus monticola is important in the sub-
alpine forest chiefly in the Sierra Nevada.
Groupings. — The large number of dominants and the extensive range make
the groupings exceedingly varied. There is a marked tendency for the domi-
nants to appear in pure consociations near timber-Une, while in the lower part
of the zone several usually occur in mixture. In the ranges of the upper
Columbia Basin,, AWes lasiocarpa and Picea engelmanni are regularly present
and usually are associated with one or more of the following: Pinus contorta,
Pinus albicaulis, Larix lyallii, and Tsuga mertensiana. Tsuga and Abies
lasiocarpa arc found together in Alaska, while farther south Picea engelmanni,
Pinus albicaulis, Larix lyallii, and Abies amabilis are commonly associated
with them, and Abies nobilis and Chamaecyparis less frequently. In the Sierra
Nevada, Tsuga occurs with Abies magnifica, Pinus contorta and P. m,onticola
through most of the zone and with P. albicaulis in the upper portion. Pinus
balfouriarui replaces or mixes with P. albicaulis in much the way that P.
aristata does with P. flexilis in the Rocky Mountains. It occurs with Pinus
contorta, Abies magnifica, and Tsuga in the lower part of the forest, with P.
monticola higher up, and with P. albicaulis at timber-Une. In the southern
Sierras and in the cross ranges of southern California Pinus flexilis is associated
with P. contorta and Tsu^a, or with either alone.
228 CLIMAX FORMATIONS OF WESTERN NORTH AMERICA.
Factor and serai relations. — Climatic data for the pine-larch association are
almost completely lacking. In the Sierras, the precipitation ranges above
50 to 75 inches, and the snowfall may be as great as 300 to 900 inches, or 50
to nearly 100 per cent of the total. The general climatic relations are as
already indicated for the formation.
The water relations of the dominants are imperfectly known. Picea,
Tsiiga, and Abies lasiocarpa grow generally in the moister areas, Pinus monti-
cola, P. contorta, Larix, and Abies magnifica in intermediate ones, and Pinus
albicaulis, fiexilis, and balfouriana in the drier. The general light relations
may be indicated by the following table of tolerance in which the order is
from the intolerant to the tolerant. The order of the dominants likewise
indicates the serai sequence in so far as it is known.
1.
2.
3.
4.
6.
Pinus balfouriana.
Pinus flcxilis.
Pinus albicaiilis.
Larix lyallii.
Pinus contorta.
6. Abies magnifica.
7. Pinus monticola.
8. Abies lasiocarpa.
9. Picea engelraanni.
10. Teuga mertensiana.
SOCIETIES.
The Sierran subalpine forest does not have a large number of societies
peculiar to it. The majority of those which occur in it have been derived
from the montane forest or the alpine meadow. This is especially true of the
shrubs, many of which extend up from the subclimax chaparral (p. 213).
The following list applies particularly to California:
Shrubs:
Arctostaphylus nevadensis.
Ribes viscosissimum.
Ribes montigenum.
Potentilla fniticosa.
Haplopappus sufFruticosus.
Lonicera conjugialis.
Juniperus communis.
Vaccinium occidentale.
Vaccinium caespitosum.
Ceanothus cordulatus.
Acer glabrum.
Herbs:
Artemisia norvegjca.
Hieracium gracile detonsum.
Sibbaldia procumbens.
Haplopappus macronema.
Potentilla breweri.
Ranunculus alismifolius.
Phacelia hydrophylloides.
Whitneya dealbata.
Orthocarpus pilosus.
Erysimum asperum,
Eriogonum marifolium.
Eriogonum ursinum.
Polygonum davisiae.
THE ALPINE MEADOW CLIMAX.
CAREX-POA FORMATION.
Nature. — The alpine climax is essentially a grassland in appearance, though
it is chiefly composed of sedges. The dominants are all grasslike in character
and the most typical regularly form a turf which rivals that of the buffalo-
grass in compactness. They are 2 to 6 inches high for the most part, though
some exceed this in subclimax situations or in the lower part of the zone. The
total number of dominants is greater than for any other formation, but the
number in a particular community is rarely excessive. A characteristic
feature of the dominants is their remarkable range, nearly half of them occur-
ring from Greenland to Colorado, California, and Alaska, wherever alpine or
arctic habitats are found. A large number of these grow in similar situations
CLEMENTS
Petran Alpine Meadow.
A. Carex-I'oa association, King's Cone, Pike's Pwik.
B. Carex consociation, Campanula society, Pike's Peak.
THE ALPINE MEADOW CLIMAX. 229
in Eurasia. This unique extension of arctalpine plants has a definite historical
as well as physical basis.
The total number of subdominants which form important societies is prob-
ably greater than for any other formation. The grassland climax approaches
it in this respect, while the prairie and the alpine meadow have much in com-
mon in so far as the number and luxuriance of the societies are concerned.
These are often so dense and continuous that the grass-like character of the
climax is completely hidden. The subdominants are even more strikingly
dwarfed than the dominants, chiefly because of a relatively greater emphasis
on the flower. In many the inflorescence is reduced to a single flower of
unusual size, while the stem is often less than an inch in height. A consider-
able number have assumed the mat or rosette habit and are essentially stem-
less, though this is more frequently the case in serai habitats.
The true character of the alpine climax is often difficult of recognition,
owing to the wide variation in conditions over what appears to be fairly uni-
form terrain. Rock fields of all degrees, gravel-slides, bogs, wet meadows,
and temporary snow-seeps in all stages of succession frequently blur the out-
lines of the climax or break it up into many fragments. The real nature of
the chmax is best seen in the Rocky Mountains of Colorado, where the alpine
areas are unusually extensive as well as free from snow during the summer.
In such places the general resemblance to a short-grass plain is striking. While
the alpine climax is ecologically a grassland, the predominance of sedges makes
it more accurate to refer to it as sedgeland. The term alpine meadow is
perhaps even more descriptive and is to be preferred to alpine heath, since
the latter is usually subclimax in character (plate 55).
Extent. — In the view advanced here, the alpine and arctic sedgelands of
North America are regarded as constituting one formation. This seems to
accord with the general opinion that the arctalpine region is a unit life-zone
(Merriam, 1898). As such, the arctalpine climax extends across Arctic
America from Greenland to Alaska. The southern hmit of it as a continen-
tal zone runs from central Labrador northwest to the lower Mackenzie River,
and then westward through Alaska. As is well known, the arctalpine chmax
extends south over the isolated alpine summits of New England, but sweeps
much farther southward in the Rocky Mountains and the Sierra Nevada.
An alpine zone is found on the volcanoes of Mexico, but its relationship to the
present climax is uncertain. Along the Rocky Mountain axis the last out-
posts of the climax are found in the Sangre de Cristo Mountains of northern
New Mexico and the San Francisco peaks of northern Arizona. In California,
the single locaUty south of the Sierra Nevada is in the San Jacinto Range
(Hall, 1902: 16), where it is reduced to a mere fragment. By far the most
extensive development of the formation is found in the central Rockies of
Colorado and Wyoming and adjacent Utah, while the most complete and
continuous is in Colorado.
Unity. — The ecologic and climatic unity of the arctalpine climax is so strik-
ing as to need little comment. The topographic and geographic unity appears
to be slight, but an adequate explanation is found in the correlating influence
of latitude and altitude. The general ecological unity appears to be fully
confirmed by the distribution and occurrence of the dominants as shown by
the table on the following page.
230 CLIMAX FORMATIONS OF WESTERN NORTH AMERICA.
DistribtUion of dominants
Genera.
No. of
species.
Eastern
Arctica.
Western
Arctica.
Petran.
Sierran.
Eurasia.
Carex
32
1
1
12
1
1
17
1
28
1
1
21
1
1
14
1?
1
Kobreaia
Elyna
Cyperaceae
Poa
34
14
18
30
23
16
15
3
2
2
2
1
1
1
4
1
2
2
2
1
1
1
5'
1
2
2
2
1
1
11
3
2
2
2
1
1
1
7
3
2
2
2
1
1
1
1
2?
1
Agrostis
Festuca
Calamagrostis
Deschampsia
Trisetum
Danthonia
Phippsia
Poaceae
Juncodes
27
14
14
23
18
6
4
6
4
3
4
5
4
5
2
3
4
3
Juncus
Juncaceae
Grand total
10
7
9
9
5
7
71
35
41
62
46
28
The occurrence of the 13 dominant genera practically throughout the four
regions seems conclusive evidence of their formational unity. This is em-
phasized by the distribution of the genera of subdominants as well. The
preeminence of Carex is obvious, as well as the importance of Poa. Juncus
probably has a higher value than it deserves, owing to the fact that some sub-
cUmax species persist into the climax. The typical character of the Petran
region is shown by the fact that nearly 90 per cent of the dominants are found
in it. The number of endemic dominants in any one of the regions is so small
as to be negligible. The close relationship to the Eurasian arctalpine climax
is evident, as well as the fact that this is largely due to Carex, Juncodes, and
JunciLS.
Relationship and contacts. — The primary relationship of the arctalpine
climax is with the corresponding Eurasian formation. The number of domi-
nants and subdominants common to both is sufficiently large to suggest that
they should be regarded as associations of the same formation. In this re-
spect, however, their difference is greater than their similarity, as one who has
seen both must readily recognize. There can be Uttle question that the two
climaxes have originated from a common ancestral community. The arctal-
pine chmax is also related to a similar community on the high peaks of Mexico.
The two have many genera in common, but the species are nearly all different
and the r6le of the grasses is emphasized at the expense of Carex. In the pres-
ent state of our knowledge, it seems best to regard the alpine meadows of
northern Mexico as a transition between the arctalpine cUmax and an Andean
alpine climax. Finally, there are certain resemblances between the alpine
meadow and the short-grass plains which suggest a broader contact than exists
THE ALPINE MEADOW CLIMAX. 231
at present, if not an actual though more remote relationship. These are largely
in the Ufe-form, habits, and size of the dominants and in the genera of many of
the subdominants. A more definite relationship is seen in the presence of
Carex filifolia as a dominant in both, in the contact maintained by such
closely related species as Carex rupestris and C. obtusata, and by the important
part which Selaginella rupestris may take in both. A similar suggestion is
contained in the presence of Festuca and Agropyrumin both communities also.
At present the chief contact of the arctalpine climax is with the subalpine
forest in the Rocky Mountains and the Sierra Nevada-Cascade axis and with
the boreal forest in northern Canada and Alaska. The ecotone is very ir-
regular, and tongues and outposts of the one may extend far into the other.
In the mountains the two are sometimes separated by a narrow belt of scrub,
and this is often, if not regularly, the case in the Barren Grounds of the north.
The lower temperatures and higher water-content of the broader mountain
valleys have afforded a ready pathway for the downward movement of alpine
species and also perhaps for the upward migration of lowland hydrophytes.
In any event, the wet meadows and grasslands of the subalpine and montane
zones furnish a meeting-place for the more mobile species of two floras.
Associations. — The arctalpine climax has received almost no ecological
study outside of the central Rocky Mountains. Much attention has been
given to the floristic differences of various portions of it, but this has taken no
account of dominance and succession, which are vital to an understanding of
the vegetation. As a consequence, it is more than usually difficult to delimit
the associations and determine their relationship. This is particularly true
of the vast Arctic portion, owing to the inherent difficulties of travel and
investigation in such a region. The table of dominants on page 230 indicates
a close relationship between the eastern and western portion of the Arctic
region, and one closer than with either the Petran or Sierran. On the basis of
dominants the latter are less closely related to each other, and the subdomi-
nants confirm the view that they should be regarded as two associations. In a
table of the characteristic alpine species of Washington, Piper (1906: 63) has
indicated their occurrence in the Arctic region, in the mountains of California,
and in the Rocky Mountains. Of 156 species found on the high peaks of
Washington, 72 occur in California, 56 in the Arctic region, and 49 in the
Rocky Mountains.
For the above reasons, it proves necessary to recognize a Petran and a
Pacific or Sierran association. The best evidence at present indicates the
presence of a single Arctic association from Greenland and Labrador to Alaska.
This is very little known, and it may prove desirable to recognize an eastern
and western association with fuller knowledge. It has not been seen by the
writer, and the general absence of ecological information in regard to it makes
it undesirable to touch it more than incidentally. Hence, the discussion below
deals only with the alpine portion of the formation and the corresponding
Petran and Pacific or Sierran associations.
232 CLIMAX FORMATIONS OF WESTERN NORTH AMERICA.
THE PETRAN ALPINE MEADOW.
CAREX-POA ASSOCIATION.
Extent. — The alpine meadow of the Rocky Mountains reaches its typical
development between 12,000 and 14,500 feet, though it descends to lower
altitudes in Montana and Alberta. In Colorado it is found in more or less
characteristic form in lake basins at 11,000 feet, but this is apparently due to
cold-air drainage and the influence of water. A number of dominants and sub-
dominants may be found still lower, but these are chiefly subalpine in nature,
or occur merely as fragmentary outposts. The northern limit of the associ-
ation is thought to be in southern Alberta, since the alpine plants of Mount
Robson (Standley, 1913: 77) are largely those of the Pacific association. The
southeastern outposts are in the Sangre de Cristo Range of northern New
Mexico, and the southwestern on the San Francisco peaks of northern Arizona.
The general western limit is thence northward along the Wasatch Mountains
of Utah into eastern Idaho and southwestern Montana. The association
occurs in reduced form in some of the ranges of Nevada. The central portion
is most typical and extensive. It occupies Colorado and Wyoming and in-
cludes the Uinta Mountains of Utah and the San Juan and Sangre de Cristo
ranges of New Mexico (plate 56).
DOMINANTS.
The Petran association exhibits 62 dominants which play a r6le of more or
less importance in the climax. Of these, 30 are sedges, 23 are grasses, and
8 are rushes. The majority of them occur also in the Pacific association, but
18 or nearly a third are lacking there. For the sake of brevity, only the most
typically alpine or the most abundant dominants are included in the following
list. In Carex and Poa the order is that of relative importance on the
alpine peaks of Colorado.
Carex rupeatris. Carex eDgelmanni. Poa rupicola.
Carex filifolia. Carex nardina. Poa pattersoni.
Carex pyrenaica. Carex illota. Poa grayana.
Carex nigricans. Carex concolor. Poa lettermani.
Carex festiva. Elyna bellardi. Trisetum subspicatum.
Carex atrata. Poa alpina. Festuca brachyphylla.
Carex nova. Poa arctica. Deschampsia caespitoaa.
Carex capillaria. Poa alpicola. Juncodes spicatum.
Carex tolmiei. Poa epilis. Juncus triglumis.
Carex alpina. Poa crocata. Juncus castaneus.
Carex petasata.
Groupings. — As a result of the large number of dominants and the con-
sequent equivalence, the number of groupings is exceptional. Pure con-
sociations are extremely rare, except in areas of a few square meters, and
mixed communities are universal. The number of dominants in each mix-
ture is large, and the groupings consequently merge into a more or less indefi-
nite pattern. Carex rupestris and C. filifoUa are the most important domi-
nants on a score of Colorado peaks, as well as on the San Francisco Mountains
of Arizona, though apparently absent on those of New Mexico. Poa, Elyna,
Trisetum, and Juncodes are commonly associated with them. Carex pyren-
aica and C. nigricans are found on a number of alpine summits in Colorado,
but they are much less important. They nowhere seem to have the dominance
characteristic of them in the Pacific association.
CLEMENTS
Pctran Alpine Meadow
A. Polygonum hiatorla society, Pike's Peak.
B. Campanula rotnndif olia socivXy, Pike's Peak.
C. Mertensia alpina society, Pike's Peak.
THE PETRAN ALPINE MEADOW.
233
Pike's Peak, Colorado
30 Jn.
FiQ. 12.— Monthly and
total rainfall for the al-
pine meadow climax,
summit of Pike's Peak,
14,100 feet.
Factor and serai relations.— From 1900 to 1906 quantitative studies were
made of alpine habitats and communities on Pike's Peak and the neighboring
Mount Garfield or King's Cone. These confirmed the general opinion as to tem-
perature and water relations, but not as to the light intensity. The annual pre-
cipitation on the summit of Pike's Peak (14,100 feet) is 30 inches; at Lake
Moraine (10,200 feet), which lies at the base of the Peak proper and in the sub-
alpine forest, it is 25 inches; at the Alpine Laboratory (8,500 feet) in the mon-
tane forest it is 22 inches; and on the short-grass plains at the base (6,000 feet)
it is 15 inches. The relative humidity on Mount
Garfield (12,500 feet) averaged 5 per cent higher than
at the Alpine Laboratory, but in spite of this the tran-
spiration was 25 per cent higher at the former. The
mean temperature is 19** on Pike's Peak, 36** at Lake
Moraine, and 47° at Colorado Springs on the plains.
During the growing season, temperatures averaged 15°
higher at the Alpine Laboratory and 25° higher at
Manitou (6,500 feet) than on Mount Garfield.
Comparative light readings have been made for several
summers at Pike's Peak and Mount Garfield and at
the Alpine Laboratory, Manitou, and Colorado
Springs. For the most part, these have given identi-
cal results at the different altitudes in spite of a range
of 8,000 feet. This is probably to be explained by the low humidity (fig. 12).
The typically climax condition of the association is marked by the sod-
forming or densely cespitose sedges, such as Carex rupestris, filifolia, pyrenaica,
nigricans, nardina, engelmanni, etc. These are also of low stature, usually
2 to 5 inches, and rarely as much as 6 to 8 inches. Juncodes spicatum and
Elyna hellardi are nearly equivalent to the low sod-forming sedges, but they
have a wider range of adjustment. In the direction of the xerosere subclimax
lie most of the grasses, some of which, such as Festuca brachyphylla and Poa
Uttermanni, are often if not usually serai in character. Most of them are
bunch-grasses and are 6 to 12 inches tall. The taller sedges, such as Carex
f estiva and C atrata, which range from 1 to 2 feet high, are more or less similar
in nature. Toward the hydrosere occur such species as Carex iolmiei, nova,
apd bella, which are tall and more or less sod-forming, and the rushes. These
lead to species of Carex and Juncus that are distinctly hydrophytic and serai.
SOCIETIES.
The number of societies is very large, and no endeavor has been made to
include them all. The following Ust is based primarily upon studies in Colo-
rado, but it is representative of the entire central portion and even of such
outlying areas as the San Francisco peaks. The endemic species drop out
for the most part in Montana and Alberta, and there is an increasing number
of species from the Arctic and Pacific associations. Of the 80 societies given,
29 are endemic, 32 occur in the Pacific alpine meadows, 32 in Arctic America,
and the same number in Eurasia. The identity in number in the last three
is merely a coincidence, for the species are not the same throughout.
The great majority of the societies listed belong typically to the climax,
but some are normally serai or subclimax dominants which persist into the
234 CLIMAX FORMATIONS OF WESTERN NORTH AMERICA.
final stage more or less frequently. These relations have been indicated for
Colorado (Clements, 1904 : 329) and have been suggested for the entire region
by Rydbci*g, who has also given a detailed account of the comparative dis-
tribution of the various species (1914:459, 89; cf. also Cockerell, 1906: 861).
The aspects are less marked than in the prairie on account of the short season,
but there is a distinct difference between the earlier and later portions of the
growing period, in spite of the fact that a considerable number occupy the
mid-season. The distinction below is based upon the time when the species
begins to bloom, as well as the maximum of the flowering period. By far the
greater nmnber of societies are mixed, and the order below is primarily that
of importance.
Sieversia turbinata.
Mertensia alpina.
Rydbergia prandiflora.
Primula angustitolia.
Silene acaulis.
Achillea millefolium.
Castilleia pallida occidentalis.
Sibbaldia procumbens.
Androsace chamaejasme.
Artemisia scopulorum.
Arenaria biflora.
Oreoxis humilis.
Polygonum bistorta.
Pedicularis pairji-
Trifolium nanum.
Eritrichium argenteum.
Potentilla saximontana.
Campaoula imiflora.
Polygonum viviparum.
Campanula rotundiiolia alpina:
Gentiana frigida.
Gentiana amarella.
Solidago humilis nana.
Agoseris aurantiaca.
Oreoxis alpina.
Saxifraga bronchialis.
Potentilla nivea.
Trifoliima dasyphylliun.
Trifolium parryi.
Vernal Societies.
Lloydi serotina.
Cerastium arvense.
Allium reticulatum.
Salix reticulata.
Saxifraga nivalis.
Saxifraga flagellaris.
Saxifraga chrysantha.
Polemonium confertimi.
Pseudocymopterus montanus.
Sedum roseum.
Erigeron uniflorus.
Draba aurea.
Draba streptocarpa.
Chionophila jamesii.
Androsace septentrionalis.
Dryas octopetala.
Phacelia sericea.
Zygadenus elegans.
Eslival Societies.
Haplopappus pygmaeua.
Antennaria alpina.
Antennaria dioeca.
Salix nivalis.
Salix arctica.
Angelica grayi.
Arnica parryi.
Aster alpinus.
Erigeron leiomerus,
Phacelia lyallii.
Anemone narcissifiora.
Erigeron compositus.
Erigeron radicatus.
Besseya alpina.
Ranunculus macauleyi.
Ranunculus nivalis.
Ranunculus eschscholtzii.
Thalictrum alpinum.
Phacelia alpina.
Phlox condensata.
Polemonium viscosum.
Primula parryi.
Douglasia nivalis.
Pedicularis lanata.
Pedicularis flammea.
Smelowskia calycina.
Trollius laxus.
Astragalus alpinus.
Myosotis alpestris.
Draba nivalis.
Ranunculus adoneus.
Ranunculus pygmaeus.
Ranunculus hyperboreus.
Pedicularis scopulorum.
Pedicularis oederi.
Swertia perennis.
Pentstemon hallii.
Pentstemon glaucus.
Claytonia megarhiza.
Selaginella rupestris.
THE SIERRAN ALPINE MEADOW.
CAREX-AGROSTIS ASSOCIATION.
Extent. — While the highest alpine peaks of the Pacific Coast are a little
higher than those of the Rockies, they are covered with permanent snow-caps
of great size, and the alpine zone is consequently much lower. In Washington
its best expression is found at 8,000 to 10,000 feet, and on Mount Shasta at
9,000 to 11,000 feet, though two species, Draba breweri and Polemonium
pulcheUum, reach 13,000 feet. In the central and southern Sierra Nevada the
alpine meadows are best developed between 10,500 and 13,000 feet. The
lowest hmit for the zone is found in the mountains of the upper Columbia
Basin, where it descends to 6,000 feet.
CLtMENTS
Sierran Alpine Meadow
A. Carex-Agrostis association, Mount Rainier, Washington.
B. Lujnnus volcanicus-Valeriana sitchensis society, Mount Rainier, Washington.
THE SIERRAN ALPINE MEADOW. 235
The northern hmit of the association is probably in northern British
Columbia, though it is uncertain where it passes over into the Arctic associ-
ation. Similar uncertainty exists as to the Umits in northwestern Montana,
where it meets the Petran community. Piper (1906:63) states that the
flora of the Blue Mountains of Washington and Oregon is as near that of the
Rocky Mountains as of the Cascades, but this is not true for the typical central
mass of the Petran association. The Sierran association occupies all the
alpine summits of the Cascades, Olympics, Blue, and other mountains of
Washington and of the Cascades of Oregon. It extends from Mount Shasta
L .uthward through the Sierra Nevada and reaches its southernmost limit on
San Jacinto Mountain, where it is reduced to less than a half-dozen of true
alpine species (plate 57).
DOMINANTS.
The genera of the dominants are the same as for the Petran association.
The small amount of ecological study which this community has received
makes it impossible to distinguish climax from serai species with certainty,
and the following Ust is necessarily provisional:
Carex nigricans. Carex festtva. Agrostis rossae.
Carex pyrenaica. Carex scirpoipea. Agrostis humilis. '
Carex breweri. Elyna bellardi. Agrostis hiemalis geminata.
Carex nardina. Kobresia bipartita. Calamagrostis vaseyi.
Carex spectabilis. Poa paddensis. Calamagrostis langsdorffi.
Carex illota. Poa suksdorfii. Trisettjm stjbspicatum.
Carex vernacxtla. Poa rxjpicola. Festtjca ovina supina.
Carex ablata. Poa alpina. Juncodes spicatum.
Carex filifolia. . Poa arctica. Juncodes divaricatxtm.
Carex phaeocephala. Poa saxatilis. Juncus parrti.
Carex atrata.
Groupings. — The general grouping of the dominants is indicated by their
respective ranges. Carex is represented by 8 species, which occur throughout
the association from British Columbia or Washington to the Sierra Nevada.
These are Carex nigricans, hreweri, spectabilis, illota, vemacula, ablata, filifolia,
and atrata. Among the grasses and rushes, those found throughout are Poa
saxatilis, Agrostis rossae, Calamagrostislangsdorffi, Trisetum svbspicatum, Festuca
supina, Juncodes spicatum, J. divaricatum, and Juncus parryi. The intimate
grouping is known only for Mount Rainier, where the climax stage is con-
stituted typically by Carex nigricans, pyrenaica, nardina, and illota, while the
taller C. f estiva, atrata, spectabilis, and ablata occur in areas more or less serai in
character. The chief grasses are Poa saxatilis, arctica, paddensis, and suks-
dorfi, and Agrostis rossae. Practically the same grouping is found in the
northern Cascades, the Olympic Mountains, and on Mount Adams (Piper,
1906:63). The alpine meadows of the Selkirk Mountains consist of Carex
nigricans, spectabilis, and /estiva, and Poa alpina, arctica, and cusickii (Shaw,
1916:491).
Factor and serai relations. — There is practically no direct information upon
the physical factors and succession, and these can only be inferred from the
cUmatic conditions in the Petran association and the Sierran subalpine forest,
and from the serai relations in the Rocky Mountains. The precipitation is
apparently much higher in the Sierran association, often exceeding 75 inches.
236 CLIMAX FORMATIONS OF WESTERN NORTH AMERICA.
Most of this occurs as snow, and results in much more extensive snow-caps
and snow-fields than occur in the Rocky Mountains at corresponding latitudes.
For the present, the serai relations must be assumed from those in the
Petran association (p. 233). This doubtless affords a fairly accurate idea
of the processes, since the two associations have so many dominants in common.
Northern {Catcadea, etc.):
Pulsatilla occideDtalis.
Lupinus lyallii.
Lupin US subalpinus.
Lupinus volcanicus.
Castilleia oreopola.
Castilleia pallida.
Potentilla flabellifolia.
Valeriana sitchensis.
Erigeron salsuginosus.
Erigeron radicatus.
Erigeron uniflorus.
Gentiana calycosa.
Southern {Sierra Nevada):
Trifolium monanthum.
Sibbaldia prociunbens.
Salix arctica.
Lupinus lyallii.
Senecio aureus borealis.
Mimulus primuloides.
Gentiana newberryi.
Caatilleia culbertsonii.
SOCIETIES.
Artuca parryi.
Sieversia turbinata.
Silene acaulis.
Veronica alpina.
Sedum roseum.
Polygonum viviparum.
Epilobium alpinum.
Epilobium hornemannii.
Epilobium anagallidifolium.
Salix arctica.
Salix nivalis.
Salix reticulata.
Pentstemon confertus.
Antennaria alpina.
Dodecatheon alpiaus.
Sedum roseum.
Horkelia gordonii.
Solidago multiradiata.
Agoseris aurantiaca.
Thalictrum alpinum.
Draba aurea.
Draba nivalis.
Arenaria biflora.
Dryas octopetala.
Sibbaldia procum^bens.
Agoseris aurantiaca.
Phacelia sericea.
Phlox condensata.
Trollius laxus.
Erythronium grandiflorum.
Ranunculus eschscholtzii.
Douglasia nivalis.
Ranunculus eschscholtzii.
Erigeron salsuginosus.
Erigeron uniflorus.
Gentiana amarella.
Cerastium arvense.
Antennaria dioeca.
Campanula rotuudifoUa
alpina.
V. AGRICULTURAL INDICATORS.
General relations. — As the basic economic practice of plant and animal
production, agriculture furnishes the standard for measuring the possibilities
of soils, climates, and regions. There are many reasons for this, chief among
them the fact that it gives relatively large and inunediate returns upon a
small capital. In addition, its operations are within the scope of the indi-
vidual or family, and farming has inevitably become the traditional basis of
the American homestead. The latter has played such a wonderful role in the
development of the West that it has come to be regarded as a fetich, able to
reclaim the most arid desert or to enrich the most sterile soil. During the
last two decades the large majority of the homesteads filed upon have proved
failures and the percentage of failures will steadily increase as still less promis-
ing regions are entered, unless the method of settlement is radically changed.
The time when individual initiative would suffice to convert a tract of virgin
land into a prosperous farm has gone. While miUions of acres of pubUc lands
still remain for settlement, these are of such a nature that land classification,
reclamation, demonstration, and cooperation are indispensable to their con-
version into successful farms and ranches (plate 58).
LAND CLASSIFICATION.
Nature. — The classification of land is an endeavor to forecast the type of
utiHzation that will yield adequate or maximum returns. Properly, it should
determine the optimum use as accurately as possible, and should insure the
conditions under which development and utiUzation take place. In actual
practice, classification has been conspicuously absent as a preliminary to the
settlement of the arid regions of the West. Hurried and incomplete classi-
fications have been made for special purposes, but these have covered only
certain portions of the vast pubUc domain and have usually suffered from in-
adequate and hasty methods. Perhaps their greatest fault has been that
they were made with a particular end in view, and the primary object was to
include or exclude as much land as possible without reference to its optimum
utiUzation. In this respect the recent classification under the Ferris Act
has been an improvement, but it has been handicapped by legislative restric-
tions and by the lack of an adequately trained field personnel. It has been
especially unfortunate that only those lands were examined which had been
filed upon, with the result that the examiner's judgment or decision was often
influenced by local pressure. To the one who is interested solely in seeing
the pubUc domain developed in such a way as to secure the best economic and
social conditions, it is incomprehensible that the prerequisite of an accurate
and unbiased classification of the land should have been so long ignored.
Such a land classification would necessarily take account of the enormous
amount of scientific reconnaissance and investigation done in the West, during
the last thirty years especially. It would rest upon a rapidly increasing
fund of practical experience and experimental study of crops and methods,
and upon the paramount importance of drought p)eriods and their recurrence
in climatic cycles. In method, it would be complete, detailed, accurate, and
237
238 AGRICULTURAL INDICATORS.
unprejudiced, availing itself of all sources of information, but based primarily
upon the relation of indicator vegetation to existing practice. The most
difficult problem would be that of a large, adequately trained, and high-minded
field force, but the rapid development of the Forest Service has shown how
this can be accomplished.
Relation to practices. — While land classification is based primarily upon the
division into agriculture, grazing, and forestry, other considerations must also
be taken into account. At the outset, it is particularly important that the
future as well as the immediate present be considered. Many areas which
are non-agricultural at present can be made available for crop production by
the development of a supply of irrigation water or by the draining of the soil
to remove the excess of alkali. On the other hand, the extension of agri-
culture into mountain regions on a considerable scale would threaten the
water-supply of existing irrigation projects. The maintenance of forests on a
scienti fie basis is more than a matter of the present demand for lumber and
fuel. Jt has a definite and often a decisive bearing upon the agricultural
possibi ities of the land in the adjacent valleys and plains. Moreover, ques-
tions of reforestation and afforestation enter in relation to agriculture and
grazing, and perhaps to climate also. While the use of land primarily for
agriculture excludes forestry or grazing on any considerable scale, tliis is not
true of the latter. Under proper safeguards, forestry and grazing can be
combined in practically all forest and woodland areas, as is the case on the
national forests. It is not improbable that the extensive sandhill areas of the
Great Plains region will some day be covered with forests of pine without
seriously reducing the amount of grazing, and in some cases with an actual
increase in the permanent carrying capacity.
The greater returns from agricultural land and the consequent possibility
of supporting a larger population will always constitute a temptation to
classify too much land as agricultural. If classification could be carried out
only during drought periods, this tendency would be corrected. On the other
hand, it would be emphasized during wet years, such as 1915, when many
r^ons received 50 to 100 per cent more than their normal rainfall. As a
consequence, the classification of land as agricultural must be made with a
definite knowledge of the existing conditions of rainfall and temperature and
their relation to the usual variations of the climatic cycle. Moreover, it must
be recognized that it is much less serious to classify a potential agricultural
area as grazing or forest land than to classify the latter as agricultural. The
former merely involves an insignificant economic waste until the real possi-
bilities of the land become recognized, while the latter often results in recur-
ring tragedies due to the attempt to make a livelihood where it is impossible.
Hence, it should become a cardinal principle of land classification to rate as
grazing or forest land all areas in which it is impossible to produce an average
crop three years out of four. This would insure an adequate and permanent
development of agriculture wherever possible and would warrant the intro-
duction of scientific and economic systems of grazing, which would change it
from a game of chance into an industry.
Proposed bases of classification. — While soil and climate have been em-
ployed in connection with various desultory attempts at classification, the
CLEMENTS
PLATE 58 _
A. Abandoned farm, Wood, South Dakota.
B. Field of com and sudan grass during the drought of 1917, Glendive, Montana.
LAND CLASSIFICATION. 239
only proposals which need to be considered here are those which deal with in-
dicator vegetation. The latter necessarily takes account of both soil and cli-
mate and furnishes the only basis for an adequate system. The first serious
proposals of such a system were made by Hilgard, as already shown in the first
chapter. As a student of soils, he was concerned primarily with the indicators
of soils (1906: 487), and especially those which were regarded as significant of
lime or alkaU. He paid alrnost no attention to indicators of climate, and was
concerned only with those which denoted agricultural land. Because of his
primary interest in the distribution of animals, Merriara (1898) emphasized
the importance of climate in agriculture, and ignored that of soil. His central
idea was to enable the farmer "to tell in advance whether the climatic con-
ditions on his own farm are fit or unfit for the particular crop he has in view,
ard what crops he can raise with reasonable certainty." Hence, he was
concerned with a use survey rather than with land classification, though his
"Ufe zones and crop zones" possess certain values in connection with the
latter.
Clements (1910:52) pointed out the difference between a classification
survey and a use survey of occupied lands, and emphasized the necessity of
employing soil and climate, native vegetation, and practical experience
to constitute a complete system for classifying the lands of a region as agri-
cultural, grazing, and forest. Several unoccupied townships of northern
Minnesota were classified on this basis and several farming townships of the
southern half were mapped in accordance with a use survey. The investi-
gations of Shantz (1911) in eastern Colorado dealt chiefly with the indicator
value of the different associations with reference to crop production and
furnished a new basis for the classification of agricultural land with respect to
probable yield. A similarly detailed and accurate study of the saUne vegeta-
tion of Tooele Valley was made by Kearney and his associates (1914), in which
the primary object was to provide a definite method of distinguishing agri-
cultural from non-agricultural lands and of determining the relative values of
the former.
The rapid establishment of national forests from 1902 to 1908 necessitated
the use of a ready method of distinguishing between forest and agricultural
land. The indicator method had not yet been definitized to a point where it
was available, and studies of soil and climate were barely begun. In spite of
this, forest and woodland constitute such obvious indicators that their use
afforded fairly satisfactory results, particularly when water regulation was
taken into account. The hmits of the forests thus drawn necessarily included
some agricultural land as well as great areas of grazing land. Much of the
former has later been ehminated by reclassification, while the latter has been
classified into various types (Jardine, 1911, 1913). Within the forests proper,
the problem of classification has naturally revolved about the question of
forest types. This has given rise to an extensive Uterature (Graves, 1899 ;
Zon, 1906; Clements, 1909; cf. Proc. Soc. Am. For., 1913: 73) and is discussed
in some detail in Chapter VH. Pearson (1913: 79; 1919) has emphasized the
importance of ascertaining the agricultural possibiUties of forested land in
order to determine with certainty whether it should be classified as one or the
other. He proposes a definite program of investigation to make the principles
and methods of land classification more accurate. This is based upon actual
240 AGRICULTURAL INDICATORS.
tests of agricultural possibilities, the study of physical factors, and the cor-
relation of crop production and plant associations, the last being regarded as
the most important feature of the whole plan.
The most extensive and adequate application of the proper principles of
and classification to the lands of the West has been made in connection with
the stock-raising homestead act of 19-16. This is based primarily upon the
ndicator method, and the details have been outlined by Shantz and Aldous
1917). While the primary object is to classify the areas filed upon for graz-
ng homesteads, it has proved necessary to deal with the classification of
agricultural and forest lands as well. In this connection the latter are rela-
ively unimportant, but the recognition of lands for dry-farming is an essential
part of the plan. This arises from the fortunate provision that a grazing
homestead must contain areas on which it is possible to produce crops of
forage. As already indicated, the only drawbacks to the method arise from
an untrained personnel and the lack of sufficient time for adequate survey.
The correlation of the indicator types upon the basis of structure and develop-
ment would have revealed additional values, but the plan marks a great
advance in land classification and it is unfortunate that its apphcation is
restricted to lands filed upon imder the act.
The indicator method of land classification. — As the above discussion makes
clear, practically all the effective proposals for classifying land into the three
main types, or for subdividing these upon the basis of crops or values, rest upon
the fundamental significance of indicator plants and communities. The
systems proposed by Clements, Pearson, and Shantz and Aldous, though
arrived at from three different angles, are practically identical so far as
essentials are concerned. They recognize the importance of actual practice
and experiment as well as of quantitative studies of soil and climate in defi-
nitizing the correlations of the indicator communities. The latter, however,
constitute the indispensable tool of the land classifier, since its use is as ready
as it is extensive and is hmited only by its accuracy and sharpness. In the
hands of a well-trained field force, it would permit the proper classification of
all the unoccupied lands of the West within a period of five years. The
essentials of such a classification are further discussed in a later section.
Use of climax indicators. — It is clear that the climaxes themselves furnish
direct indications of great value for land classification. Thus, grassland,
chaparral, and scrub are obviously indicators of grazing land, while forest and
woodland are indicators of forest land. However, these comprise all the types,
and a different method is necessary for the determination of agricultural land.
This may be furnished by actual test, by the measurement of factors, or by
the use of indicator correlations already established in other regions. As a
matter of fact, some kind of farming test can be found almost anywhere in
the West, in the driest deserts as well as at almost any altitude. The studies
of the last decade have made the application of indicator correlations almost
universal, and the measurement of soil and climatic factors has at least been
begun in practically every climax. As a consequence, it becomes a relatively
simple matter to use climax communities to indicate those grazing and forest
lands which are also agricultural, in that they yield a larger return from crop
production than from grazing or forestry (plate 59).
CLEMENTS
PLATE 59
A. True prairie indicating agricultural land, Lincoln, Nebraska.
B. Oak chapamil indicating grazing land, Sonora, Texas.
C. Aspen, spruce, and pine indicating forest land. Minnehaha, Colorado.
LAND CLASSIFICATION. 241
In the West, the cUmax which serves as the best indicator of crop produc-
tion is naturally grassland. As the most extensive of all the formations con-
cerned, its various associations serve also to indicate all the types of farming
from humid and semi-arid on the east to dry-farming and irrigation farming
in the west. While the alpine meadow climax has many points of resemblance
to the grassland, it is a clear-cut indicator of grazing land, since neither trees
nor crops can thrive in it. The various scrub cUmaxes, sagebrush, desert
scrub, and chaparral, as well as tree and scrub savannah, are primarily indi-
cators of grazing land, unless irrigation is resorted to. Dry-farming is pos-
sible in certain areas in them, but these are usually in the transition to other
formations or in the serai habitats. A notable exception occurs in the
Coastal chaparral, in which the winter rainfall makes certain crops possible
by evasion of the drought period of summer. The woodland climax is pri-
marily an indicator of combined forest and grazing land. It has some agri-
cultural possibiUties, but these are rarely to be realized except under irrigation.
Of the three forest chmaxes, the Coast forest is a distinct indicator of crop
production, and the subalpine forest is just as distinctly an indicator of non-
agricultural land. The montane forest in general is Uke the subalpine in
indicating forest-grazing land, but this depends upon the consociation and
topography. The yellow pine consociation often indicates agricultural land,
but the indication of the community must be checked by the nature of the
topK)graphy and soil.
In the case of all climaxes, the relations of formation, association, consoci-
ation, and society to each other lie at the basis of the indicator correlations of
the various communities. The indicator value of an association must be
imderstood with reference to its formation, and that of the consociation with
reference to its association. In general, these will be consistent with each
other, and hence they serve to denote smaller and smaller areas, and particular
crops and methods rather than types of practice. This is especially true of
the many local groupings of dominants and subdominants. The societies
formed by the latter are particularly sensitive indicators of local variations in
clunax conditions (Shantz, 1911).
Soil indicators. — The significance of soil indicators is local, as well as sub-
ordinate to that of climax or cUmatic indicators. The soil is especially im-
portant in the actual practice of land classification, since it is more tangible
than climate and is subject to much greater local variations. Consequently,
in any particular region climax indicators should be employed for general
climatic values, while soil indicators should be used for the special values which
will determine the proper classification of a particular area. In view of the
paramount importance of water-content in arid and semi-arid regions, the
general correspondence between rainfall and water-content from east to west
becomes especially helpful. While texture and topography will cause soils
to vary much locally in their water-content, the water-content of tillable soils
decreases more or less steadily to the westward or south west ward. This
relation of climate and soil is readily seen in the soil regions of the West as
recognized by the Bureau of Soils, namely, Great Plains, Rocky Mountain,
Southwest Arid, Great Basin, Northwest Intennountain, and Pacific Coast.
As would be expected, these regions also show more or less correlation with the
climax formations.
242 AGRICULTURAL INDICATORS.
The loess and glacial soils of the prairies are so completely cultivated that
they hardly need consideration as to their indicators. The luxuriance of the
three prairie associations and the large number of societies, especially of
l^umes, denote an agricultural region of the first importance. To the west-
ward, the most extensive and important soils are gumbo or "hard land,"
saline soils, and sandy soils, usually of the sandhill or dune type. Where it
is derived from the weathering of shales, as is frequently the case, the soil is
usually both gumbo and saline. As Shantz (1911) has shown, "hard land"
is primarily agricultural in the Great Plains, though its high echard is a serious
disadvantage during drought periods. Soils recently derived from shales, such
as the Pierre and the Graneros, however, bear a vegetation which suggests
that their greatest value is for grazing. The work of Hilgard (1906) and of
Kearney and his associates (1914) has shown that, in the Great Basin and
similar saline regions, sagebrush is the one reliable indicator of agricultural
land. While crops may be produced on land covered with Atriplex conferti-
folia or Kochia, it is only during years of exceptionally favorable rainfall,
which are too rare for successful farming. Hence, practically all saline
communities are indicators of grazing land, though such land may be con-
verted to agricultural use when the removal of alkali is economically feasible.
The numerous sandhill and dune areas of the West bear distinctive indi-
cators which denote the varying degrees of fixation of the sand. Typically,
they are grazing areas, though they are usually interrupted or surrounded by
more stable areas, such as the wet valleys of the sandhills of central Nebraska
or the wire-grass lands of eastern Colorado, in which farming is possible.
Even for grazing, their value is much less than it should be, and in addition
there is a rapid deterioration of the cover where overgrazing is practiced.
There is no question that the carrying capacity could be greatly increased and
the tendency to "blow" correspondingly decreased by protection and seeding
or planting. The Bad Lands, which occur throughout the West, but especially
in the Rocky Mountain regions, likewise ofifer attractive regions for reclam-
ation. Although the soil is a hard clay instead of blow-sand and the erosion
is due to water in place of wind, sandhills and bad lands have much in common.
The destruction due to erosion is often rapid and complete, as well as recur-
rent. They occur almost wholly in grazing communities, and the study of
succession in both has reached a point where it is possible to make use of it as
the chief method of reclamation, as is shown in Chapter VI. The extremely
dissected topography of bad lands practically excludes agriculture, and in
general the communities of rugged and rocky areas indicate their classification
as grazing lands, even when climatic conditions might permit agriculture. In
the case of swamp and bog conununities, the direct indication is for grazing,
but since they need drainage in order to be put into adequate commission,
their classification should take this into account. When they are not too
high or too far north, the drained areas will permit farming, but when they
occur in the montane zone, or above, their chief value is for grazing (plat« 60) .
Shantz's results. — Shantz's studies of indicators in eastern Colorado are
still the most complete and detailed account of the correlation of indicator
communities and soil. His conclusions apply with slight modification to the
entire short-grass association, and they also have much value for mixed
prairies:
CLEMENTS
A. Artemisia filifolia indicating sandy soil, Canadian river, 'I'cxas.
B. Grama and buffalo-grass on hard land, CJoodwell, Oklahoma.
C. Atriplex ntUtallii indicating non- agricultural saline land, Thompson, Utah.
LAND CLASSIFICATION. 243
"The chief plant associations of eastern Colorado which indicate land of
agricultural value are the grama-bufifalo-grass association and the wire-grass
association (both of which belong to the short-grass formation) and the bunch-
grass association and the sand-hills mixed association (both of which belong
to the prairie-grass formation).
"The chief vegetation types of eastern Colorado which indicate nonagri-
cultural land are the lichen formation, the Gutierrezia-Artemisia association
of the short-grass formation, and the blow-out association of the prairie-
grass formation.
"Of the associations indicating land of agricultural value in eastern Colo-
rado, the grama-buffalo-grass association is most extensive, occupying the
greater part of the hard land. The bunch-grass and the sand-hills mixed
associations occur only in the sand-hill regions, while the wire^rass association
occurs on land of intermediate character.
"In eastern Colorado the rainfall records show that the average monthly
rainfall is greatest during the period April to August. The increased heat in
July and August makes it almost certain that drought will occur in these
months. September and the later fall months have normally very Uttle
rainfall, and fall-sown grain often fails to germinate unless planted on land
in which water from rains earUer in the season has been conserved by summer
tillage.
"Measurements show that from grama-buffalo-grass land a great amount
of water runs off and does not enter the soil.
"Soil-moisture determinations in this type of land show that even during
periods of more than normal rainfall available soil moisture is limited to a few
inches of the surface soil.
"On this account the vegetation is composed largely of short grasses which
have a great number of roots limited to the surface foot or two of the soil.
"Moisture, even in the surface few inches of the soil, is often lacking ex-
cept during a few weeks in spring and early summer. The short grasses have
a comparatively short growing season.
" Deep-rooted species are shut out by the lack of soil moisture in the deeper
layers of the soil and later-season plants are excluded because available
moisture is usually lacking, even in the surface layers, during late summer
and autumn.
"An open cover of the short grasses indicates conditions less favorable for
crop production than a close cover.
"The presence of deeper-rooted plants mingled with the short-grass vegeta-
tion indicates better conditions for crop production than those found where
the cover is purely of the short grasses.
"The occurrence among the short grasses of plants characteristic of the
associations which indicate land without agricultural value suggests a less
favorable condition for crop production than where short grasses only are
found.
"The presence of the wire-grass association indicates that there is a con-
siderable amount of water in the deeper layers of the soil, owing to the lesser
run-off and to the fact that the lighter soil permits deeper penetration.
"Conditions indicated by the wire-grass association are favorable for both
shallow-rooted and deep-rooted plants and for a considerably longer period
of growth than those indicated by the grama-buffalo-grass association.
"The bunch-grass association indicates a soil that is moist to a considerable
depth. Here conditions are more favorable for deep-rooted and late-season
plants than in land characterized by either the short-grass or the wire-grass
vegetation.
244 AGRICULTURAL INDICATORS.
"The sand-hills mixed association indicates conditions very similar to those
of the bunch-grass association, but rather less favorable, as shown by the
smaller amount of plant growth.
"The short-grass vegetation represents the final stage in a succession which
may begin with the hchen formation and pass through the Gutierrezia-
Artemisia association. Or the succession may begin with the blow-out asso-
ciation and pass through the sand-hills mixed and the bunch-grass associa-
tions and (by the aid of fires and grazing) through the wire-grass association
to a pure short-grass vegetation.
"When short-grass land is left without cultivation after breaking it will be
revegetated by either the wire-grass or the Gutierrezia-Artemisia association,
depending upon the physical conditions.
"The vegetation which establishes itself after wire-grass is turned under is
that which is naturally characteristic of a lighter soil.
"When the native sod of the bunch-grass or the sand-hills mixed associ-
ations is broken, a blow-out may result. Usually, however, the original
vegetation is soon reestabUshed.
" When the vegetation of any of the plant associations is destroyed by break-
ing and the land is then abandoned the land will be reoccupied (after a weed
stage) by vegetation that is characteristic both of a lighter type of soil and of
an earUer stage in the natural succession. These successions are the result
of changes in the physical conditions brought about largely as a result of the
destruction and reestabUshment of the plant cover itself.
"The taller, deeper-rooted plants are easily shut out by the shallow-rooted
short grasses when the water that falls as rain is not sufficient to penetrate
beyond the layer of soil occupied by the roots of the short grasses before it
can be absorbed by them.
"Where water can readily penetrate below the depth ordinarily reached by
the roots of the short grasses the conditions are favorable to the growth of
deeper-rooted and taller species, which shut out the short grasses by over-
shading them. This increased penetration of water may be due either to
greater rainfall or to fighter soil texture.
"When well suppfied with water short-grass land is the most productive
imder cultivation of any in eastern Colorado. During drought, however,
crops suffer on this land sooner than on any other type.
"During exceptionally dry years bunch-grass land produces the best crops
of any in eastern Colorado, but during wet years its production is surpassed
by that of all others except the land characterized by the sand-hills mixed
association. The soil under both of these types of vegetation is likely to
blow badly.
" Wire-grass land represents a safe intermediate condition where in years of
ample rainfall crop production compares not unfavorably with that on short-
grass land and where, even during dry years, a fair crop can often be produced.
"One of the chief reasons for the superiority of light land over heavy land
in eastern Colorado is that crop growth is rapid on the latter and that the
total available supply of soil water Ues near the plant roots, the crops, there-
fore, being in somewhat the same condition as potted plants. These con-
ditions favor a rapid exhaustion of soil moisture and, consequently, bring
about sudden drought. On the fighter land water is distributed to greater
depths, the plant growth is slower, and plants, by gradually increasing their
root area, can resist much longer periods of drought.
"Investigations of soil conditions, as weU as actual observations of crops
in the field and studies of the native plant cover, show that as we pass from
the prairie westward to the more arid p)ortion of the Great Plains, the fighter
soils present relatively more favorable moisture conditions and, therefore,
conditions more favorable to plant growth than do the heavier types of land."
LAND CLASSIFICATION. 245
A SYSTEM OF LAND CLASSIFICATION.
Bases. — As has been repeatedly emphasized, a system of land classification
which is both practically and scientifically adequate must ignore no source
of evidence. While indicator vegetation must be regarded as the chief tool,
the latter is valueless unless it is correlated with practical experience and
experiment on the one hand and with factor measurements on the other.
Some indicator values can be disclosed by the use of a single one of these
correlations, but all of them are necessary for complete certainty and accuracy.
They not only serve to check each other, but also to reveal additional and final
values. Furthermore, it must be recognized that all the climatic and hence
many of the soil factors vary considerably and sometimes critically from year
to year, and that this means a corresponding difference in crop production,
and often in tillage methods. As a consequence, the annual variations in
factors, indicators, and production must always be taken into account and
related, as far as possible, to an aversige or norm. The normal rainfall or mean
temperature is insufficient for this purpose, especially since it fails to disclose
the number and occurrence of the critical dry years. For this purpose the
use of climatic cycles is necessary, and in consequence they must be assigned
an important part in the classification of lands in arid and semi-arid regions.
The existence and effect of such cycles are established beyond a doubt, and the
chief task at present is to learn how to make the fullest possible use of them.
This naturally depends upon the certainty and accuracy with which the dry
and wet phases of the cycle can be predicted (Clements, 1917: 304, 1918: 295).
The nature and utilization of climatic cycles are discussed in the following
section.
Classification and use. — The close relationship between classification and
use surveys and the importance of developing the one into the other can hardly
be emphasized too strongly. The vital connection between the two in the
proper development of the possibilities of the land may be seen from the
following (Clements, 1910:52):
"The first step in determining the final possibilities of plant production is
to ascertain just what the conditions of soil and climate are from the stand-
point of the plant. This must be determined separately for the two great
groups of lands, those still unoccupied and those now in use. For the former,
a knowledge of soil and climate, and of the plant's relation to them, is necessary
to decide what primary crop, grain, forage, or forest, is best. For the farms
of the State, the best use is a matter of knowing the soil and climatic differ-
ences of regions and fields, and of taking advantage of this in crop production.
For the unoccupied lands of Minnesota, we need a classification survey to
determine the best use of different areas; to prevent the waste of human effort
and happiness involved in trying to secure from the land what it can not give,
and yet to insure that the land will reach as quickly as possible its maximum
permanent return. For occupied lands, the study and mapping of soil and
climatic conditions would constitute a use survey of the greatest value in
adjusting plant production to the conditions which control it.
"A use survey is the logical outcome of the classification of land. Its
greatest importance is with agricultural lands, since grassland and forest
permit less specialization in crop production. The period of the one-crop
farm seems nearly closed; that of the special-crop farm is barely begun in
this country. As a method of conservation, diversified farming is a perma-
nent step in advance. It is the foundation upon which a distinctively success-
246 AGRICULTURAL INDICATORS.
ful country life is possible. But intensive cultivation is the open secret of
scientific farming, and it demands the closest possible harmony between the
plant machine, the raw materials which it uses, and the conditions under which
it works. This makes possible the successful specialization of a region in the
crop best adapted to the soil or climate more or less peculiar to it. The task
of a use survey in this connection is to determine the special advantage of soil
or cUmate, and to suggest the particular kind of plant machine and the
method of production adapted to it. The same careful method of survey,
which makes possible the best use of the different agricultural lands of the
State, is hkewise of great value on the individual farm, whenever differences
of soil or exposure exist. The general nature of the soil and climate of a farm
must determine its special crop, and in a degree the secondary crops as well.
But the complete success of the farm will rest upon a thorough knowledge of
its differences of soil and climate, as well as upon a knowledge of the best
varieties to grow or the best way to improve them. "
Methods. — While it is undesirable to discuss in detail the actual methods of
classification and use surveys, it must be pointed out that they depend in the
first instance upon accuracy and thoroughness. This is exempUfied in the
work of the Botanical Survey of Minnesota ("Plant Succession," 436), in
which the natural and cultural vegetation was mapped for every "forty" of
the townships concerned, and quadrats, instruments, and photographs were
employed throughout. Similar though less detailed methods have been used
in the grazing reconnaissance of all the national forests (Jardine, 1911) and
in the classification of grazing homesteads under the Ferris Act (Shantz and
Aldous, 1917). The essential features of these are touched upon in the dis-
cussion of the methods of range survey in Chapter VI.
A logical and desirable outcome of a classification survey is a valuation of
the various parcels of land, with respect to both leasing and purchase. It has
been a natural assumption that the nation could well afford to dispose of the
public domain at merely nominal prices, and such a policy was warranted
in the Middle West. In the arid regions, however, values vary so greatly
that it constitutes a serious mistake. This is readily seen when it is recognized
that the best grazing lands will support more than 100 cattle to the section,
while the poorest will support scarcely one. This is particularly true in the
case of leasing, where proper valuation based upon actual carrying capacity
wiU determine whether lands are to constitute a public asset or to be the usu-
fruct of politicians. While the nation or State can afford to be generous to
bona fide settlers, it can treat them all alike in fact only by fitting prices to the
production value of the land and by making the operations of the speculator
difficult if not impossible. Moreover, it should insure the success of each
settler by means of use or management surveys which will give him a detailed
and adequate knowledge of his particular farm and of the crops and methods
to be used upon it. Since such surveys are of the greatest importance in
connection with the combined grazing and dry farming which it seems must
become typical of the West, their further discussion is deferred to the next
chapter.
CLIMATIC CYCLES. 247
CLIMATIC CYCLES.
Nature. — The general nature of climatic cycles as well as their universal
occurrence and fundamental importance is summed up in the following state-
ment (Plant Succession, 329):
"It is here assumed that all climatic changes recur in cycles of the most
various intensity and duration. In fact, this seems to be established for
historic times by Huntington and for geologic times by the studies of glacial
periods which have made possible the table compiled by Schuchert. The
cyclic nature of climatic changes has been strongly insisted upon by Hunting-
ton: 'The considerations which have just been set forth have led to a third
hypothesis, that of pulsatory climatic changes. According to this, the earth's
climate is not stable, nor does it change uniformly in one direction. It appears
to fluctuate back aftd forth not only in the Uttle waves that we see from year
to year and decade to decade, but also in much larger ones, which take
hundreds of years or even thousands. These in turn seem to merge into and
be imposed upon the greater waves which form glacial stages, glacial epochs,
and glacial periods.'
" Climatic changes, then, are assumed to be always related in cycles. No
change stands out as a separate event; it is correlated with a similar event
which has preceded it, and one that has followed or will follow it, from which
it is separated by a dissimilar interval. Climate may thus be hkened to a
flowing stream which rises and falls in response to certain causes. It is not
a series of detached events, but an organic whole in which each part bears
some relation to the other parts. Considering climate as a continuous pro-
cess, it follows that we must recognize changes or variations of climate only
as phases or points of a particular climatic cycle, which lose their meaning and
value unless they are considered in connection with the cycle itself. It is in
this sense that changes and variations are spoken of in the following pages,
where the cycle is regarded as the climatic unit. "
Ignoring the familiar cycle of the year, there is more or less conclusive evi-
dence of cycles of 2.5, 11, 22, 35, 50, 100, 400, and 1,000 years, approximately.
In addition, there are the great geological cycles of unknown duration, which
are discussed at some length in "Plant Succession" (337).
The 11-year cycle. — The best^known and most significant of climatic cy-
cles for the present day is the 11-year cycle and its multiples. So far as its
relation to tree growth, and hence to vegetation, is concerned, our knowledge
of this cycle is due chiefly to Douglass (1909, 1914, 1919), though Huntington
(1914) and Kapteyn (1914) have had a share in establishing the certainty of
this relation. The effect of cycles upon succession, and consequently upon
indicator communities and crop production, has been pointed out by Clements
(1916: 342; 1917: 304; 1918: 295). The relation of the 11-year cycle to changes
in native vegetation and to variations in plant production has received con-
stant study since 1914. It has proved so universal and fundamental as to
warrant its being made the basic feature of production systems in the arid
West (fig. 13).
The 11-year cycle is known also as the sun-spot climatic cycle, owing to the
striking correspondence with the sun-spot period. The correlation of the
dry and wet phases of cUmate and of the variations of tree growth with the
sun-spot cycle is often so exact as to warrant the assumption of a causal
relation between the two. Such a relation has not yet been established, how-
248
AGRICULTURAL INDICATORS.
I6S9
/727
l7Za
to
/78<h
.35
to ^ ^
lesz I
1853
to
1909
M
-h
.95
.90\
//^
y»e^r 9
1. 10
I.IO
1.00
I.IO
1. 00
.30
.80
I.IO
WO
JO
ever, and investigation at present is chiefly confined to the nature and extent
of the coincidence between them. The outstanding fact is that our knowl-
edge has reached a point where it seems increasingly possible to employ the
sun-spot cycle as a method of anticipating the coincident or related changes
in climate and vegetation.
Evidences.— The evidence of the cycle of sun-spots has all the certainty
of astronomical data. The number of sun-spots has been recorded for every
year since 1750, and the dates of the maxima and minima are definitely known
as well as their intensity. Cycles
in the annual growth of trees have
been found by Douglass in a num-
ber of diverse regions, in Europe as
well as in America. It is obvious
that trees growing in the most fa-
vorable conditions will not exhibit
cycles, since there is no limiting
factor to produce variations in the
width of the rings. Moreover, the
same tree sometimes fails to show
cycles throughout its Ufe, or does not
show them with equal clearness. This
is not difficult to understand when
the complex relations of factors, of
competition and reaction, parasites,
fire, lumbering, and other disturb-
ances are taken into account. By
far the greater part of the evidence
of existing cycles has been furnished
by Douglass (1919) . In his study of
Arizona trees, he has found that,
during the last 160 years, 10 of the
14 sun-spot maxima and minima
have been followed about four years
later by pronounced maxima and
minima in tree-growth, and that the
same trees show a strongly marked
double-crested 11-year cycle during
some 250 years of their early growth.
They Hkewise exhibited a relation to the temperature curve for southern
California, and this curve in turn resembled in form and phase the inverted
curve of the sun-spot cycle.
In the investigation of trees growing in wet climates, Douglass has also
found conclusive evidence of cycles. The trees of Eberswalde near Berlin
showed the 11-year sun-spot cycle since 1830 with accuracy. In the group as
a whole, the agreement is marked, the maximum growth falUng within 0.6
year of the sun-spot maximum. In six groups of trees from England, north-
em Germany, and the lower Scandinavian peninsula the growth since 1820
shows pronounced agreement with the sun-spot cycle, every maximum and
minimum since that date appearing in the trees with an average variation of
20 per cent.
33
1.20
I.IO
1.00
O 2 4- 6 8 10
Years
Fig. 13. — The 11-year cycle during the last
250 years, as shown by the yellow pine and
Sequoia. After^Douglasa.
CLIMATIC CYCLES. 249
Kapteyn (1914: 70) has studied the growth of oak trees in Holland and Ger-
many and reaches the conclusion that during fairly long intervals of time they
exhibit not only a regularity, but also an actual and fairly constant periodicity
in growth. From 1659 to 1784, or for a stretch of 125 years, a period of about
12.4 years is clearly indicated. While this period disappears in certain groups,
it persists in others, so that its recurrence for two centuries is demonstrated,
with only one minimum missing. Huntington (1914: 135) has devoted his
attention chiefly to the major sun-spot cycles indicated in the rings of trees
and has secured some exceedingly suggestive evidence of cycles of 100 years
and more. Douglass (1919: 111) has examined the trees studied by Hunting-
ton, in order to obtain evidence from them as to the shorter cycles, especially
that of 11 years, and to carry the existence of such cycles back for a period
of 3,200 years:
"The variations in the annual rings of individual trees over considerable
areas exhibit such uniformity that the same rings can be identified in nearly
every tree and the dates of their formation estabhshed with practical certainty.
"In dry climates the ring thicknesses are proportional to the rainfall with
an accuracy of 70 per cent in recent years, and this accuracy presumably ex-
tends over centuries; an empirical formula can be made to express still more
closely this relationship between tree growth and rainfall; the tree records
therefore give us reliable indications of climatic cycles and of past climatic
conditions.
"Certain areas of wet-climate trees in northern Europe give an admirable
record of the sun-spot numbers and some American wet-climate trees give a
similar record but with their maxima 1 to 3 years in advance of the solar
maxima. It is possible to identify living trees giving this remarkable record
and to ascertain the exact conditions under which they grow.
" Practically all the groups of trees investigated show the sun-spot cycle or
its multiples; the solar cycle becomes more certain and accurate as the area
of homogeneous region increases or the time of a tree record extends farther
back ; this suggests the possibility of determining the climatic and vegetational
reaction to the solar cycle in different parts of the world.
"A most suggestive correlation exists in the dates of maxima and minima
found in tree growth, rainfall, temperature, and solar phenomena. The
prevalence of the solar cycle or its multiples, the greater accuracy as area or
time are extended, and this correlation in dates point toward a physical
connection between solar activity and terrestrial weather.
"The tree curves indicate a complex combination of short periods including
a prominent cycle of about 2 years. "
In addition, Douglass has made a preliminary study of sections of fossil
trees, which show a similar cycle for some of the more recent geological periods
Considerable preliminary work has been done in tracing the effects of the
11-year cycle in plants other than trees and in plant communities. It has
been discovered that the dominant shrubs of sagebrush, chaparral, and desert
scrub often show this cycle in the growth-rings and that, in some cases at
least, the age of the shrub suggests that establishment takes place largely
and sometimes only during the wet phase of the cycle. Studies of the ex-
tension of forest and woodland into grassland or other arid communities has
shown that the entrance of the young trees occurred during the wet phase.
Henry (1895: 49) has shown that the height-growth of trees varies greatly
from wet to dry periods, and it seems certain that a similar relation exists
250
AGRICULTURAL INDICATORS.
for seed-production. In the special study of grazing during the past five
years a large amount of material has been collected which shows the critical
effect of the wet and dry phases upon growth and reproduction. As is well
known, field crops also exhibit a striking response to years of abundant rain-
fall as well as to those of drought. While methods of tillage influence crop
production profoundly, the latter clearly reflects the wet and dry phases of
the climatic cycle at those stations in the arid regions where the record is
suflBciently long. The effect of the 11-year cycle upon animals is most strik-
ingly seen in the case of range cattle, which live under semi-natural condi-
tions, but it is also readily discovered in all animal populations which are
directly dependent upon the natural vegetation of arid regions for their food-
supply.
Periods of drought. — While both wet and dry phases have a marked effect
upon the annual production of natural and cultural crops, the periods of
drought stand out with especial vividness. While this is particularly true of
arid regions, it holds likewise for semi-arid ones during the period of early
settlement, when economic resources are at a minimum. The consequences
are sufficiently disastrous even in such cases, as the history of settlement in
the Middle West proves. In the case of a native a^icultural population held
more or less rigidly within its own boundaries by the pressure of other tribes,
they led to famine with attendant wars and revolts. As a result, there is much
historical evidence of the periods of drought and famine in the Southwest,
and this makes it possible to discover how closely these correspond with the
phases of the 11-year cycle. As would be expected, there is frequent mention
of droughts in the chronicles of Mexico and the Southwest from 1600 to 1850.
A much smaller number of these were accompanied by famine, and appear to
represent drought periods. Of more than a dozen such periods, all but two
occurred at the sun-spot maximum, or within a year or two of it, and furnish
a record of agreement comparable to that of the last half-century (fig. 14).
noo
nso
itso
Fro. 14.-
1000
Ytars
-Double and triple sun-spot cycle in yellow pine from 1700 to 1900 A. D.
After Douglass.
The agricultural development of the West began with the passage of the
homestead act in 1862, and the consequent inrush of settlers. Since that time
the drought periods are known with certainty, and their correlation can be
made without question. In this connection it is essential to distinguish be-
tween drought periods and drought years. The former consist of two to three
or even four years and are felt generally throughout the West. In the Great
Basin, as well as in the Southwest, a single year of drought for a particular
r^on or locality may occur at almost any time, since the normal rainfall is so
CLIMATIC CYCLES. 251
low that almost any deficit is equivalent to a drought of some degree. How-
ever, while a dought year involves inconvenience and loss, it rarely causes
disaster and the general abandonment of recently settled regions. Hence, in
the discussion of climatic cycles and drought, the latter is understood to be a
drought period several years in length and extending over all or nearly all of
the West.
Recurrence of drought periods. — The assumption that the 11-year cycle
could be traced in the present and future as well as in the past (Clements
1916: 330; 1917: 304; 1918: 295) led to a study of the coincidence of drought
periods and sun-spot maxima from 1860 to 1915. The sun-spot maxima for
this interval of 55 years occurred in 1860, 1870-72, 1883, 1893, and 1907.
The maxima of 1870-72 and 1893 were known to coincide with times of
general and critical drought in the West, and it was found that similar con-
ditions had prevailed in 1859-60. In the case of the maximum for 1907, the
deficit fell in 1908-09 for most regions and was less marked, while for the
maximum of 1883 the record showed an excess of rainfall quite as often as a
deficit. The close correspondence of sun-spot maxima and drought in 1870-
72 and 1893-95, and the decrease or absence of agreement in 1883 and 1907,
suggested that the maximum effects occurred in multiples of the 11-year
period (Plant Succession, 336) . The period involved in the two major droughts
was 21 to 23 years, and this appeared to warrant the suggestion that a similar
critical drought would recur in connection with the sun-spot maximum of
1917. The year 1915 proved to be exceptionally rainy, perhaps due to a lag
of the effects expected at the sun-spot minimum in 1913, with the result that
the ensuing drought period of 1916-18 appears to have been the most general
and severe ever known in the West.
Drought periods not only bear a relation to the maximum of the sun-spot
cycle, but also to periods of increased rainfall, with which they show a definite
alternation. This alternation of dry and wet phases constitutes the climatic
cycle which corresponds with the 11-year sun-spot cycle. As Douglass has
found in the case of tree growth (1919), the drought period is much more
marked, at least in its effects, and its rings are consequently used as basing
points. The wet phase is related to the dry one in a cause-and-effect sequence,
in accordance with which a deficit is followed within a year or two by an excess,
or an excess by a deficit. While a prehminary investigation of this point
indicates that it is the general rule, it is often obscured by local variations in
the spatial distribution of rainfall. The wet phase likewise shows a correla-
tion with the minimum of the sun-spot cycle, but it is usually less definite and
striking than that of the dry phase. However, in a large number of localities \
representing different regions of the West, the rainfall at the sun-spot minimum
is usually above the noniial. It seems more or less probable that periods of
excessive rainfall for 1 to 3 years occur on the second or third multiple of the
11-year cycle, and that they precede or follow a drought period as a rule.
The evidence that drought has occurred at frequent intervals during the
past 300 years is conclusive. It is equally certain that drought periods have
regularly alternated with wet ones, though these are naturally less frequently
noted in the human record. Moreover, it must be recognized that the alter-
nation of dry and wet phases will be seen most clearly in the grassland climax
of the prairies and plains, where the rainfall ranges between 15 and 30 inches.
252 AGRICULTURAL INDICATORS.
East of this, only the most intense droughts will be noted as such, and the
minimum crop production is apt to occur in years of excessive rainfall. In
the Southwest, where the rainfall is always low, the economic effects of drought
may occur in almost any year when the distribution or timeliness of the rain
is at fault. The existence of a chmatic cycle coinciding with the sun-spot
t cycle, and consisting of a dry and a wet j)hase which falls respectively at the
\ sun-spot maximum and mininium, appears to be estabUshed beyond a doubt
j by the work of Douglass, Huntington, and Kapteyn, as well as by the study of
j vegetation. Much more work is required to explain certain apparent excep-
i tions and contradictions in widely divergent climates, but none of these seem
to invahdate the general principle.
Significance of the sun-spot cycle.— The establishment of a cycle of rela-
tively dry and wet periods with a usual length of 10 to 12 years is of para-
mount importance to the practice of agriculture, forestry, and grazing in the
West. Since rainfall is the Umiting factor over most of the region, a knowl-
edge of what can be expected in the way of variation in rainfall and changes
of climate will be of the greatest help. The most serious handicap to the
proper agricultural development of the West lies in the almost universal
misconception of climate and the nature of its changes. Much of this
arises from the mistake of the earher geographers in regarding the Missouri
Valley as a part of the "Great American Desert." The rapid development
of this region was sufficient proof that it had never been desert, but the per-
sistence of the old idea could be reconciled with the facts only by the assump-
tion that the rainfall had greatly increased as a result of cultivation. This
\ impression that the rainfall was increasing was further strengthened by the
luxuriant development of the tall-grasses as a consequence of the disappear-
i ance of the buffalo. This mistaken idea still persists over much of the West,
i where a marked and permanent increase in rainfall is confidently expected to
follow settlement. This error has further serious consequences in that it leads
to each drought period beingj-egarded as the last, and consequently prevents
the adoption of systems of settlement and management which will reckon
with drought periods as certain to recur. Even where experience made it
clear that droughts still occurred, the prejudice in favor of a changing cli-
mate, together with the general optimism and inertia of the pioneer, pre-
vented the recognition of the patent fact. Moreover, during the disastrous
drought of 1916-18, stockmen were often found who admitted that drought
had occurred before and probably would again, but stated that this fact
would be readily forgotten when the rains came.
The meteorologists have proved repeatedly, from the weather records, that
there has been no progressive change in the climate of the West during the
settlement of the latter. This has been conclusively shown by Swezey and
Loveland (1896: 137) for Nebraska, the central position of which makes it
typically representative of the climate and vegetation of the grassland climax:
"If we examine the precipitation for the series of years from 1849 to 1895
inclusive given in Appendix II, we shall find that, although the rainfall of the
past few years has been less than that of the earlier years of the series, so far
as we can judge from the rather meager records of those earlier years, yet
there is afforded no evidence of any considerable progressive change in the
climate of the State, either toward wetter or drier conditions. There have
CLIMATIC CYCLES. 253
been excessively wet and excessively dry years, the annual rainfall having
ranged from 13.30 inches to 47.53 inches; there have been groups of wet years
and groups of dry years succeeding one another in a rather irregular manner.
Thus the 47 years may be grouped into five periods as follows: The first 10
years were mostly wet years, only one of them, viz, 1852, having a rainfall
less than normal; the next 9 years, 1859 to 1867 inclusive, constituted a period
of scant rainfall, including particularly the exceedingly dry years of 1863
and 1864 and the scarcely less dry years of 1859 and 1860; the 9 years from
1868 to 1876 inclusive included years of plenteous and years of scant rainfall
succeeding each other in a quite irregular manner; then followed 10 years,
1877 to 1886 inclusive, of rainfall generally above the normal; and finally the
last 5 years have been, with the exception of 1891 and 1892, years of deficient
rainfall, with the year 1894 the driest of the whole 47.
" But if we divide the entire series of 47 years into two periods of 24 and 23
years respectively, the average rainfall of the first period will exceed that of
the last by only about an inch. The first year of the series, 1849, was one of
excessive rainfall, not only as shown by the record made at Fort Kearney,
the only station in Nebraska at which records were kept, but also as confirmed
by records in the adjacent Territories. This difference of a little more than
an inch between the mean rainfall of the first 24 years and that of the last 23
years of the 47 would almost disappear if this year of 1849 were omitted from
the series; the mean precipitation for the 23 years from 1850 to 1872 is 23.55
inches, while that of the 23 years since is 23.46 inches.
"The conclusion, therefore, seems to be a safe one that the average rainfall
of Nebraska, although subject to great fluctuations from year to year, yet
in the long run remains substantially unchanged, so far as we can discover
from the records of nearly haK a century. "
Prediction of drought periods. — The sun-spot cycle furnishes a ready method
of predicting the occurrence of dry and wet periods. The sun-spot numbers
are recorded with the greatest accuracy and detail, and the number for each
month and year is readily obtainable. These numbers, taken in conjunction
with the length of the recent cycles, make it possible to forecast the date on
which the next maximum and minimum will fall, as well as something of their
intensity. During the past century the average of 11.4 years for the cycle
has been strikingly evident, practically all the cycles being from 10 to 12 years
long. The accuracy of the correlation between the sun-spot cycle and the
climatic cycle as recorded in the growth of trees is 85 per cent, according to
Douglass's results (1919). This compares favorably with the accuracy
of the daily forecasts of the Weather Bureau, and still more favorably with
that of the weekly forecasts. However, there is one essential difference, in
that the latter are actual forecasts, while the prediction of dry and wet phases
has been attempted as yet only for the dry and wet phases of the current cycle
(Clements, 1917, 1918). The close correspondence between the sun-spot
cycle and the curve of tree growth strongly suggests a similar degree of
accuracy in actual prediction, but repeated trial can alone determine this,
as well as disclose the reasons for failure.
While it is thought and expected that the use of the sun-spot cycle will
permit the prediction of drought periods for the West in general, as well as
the occurrence of intervening but more diffuse wet periods, the prediction for
a particular locality is subject to more uncertainty. In this respect, cycle
predictions resemble the daily and weekty weather forecasts. The failure of a
254 AGRICULTURAL INDICATORS.
relatively small number of these to be verified is due chiefly to changes of
intensity or of pathway in the cyclonic area. In addition, there are more
obscure local differences in evidence in almost every storm by which the
amount of rain may vary greatly at two neighboring points. As KuUmer and
Huntington have pointed out (1914), the shifting of the storm-belt seems to
afford a causal explanation of cUmatic differences at the sun-spot maximum
' and minimum, as well as of variations from one locality or region to another.
Thus, while drought periods are general for the West at the double sun-spot
cycle, as in 1870-72, 1893-95, and 191&-18, not all regions showed 3 years of
drought, and during any one year a few regions recorded a rainfall approach-
ing normal. Naturally, the drought was most intense and prolonged in the
areas of normally scanty rainfall, and it decreased more or less regularly in the
direction of regions of medium precipitation. During such periods, it is even
possible that high mountain regions may receive an excessive amount of
rain. This seems to result from the principle of compensation, in accordance
with which deficit and excess are regularly linked together in time or in space.
For the present, this is regarded as the most plausible explanation of variations
and inconsistencies in the behavior of the climatic cycle, but it is probable
that further knowledge will show that these are connected with the differentia-
tion of contiguous climates. Hence, while the method of cycles can not as-
sume to forecast the number of inches of rain for any locality during a certain
year, it can predict the recurrence of drought periods and of succeeding wetter
years for the West in general. The drought period will concern three regions
out of four during most of its duration, and it will affect practically every
' locality at some time during its phase.
Utilization of cycles. — A study of settlement in the West since 1865 reveals
the fact that it corresponds more or less closely to the climatic cycle. The
exceptions are afforded by the rapid inrush after the homestead act, the Kin-
kaid act, etc., or after the opening of new regions. The general movement of
settlers has advanced and receded in almost perfect agreement with the wet
pha-ses and drought periods of the climatic cycle (cf. Bruckner, Huntington
1914: 89). A few years of unusual rainfall have afforded unscrupulous real-
estate dealers and immigration commissioners an opportunity to dispose of
even the most worthless land. The ensuing drought period then led to crop
failure and the wholesale abandonment of the region, to be followed by
another influx of settlers during the next wet phase. In more than one region
of the West this process has been repeated three or four times, and its dis-
, astrous operation will continue until the States and the National Government
, recognize the necessity of prop)er land classification and of adequate regulation
of settlement.
The knowledge that drought periods will recur is indispensable to any
accurate and successful classification of land and to the economic manage-
ment of dry-farm, grazing range, or forest. These results, which are of the
first importance for the West, do not depend necessarily upon the accuracy of
predictions based upon the sun-spot cycle. They are clearly indicated by the
actual experience of the last 60 years, which not only confirms the recurrence
of drought periods, but also suggests the interval. However, it is clear that
it would be of the greatest value to be able to forecast the date, duration, and
intensity of each drought period with some accuracy, as well as to anticipate
FARMING INDICATORS. 255
the increasing rainfall of the wet phase. This would not only permit the tak-
ing of the necessary precautions against the disasters due to drought, but it
would also make possible the development of an optimum system of manage-
ment. This would enable the farmer to fit his crops and methods of tillage
to the variations in rainfall and would permit the stockman to increase or
decrease his herds or to vary his supplies of forage with the wet and dry phases
of the cycle. In short, the cycle management of all the basic practices of the
West would provide the maximum insurance against loss or disaster and would
afford the greatest possible annual returns. _^ It is further discussed in con-
nection with agricultural and forest indicators, but its value is especially
emphasized under grazing, since the latter and the related dry-farming are
most dependent upon climatic conditions.
FARMING INDICATORS.
Types of farming. — With reference to indicators, types of farming may
be based upon conditions or upon crops. Since the former determines the
methods and return (and often the crop as well), it seems to afford the better
basis. Accordingly, the usual division into humid and arid farming is em-
ployed here, with a further division of the latter into dry-farming and irrigation
farming. It is clear that no sharp line exists between the types of agriculture
in humid and arid regions. Between the two lies a broad belt of semi-arid
country in which there is a gradual adjustment of methods and crops to
increasingly arid conditions. The distinction is further obscured by the
variation in rainfall from the wet to the dry phase of the climatic cycle. Dur-
ing the wet period humid farming is possible through most or all of the semi-
arid belt and the need of drainage becomes felt over a much wider area.
During the dry period arid conditions are pushed across much of the semi-arid
country and semi-arid conditions develop in the outlying humid areas. How-
ever, practices change much less than conditions; the general area of the humid,
semi-arid, and arid regions remains essentially the same, with their mutual
relations identical.
The humid region is regarded as possessing a lower limit of 25 inches of
rainfall, while the semi-arid has a range of 15 to 25 inches, and the arid from 2 to
15 inches. As would be expected from variations in the annual amount and
distribution of the rainfall, semi-arid areas with 20 to 25 inches of rain are
characterized by the humid type of farming, and those with 15 to 20 inches
by dry-farming. The latter type usually reaches its lower limit at 12 inches,
or at 10 inches where the rainfall is largely of the winter type. Below 10
inches, farming is profitable only by means of irrigation. Naturally, the
latter is also extensively practiced in regions with 10 to 20 inches of rain, and
to some degree under even higher rainfall. As Briggs and Belz (1911) have
shown, the eflficiency of rainfall depends upon the amount of evaporation, and
hence decreases more or less regularly from the northeast to the southwest in
the western United States.
Relation of types of farming to indicators.— Because of the control made
possible by irrigation, methods of tillage, and variation in crop or variety,
indicator values are less definite in the case of types of farming than in grazing
or forestry. Their significance is further reduced by the possibility of irri-
256 AGRICULTURAL INDICATORS.
gation and by such economic considerations as markets and transportation.
Moreover, the method of conserving water-content by means of summer
fallow enables dry-farming to be practiced in regions where otherwise irriga-
tion would be the only successful method. On the other hand, where annual
cropping is the rule, dry-farming methods pass imperceptibly into those of
ordinary farming with good tillage in semi-arid and subhumid regions. In
spite of this, there is a general correspondence between cUmax associations
and types of farming. The tall-grass prairies are typical of regions in which
humid farming prevails. The mixed prairies and short-grass plains denote
country in which dry-farming of the annual crop type is more or less success-
ful. The bunch-grass prairies and desert plains characterize regions of scan-
tier rainfall, for the most part of the winter type, and hence are chiefly to be
correlated with dry-farming by means of summer fallow. Subclimax sage-
brush has practically the same indicator value as the associated grasses.
When these are tall-grasses the indications are of dry-farming with annual
cropping, and when they are bunch-grasses they indicate summer fallow
methods. Climax sagebrush is also an indicator of the latter when the rain-
fall does not fall below 10 inches. Over the major portion of the central Great
Basin, sagebrush indicates a cUmate in which crop production is impossible
without irrigation. This is likewise true of practically the whole desert scrub
cUmax except for small areas at higher altitudes or near its eastern limit,
where it approaches or mixes with the grassland. The indications of chaparral
are variable. While they are largely non-agricultural, chaparral resembles
scrub generally in its indication of dry-farming or irrigation practices, as is
true also of woodland where soil and topography are favorable. Montane
forest usually receives enough rainfall to make humid farming possible,
though both dry-farming and irrigation are practiced in the lower yellow-pine
belt. Most of the montane zone hes above the Umit of profitable agriculture,
and the occasional fields of hardy cereals are restricted to the warmer valleys
and lower slopes (plates 61 and 62).
Edaphic indicators of types of farming. — These are more local and hence
less important than the chmatic indicators just discussed. They are primarily
related to soil and water-content, and consequently are of the greatest service
in regions with marked soil characteristics, such as sandhills, bad lands, saline
basins, or in river or lake valleys with relatively high water-content. The
same farm may have lowland and upland areas, or may show considerable
variations in soil with corresponding indications as to types of farming. This
is particularly true of the wet valleys in the sandhills of Nebraska and of the
many river valleys with a generally westward direction in Nebraska and
Kansas. The wet valleys are marked by meadow communities, and many
of them are susceptible of farming by the usual methods. The river valleys
are occupied by similar communities of which Andropogon, Agropyrum, Cala-
movilfa, Elymus, or Spartina are the dominants, or they may be characterized
by the presence of scrub. In either case the indications are for subhumid
farming, especially during the wet period of the climatic cycle.
Shantz (1911:85) has pointed out the agricultural significance of the
difference between lighter and heavier soils in passing to the westward. The
lighter soils conserve water to a much larger degree, and hence require less
intensive methods of cultivation than do the heavier ones. In some regions,
CLEMENTS
PLME 61
iM IMI
^v,;:4>i*
■^^
A. Tall valley sagebrush im i deep toil for irrigation, Carhind, Colorado.
B. A legume, Lupinus plattensis, indicating a rich moist soil, Monroe Canyon, Pine Ridge, Nebraska,
C. Relict Slipa and Balsaviorhha in sagebrush, indicating a bunch-graes climate for dry-farming,
CROP INDICATORS. 257
and especially during certain years, this may amount to ordinary cropping
on one and dry-farming on the other. Kearney and others (1914: 416) have
shown that sagebrush {Artemisia tridentata) is an indicator of both dry-farm-
ing and irrigation farming in Utah when it makes a good stand and vigorous
growth. Communities of Kochia vestita or Airiplex confertifolia generally
indicate the necessity of irrigation to rid the soil of the excess of salts. The
mixed community of SarcobatiLS and Atriplex has essentially the same signifi-
cance, though it indicates the desirability of drainage as well. Hilgard (1906:
536) regards Sporobolits airoides, Spirostachys, Salicornia, Sitaeda, SarcohatuSy
Frankenia, Cressa, and Distichlis as indicators of the necessity of underdrainage
as a prerequisite to successful irrigation farming.
CROP INDICATORS.
Nature and kinds. — While the factor-complex must always be kept in mind
in the correlation of indicator communities and crops, water is the paramount
factor practically throughout the West. The importance of temperature as
a direct factor increases with latitude and especially with altitude, but it is
regularly less than that of water. The water relations are primarily a ques-
tion of rainfall and evaporation, more or less modified locally by topography
and soil. As a consequence, it is desirable to distinguish climatic and edaphic
indicators of crops. The former denote tlie general climatic regions for
particular kinds or varieties of crops, the latter the soil or topographic differ-
ences which break up the climatic imiformity of a particular region and render
other kinds or varieties preferable. Climatic indicators are primarily climax
communities of varying rank, while edaphic indicators are mostly serai or
developmental communities. Crop indicators may serve to denote (1) the
type of crop, as grain or forage; (2) the species in a general sense, as wheat,
oats, or rye; (3) the kind, as winter and spring, or hard and soft wheat; and
(4) the variety, such as Marquis, Fife, or Preston. They also permit cor-
relations with differences in methods of practice, such as dry-farming with and
without summer tillage, etc.
Little use has been made of plant communities as indicators of the type or
kind of crop. This has been a natural outcome of the enormous amount of
crop experimentation carried on by the Department of Agriculture and the
various State experiment stations during the past two decades. Nearly 100
stations and substations have been concerned in this work, and it is a logical
conclusion that they have made the use of crop indicators unnecessary. It
seems, however, that the very extent and thoroughness of the experiments
with various crops must increase the accuracy and readiness with which
indicator'? can be used. In spite of the numerous stations, there are many
large regions still unrepresented. In addition, the cUmatic gradations and
edaphic variations are so numerous that the native vegetation alone affords an
adequate method of taking them all into account. As a consequence, the
opportunity for working out a general system of crop indicators seems excep-
tionally good. This would be based upon the correlations between native
communities found about each station and the types and kinds of crops dem-
onstrated to be the most desirable for that region. While such correlations
can be obtained from the results of practically all stations, the investigations
carried on at those of the OflSce of Dry-Land Agriculture are of the greatest
258 AGRICULTURAL INDICATORS.
value. This is due to a number of causes, chief among which are the use of
the same crops and methods, the wide extent of the studies, the large number
of stations in a single great climax, the grassland, the more or less gradual
decrease in rainfall to the westward, and the consequent readiness and accuracy
with which comparative results can be obtained. The correlations discussed
below have been based chiefly upon the results obtained by this Office, supple-
mented for the more or less representative- central portion by the studies made
at the experiment stations of Nebraska and Kansas. In all of them, it should
be borne in mind that the correlation and the corresponding indicator com-
munity have the greatest accuracy in the region of the particular station or
stations, and that this value decreases more or less regularly iix the direction
of stations with different correlations. However, the practical usefulness of
the indicator increases with the remoteness from a particular station, providing
always that the plant community remains the same, since the latter indicates
that the conditions are essentially unchanged.
Climatic indicators of the types of crops.— The correlations considered here
are based upon the fact that crops, like natural dominants, have an area of
maximum production about which they shade out in all directions. This
diminution is generally less marked in the case of crops, owing to the modi-
fying influence of culture as well as of economic factors. Corn affords the
most striking example of a crop grown throughout an extensive region, but
with a well-defined area of maximum production. As a crop it extends over
the major portion of several climaxes, but its optimum area, the "corn belt,"
is more or less clearly limited. The limits of this belt fall within the main area
of the subclimax and true prairies, which are to be regarded as the indicators
of maximum com production. In this connection, it is at least suggestive
that four of the dominants of these communities belong to the genus Andropo-
gon, which systematically and ecologically resembles corn more closely than do
any of the other grassland dominants. As might be expected, wheat exhibits
an even more extensive correlation with the grassland. The region of max-
imum production is from Saskatchewan to Oklahoma, with secondary maxima
in Indiana and Illinois, and in Washington and Oregon. The maximum falls
almost wholly within the region occupied by the true and mixed prairies.
Here also it is perhaps significant that Agropyrum, with its close relationship
to Triticum, is an important dominant in these communities and is the major
dominant in the great wheat region of the Palouse. Oats show a somewhat
similar relation to grassland, as does barley, but rye manifests no clear cor-
relation. On the whole, however, there is good evidence for regarding grass-
land made up of tall-grasses as the primary indicator for the optimum pro-
duction of cereals (cf. Smith, Baker and Hainsworth, 1916; Waller, 1918).
Hay and forage crops generally are more or less evenly distributed through
the deciduous forest and grassland cUmaxes, but there is a clear regional
differentiation in the case of alfalfa and sorghums. The chief center for
alfalfa is in central Nebraska, Kansas, and Oklahoma, with local centers in
the main irrigated sections of the West, practically all of which occur in grass-
land or sagebrush. The sorghums, whether grown exclusively for fodder or
for grain as well, have their center of maximum production in western Kansas,
Oklahoma, Texas, and eastern New Mexico. It corresponds closely with the
eastern half of the short-grass association, in which BuUnlis and Bouteloua
A. Mixed prairie (.S'/i'/xi (omata) indicating? dry-farming, Scenic, South Dakota.
B. Tall-grass {Andropogon furcatus) indicating humi<l farming, Madison, Nebraska.
C. Bunch-grass prairie {Agropyrum-Feslttca) indicating dry-farming with winter rainfall, The
Dalles, Oregon.
CROP INDICATORS. 259
gracilis are the dominants. Cotton reaches its maximum in a well-marked
region which corresponds with the southern forest, except in central Texas
and Oklahoma. Under irrigation it promises to develop a secondary center
for long-staple varieties in the desert scrub climax of the Southwest. Of
the other types of crops, vegetables are more or less evenly distributed over
the eastern half of the country, with marked regional differentiation for cer-
tain kinds and many local foci. Fruits and nuts show a similar uniform dis-
tribution in the East, but they are almost wholly confined to the forested
region and its extension into the southeastern prairies. This correlation is
.v'holly to be expected on the basis of similarity in life-form. The most im-
portant fruit districts of the West he in the sagebrush and chaparral cUmaxes
and depend upon irrigation, as the difference in the life-forms indicates.
Climatic indicators of kinds of crops. — The correlation of the kind of crop
with indicator communities has already been touched upon. It is often less
definite than with types of crops, but there are a number of correspondences
of much interest and value. These are perhaps best shown by the three kinds
of wheat, namely, winter, spring, and durum. Winter wheat has its center
in the true prairies of Kansas and Nebraska, in which Andropogon plays an
important part. Spring wheat and durum reach their best develepment in
the mixed prairies or in the northern portion of the true prairies, where Stipa
spartea and Agropyrum glaucum are especially important. They are more or
less equal in value in the eastern portion of the true prairies, but durum shows
an increasing advantage to the west, and is superior to spring wheat practi-
cally throughout the mixed prairies. In the bunch-grass prairies of the North-
west the advantage is reversed, and spring wheat outyields durum. The
general use of summer tillage in connection with the winter precipitation favors
winter wheat because of its earlier period of growth.
Tbg^ region of the maximum production of barley comprises the northern
half 'f the true prairies, while that of oats includes the major portion of both
.ae bubclimax and true prairies. Flax finds its maximum in the transition
^' om the true to the mixed prairies, but it is extending more and more into
the Lvtter in western North Dakota. While there is a marked correlation
between the sorghums as a group and the short-grass plains and their transi-
tion to the tall-grasses, the various kinds of sorghums show no clear correla-
tions with indicator communities. This is perhaps due in some measure to
the relatively short period of trial, but probably results chiefly from the fact
that qualities of earliness and dwarfness are more significant than the group
differences (Ball, 1911; Ball and Rothgeb, 1918:88). In contrast with the
grain-sorghums, the sorgos show an increasing correlation with the tall-
grasses, and in western Nebraska and the Dakotas are to be related to the
mixed prairies.
Climatic indicators of varieties. — The significant correlation of indicator
plants with varieties is naturally more difficult and less satisfactory than in
the case of types and kinds of crops. This is largely because the differences
between varieties can be modified or reversed by seasonal variations or cul-
tural methods, as well as by the complex of local conditions. It is also due
in part to the fact that the minor differences in indicator communities arising
from varying grouping of the dominants and from changes in the subdomi-
260 AGRICULTURAL INDICATORS.
nants have received little careful study. In spite of these facts, there are
certain obvious correlations where varieties differ in some clear-cut quality,
such as earhness or dwarfness. Both of these are related to the evasion of
drought or frost, and can be correlated in some measure with indicators of
changing altitude or latitude, or with decreasing rainfall. It should be borne
in mind also that each variety primarily represents a certain degree of adjust-
ment to particular conditions, and that some of them are certain to be replaced
by other varieties as a result of longer trial or changing demands.
Wheat exhibits the best indicator correlations with varieties because of its
greater differentiation and wider area. Among the durum wheats, Arnautka
is indicated as the best variety by the true prairies with greater rainfall and
shorter season. Of the spring wheats, Preston is generally indicated by true
prairie. Marquis by mixed, and Bart by the bunch-grass prairie. Winter
wheats are less clearly indicated owing to their greater drought evasion, but
the Turkey and Kharkof are the principal varieties in the true prairies, and
various strains of Crimean in the short-grass plains and the sagebrush. The
soft winter wheats correspond with the subclimax prairies more or less nearly,
while the hard varieties correspond with the true prairies and short-grass plains,
which are relatively drier and colder. The varieties of oats show a fair degree
of correspondence with the grassland associations. ICherson generally gives
the best yields in the true prairie, Burt in the short-grass association, 60-day
in the mixed prairie, and 60-day or Kherson in the bunch-grass prairie. In
Kansas, Blackhull kafir is the best variety in the subclimax and true prairies,
Pink kafir in the broad transition to the short-grass, and Dwarf Blackhull in
the short-grass proper, where it enters into competition with Dwarf milo and
feterita. Orange sorgo is correlated with the subclimax and true prairies,
and Red Amber with the transition and the short-grass plains.
Life zones and crop zones. — Merriam's classic paper upon the life zones and
crop zones of the United States recognized seven divisions, the Arctic-Alpine,
Hudsonian, Canadian, Transition, Upper Austral, Lower Austral, and
Tropical (1898: 18; 1890:18). The most important of these were sub-
divided into faunal areas, of which the Arid Transition, Pacific Coast Transi-
tion, Upper Sonoran, and Lower Sonoran are the ones found chiefly in the
West. Lists of crops and their varieties were given for each of the areas and
the zone ranges of crops were indicated by tables. These represented the
most important correlations and were undoubtedly of value as a record of the
results of experience and experiment up to 1898, though naturally many of
the varieties have since been superseded. Many of these correlations were
necessarily the same as for indicator communities in the same regions. Since
the basis of Merriam's work was floristic and faunistic rather than ecological,
the correlations were for the most part more general and less accurate. As
has been indicated earlier, this was a necessary outcome of regarding tem-
perature and fauna as the primary bases for such correlations rather than
water and vegetation. One interesting consequence was the much greater
use made of perennial crops, particularly the fruits, since these are naturally
more subject to unfavorable temperatures than the annual ones. The need
for a finer division of the faimal areas is well illustrated by the Upper Sonoran,
which includes the grassland, sagebrush, chaparral, and woodland climaxes.
The difiiculty of correlating crops with such an extensive and varied area is
mentioned by Gary in his discussion of this zone in Colorado (1911: 30):
CROP INDICATORS. 261
"The distribution of Upper Sonoran crops is at present local; and so de-
pendent are many of the crops upon natural protection, adequate water supply,
and suitable soils, entirely aside from temperature, that they can not be grown
over the whole of a region so varied as the Upper Sonoran of Colorado."
Whatever may be the shortcomings of the life-zone concept, they are more
or less inevitable in a pioneer work covering such a vast field. With Hilgard
and ChamberUn, Merriam must be given great credit for having recognized
the value of natural indicators so early, and for pointing out many of the
major correlations. His method has formed the basis for the surveys of
Western States made by the Bureau of Biological Survey during the past 15
years. The first of these was that of Texas, made by Bailey (1905), in which
little attention was given to crop correlations. In a similar study of New
Mexico (1913; cf. Wooton, 1912: 10) he has discussed the crops of the Lower
and ITpper Sonoran zones in some detail, especially as to the fruits (23, 38).
Cockerell (1897) was the first to give a general discussion of the life zones of
New Mexico, as well as the first t^ make use of insects as zone indicators.
Gary (1911: 29, 40) has dealt with the agricultural importance of the Upper
Sonoran and Transition zones in Colorado. He has also characterized briefly
the agriculture of the same zones in Wyoming (1917: 30, 39) and has pointed
out the economic importance of the boreal zones (52). Robbins (1917) has
described briefly the native plant conmiimities in Colorado with especial
reference to altitude and has discussed the general agricultural relations of
the grassland, sagebrush, chaparral, woodland, and montane forest.
Edaphic indicators of crops and methods. — Variation in crop possibilities
within a cUmate, due to edaphic or soil conditions, may be regional or local.
Regional and local variations are both caused chiefly by variations in water-
content arising from differences in soil, solutes, or topography, and the only
important difference between them is that the one determines the general
agricultural practice of a region, and the other that of a neighborhood or of a
single farm. The responses of plants to local differences in water-content are
readily seen, and the corresponding edaphic indicators are of much value
in suggesting desirable or necessary local variations in crops or methods.
Since practically all such local differences have to do with water-content or
temperature, their indicators have the same general significance as in the case
of the more general climatic differences. Such local variations in conditions
may often be quite as great as those between adjacent climatic regions and
edaphic indicators may consequently denote differences in crops and methods
quite as great as climatic ones do. Since the number of such indicators is
-legion, and every small difference of soil or topography has a corresponding
indicator, the adjustment of crop and method to any particular variation in
conditions is largely a matter of practicability. Locally as well as generally,
the chief differences in soil are represented by saline soil, hard land or gumbo,
and sand. All of these have their proper indicators, as is well known, and it
is only necessary to recognize that their local occurrence has much the same
significance assigned to them by Hilgard, Shantz, Kearney and others for
more extensive regions. This is particularly well illustrated in the case of
dune-sands, which are found in sandhill areas through the prairies and plains.
It is best seen in the great sandhill region of Nebraska, where soil and topo-
graphy have combined to present an unusual set of conditions. The loose
262 AGRICULTURAL INDICATORS.
sandy soil, lack of humus, and the maze of steep hills with intervening wet and
dry valleys constitute a complex of factors marked by distinctive indicators
and demanding a specialized type of agriculture (Cowan, 1916: 5). Such a
region not only requires different methods and crops from those of the general
climati* area, but the varying areas of wet valleys, dry valleys, and hillsides
demand corresponding differences in treatment.
Indicators of native or ruderal forage crops. — The detailed study of sec-
ondary seres in fallow fields and similar disturbed areas has revealed a num-
ber of species of native herbs and weeds which give more or less promise as
forage crops. During the three years of drought from 1916 to 1918, particular
attention has been directed to those which made a vigorous growth or a good
stand in fields in which forage crops were a failure, or in areas adjacent to such
crops. A considerable number of weeds of much promise has been observed
over an extensive region, and in addition a number of native species have
been suggested as of possible forage value by their behavior during drought.
By far the most valuable are Melilotus alba, Helianthus annuus, and Salsola
kali. The former is rapidly taking its place as a forage crop in some regions
and there seems little doubt that it will ultimately be grown as a dry crop
over a wide area. Helianthus annuus has but recently been tested under field
conditions (Arnett, 1917), but the results agree with the evidence in nature
to the effect that it is of much value in dry regions, and especially during
drought years. Salsola has been grown scarcely at all as a crop, but it has
been cut as a weed crop and utiUzed as hay of a fair quaUty at least. While
its tonnage is less than that of sunflower, it will often grow luxuriantly in
places where the latter will not. This is true also of Helianthus petiolaris,
which may be regarded as a dwarf native form of the conmion sunflower.
The other coarse weeds whose behavior indicates that they will be found to
have some forage value are Chenopodium album, Amarantus retroflexus, A.
hybridus, Erigeron canadenMS, Iva xanthifolia, I. axillaris, and Brassica nigra.
The native species of weedy habit and of such vigorous growth as to suggest
the probabiUty of forage value are Amarantus palmeri, A. powellii, A. torreyi,
A. wrightii, A.jimbriatus, Acnida tamariscina, Psoralea lanceolata, Franseria
tenuifolia, F. discolor, Atriplex rosea, A. expansa, Corispermum hyssopifolium,
and Cycloloma platyphyllum. The last four are adapted to saline soils, and
the last two to sandhill areas as well (plate 63).
AGRICULTURAL PRACTICE AND CLIMATIC CYCLES.
Cycles of production. — The close dependence of annual crops upon seasonal
and annual rainfall makes it clear that they will reflect the various climatic
cycles in some degree. The correlation is less exact than with the natural
perennial crops of grasses, shrubs, and trees, owing to the effect of cultural
methods and the choice as to times of planting. It is also more or less ob-
scured by rotation and by changes of variety and method such as are con-
stantly taking place in ordinary practice. Moreover, it may be completely
destroyed for a particular year by hot winds of a few days' duration if they
occur at a critical period, such as that of the tasseUng of corn. In addition,
the correlation of cycles, rainfall, and crop production is most in evidence in a
region such as the prairies and plains, where the rainfall is moderate, ranging
AGRICULTURAL PRACTICE AND CLIMATIC CYCLES.
263
for the most part from 15 to 30 inches. Above 30 inches the compensating
effect of accumulated water-content tends to minimize the consequences of
drought, while below 15 inches the margin of safety is so small that it is easily
destroyed by local or incidental causes.
The evidence of definite cycles in crop production is difficult to obtain for
the further reason that accurate records in a particular place for a long period
are extremely rare. Few of these extend through a sun-spot cycle of 10 to 12
years, and practically none through the more significant double cycle of 21 to
23 years. However, the drought periods of 1870-72, 1893-95, and 1916-18
were so intense that a corresponding production cycle is shown in the crop
averages for the regions concerned. The sun-spot maximum of 1907 marked
a minor drought period which in most regions reached its culmination two or
three years later. This discrepancy seems to be explained, in part at least,
by the interference of a shorter cycle, probably the pleion or quarter cycle of
2.5 years, and by the action of the excess-deficit balance. Arctowski (1912:
745) has shown the relation of the corn crop by States and regions to the
interaction of these two cycles. He has found not only that areas of excess
and deficit in production bear a definite relation to each other, but also that
this relation is preserved as they shift about from year to year. Douglass
(1919: 106) has found that the 2.5-year cycle is regularly present in the
growth of trees. Hence, it seems probable that the major cycle of crop
production is the double sun-spot cycle of 21 to 23 years, and that this is
made up of smaller cycles resulting from the interaction of the sun-spot
cycle of 11 years and the quarter cycle of 2.5 years. Intensive research only
can determine how distinct and universal these may be. At present, it must
be admitted that they are often much disturbed by the compensating action
which follows an excess or deficit of rainfall. This is termed the excess-
deficit balance, and is itself a short-period cycle, based apparently upon
the fundamental physical correlation of action ajid reaction. Since it is
usually 2 to 3 years in length, it is not improbable that it may be the 2.5-
year cycle heightened by spatial variations in rainfall (fig. 15).
A
h
a.aI
I\J
^ u
^
^
4\^
V
v/WV'
[ \j\r
^\f[
v^
£yen »
umhers
wmbers
-
—
-
7S0 *C Ja 20 /a 700 SO go 70
)tar-a.c.
Fio. 15. — 2-year cycle in a Sequoia. After Douglass.
60
An analysis of the production of grain-sorghums at Amarillo from 1907 to
1918 has been made to illustrate the possible relation to the various cycles.
This has been drawn from the results of Ball and Rothgeb (1918), but is
limited to the production in bushels of grain, as representing the more com-
plete response of the plant to growing conditions. The seasonal rainfall has
been reckoned for the five months beginning with April and ending with
August.
264
AGRICULTURAL INDICATORS.
Rainfall and the production of grain
\-8orghum.
Annual
Seasonal
Milo.
Dwaif
White
Durra
Black-
Dawn
Red
Brown
Year.
rainfall.
rainfall.
milo.
duira.
kagr.
hull.
kafir.
kagr.
kao-
liang.
1907
1908
18.09
19.05
11.90
15.33
36
41
33-
33
34
29
33
31
1909
19.59
10.80
6
11
12
4
6
14
5
11
1910
11.15
10.00
18
19
10
12
3
9
5
10
1911
22.73
15.66
32
38
29
30
19
40
19
22
1912
14.33
8.76
19
23
17
7
4
10
4
12
1913
18.97
7.90
0
0
0
0
0
0
0
0
1914
19.18
10.17
11
27
22
15
10
15
15
17
1915
27.65
17.78
61
68
37
28
60
53
51
35
1916
16.43
9.54
7
7
5
4
0
4
?
4
1917»
17.06
12.88
13
22
11
6
5
5
2
8
1918
18.11
8.73
7
10
0
3
t)
1
0
2
* Unpublished data from the OflSce of Cereal Investigations, Bureau of Plant Industry, U. S.
Department of Agriculture.
Ball and Rothgeb (1918: 22) have given a very instructive account of the
distribution and timeliness of the rainfall of the various years in relation to
yield. Their discussion makes clear the number of apparently chance factors
which enter into the production of a crop. In spite of this, however, both the
11-year and the 2 to 3 year cycle can be recognized in the production as well
as in the rainfall. As seems to be the rule, these show more clearly in the
IflOQ
1905
1910
1915
Fio. 16. — Graph of total and seasonal rainfall at Williaton, North Dakota.
AGRICULTURAL PRACTICE AND CLIMATIC CYCLES.
265
summer than in the winter rainfall, and hence more clearly than in the annual
rainfall. There is a tendency to maximum rainfall about the sun-spot
minimum of 1913, and to minimum rainfall about the sun-spot maximum of
1918. However, it is much less decisive at Amarillo than at other places in
the Great Plains, indicating the action of a spatial balance in the rainfall of a
particular year. The evidence of the excess-deficit cycle of 2 to 3 years is
much clearer. From 1908 to 1911 and 1911 to 1914, the cycle was 3 years,
while from 1915 to 1916 and 1917 to 1918, it was 2 years. This is reflected in
the production, the maximum yields occurring in 1908, 1911, 1915, and 1917.
The yield does not correspond with either the annual or seasonal rainfall alone,
though it follows the latter more closely. This is due to the fact that while
the grains are like the grasses in being chiefly dependent upon the summer
rainfall, they also show the effects of a water-content surplus or deficit aris-
ing from the year before. There can be Uttle question that the water-content
of the soil shows cycles corresponding closely to those of rainfall, and that
scientific agriculture must come to take these into account in connection with
forecasting the kind of crop and the yield for any particular year. Thus,
while the investigation of rainfall and crop cycles presents many complexities,
it appears that these are all worked out on the basic pattern of the 22-year,
1 1-year, and 2 to 3 year cycles. If this proves to be the case as the result of
intensive studies throughout the West, it is probable that annual crop pro-
24
Mill
1000 1905 1910 18fl5
Fio. 17. — Graph of total and seasonal rainfall at Cheyenne, Wyoming.
266
AGRICULTURAL INDICATORS.
duction may ultimately be forecasted with something of the accuracy of daily
weather forecasts at present.
The excess-deficit balance. — The fact has already been emphasized that an
excess of rainfall in one year is almost certain to be balanced by a deficit in
the next year, while a great excess is often followed by two or rarely three
years of deficit. As a rule, an excess is an amount above the normal rainfall
and a deficit is an amount below it. Moreover, an excess in one region is often
counterbalanced by a deficit in another, or an increase or decrease in one
region is not met by a corresponding change in an adjacent one. When the
balance operates from one year to another, it produces a cycle of 2 to 3 years.
This cycle exhibits marked variations in rainfall, so much so that it may
obscure the normal effect of the 11-year cycle at its maximum or minimum,
though apparently not that of the 22-year cycle. In order to illustrate the
operation of the excess-deficit cycle, use has been made of columnar graphs of
the rainfall at widely separated points in the grassland climax. The points
selected are Williston (North Dakota), Cheyenne (Wyoming), Akron (Colo-
rado), and Amarillo (Texas). In the case of the first three places, the graphs
have been adapted from those prepared respectively by Babcock (1915:5,)
Jones (1916:4), and McMurdo (1916:4). The graph of Williston rainfall
1900
lf)05
1910
1915
Fio. 18. — Graph of total and seasonal rainfall at Akron, Colorado.
AGRICULTURAL PRACTICE AND CLIMATIC CYCLES.
267
(fig. 16) shows five 2-year and two 3-year cycles since 1900, while the record
since 1885 shows an almost complete series of 2-year cycles. The Cheyenne
graph shows a preponderance of 3-year cycles, and with the exception of a
single year (1908), there is a perfect succession of 2-year and 3-year cycles.
At Akron the first two cycles are 2-year and the last three are 3-year. At
Amarillo the cycles are much less distinct, but the 3-year cycle is fairly well
marked, especially in the seasonal rainfall. A comparison of the respective
graphs will disclose the regional rainfall balance during a particular year.
The year 1905 was excessively wet at Amarillo, Akron, and Cheyenne, but
was very dry at WilUston, 1906 being the wet year. Likewise, a slightly less
wet year (1915) was excessively wet at Amarillo and Akron, only a little above
the normal at Cheyenne, and slightly below normal at Williston, the excess
faUing the next year again. The year 1911 was the driest of the record at
ao
„ ^'f i|
llllllll
mm
1900
1905
1910
1915
Fio. 19. — Graph of total and seasonal rainfall at Amarillo, Texas.
268 AGRICULTURAL INDICATORS.
Akron and Cheyenne, while it was nearly normal at Williston and above
normal at Amarillo, 1910 being the driest year at both these places. The year
1914 was dry at Akron and Cheyenne, nearly normal at Amarillo, and above
normal at Williston. The regional variations in seasonal rainfall, both abso-
lute and relative, are even more marked. In 1915, the year of greatest sea-
sonal rainfall at Amarillo and Akron, they received 18 inches from April to
August inclusive, Cheyenne 10 inches, and Williston 6 inches. The sea-
sonal rainfall was respectively 66, 55, and 50 per cent of the annual for the
year. The year of greatest relative seasonal rainfall was that of 1910 at
Amarillo, when 90 per cent of the annual rainfall came during the growing
season. The corresponding values for Akron, Cheyenne, and Williston were
73^ 50, and 70 per cent respectively (figs. 16-19).
Anticipation of cycles. — Crop production makes much greater demands as
to the forecasting of rainfall than either grazing or forestry. These deal
primarily with perennials, and in the case of trees in particular the depen-
dence upon the summer rainfall is much less marked. As a consequence, a
knowledge of the probable occurrence of the wet and dry phases of the 22-
year and 1 1-year cycles or of the approximate total rainfall for any year is of
much value. With annual crops the case is very different. While there is a
general relation between annual and seasonal rainfall, the latter may vary
between 50 and 90 per cent of the annual, as at Amarillo. Moreover, the
distribution and timeliness of the seasonal rainfall are even more critical (Ball
and Rothgeb, 1918:24, 6). It must be frankly admitted that at present
there are almost no clues to either distribution or timeliness, but this is due
largely to the fact that their correlations have received almost no intensive
study. It seems not improbable that the same basic processes of action and
reaction and of compensating balance apply during the year and season as
during cycles, and that they must be considered with reference to spatial
variations as well. It is probable that the most important clue to the annual
and seasonal rainfall of a particular year lies in the excess-deficit cycle of 2 to
3 years, which Arctowski has noted in crops and Douglass in trees. The
assumption that a cycle of similar character may apply to the months receives
striking confirmation from the studies of Douglas (1919) on the relation of
weather to business. The general correlations of climate with production
and prices and the existence of economic cycles have been dealt with by Moore
(1914, 1917). All of these represent independent investigations and can hardly
fail to strengthen the view that both long-period and short-period cycles occur
in crop production (figs. 20 and 21).
In the endeavor to definitize climatic and production cycles and to discover
a working basis for their prediction, investigations are under way to determine
the climates and subclimates of the West on a plant basis. It is hoped to
ascertain the response to the 22-year, 11-year, and 2 to 3 year cycles in t^rms
of tree growth, grass yield, and crop production for different regions, suggested
by the type or amount of rainfall. It is expected that the general correlations
between rainfall and production will serve to mark the climates proper, but
that the latter will show a series of subdivisions leading to restricted locaUties
as the units upon which the practical anticipation of rainfall must be based.
CLEMENTS
PLATE 63
»(.r
A. Ruderal crop of Russian thistle, Sabsola, in a field of fcterita, Tulia, Texas.
B. Ruderal crop of borseweed, Erigeron canadensis, in a fallow field, Goodwell, Oklahonia.
AGRICULTURAL PRACTICE AND CLIMATIC CYCLES.
269
In any event, it seems clear that the attack upon this vital problem from
both the intensive and extensive approach will disclose new facts and leads
and will bring nearer the actual utilization of cycle predictions in crop pro-
ductions.
1870 1£78 1886 1894 1902 1910
Fig. 20. — Cycles of rainfall in the Ohio valley, , and in Illinois,.
aai8
After Moore.
T — I — I — I — I — I — I — r
i870 1876 1882 1888 18M 1900 1906 3912 1918
Fig. 21. — Cydes in the yield of corn and in the rainfall of its critical period
of growth. After Moore.
VI. GRAZING INDICATORS.
Kinds of grazing. — Grazing practice depends priraarily upon the kind of
stock, the nature of the vegetation, the season, and the degree of control of
the range. It varies more or less with all of these, but often to a much smaller
degree than the best management would require. The four kinds of stock
usually handled, namely, cattle, horses, sheep, and goats, not only have more or
less definite preferences as to the type of grazing, but their effect upon the latter
is also markedly different. In addition, they differ much in herding manage-
ment and its relation to carrying capacity. With respect to grazing type,
cattle and horses prefer grasses, sheep prefer herbs and weeds, and goats
prefer shrubs or "browse." While this distinction is far from absolute, it
marks a fundamental preference upon which the best practice must be built.
It is the basis of mixed grazing, in which cattle and sheep, or cattle, sheep, and
goats, are grazed upon a range at the same time. Mixed grazing is especially
indicated in the ecotone between the chaparral, desert scrub or sagebrush
and grassland, but it is desirable in practically all associations except such
pure grass types as the short-grass plains. The maintenance of the proper
carrying capacity in any type depends upon a knowledge of the difference in
habits of stock with respect to the closeness and thoroughness with which each
grazes, the amount of trampUng, trailing, etc.
The handhng of both herd and range depends in the first degree upon the
season during which grazing is possible or desirable. The time and duration
of the grazing season are determined partly by the behavior of the natural
cover and partly by cUmatic conditions, chiefly the cold and snowfall of win-
ter. In the North, where the winters are long and severe, summer con-
stitutes the sole grazing season and both feeding and protection are either
highly desirable or absolutely necessary for approximately half of the year.
In the central portion of the West the summer grazing lies largely in the
mountains and the winter grazing in the plains and valleys, permitting the
regular movement of stock from one to the other. This is determined chiefly
by the period during which the high summer ranges are accessible, but in some
cases by the furnishing of water through winter snows, as in the Red Desert
of Wyoming. In the Southwest the mild climate of winter permits handling
stock on the range throughout the year, and the only limitations to this method
are set by lack of water or feed. However, while year-long grazing has been
the rule for many years throughout this region, the frequent recurrence of
drought has shown the necessity of complete utilization of the high summer
ranges, and the desirability of more or less winter feeding. This is the one
region in which there is a distinct winter forage composed of annual herbs,
with the interesting consequence that summer and winter grazing are normally
possible on the same area.
The nature and degree of control of the range have a definite bearing upon
grazing. This is largely concerned with the carrying capacity, but in cases of
overgrazing it is the latter which determines the sufl^iciency of summer or
winter range and the kind of grazing possible upon it. It is a well-known fact
that the open range of the West has greatly deteriorated under existing con-
ditions, in which the only title the stockman can acquire inheres in keeping
270
GRAZING TYPES. 271
his particular range so constantly overgrazed that no one else will be tempted
to use it. It is evident that a proper carrying capacity can be redeveloped
and maintained on such areas only through the assurance of control. This
has been secured in Texas by the private ownership of grazing lands, while
in the case of the sunmier ranges of the national forests it has been provided
by a system of grazing allotments. For the inmiense acreage still in the pub-
lic domain, adequate control can best be obtained by a proper leasing system,
as is shown in a later section. After the individual stockman has secured the
exclusive use of his range under proper restrictions as to overgrazing, it is of
secondary importance whether control is maintained by herding, drift fences,
or complete inclosure. As will be seen, however, the latter method alone
permits the maximum conservation and utiUzation of the natural forage crop.
GRAZING TYPES.
Kinds of grazing indicators. — The simplest and most obvious indication of
a plant community is that which denotes the possibiUty of grazing. To-day
this is so axiomatic for grassland and scrub associations as to be entirely taken
for granted. This has not always been the case, however (Wilcox, 1911 : 35),
and even at present there are forest and serai communities in which grazing
indicators furnish a decisive test of the desirabihty of utilizing them. In the
first instance, grazing types may be grouped as grass, weed, browse, and
forest, and used to indicate the kind of grazing. The general principle in
effect here is that a uniform community of grass, weed, or browse indicates
cattle, sheep, or goats, respectively, while a prairie or a grass-scrub mictium
or savannah denotes mixed grazing of two or three kinds of animals. The
most striking and useful indicators are those which have to do with carrying
capacity and overgrazing. These make it not only possible to measure the
amount of carrying capacity and the degree of overgrazing, but they also
reveal any failure to secure proper utilization. In addition, they serve to
indicate the annual variations in forage production and to permit the cor-
relation of these with the wet and dry phases of the cUmatic cycle. They
likewise disclose the effect of local disturbances, especially those due to rodents,
and they furnish a means of tracing the effects of eradication. As a conse-
quence, they afford a complete basis for maintaining a proper balance between
the utilization and conservation of the range and are of the greatest service in
developing and applying an adequate system of range or ranch management.
The grouping of indicator communities as grass, weed, browse, and forest
(Jardine, 1911) is one of both general and practical value. It permits sub-
division into as many minor communities as desirable (Shantz and Aldous,
1917), and the chief consideration is to correlate these as naturally and effec-
tively as possible. For this, no system approaches in value that of the de-
velopmental relationship as exhibited in the various cUmaxes and their suc-
cessional stages. The climaxes discussed in Chapter IV illustrate the three
main types, grass, scrub, and forest, while the serai communities and sub-
dominants frequently exemplify the weed type as well. With reference to the
grazing value, however, forest and woodland are to be classified on the basis
of their undergrowth as grass, weed, or browse. It makes Uttle difference
practically whether grazing types are first grouped on the basis of their nature,
as grass, browse, etc., or on that of development, as climax and serai. The
272 GRAZING INDICATORS.
best system will necessarily employ both, but the vast extent of the climaxes
and their obvious dependence upon the vegetation-form suggests them as the
preferred basis. This has the further advantage of making the practical and
the ecological system the same and of avoiding the confusion which exists in
forestry, where the practical types and ecological units are often wholly
different. The developmental method is also desirable in that it furnishes a
uniform method of dealing with fin6r and finer divisions upon the basis of
climate, soil, and region, as well as upon that of ecology and floristic. As all
of these enter into practice sooner or later, it seems clear that the best treat-
ment of grazing indicators is that which relates them to the proper formation
and association. In consequence, the following discussion deals first with
climax communities as indicators as much the most important, and then with
the more localized serai communities. In addition, some account is taken of
artificial communities due to planting or other modification, since it is assumed
that these will play an increasingly larger part in the grazing industry of the
future (plate 64).
Significance of climax types. — The value of the climax community as an
indicator rests primarily upon the characteristic life-form. This is clearly
seen in the three types, grass, weeds, and browse, but in the case of forest
it depends upon the life-forms of the layers and serai stages. Climax forma-
tions are far more extensive than the developmental stages which occur here
and there in them. Moreover, such stages are constantly moving toward
the climax condition, slowly in the case of priseres and rapidly in the case
of subseres. The climax communities are extensive and permanent, the serai
ones local and temporary as a rule. As a consequence, the grazing practice
of large regions must be based upon the indications of the climax formation or
its subdivisions, while in a particular locality the importance of certain serai
communities may demand some modification in practice. Apart from the
vegetation-form as shown in grass, herb, shrub, or tree, the habitat-form and
growth-form of the dominants must also be taken into account. Communi-
ties of sod-forming grasses indicate different values and treatment than those
of bunch-grasses, while there is a striking difference between the associations
of taU-grasses and of short-grasses. Climax communities of dominant herbs
do not exist, but prairie and alpine meadow often contain so many mixed
societies that the grazing value depends largely upon them. The indications
of shrubs vary with the deciduous or evergreen nature of the leaf, succulence,
form, ability to make root-sprouts, fruit, etc. The dominant trees of climax
forest enter the question of grazing very little if at all, and the grazing type of
each forest is determined by the greater abundance of grass, weeds, or browse.
Finally, the grazing value of a community, and hence its indicator meaning,
depend greatly upon whether it is pure or mixed. This is partly a matter of
the relative value of the dominants as forage, and partly of the degree to
which each is grazed and of its ability to grow and reproduce under the existing
conditions. Mixed communities greatly predominate, and their utilization
is determined to a large degree by the kind of mixture. They may consist
almost wholly of dominants of the same vegetation-form, such as the short-
grasses of the Bulbilis-Bouteloua plains, or they may contain shrubs and
grasses, as in savannah. In addition, grassland which exhibits a marked
development of societies is essentially a mixed community with respect to
grazing, since it permits selection by cattle or sheep, or mixed grazing by both.
CLEMENTS
A. Grass tyjHJ, Andrapogon-BuUnlis-HouUloua, Smoky Hill Hiver, Ha\-s, Kansas.
B. Weed type, Erigeron, Geranium, etc., in aspen forest, Pike's Peak, Colorado.
GRAZING TYPES. 273
Formations as indicators. — As has just been seen, the grazing value of a
climax formation is determined primarily by the vegetation-form, though
other factors enter locally to modify it more or less. The grassland cUmax
is by far the most important of all, and there is Uttle doubt that its develop-
ment and extension have controlled the evolution of grazing animals in the
past. The fact that the word graze is formed directly from grass proves that
grassland has long been the primary grazing type, and that all others are
secondary, resulting from the natural extension of grazing into scrub and
forest. The alpine meadow ranks next to prairie and plain in primary
grazing value, though the short season finds expression in the low growth-
form as well as in the short period for grazing. The savannah marks the
transition from primary grazing land, i. e., grassland, to scrub. In spite of
the unique importance of the latter for mixed grazing, its actual grazing value
is secondary, as is indicated by the appUcation of the word browse to it. Of
the scrub climaxes, the chaparral usually stands first in importance, the sage-
brush next, and the desert scrub last, though this varies greatly with the
grouping of the various dominants. Of the forest formations, montane
forest has the greater value, due largely to the open grassy nature of the
yellow pine consociation. The woodland resembles the latter more or less
and often ranks next to it in amount of grazing. The subalpine forest varies
greatly in importance. The grazing value of its meadows, natural parks, and
aspen areas is high, but the cHmax forest is usually too dense and closed to
permit the growth of a uniform ground cover. This is even truer of the
luxuriant Coast forest, in spite of the fact that the latter often exhibits a
dense tangle of shrubbery.
Associations as indicators. — The indicator significance of an association is
essentially that of the formation to which it belongs. As a subdivision, it
represents a closer response to regional conditions, and the various associations
of a climax permit the recognition of more or less different grazing values.
This is characteristically true of the grassland and alpine meadow formations.
It holds to a somewhat smaller degree for the scrub and is least evident for the
forest cUmaxes, in which the number and extent of serai conmiunities are
more significant for grazing than the cUmax areas themselves.
In determining the relative grazing value of the associations of the grass-
land chmax, this is found to depend upon density, height, and mixture. Upon
this basis, the subclimax prairies are perhaps the most valuable, though the
true prairies are nearly as valuable, and in some cases even more so. The
mixed prairies come next, and are followed by the short-grass plains. The
bunch-grass prairies at their best may equal the latter, but generally the stand
is too open. While the desert plains are of the same character as the short-
grass association, the bunch habit is more pronounced and the total production
usually less. Quite apart from the question of yield, however, is that of time
of development and ability to cure on the ground. From this standpoint,
the mixed prairie of tall Stipa or Agropyrum, and short BuWilis, Bouteloua, or
Carex, or the transition area of Andropogon and short-grasses has a distinct
advantage. The tall-grasses either develop earUer or grow with such rapid-
ity as to furnish the bulk of spring and sununer feed, while the short-grasses
become cured in late summer to furnish feed for fall and winter. Finally,
it must be recognized that the tall-grass associations are agricultural indicators
274 GRAZING INDICATORS.
as well, and that economic considerations give them greater significance in
this r6le. Our knowledge of the Pacific alpine meadow is too small to enable
us to draw an accurate comparison with the Petran association. They are so
nearly alike in the growth-form and genera of the dominants and in the
number and luxuriance of the societies that they exhibit no clear difference
in yield per unit area. In spite of this, the Petran association is actually
very much more important, for it covers an area many times greater, is more
coherent, and for the most part covered by snow to a less degree and for a
shorter period.
The grazing value of the chaparral associations depends largely upon the
presence of oak, which is usually the most important of the dominants for
browse. For this reason, the Petran chaparral is usually more important
than the Coastal, though its value decreases greatly with the dropping out
of the oak to the northward, just as it increases to the southeast with a larger
number of species of Quercus. In the sagebrush formation, the Basin associ-
ation is all-important, the Coastal community being of relatively small extent
and containing but one or two dominants of value. The differences between
the associations of the desert scrub are not so clear-cut, but the advantage
lies in general with the western community, owing largely to the much greater
number of succulents. The three associations of the woodland exhibit a
thin ground cover of grass and shrubs, resulting from the combined effect of
dryness and shade. They produce savannah where they are in contact with
grassland or scrub, and in such cases possess more or less of the grazing value
of the latter. The presence of oak gives woodland some value as browse,
and in this respect the oak-cedar community stands first and the pine-oak
next. The montane associations differ strikingly in ground cover, the Petran
having the herbaceous layers best developed, and the Sierran, the shrub
layer or so-called subcUmax chaparral. The former has usually the greater
importance for grazing, since many of the shrubs of the chaparral are un-
palatable. The comparative value of the associations of the subalpine forest
is less certain, but on the whole the Petran has the advantage, especially
when the serai grasslands are taken into account.
Consociations as indicators. — The value of the consociation as an indica-
tor is determined primarily by the life-form. Grassland derives its unique
importance for grazing from the grass dominants, while the value of scrub
dominants is much lower and more variable, and that of forest consociations
almost wholly dependent upon the undergrowth. In the grassland the chief
value lies in the consociation, with the scrub in the consociation and its socie-
ties, and in the forest it lies in the shrub and herb societies alone. Moreover,
grass consociations are true grazing types, scrub are primarily browse types,
and forest and woodland are grazing or browse, depending upon the relative
abundance of herbs and shrubs. Consociations may be pure or mixed, and
the indicator meaning naturally varies accordingly. While mixed communi-
ties are the rule, pure consociations are sufficiently frequent to permit the
determination of carrying capacity, response to overgrazing, and other fea-
tures which make up the total grazing value. In the case of mixed communi-
ties the analysis is based upon the normal response of each pure consociation,
modified by their varying relations to the grazing animals and their com-
petitive reactions upon each other. In dealing with the actual grazing types
GRAZING TYPES. 275
of a particular region, pure consociations play an even smaller part on account
of their relatively small extent. While they are very helpful in ecological
analysis, they are of little importance in practical management.
Local grazing types. — While the main grazing types, such as the formation
and association, indicate the comparative value of great regions, as well as
the groupings possible in any one> it is the local groupings which determine
the carrying capacity of a particular ranch and the proper system of manage-
ment to be employed upon it. For this reason, they may well be termed
practical grazing types. In areas relatively uniform, a single grazing type
composed of the two or three major dominants of the association may cover
a wide extent. This is the case with Stipa and Bouteloua in North Dakota
and Montana, BuWilis, Agropyrum, and Bouteloua in the region of the Black
Hills, and Bulbilis and Bouteloua in Oklahoma and Texas. As a rule, how-
ever, changes in topography or soil or in the number and grouping of the
subdominants bring about important changes every few miles, and very
frequently adjoining sections will be found to have a different grouping or an
effective difference in relative abundance. Hence, it is clear that the local
community must determine the careful classification of the land section by
section, especially with reference to carrying capacity, as well as the method
of management. For example, while all the climax groupings in the mixed
prairie resemble each other in structure and treatment much more than they
do groupings of the true prairie or short-grass plains, they show decisive
differences among themselves. The carrying capacity and relation to over-
grazing of the Stipa-Bouteloua community differ from that of Agropyrum-
BuUnlis, and of both of these from that of Bulbilis-Agropyrum-Bouteloua.
The marked development of societies reduces the abundance of the dominant
grasses, and at the same time affects the carrying capacity. The relation
between the two effects depends upon the degree to which the subdominants
are grazed, but as a rule they are less palatable than the grasses. Over
regions of rolling topography, such as prairies and sandhills, the climax
groupings are regularly interrupted by valley and ridge conmiunities which
are successional in nature. These are of relatively small extent and may fre-
quently occur with the climax grouping on a ranch of a section or less in
extent. In the case of the more level plains, the serai communities are con-
fined to stream valleys and breaks and cover much larger areas. They often
serve to mark the distinction between valley and upland ranches. They are
not confined to one association, but such a grouping as that of the Andropogons
may be found repeatedly from the true and mixed prairies through the short-
grass and desert plains.
The number of such groupings is legion, and the most important occur
again and again in the region where they are characteristic. They have been
found in sequence over many thousands of miles in the West, and the most
frequent and important have been noted in connection with the frequence
and grouping of dominants under each association in Chapter IV. They are
of the first importance in determining local variations in grazing value and
are regarded as the basic indicators to be used in the range survey discussed
later. As already indicated, the major indication of the grouping must al-
ways be interpreted in connection with the minor indication of the societies
present. In its application to grazing at least, the grouping is so important
276 GRAZING INDICATORS.
that the need of a more distinctive term is clearly felt. In so far as grazing is
concerned, the term grazing type might well serve the purpose, though forma-
tions and associations, as well as serai communities, are also grazing types.
The grouping of consociations within the association is typical of all climaxes,
however, and seems to warrant a special term for those who need a complete
and detailed analysis of vegetation. After an extended consideration of the
possibilities, it has seemed desirable to definitize the term fades for serai
groupings and to make a new word, faciation, for climax groupings. These
are derived from the same root, fac, shine, and possess the same basic mean-
ing, namely, appearance, aspect, or form. The two terms conform to the
mutual relation seen in associes and association, consocies and consociation.
Savannah as an indicator. — Throughout the present treatment, the word
savannah is used for the community which characterizes the ecotone between
two chmax formations. In its most typical expression, it consists of grasses
and low trees or tall shrubs, and occurs in the hot, dry regions of the South-
west. Other communities are so similar that it is impossible to exclude them,
and hence open pine forest and woodland with a grass cover are also called
savannah. Closely related to these are the so-called natural parks of the
Rocky Mountains in which serai grassland is surrounded and more or less
invaded by trees. Such parks occur in both the montane and subalpine zones.
When the ecotone Ues between forest or woodland and scrub, the general
ecological relations are similar to those of savannah, but the grassland is
replaced by sagebrush, chaparral, or desert scrub. The trees stand more or
less scattered in the scrub, and the indications of the community are primarily
those of the latter. The failure to recognize this similarity to savannah has
led to confusion with reference to the distinctness of the scrub climaxes in
rough regions where they are interspersed with trees. Savannah has been
so generally Unked with the presence of grasses that it seems unwise perhaps
to broaden its meaning to include areas of scrub with taller trees, and conse-
quently the word park has been used for the latter. Thus, a sagebrush
savannah is one in which sagebrush is scattered through grassland, while
a sagebrush park is a community in which sagebrush is surrounded and
more or less invaded by trees or tall shrubs.
In their typical form, both savannah and park are controlled by the grasses
or scrub, and the trees are more or less incidental. The transition to forest
or woodland is usually gradual, and it is impossible to draw a sharp Une be-
tween the two. However, it is a simple matter to distinguish the general
areas from each other. As long as the trees or shrubs are far enough apart
so that their shadows do not touch, the grassland or scrub remains in control.
When they are sufficiently close to have their shadows overlapping during
most of the day, the grass or scrub dies out for lack of sun, or persists only in
small groups of much modified individuals. Tree and scrub savannah often
cover extensive areas to which they give the appearance of open woodland,
but the true nature of the community is indicated by the continuous carpet of
grass, which serves as the indicator. Sagebrush and chaparral parks are
usually more local, and they quickly pass into woodland on the one hand and
scrub on the other. They recur constantly, owing to the relatively small
difference in requirements between shrubs and small trees. Savannah proper
is probably due to the effect of climatic cycles and is thought to serve as an
CLEMENTS
PLATE 06 ^^
97^ -
A. Savannah of desert scrub, Flourensia-Larrea-Prosopis, and desert plains grasses, BotUeloua
gracilis, eriopoda, and raanwrn, Van Horn. Texas.
B. Bum park in subalpine forest, Uncompahgre PUiteau, Colorado.
GRAZING TYPES. 277
indicator of the wet phase of the cycle. The control of the grasses is so com-
plete that the additional water-content necessary for the germination and
estabUshment of the trees or shrubs is present only during the maximum of the
wet phase, often only a single year. Once estabUshed, and with their roots
at greater depths than those of the grasses, the trees or shrubs persist indefi-
nitely. During succeeding wet phases they tend to increase in number, while
in critical drought periods the number may be reduced, as is regularly the
case where fires are frequent. Counts of the annual rings of a number of
shrubs in different savannah areas confirm the view that ecesis is normally
confined to wet phases of the cUmatic cycle (plate 65).
The indicator significance of savannah or park naturally depends upon the
kind and the region, as well as upon the dominants. The best examples of
tree savannah are to be found along the line of contact of forest or woodland
with grassland. Oak savannah is the most common, occurring typically in
central Texas, in Arizona, New Mexico, and Mexico, and in CaUfornia and
Lower CaUfornia. Savannah in which yellow pine is the tree is frequent
along the lower edge of the montane forest, where it extends out upon plateaus
or plains. It is well-developed in northern Arizona and New Mexico, but is
most extensive on the low ranges and high plains east of the central Rockies
and around the Black Hills. Both pifion and cedar form savannah, but the
latter is much more frequent and extensive. Typical scrub savannah is
largely confined to the Southwest, ranging from Texas through southern New
Mexico and Arizona, and northern Mexico. Its most characteristic shrub is
mesquite, Prosopis juliflora, but Yucca, Acacia, Ephedra, and other domi-
nants of the desert scrub occur frequently. Owing to its habit of growing in
clumps or groups, chaparral tends to form grassy parks rather than typical
savannah, especially along the edge of the Petran association. Sagebrush
extends into several of the grassland associations to form what is essentially
sagebrush savannah, though its low stature tends to obscure the exact re-
lation. This is especially true where it meets the tall-grasses, as in Wyoming
and Oregon, but the savannah nature is obvious where tall sagebrush is
scattered through short-grass, as in southeastern Utah.
Parks differ from savannah chiefly in that the two conmiunities concerned
mix by alternating groups or areas rather than by scattered individuals.
Excellent examples of grass parks occur in the subalpine forests of Colorado,
where spruce and balsam inclose extensive meadows of Festuca, dotted with
groups of young conifers or aspens. Somewhat similar parks occur at timber-
Une, where the forest breaks into groups which extend well up into the alpine
meadows. Sagebrush parks occur most commonly in the lower subclimax
portion of the woodland zone, while sagebrush areas dotted with groups of
lodgepole pine or aspen are frequent on the western slope of the Rocky
Mountains in Colorado and Wyoming. Chaparral parks are best developed
in CaUfornia, especiaUy in the case of subclimax chaparral in the pine forest
and where the cUmax type meets the pine-oak woodland. In the Rocky
Mountain region they occur chiefly as scrub openings in the pifion-cedar or
oak-cedar woodland.
Savannah and park are aUke as indicators in that they denote a transition
from one community to another. They differ for the most part in that savan-
nah is an indicator of cUmate, and park usually of local or edaphic conditions.
278 GRAZING INDICATORS.
Savannah has to do with the relations of two contiguous climaxes, and park
with that of a subcUmax to its climax. The former is a permanent condition,
varying more or less under the influence of the wet and dry phases of climatic
cycles, while the latter is usually a temporary community, occupying its
proper place in prisere or subsere, and passing ultimately into the climax.
Hence, the indicator values of different types of parks are dealt with in the
next section, while those of savannah are ^considered here. True savannah
has value as an indicator of climate as well as of practice. It not only
indicates a transition between the cUmates of the respective cUmaxes, but
also serves to record the course of the climatic cycle. The amount to which
it increases its area and density under the same conditions is a measure of the
effect of the wet phase, and the dying-out of individuals, of the dry phase.
Such measurements are possible only under control, however, owing to the
almost universal disturbance of fire or overgrazing.
Kinds of savannah. — With reference to practice, savannah indicates the
general possibility of agriculture. For the most part, this is of the dry-
farming type, though in central Texas it indicates humid or subhumid farm-
ing, and in California farming by means of drought-evasion. With respect
to grazing, the indications of savannah depend primarily upon the grass
dominants. In fact, the indicator value of savannah is essentially that of
the grassland community, unless the trees or shrubs are sufficiently close to
reduce materially the amount of grass. When the shrubs themselves have
distinct value as browse, the carrying capacity becomes greater than that of
the grassland alone, and mixed grazing is also favored. The yellow pine
savannah of the Black Hills and eastern Rocky Mountain region occurs in
the mixed prairie, while in the Southwest it hes in the short-grass association.
In both cases, the grazing value of the grassland is practically unchanged,
except for some reduction in cover just beneath the trees. Pine savannah
also occurs along the upper edge of the bunch-grass prairie, but it is rarely
extensive here. Cedar savannah is found chiefly in the short-grass com-
munity, but is frequent also in the desert plains and mixed prairies. Where
the cedar is low, it materially reduces the total carrying capacity, though this
is often offset by the presence of browse shrubs. Mesquite savannah lies
typically in the desert plains, though the mesquite itself extends northward
into the short-grass association of the Staked Plains. The shrubs have little
effect upon the amount of grass, and they change the indications of the com-
munity only to the extent that they are valuable for browse. Toward the
lower edge of the savannah the shrubs become denser as they pass into the
desert scrub, and the grassland rapidly decreases to the point of disappearance.
Oak savannah may be of the tree or shrub type. The latter is most typical
on the plateaus and mountain ranges of southwestern Texas, New Mexico,
Arizona, and Mexico, where it is formed chiefly by live-oaks. It lies in the
desert plains grassland, or in the Andropogon zone just above. The grazing
value due to the grasses is greatly increased by the abundant browse, and
such savannah may well be regarded as one of the best of all grazing types,
owing to the assurance it gives against drought in connection with mixed
grazing. Tree savannah consisting of oaks usually has little or no browse
value, and its indication is essentially that of the grass community in which
it is found, with some reduction caused by shading. In CaUfornia, the
CLEMENTS
PLATE 68 ,
A. Glass park of Klyniua and Agropijrum arisint; from sagebrusli, Boise, Idaho.
B. Sagebnish dying out as a result of competition with Agropynttn, Ciaig, Colorado.
GRAZING TYPES. 279
original Stipa bunch-grass prairie has been almost wholly replaced by the
wild-oats, Avena fatua, and the latter determines a relatively lower value for
the community. The sagebrush savannah so characteristic of northeastern
Wyoming lies in the edge of the mixed prairie, and the sagebrush is chiefly
associated with Stipa, though Agropyrum and Bouteloua are also present to a
large degree. The relative abundance of grass and sagebrush varies widely,
and the indicator value of the mixture in accordance. Since the sagebrush
is eaten to a much less degree during the summer, the carrying capacity is
somewhat reduced, though this is partly compensated by its availability
during the winter.
Savannah in relation to fire and grazing. — The general view in the Southwest
is that mesquite and oak savannah are limited or destroyed by fire and that
they have spread rapidly in recent years, since the annual burning has ceased
(Cook, 1908). In the absence of definite measurements, many of the state-
ments can be accepted only in part, though the general relation to fire seems
evident enough. Tree savannah appears to be affected Uttle by burning,
except that this must have been a powerful factor in spreading the annual
Avena in California at the expense of the perennial Stipa. The effect of fire
upon scrub savannah depends upon a number of factors, chief among which
are density and height of both shrubs and grasses, the ability of the shrubs
to form root-sprouts, and the frequency of fires. It seems certain that an-
nual fires in scrub savannah that is densely covered with tall-grasses would
destroy the shrubs completely in a few years, no matter how great their abiUty
to form root-sprouts. Less frequent burning of open savannah, in short-
grass especially, would damage the shrubs much less and might well increase
their control by promoting root-sprouting. Moreover, in the more xerophy-
tic grasslands, frequent burning during dry seasons injures the grass and
would tend to favor the shrubs in consequence (plate 66).
The general effect of grazing is to increase the shrubs at the expense of the
grass. As has been seen, savannah owes its character to a dry cUmate in
which the ecesis of shrubs is regarded as usually possible only during the wet
phase of the cycle. This means that shrubs and grasses live constantly under
keen competition for water, and that anything which reduces the amount of
grass will be to the advantage of the shrubs. Since grasses and herbs are
usually eaten to a much larger degree, intensive grazing, and especially over-
grazing, will reduce their hold upon the soil and correspondingly improve
conditions for the spread of shrubs. The seeds of the mesquite and other
shrubs are widely scattered as a consequence of being eaten or through unin-
tentional carriage, and the seedHngs are more readily estabUshed in areas
where the hold of the grasses has been weakened. The local spread of the
scrub clumps is chiefly by means of root-sprouts and is promoted by light
browsing, but restricted by heavy browsing. Thus, while savannah is pri-
marily an indicator of cUmate, its secondary indication is one of grazing and
absence of fires, upon which its practical utiUzation must be based. As sug-
gested in a later section, this can be done readily only after quadrat measures
have made clear the exact behavior of savannah under different methods of
burning and grazing.
Significance of serai types. — While serai communities are temporary in
comparison with climax ones, many of them persist for tens or even hundreds
280 GRAZING INDICATORS.
of years, and in actual practice may be regarded as permanent. The great
majority of them result from disturbance, however, and last for a period of a
few years, or at most for a decade or two, unless the disturbance is continuous
or recurrent. In addition, they show rapid changes of population from year
to year. Such conmaunities are usually local and of small extent and have
resulted from fire, overgrazing, or cultivation. They belong to secondary
successions or subseres in contrast to the larger and more permanent com-
munities which constitute stages in the primary succession or prisere. These
distinctions apparently disappear in the case of great stretches which are kept
more or less permanently in the lodgepole or aspen community as a consequence
of repeated fires, or in the Aristida or Gutierrezia stage as a result of continued
overgrazing. Even here, however, the differences in the kind and rate of
development are of great practical value in determining the proper manage-
ment. As a consequence, it is desirable to distinguish serai communities as
indicators upon the basis of primary and secondary succession, and then to
deal with the indicator value of the respective dominants. Each of these is
known as a consocies when it is controlUng, and corresponds with the con-
sociation among climax types. Two or more consocies regularly occur to-
gether to constitute a particular stage or associes, while their subdominants
are known as socies, which correspond with the societies of climax communi-
ties. A complete treatment of serai indicators is neither possible nor desirable
at present, but the following account will serve to illustrate all the important
types.
Prisere communities as indicators. — The four great types of primary suc-
cession are those which start in initial bare areas of water, rock, dune-sand, or
saUne lake or basin respectively. The initial communities and some of the
medial ones may be used as negative indicators, denoting that conditions
have not reached the point where they can support a plant cover of such
density or quality as to furnish grazing. The later communities, and espe-
cially the subclimax one that immediately precedes the cUmax, form a more
or less complete cover in which grasses or shrubs are usually in control. The
density of the cover and the quaUty of the grazing increase more or less
regularly from the medial stages to the climax, and the position of a particular
community in the sere indicates its value in a general way.
The most important serai indicators of grazing are the later stages of the
priseres in dunes and sandhills, in bad lands and in salt basins. These often
cover many thousand square miles and frequently occur in agricultural
regions, where the indicator distinction between grazing and farming land is
especially important. In addition, there are the sedge and grass meadows
which are stages of the hydrosere, and are often characteristic of mountain
parks in the montane and subalpine zones. Grassland and scrub also develop
in rock fields and on talus slopes where the formation of soil is not too slow.
While such parks and gravel-slide areas often afford excellent grazing, they
are usually both local and relatively small and serve chiefly to increase the
grazing value of the forest areas in which they occur.
Of all the prisere communities, those of sandhills and dunes are probably
the most widely distributed and most important. They have been found and
studied in each of the 16 Western States, where they may occur as sandhill
regions of large extent, as river dunes or ocean dunes. The most extensive
CLEMENTS
PLATE 67
A, Serai staRes in sandhills, the subcUmax grasses Andropogon and CalamovUfa, Agate,
Nebraska.
B. Serai stages in bad lands, Alriplex corrugata, nuitallii, and confertifdia the chief domi-
nants, Cisco, Utah.
GRAZING TYPES. 281
sandhill areas occur in Nebraska, Kansas, and Colorado, though they are
scattered throughout the grassland cUmax from North Dakota to Texas and
New Mexico. Such areas differ from dunes chiefly in extent and complexity,
and in the fact that they are no longer connected with an active shore-line
from which the sand is derived. They are essentially stable dunes with blow-
outs as characteristic features, and for the most part they exhibit subcHmax
communities. The succession in sandhills and dunes is practically identical
for the same cUmax, but differs greatly between climaxes, especially in the
later stages. The largest and most important sandhill region is that of cen-
tral Nebraska, which covers an area of about 20,000 square miles. It has
received much study during the past 30 years, and the ecological results have
been summarized by Pool (1914) in a monograph on their vegetation. The
typical conmiunity of the sandhills is the bunch-grass subcUmax, consisting
of Andropogon hallii and A. scopariiis. The blow-sand condition, typical of
blowouts especially, is indicated by Redfieldia, Psoralea, and Petalostemon,
which have little or no grazing value. More stable conditions are denoted by
Muhlenbergia and Calamovilfa, and these are correlated with increasing graz-
ing value. The next stage is that of the Andropogon subclimax, which pos-
sesses a much higher value. By the entrance of Stipa and Koeleria, the bunch-
grass subchmax passes into the true prairie, while in the western portion the
invasion of Bouteloua and Bulbilis indicates the appearance of the short-grass
climax, or of mixed prairie when Stipa and Agropyrum occur also. The hydro-
sere is a regular feature of the innumerable wet valleys and of the extensive
lake region. The first community to indicate grazing is composed of rushes
and sedges, and this changes slowly into the typical meadow associes of
Agropyrum, Andropogon, Elymus, Panicum, and Spartina, which is essentially
an extra-regional portion of the subclimax prairie. The grazing value of
such a group of dominants is obvious, but in practice such meadows are used
for hay, since the hills furnish ample summer grazing (plate 67).
Like the sandhills, bad lands are found throughout the West. Massive
bad-land complexes are most typical of the States which touch the Black
Hills, but they are frequent also in practically all those along the Rocky
Mountain axis, while outlying areas of much interest are found in Texas,
Oregon, and California. The actual communities of the sere likewise differ
with the climax. The two most important seres are the xerosere of the
Tertiary bad lands in the Great Plains region of the grassland climax, and the
halosere of the Great Basin sagebrush climax. The former possesses a num-
ber of herbaceous stages which have an increasing value for sheep-grazing as
they become denser, but grazing proper is indicated only when Agropyrum
becomes abundant. Bouteloua and sometimes Bulbilis also enter somewhat
later to form mixed prairie, and the latter then becomes definitely constituted
by the appearance of Stipa. The lower valleys are often controlled for a time
by sagebrush, but this ultimately yields to the grasses. The juxtaposition of
weed, grass, and sagebrush types indicates the value of bad land areas for
mixed grazing, and suggests the importance of hastening the course of suc-
cession in them. The bad lands of the sagebrush climax are characterized in
the intial stages by colonies of halophytic annuals, which have some grazing
value where they make a definite cover. The first stage of much importance
is formed by the low perennial species of Atriplex, such as A. nuUaUii, A.
282 GRAZING INDICATORS.
comigata, and A. pabularis. These are followed by Atriplex confertifolia and
Grayia, which furnish forage of much better quality and larger amount, and
these are finally invaded by Artemisia tridentata to form the mixed or pure
grazing type so characteristic of the Great Basin and its outlying regions.
In the bad lands of the Painted Desert in northern Arizona, the general course
of the sere is much the same, but the grasses replace Atriplex. The normal
sequence in the subcUmax stages is the replacement of Sporobolus airoides by
Hilaria jamesii, and this by Bouteloua, often with Muhlenbergia also. The
course of development in the halophytic bad lands is essentially a part of the
widespread succession in saline basins, except that the latter often begins in
water. Shantz (1916:233) has indicated the course of the succession in
detail, and it must suffice to point out that the first important indicators of
grazing are usually scrub dominants, Sarcohatus and Atriplex. Some of the
playas of the Southwest are intensely saline, and show essentially the same
communities, but the majority are secondary in nature and belong to the
subsere.
Subsere communities as indicators. — Subseres are developed in secondary
areas, such as are regularly produced by fire or cultivation. They occur also
in other bare areas in which the disturbance is not sufficient to destroy the
soil or to make extreme conditions for ecesis. They are a constant feature of
overgrazing and a normal consequence of the presence and activity of man.
They are usually local and of small extent, but in the case of fire they may
occupy hundreds of square miles. The successional movement is normally
rapid, but its progress may be slowed or stopped by the recurrence of the
disturbing agency. When this is the case, the area concerned may be held
more or less permanently in a subclimax or other serai stage. The most im-
portant and extensive subseral communities are those due to fire. The con-
sequences of overgrazing often cover great stretches, but the actual com-
munities change more or less, or they are much interrupted. Those due to
cultivation are usually confined to fields, though many of the dominants
become extended to roadsides, and some even enter the natural vegetation.
While they often have grazing value, it is incidental and temporary and their
chief value hes in connection with utilization as supplementary forage crops,
as already indicated for Salsola, Helianthus, Melilotus, and others (plate 68).
Certain grasses, such as Poa, Avena, and Bromus, have become widespread
dominants as a consequence of the combined action of two or more agencies.
In the case of Avena and Bromus, the species concerned, A. fatua, B. tedorum,
B. rvhens, etc., are annuals which have replaced the native dominants as a
general result of the combined effect of overgrazing and fire. As annual
grasses, these should have a low grazing value, but this is much less true of
Avena than Bromus, owing largely to the difference in size and habit. Even
Avena is less valuable than the native perennial grasses which they usually
replace, and this suggests the desirability of taking advantage of the principles
of succession to restore the original community where it has not been com-
pletely destroyed. Poa pratensis as a perennial grass of meadows has practi-
cally the same ecological habits and grazing value as the prairie dominants
which it replaces. Its rapid spread .in the valleys and ravines of the true
prairies seems to have been the result of a certain amount of disturbance, but
CLEMENTS
PLATE 68.
>M
A. Broimis teclorum marking a burn in siigcbrusli, Hoiso, Idaho.
B. Erodium cicuiarium indicating trampling in dcsrrt plains gra.-sland, (>ra<-I«', .Vrizonji.
GRAZING TYPES. 283
Poa is not a true serai consocies, such as the annual Avena and Bromus.
Among other such consocies of importance are Plantago patagonica, Portu-
laca oleracea, Boerhavia torreyana, and Polygonum aviculare. These are all
indicators of disturbance, particularly overgrazing, but in the green condition
they also have more or less value as indicators of an available weed type.
Other indicators of disturbance are represented by such plants as Hilaria
mutica, Scleropogon brevifolius, Franseria, and BuUnlis. These occur in playas
or "swags" which are subject to flooding and in which a thin annual layer of
silt is often deposited as well. The first two are commonly associated, partly
o^-" ^ to the fact that the disturbance of the Hilaria consocies by tramphng
and overgrazing favors the spread of Scleropogon. Tobosa swags are typical
serai areas in the desert scrub as well as in the zone of savannah which lies
between this and the desert plains. In the latter particularly, Hilaria is a
characteristic subclimax, in which Scleropogon is usually an indicator of
giarin" disturbance, frequently with a similar associate, Sporobolus auri-
culatus. Hilaria is an indicator of summer grazing, while the other two are
rarely grazed except under drought conditions. The playas of the southern
Great Plains are marked by a similar subsere, in which Franseria is the im-
portant early stage and Bulhilis the subchmax. Both of these are grazing
indicators, though the value of the Franseria is relatively small (plate 69).
Fire indicators and grazing — The typical indicators of j&re are trees and
shrubs, and they may have a direct or indirect relation to grazing. The
indicators may themselves be browsed, or they may be associated with layers
of herbs or shrubs which furnish feed. Grasses and other herbs may indicate
fire, but are usually associated with woody indicators or their relics. The
most important "burn" communities are pine forest, aspen woodland, chap-
arral, and savannah. In addition, there are grass and sagebrush parks which
also represent subseres initiated by fire. Savannah has already been con-
sidered, while the grazing value of grass parks is obvious. Sagebrush and
chaparral are primarily browse types, though they contain a larger or smaller
amount of grass or herbs as well. When young, aspen woodland furnishes a
large amount of browse, but it is chiefly valuable for the more or less luxuriant
ground cover. This changes with the course of succession from firegrass,
fireweed, and other pioneers to the characteristic mixed layer communities
of the mature aspen subclimax. The latter exhibits three chief grazing types,
herb, grass, and shrub, of which the first is the most common and the second
the most valuable. The pine communities which regularly indicate burns are
lodgepole and knobcone forests. The subclimax of lodgepole, Pinus contorta,
is much the most extensive and important, occurring in both the montane
and subalpine zones of the Petran and Sierran regions. The community of
knobcone pine, Pinus aUenuaia, is a similar fire subclimax, but it is confined
to southern Oregon and Cahfornia. In the Rocky Mountains, the mature
lodgepole forest is almost completely without a ground cover, and hence pos-
sesses almost no grazing value. In its earUer stages, herb and grass associes
are well-developed, and for a time aspen scrub may form a typical stage. In
the Coast forest, Pseudotsuga and Larix are fire indicators and their commu-
nities exhibit herb and shrub layers in the early stages especially.
284 GRAZING INDICATORS.
CARRYING CAPACITY.
Nature and significance.. — The practical measure of tlie value of a range is
its carrying capacity. By this is meant the number of animals which can be
grazed upon it, expressed in terms of unit area, such as the number of head
grazed upon a section (640 acres), or the number of acres required to support a
single animal. It is usually expressed in terms of cattle as a basis, though it
is better to indicate it in terms of the animal to which the range is best adapted,
especially in the case of mixed grazing. As used at present, carrying capacity
is only a relative measure of the food value of a range or type. This is due to
several facts which introduce elements of uncertainty. Few grazing types are
uniform, either in density or composition, and the utilization of any dominant
depends to a great extent upon its associates. Even greater variation in
carrying capacity results from annual fluctuations in rainfall. On the animal
side, each kind of stock has its own preferences, as that of cattle for grass and
sheep for herbs, while horses and sheep utilize a forage cover much more
completely than cattle. Similar great differences result from the methods of
handling stock, especially with reference to the manner of herding by ages or
classes, or in the open or band system, with respect to water, salting, etc.
Carrying capacity may vary significantly with the breed of stock, and it is
obviously affected by winter feeding in regions of year-long range. Finally,
perhaps the largest element of uncertainty lies in the great variation in the
size and condition of stock when turned off of the range. As a consequence,
it is clear that more exact measures must be introduced, which will permit an
accurate comparison of different ranges and at the same time furnish a guide
to the varying conditions of the same range. The Forest Service (Jardine
and Hurtt, 1917) has already done much in this connection, especially with
respect to the extensive measurement of carrying capacity, while the office of
Dry-Land Agriculture (Sarvis, 1919) has developed a basic method of inten-
sive measurement. By the proper combination of these two methods, it will
be possible to secure an exact measure of the carrying capacity of all grazing
types, as well as of the fluctuations from year to year and under different
kinds of management.
Determining factors. — ^With respect to the plant cover alone, the carrying
capacity of a grazing type is summed up in the total amount of the annual crop
of forage. But the total yield must be interpreted in terms of value and
utihzation. Hence, it is necessary to take into account the composition of
the type, the palatability and nutritive value of the dominants and sub-
dominants, the duration and timeliness of the grazing season, and the effects
of the climatic cycle. Most of these factors are susceptible of exact measure-
ment, particularly the structure and yield of each type, the chemical com-
position of the dominants, and the response to annual variations in rainfall.
Their- practical significance, however, is subject to the test of actual graz-
ing, and hence it is imperative to take into account the relation of each to
the type of grazing indicated by the community. All of these relations are
summed up in grazing management, in which the kind of stock, the organi-
zation of the range, and the method of handling are the determining factors.
These are determined by the kind and amount of the annual yield of forage,
and in turn react decisively upon it. They are considered briefly in the fol-
CLEMENTS
A. Tobosa "swag," HUaria and Scleropogon subclimax to desert plains grassland,^ Las
Cruccs, New Mexico.
B. Playa in the IiuU)iliis subclimax stage, the old shore- line marked by Euphorbia, Texhoma,
Oklahoma
CARRYING CAPACITY. 285
lowing paragraphs, while their part in overgrazing is discussed in the next
section, and their relation to increased carrying capacity under that dealing
with range improvement.
Relation to communities and dominants. — The general value of climax
and serai communities as grazing indicators has already been discussed. This
is related directly to the carrying capacity, which is determined by the nature
of the dominants and subdominants and their groupings. The value of a
dominant is determined primarily by its total yield, palatability, and nutri-
tion content, but it is affected in the most striking fashion by associated
dominants. In fact, palatability is regularly the controlling factor, since a
grass of high yield and nutrition content may remain untouched in a com-
munity of more palatable species, while it may be completely utilized when
foi-ming a pure community or in the absence of more succulent forage. Thus,
the question of relative palatabiht> becomes of the first importance in the
study of overgrazing and of range improvement. It varies with the kind and
breed of stock, with the phases of the climatic cycle, and with the year or
season.
With respect to total yield, the relative importance of dominants may
be best illustrated by the grassland climax. The tall-grasses produce more
forage than the short-grasses, and the sod-grasses more than the bunch-
grasses; but a tall bunch-grass, such as Agropyrum spicatum or Andropogon
hallii, may yield more heavily than a short-grass like BovieUma gracilis, though
the latter is more palatable and hence more completely utilized. A short-
grass like Bulbilis, which forms a compact turf, has a higher carrying capacity
than Bouteloua gracilis with an open turf, v/hile the latter excels the more
open B. eriopoda as well as the bunch-Uke B. rothrockii. A mixed community
of tall- and short-grasses has much the higjiest carrying capacity of all, and of
these the most productive is one in which the lower layer is Bulbilis. Sub-
dominants which approach the grasses in palatability have a similar r6le in
increasing carrying capacity, but the great majority are less palatable and
decreiise the yield in proportion to their luxuriance. Grasses also affect the
carrying capacity by virtue of different times of development. A community
which contains Stipa spartea or comata permits earlier grazing than others,
while a mixed prairie with Stipa, Agropyrum, and short-grasses not only
affords the longest season, but likewise the most continuous production of
forage. The relative yield of tall- and short-grasses is also affected by the rain-
fall of wet and dry periods. The yield of tall-grasses seems to be reduced
proportionately more than that of short-grasses by a drought period and is
correspondingly greater during a wet period (plate 70).
The relation of grouping to palatabiUty is perhaps best seen in the mixed
prairie and true prairie, though it exists in all communities where two or more
dominants differ in this respect. In general, Stipa comata is most readily
eaten, Agropyrum glaucum slightly less so, and Andropogon scoparius little or
not at all, when they occur in mixture or as altemes. As a consequence, Stipa
is often eaten out or kept down to such an extent that it fails to fruit. In its
absence Agropyrum bears the brunt of the grazing and sooner or later decreases
to a marked degree, thus making the short-grasses more available. In spite of
their high value, the latter are less succulent and seem to be less palatable
during the growing season. It is only after Stipa and Agropyrum have dis-
286 GRAZING INDICATORS.
appeared and the short-grasses have been grazed closely that Andropogon is
brought into requisition. Under such conditions, which obtain frequently
during drought periods, it is grazed fully as closely as the other grasses are
normally. In ordinary years a similar result can be secured by burning the
dead stems and keeping the bunches grazed while they are green. The
relation of Koeleria to its associates isJess clear, yet the fact that it is often
present but rarely dominant, combined with its early growth and succulence,
suggests that it resembles Stipa in being grazed heavily.
With reference to the dominants, conditions are similar in the true prairies,
except for the absence of the short-grasses. Differences in palatability are
expressed chiefly in the emphasis of the subdominants, with the result that
they often exceed the grasses in total yield. Practically all the herbs are
inferior to the grasses in palatability, and they are lightly grazed as a rule,
until the grasses have begun to disappear. Various stages of this process are
seen in pastures, the more palatable species dropping out first, followed by
those less and less palatable until only the most unpalatable ones, such as
Solidago, Artemisia, Verbena, etc., remain as indicators of overgrazing. The
desert plains have a large number of dominants and a corresponding number
of groupings. As a consequence, differences in palatability play a decisive
part in them also. The species of Bouteloua are most readily eaten, those of
Arisiida less readily, while Andropogon and Heteropogon are eaten little or not
at all until the supply of the others runs low. As a result, the presence of
Arisiida and Heteropogon serves to indicate overgrazing of Bouteloua, while
their increase may be used as a measure of the degree.
Nutrition content. — A scrutiny of the following tables will show that differ-
ences in palatability are much more important than those of nutrition content,
as shown by the chemical analysis of dominants and subdominants. It is
surprising to find some grasses which ordinarily are grazed little or not at all
possessing as high a nutrition content as the best species of the range. It is
equally surprising to find that many annuals possess apparently a higher
nutritive value than related perennial species of much greater grazing
value. The native grasses have much the same composition as the cultivated
ones, while the sedges run higher in protein and carbohydrates than the
grasses. The rushes have about the same protein content as the sedges, but
are slightly higher in carbohydrate. The legumes, other herbs, and dicotyl
shrubs are the highest in protein, and low in crude fiber, while the shrubs
contain as a rule the species of highest fat content. The emergency forage
plants, such as Dasylirium, Nolina, and Yucca, are lowest in protein and high-
est in crude fiber. The cacti are lowest in crude fiber, low in protein, highest
in ash, in starch, sugars, etc., and in the water-content of the green plants.
The data in the tables below have been gathered chiefly from the following
sources: Cassidy and O'Brine (1890), Shepard and Williams (1894), Shepard
and Saunders (1901), Knight, Hepner, and Nelson (1905, 1906, 1908, 1911),
Kennedy and Dinsmore (1906, 1909), Griffiths and Hare (1907), Vinson (1911)^
Griffiths (1915), and Wooton (1918). The table of the average composition
of different groups of plants is from Knight, Hepner, and Nelson (1911: 12),
and that of average digestion coefficients from Kennedy and Dinsmore
(1909:35).
CLEMENTS
PLATE 70 ^ . ^
A. Mixed turf of tall-gni.«.s i'-'l{//-o/>//ru;/()andshort-grii.ss (/i«//>j7Ks),WinmT, South Dakota.
B. Pure turf of short-grass {liulbilis), Ardinore, South Dakota.
CARRYING CAPACITY.
Grasses.
287
Speciea.
Ash.
Ether
extract.
Crude
fiber.
Nitrogen-
free
extract.
Protein.
Ajiropyrum caninum
glaucum
sciibneri
spicatum
Agroetia alba
hiemalia
Andropogon f urcatus
hallii
nutans
saccharoides .
8copanu9
sorghum halepense
Aristida calif ornica
divaricata
purpurea longiseta
micrantha. . .
baairamea
Avena f atua ,
Bouteloua bromoidea
eriopoda
gracilis
hirsuta
racemosa
rothrockii
aristidoidea
polystachja
Bromus ciliatus
inermis
marginatus .
hordeaceus .
maximua
rubens
tectorum
Bulbilis dactyloidea
Calamagrostis canadensis . . .
purpurascens.
Calamo\'ilfa longifolia
Cenchrua tribuloides
Chloris elegana
Dactylis glomerata
Danthonia intermedia
Deachampsia caespitosa
Diatichlia apicata
Echinochloa crus-galli ......
Elymua canadenais
condensatus
sitanion
triticoidea
Eragroatis piloaa
major
Eriocoma cuapidata
Festuca ovina
scabrella
megalura
octoflora
p. ct.
4.73
8.23
3.86
9.90
11.40
7.21
6.66
6.52
6.94
7.16
6.05
6.33
8.05
7.20
8.10
9.11
10.09
8.25
7.64
10.27
4.86
11.07
9.63
6.53
6.84
10.07
7.68
6.21
7.39
11.15
9.51
4.16
23.96
10.51
6.92
4.34
6.39
10.96
12.93
10.68
4.68
7.21
10.66
9.96
8.85
7.96
10.10
6.33
10.10
14.53
8.09
6.30
10.64
6.23
7.44
p. ct.
2.00
2.90
2.99
3.02
1.61
3.34
3.19
1.97
1.70
1.64
2.29
3.01
0.90
2.55
1.42
2.01
2.29
3.18
1.87
1.74
1.43
2.59
1.94
1.58
2.12
1.90
2.21
2.71
1.79
2.35
1.82
2.15
1.96
3.45
2.56
1.57
2.15
2.28
2.23
2.81
2.27
1.97
2.44
2.60
2.22
2.09
1.40
1.67
2.47
p. ct.
36.15
34.30
31.26
30.84
32.17
31.84
33.81
38.70
37.64
36.78
34.39
32.36
34.50
34.89
36.87
28.24
16.28
30.55
30.94
33.92
34.68
34.97
32.86
36.67
35.11
30.90
35.23
29.50
35.80
29.91
28.66
33.24
24.11
25.29
34.92
35.52
39.59
16.69
32.19
27.24
18.71
35.75
29.06
31.08
34.51
37.77
35.61
39.55
28.79
17.70
32.19
35.81
35.58
31.17
29.45
p.ct.
48.56
44.92
52.12
50.09
47.82
49.54
49.35
44.87
49.54
48.00
61.31
44.13
50.54
49.71
46.18
55.36
67.28
50.95
54.84
48.76
50.79
45.10
49.23
50.55
46.96
42.00
43.94
52.11
44.68
38.28
49.88
55.00
29.86
54.74
46.88
49.29
46.14
63.62
42.44
44.53
64.57
47.84
49.50
47.12
46.24
41.93
43.21
46.32
43.44
56.24
48.30
50.66
43.02
53.50
50.49
p. ct.
8.66
9.65
. 9.77
6 15
7.00
8.07
6.99
7.94
4.17
6.42
6.96
14.17
6.01
6.65
7.43
5.28
4.06
7.07
4.71
6.31
8.24
6.27
6.34
4.67
8.97
9.80
10.94
9.47
10.34
15.71
9.06
5.53
18.51
7.35
9.13
8.50
6.06
6.68
10.48
14.10
9.48
7.63
8.63
9.66
8.17
9.53
8.81
5.83
15.23
8.93
9.20
6.14
9.36
7.42
7.15
288
GRAZING INDICATORS.
G BASSES — continued.
Species.
Ash.
Ether
extract .
Crude
fiber.
Nitrogen-
free
extract.
Protein.
Heteropogon oontortus
p. ct.
6.01 -
9.37
8.56
8.17
10.83
11.77
6.86
5.50
7.45
25.79
5.12
12.36
6.53
11.82
11.96
6.26
10.45
4.83
7.34
7.80
5.36
7.14
5.74
6.26
5.05
7.77
4.38
5.09
9.45
11.57
7.98
8.59
13.32
11.17
12.15
6.16
7.65
8.39
7.76
10.46
7.16
7.05
6.49
8.53
6.70
6.53
8.23
4.78
7.80
8.04
6.36
7.30
p. ct.
1.44
2.09
2.41
1.66
3.39
1.96
2.00
2.62
3.03
3.17
2.69
2.63
2.28
1.67
2.38
2.25
1.73
2.33
1.94
2.92
1.80
2.68
2.97
2.59
2.06
3.17
2.64
4.11
2.92
2.58
1.77
2.02
4.34
3.24
2.87
2.25
2.00
1.78
2.31
2.26
2.40
1.67
1.31
1.70
2.31
2.37
1.67
2.46
2.77
2.61
2.46
0.70
p.ct.
33.28
24.61
31.95
32.77
31.90
33.02
35.99
30.70
33.94
29.90
25.72
31.03
35.63
35.31
29.97
33.52
30.26
32.20
37.44
35.97
29.89
36.76
33.73
31.92
33.68
34.39
26.11
31.43
19.40
24.41
38.15
30.41
16.97
35.22
16.40
36.79
35.21
32.19
33.70
33.42
33.30
33.49
34.01
32.27
34.40
38.57
36.90
23.81
34.08
30.87
32.91
28.80
p. ct.
54.79
66.26
48.39
60.32
42.40
44.65
47.72
49.47
46.98
36.21
69.72
46.31
49.59
38.71
46.72
51.52
46.97
51.69
46.30
44.40
60.65
47.90
60.31
51.60
52.17
46.38
58.19
51.07
69.47
62.17
45.94
51.20
56.91
38.21
69.91
47.16
47.74
48.92
60.31
48.11
50.37
60.03
61.13
47.93
49.73
45.38
47.20
60.61
41.30
49.77
47.08
49.30
p. ct.
4.48
8.77
8.69
7.08
11.48
8.60
7.43
11.66
8.60
4.93
6.85
7.77
5.97
12.69
9.97
6.46
10.69
8.96
6.98
8.91
12.30
6.62
7.26
7.63
7.04
8.29
8.68
8.30
8.76
9.27
6.16
7.78
9.46
12:16
8.67
7.64
7.40
8.72
6.92
6.76
6.77
7.86
7.06
9.57
6.86
7.16
6.20
8.34
14.05
8.71
12.20
3.80
Hilftna '^^nrhmidfts
jamesii
mutica
Hordeum jubatum
maritimum
murinum
nodosum
Koeleria cristata
Lamarckia aurea
Muhlenbergia gracilis
gracillima
porteri
Munroa squarrosa
Panicum lachnanthum
virgatum
capillare
Phleum alpinum
pratense
Phragmites communis
Poa arctica
arida
compressa
nemoralis
nevadensis
pratensis
rupicola
sandbergii
tenuifolia
Polypogon monspeliensis
Schedonnardus texanus
Scleropogon brevifolius
Setaria glauca
it.]^licA ,
viridifl
Spartina cynosuroides
gracilis
Sporobolus airoides
asperif olius
auriculatus
brevifolius
cryptandrufl
flexuosus
wrightii
Stipa comata
eminens . . . . ,
setigera
spartea
vaseyi
viridula
Trisetum subspicatum
Zea mays
CARRYING CAPACITY.
Sbdqes, Rushes, and Horsetails.
289
Species.
Ash.
Ether
extract.
Crude
fiber.
Nitrogen-
free
extract.
Crude
protein.
Carez aristata
p.ct.
6.49
6.99
6.81
7.41
6.24
6.71
8.46
7.85
6.94
9.69
9.12
10.30
11.13
8.72
8.03
9.43
10.55
13.30
18.62
7.25
10.24
11.30
13.42
3.73
6.47
5.51
6.39
9.32
6.38
5.79
21.58
p. ct.
2.45
2.17
1.44
1.46
3.09
1.79
1.94
3.39
2.85
2.66
1.96
2.40
2.52
2.32
1.61
2.18
2.39
2.73
2.14
1.55
1.59
1.14
1.69
2.78
2.09
1.53
1.65
1.11
1.66
1.82
2.26
p.ct.
31.66
29.08
31.84
36.27
29.74
29.04
34.28
28.50
31.67
27.00
32.33
26.79
30.13
34.16
30.84
30.93
32.65
29.41
26.94
34.20
29.07
32.56
30.81
26.34
29.01
35.64
24.38
31.25
25.90
37.07
23.60
p.ct.
49.51
50.03
43.74
47.02
61.87
51.09
45.83
53.21
47.66
44.00
48.51
45.66
44.97
46.56
47.28
47.25
47.51
44.47
42.79
53.21
48.18
44.95
44.56
59.44
54.72
46.47
54.06
45.95
49.31
48.39
42.00
p.ct.
10.00
12.72
16.17
7.85
9.06
12.37
.9.50
7.05
11.88
16.84
8.08
14.85
11.24
8.24
12.24
10.21
6.90
10.09
9.50
3.79
10.91
10.05
9.52
7.71
8.71
10.85
13.52
12.37
16.75
6.93
10.56
atrata
aquatilis
bella
* douglasii
f estiva
lanuginosa
xnarcida
nova
pennsylvanica
rupestris
nccata
Btrieta
straminea
utriculata
vulpinoidea
Heleocharis acuminata
obtusa
palustris
Scirpus atrovirens
fluviatilis
lacustris
pungens •. . .
Juncodes spicatum
parviflorum
Juncus balticus
mertensianus
nodosus
parryi
tenuis
Equisetum levigatum
Legumes, Nattve.
Species.
Water.
Ash.
Ether
extract.
Crude
fiber.
Nitro-
gen-free
extract.
Crude
protein.
Astragalus bisulcatus . . .
carolinianus .
Hedysarum philoscia. . .
Lotus americanus
Lathyrus coriaceus
Lupinus argenteus
holosfcriceus. ...
leucophyllus...^
lyalU....
plattensis
rivularis
Thermopsis divaricarpa.
Trifolium dasyphyllum .
monanthum. .
parryi
Vicia linearis
6.87
8.23
9.09
6.80
9.06
7.32
8.12
6.28
6.12
11.69
9.17
10.63
6.71
9.76
9.37
8.42
7.93
1.42
1.34
1.13
2.96
4.02
3.18
6.62
3.64
6.08
1.98
7.11
2.87
1.91
6.04
2.69
1.96
28.76
28.00
22.42
23.28
27.65
27.01
14.43
15.76
21.37
17.93
16.36
26.93
27.37
18.83
23.78
27.16
43.90
40.23
51.69
45.67
44.83
40.05
48.80
61.64
42.58
57.24
38.63
49.32
45.72
41.19
46.17
40.73
17.69
21.34
17.96
19.04
9.31
21.63
25.87
13.84
19.38
13.68
27.27
15.17
15.24
24.67
20.04
22.22
290
GRAZING INDICATORS.
Leoumes, Cultivated.
Species.
Water.
Ash.
Ether
extract.
Crude
fiber.
Nitro-
gen-free
extract.
Crude
protein.
Medicago sativa
p. ct.
p. a.
9.96
10.18
6.57
8.64
12.90
10.23
12.34
p.ct.
1.33
2.62
1.72
2.02
2.34
2.68
3.19
p.et.
33.34
23.16
42.47
31.46
32.68
19.01
15.70
p.et.
37.67
44.99
34.66
44.34
38.60
49.19
44.97
p.ct.
17.70
19.15
14.68
13.63
13.69
18.89
23.80
Melilotus alba
^
oiliciDalia
Trifolium hybridum
incarnatum
pratense
repens
Other Herbs, Perennial.
Ataenia gairdneri
6.79
9.05
16.99
10.73
11.83
9.52
10.21
8.81
20.55
9.89
20.62
8.88
10.21
1.25
9.16
17.79
10.99
16.16
4.77
1.66
6.46
5.71
5.26
9.74
3.37
4.02
6.46
6.36
7.04
9.74
6.07
5.89
2.41
12.76
3.87
25.74
28.01
21.32
14.17
12.43
20.62
23.47
11.10
17.62
11.60
21.71
20.62
22.11
26.68
27.53
10.60
16.98
46.47
48.24
36.18
36.70
47.23
49.27
49.19
43.35
48.78
47.07
46.35
49.27
63.60
39.09
33.58
60.58
46.93
7.18
6.11
26.32
15.44
25.56
10.16
8.44
20.98
17.35
14.35
9.87
10.16
17.97
19.18
18.69
16.07
16.25
Arenaria hookeri
Aster campestris
Balsamorhiza sagittata
7.12
Castilleia miniata
nevadensis
Crepis intermedia
6.74
Franseria discolor
Helianthella uniflora
I va axillaris
Leptotaenia multifida
6.16
Pentstemon procerus
Senecio serra
triangtilaris
Triglochin maritima
Wyethia amplexicaulis
mollis
6.81
Other Herbs, Annual.
Atriplex volutans
18.47
4.47
10.12
19.04
12.66
6.86
2.37
6.69
7.40
.93
32.78
9.00
2.11
7.12
2.87
3.63
1.80
1.91
29.66
7.77
17.00
24.13
14.00
20.34
14.60
32.11
30.19
37.41
23.31
47.04
42.35
47.65
52.06
70.19
48.11
44.98
13.63
31.67
16.84
12.37
18.67
18.87
9.21
11.39
15.62
Brassica arvensis
Cleome integrif olia
Erodium cicutarium
Lactuca ludoviciana
Polygonum aviculare
convolvulus
erectum
ramosissimum
Shrubs and Halpshrubs, Di
cottledo
NS.
Ani'^l^mnhip'' P-Ififolia
8.11
6.68
7.08
10.66
25.39
13.76
20.27
7.61
11.66
4.23
9.47
8.37
8.34
10.93
3.73
20.95
2.01
1.52
0.82
1.22
1.61
13.93
3.17
10.26
14.04
6.60
14.38
21.98
21.99
29.89
17.89
16.45
19.21
37.66
20.38
14.90
6.76
10.18
17.74
60.46
46.57
38.81
40.15
42.41
61.52
42.86
40.41
45.07
67.98
61.24
46.91
46.63
16.12
21.04
11.17
9.76
12.79
17.46
16.46
12.81
8.96
12.37
13.27
20.50
22.79
Artemisia rigida
tridentata
Atriplex canescens
7.64
conf ertif olia .
nuttallii
Eurotia lanata
Prunus demissa
Pursbia tridentata
Ribes cereum
Rosa pisocarpa
Sallx spp
CARRYING CAPACITY.
Shbubs and Halfshbubs, Monocottledons.
291
Species.
Water.
Ash.
Ether
extract.
Crude
fiber.
Nitro-
gen-free
extract.
Crude
protein.
Agave lechuguilla
Dasylirium texanum:
Leaves
Stems
Dasylirium wheeleri, leaves . . .
Nolina enunpens
microcarpa, leaves
Yucca baccata
glauca, leaves
glauca, stems and roots.
macrocarpa
radiosa:
Leaves
Stems
p. et.
p. ct.
8.9
3.6
7.3
4.5
6.6
2.9
7.6
8.8
7.3
4.6
6.8
9.8
p. et.
1.7
1.6
2.3
2.4
2.8
1.6
1.2
2.8
0.8
0.6
2.7
2.1
p. ct.
32.6
41.7
26.6
39.6
41.8
46.6
34.1
32.7
25.2
43.1
28.9
25.9
p. ct.
62.6
48.1
46.3
48.9
41.2
45.3
53.5
49.3
61.0
48.8
48.7
55.9
p. ct.
4.4
6.1
17.6
4.6
8.6
3.7
3.6
6.4
5.7
2.9
2.9
6.3
Cacti, Aib-Dbt.
Opuntia arborescens.
arbuscula . . .
basilaris
bigelovii . . . .
chlorotica . . .
f ulgida
leptocaulis. .
lindheimeri . ,
macrocentra
mamillata . . .
phaeacantha
polyacantha ,
robusta
versicolor. . .
Cereus giganteus
6.26
5.31
5.08
5.89
6.03
5.60
6.15
5.33
7.18
6.26
6.50
6.68
6.68
5.96
8.98
27.71
14.55
19.98
15.88
18.80
13.40
16.85
21.78
16.45
16.75
15.80
23.23
26.81
17.49
15.75
1.40
1.61
1.90
1.70
1.85
1.48
6.45
2.08
2.00
1.70
1.48
1.16
2.13
1.58
1.20
13.72
19.75
11.75
17.18
20.55
5.96
12.33
10.65
11.05
15.13
12.56
10.95
15.98
17.85
19.35
46.43
46.63
56.52
54.43
49.21
70.27
53.29
53.37
55.21
54.68
60.81
53.04
43.70
50.84
57.92
Cacti, Green.
Opuntia engelmannii
f ulgida
lindheimeri.
robusta
spinosior. . .
Cereus giganteus
77.21
77.79
80.72
89.62
75.64
87.31
4.18
4.24
4.44
2.95
4.63
2.20
0.39
0.34
0.42
0.23
0.49
0.17
2.62
1.66
2.17
1.76
2.56
1.44
14.71
14.37
10.87
4.81
16.01
8.07
6.48
12.35
3.77
6.79
4.71
5.48
2.85
3.94
6.70
6.28
6.80
0.89
1.60
1.38
0.63
1.77
0.81
292
GRAZING INDICATORS.
Average Composition of Plants.
No. of
samples.
Ash.
Ether
extract.
Crude
fiber.
Nitro-
gen-free
extract.
Crude
protein.
A. Native.
I. Grass-like:
1. True grasses.
a. Bottom lands
44
69
54
32
19
22
16
7
8.64
7.48
6.12
8.34
6.79
6.24
8.68
14.18
6.88
8.06
9.91
26.94
1.98
2.05
2.23
2.26
2.51
1.85
2.06
1.45
11.84
2.35
1.92
1.28
34.48
35.92
33.00
30 06
29.57
31.21
25.02
28.28
21.98
32.85
30.63
17.02
45.89
46.53
49.15
47.49
49.47
50.20
44.87
41.62
42.69
47.28
40.28
37.11
9.01
8.02
10.60
11.85
11.66
10.50
19.37
14.47
16.10
9.46
17.26
17.65
b. Bench lands
c. Mountains
2. Sedges.
a. Bog
b. Dry-land
3. Rushes
II. Not grass-like :
1. The legumes — clovers, vetches,
etc
2. Salt-bushes
3. Sagebrush, etc
B. Introduced.
I. True grasses
7
18
3
II. Other than grasses:
1. Alfalfa, clovers, etc
2. Salt-bushes, etc
Average Digestion Coefficients.
Dry
matter.
Protein.
Ether
extract
(fat).
Crude
fiber.
Nitro-
gen-free
extract.
Ash.
Nutritive
ratio.
Indi
Con
an potato (Ataenia gairdneri) .
imon sunflower (Wyethia
mollis)
66.59
60.65
66.38
68.76
56.74
69.46
77.28
71.10
77.19
63.19
74.21
81.49
74.38
54.41
58.69
47.39
65.21
61.19
74.90
83.04
50.10
53.01
38.29
63.07
1:15.0
1: 3.8
1: 3.9
1: 9.2
Bah
am-root sunflower (Balsamo-
rhiza sagittata)
Wile
J carrot (Leptotaenia multi-
fida)
Moi
Broi
Nat
Dan
Bitt
Bitt
Litt
intain Indian pink (Castilleia
miniata), western variety
megrass (Bromus marginatus) . .
ive bluegrass (Poa sandbergii) .
delion (Crepis intermedia) ....
er brush (Kunzia tridentata) . .
er vetch (Lathryus coriaceus) .
e lupine (Lupinus sellulus) . . .
66.
59.
52.
62.
76.
50.
68.
94
79
71
30
86
38
21
64
68.
63.
62.
81.
48.
74.
76
03
90
88
70
03
78
76.
15.
49.
33.
71.
32.
57.
82
69
87
13
36
42
22
49.
53.
44.
35.
69.
36.
55.
05
05
68
90
54
39
71
80.28
66.91
60.16
77.45
86.10
64.55
75.40
46.82
42.43
22.69
48.66
57.48
28.35
67.39
1: 8.9
1: 8.5
1: 8.7
1: 9.5
1: 6.9
1: 9.4
1: 4.2
Relation to climatic cycles. — No other factor produces such rapid and
striking changes in carrying capacity as does rainfall. The difference in the
total yield of the same range in two successive years of dissimilar rainfall may
be greater than 100 per cent, and in the wet and dry phase of the same cycle
it may be even greater. Such differences are often greatly augmented by the
critical overgrazing which is more or less unavoidable during a drought period
under, existing methods of management. Since grassland is typically cor-
related with summer rainfall, the amount of the latter is at once reflected
in the growth of the dominants. A single year of deficient rainfall affects
the yield at once by decreasing vegetative growth. At the same time,
CLEMENTS
PLATE 71
A. Bouttloua-Arhtulu association in l<J17v Santa Rita KostTve, Tucson, Arizona.
B. The same area in 1918 after serious drought and overgrazing by eattlc and rodents.
CARRYING CAPACITY. 293
the storage in the propagative organs is reduced and seed production is like-
wise affected. If the drought continues for a second or third year, these
effects become cumulative and the stand diminishes greatly in density as
well as in height. During wet phases, the growth of the vegetative organs
is favored and this in turn promotes propagation and reproduction, but the
former especially. As a consequence, the sun-spot cycle of 11 years is clearly
expressed in carrying capacity, and this is often true hkewise of the 2 to 3-
year cycle, particularly in the more arid Southwest. In short, grass types
show a carrying capacity cycle of excess and deficit, which must be taken into
account if alternate lack of utilization and overgrazing are to be avoided.
Such a cycle has a peculiar significance for overgrazing and range improve-
ment and is further discussed under these heads (plate 71).
Relation to rodents. — While the damage done by prairie-dogs to native
vegetation has long been known and the indicators recognized (Pound and
Clements, 1898: 299; 1900: 414), it is but recently that the full importance of
rodents has been reaUzed. This has led to the extensive campaigns for the
eradication of rodents, organized and carried out during the last five years by
the Biological Survey, and to the cooperative studies of the kind and amount
of damage to different grazing types. The plans for the first of these were
drawn up by the writer, and they have been carried out on the Santa Rita
Range Ileserve near Tucson through cooperation with the Forest Service, the
Biological Survey, and the University of Arizona. The results have already
demonstrated the serious and often critical effect which jack-rabbits have
upon the range and have added the kangaroo-rat to the list of rodent pests
of the first importance (Vorhies, 1919). While prairie-dogs, ground-squirrels,
jack-rabbits, and kangaroo-rats are the most important, pack-rats and pocket-
gophers also do much damage, and there are doubtless other rodents which
must be reckoned with. The reduction of carrying capacity by rodents is a
serious matter at all times, but it becomes critical during drought periods.
This is due to its added effect upon a range which is already overgrazed by
the stock. The frequent occurrence of drought in the Southwest has greatly
magnified this effect, and in some areas the grass (and even the desert scrub)
has been almost completely destroyed as a consequence. It is probable that
there is a rodent cycle, due to the effect of dry and wet phases upon vegetation
as the food-supply, but in a local area this must be more or less modified by
the effects of migration. Rodents resemble grazing animals in showing a
preference for certain life-forms and dominants, as well as in adjusting them-
selves to less palatable species under the spur of necessity. The general
features of the methods by which their habits are studied and their effects
measured are given under the discussion of range improvement (plate 72).
Relation to herd and management. — The recognition of the proper meth-
ods of handling stock to secure the maximum carrying capacity was first made
by Smith (1899), and the importance of such methods has since been em-
phasized by Griffiths (1904), Davy (1902), Wooton (1908), and others. Their
development into a practical system is due chiefly to the work of the Forest
Service in connection with the grazing problems of the national forests (Jar-
dine, 1908; Sampson, 1908; Barnes, 1913). The most complete discussion of
the system for handUng cattle has been given by Jardine and Hurtt (1917),
294 GRAZING INDICATORS.
and for sheep by Jardine and Anderson (1919: 48). The essential features
are fencing or proper herding, adequate water development, deferred or rota-
tion grazing, winter and drought feeding, and improvement of the herd. Fenc-
ing is first of all important in enabling the stockman to control his own range,
but it is also necessary in order to minimize bunching and trampling, as well
as to permit rotation. In the case of sheep in the national forests, the carry-
ing capacity of the range is greatly Conserved by the open or "blanket"
method of herding. Proper water development insures fairly uniform
utilization by reducing the distance to water, and hence decreasing the ten-
dency of cattle to overgraze the areas about wells or tanks and to undergraze
distant ones. Rotation grazing permits the utilization of types or areas under
conditions which maintain the yield, and affords an opportunity for the de-
velopment of reserve pastures against periods of drought. It likewise en-
courages the grazing of cattle by classes, such as breeding-cows, steers, etc.
Feeding during winter or drought has an obvious effect upon carrying capacity.
It not only conserves the actual supply of natural forage, but it also reduces
the intensity of grazing in early spring, owing to the fact that the stock come
out of the winter in good condition. This is especially important, as the
rapid growth of the leaves in spring determines not merely the amount of
summer forage, but is even more important in deciding the amount of storage
in rootstock and seed, and hence the yield of the following year. In its re-
lation to carrying capacity, the improvement of the herd depends chiefly
upon eflSciency in transforming grass into flesh, but partly also upon the
abiUty to "rustle." It is evident, moreover, that carrying capacity will
vary with the breed as well as the animal, and that certain breeds will be more
eflScient in one grazing type than in another.
Measurement of carrying capacity. — Spillman (Griffiths, 1904: 5) has
emphasized the importance of carrying capacity as a basis for the grazing
industry:
" A knowledge of the canying capacity of the ranges is of the most import-
ance, for it must form the basis of any intelligent legislation relating to the
range question. This knowledge determines the rental and sale value of
range lands, and should also determine the size of the minimum lease or home-
stead for range purposes in case laws are passed providing for such disposal
of the public ranges. "
It is evident that definite knowledge of carrying capacity can be obtained
only through its measurement, and hence methods of measuring it come to
be of the first importance. The best measure of carrying capacity is that
furnished by actual grazing test, and all other methods find their warrant in
the use of this as a final criterion. However, so many factors enter into
practical grazing that experience alone is not a reUable guide to actual carrying
capacity, and still less to potential carrying capacity. It must be refined and
supplemented by experimental tests under controlled conditions which per-
mit varying one factor, such as grazing type or kind of animal, while the other
factors remain esssentially the same. Such grazing experiments may be in-
tensive or extensive in scope, though it is desirable to make use of both kinds
in connection with putting experimental results into practical commission.
Extensive experimentation has been carried on for several years on the Jor-
nada and Santa Rita Range Reserves by the Forest Service (Jardine and
CLEMENTS
A. Denuded area about a kuiifiai..,, -I. li mouiitl ii» ni'i-'^sland.Saiaa ivua iuMr\f, Iiu-mhi, Arizona.
B. General denudation by kangaroo-rats in desert serub, Ajo, Arizona.
OVERGRAZING. 295
Hurtt, 1917), while intensive experiments have been made at Mandan and
Ardmore by the Office of Dry-Land Agriculture (Sarvis, 1919). Whether
carrying capacity is determined by general experience or measured by actual
experiment, the extension and use of the measures obtained depend upon the
composition of the grazing type and the abundance and size of the dominants,
as determined by the quadrat method. The degree of carrying capacity de-
pends, first, upon the number and kind of the dominants associated in any
grouping; second, upon their density; and third, upon the abundance of sub-
dominants. Once it has been found for any particular grouping by experience
or experiment, it can be extended to the same or similar types in other regions
by using the dominants as indicators and checking this by means of the quad-
rat as a measure of composition, abundance, and yield. This is especially
true where protection inclosures are employed, since they readily show the
increase possible in the particular grazing type.
Present and potential carrying capacity — The present capacity of a par-
ticular grazing type is determined by its structure and the degree to which it is
overgrazed. Its potential capacity depends upon the recovery possible
under proper grazing management and the increased utiUzation brought
about by supplementary forage crops. The actual present capacity of a
range is determined by the yield during drought periods, while the potential
capacit}'^ is suggested by that of wet periods, which may be several times
greater. Wliile the open range in the grassland cUmax has been more or less
constantly overgrazed since the advent of the buffalo, the evidence indicates
that the carrying capacity was higher for a decade or two after the disappear-
ance of the buffalo and that it has steadily decreased up to the present time,
except in the regions where settlement and fencing have brought about some
degree of protection. During the last decade, the carrying capacity of ranges
in the national forests has been increased 20 per cent or more as a result of
grazing control, and it appears certain that the open range will permit much
greater improvement. The amount of the latter will depend upon the differ-
ence between the present and the potential capacity. A mixed type of tall-
grasses and short-grasses will have a higher potential capacity than one of
either grass-form alone, though overgrazing may reduce its present yield
practically to that of a short-grass type. The mixed prairie of North Dakota
has been shown by Sarvis (1919) to have a carrying capacity of 1 to 7 during
the drought years of 1917-18, while it might well equal 1 to 3 during wet
periods. The short-grass type of the Texas Panhandle has an average capac-
ity of 1 to 12 (Smith, 1899: 11), while in New Mexico it seems to be somewhat
lower (Wooton, 1908:27). In the desert plains, the BouUloua eriopoda
consociation has a capacity of 1 to 20 (Jardine and Hurtt, 1917: 17), while
Wooton (1916:22) assigns a similar value to the Boutelona-Aristida com-
munities of the Santa Rita Reserve. The short-grass types are grazed for a
longer period, however, and their comparative canying capacity is relatively
higher.
OVERGRAZING.
Nature. — In practice, a range is regarded as being overgrazed only when its
carrying capacity has actually decreased. Such a test is often indefinite
because of the conditions under which the stock industry is carried on, and
this explains the divergent views as to the condition of particular ranges.
296 GRAZING INDICATORS.
While conclusive evidence as to the degree of overgrazing must be obtained
from the failure of a range to maintain the herd upon it, such evidence can
rarely be secured except from experimental tests. This is due to many fac-
tors, of which variations in carrying capacity with the climatic cycle and differ-
ences in management are the most important. As a consequence, it is most
satisfactory to draw evidences of overgrazing from the behavior of the plant
cover and to determine the degree by means of quadrat measurements. The
competition between the individuals and species of the plant community is so
keen and the balance so exact that the slightest disturbance can be readily
detected. Grazing itself constitutes such a disturbance, and its effects upon
growth, propagation, and reproduction can be minutely measured by means
of the various kinds of quadrats. Such dominants as the grasses, however,
have such an advantage over the subdominant herbs because of their under-
ground parts and methods of growth that only a severe disturbance can
throw the balance in favor of the herbs. When this happens, the first evi-
dence is afforded by the increase in the number and vigor of the latter, which
consequently serve as indicators. With increasing disturbance due to over-
grazing, the annual members of the native flora appear in the most disturbed
areas as the pioneers of minute subseres, and are later followed by introduced
weeds. In the final condition the grasses will have disappeared, largely or
completely, only the more weedy societies will persist, and the ground will be
chiefly or wholly occupied by weedy annuals and biennials. Such a com-
munity represents one or more stages of the secondary succession and its
tenure depends upon the continuance of the disturbance that initiated it. If
the latter ceases, the successional process begins and soon terminates in the
original climax if the grass dominants have not been killed out. Under such
conditions, succession is universal and inevitable in all cUmaxes, and this fact
lies at the basis of all methods of range improvement (plate 73).
On the basis of the maximum annual production of forage, overgrazing
occurs whenever the yield drops below this point. It is evident that the
maximum production can not have a fixed or average value, but that it must
be correlated with the periods of the cUmatic cycle. A degree of grazing
which would be disastrous in a drought period would fall far short of adequate
utilization during a wet one. Coville (Sampson, 1908 : 5) has apphed the
tenn "destructive overgrazing" to the condition in which all or part of the
native dominants are killed. It is characteristic of areas overgrazed during
the critical drought periods of the double sun-spot cycle. For the sake of
clearness, three types of grazing are recognized here. These are overgrazing,
close grazing, and reserve grazing. Overgrazing results when the proper
maximum yield of a particular year or period is not obtained because of the
failure to make enough food for propagation or seed-production, or because
the seed-crop has been destroyed. There are varying degrees of overgrazing
from a slight reduction in yield to the complete destruction of the range.
Close grazing is the type in which the total annual yield is utilized in such a
way as to maintain the carrying capacity. Reserve grazing is the process in
which part of the annual yield is held in reserve, either by means of a reserve
pasture or by understocking. It constitutes an insurance against emergencies
and is specially adapted to periods of drought. In actual practice, close
grazing is usually preferable for the wet phases of the cUmatic cycle, and re-
serve grazing imperative for the dry phases.
CLEMENTS
PLATE 73 A
A. Relict Boulrloua and Ari^ti da indicating forintT urass rowv in dcstrt scrub, Tucson,
Arizona.
B. Relict Stipa and Balsamorhiza indicating replacement of grassland by sagebrush, Hager-
man, Montana.
OVERGRAZING. 297
Causes. — The primary cause of overgrazing is stocking the range with more
animals than it can carry and still maintain its annual yield. This has been
the universal method by which the stockman has maintained a title to his
portion of the open range, since an overgrazed range offered little attraction
to a new-comer. Overstocking has become such a general practice through-
out the West, on private lands as well as upon the open range, that stockmen
have almost completely lost sight of the potential carrying capacity of their
ranges. A corollary of this is the prtictice of year-long grazing or of grazing
during too long a season, with the result that the grass does not make a proper
growth in the spring or fails to ripen and drop its seeds in the fall. TrampUng
is an inevitable concomitant of overstocking and frequently does more
damage than the actual grazing, especially in the vicinity of wells and tanks.
In addition, there are several important contributory causes of ovei^azing.
The most important of these is the drought period of the climatic cycle. The
general practice of stockmen takes no account of the great variation in yield
between the dry and wet phases. The interval between them usually per-
mits the building up of the herd to the point where the range can not carry it
during the dry phase. For a year or more the range is destructively over-
grazed, until the herd is moved or a large portion has died. During such
drought periods as those of 1893-95 and 1916-18, the range may be so
damaged as to require several years to regain a fair carrying capacity and
many years to permit the development of its potential capacity. The efifect
of rodents upon the range is essentially a matter of overstocking. A range
which is carrying thousands of prairie-dogs or jack-rabbits is in efifect already
stocked with a considerable number of cattle. In the usual practice, however,
no allowance is made for this fact, and the rodents steadily increase the
damage done by the prevailing overstocking with cattle. This double effect
becomes most disastrous during the drought period and frequently results
in the complete destruction of the range over large areas, especially in the
Southwest. The efifect of fire upon the range is relatively unimportant by
comparison, but it does sometimes do serious damage to the short-grass and
desert plains by killing the rootstocks, particularly during dry seasons or dry
years.
Indicators of overgrazing — In grassland and scrub practically every species
may serve as an indicator of overgrazing. This is true also of herbs and shrub
associes, especially those of the subsere. In the case of woodland and forest
the dominants can act as indicators only in the seedUng or sapUng stage, but
the herbs and shrubs may indicate overgrazing as clearly as in other com-
munities. The primary basis of ovei^razing indicators lies in the fact that
at any particular stage some species are eaten and others are not. Thus, at
any time the degree of overgrazing can be determined from both sets of
plants. The best method consists in using one set as positive indicators of
excessive grazing, and the other as a check upon these results; but in actual
practice the most convenient indicators are naturaly those that are not eaten.
In any community such relict indicators owe their importance in the first
place to the fact that the more palatablfe species are eaten down, thus render-
ing the uneaten ones more conspicuous. This quickly throws the advantage
in competition to the side of the latter. They receive an increasingly larger
share of water-content and light, and their growth increases accordingly.
298 GRAZING INDICATORS.
This leads to greater storage in the propagative organs as well as to larger
seed-production. At the same time, the grazed species are correspondingly
handicapped in all these respects, and the gap between herbs and grasses, for
example, constantly widens. With the increase of the less palatable species,
especially when they are bushy, the grasses are further weakened by tramp-
ling. This soon produces small bare spots which are colonized by annual
weeds or weed-like plants. The latter set up a new and intense competition
with the grass survivors, and these are still further decreased as a result. The
weed areas widen, and sooner or later come to occupy most or all of the space
between the relict herbs or half-shrubs. Before this condition is reached,
however, the latter are brought into requisition for grazing and they then
begin to yield to the competition of the annuals. In the case of the severest
overgrazing, they too finally disappear, unless they are woody, wholly un-
palatable, as in Gutierrezia, or thoroughly protected by spines, as in Opuntia.
In the grassland climax, where the effects of overgrazing have been most
studied, it is possible to recognize three or four stages. The first is marked
by the decrease or disappearance of Stipa or Agropyrum, or of both of them,
and the corresponding increase of the short-grasses wherever these are associ-
ated; the second stage is characterized by the greater vigor and abundance
of the normal societies, as well as by the increased importance of some; the
third stage begins with the replacement of the grasses by annuals, while the
fourth is marked by the spread of annuals and of introduced weeds generally
over the area. Not all of these necessarily occur in the same spot, especially
when the process of overgrazing takes place rapidly. Destructive over-
grazing may result in a few years, or even in a single year, and in such in-
stances the native vegetation may disappear completely or nearly so. It is
replaced by a pioneer associes of native and introduced weeds, whose persist-
ence will depend upon the continuance of the disturbance. These four stages
indicate so many primary degrees of overgrazing, while minor degrees are
denoted by the dropping out of particular dominants or subdominants. Thus
in the mixed prairie, Stipa drops out before Agropyrum, because it is grazed
more heavily in spring, and Bouteloua disappears from the desert plains before
Aristida, owing to its greater palatability. Palatability is the chief factor in
determining the successive disappearance of species, and hence the indicators
of the corresponding degrees of overgrazing, though the sequence is often
disturbed by the vigor of certain dominants. Since there are few species
that are wholly unpalatable or inedible, it becomes possible to construct for
a particular community a complete sequence of indicators, reflecting each
appreciable degree in the process of overgrazing. In severe periods of drought,
overgrazing may reach the point where even the annuals are eat^n out and the
plant covering vanishes completely. This happens regularly in pastures,
corrals, and bedding-grounds where animals are kept in masses. It has
even been found in desert scrub and savannah where the effects of over-
grazing are supplemented by the work of kangaroo-rats (plate 74).
Societies as indicators. — The number of overgrazing indicators for the sev-
eral climaxes is legion, and it is possible to consider only the most widespread
and important. With the perennial grasses as a background, it is convenient
to distinguish several groups of such indicators, namely, herbs, subdominant
halfshrubs, cacti, serai annuals, introduced weeds, and shrubs. The first
CLEMENTS
PLATE
^9
A. AriUula purpurea and divaricala indicating moderate overgrazing on Bulbilis plains,
Texhoma, Oklahoma.
B. An annual, Lepidium alyssoides, indicating complete overgrazing in a pasture, Fountain.
Colorado.
OVERGRAZING.
299
three groups comprise the characteristic relict indicators, and for the most
part mark the early stages of overgrazing. The annuals and weeds are typical
of the later and final stages, while the shrub indicators are typical of savannahs
and other ecotones where grass and scrub mix. The increased importance of
societies marks the beginning of overgrazing in those associations where they
are regularly present. These consist for the most part of climax herbs, but
subclimax half-shrubs and grasses, such as Gutierrezia and Aristida, are often
of especial significance. Moreover, many of the herbs, though regularly
present in the climax, have subclimax qualities also, as is readily understood
from their competitive relations to the grasses. Practically all the societies
listed under the various associations of the grassland, as well as those of the
other climaxes, have some value as indicators of overgrazing. In most cases
this value is overshadowed by that of the most controlling and extensive
societies, and the latter alone need to be taken into account.
In the following list the general order is that of importance, but this
naturally varies with the locality and the season. The composites and other
late-blooming species are especially serviceable, owing to their persistence
(plate 75).
Artemisia gnaphalodes.
Artemisia dracunculoides.
Artemisia canadensis.
Grindelia squarrosa.
Solidago rigida.
Solidago missoiiriensis.
Solidago speciosa.
Solidago canadensis.
Solidago mollis.
Liatris pimctata.
Liatris scariosa.
Liatris spicata.
Liatris pycnostachya.
Lepachys columnaris.
Kuhnia glutinosa.
Malvastnim coccineum.
Vernonia fasciculata.
Vemonia baldwinii.
Achillea millefolium.
H^anthus rigidua.
Csrduus imdulatus.
Senecio douglasii.
Aster multiflorus.
Aster oblongifolius.
Aster sericeus.
Senecio aureus.
Balsamorhiza sagittata.
Balsamorhiza deltoidea.
Psoralea tenuiflora.
Psoralea argophylla.
Petalostemon candidus.
Petalostemon purpureus.
Amorpha canescens.
Amorpha nana.
Dalea laziflora.
Tradescantia virginiana.
Verbena striata.
Verbena hastata.
Glycyrhiza lepidota.
Braimeria pallida.
Chrysopsia villosa.
Lygodesmia juncea.
Aragalus lamberti.
Polygala alba.
Antennaria dioeca.
Astragalus mollissimus.
Astragalus bisulcatus.
Astragalus racemosus.
Astragalus crassicarpus.
Lupinus plattensis.
Erigeron ramosus.
Haplopappus spinulosua.
Hymenopappua tenuifolius.
Rosa arkansana.
Euphorbia corollata.
Salvia azurea.
Asclepias verticillata.
Monarda fistulosa.
Baptisia leucophaea.
Castilleia sessiliflora.
Allium canadenae.
Ilalfshrubs as indicators. — Halfshmbs are best developed in the South-
west, where they are typical indicators of overgrazing in both the desert scrub
and the desert plains. A few attain even greater importance in the short-
grass plains and the mixed prairies. These are Gutierrezia sarothrae, Artemi-
sia frigida, and Yucca glauca. The relation of the first two to grazing in a
short-grass cover has been shown by Shantz (1911:42). Over the central
portion of the Great Plains they are associated as the two most serviceable and
universal of overgrazing indicators. Artemisia is more abundant to the
northward, and Gutierrezia to the southward, but they indicate essentially the
same conditions whether alone or mixed. Differences in the degree of over-
grazing are designated by variations in the density and vigor of the plants.
In rough or sandy r^ons Yucca glauca is an indicator of overgrazing, though
it is less important than the two just mentioned, largely because the flower-
clusters are often eaten by cattle. Eriogonum microthecum and its variety
effusum are conmion indicators in the central Great Plains, especially in more
300 GRAZING INDICATORS.
sandy areas or in sandhills. Eriogonum jamesii is even more frequent in a
similar role, though it is barely shrubby (plate 76).
Gutierrezia is also the most irapK)rtant ndicator of overgrazing in the eastern
portion of the desert plains and in the Larrea-Flourensia scrub. In western
Mexico and Arizona it is largely or completely replaced by Isocoma coronopi-
folia and its varieties, which are the characteristic indicators from the lower-
most Prosopis valleys upward into the Bouteloua-Aristida grassland. On the
Parkinsonia-Cereus bajadas and hills, Franseria deltoidea is the indicator on
lower slopes and Encelia farinosa, or more rarely Chrysoma laricifolia, on the
upper, while Franseria dumosa and, to a less extent, Hilaria rigida, play a some-
what similar r61e in the Larrea plains of western Arizona and adjacent Cali-
fornia. In the higher desert plains, Calliandra eriophylla and Eriogonum
wrightii largely replace Isocoma as the most important indicator, while
Baccharis wrightii is more local. Other halfshrubs that occur through the
desert scrub in varying importance are Zinnia pumila, Psilostrophe cooperi,
Krameria glandulosa, Bebbia juncea, and Hymenoclea salsola. While all of
the halfshrubs of the desert scrub and grassland are normally indicators of
overgrazing, they follow the rule in that practically every one is grazed to
some degree when more palatable forage is lacking. This is altogether
exceptional in the case of Gutierrezia, Isocoma, and Franseria, but all of these
were found to be grazed more or less during the severe drought of 1918.
Cacti as indicators. — Cacti owe their value as indicators of overgrazing to
the protection afforded by their spines. Under ordinary conditions this is
almost complete protection, but during drought periods in the Southwest,
cattle in particular make much use of cacti and often keep aUve upon them as
an exclusive diet. At such times they are utihzed by jack-rabbits and pack-
rats also, and the work of these rodents frequently renders the prickly pears
and barrel cacti available for stock. The cacti which serve to indicate over-
grazing belong almost wholly to the genus Opuntia. The species with flat
joints are commonly known as prickly pears, and those with cylindric ones as
choUas. In the short-grass plains and mixed prairies Opuntia polyacantha
and 0. mesacantha are the chief indicators, while Opuntia arborescens is often
the most important species from the Arkansas Valley southward. Both owe
their abundance as much to the great ease of propagation as to their spiny
protection. In the case of the choUas especially, the joints a v readily broken
off and carried about by cattle, and in addition they are blown off by the wind.
Moreover, they are well adapted to ecesis in disturbed places, owing to their
succulence and the shallow root-system. In the Southwest the most import-
ant cactus indicators in the desert scrub and savannah are Opuntia fulgida,
0. f. m/imillata, and 0. spinosior among the chollas, and 0. engelmannii, 0.
discata, and 0. phaeacantha among the prickly pears. All these extend up
into the grassland to some degree at least, but in the foothills the most com-
mon species are Opuntia versicolor, 0. arbuscula, 0. bigelovii, and 0. chlorotica.
Nolina, Dasylirium, and Agave resemble the cacti more or less in indicator
value (plate 77, a).
Shrubs as indicators. — The shrubs that indicate the overgrazing of grass-
land are chiefly such dominants of sagebrush, scrub, or chaparral as mix with
the grasses to form savannah. The most important are Artemisia, Prosopis,
CLEMENTS
PLATE 76 ^ ^
3a^ '
A. Griruklia iiulicating overgrazing in original Slipa bunch-grjiss prairie, VViUiams, California.
B. Vermnia indicating overgiazing in short -grass plains, Stratford, Texas.
CLEMENTS
A Gutierrezia and Arislida in short-griiss plains, AlbuqiR-rquc, New Mexico.
B. Yxuxa and Arislida in mixed prairie, Hays, Kansas.
OVERGRAZING. 301
Acacia, Yucca, Querciis, and Adenostoma. They resemble each other in that
grazing gives them the advantage in competition with the grasses, partly by
decreasing the hold of the latter through eating and trampUng, and partly
by disseminating the seeds and rendering their germination more certain.
This advantage is largely or completely lost in the case of browsing animals,
such as goats, since all of these are readily browsed, with the exception of Yucca
and Arctostaphylus. Species of Artemisia are the chief shrub indicators of
overgrazing in the mixed prairies, short-grass plains, and Agropyrum bunch-
grass prairie, though various dominants of the chaparral not infrequently assume
this role also. The most widespread and important is Artemisia tridentata,
while A. cana is perhaps the most common in the mixed prairies and A.
filifolia in .«andy areas and sandhills. The lower forms, such as A. trifida. A,
arbuscula, A. rigida, and A. spinescens, might well be regarded as half shrubs.
They are more or less widely distributed, but their contact with grassland is
more local. In CaUfomia, fragments of savannah composed of Artemisia
calif omica and Stipa indicate a similar relation between sagebrush and grass-
land. This appears to have been true formerly of Adenostoma as well, but the
observed contacts with Stipa grassland are as yet too few for certainty. In
the desert plains, Prosopis, often with Acacia or Celtis, is the characteristic
shrub indicator of overgrazing. It also extends northward in the short-grass
plains to southern Colorado and Kansas. It is perhaps the most typical of
all such indicators, owing to its height and the ready dissemination of its seeds
by cattle. Quercus virens, Q. breviloba, and Q. undulata, as well as other mem-
bers of the chaparral, take similar parts in the grassland of southwestern Texas
and adjacent New Mexico. The role of Yu,cca radiosa and macrocarpa as
indicators of overgrazing is somewhat less clear, but their constant occurrence
in the sandy grasslands of the Southwest and the connection between their
propagation and disturbance by cattle seem to leave little doubt of a similar
correlation (plate 77, b).
Annuals as indicators. — Annuals are tjrpically indicators of serious disturb-
ance, and hence serve to mark the existence of serious overgrazing when
abundant. They are the universal pioneers of secondary successions, and
they regularly disappear in the course of development. When the disturb-
ance is continuous or recurrent, they may persist for years, but their serai
nature is readily disclosed by protecting an area. In a few cases they become
suppressed by the perennials and continue as a dwarfed ground layer. In the
Southwest the winter rains pennit a characteristic development of annuals,
which complete their growth and mature their seeds before the perennial
communities of the summer become controlling. Annuals usually first
appear in spots denuded by tramphng and extend from these throughout the
community in proportion to the degree of overgrazing. Their mobility is
often very great and they may take more or less complete control of a badly
overgrazed range in a few years. Indications of varying degrees of over-
grazing are given by differences in species as well as in density and vigor. The
first annuals to appear are native specie^, or subruderals, which are given a
chance to spread or develop because of the trampling and overcropping of the
climax dominants. These often give way to more vigorous subruderals, or
they become mixed with introduced weeds or ruderals, and are sometimes
302
GRAZING INDICATORS.
completely replaced by them. This is usually only when the disturbance
has been long continued and the supply of ruderals maintained by the presence
of man. In the case of complete replacement, such as by Avena or Bromus,
fire has often played an effective part. When more palatable species have
disappeared, annuals often furnish considerable grazing, though it is usually
inferior in all respects to that afforded by the climax dominants displaced.
Avena fatua is an exception to some extent, while in the Southwest the winter
annuals are extremely important in tiding over the cattle until the summer
grasses appear.
There are several hundred annuals which serve in some degree as over-
grazing indicators. The most important ones are found chiefly in the grass-
land climax and its contacts with the scrub formations. Some of these extend
upward into the grasslands of the montane zone, while the indicators of over-
grazing in the higher zones usually belong to the same or similar genera. A
few of the annual indicators extend more or less throughout the grassland
formation, but most of them occur in their particular region. Hence, it seems
most convenient to group them under the three heads, namely, prairies and
plains, desert plains, and bunch-grass prairies.
Prairie and plains indicators. — WTiile different species of annuals indicate
small differences in the degree of overgrazing, the abundance and height of
the plants is usually of greater importance. In addition, annual indicators
have received little quantitative study, and hence it is possible only to list
them in the general order of their importance. Some of those listed are either
annual or biennial, and a few are typically biennial (plate 78, a).
Plantago patagonica.
Festuca octoflora.
Hedeoma hispida.
Lepidium intermedium.
Lepidiimi alyssoidea.
Lepidium ramosum.
Lappula texana.
Verbena bracteosa.
Helianthua petiolaria.
Helianthus annuus.
Erigeron canadensis.
Erigeron divergens.
Erigeron ramoaus.
Chenopodium leptophyllum.
Chenopodium album.
Eriogonum annuum.
Eriogonum cemuum.
Desert plains indicators. — These fall into two groups, depending upon their
time of appearance. The sunmier annuals correspond to those listed above.
They occur with the grasses, and hence are a more exact measure of over-
grazing than the winter annuals. Most of them are distributed throughout
the region, but are more typical in New Mexico. The winter annuals de-
velop most abundantly in overgrazed areas also, but they finish their growth
before the grasses appear and hence indicate conditions of the previous year.
They are characteristic of southern Arizona and adjacent Mexico. The most
important ones, such as Plantago fastigiata, EschschoUzia mexicana, Lesquerella
gordoni, Lejyidium lasiocarpum, Pectocarya linearis, etc., often form a dense
cover and are invaluable for spring grazing (plate 78, b).
Eragrostia pilosa.
Eragroatis major.
Ambrosia artemisifolia.
Salsola kali.
Solaniun roatratum.
Argemone platyceraa.
Dysaodia pappoaa.
Hordeum jubatum.
Schedonnardus texanus.
Munroa aquarroaa.
Euphorbia marginata.
Croton texensia.
CoUomia linearis.
Verbesina encelioidea.
Orthocarpus luteus.
Polygonum aviculare.
Polygonum ramosiasimum.
Aater tanacetifolius.
Aster canescens.
Phacelia heterophylla.
Allionia linearis.
Cassia chamaecriata.
Coreopsis tinctoria.
Salvia lanceolata.
Lupinus pusillus.
Lotus americanus.
Draba caroliniana.
Myosurus minimus.
Androsace occidentalis.
Pectis angustifolia.
Sophia pinnata.
Phyaalia lobata.
Solanimi triflortun.
CLEMENTS
PLATE 77 «V
A. Opuntia poli/dcantha imlicatinn ovcijiuizing in mixed pniiric, Cjucrnsey, Colorado.
B. Prosopis and Calliandra indicating overgrazing in desert plains, Santa Rita Reserve,
Tucson, Arizona.
OVERGRAZING.
303
Ariatida bromoides.
Bouteloua aristidoidea.
Bouteloua polystachya.
Boerhavia torreyana.
Boerhavia intermedia.
Kallatroemia grandiflora.
Kallatroemia parviflora.
Plantago fastigiata.
Eachscholtzia niexicana.
Lesquerella gordoni.
Lepidium laaiocarpum.
Pterocarya linearis.
Bowlesia lobata.
Plagiobothrya arisonicus.
Amsinckia tessellata.
Sophia pinnata.
Summer Annuai^.
Kallatroemia brachyatylia.
Kallatroemia hirautiaaima.
Cladothrix lanuginoaa.
Croton corymbuloaua.
Solanum elaeagnifolium.
Tribulua terreatris.
Portulaca oleracea.
Winter Annuals.
Daucua pusillua.
Erodium cicutarium.
Erodium texanum.
Phacelia diatana.
Phacelia crenulata.
Lupinua aparsiflorus.
Thelypodium lasiophyllum.
Thyaanocarpua curvipea.
Lotus humiatratus.
Haplopappua gracilis.
Eriogonum abertianum.
Eriogonum polycladum.
Pectis angustifolia.
Pectia proatrata.
Chloria elegana.
Eragrostia piloaa.
Malacothriz aonchoidea.
Malacothrix fendleri.
Oenothera primaveria.
Calandrinia mensieaii.
Baeria graciiia.
Lappula texana.
Featuca octoflora.
Gilia graciiia.
Salvia columbariae.
Bunch-grass prairie indicators. — The most remarkable development of
annual indicators of overgrazing has taken place in CaUfomia. This is un-
doubtedly a consequence of its early settlement, together with its mild cU-
mate and winter rainfall. In addition to a large number of summer and winter
annuals derived from the native vegetation, the most widespread and typical
indicators are European weeds, which are nearly all grasses. Many of these
were probably introduced from Europe during the period of Spanish occupa-
tion, and spread rapidly as a result of overgrazing and fire. These agencies
would have first brought about the replacement of the native Stipas, but
sooner or later fire and clearing would have caused weeds to spread through
much of the chaparral as well. This problem of successive invasions and
replacements is now under investigation by means of permanent protected
quadrats. Meanwhile, the conclusions reached by Davy (1902:38) afford
the best sunmiary of the probable course of development (plate 79) :
"1. The primitive forage plants were the 'bunch-grasses' (Danthonias,
Stipas, Melicas, Poas and perennial Festucas), with annual and perennial
clovers, wild-pea vines and wild sunflowers; these were much more abundant
in former times than now, and on account of their palatableness they largely
disappeared with overstocking.
"2. With the advent of white settlers and their domestic animals, wild
oats (Avena fatua) and alfilerilla {Erodium cicutarium) took possession of the
country; these increased in relative abundance as the native forage plants
became scarce; as the latter diminished in quantity, the cattle took to eating
the former until they in hke manner succumbed, while other plants took their
place.
"3. Small barley grass (Hordeum maritimum gussoneanum), squirrel tail
(Festuca myurus), and soft chess (Bromus hordeaieus) were among the next
weedy introductions; the two former, when in a maturing condition being
disUked by cattle, have had a chance to spread and cover the ranges; but
cattle having acquired a taste for soft chess, it is being kept in check, if not
diminishing, on closely grazed ranges.
"4. A third immigration is now taking place, in which musky alfilerilla
(Erodium moschatum), broncho grass (Bromus maximus gussont), barley grass
(Hordeum murinum, locally called fox-tail), tacalote (Centaurea melitensis),
hawkbit (Hypochaeris glabra), bur-clover (Medicago denticulata) , and other
304
GRAZING INDICATORS.
weeds are establishing themselves along the roadsides and around ranch
houses. Of these, the bur-clover and musky alfilerilla have some forage
value. Barley grass is eaten green in the spring before heading out, but
afterwards becomes one of the most objectionable weeds for a stock range.
The other aliens are destined to cause irreparable injury to the ranges unless
kept in check and prevented from becoming firmly established. "
With few exceptions the species listed below are summer annuals. The
winter annuals of southern CaUfornia are largely those noted for the desert
plains, but they are here relatively unimportant. It should be borne in
mind that, while the indicators given originally denoted overgrazing, some of
them, such as Avena and Erodium, have become valuable forage plants as a
consequence of the displacement of the native bunch-grasses, and in turn their
overgrazed condition is indicated by still more weedy invaders.
Avena fatua.
Bromus maximus.
Bromus rubena.
Bromus hordeaceus.
Erodium cicutarium.
Erodium moschatum.
Centaurea meliteusis.
Medicago denticulata.
Hypochaeris glabra.
Hypochaeris radicata.
Eriogonum vimineum.
Eriogonum nudum.
Lupinus micranthus.
Lupinua affinis.
Lupinus truncatus.
Trifolium microcephalum.
Grass Indicators.
Bromus tectonim.
Festuca myurus.
Hordeum maritimum gusso-
neanum.
Herb Indicators.
Trifolium amplectens.
Trifolium gracilentum.
Trifolium tridentatum.
Medicago lupulina.
Melilotus indica.
Raphanus raphanistrum.
Eryngium vaseyi.
Hemizonia fitchii.
Hemizonia clevelandii.
Madia exigua.
Madia dissitiflora.
Lotus strigosus.
Hordeum murinum.
Polypogon monspeliensis.
Lamarkia aurea.
Trichostema lanceolatum.
Plantago patagonica.
Epilobium paniculatum.
Phacelia heterophylla.
Lagopbylla ramosiasima.
Ptilonella scabra.
Orthocarpus purpurascens.
Centaurea cyanus.
Eremocarpus setigerus.
Lithospermum ruderale.
Navarretia leucophaea.
Great Basin indicators. — These are limited in the present discussion to
the annuals that spread over the grassy intervals of the sagebrush, especially
along the northern border where it is mixed with Agropyrum spicatum. While
a number of the annuals of the preceding list assume this role along the
western edge, three species of introduced weeds are more important than all
others combined; these are Bromiis tedorum, Sisymbrium altissimum, and
Lepidium perfoliatum. These occur singly or variously mixed. The most
extensive community is that of Bromus tedorum, while the mixed community
of Bromus and Sisymbrium is almost equally important. Lepidium is most
abundant in the Northwest, but is rapidly spreading to other regions. While
they owe their establishment originally to overgrazing, fire is a large factor in
their rapid spread. They have now replaced the native grasses and herbage
almost completely over thousands of square miles, and have reduced the
grazing value practically to that of the sagebrush alone. Bromus is the only
one with any real value, and this is frequently slight. It furnishes some graz-
ing for sheep in the spring, but quickly becomes dry and nearly worthless.
Overgrazing in the past. — The condition of the great ranges of the prairies
and plams before the settlement of the West and the effect of settlement upon
the grasses have long been mooted questions. It has frequently been assumed
that certain grasses have disappeared with the coming of the early settlers
CLEMENTS
PLATE 78 _ ,.
A. A summer annual, Euphorbia marginatn, inilic-atiu};; coniplL-lc oviTuraziag m a i):ujture,
Fountain, Colorado.
B. A winter annual, EschicholUia mexicana, Indicating both overgraiing of grasses and
grazing capacity, Santa Rita Reserve, Tucson, Arizona. «
OVERGRAZING. 305
and that others had entered to take their place. For example, it has been
the almost universal opinion of farmers and stockmen that bufifalo grass
vanished from the prairies with the going of the buffalo and that the blue-
stems had come in from the East to replace it. This opinion has been
shared to a large degree by scientific men. Bessey (1887: 216) early noted
the general relations of the grasses to cultivation and fire :
" Several entirely distinct species are popularly known as buffalo grass. All
are, however, short grasses, unfit for making into hay, and although appar-
ently quite nutritious, they supply so small an amount of food per acre that
as the land becomes more valuable the farmer can not afford to retain them.
But even should he wish to retain them, he can not; for they are unfitted to
battle successfully with bluegrass and white clover, with the bluestems and
rank weeds which always spring into prominence upon the prairies when the
settler stops the annual prairie fires. Moreover, they can not endure the
close cropping and tramping to which they are subjected when the land is
inclosed and used for regular farming purposes. Already the genuine buffalo
grass (Buchloe dadyloides) has practically disappeared from the eastern third
of the State. Of course I know very well that there are patches of it here
and there in these older counties; it may be found in such patches within a
mile or two of the capitol building; but these Httle patches are as nothing when
compared with its for - ^r extensive distribution. A second grass commonly
known by the name of buffalo grass (Bouteloua oligostachya) is fast following
the first.
"Buffalo grass, Bulbilis dadyloides, is widely spread throughout the Sand-
hill region. This valuable forage plant is rapidly disappearing. Its hard-
awned fruits were especially suited for distribution by the buffalo, and since
these have disappeared and the prairie fires are no longer allowed to sweep
the plains, the buffalo grass is being rapidly choked out by the ranker species.
It is the most valuable native pasture grass, but is rapidly passing toward
extinction" (1893:288).
Webber (1890: 37) states that "the buffalo grass, once the prevailing plant,
is, in eastern Nebraska, found only in small patches, and is fast becoming
rare, " while Crandall (1890: 136) says that "this, the true buffalo grass, which
once formed so large a portion of the prairie turf, is now found in this region
only in isolated patches. "
Pound and Clements (1898 : 246, 1900 : 350) found evidence to indicate
that the buffalo grass had disappeared only where the land had been broken
for cultivation.
"The buffalo grass was, until recently, supposed to have once covered the
greater portion of Nebraska; its disappearance has, as a matter of sentiment,
been connected with that of the buffalo. That such a supposition is entirely
erroneous is beyond a doubt. The patches of buffalo grass, which are found
scattered here and there over the State, are to be regarded as intrusions rather
than stragglers left by a retreating species. "
In 1897, Williams wrote:
"This famous range grass is still quite abundant in the regions west of the
James Valley in both Dakotas. It is by no means as rare as most people
suppose, being frequently overlooked on account of its similarity to certain
of the grama grasses and because it seldom fruits in any great quantity. " (14)
306 GRAZING INDICATORS.
In speaking of the changes accompanying overgrazing in the Texas prairies,
Smith (1899: 28) makes the following statement:
"Before the ranges were overgrazed, the grasses of the red prairies were
largely bluestems or sage grasses (Andropogon) , often as high as a horse's back.
After pasturing and subsequent to the trampling and hardening of the soil,
the dog grasses or needle grasses (Aristida) took the whole country. After
further overstocking and trampling, the needle grasses were driven out, and
the mesquite grasses {Hilaria and Bulhilis) became the most prominent species.
The occurrence of any one of these as the dominant or most conspicuous grass
is to some extent an index of the state of the land and of what stage in over-
stocking and deterioration has been reached. There is often a succession of
dominant grasses in nature through natural causes, but never to as marked an
extent as on the cattle ranges during the process of deterioration from over-
grazing. On overstocked lands there is uniformly an alternation of needle
grass and mesquite at short intervals, unless the overstocking is carried too
far, when these perennials give way to annuals and worthless weeds."
Smith (1893: 281) has suggested part of the explanation as to the varying
opinions upon the condition of the range since the disappearance of the buffalo,
in discussing the Sandhills of northern Nebraska:
" The theory is quite commonly advanced by stockmen and others interested
in the country that the sandhills were quite bare of vegetation at a compara-
tively recent date and have only commenced to be grassed over since the days
of the Indian and buffalo. I doubt very much the correctness of this idea.
We have accounts of the sandhills written in the early part of this century
which gave the salient features of the landscape about as they exist today.
The region is one where physical conditions may vary greatly in a term of
years. We were told by stockmen who have been located in the hills for a
long time, that the soil is very susceptible to drying, that the lakes sometimes
entirely disappear during periods of drought, and that one year a crop of hay
may be cut where the year before there was a fine body of water. In wet
years the vegetation of the valleys, which is always more luxuriant than that
of the drier hills, may extend far up their slopes, while in dry years opposite
conditions may prevail. If one sees the sandhill region for the first time
when bare of vegetation in winter or early spring, or after the drying out of
July and August, one may easily get the idea that the sandhills have never
been grassed over. When the freshening up comes after the rains, he may
conclude that they are becoming turfed over for the first time. " .
Wilcox (1911 : 26) has compiled the opinions and statements of a very large
number of explorers and travelers with reference to grazing conditions over
the prairies and plains during the past century. These show great divergence,
and many of them are directly contradictory. On the whole, however, they
support his general conclusion that the range has not changed essentially,
whatever its fluctuations may have been.
"The present condition of the Great Plains is essentially the same as that
described by early travelers. The prevailing grasses are still the buffalo and
grama, of low habit. The immense number of buffalo in the early days and
later of cattle have not been sufficient to produce any marked change in the
character and amount of range forage upon this area. " (47)
"To one who is famiUar with the present range conditions of the arid west
as a whole, or any particular section of it, these statements must indicate a
A. Slipa seligera indicating the original bunch-grass prairie, Fresno, California.
B. Avena fatua on bunch-grass hills, Rose Canyon, San Diego, California,
OVERGRAZING. 307
striking similarity in the appearance of the range in former times and at pre-
sent. So far as the numerous statements which have been consulted indicate,
the general appearance and conditions of the range country have changed
but little since the time when they were first explored by white men. " (45)
Succession and cycles. — The range studies of the past six years have fur-
nished a complete explanation of the sharp difference in views as to the past
conditions of overgrazing. There is no question that Smith, Wilcox, and others
are correct in stating that there has been no essential permanent change in the
composition and structure of the great grassland associations. On the other
hand, it is equally certain that there have been great local or temporary
changes, which critically reduced the carrying capacity, or actually destroyed
the climax community. A broad view of the grassland climax would warrant
the opinion that it had never undergone serious change, while the observation
of a particular range would justify the statement that the original grasses
were completely destroyed. This apparent contradiction is readily explained
by the student of succession, as is likewise the fact that one observer may
find good grass in the same locality where another had seen a barren waste.
It is obvious that an area destructively overgrazed would be abandoned by
grazing animals for an untouched portion of the same climax, and that the
bare area would then pass through the various stages of succession to again
reach the climax in 20 to 30 years. This is recognized by Wilcox (31) in
connection with the overgrazing caused by buffalo:
"These accounts indicate what would naturally be expected, viz, that
where buffaloes congregated in immense herds the grass was totally destroyed
for the time and the ground was much cut up or packed down, according as
dry or wet weather prevailed. The result of such accumulations of large
herds was the apparent total destruction of the grass. It should be remem-
bered, however, despite the fact of apparent total destruction wrought by the
buffalo along the Une of their migration and during their close association at
breeding seasons, the range recovered so that the evidence of their destructive
grazing was entirely lost within a few years. This fact indicates also the
possibility of range improvement at present."
While great variations in the condition of the range can be explained by
local overgrazing and subsequent recovery as a consequence of succession,
further explanation can be found in the action of climatic cycles. The chief
effect of the dry phase of the cycle was found in the impetus given to over-
grazing, while the wet phase favored successional processes and hastened
recovery. Climatic changes also serve to explain many of the contradictory
statements as to the same locaUty. Even under ordinary conditions of graz-
ing, the same area would be strikingly different during a drought period and
the preceding or foUowmg wet phase. If it were visited at a time when
drought and overgrazing coincided, and then at one in which more or less
complete recovery were followed by a wet period, no greater contrast could
be imagined. Moreover, while the effects of overgrazing were usually local,
those of drought j)eriods were general for the most part, and hence climatic
cycles are especially important in furnishing the explanation of the discordant
statements of explorers. The effect of drought in changing the dominants
of the range is illustrated by the grassland south of the Niobrara River. In
1893, this was dominated by Aristida purpurea and A. basiramea as a result
of drought and overgrazing, while by 1915 the awn-grasses had been com-
308 GRAZING INDICATORS.
pletely replaced bj' the mixed prairie of tall-grasses and short-grasses, which
was undoubtedly the original cUmax.
Relations of tall-grasses and short-grasses. — The explanation of the ap-
parent replacement of buffalo grass by the bluestems, as well as the general
replacement of tall-grasses by short-grasses, has been found in the effect of
grazing upon such a mixed community. This effect is naturally increased by
drought periods, and it is especially in connection with such periods that the
impression of a permanent change arises. Mixed prairies of tall Andropogon
or Stipa spariea with short Bulbilis and Bouteloua are found in central Ne-
braska and Kansas, and also in the eastern Dakotas, while in western Nebraska,
the Dakotas, Montana, and Wyoming they consist of Agropyrum or Stipa co-
mata with Bulbilis, Bouteloua, or both of them. It is in these regions that the
view has been more or less general that the tall-grasses have replaced the short-
grasses as a consequence of the disappearance of the buffalo and the coming
of man. This view has been held by so many keen observers, both practical
and scientific, as to indicate that it has an actual foundation of fact. This
has proved to be the case, but it was impossible to recognize the basic facts
until the principles of successions were brought into use. A particular study
of the effects of overgrazing upon mixed prairie with respect to wet and dry
periods has been made since 1914. Thi> quickly revealed the fact that the
short^rasses were often completely hidden by the tall ones in times of unusual
wetness, such as 1915, and that overgrazing regularly brought the tall-grasses
to the point of apparently complete disappearance during drought periods.
These facts have been repeatedly confirmed in adjacent grazed and ungrazed
areas throughout the mixed prairie from North Dakota to Kansas, and they
are regarded as furnishing a complete explanation of the apparent disappear-
ance of the short-grasses and the invasion of the tall ones.
There is general agreement as to the damage done to the range by buffalo,
as well as to the enormous number found on the prairies and plains from 1865
to 1875, when settlement was taking place most rapidly. In fact, the appli-
cation of the term buffalo grass to the short-grasses is in harmony with the
action of overgrazing in suppressing or destroying the tall-grasses. The
westward movement of the buffalo and their decrease in numbers coincided
with the incoming of settlers and the decrease of prairie fires. The im-
mediate result was renewed growth of the tall-grasses, especially Andropogon,
in areas where it had not been completely killed, and its invasion into others
where it had disappeared. This tallies with the statement that the blue-
stems followed in the wake of the settlers, and drove out the buffalo grasses.
The error involved in this is best illustrated by the statements of Bell (1869:
1:26,43):
"Before we reached Sahna, trees had become very scarce; but as we moved
farther, the short tender buffalo grass gradually appeared — at first only here
and there, but at last it abounded everywhere; and ever and anon we crossed
the well-beaten path of the monarch of the plains. Doubtless no grass could
bear so well the heavy tramp of thousands of buffalo continually passing over
it; but it is a good thing for the land that, as settlers advance and domestic
herds take the place of big game, the coarser, more vigorous, and deeper-
rooted grasses destroy it and take its place. These new-comers grow with
great luxuriance, yielding very fine hay; and at the same time loosening the
sod, opening up the soil, and retaining the moisture in the ground. "
CLEMENTS
PLATE 80
A. Mixetl prairie of Andropogon-BouU.luua laceimsa, and BuUnlis-Bouieloua ffracilis, Wilson,
Kansas.
B. The same prairie in an overgrazed pasture, showing pure short-grass sod, Wilson
Kansas. '
OVERGRAZING. 309
The route followed by Bell from Manhattan to Salina, Fort Harker, and
Hays was retraced in 1918 for the express purpose of determining the relations
of the bluestems and buffalo grasses. Both buffalo grass and grama were
found on the ridges and upper slopes about Manhattan, though they were
secondary to the tall-grasses in importance. This relation continued west-
ward to the Dakota hills about Kanopolis, where the short-grasses became
more abundant, equaling the tall-grasses, and mixed or alternating with them.
This general condition continued to Hays, but with the short-grasses increas-
ing in abundance. Beyond Hays, they soon became controlling, though the
rough bluffs along the streams maintained their mixed cover. Throughout
the region from Kanopolis to Hays, overgrazed pastures exhibited a pure
short-grass cover, while protected or less grazed areas showed a mixture of
tall-grasses and short-grasses. It is clear that the short-grasses could not
have been replaced by the tall ones as a consequence of settlement, and then
have reentered the same areas under conditions of increasing cultivation. The
obvious explanation is that while they have been associated in the mixed
prairies for thousands of years, the tall-grasses were kept down by the buffalo
in the zone of concentration resulting from advancing settlement. They
reappeared with the going of the buffalo, and the disappearance of the buffalo
grasses was nothing more than their being overtopped by the bluestems
(plate 80).
Drought periods doubtless played a part in the behavior of the bluestems
and buffalo gra ses, as they certainly did in the mixed prairies of Nebraska
and the Dakotas. In 1893 the gumbo plains north of the Niobrara River
were dominated chiefly by Bulhilis and Bouteloua gracilis, as a consequence of
excessive drought and overgrazing. In some places a pure cover of BuUrilis
stretched for many miles, almost unbroken by societies. This region has
been revisited several times from 1915 to 1918. The stretches of buffalo grass
and grama have disappeared, and in thei • stead is a mixed prairie of Andro-
pogons, Agropyrum, and Stipa, below which is a more or less well-developed
layer of short-grasses. The drought of 1893-95 had a similar effect upon the
mixed prairies of western Nebraska, in which Stipa was the most conspicuous
dominant. This disappeared so completely, leaving a pure short-grass cover,
that it was regarded as a new grass invading for the first time when it re-
appeared in great quantity during the rainy years of 1897-98. Williams
(1898 : 54) has shown that dry periods have the same effect upon the appear-
ance of Agropyrum in the mixed prairies of the Dakotas. It was thought
that the tall-gra-sses might again disappear apparently during the drought
period of 1916-18, but this took place only in overgrazed pastures, showing
that overgrazing is an essential feature.
Overgrazing cycles. — The existence of cycles of overgrazing is beyond ques-
tion, and it is possible to recognize several kinds. The simplest and shortest
is brought about by such destructive overgrazing that the area will no longer
support the animals upon it. In the case of wild animals, such as the buffalo,
horse, etc., the herds sought a new range, while on restricted areas the cattle
died from starvation or were shipped out. In either event the grasses were
given an opportunity to regenerate, or in the worst cases the processes of
succession brought about a gradual return to the original conditions Such
overgrazing cycles correspond to the cycle of a subsere, and are relatively
310 GRAZING INDICATORS.
short, lasting 10 to 15 years on an average. Such cycles also occur when
overgrazed or worn-out pastures are permitted to "rest." A much more
important cycle is that of the double sun-spot period, namely, 22 to 23 years.
This is due to the fact that overgrazing has much more serious consequences
during maximum periods of drought, such as 1871-73, 1893-95, and 1916-18.
The effects upon the range and the herd are much more marked than when
overgrazing alone is concerned, but an enforced period of rest ensues, during
which successional processes bring about the restoration of the original grass
cover, unless again disturbed by overgrazing. It is this cycle which, in its
beginning, has been especially disastrous to the grazing industry of the West,
just as the subsequent and inevitable regeneration through succession offers the
solution of all overgrazing problems. In addition, there are major cycles of
overgrazing, such as are involved in the permanent migration of great herds
from one region to another, or in the appearance of new species or groups of
grazing animals. Some such cycle must have marked the reintroduction and
spread of the horse over the plains of the Southwest. The consideration of
such cycles is beyond the scope of the present treatment, and is reserved for
another place.
The recognition of past and present cycles of overgrazing is of great practical
importance. Its greatest value Ues in the certainty that a range will return to
its normal condition once it is given a chance to regenerate. It also empha-
sizes the fact that it usually takes several to many years to really "wear out"
a range, and that the rate of recovery is roughly proportional to the length
of the period of overgrazing. All the statements agree as to the excessive
damage done to the range by buffalo, but it seems certain that the more or
less complete rest which followed brought about a fair degree of recovery in a
few years. This is not an excuse for overgrazing, since the latter always
involves a distinct economic loss, the amount depending upon the period
and the intensity, but it does make it clear that all overgrazed ranges can be
certainly and greatly improved by proper rest or rotation. This is the basis
of all range improvement, as is shown in some detail in the next section.
RANGE IMPROVEMENT.
History. — The first proposal to improve the ranges of the West by rotation
grazing was made by Smith (1895:323), although suggestions for their im-
provement by planting cultivated species had been m^e by Bessey (1887,
1893, 1897), Georgeson (1895), and others. It is probe^le that the first
suggestion as to the good effects of resting the range came from the ranchmen
(Williams, 1898: 72), and it is not impossible that the practice of the buffalo
in leaving overgrazed regions had also led to this conclusion. In his two
papers of 1895 and 1899, Smith outlined the major features of range improve-
ment, while at the same time Williams (1897, 1898) proposed those which had
to do with the artificial treatment of the range. The system advanced by
Smith comprised (1) proper stocking, (2) rotation, (3) adequate water de-
velopment, (4) destruction of rodents, (5) destruction of weeds and cacti
(6) disking the soil, (7) sowing and planting, (8) provision of forage, and (9)
winter protection. He was also the first to organize definite grazing experi-
ments to determine carrying capacity and the effects of rotation. The method
suggested by WilUams involved (1) proper stocking, (2) harrowing the soil,
RANGE IMPROVEMENT. 311
(3) top-dressing with stable manure, (4) sowing wild or cultivated forage
plants, (5) keeping weeds mowed, (6) water development, (7) rest. Since the
work of these two pioneers in range improvement, the subject has been dis-
cussed more or less completely or from various sides by Bentley (1898, 1902),
Nelson (1898), Shear (1901), Griffiths (1901, 1902, 1903, 1904, 1907, 1910),
Davy (1902), Cotton (1905, 1908), Wooton (1908, 1915, 1916), Sampson
(1908, 1909, 1913, 1914, 1918, 1919), Jardine (1908, 1911, 1912), Thornber
(1910, 1914), Wilcox (1911), Barnes (1913), Darlington (1915), Barnes and
Jardine (1916), Potter (1917), Jardine and Hurtt (1917), Clements (1917,.
1918, 1919), Sarvis (1919), and Jardine and Anderson (1919).
The first experimental study of grazing was carried on at Abilene and
Channing, Texas, from 1899 to 1901 by Smith and Bentley (p. 20). Experi-
ments under practical grazing conditions have been made on the Jornada and
Santa Rita Range Reserves of the Forest Service for the past seven years.
Intensive studies in smaller pastures and hence under closer control have
been carried on by the Office of Dry-Land Agriculture at Mandan, North
Dakota, since 1915, and at Ardmore, South Dakota, since 1918. Both the
field and experimental studies have conclusively demonstrated the essentials
of range improvement and have made it ik)ssible to outline a complete system
based upon investigation as well as practice.
Prerequisites. — In addition to the actual processes concerned in improving
the range, certain factors are prerequisite to any hnprovement or necessary
for the best results. By far the most important of these is adequate control,
without which improvement is all but impossible. It is immaterial whether
control is secured through ownership or leasing, provided it permits fencing.
However, leasing has the indirect advantage that it enables the State to exact
certain conditions as to utilization. The value of control in preventing over-
stocking and permitting rotation is obvious. Next in importance is a practi-
cal appreciation of the inevitable recurrence of dry and wet periods and their
critical effect upon the range. It is imperative that the ranchman be pre-
pared to reduce the pressure upon his range as the dry phase of the climatic
cycle approaches and that he be ready to take full advantage of the excess
carrying capacity of the wet phase. In fact, the whole system of improve-
ment must be focussed upon the destructive effect of overgrazing in dr>^ years
and the possibility of greater utihzation and of successful sowing and planting
during wet years. Furthermore, there must be some recognition of the
universal processes of succession and their importance in regeneration. It is
necessary to take into full account the fact that destructive overgrazing,
trampling, and other disturbances will destroy the grass communities and
make place for one of weeds. Even more important is the recognition of the
fact that weed communities will be maintained indefinitely by continued
overgrazing or disturbance, or that they will slowly give way to the returning
grasses if the area is protected for a time. In short, an elementary under-
standing of successional processes furnishes a tool for manipulating the graz-
ing cover more or less as desired. Finally, a trustworthy idea of the con-
dition and tendency of the range is impossible without adequate methods of
measurement. In practice, such methods can best be supplied by indicator
plants, and by a careful check upon the condition of animals when they enter
and leave the range. In both investigation and demonstration, however,
312 GRAZING INDICATORS.
more accurate measurements are necessary, especially in connection with the
varying carrying capacity of wet and dry periods. Changes in composition
and variations in production year by year can be determined only by the
use of permanent quadrats. Some of these are charted, while others are
clipped and the herbage weighed. The most significant measurement, how-
ever, is that furnished by weighing the individual animals from month to
month, or at the beginning and end of the season.
Essential factors. — Range improvement may be effected in some degree by
any one of a large number of processes. Thoroughgoing improvement, how-
ever, must take them all into account, in so far as they are concerned in a
particular range. It is obvious that some of these, such as proper stocking
and rotation grazing, are of universal importance, while others, such as the
eradication of prairie-dogs or poisonous plants, apply only to certain ranges.
The essential features of the complete system of range improvement proposed
here are: (1) proper stocking; (2) rotation or deferred grazing; (3) eradication
of rodents, poisonous plants, weeds, etc.; (4) manipulation of the range by
clearing, burning, etc.; (5) improving the cover by sowing and planting; (6)
forage development; (7) water development; (8) herd management. Con-
tributing factors are found in classification and range surveys, the economic
aspects of ranch management, and an adequate land system. Practically all
of these have been regarded as more or less essential to range improvement
since the first proposals of Smith, 25 years ago, and the present treatment as-
sumes only to correlate them more closely and to work some of them out in
greater detail. The distinctive features of the system are the use of climatic
cycles and succession as universal bases, the employment of indicator plants,
the use of inclosures and exclosures together with permanent quadrats as
measures, and the development of new methods of manipulating and modify-
ing the range, especially in the production of mixed grazing types.
Proper stocking. — ^The primary object of range improvement is to secure
and maintain the maximum carrying capacity. The chief factors in this are
proper stocking and rotation grazing. The optimum degree of stocking, how-
ever, can be determined only by actual trial accompanied by measurement of
the results. Such trials can be made by the ranchman himself wherever he
has control of his range, but until their necessity becomes generally recognized
they must be made for the different grazing types by the experiment stations
and similar agencies. The investigation of carrying capacity by actual
grazing test can be made by either the extensive or intensive method. The
first is more practical on ranges as they exist; the latter is more accurate and
demands a greater equipment. The results of an extensive study of carry-
ing capacity on the Jornada Reserve have been brought together by Jardine
and Hurtt (1917: 12). Eight different grazing types occur on the reserve
and the carrj'ing capacity varies greatly for the different communities. Per-
manent quadrats were employed to determine variations in yield from year
to year, as well as the rate of increase under rotation or protection. Since
both rotation and reserve grazing were necessarily practiced, no definite
studies were made of the basic carrying capacity under full grazing for the
entire season. Such studies are possible only under the intensive method
and in an essentially uniform type. Their great value lies in making it pos-
RANGE IMPROVEMENT.
313
sible to check the assumed optimum carrying capacity by rates of grazing
which reveal both over- and under-utilization, and in demonstrating the
additional gain resulting from rotation methods. Installations for the inten-
sive study of carrying capacity and rotation grazing have been made by the
Ofl&ce of Dry-Land Agriculture at Mandan and at Ardmore. Both are
located in the mixed prairie, the one in Stipa-Bouteloua, and the other in
Bulbilis-Agropyrum-Bouteloua. Since the methods are essentially alike, it
will suffice to describe briefly the experiments at Mandan, which have been
under way since 1915.
Reserve pasture
ao acres)
8 K
164 acres
T.
U
80 acres
Q
70 acres
70 A. rotation
»T.
70 acres
le )n feet
560 ~ Tiw
Fio. 22. — Pastures for the intensive study of carrying capacity and rotation
grazing, Mandan, North Dakota. After Sarvis.
There are four pastures for the investigation of carrying capacity under
continuous grazing, two for rotation grazing, a reserve pasture, and one for
the study of hay development (fig. 22). At Ardmore two pastui-es are de-
voted to continuous grazing and the same number to rotation. The four
pastures contain respectively 30, 50, 70, and 100 acres. Since each pasture
is grazed by 10 two-year-old steers, the corresponding rates of grazing are
1:3, 1:5, 1:7, and 1 : 10. Each pasture contains an exclosure termed an
isolation transect (fig. 23), which is 300 feet long and 60 feet wide. This con-
sists of three strips, of which the central one, P, serves as permanent transect
for annual comparison with the grazing and regeneration transects on either
side, as well as for the installation of permanent quadrats of various types.
One unit of the grazing transect, G, is unfenced for each year of the climatic
cycle, while one of the regeneration transect, R, is fenced for each successive
314
GRAZING INDICATORS.
year of the cycle. The central position of the permanent transect permits
ready comparison between the protected area and those fenced and unfenced
for each successive year, as well as actual measurement in all three areas by
means of chai'tand cUp quadrats. Similar quadrats are located in the open
pasture, thus completing the measurement of all areas year by year. It is
evident that the grazed transect will also show in series the effects of unfencing
for 14, 13, etc., years down, to 1, and- that the regenera-
tion transect will show those of fencing for a similar series of
years. Finally, special quadrats are located in the transect
to reveal the effects of burning or clipping at various times
and intervals.
With reference to the cattle to be used, it is necessary
that they be of the same breed, age, and class, and in as
nearly the same condition as possible. It will probably
prove desirable to determine the carrying capacity of the
same grazing type for different species, as well as for dif-
ferent breeds, etc., but this will require pastures of the same
size and involves an expansion of the work which is un-
necessary at present. The cattle are weighed at the begin-
ning and end of the grazing season and at monthly intervals
during it. This is accomplished by means of four corrals, one
for each pasture, leading to the scales for weighing (fig. 24).
A special method of management has been developed for
handling the cattle in the pastures and at the times of weigh-
ing, the main details of which have been given by Sarvis
(1919). The detailed results of the experiment have not
yet been published, but the evidence furnished by the
various pastures, in terms of cover and indicator plants, has
been most striking (plate 81), and these have been verified
by the behavior and weights of the different herds.
Rotation grazing. — First suggested by Smith in 1895 and
begun experimentally by him and Bentley in 1899, rotation
grazing has been developed chiefly by the Forest Service
since 1910. The scientific basis for deferred and rotation
grazing was largely developed by Sampson (1908, 1909,
1913), and it has been appUed to actual grazing on the
national forests. It has had its most thorough demonstra-
tion on the Jornada and Santa Rita Range Reserves, but
especially on the former. Pastures for the study of rotation were installed
at the Mandan and Ardmore stations in 1918, but conclusive results can not be
expected for several years. Rotation grazing is an inclusive term which is
regarded as applying to all methods of alternate grazing and rest, partial or
complete. Deferred grazing is the type in which the pasture is completely
protected or only lightly grazed during critical periods in the life-history of
the chief dominants. This is usually the period of seed-production, but on
certain types it may fall at the opening of the growing season. Reserve
grazing is that in which a pasture is kept in reserve for emergencies, especially
those due to drought, or where the grazing during the season, though uniform,
is sufficiently light to permit a fair amount of seed to be produced.
G
P
R
1919
1918
1919
1920
1920
1921
1921
1922
1922
etc.
etc.
.
60 ft.
Fig. 23.— Isolation
transect for meas>
uring cyclic
changes in yield
under protection
and under grazing.
CLEMENTS
PLATE 81 O
A. Isolation transect in Slipo-Houkloua pasture, Mandan, North Dakota.
B. Isolation transect in Agropyrum-Bulbilis pasture. Anliimre, South Dakota.
RANGE IMPROVEMENT.
315
The classic experiment in rotation grazing is that carried on by the Forest
Service in cooperation with Mr. C. P. Turaey on the Jornada Reserve near
Las Cruces, New Mexico. This has been described in detail by Jardine and
Hurtt (1917: 28), and their conclusions as to range improvement by natural
revegetation are given here:
"Primarily as a result of (1) reducing the number of stock during the main
growing season of about four months — July to October — to about half of the
average number the area will carry for the year, (2) not overstocking during
the other eight months, and (3) better distribution of stock watering places,
grama-grass range on the Jornada Range Reserve has improved in three
years at least 50 per cent as compared with similar adjoining unfenced range
grazed yearlong.
60-acre pasture
lOO-acre pasture
/ Scales \
Corral leading:
to scales
Corral for 50 a.
4
40 ft.
SKed
7
■£)
KX
Corral
leading to
braiuling
chute
Plank corral for 100 a.and
for cutting out to wtigh
Tank
7
Corral for 80 a.
/
Corral for TO a.
40 ft.
Shed
<Wft.
74 ft
80-acre pasture
7D-acre pasture
Fio. 24. — Arrangement of corrals, bheds, and scales, Mandan, North Dakota.
After Sarvis.
"On fenced grama-grass ranges of the Southwest where the stock are car-
ried mainly on range feed throughout the year, light stocking during the
growing season is profitable. It will probably not reduce the total animaJ-
days feed furnished on a given area during the year, and will reserve feed for
the critical period from February to July, and later in case <rf prolonged
drought.
"Where the whole of a range unit is made up of grama or similar grass
about one-third of the area should probably be reserved for light grazing
during the growing season two years in succession. Each third in turn should
be given as nearly as practicable this amount of protection. By light grazing
is meant grazing by not more than half the average number of stock that the
area will carry for the year as a whole. "
316 GRAZING INDICATORS.
Rodent eradication. — Smith (1899: 15) was apparently the first to emphasize
the damage done by rodents to the range and to urge the systematic extermi-
nation of prairie-dogs and jack-rabbits. While much has been said and
written on the control and extermination of prairie-dogs in particular since
1900, effective campaigns against these and other rodents are recent develoj)-
ments. During the last five years especially, the Biological Survey has
carried on systematic and effective work in the eradication of both prairie-
dogs and ground-squirrels, in cooperation with various States, as well as with
the Forest Service and with private individuals (Bell, 1917; Lantz, 1918).
In additiMi, California has organized an extensive campaign through its
Rodent Control Section. It has also come to be recognized that jack-rabbits
are often exceedingly destructive to the range, and the work of Vorhies (1919)
has shown that the kangaroo-rats of the Southwest must also be included
among the major pests. While various methods have been used to extermi-
nate or control rodents, that of poisoning has become the standard, because of
its economy and efiiciency. However, it has become clear that complete
eradication is possible only through poisoning for two or three successive
seasons, and that re-immigration can be controlled only by dealing with large
and more or less natural areas and by the extermination of invading colonies
from time to time.
The absence of accurate knowledge as to the amount and kind of damage
done to the range by rodents, and especially of the rate and degree of recovery
in various types after eradication, led the writer to suggest the desirabiUty of
cooperative studies to the Biological Survey, the Forest Service, and the Uni-
versity of Arizona. As a consequence, fenced areas for such investigations
were established in 1918 in the Bouteloua-Aristida grassland of the Santa Rita
range reserve and in the Bouteloua gracilis climax of northern Arizona near
Seligmann and WiUiams. The latter were designed to study the recovery
after the eradication of prairie-dogs, while the former were to permit a more
intensive study with reference to jack-rabbits, and especially kangaroo-rats,
which had just been shown by Vorhies to cause even more serious damage.
A series of three exclosures was installed in the Bouteloua rothrockii-Aristida
calif omica type of the reserve (plate 82). The first was fenced against both
rodents and cattle, and the second and third against cattle alone, but differing
in that the rodents were killed out of one. A second exclosure was established
in the Bouteloua eriopoda-Aristida divaricata type, which was also fenced
against rodents and cattle. For the sake of a direct determination of the
amount of forage consumed by jack-rabbits and kangaroo-rats, two inclosures
were located in one of the best areas of Bauieloua rothrockii. In one of these
were placed two rabbits, in the other two kangaroo-rats. Permanent quad-
rats were located for measuring the effects in the various inclosures as well as
in the pastures by means of charting and cUpping. The critically dry sum-
mer of 1918 almost completely prevented the growth of grass and sunmier
annuals, and practically all quadrats contained less growth in the fall than in
the spring. The winter rains were nearly normal and so well distributed that
the growth of winter annuals was exceptional. As a consequence, the various
fenced areas showed striking improvement in total production over the
pastures. This was not only true of the cattle-proof exclosures, but of the
rodent ones likewise, proving that the rodents also take heavy toll from the
winter annuals as well (plate 82, b).
CLEMENTS
PLATE I
A. Rodent exclosuro sliowiriK combined effect of cattle and ro<ients on the crop of winter
annuals, cliiefly poppy {EschxchoUzta mexicana), Santa Rita Resor%e.
B. DifTerence in yield of poppies in rotient exclosure, cattle exclosure and pasture, Santa
Rita Reserve.
RANGE IMPROVEMENT. 317
Special studies were made of the life history and food habits of the kangaroo-
rat in particular, and the latter were found to have a decisive bearing upon the
dominance of the grasses (Vorhies, 1919). Burrows excavated in the winter
of 1917-18 showed that the kangaroo-rat stored large amounts of food and
that this consisted chiefly of the spikes of Bouteloua. Those excavated in
1918-19 exhibited no grass spikes, owing to their failure to form during the
drought of the preceding sunmier, but the bulk of the stored food consisted of
the crowns of Bouteloua rothrockii. When the size of the denuded area about
each burrow is taken into account, it is readily seen that the damage done by
kangaroo-rats is exceedingly serious, especially in periods of drought. While
they occur throughout the desert scrub, it seems probable that the majority
have migrated upward into the desert plains as the grasses were eaten off at
the lower levels. The persistence of the grasses in sheltered spots and their
reappearance in fenced areas in the desert scrub suggests that they can be
successfully reintroduced into the deserts about Tucson after the kangaroo-
rats have been exterminated. The rats which persist in the desert now live
in part upon the shrubs, it seems, and in consequence the latter are now being
killed out over great stretches from Ajo to Yuma and beyond.
In addition to the major pests, the pocket-gopher, wood-rat or pack-rat, and
several of the field mice do more or less damage to the range. The gopher
damages the range by eating grass roots and disturbing the soil with his
burrows, but the injury is usually restricted to small areas. The pack-rat
lives on leaves of Yucca by preference, especially Y. radiosa and Y. arhorescens,
and may do considerable damage in regions where these are important sup-
plementary forage. In the desert scrub and plains, it seems to feed largely
upon various species of Opuntia, which are heaped up about its nest (plate 72).
Eradication of poisonous plants. — The loss of range stock from eating poison-
ous plants is so evident and often so serious that the importance of its pre-
vention requires no argument. The chief difficulty in the way lies in the
general ignorance of poisonous species and of the best methods of dealing with
them. Quite apart from their poisonous properties, such species are usually
undesirable weeds which compete successfully with the grasses and thus re-
duce the carrying capacity of the range. As a consequence, eradication is
theoretically the most satisfactory way of dealing with them, but this is per-
haps economically possible only in small pastures and other local areas.
Where they grow over hundreds of square miles, as in the case of the loco-
weed, Aragalu^ lamberii, on the plains and foothills along the eastern front of
the Rocky Mountains, eradication is practically impossible under existing
conditions, and controlled grazing is the only practicable method of preven-
tion. Marsh (1918: 21) has stated:
" Most of the losses from poisonous plants occur at times when the animals
are short of feed and the larger part of the stock poisoning is indirectly due
to scarcity of proper forage. This fact of the intimate relation of scarcity
of feed to stock poisoning can not be too strongly impressed upon the people
who handle range animals in the West. There is apparently a popular idea
that range animals will voluntarily seek out poisonous plants and eat them by
preference. It may be stated as a general fact that this is not true. Animals
seldom eat poisonous plants except as they are driven to do so by the lack of
other food. Almost all poisonous plants are actually distasteful to live-stock
and under ordinary circumstances will be avoided. The only exception to
318 GRAZING INDICATORS.
this, perhaps, is the group of loco plants. Animals do frequently acquire a
taste for loco and under some circumstances will eat nothing else, even in the
presence of other forage; and yet the initial feeding in the case of loco plants
is almost invariably brought about by the scarcity of food.
"It has long been known that loco eating is ordinarily commenced in the
winter season or in the early spring, when the loco plants are green and lus-
cious and before the grass has started. The loco plants at that time are the
most prominent plants on the plains and animals commence to eat them be-
cause of lack of other food. In the matter of other plants, the relation be-
tween starvation and the eating of the poisonous plant is still more marked.
For instance, the larkspurs spring up immediately after the snow leaves the
mountains and grow much more rapidly than the surrounding grasses, and if
cattle are allowed to go up to the upper ranges before the grasses have had a
fair start they find already occupying the ground the succulent larkspur
plants in large numbers. Sometimes the cattle come from dry winter feed
and are anxious to gorge themselves with any green material they find. Under
such circumstances, if they come upon a field of larkspur they frequently eat
enough to produce fatal consequences. Later in the season there is very
much less danger from larkspur because of the abundance of other food. If,
however, cattle are driven from one range to another and the trail passes
through a mass of tall larkspur, it is not at all unusual for the hungry animals
to grab hastily at the plants and this may result in disastrous consequences.
Under such circumstances it is important that the cattle shall not be driven
rapidly, for they will snatch all the more, and they should also have been
thoroughly fed before going on such a drive.
"It is also evident from what has been said earlier in this paper, that if
cattle can be kept off fields of larkspur until after the plant has blossomed,
httle trouble may be expected. This method has been employed for many
years in Colorado, where it is a common practice to "ride for poison," as it is
called; that is, the herders ride and keep the cattle down from the higher
ranges until the larkspur has blossomed and matured, after which there is no
further danger. The same thing has been accomplished in certain regions by
putting up drift fences which are designed to keep the cattle on the lower
ranges until the danger is past. There are valleys known as death traps for
cattle. Frequently it will be found that in these valleys the tall larkspur is
thriving in large clumps and cattle drifting in will feed freely upon it. It is
often possible, under such conditions, to clear out this larkspur or enough of it
so there will be no danger. In order to kill the plants the roots of most species
should be cut off at least 6 or 8 inches below the surface.
"The losses of sheep from death camas {Zygadenus) occur under very
similar conditions to those of cattle from larkspur. Zygadenus grows very
early in the spring. It precedes the grasses in its growth and is present in a
succulent condition at a time when other forage is extremely scarce. Inas-
much as it occurs frequently in large masses, if sheep are trailed over these
places they are Uable to get enough to cause heavy losses. It is particularly
important in the handling of sheep in such localities that, if possible, they be
grazed in loose order. When the animals are massed together, they will eat
everything in their course, and because of jealousy will take particular pains
to get every available plant.
"This apphes equally well to lupine poisoning. When sheep are allowed to
feed freely upon a lupine patch and are moved without haste, no harmful
results will occur. If, however, they are massed together and driven in close
formation over such a patch, they are almost certain to be poisoned if the
plants are in pod at the time. The remedy in such cases clearly is to see that
RANGE IMPROVEMENT. 319
the sheep, when it is necessary to trail them through a patch of lupine, are
drifted rather than driven, and that they are well fed when they come upon
this locahty. It seems probable that intelligent handling of bands of sheep
may reduce to almost nothing the losses occasioned by Zygadenus and lupine.
If, however, hungry sheep come in contact with fields of Zygadenus in the
spring or with fields of lupine in the late summer and fall, at a time when the
plants are bearing pods, fatal results must be expected. "
Poisonous plants can be eradicated or kept down to a point where they are
not dangerous in various ways. The most thorough and Ukewise the most
expensive is that of grubbing out the roots. At the Utah Experiment Station
of the Forest Service, Sampson has found that cutting or mowing two or three
times during the first growing season and once or twice the second prevents
storage in the rootstocks and leads to the dying-out of the plants. Where
thp ground is not too uneven or covered with brush, it is much cheaper than
grubbing, and nearly as efficacious. Sheep have also been used to graze off
larkspur on cattle ranges, and it appears probable that overplanting with
vigorous innocuous species during favorable seasons would largely eliminate
poisonous plants as a result of competition.
Aldous (1917: 22) has summarized the results of the methods of grubbing
out and grazing off larkspur on the national forests :
"Grubbing out the plants is the most feasible method of preventing loss
of cattle from tall larkspur poisoning. The first grubbing costs from $3.65
to $10.10 per acre, the cost depending upon (1) the number of plants per acre,
(2) the texture of the soil, and (3) whether or not the plants are growing in the
open or in willows or other brush. The cost of the second grubbing should
not exceed $1 per acre. Extensive eradication on four forests has been done
at a cost of less than one-half the value of the cattle saved annually. An
average of 93 per cent of the plants in the experimental work and of from 80
to 95 per cent in extensive work were killed by the first grubbing. By a
regrubbing of the area one year after the first grubbing practically all of the
larkspur plants were killed.
"The use of sheep to graze off larkspur-infested cattle range has a limited
appUcation. Its success depends (1) on the palatabiUty of the larkspur, (2)
the availability of sheep to graze the infested area at the proper time, and (3)
whether the infested areas furnish sufficient forage to justify trailing sheep to
them. "
On the lower ranges, especially those of the grassland cUmax, overgrazing
is either a direct or a contributing cause of stock poisoning. This is naturally
the consequence of the disappearance of the more palatable species and the
correspondingly greater abundance and attractiveness of the poisonous weeds.
Since the evil effects of overgrazing are most in evidence during the dry phase
of the climatic cycle, methods of control and eradication should be focussed
especially upon drought periods. For example, the grubbing out of plains
larkspur or loco would be a simpler matter at the end of a drought period, and
the grasses would be enabled to develop a much more effective competition
during the ensuing wet period.
Eradication of weeds and cacti.— It has been repeatedly shown that annual
herbs are replaced in the course of succession by perennial ones, and these to a
large degree by grasses. The weedy nature of the annuals is evident, but
perennials are often also to be regarded as weeds in a grass range, especially
320 GRAZING INDICATORS.
one used by cattle or horses. Under climax conditions, the grasses are able
to maintain their dominance in competition with the herbs, but in the case of
overgrazing or other disturbance, the latter gradually get the upper hand.
When the area is protected or the grazing reduced, the advantages of the grass
life-form again come into play in the competition, and the herbs disappear or
become subdominant. As a consequence, the best method of eradicating
weeds is by protection or regulated grazing. Complete protection is more
rapid in its effects, but it is usually out of the question. Regulated grazing
is the most practicable method as a general rule, but it is sometimes too slow
in operation, or the area is too thoroughly dominated by weeds to permit it.
This is particularly the case with areas densely covered with prostrate species
of prickly pears, such as Opuntia mesacantha and 0. polyacantha, or with
half-shrubs, such as Gutierrezia.
When it is desired to get rid of annual weeds more rapidly than by means of
regulated grazing, they may be grazed off by sheep, especially where mixed
grazing is practiced. They may be greatly reduced by burning at the time
when their seeds are ripening, and they may even be mowed where the area
permits. During favorable seasons, their disappearance may be hastened by
overplanting with more vigorous species, especially perennials, which increase
the natural rate of succession. Perennial weeds are more difficult to get rid of,
since they are less affected by burning or mowing, and it is too expensive to
grub them out on the range as a rule. Fortunately, the most serious pests
are cacti and half-shrubs, which lend themselves to various methods of clear-
ing. Since cacti furnish succulent forage when more or less spineless, the
most satisfactory method of eradication is by burning, when the tract con-
tains enough grass to permit this, or by singeing with a torch when the area
is almost pure. Once the spines are removed from the prickly pears, they
will be grazed down to the ground by cattle, and in a few years will practically
disappear from the range if overgrazing is prevented. Halfshrubs, Uke other
weeds, can best be eUminated by protecting the areas or grazing them lightly,
but many ranges are so densely covered with Gutierrezia or Isocoma, for ex-
ample, that other methods must be employed. Since these rarely root-
sprout, burning is the quickest and most economical method, though in small
areas they may be cut out with profit.
Eradication of brush. — ^The range value of brush is determined primarily
by its palatabiMty, but it depends in a large measure also upon whether it is
pure or mixed with grass. As has already been emphasized, a range made up
of grass and browse in more or less equal degree permits mixed grazing and
furnishes the best insurance against drought and other disasters. The
burning of unpalatable brush to clear the ground for herbaceous growth seems
to have been long practiced in California, and it has also been employed to
maintain the stand of grass against the encroachments of shrubs in mixed
types. In the case of the Coastal chaparral, the dominants form root-sprouts
in great abundance and repeated burning is necessary to maintain the herb
cover. This is less true as a rule in the Petran type, where burning is chiefly
important in enlarging the grass areas, as is the case Hkewise in the subclimax
chaparral of Texas. In the typical savannah of the Southwest, the mesquite
and its associates are kept down by burning and the grassland chmax favored.
In the case of sagebrush, grazing by cattle favors the shrubs at the expense of
CLEMENTS
A. Wheat-grass tAgropyrum giauaim) following sagebrush after clearing, Brookings, Oregon,
B. Bunch-grass {Agropyrum spicatum) following fire in sagebrush, Boise, Idaho.
RANGE IMPROVEMENT. 321
the grasses, and the latter can be maintained only by some practice which
handicaps the brush. Since Artemisia and its associates usually form few
root-sprouts, fire furnishes the simplest way of restoring the balance from
time to time. Clearing is even more effective, but out of the question because
of the expense. Sagebrush may also be driven out by the grasses where
irrigation or flooding occurs, but this is rarely feasible in range practice
(plate 83).
Manipulation of the range. — Fire is but one of several processes which may
be used to bring about modifications of the forage cover. In addition to the
similar process of clearing are (1) cultivating, (2) irrigating, (3) fertilizing,
(4) cutting and pruning, and (5) sowing and planting. Besides its use in
handicapping scrub in mixed types, fire is of especial value in destroying the
old stems of bluestems and bunch-grasses, and making the new growth avail-
able for grazing. Throughout the grassland climax from Canada to Me.xico
occur frequent and extensive areas of Andropogon which are utiUzed Uttle or
not at all, except when hunger drives the cattle to graze them during drought
years. However, when the dead stems are burned in the winter or early
spring, the new growth is readily eaten, and with proper management the
bluestems and similar coarse grasses can be kept in constant commission in
the grazing practice. There is still a wide difference of opinion as to the ordi-
nary effect of fire upon grassland, and this is one of the many grazing problems
which need exact investigation in various types. Theoretically the burning
of prairie every few years should constitute a desirable practice, if the year
and season are chosen in such a way as to avoid injury to the underground
parts. In the short-grass and desert plains, fire would probably always do
more harm than good, owing to the dry soil and the certainty of injuring the
roots and rootstocks. Annual fires in grassland are probably always harmful,
especially in regions where less desirable annual species are present. Fire
has undoubtedly played a large part in the spread of Bromus iedorum and re-
lated species, as well as of Avena fatua, and it now is largely responsible for
maintaining them against the perennials. However, in the regions where
Avena is a desirable range or hay grass, fire is of value, since this annual would
slowly yield to other dominants if fire and other disturbing agents were re-
moved. Apart from farming operations, clearing is practicable only in the
case of particular species and over limited areas, as has already been noted
for poisonous plants. In such cases, grubbing, cutting, and mowing are all
modifications of clearing, which are of restricted application. In the case of
browse plants, however, cutting and pruning offer means of increasing the
amount of fresh browse, as well as its accessibility. These again are methods
for small areas, but they promise to have real value in the case of such shrubs
as the salt bushes, oaks, mesquites, catclaws, etc.
The improvement of the range by the use of some of the methods of culti-
vation has been tried from time to time. The first experiments in the appU-
cation of surface tillage to the range were those of Smith (1899:20) and
Bentley (1901: 18), which led to the conclusion that it would be profitable to
cultivate pastures with disk and iron-tooth harrows, especially in the semi-
arid regions. While the practice of stirring the surface soil and loosening up
the root-bound sod has been frequently recommended (Georgeson, 1895:43;
Williams, 1897; cf. Thornber, 1910: 324), it has never been adopted for many
322 GRAZING INDICATORS.
reasons, chief among them the labor and expense involved and the great
difficulty of applying intensive methods to large areas. This is equally true
of the appUcation of fertiUzers to increase the growth of grasses, and of the
use of irrigation. The application of manure to worn-out pastures was a
logical extension of good farm practice, and there is little question that the
comjK)sition as well as the yield of native and artificial pastures can be varied
more or less at will by the scientific manipulation of different fertiUzers
(Skinner and Noll, 1919). However, such methods are limited to pastures
in which intensive yields are possible, and are not apphcable as yet to even the
smaller pastures of cUmax grassland. Irrigation has a somewhat broader
application to western ranges, because the lack of water is the chief limiting
factor to production. The cost of irrigation, however, is regularly too great
to permit its use, except in restricted areas, where an exceptional production
can be obtained. Even in the majority of such cases, the forage is worth
more as hay, and is handled in that form.
Plant introduction on the range. — The sowing or planting of desirable native
or cultivated species on the range has universally been suggested and often
attempted. One of the earliest trials was that of Georgeson (1895: 43), who
sowed a mixture of perennial grasses, clover, and bluegrass in the prairie near
Manhattan, Kansas. The tame grass made a splendid growth early in the
season, but by autumn it had everywhere yielded to the native dominants.
Bentley (1901: 16, 30) made extensive tests of native grasses when sown or
transplanted in the native cover. Transplanting gave much the best results,
practically all the native dominants establishing themselves successfully when
due care was taken as to the time and method of transplanting. The most
extensive series of experiments in seeding native grassland have been carried
on in the Southwest by Griffiths, Thomber, and Wooton between 1900 and
1915. As this is the most trying region for the introduction of new plants, it
affords the best idea of the difficulties involved. Griffiths has summarized
the results of seeding operations on the range reserves near Tucson, as follows :
" Experimental work carried on thus far in attempting to introduce peren-
nial forage plants upon the mesas has given very little encouragement. Pani-
cum texanum, an annual, has given the best results of anything thus far intro-
duced, and it is believed that more success will be secured with annuals than
with perennials. They are not as good feed, but short-lived plants with good
seed-habits now furnish the main feed upon the mesas (1904: 61).
"Many attempts have been made to introduce forage plants in this section,
both in the large enclosure and upon the holdings of private individuals.
There is but one species, alfilerilla {Er odium cicutarium), that has given any
beneficial results. In all, 200 species of forage plants have been tried in this
enclosure. Many native species were tried, but the vast majority used were
of foreign introduction. At one time the Office of Forage-Plant Investigation
of the Bureau of Plant Industry furnished more than 100 varieties for testing.
In some cases the seed was covered and in others scattered without any further
attention. The plan has been, whenever the quantity of seed permitted, to
sow one-half in the fall and one-half in the early summer. In some cases the
ground was worked up sufficiently to kill about half of the original vegetation.
The net economic result of all this foreign introduction has been practically
nil. Most of the species in our experience have never come up, and the few
things that did make any growth usually died before seed was produced.
RANGE IMPROVEMENT. 323
"A number of native grasses have been caused to spread successfully by
gathering the seed in advantageous localities and simply scattering it where the
ground was badly denuded. Better results have been obtained when seed-
ing was done the last of June or the first of July. When sown in autumn the
ants pick up too many of the seeds. Beneficial results have been secured in
this way by the use of the seed of Andropogon saccharoides, Botiteloua vestita,
and B. rothrockii. Less positive results have been secured by the use of
native seed of Bouteloua curtipendula and Leptochloa dubia. Indifferent
results have been secured with Bouteloua oligostachya. The above illustrations
of the successful use of native species are important and interesting, but they
have no applicabiUty to open-range conditions. However, where the land is
under fence, and seed can be secured in the vicinity without too much expense,
improvements can be made in very badly trampled areas. When the roots
of the native growth are not completely destroyed, it is questionable whether
in such situations as this, recuperation would not occur fully as rapidly by
proper protection from overgrazing without the use of seeds as with it."
(1910: 12.)
Thornber (1910:312) has furnished a detailed and comprehensive account
of seeding and planting operations in connection with the small range reserve
near Tucson :
"The almost complete failure of the above experiments in a reasonably
favorable year led the writer to undertake a series of experiments on similar
land receiving more water than the annual rainfall. To this end the storm
water embankments or dams already noted were built and the small areas over
which their flood waters occasionally extended were cultivated and sown from
time to time with the more promising of the native grasses, saltbushes, and
other forage plants, in addition to a number of introduced ones. For pur-
poses of comparison, most of these varieties were sown on adjacent areas not
so flooded, and also in the forage garden on the University grounds where
moderate irrigation was given.
"Good stands of blue grama (Bouteloua gracilis), hairy grama (B. hirsuta),
and side-oats grama (B. racemosa) were secured with heavy sunmier rainfall
in addition to flooding, on the small range enclosure. These, however,
gradually died out with average summer rains and little or no flooding from
storm water. Crowfoot or mesa grama (B. rothrockii), though more or less
common on the lower mesas, killed out badly with prolonged droughts. With
moderate irrigation practically all the grama grasses did well in the forage
garden, while without such irrigation their growth was short and they showed
signs of dying out. It is quite evident therefore that the rainfall at the lower
altitudes is too hmited for the successful growth of these species. Silver-top
or feather bluestem (Andropogon saccharoides) has become estabhshed where-
ever sown on areas subject to annual flooding, after which with average rain-
fall it has yielded at the rate of three-fourths to one ton of hay to the acre.
It has resisted in a remarkable degree prolonged drought, never having suffered
any injury therefrom when once established, and is gradually spreading over
cultivated areas, and swales and mesa depressions. When sown on the higher
creosote land not subject to flooding, or during seasons with less rainfall than
the average, it has failed. Tangle head (Heteropogon contortus) has also made
a good showing on the small range enclosure, while in the forage garden it has
yielded even more heavily than silver top. The sacaton grasses made little or
no growth from the start with rainfall heavier than the average on land not
flooded, and this was true of a number of other grasses, including Hilaria,
Stipa, and Aristida.
324 GRAZING INDICATORS.
"No introduced forage plants, including species from cool, moist climates
and higher altitudes, made any growth on the small range enclosure, and but
few of them persisted in the forage garden for any considerable length of
time. Both the native and Australian saltbushes failed repeatedly to secure
a hold or make any growth of extended duration, though they were planted
on land occasionally flooded with storm water. The growth of summer
annuals with average rainfall and no flood water was short, and they matured
little or no seed. Of the winter-growing species alfilaria and Indian wheat
(Plantago) made good growth when the rains were favorable, and invariably
matured seeds. Root-planting experiments were generally unsuccessful."
Wooton (1916: 38) gives an account of reseeding studies on the Santa Rita
Range Reserve which is in entire accord with that of Griffiths and Thornber:
"Practically all attempts to introduce new species of forage plants or to
increase the relative abundance of particular endemic species beyond their
natural importance in the plant associations of the region have resulted
negatively. In a few cases introduced plants, like alfilaria or some aggres-
sive annuals, have seemed to promise returns, but in the course of a few years
the native perennials have crowded them out. The scattering of seeds of the
local native species upon bare ground has proved to be well worth the trouble,
since the practice has resulted in the more rapid recovery of such areas. This
procedure has also put a crop of grass upon some soils where it was predicted
that nothing would grow. "
Introduction and reseeding have been generally successful in mountain
meadows and other regions where the rainfall is relatively high, as well as in
local areas of the sandhills and in river valleys where the water-content is above
normal as a result of runoff or underground drainage. Griffith (1907:22)
concludes:
"Profitable partial cultivation of native pastures must be confined to
productive areas in regions of sufficient rainfall to permit at least the occa-
sional cultivation of some of the hardier crops. The areas where reseeding
methods on an economic basis are applicable extend to the western plains,
and are scattered throughout the mountains in meadows, high valleys, and
other situations where the requisite moisture occurs."
Cotton (1908: 23) states that experiments carried on in the mountain
meadows of the Pacific coast "show that the carrying capacity can be greatly
increased by reseeding with tame grasses. The grasses best suited to this
purpose are timothy and redtop."
Vinall (1911:9), in discussing forage crops for the sandhill region of
Nebraska, strongly urges that "a good percentage of clover be mixed with
the native hay, as all the clovers grow naturally on the moist lands of the hay
flats. In fact, no part of the United States seems able to produce clover with
less care or attention than this wet-valley region, and its use here is strongly
urged. Red clover seeded in 1895 in meadow sod, without plowing or other
cultivation, has reseeded itself from year to year in haying land, and is today
in better condition and shows a better stand than ever before. "
Prerequisites for seeding and planting. — The above accounts make it clear
that water is the chief hmiting factor in the estabhshment of seedUngs or
mature plants and that competition for water determines their persistence.
Where the water-content is more or less in excess of the needs of the native
RANGE IMPROVEMENT. 325
population, as in mountain meadows with high rainfall, or in wet valleys with
littlfe drainage, tame grasses or forage plants can be introduced into the com-
munity successfully and without disturbing it unduly. Such areas constitute
a relatively small amount of the total range, and they are rarely in such need
of revegetation as the grasslands of low water-content. In deaUng with the
latter, the first great need is to take advantage of times of greater rainfall.
This has generally been done with reference to the season, but no method has
heretofore been available for anticipating periods of several years with rain-
fall above the normal. Such a method now exists in the use of the sun-spot
cycle to determine the probable duration of the wet and dry phases of the 10
to 12-year climatic cycle. While the annual rainfall varies more or less dur-
ing the wet phase, it is regularly higher than during the dry one. Moreover,
drought periods of 2 to 3 years' duration have been found to fall only at the dry
phase for the past 60 years. Hence, it is obvious that the difficulties attendant
upon reseeding or introduction will be least during the wet phase and greatest
during the dry one, and that all operations of this kind should be confined to
the former. Moreover, it is especially desirable that sowing or transplanting
be repeated for the first two years of the wet period in order that an adequate
stand be secured in the event of the seasonal distribution of the rain being
unsatisfactory. This would also accord with the probabiUty of two or three
fairly wet years for the proper establishment of the plants, before the begin-
ning of the dry period.
A second prerequisite of great importance is the eradication of rodents.
Where seeding is the method used, it is probable that the failure to secure a
good stand is often due as much to the destruction of the seeds as to the lack
of water. This is probably true even in the arid Southwest, since it is here
that rodent damage is greatest. As a consequence, it is imperative to kill out
the rodent population before seeding operations are begun on an area. It is
almost as important to make sure that the rodents are kept out of such areas,
since they may turn the scale against the establishment of plants which have
germinated successfully. The food habits of the kangaroo-rat help to explain
why the grama grasses fail to make seed and gradually disappear in the experi-
ments mentioned above. In certain regions, at least, they would Ukewise
render the establishment of transplants much more difficult. It is also
obvious that areas in which reseeding is being carried on must be protected
against grazing for several years. As a consequence, reseeding and trans-
planting should be fitted into the rotation system, and carried on with refer-
ence to the period of complete or partial rest given the different areas. It is
assumed that all such operations must still be regarded as actual investigations
and that they will be begun only where fencing assures control, and a pre-
liminary study of conditions presupposes some degree of success. Under such
conditions, it is possible to take the factor of competition into account also.
The success attained in artificially reseeding bare and especially trampled
areas in pastures has been largely due to the absence of competition for water.
When reseeding is employed to increase the density of an existing com-
munity or to introduce new dominants, competition becomes a critical factor.
It can be adequately modified only in small pastures where disking or harrow-
ing is economically desirable, or irrigation possible. On the ranges of the
Southwest, with two growing seasons, it can be avoided by the use of winter
annuals, which do not come into direct competition with the summer grasses
at all.
323 GRAZING INDICATORS.
New investigations. — In connection with grazing studies throughout the
grassland and scrub cUmaxes of the West, it is proposed to extend experi-
ments in reseeding and transplanting to all the associations. These are being
established with especial reference to the prerequisites discussed and they
have been planned for the next four or five years in the expectation that these
will constitute the wet phase of the cycle. Protection and eradication have
been emphasized, and particular attention has been devoted to methods of
evaluating the r61e of competition, since actual practice will require the re-
seeding of both bare areas and overgrazed communities. This is done in
protected inclosures, where tillage methods may be employed in so far as
desirable, and where permanent quadrats can be maintained for charting
changes in composition and measuring the annual variations in yield (Cle-
ments, 1917, 1918, 1919). By the use of transplanting in addition to reseed-
ing, it is expected to determine the ecological requirements of practically all the
dominants and many of the subdominants, within the same association or
local grouping, as well as between associations.
In addition to improving the carrying capacity of overgrazed areas, it is
hoped that it will prove possible to extend and develop mixed grazing types,
such as the mixed prairie, and the mesquite and sagebrush savannahs. The
mixed prairie has the highest carrying capacity of all grass types, and also
possesses essentially the same high resistance as the short-grass plains to
trampling, overgrazing, and drought. It owes this property especially to the
presence of buffalo grass, Bulbilis dactyloides. The runners of this grass make
it one of the very best for transplanting experiments and it should prove
possible to estabhsh sods as centers of ecesis throughout the grassland where
the rainfall ranges between 15 and 30 inches. Hilaria cenchroides has similar
values, but its range is more restricted and trials with it should perhaps be
confined to the Southwest. The production of mixed prairies, and of all
mixed types indeed, contains promise only in those climates or edaphic regions
where there is some water-content in excess of the needs of the existing domi-
nants. For this reason, it is practically certain that success can be attained
only by transplanting short-grasses into tall-grass areas, or into existing mixed
areas, rather than the reverse (plate 84).
The value of mixed grass and palatable scrub in permitting the grazing of
cattle and sheep, often with goats, and in providing a double insurance against
drought or other disaster is so great that the possible extension or production
of such types is of the greatest importance. In many cases it is expected that
the carrying capacity of the type will be increased by replacing one shrub
with another more palatable. Where savannah already exists or desirable
scrub is already in contact with grassland, the extension of the scrub can be
secured by a system in which grazing and fire are used to maintain the balance
at the point desired. Fire in conjunction with planting furnishes a ready
means of developing grassland in the midst of scrub. The actual planting of
shrubs in grassland is more difficult because the demand for water then tends
to exceed the climatic supply. As a matter of fact, the demands of shrubs
and tall-grasses are so nearly alike that shrubs can be readily introduced into
true, subclimax, and mixed prairies during wet periods, as nature has often
proved. Once estabUshed, their deeper root-systems and taller stems enable
them to persist. Certain subclimax shrubs, such as the saltbushes, will
CLEMENTS
PLATE I
A. Mixed grazing type of oak chaparral and grass, Sonora Grazing Station, Edwards
Plateau, Texas.
B. Mixed type of tall-grass (Agropyrum) and short-grass (BuUbUis-Boukloua) with relicts
of Sarcobatus, Ardmore Station, South Dakota.
RANGE IMPROVEMENT. 327
probably permit similar treatment in moister situations in the short-grass and
desert plains. Finally, the latter may be regarded as constituting a curiously
mixed type in which the two elements, winter annuals and perennial grasses,
occupy the same ground but become dominant at two different seasons. Since
grasses depend almost wholly upon the summer rainfall for their growth, such
a mixture is especially valuable in utilizing the annual rainfall to give the
maximum amount of forage. While Thornber (1910) and others have em-
phasized the unique value of the winter annuals in the Southwest, their im-
portance and the possibiUty of extending or developing this mixed type have
not been generally understood. The chief annuals possess the vigor and the
seed-production of weeds. Hence, the seeds germinate readily and the new
plants quickly become established. Like all plants, however, they can not
grow without rain, and their yield follows the variation in winter rainfall even
more closely than grasses do that of the summer.
Forage development. — It is obvious that the utilization of hay and other
forage to supplement the range during winter or periods of drought reduces
the demand upon the range and hence helps to improve it. Fundamental
as this is, it is far from a general practice among stockmen. While there has
been utiUzation of native hay areas, few attempts have been made to develop
them. Moreover, the use of native forage plants of an emergency character
has been exceptional until recently, while the production of cultivated forage
and silage crops by the stockman has barely been begun. Smith (1899: 22)
was the first to emphasize the importance of the production of hay and stack
silage as aids to the improvement of the range. Thornber (1910:305) has
discussed the use of methods for developing artificial meadows and fields by
means of storm-water dams, but concludes that these are in general not very
satisfactory. However, the majority of ranches perhaps contain areas on
which a fair amount of native hay can be developed, or on which cultivated
forage can be grown by means of irrigation, use of storm-water, or by the
methods of dry-farming. This is especially true during the heavier rainfall
of the wet phase of the climatic cycle. When the value of hay and silage as
insurance against drought is fully realized, it will usually be possible to pro-
duce enough during the wet years to tide stock over drought periods. This
is especially true of silage, because of the long period for which it can be kept.
In view of the enormous difference in the production of forage crops in wet and
dry years, it is imperative for the ranchman to realize that his most certain
insurance against the disasters of drought is an adequate forage reserve.
While increased hay production plays a part in this, maximum production
of silage diiring the wet phase especially is much more important. Silage can
be kept almost indefinitely in properly constructed silos, but it would prob-
ably never need to be kept more than four years, since even the most serious
drought periods have been only three years long. With the use of the method
of climatic cycles to determine the approximate date and length of wet and
dry phases, it will be possible to develop this drought insurance into a practi-
cal certainty. In the case of single years, it is a much more difficult matter
to anticipate the probable rainfall, and during the dry phase additional insur-
ance can be obtained by planting such forage crops as sunflower and Russian
thistle. In fact, in the Southwest at least, it will be the part of wisdom to
plant a certain amount of these every year, against the chance that the distri-
bution of the rainfall may be abnormal.
328 GRAZING INDICATORS.
Thornber (1911) and Griffiths (1905, 1908, 1909) have discussed in detail
the utilization of native cacti as emergency forage plants and have shown how
they can be cultivated in dry regions. The value of cacti as a supply of re-
serve food for drought periods is generally understood, but too little trouble is
taken to see that it is available when needed. Other plants that are grazed
little during wet periods but are eaten njore or less by the cattle directly during
drought are bear-grass or sacahuiste (Nolina), sotol (Dasylirium) and soap-
weed (Yucca). The first direct utiUzation of any of these species as emergency
forage was made by Mr. C. P. Turney on the Jornada Reserve in 1915 (Jar-
dine and Hurtt, 1917: 26). The critical nature of the drought period of 1916-
18 gave an impetus to the development of machinery for chopping the plants
into feed and resulted in a great extension of their use (Thornber, 1918;
Wooton, 1918; Forsling, 1919). While they should be regarded strictly as
emergency forage and not be permitted to take the place of proper forage
development, there can be no question of their value as roughage in times of
severe drought. If used as such, the supply in many regions of the Southwest
is practically inexhaustible, but the tendency will almost certainly be to con-
tinue using soapweed in particular until it completely disappears from the
accessible areas (plate 85).
Water development. — The importance of water development for range im-
provement has been generally recognized and has been discussed in consider-
able detail by Smith (1899), Bentley (1898), Griffiths (1904), and Jardine
and Hurtt (1917). These are all in complete agreement, and the conclusions
of Smith and of Jardine and Hurtt are quoted in some detail, as representing
the earhest and latest experiments in range improvement :
"Another precaution that must be taken, if the stock ranges are to be re-
stored to anything like their former value, is that water must be provided in
sufficient amount so that cattle will not have to travel long distances for it in
times of severe drought. Nearly the entire western portion of Texas is under-
laid by artesian waters ranging from 150 to 1,500 feet below the surface.
Wherever the drainage slopes are not too precipitous, artificial tanks may be
formed across the draws by building dams, and if the bottom of the tank is
carried down to hardpan, or is puddled before being filled, a supply sufficient
to last through the dry season may be secured at small expense. Such tanks,
or wells, either artesian or where the water is lifted by windmill pumps,
should be provided at least every 4 miles over the range, so that cattle will
never have to travel more than a couple of miles to water. Where the wells,
water-holes, or tanks are 8, 10, or more miles apart, as they very frequently
are on some of the western ranges, cattle greatly overstock the range in the
vicinity of the water, especially during midsummer, while the back country is
thickly covered with good feed. Thus a portion of the range will be over-
stocked while another portion will be undergrazed. In the one case the grasses
are eaten down and trampled for a few miles back from the water so that it
may require several good seasons to undo the injury done in one bad year.
In addition, the forage on the large area back "from the water is entirely lost
through not being grazed. The cost of constructing dams or providing wind-
mills will often be but a small percentage of the loss incurred when no water
is provided. It has been often observed that the period of flow of the rivers
in countries which have been overgrazed is very much less than it was formerly.
This is because the trampling of the herds has compacted the soil, and also
because the waters are not retarded from running off the surface as they
CLEMENTS
i ifi^:it
A. Park of Nolina and ^;i;i.>,o m uak ili.ipini.ii, .>.>ii.,i.i i.i;./iii>^ Maiiun, ]>ii,\..ia.T i'iaUau,
Texas.
B. Yucca radiosa in desert plains, p]inpire Valley, Elgin,' Arizona.
RANGE IMPROVEMENT. 329
would be when the land is covered with a thick coating of grasses. Hence the
drainage of the surplus water takes place in a very much shorter time. There
are many streams and springs which in former years afforded a continuous
supply throughout the dry season, which now only run during or immediately
succeeding periods of abundant rainfall. Thus less dependence is to be placed
upon the streams as a source of stock water. New artificial sources of supply
must be provided. " (Smith, 1899: 26.)
"Fairly efficient \ise of plains and mesa range in the Southwest can be
secured where stock do not have to travel more than 2^ miles to water. This
means one watering-place for each 13,200 acres. Such an acreage of grama-
grass range will carry about 500 cattle throughout the year if properly man-
aged. As the distance in excess of 2^ miles which stock have to travel to
water increases, the barren area around water increases, as does also the
partly used forage beyond 2| miles from water. Consequently the number
of stock the range will support is reduced. When feed is short, a long dis-
tance between feed and water tends to increase the loss of stock, to decrease
the calf crop, and to retard development of the young animals. Observations
to date appear to justify one permanent watering place for each 500 head of
cattle. Where conditions are favorable, the construction of tanks to catch
flood waters for the purpose of supplementing the permanent watering places
will be a paying investment. They will aid (1) in getting more green feed for
the stock during the year, (2) in more even utiUzation of the range as a whole,
(3) in the protection of feed and range near permanent wat€r, and (4) in re-
ducing the cost of maintenance and operation of wells." (Jardine and
Hurtt, 1917:29.)
Herd management. — Better methods of handling stock may improve the
range or prevent its deterioration directly, as in the open herding of sheep, or
may be of indirect benefit, as in the production of a more efficient animal.
Since the ultimate objective of range improvement is the maximum permanent
production of stock, all methods which lead to this end are more or less con-
cerned in it. While many of the factors in proper herd management have
been worked out by the experiment stations in feeding and breeding experi-
ments, the chief contributions to the management of range stock have been
made by the Forest Service. These deal mainly with the handling of cattle in
large range pastures, and of sheep in coyote-proof pastures and under new
systems of herding. The immediate objectives have been (1) maintenance
and improvement of the carrying capacity, (2) improvement in grade of stock,
(3) increased calf or lamb crop, and (4) prevention of loss. The results secured
on the Jornada Range Reserve have been summarized by Jardine and Hurtt
(1917:30), as follows:
"The big opportunity for increasing the calf crop is to keep poor cows in
thrifty condition. This can be done by not overstocking the range used by
breeding stock and bj'^ feeding a small quantity of cottonseed cake or other
supplemental feed to the cows that need it. All bulls should be fed during
the winter and early spring.
"The small loss at the Jornada reserve is attributed to careful, systematic
vaccination against blackleg, to the reservation of grama-grass range for
poor stock during the critical spring months, to feeding the animals a small
quantity of cottonseed cake, and to prevention of straying.
"In order to provide for extra range for the breeding stock in poor years,
one-third of the stock on a range unit should be steers. It is then possible
to reduce the number of stock when necessary by selling steers, without great
330 GRAZING INDICATORS.
sacrifice and without interfering with the breeding stock. In good years the
number of steers can be increased and in bad years decreased.
"To provide against loss in extremely bad years, some kind of roughage to
supplement the range forage, for feeding with cottonseed cake or other con-
centrated feed, would be a decided advantage on southwestern ranges. Feed-
ing cottonseed cake to calves weaned during the late fall, winter, and early
spring is an important factor in cutting down loss and increasing the size of
the stock, as well as in increasing the calf crop. Where this is done, young
calves can be taken from poor cows, thus reducing loss from starvation among
both cows and calves and stimulating earlier breeding."
The value of coyote-proof fences for sheep pastures and range lambing-
grounds has been studied by Jardine (1908, 1911). His conclusions are that
the carrying capacity under this system is about 100 per cent higher than
under the ordinary one, and that the percentage of lambs is higher, the sheep
are much better, the loss almost nothing, and the expense of handling materi-
ally decreased. The advantages of the " bedding-out, " " blanket " or " burro"
system of herding sheep have been studied by Jardine, Fleming, and Douglas,
and have been summarized by Jardine and Anderson (1919: 50). The latter
have given the most complete account available of the management of cattle
and of sheep on the ranges of the national forests, with respect to the range
as well as the herd (pp. 30, 49).
ESSENTIALS OF A GRAZING POLICY.
A proper land system. — It has long been recognized by students of grazing
that overgrazing and its attendant evils were the result of an unfortunate
land policy. This fact has never been understood by the public, even in the
West, and it is but recently that the stockmen themselves have realized it.
A large portion of the country still holds the vague opinion that the West
contains the possibility of unlimited homesteads, a delusion which western
poUticians and real-estate dealers have found it profitable to encourage. It
is a national misfortune that the entire open range was not brought under
adequate control at the time when the conservation movement was at its
height, as the West contained few resources of greater importance. At
present, every competent and disinterested student of the situation realizes
that an adequate and just leasing system furnishes the only economic solu-
tion of the problem. The administration of the grazing lands upon the
national forests has convinced the vast majority of stockmen of the advantages
of leasing or allotment, and has dissipated the fears that the "Uttle man"
would suffer under such a system. In spite of this, public opinion has hardly
advanced beyond that of the days of the " cattle kings, " who were more or less
justly regarded as the foes of the homesteader. This is not to be regarded as
strange in view of the failure of the West to comprehend the grazing industry
as perhaps its major problem. When the West realizes, and causes both
public and lawmakers to realize that half a billion acres of its land can
never be used profitably for anything but grazing, it will become possible to
enact the necessary legislation for an intelligent economic and social treatment
of the pubhc domain, such as was provided in the Kent grazing bill of 1913.
Essentials. — Coville (1898) and Smith (1899: 43) have pointed out the es-
sentials of a proper land system with respect to the needs of grazing, and
Smith has summarized these as follows:
ESSENTIALS OF A GRAZING POLICY. 331
"The only way in which the non-mineral lands can be filed upon is either
under the right of preemption, under timber claim laws, desert-land laws, or
those relating to irrigated lands. There is no system for disposing of areas
unsuited for agriculture other than under some one of these laws, and the
result is that the grazing lands are held as commons open to any stockman
who can run his cattle upon them. The first and foremost necessity, if the
extravagant waste of the public domain is to be prevented, is to devise some
system by which grazing lands can be placed in a class separate from agri-
cultural lands, and under which property rights in lands now free to everyone
may be assumed by individual stockmen. It has been the experience in all
pastoral countries that proper care and conservation of the forage resources
can only be secured and will only be practiced where the tenure of the land
is sure. The necessary fixity of tenure might be legally provided for by long-
term leases directly from the General Government at a nominal rental per
acre.
"Aside from the effect of overgrazing on the lands themselves and on the
natural grasses with which they are covered, it is well to note that millions
of cattle and sheep are grazed on free lands in every Western State and Terri-
tory. These lands contribute no taxes for the support of the State govern-
ments. The cattle when marketed may be sold at a much lower figure than
those raised on taxed lands owned by the stock grower and still make a profit.
It is not fair to the people who are compelled to bear the expenses of local
government for large untaxed areas, nor on the other hand to the cattle men
and woolgrowers of the East whose products come into competition with those
grown almost without expense on free Government lands. The policy which
governed the settlement of the prairie States might well be modified to meet
the demands of the stock raisers, especially as a very large percentage of the
Government land now remaining is not agricultural and can not be made so
by irrigation. The best policy is that which will the best promote permanent
settlement. It is necessary that timely action shall be taken to open up the
pubUc lands for settlement in tracts extensive enough to encourage men to
build ranches and make permanent improvements upon them. The con-
tinued existence of great bodies of free lands covered with free grass is de-
moralizing to all those who take advantage of the opportunities presented
thereby. As suggested above, probably the most feasible plan would be to
provide for long-term leases of the public lands for grazing purposes. "
The Kent grazing bill. — As an epitome of the best experience and results
in grazing practice and administration, the grazing bill introduced into Con-
gress in 1913 by Mr. Kent, of California, is unrivaled. It is such a complete
and concise exposition of the proper land policy for the West, and of the needs
of the grazing industry, that it is given here in its entirety, because of the
conviction that such a measure, and such a measure alone, can solve the land
problem of the West.
H. R. 10539.
In the House of Representatives, December 15, 1913.
Mr. Kent introduced the following bill ; which was referred to the Committee
on the PubUc Lands and ordered to be printed.
A bill for the improvement of grazing on the public lands of the United States and to regu-
late the same, and for other purposes.
Be it enacted by the SencUe and House of Representatives of the United States
of America in Congress assembled, That the unreserved, unappropriated public
lands of the United States shall be subject to the provisions of this Act, and
332 GRAZING INDICATORS.
the President of the United States is hereby authorized to establish from time
to time, by proclamation, grazing districts upon the unreserved, unappropri-
ated public lands of the United States, conforming to State and county lines
so far as practicable, whereupon the Secretary of Agriculture, under rules
and regulations prescribed by him, shall execute or cause to be executed the
provisions of this Act, appoint all officers necessary for the administration and
protection of such grazing districts, regulate their use for grazing purposes,
protect them from depredation, froni injury to the natural forage crop, and
from erosion; restore and improve their grazing value through regulation, by
the eradication of poisonous plants, and by the extermination of predatory
animals and otherwise; eradicate and prevent infectious and contagious dis-
eases injurious to domestic animals; issue permits to graze live stock thereon
for periods of not more than ten years, which shall include the right to fence
the same, giving preference when practicable to homesteaders and to present
occupants of the range who own improved ranches or who have provided
water for live stock grazed on the public lands; and charge and collect reason-
able fees for such grazing permits, based upon the grazing value of the land
in each locaUty: Provided, That for ten years after the passage of this Act
such charge for grazing shall not exceed four cents per acre nor be less than
one-half cent per acre, or the equivalent thereof on a per-capita basis, and the
Secretary of Agriculture shall revise and reestablish maximum and minimum
rates of charge for grazing for each succeeding period of ten years.
Section 2. That homestead or other settlement, location, entry, patent
and all other disposal of public lands under the public-land laws shall be in no
wise restricted, Umited, or abridged hereby; nor shall anything herein be
construed to prevent bona fide settlers or residents from grazing their stock
used for domestic purposes, as defined under the regulations of the Secretary
of Agriculture, on the public lands affected hereby : Provided, That after the
establishment of any such grazing district no form of location, settlement, or
entry thereon shall give a right to grazing privileges on public lands except
when made under laws requiring cultivation or agricultural use of the land:
Provided further, That permits to graze live stock upon land which is subse-
quently appropriated under any public-land law shall not be affected by such
subsequent appropriation, except as to the land actually appropriated, until
the end of the current annual grazing period: Provided further. That no
permit shall be issued which will entitle the permittee to the use of any build-
ings, corrals, reservoirs, or other improvements owned or controlled by a prior
occupant until he has paid such prior occupant a reasonable pro rata value
for the use of such improvements. If the parties interested can not agree,
then the amount of such payment shall be determined under rules of the Secre-
tary of Agriculture: And provided further, That when buildings, corrals, reser-
voirs, wells, or other improvements, except fences, shall have been established
on any forty-acre tract to the value of more than $100, as determined by rules
of the Secretary of Agriculture, such forty-acre tract shall not be subject to
settlement or appropriation under the public-land laws during the permit
period without the consent of the owner of such buildings, corrals, reservoirs,
wells, or other improvements.
Sec. 3. That all water on public lands or subject to the jurisdiction of the
United States within such grazing districts may be used for milling, mining,
domestic, or irrigation purposes under the laws of the State or Territory
wherein such grazing districts are situated, or under the laws of the United
States and the rules and regulations thereunder.
Sec. 4. That no grazing permits issued under this Act shall prohibit settlers,
prospectors, and others from entering upon such grazing districts for all proper
ESSENTIALS OF A GRAZING POLICY. 333
and lawful purposes, including the use and enjoyment of their rights and
property, and prospecting, locating, and developing the mineral resources of
such districts; and wagon roads or improvements may be constructed thereon,
in accordance with law, and all persons shall have the right to move live
stock from one locality to another within such grazing districts under such
restrictions only as are necessary to protect the users of the land which will be
driven across.
Sec. 5. That the users of the public lands under the provisions of this Act
may select a committee of not more than four members from the users of
any such grazing district, which committee shall represent the owners of
different kinds of stock, and, with the officers appointed by the Secretary of
Agriculture in charge of such grazing district, shall constitute an executive
board, which shall determine whether the permits for such grazing districts
shall be issued upon an acreage or upon a per capita basis, shall make such
division of the range between the different kinds of stock as is necessary, and
shall decide whether the distribution of the range shall be by individual or
community allotments. The executive board shall also determine the total
number of animals to be grazed in each grazing district and shall decide upon
the adoption of any special rules to meet local conditions and shall establish
lanes or driveways and shall prescribe special rules to govern the movement of
hve stock across the pubUc lands in such districts as to protect the users of
the land in their rights and the right of persons having the necessity to drive
across the same. The executive board, after thirty days' notice by publi-
cation, shall also determine the preference in the allotment of grazing privi-
leges provided for in section one of this Act, and shall, under rules of the Secre-
tary of Agriculture, determine the value of the improvements and the use of
the same whenever that may become necessary under the provisions of this
Act in the administration of the same. Fences, wells, and other improvements
may be constructed with the permission of the Government officer in charge,
who shall record the ownership and location of such improvements. Any
differences between a majority of the executive board and the officer in charge
shall be referred to the Secretary of Agriculture and shall be adjusted in the
manner prescribed by him. Any interested party shall have the right to
appeal from any decision of the board to the Secretary of Agriculture. If the
users of the land fail to select the committee as herein provided, the President
of the United States shall name such committee from such grazing districts,
representing the owners of the different kinds of stock, as above provided.
Sec. 6. That the Secretary of Agriculture shall fix a date which shall not
be less than one year from the estabhshment of any grazing district, and after
such date the pasturing of any class of hve stock on pubhc land in said grazing
districts without a permit, or in violation of the regulations of the Secretary
of Agriculture, as herein provided, shall constitute a misdemeanor and shall
be punishable by a fine of not less than $10 nor more than $1,000, or by im-
prisonment for not less than ten days nor more than one year, or by both such
fine and imprisonment in the discretion of the court.
Sec. 7. That twenty-five per centum of all moneys received from each
grazing district during any fiscal year shall be paid at the end thereof by the
Secretary of the Treasury to the State or Territory in which said district is
situated, to be expended as the State or Territorial legislature may prescribe
for the benefit of the pubUc schools and public roads of the county or counties
in which the grazing district is situated: Provided, That when any grazing
district is in more than one State or Territory, or county, the distributive share
to each from the proceeds of said district shall be proportional to its area
therein. The sum of $500,000 is hereby appropriated, to be available until
334 GRAZING INDICATORS.
expended, for the payment of expenses necessary to execute the provisions of
this Act.
Sec. 8. That the President is hereby authorized to modify any proclamation
estabhshing any gi'azing district, but not oftener than once in five years, to
take effect in not less than one year thereafter, and by such modification may
reduce the area or change the boundary lines of each grazing district.
Classification and range surveys.— The necessity of a classification survey
to determine the primary division of the public domain into agricultural,
grazing, and forest lands has been discussed in the preceding chapter. Here
it will suffice to emphasize the importance of classifying as grazing land all
areas in which there is not convincing evidence of permanently successful
agricultural production. In view of the fact that dry-farming in many
regions is largely confined to forage production, by far the best plan would
be to treat the remainder of the public domain as grazing land and to organize
it into districts and units in such a way that the forage areas could be in-
tensively utilized.
The primary task of a range survey is to determine the grazing types and
subtypes of a region and to approximate the carrying capacity of each. It
must ascertain the character, composition, extent, and value of each type, as
well as its present condition and its future development. It is essentially
ecological in nature, and hence must be based upon the climax formations and
their subdivisions, and upon their successional development. The most
important unit is the grouping or faciation, which represents the local type
with which an individual range must deal, though the larger ranches might
have a number of different types. A range survey will necessarily devote
much time to the need and the possibility of range improvement in the
different types. It will pay especial attention to the indicators of overgraz-
ing, and to the successional evidences of the best method of regeneration. It
will locate the areas infested with rodents or with poisonous plants, and will
suggest the most promising methods of eradication. It should likewise
take note of all areas in which there is actual or potential development of hay
and forage, and of the location and extent of communities of emergency
forage plants. It must also deal with the possibilities of water development,
by means of mills as well as by tanks. Finally, it will take account of sand-
hill, bad land, and other areas in which some form of grazing reclamation is
possible. In its complete expression the range survey should lead to the
production of ecologic sheets and folios which would do for the range what
topographic sheets and geologic foUos do for the topography and geology of a
quadrangle.
Production cycles. — The recurrence of wet and dry periods in general
harmony with the sun-spot cycle has already been shown to have a profound
effect upon the carrying capacity and water supply of the range. As a con-
sequence, the climatic cycle is clearly reflected by a corresponding grazing
cycle. The carrying capacity and water supply are high during wet periods,
and they are at a minimum during drought periods. For successful ranch
practice in the drier regions especially, the grazing cycle must be made the
basis of a production cycle. In fact, it is already the basis of such a cycle,
owing to the fact that production is necessarily reduced to the minimum dur-
ing a drought period. It is imperative that the actual existence of such a
ESSENTIALS OF A GRAZING POLICY. 335
cycle be recognized, and that its operation be anticipated and modified in such
a way as to stabilize production. In existing practice, a series of wet years is
a period of voluntary expansion, and a drought period one of involuntary
contraction. With the increasing probability of forecasting wet and dry
phases, the ranchman should make his plans accordingly. Expansion must
still be the rule for wet phases, and contraction for dry ones, but the change
from one to the other must be definitely anticipated and prepared for. This
is particularly true of the critical change from expansion to contraction, but
it is also true in a large measure for the reverse process.
Most of the essentials of a contraction-expansion system have already been
discussed under range improvement. It is imperative to have the largest
possible amount of insurance against drought in the form of rotation grazing
and reserve pastures, and of water development. Even greater possibilities
of adjustment are afforded by the management of the herd to secure necessary
contraction and desirable expansion. On the Jornada Reserve this has been
obtained by maintaining the number of steers at about one-third the total of
the herd, but increasing the number in good years and decreasing it in bad
years as the range warrants or demands (Jardine and Hurtt, 1917:31).
Still greater elasticity is provided where it is possible to employ mixed graz-
ing, running cattle and sheep together, or cattle, sheep, and goats. Mixed
grazing not only permits readier adjustment to cUmatic conditions, but also
serves in some measure as insurance against unfavorable market conditions.
Ranch management surveys. — The task of placing the grazing industry upon
a sound economic and social basis is not solved until costs- of production can
be determined. Until this is done and net income ascertained, it is impossible
to know the efficiency of any particular ranch in either economic or social
terms. It is felt that the only proper objective of any productive system is
to secure an equitable balance between the needs of the producer and the
consumer. Such a balance is possible only when the actual cost of production
is known, so that its relation to the proper cost can be determined. In its
present condition the stock industry of the West is httle better than a game
of chance, in which both the stockman and the pubUc are regularly losers.
It can be converted into a productive business that does its full duty to the
individual and the nation only by means of proper land legislation, adequate
methods of range improvement, and by ranch management surveys, which
will disclose the exact status of each ranch as a productive unit. Such sur-
veys may well serve to usher in a period of cooperation in ranching, which will
make possible great improvements in range and herd management as well as
in marketing and distribution. They would probably lead also to the stabili-
zation of land values and the reduction of interest rates, and to the production
of social values such as rarely obtain at present.
VII. FOREST INDICATORS.
Nature. — Forest indicators are of three chief types, namely, (1) those that
have to do with existing forests; (2) those that indicate former forests; (3)
those that indicate the possibihty of establishing new forests. A community
of trees is axiomatically an indicator of forest, but it carries with it indications
of habitat, structure, and development which are not so obvious. More-
over, it involves important indications as to use, such as lumbering, water
regulation, grazing, etc. Indicators of former forests are either actual re-
licts of the forest itself or serai communities which mark particular stages of
the successional reforestation. They may consist of the dominant trees as
individuals or communities, of the subdominant shrubs or herbs of the climax
forest, or of the dominants or subdominants of any successional stage. Their
great value lies in the fact that they not only indicate the possibility of re-
forestation, but also the stage which has been reached and the further methods
to be employed. They are by far the most important and practical of all
forest indicators when the vast extent and significance of deforested areas are
taken into account. They pass more or less gradually into indicators of the
possibility of forest production in regions which have been repeatedly de-
forested and which show neither relicts nor serai stages of the original climax.
Such are the transition regions between forest and scrub or prairie, in which
the latter appear to be climax, but are really subclimax and will consequently
yield to forest when artificial regeneration is employed. In addition, chaparral
and grassland may also indicate afforestation in regions which have not borne
forest for hundreds or thousands of years. These are primarily edaphic areas
in which the indicator community owes its presence to a higher water-content
resulting from soil or topography. Such are the sandhills of Nebraska and
the river valleys throughout the prairie associations.
Kinds of indicators, — Both the individual and the community may be used
as indicators. The latter is naturally more complete and definite, but in
many cases the change following clearing or fire is so complete that a single
relict individual gives information of great value as to the original climax.
This is true also of subclimax forests which have more or less completely
disappeared in the reestablishment of the climax forest. The forest formation
which is climax for a certain region is itself the indicator of the permanent
type of the region, and hence of the forest which will naturally develop or
redevelop in all bare or cleared areas. As a consequence, it is an indicator of
site and likewise of the type of management to be employed. Each associ-
ation is an indicator of climate, while the various groupings and alternations
of the consociations indicate different edaphic conditions as well. The
societies indicate variations in water-content or light primarily, but the layer
societies are especially related to light. Differences in the density and growth
of dominants and subdominants serve as indications of minor changes in the
factor complex. Indicator values may be derived from growth in height,
diameter, or volume. The former is the most convenient for use, but the
latter is probably the most accurate. Seedlings are among the best of domi-
nant indicators, especially when their growth, habit, and abundance are taken
into account. The minute structure of leaves is an excellent indicator of
336
CLEMENTS
PLATE 86
A. Cliiniix subalpirio fon'st o( Abks and Pinuts as a climatic indicator, Yowmitc National
Forcfet, California.
B. Consociep of Rudlerkia occidentalis as an edaphic indicator of clearing and fire, Utah
Experiment Station, Ephraim.
FOREST TYPES. 337
light and water relations, and that of stems is an indicator of annual fluctu-
ations in rainfall, and hence cUmatic cycles. Flowering and seed-production
also have their indicator values, but these are of secondary importance.
Serai communities differ chiefly from climax ones in indicating edaphic
conditions or habitats rather than cUmate. Their pecuUar value lies in the
fact that they may at the same time indicate the nature of the initial area or
disturbance, the particular stage of development in the succession and the
habitat, and the final association or climax. Such stages are denoted by the
associes, and minor stages or variations by the consocies, while the socies
denotes subordinate differences within these. These three types of com-
munity, and the series of associes which constitute the sere, form a complete
scale of variations and changes, upon which the problems of forest mainte-
nance, of reforestation and afforestation, must be based. In short, while the
rlimax indicates the permanent forest of a region, the seres indicate the
methods and materials which must be used in hastening, maintaining, or
postponing the climax community, which is inevitable under natural con-
ditions. It is obvious that serai communities fumLsh indications from compo-
sition, density, and growth essentially similar to those of the climax (plate 86).
FOREST TYPES.
Bases. — The nature of forest types and the bases for their distinction have
been fruitful subjects of discussion among foresters. Graves (1899) seems to
have been the first to characterize forest types definitely:
"If nature is left imdisturbed, the same type of forest will tend to be pro-
duced on the same classes of situation and soil in a specified region. There
will be variations within the type, but the characteristic features of the forest
will remain constant, that is, the predominant species, density, habit of trees,
reproduction, character of undergrowth, etc. If a portion of the forest is
destroyed by fire, wind or otherwise, the type may for the time being be
changed, but if left undisturbed, it will revert to the original form, provided
the condition of the soil is not permanently changed."
Zon (1906) states:
"The first step in any silvical study or attempt at forest management is to
reduce the great variety of stands to a small number of types, each having
characteristic features of its own and requiring a distinct treatment. The
nearer we come to establishing natural types of forest growth, the deeper
we penetrate into the true relationship existing between these types and the
factors that produce them, and this is the most important contribution to
silvics. "
The changes brought about in a forest by man or by accidents are not
regarded as a basis for the establishment of fundamental forest types, but it
is recognized that such changes do produce temporary or transient types.
The essential agreement of the basis proposed by Graves and Zon with the
principles of succession and the distinction between climax and developmental
communities was pointed out by Clements (1909 : 62) :
"Reproduction is the forester's term for development or redevelopment;
it is the complex response of a formation to its habitat, which leads to succes-
sion. The result of reproduction is a forest type of succession, an ultimate or
338 FOREST INDICATORS.
stable formation, i. e., a forest type and a stable formation of a succession are
identical. This identity is made clearer by the author's insistence upon
stability as the ideal for which the forester must strive in regenerating and
caring for his forest. The change in stabilization is perhaps the most essential
feature of a succession, and the succession terminates only because the habitat
is finally occupied by a formation which, accidents excepted, is best suited
to it and hence is permanent. "
The varying concepts and applications dealing with the forest type are well
illustrated by a symposium on the subject, the papers of which are briefly
abstracted here. Dana (1913: 55) defines the different kinds of types which
seem to serve a useful purpose and should be recognized :
"A forest type, known often as simply a type, is a stand of trees with dis-
tinctive characteristics of composition. A cover type is a forest type now occu-
pying the ground. The term conveys no implication as to whether the type
is temporary or permanent, or one which we shall strive to maintain under
forest management. A temporary type is a forest type which has come in as
a result of some interference with natural conditions, such as fire or lumbering,
and which will eventually, if nature is left undisturbed, be replaced by a
different type. A permanent type, or natural type, is a forest type which will
eventually take possession of and perpetuate itself on any given area if natural
conditions are undisturbed. A management type is a forest type that we shall
strive to maintain under forest management, irrespective of whether or not
it is the type that would occupy the area under natural conditions. "
Munger (1913: 62) emphasizes the following point:
"The term forest type must above all be used for a classification of timber-
land that will be useful to the practicing forester in forest management in a
broad sense. Forest typing must not merely be a theoretic grouping of simi-
lar areas convenient for wall-map purposes or a classification of merely botani-
cal or ecological interest. Their distinctions must be based on fundamental
points of difference which have significance to the forester. In every form of
intensive reconnaissance which a forester is doing preparatory to making
working plans, he should include the collection of data showing both the
present composition by species and the physical conditions of the site.
Though both of these classes of data may be shown on his maps, I feel that
the term 'forest type' should be reserved for a classification based upon per-
manent basic physical factors. I should define, therefore, a forest type as an
aggregation of areas of forest land upon which the physical conditions of
clipiate, soil, and moisture are so similar that an identical form of silvicultural
management may be applied on all."
Woodward (1913:69) states:
"In the examination of lands offered for purchase under the Weeks law, it
has been found desirable to classify the kinds of forest stands and sites from
two points of view. In the first place, it is necessary to know the composition
of the present stands in order to arrive at the value of the timber. The second
way in which sites need to be classified in valuing the lands offered is to de-
termine the value of the site for producing timber. In a virgin stand, the
present composition is a very good index of what can be grown on the area in
question. However, it is conceivable that under forest management it may
not be advisable to wait for the struggle for existence to proceed so far that
temporary species are eliminated. As a means of classifying stands and sites,
FOREST TYPES. 339
a system of types and subtypes is now in use. A forest type is understood to
be an area in which the climatic and soil factors are uniform and which may
therefore produce stands of like composition. A subtype is a subdivision of
a type in which the struggle for existence is not yet completed and whose
composition is therefore changing. Generally this temporary condition is
caused by fire, lumbering, windfall, etc. The most common species in sub-
types are light-needing ones which occupy the ground quickly, but which will
ultimately give place to more tolerant species. "
Moore (1913: 75) summarizes his views of forest types as follows:
"A forest type is a tree society having such differences of composition from
other tree societies as to make necessary a separate study of yield. Physical
factors are the cause of forest types, but not forest types themselves. They
cause confusion when used in classifying forest types. Yield studies are at
the foundation of forest management, and must be based on forest types
distinguished by composition. Reconnaissance must furnish material to
which yield studies can be applied. For this purpose it must distinguish
forest types by composition, whatever other method may be used in addition.
Fortunately, this is, for most regions, the easiest way of distinguishing forest
types. "
Greeley (1913: 76) points out:
"There have been three general stages in the work of the Forest Service,
each invoh-ing a somewhat different point of view in the classification of
forest types. During the first stage the 'cover type' in its simplest terms was
adequate. In the second stage, the 'cover type' in itself is inadequate. We
need rather the 'management type.' In the third phase of the work to which
I have alluded, we need possibly an additional type — the 'physical type' or
'land type.' The type needed for the classification and description of National
Forest lands is the 'management type.* The classification of forested areas
should be attacked from the standpoint of what those areas will grow best
under scientific administration. Let us have, then, a classification of forest
types based upon present cover interpreted where necessary by the uses which
we will make of it in management. Let us leave the intensive study of
physical factors to the working-plan expert or the siUdcist. The 'manage-
ment type,' in my judgment, is the key to the classification of complex stands
arising from changes in composition at different periods in the life-history of
the forest. I would apply this principle to any complex situation where a
temporary type is followed by a permanent type, selecting for the purposes of
our classification the stage in the natural rotation of species which, as far as
we can now see, will be the basis of the forest management. In a word, the
existing cover interpreted by our knowledge of the Ufe-history of the type
and of what the land should produce under management will, I believe, furnish
the best basis for classification."
Pearson (1913: 84) emphasizes the value of communities as indicators and
summarizes the bases for the classification of forest land into types, as follows:
"The only scientific basis for such a classification is that of potenti{il pro-
ductiveness, considering both agricultural and forest crops. The productive
value may be ascertained in two ways: The first measures directly, as far as
possible, all physical factors on the site and gauges the productive capacity
by the measure in which the sum of these factors meets the requirements of
various crops. The second method uses characteristic forms of v^etation
340 FOREST INDICATORS.
on the ground as an indicator of the physical conditions present, and upon this
basis ascertains the adaptabiUty of the site for different crops. The obvious
objection to the first method is the need of climatological data and soil analy-
ses on each site to be classified ; and, owing to the diversity of sites in our forest
regions, together with the almost entire absence of climatological records in
many sections, the collection of data would involve an expense which, at this
stage of our advancement in forestiy, would be almost prohibitive. The
second method requires a thorough preliminary investigation in each region
to be covered, in order to secure a working knowledge for the actual land classi-
fication, and obviously reliable results can only be obtained by the employment
of trained men. This method is the simpler and probably the more reliable
of the two, and it is considered entirely applicable to the needs of the forester."
Rockwell (1913: 85) defines four types, as follows:
"The temporary type is a transitional condition, in which a forest of a
temporary character is established as a result of some disaster which over-
whelmed the original stand, but which will, if the disaster is not repeated, in
time revert to the original climax form. The climax type is named for the
species which will eventually predominate as a result of the physical factors
concerned, provided the stand is left indefinitely undisturbed. The cover
type may be either temporary or permanent; in mature and over-mature
stands the name is based on the present composition; in immature stands it
is based ujx)n the probable composition at jnaturity. A fundamental type
which, similarly to the chmax type, is based on physical factors of site, but
named for the commonly occurring species most important from a manage-
ment standpoint, instead of for the climax species, will here be called, for want
of a better name, the 'physical type.' In addition to furnishing a better basis
for the estimate of future yield and the regulation of the annual cut, the
knowledge of site conditions which a 'physical' type map supplies is of great
assistance in handling all the problems of forest management. After the
types have been thoroughly studied, we will know definitely the range of
climatic conditions in each type — knowledge of great value in forestation,
fire protection, and land classification work. We will know what species can
grow in each type, their rate of growth, and what they will yield. We will
know about the behavior of different species within the type, and can then
plan intelligently the management of cutting operations, methods of brush
disposal, and other problems of forest management. Not until the physical
types are properly classified and mapped can these problems be definitely
worked out. "
Mason (1913:91) recognizes —
"Two classes of forest types. One of these types is based upon physical
factors and will be called the 'physical type' ; the other, based on the forest
cover found on the area in question, will be called the 'cover type.' A physi-
cal-type map is principally valuable in forest management to indicate the
species which can be grown most profitably on a given area. It is useful in
case planting is to be done, or if a method of cutting merchantable timber is
to be selected which will reproduce the proper species. A physical-type map,
then, shows the potentialities of the area mapped. It need show nothing
with relation to the present forest cover, or even the presence or absence of
forest growth. The cover-type map, on the other hand, shows whether or
not the area is timbered at all. It shows what kind of timber is now present
on the area and its age. It indicates the nature of the crop which will be
FOREST TYPES. 341
harvested during the present rotation. The physical-type map, then, shows
what the land is capable of producing, while the cover-type map shows what
the land is producing. If the cover type is important in connection with the
present rotation, the physical type is important with relation to the next
rotation. The physical-type map indicates the species which may be best
grown upon a particular area. This, however, is a matter of comparatively
secondary importance in forest administration. Furthermore, questions as
to proper species for planting and suitable methods of cutting are solved by
special studies rather than in the course of the work of the general reconnais-
sance crew. Physical-type maps are doubtless of great silvical and ecological
interest, but cover-type maps are more valuable at present to the men who are
managing forests in a practical way."
Tillotson (1913:95) has emphasized the importance of permanent forest
types:
"Ordinarily it is Undoubtedly true that better success will attend silvi-
cultural operations if due regard be given to the establishment and main-
tenance of permanent forest types. It therefore becomes important to learn
to distinguish and to classify them. It seems that this will necessitate the
division of th0 country into rather large areas, over which the same general
conditions of temperature prevail at similar altitudes, these units to be sub-
divided into smaller areas, where similar conditions of precipitation both as to
amount and distribution exist, and these still further into smaller units, where
differences in exposure, topography, or soil exist. On similar areas of this last
division the ultimate forest growth may be expected to be the same, both in
composition and in character, and it makes Uttle difference in speaking of the
permanent types whether they are called, for instance, the north-slope and the
south-slope type, or the north-slope Douglas-fir type and the south-slope
Douglas-fir type, providing the character of the growth in the region under
discussion is known. The physical factors of the habitat will determine the
type, and if these are known the character of the ultimate growth will be
known by one famiUar with the region. To one not famihar with the region
any designation of types will in any case necessitate a description of them. "
Zon (1913: 103) points out:
"One of the most urgent and fundamental silvical tasks of the present
moment is the working out of a natural classification of our forests. Since
there are no characteristics within the stands themselves which could be used
as unmistakable guides for dividing the forest into homogeneous silvicultural
units and for acquiring exact knowledge of their silvical requirements, one
must necessarily seek such characteristics outside of the stands. Such guides
are found in the external environment, with its climatic and soil pecuUarities.
These alone determine the composition and combination of the species as
well as the silvical requirements of the stand. It does not make any differ-
ence whether the name of the forest type is derived from the distinctive com-
mercial species or topography, provided that in differentiating the forest into
types the physical conditions of growth, which are the fundamental and
primary causes of the real differences in the stands, are taken as the basis.
If forest types are based upon physical conditions of growth, they will neces-
sarily also determine the character of growth and make superfluous the further
subdivision into quality classes.
"In a proper forest classification, two things must be distinguished: (a)
types of forest as the product of physical conditions of growth, and (6) the
condition of the stands as the product of the interference of man or natural
342 FOREST INDICATORS.
accidents. In the latter group will belong temporary types — sprout forests,
abnormally open forests, the absence of undergrowth on account of grazing,
etc. The classification into types is fundamental and is of importance not
only for the present but also for the remote future. Classification on the
basis of secondary characteristics, which are merely stages in the evolution of
the type, is important only for the immediate future.
"A comprehensive classification of forests into types should begin by
establishing, first, silvicultural units of various orders. The country as a
whole should be divided into botanical-geographical regions — as, for instance,
northern conifers, central hardwoods, etc.; each region must be subdivided
further into subregions — thus the northern conifers into spruce subregion,
pine subregion, etc. Within each subregion the forest should be divided on
the basis of marked differences in topography and geology into types of forest
massives. Each forest massive should then be divided into forest types, and
within the boundaries of each type the stands may be further grouped by age,
by origin, or by any other distinction which may be due to the interference of
man or accident.
"Without denying the importance of the secondary characteristics in
describing and differentiating forest stands, these characteristics must be
placed, it seems to me, in a different perspective — at the end and not at the
beginning of the work. All attempts at forest classification so far made have
been based either upon artificial characteristics or upon characters in which
the interference of man was not separated from the natural factors. Such a
classification inevitably included in one group stands extremely heterogeneous
silviculturally. In order to secure a natural classification and at the same time
a complete knowledge of the silvical requirements of the stand, it should em-
body in the classification both the natural characteristics and the character-
istics produced by the interference of man, but subordinate the latter to the
former — that is, the characteristics produced by man should be used for
classification only within uniform conditions of growth — the physical con-
ditions for growth for the same type must be so similar as to guarantee a
biological uniformity of stands."
Comparison of views. — A careful scrutiny of the opinions just summarized
makes it evident that they differ more in emphasis than in fact. While the
majority prefer to make use of the community, either actual or potential,
they do this as an index to conditions and management. Those who regard
the physical factors as the most important recognize the necessity of knowing
the composition. The fact that the physical type is defined as one in which
the climatic and soil factors are uniform shows that even this view takes
proper account of the community, since there is at present no other measure
of the uniformity of the factors concerned. In fact, practically every author
regards both habitat and community as essential to the adequate under-
standing of forest types, and this agreement extends also to the desirability
of recognizing and using various kinds of types. This is especially true with
respect to permanent and temporary types, and largely also for management
types, all of which may be cover types, when the community is emphasized.
They are Hkewise physical types when the chief emphasis is placed upon the
habitat or site, but technically, temporary types would usually be excluded.
It thus becomes clear that forest types must take full account of both habitat
and community, and that the community is the visible sign of any type. It
is the indicator of the physical factors of the site as well as of the kind of
management which such a community demands to produce the maximum
FOREST TYPES. 343
return. In short, it is the indicator value of the community, which the forester,
consciously or subconsciously, has constantly in mind when he is defining or
classifying forest types. As a consequence, the major objectives of forester
and ecologist are the same in the study of vegetation, and the system of
classification and of indicators which the latter estabhshes as the result of
successional and quantitative studies should be equally serviceable for the
former.
Forest sites. — To the ecologist it seems that much confusion has resulted
among foresters from the fact that they have constantly used the indicator
method, but usually without a clear recognition of this or of its connotations.
As a consequence, there is frequent doubt as to the meaning of the terms type
and site. The causes for this confusion have been discussed by a number of
foresters. Dana (1913: 58) points out:
'The use of the term 'physical type' in this sense is practically the same
as the generally accepted meaning of 'locality' or 'site.' This is defined in
Forest Service Bulletin 61 as 'An area, considered with reference to forest-
producing power. The factors of the locality are the altitude, soil, slope,
aspect, and other local conditions influencing forest growth. Locality class,
or quality of locaUty, includes all localities with similar forest-producing
power.' Such a classification is undoubtedly a useful one for many purposes,
but it would be better to drop the misleading term 'type' and to substitute
for it either of the approved terms 'locality' or 'site.' In any event, it should
be clearly imderstood that the term refers to the area and not directly to the
stand. "
Moore (1913:75) says:
"The main point at issue becomes, therefore, one of terminology: Shall we
call the environment or physical factors a 'forest type,' or shall we apply the
term 'forest type' only to the tree growth? It is evident that we require a
separate term for each. Common usage in this country has generally made
the term 'forest type' apply to the forest cover. It would therefore simplify
matters, I believe, if some other term such as 'site' were recognized as applying
to physical factors, while the term 'forest type' is reserved for the forest cover."
The argument for a clear-cut distinction between forest type and site
receives strong support from a comparison of the statements of Moore and
Zon. The former (l. c, 75) states:
"Mr. Zon, in his article 'Quality Classes and Forest Types,* uses the term
'forest type' to indicate environment or the sum of all physical factors; used
in this sense, the 'forest type' becomes synonjonous with site quality."
Zon (1913: 102), however, merely says:
"An attempt to use such site classes for forest types as an expression of the
physical conditions of growth must necessarily lead to confusion."
Zon's further conclusions as to forest types and site classes have a direct
bearing on this question :
"The division of a forest into stands having different average heights or
site classes is perfectly justifiable as long as the end sought is purely an
economic one. Site classes based upon the average height of the stand can
344 FOREST INDICATORS.
not always represent physical conditions of growth, as the same site classes
may be found in stands which have entirely different physical conditions of
growth; in other words, belong to two distinct forest types. Site class, there-
fore, while it indicates the actual character of the timber found on the ground,
is not a silvicultural unit which can be used in management. The average
height of the stand or site class may be the result of the interference of man,
fire, animals, etc., and for this reason can not always be taken as the true
measure of the productive capacity of the soil, even within the same type.
The classification of stands on the basis of their average height is still further
deceptive, because it does not take into effect the taper or the soundness of
the timber, two qualities closely connected with the physical conditions of
growth of the stand. The use of quality classes alone as indicators of the phys-
ical conditions of growth is as misleading as to use the composition of the
stand for determining forest types. Both at best show only the actual
condition of the stand, but are entirely mute as to the physical factors that
are the cause of it. "
The question of sites and their recognition has received much attention at
the hands of foresters. It is essentially a matter of indicator values, in which
growth, or its consequences, furnishes the indications desired. For this
reason it is discussed briefly in a later section on growth as an indicator.
Succession as a basis. — A complete and satisfactory solution of the forester's
diflBculties in the recognition and use of types and sites is possible only on the
basis of successional studies. Succession at once removes the confusion be-
tween sites and types, since it emphasizes the basic relation of the two as cause
and effect. The site or habitat is the controlling cause and hence the explana-
tion of the type or community, but is itself reacted on by the latter in such a
way that it passes through a number of developmental stages to the final
climax condition, each stage marked by its characteristic community. An
adequate study of the community can no more neglect the habitat as cause
than it can the community as effect, and also as the cause of modifications in
the habitat. Moreover, it leads to confusion in the minds of others to use
such terms as physical type and cover type, which appear to ignore one or the
other. This is abundantly shown by the opinions cited above, in which essen-
tial uniformity is often completely hidden by superficial disagreement.
But succession does not merely put type and site in this prof)er relation to
each other. It is even more important in furnishing the only basis for the
natural classification of types, and hence of sites also. Other bases may be
natural in some degree, depending upon the criteria used, but development is
the only one which takes into account all the factors and processes concerned
and in their proper relation (Plant Succession, 111). Its essential feature
is the recognition of the forest as a complex organism with a characteristic
structure and development. The mature or adult stage is the cUmax forest
while its development is represented by a series of typical stages or com-
munities arising in bare or denuded areas. The climax communities corre-
spond with permanent types, and the developmental or serai ones with tem-
porary types, while both are cover types where they actually occur on the
ground. The management type, whatever its name may be, is peculiarly
successional in nature, since it depends not only upon the climax and its
succession, but also upon the degree to which the latter can be controlled in
the interests of optimum production.
CLIMATIC AND EDAPHIC INDICATORS. 345
The greatest importance of the successional basis for the classification of
forest types lies in its indicator values. The climax communities of different
degree are the indicators of the climates and subclimates, while the serai com-
munities indicate soil and other local or edaphic conditions. At the basis of
succession Ue competition and reaction, and within the control of the climate,
these are the forces which largely determine the density and growth of stands.
But even greater indicator values inhere in the sequence typical of succession.
Each stage indicates not only its particular habitat, while its variations in
composition or structure indicate similar variations in the controlUng factors.
In addition, it serves to indicate communities and habitats which have pre-
ceded it, and those which will follow it. Seen in its successional relation, each
community or cover type is an indicator not only of physical conditions, but
also of the past history and future possibilities of the area concerned, and hence
of the system of management or of planting.
Significance. — The primary value of forest indicators lies in denoting the
physical factors in control. The climax conmiunities of different degree indi-
cate the corresponding climates and their subdivisions. The serai communi-
ties indicate local or edaphic conditions, usually of water-content, and at the
same time mark the presence of progressive changes due to reaction. The
dominants of both climax and serai communities serve to measure the light
relations, and this is especially true of tree seedlings and of the subdominants
that form the societies of the forest floor. Processes, such as fire, lumbering,
grazing, etc., that produce disturbance, are either marked by relicts of the
original vegetation, or by subseres more or less typical of the particular pro-
cess. Growth is one of the most sensitive and hence one of the most important
of indicators in the detailed study of conmiunities and stands. Furthermore,
the climax and the serai stages of a region taken together determine the
general type of management possible or desirable. The composition and
successional position of the coramunity in any particular spot furnish a clear
indication of the type of management necessary to the utilization of a certain
species or stage as the preferred crop. Since succession is essentially progres-
sive in nature, the maintenance of a particular crop or rotation depends upon
a knowledge of the competition and reaction of the dominants, and the relation
of these to the successional movement. In any climax, there will be seres in
all possible stages of development. Some of these will need to be held in the
present stage, while in other cases the progressive movement must be favored
or hastened, and in still others it wiU need to be retarded. Whatever the
desired method, when the dominants in possession are used as indicators of
the forces which initiate and maintain the succession, it becomes possible
to adjust the system of management to all the differences in composition and
development.
CLIMATIC AND EDAPHIC INDICATORS.
Climatic indicators. — It is axiomatic that all forest climaxes are indicators
of forest climates. The four cUmax formations, woodland, montane forest,
Coast forest, and subalpine forest, indicate as many corresponding forest
cUmates, while the scrub formations and especially the chaparral indicate
climates in which water conservation is important. It is well understood
that the three mountain climaxes indicate climates with a progressive in-
346 FOREST INDICATORS.
crease of rainfall from woodland to subalpine forest, while the Coast forest
has the highest rainfall of all. In similar fashion, woodland, montane, and
subalpine forest indicate a progressive decrease in the length of season and the
temperature values, though the Coast forest marks the longest growing season
and the most equable temperatures. The rainfall and temperature relations
of the several formations have already been suggested in Chapter IV and need
not be repeated here. The associations indicate subdivisions or subclimates
of the formational climates. In general, the Petran associations are drier and
colder than the Sierran associations of the montane and subalpine climaxes.
For the three woodland associations, the total rainfall varies less than its
seasonal distribution, and the temperature relations seem more decisive than
the rainfall. The pifion-cedar indicates the coldest climate with much of the
precipitation as snow, the oak-cedar the warmest, and the pine-oak the most
equable. The first two have from 40 to 70 per cent of their rainfall in the
summer, and the latter about 20 per cent. The two associations of the Coast
forest show two subclimates strikingly different in both rainfall and tem-
perature.
The consociations serve to indicate still finer climatic divisions, both as to
altitude and latitude, though in general their indications are merged in those
of the association or formation to which they belong. This is well illustrated
by the montane forest, in which Pinus ponderosa indicates drier and warmer
climatic conditions than Pseudotsuga taxifolia, while Abies concolor is more or
less intermediate. Consociations also indicate potential climates, with
especial reference to the wet phase of the climatic cycle, where they form
savannah, as in the case of Pinus ponderosa in the grassland climax, or Juni-
perus in the sagebrush. The varied groupings of consociations throughout
an association also have some climatic indications, but these are often obscured
by edaphic indications of more importance.
Two outstanding investigations have been made of the physical factors of
climatic types. The first is that of Bates, Notestein, and Keplinger (1914: 78),
the second, that of Sampson (1918). The former deals with yellow pine,
Douglas fir, and Engelmann spruce groupings of the central Rocky Mountains.
The factors of the air and soil were measured during 1910-1911, and the fol-
lowing conclusions were reached as to the differences of the several types:
"There are wide differences in the heat requirements of the species and in
the temperatures of the types. The types vary somewhat in air temperatures,
but much more distinctly in soil temperatures. The length of the growing
season as determined from soil temperatures is a fairly accurate basis for
determining what tree should be grown on the site. It is possible that after
a series of careful observations a rule may be laid down by which the growing
season may be determined from a very few soil-temperature measurements, or
a direct relationship between the degree of solar radiation at any time and the
length of growing season may be established. This last, of course, will simply
be a scientific method for 'sizing up' the combined effects of slopes, aspect,
and altitude — a thing which is done roughly by the forester every day.
"The soil moisture of the types varies greatly, the spruce requiring the
most and the pine the least soil moisture; but the soil-moisture percentage is
not a good basis for comparing types except in the same immediate vicinity,
where it is Imown that the physical properties of the soils are uniform. In any
locality the spruce type probably always receives a greater amount of pre-
CLIMATIC AND EDAPHIC INDICATORS. 347
cipitation than the pine, and if all sites had the same aspect and gradient the
amount of precipitation might determine the type. There are, however, too
many influences affecting the final value of precipitation to make this element
a safe criterion.
"From the above it is readily seen that the measurement of soil temperature
affords the simplest means for determining the quaUties of the site. In this
measurement are involved the effects of the slope and aspect; the direct or
indirect solar insolation; the effect of retained snow or precipitation which
cool the soil; the effect of wind movement and humidity as they may cause
evaporation from the soil, and the effect of wind movement as it may bring
heat or cold from areas of different temperature. "
Sampson (1918:69) has determined the physical factors of the chaparral,
montane, and subalpine associations of the Wasatch Mountains in central
Utah, employing standard plants as well as instruments for habitat analysis,
and showing the differences with respect to the various factors and responses
in graphic fashion. His general conclusions are as follows:
"The mean annual temperature increases gradually from the highest to
the lowest type, and this results in the longest growing season in the lowest
type and a gradual decrease in the period of growth with increase in elevation.
Thus from the time of the beginning of growth to the occurrence of killing
frosts there are about 120 days in the oak-brush type, 105 in the aspen-fir type,
and 70 in the spruce-fir type.
"The normal annual precipitation is greatest in the aspen-fir association,
but is only slightly heavier in this association than in the spruce-fir. Less
than half as much precipitation is recorded in the sagebrush-rabbit-brush as
in the aspen-fir association; and in the oak-brush type it is only slightly
greater than in the sagebrush-rabbit-brush type. The precipitation is rather
uniformly distributed throughout the year.
"Of the three associations critically studied, the evaporation during the
main growing season is greatest in the oak-brush type; but owing to high
wind velocity in the spruce-fir type the evaporation is nearly as great as in the
oak-brush type. In the aspen-fir type the evaporation factor is notably less
than in the types immediately above and below. This is accounted for
largely by the lack of high wind velocity, which is due to the luxuriant vegeta-
tion and to topographic features.
"In the case of all species employed, the total, and, indeed, the average
leaf length and total dry weight produced are notably greatest in the aspen-
fir association, these activities being rather similar in the spruce-fir and oak-
brush types. The decreased production in leaf length and the production of
dry matter in the respective types are in direct proportion to the evaporation.
"The elongation of the stem is greatest in the oak-brush type, intermediate
in the central type, and least in the aspen-fir type. Thus stem elongation
appears to be determined largely by temperature and seems to be little in-
fluenced by the intensity of the evaporation.
"The efficiency of the leaves per unit area as manufacturing agents, that
is, in the production of dry matter, appears to vary inversely with the evapor-
ation, though, indeed, temperature appears to be one of the important factors.
The largest amount of dry matter per unit of leaf area is produced in the aspen-
fir type and the least in the oak-brush type, while in the spruce-fir type, where
the evaporation is only shghtly less intensive than in the oak-brush type, the
dry matter produced is only slightly greater than in the oak-brush type. "
348 FOREST INDICATORS.
Edaphic indicators. — These are either climax or serai dominants and sub-
dominants. Serai dominants are typical edaphic indicators, since they mark
the changing conditions of the habitat in its progressive development to the
final climax condition. Climax dominants differ in their requirements and
necessarily show indicator responses to local edaphic as well as general cli-
matic conditions. Subdominants, whether serai or climax, mark minor differ-
ences in the habitat, and serve also to indicate the dominants in many cases
where these have been destroyed or removed. The most striking edaphic
indicators are the seres which arise in bare or denuded areas. Each prisere
not only marks a particular type of initially bare area, such as water, rock, or
dune-sand, but it also indicates the changes of the habitat complex, as well as
the final climax. As already mentioned, each serai stage or community
indicates a certain set of factors, and at the same time the stages which are to
come in the development of the climax. This is likewise true of subseres,
which differ from priseres chiefly in arising in areas denuded by fire or other
accident, or by the agency of man. They are much more numerous than
priseres, the successional movement is much more rapid, and the stages fewer.
Each subsere is an indicator of the disturbance process that originated it, and
its stages mark the different degrees of development of community and habitat
on the way to the climax. Such stages, or associes, occur in both subsere and
prisere. Each marks a particular stage of the habitat which controls it, and
in turn reacts upon the habitat to produce the next stage. It consists of two
or more consocies, or serai dominants, which indicate minor changes in the
stage and hence perhaps different areas of habitat. In addition, each serai
community contains a varying number of subdominants which constitute
socies, corresponding to the societies of climax communities. The socies
mark the more minute differences of the habitat, and perhaps also the minor
movements within the associes.
The most important edaphic indicators are those which denote differences
in water-content, light, or soil, or mark the effect of disturbing agencies, such
as fire, grazing, etc. In addition to the presence or composition of a com-
munity, its growth or the growth of one of its dominants serves as an indi-
cator of variations in the habitat complex or of site quality.
Water-content indicators. — In the several forest climaxes, the physical pro-
perties of the soil in relation to water-content are so much more important
than the chemical that the latter require Uttle attention. As a consequence,
the indicators of water-content serve as indicators of soil texture, aeration, and
temperature as well. The water relations of the climax and subclimax
dominants have been considered briefly under each forest association. The
climatic relations of the dominants of a community are reflected in the edaphic
ones, and this may even be true of the dominants of different formations.
The dominants of drier climates or subclimates take the drier slopes and ridges
of the local area, and those of moister climates grow on northerly slopes and
in canyons or valleys. Picea engelmanni frequently reaches the lower limit
of the montane forest along the moist canyons of north slopes, while Pinus
panderosa extends to the middle of the subalpine forest zone or even higher on
dry and warm south slopes. In short, dominants indicate the total water
relation, and hence their climatic indications may be completely subordinated
to local conditions.
CLIMATIC AND EDAPHIC INDICATORS. 349
It is Eissumed that all dominants have different water requirements, and
that each in consequence indicates a different water-content. It is believed
that the results of further quantitative studies will show that the dominants
of a sere can be arranged in a linear sequence from the pioneer stage to the
climax. At the same time, it seems completely established that this sequence
falls naturally into stages or associes, characterized by dominants of the same
Ufe-form and similar requirements. As a consequence, it becomes possible
to use the dominants or consocies of a sere to indicate the successive small
steps in the changing water-content from the initial bare or denuded area to
the climax, while the associes indicate the stages of longer duration which are
characterized by a certain set of water conditions. In the prisere, such con-
ditions and their indicators have some relative permanence, but in the subsere
the successional movement is much more rapid and the stages sometimes
obscured. In both cases, however, the basic principle holds that a complete
series of indicators marks the changes of water-content from an originally
hydrophytic or xerophytic bare area to the relatively mesophytic forest cUmax.
The exact value of each community or dominant as an indicator must await
more general quantitative study, but the approximate values that can be
assigned them at present are of genuine service in forest problems.
Light indicators. — The general principles which underlie light indicators in
the forest have been discussed at some length in Chapter III, and the Ught
relations of the dominants of the various forest associations have been touched
upon in Chapter IV. The tolerance of western dominants has been indicated
by Zon and Graves (1911:21), Sudworth (1908), Larsen (1916:437), and
others. In a study of the tolerance of New England forest trees. Bums (1914,
1916) concludes that tolerance "really expresses not a light relationship, but
the total relationship of a tree to all the factors of its habitat. " While the
results of Fricke (1904) and Burns have shown that competition for water
must be taken into account in studies of tolerance, light is still to be regarded
as playing the paramount role. Bums's further conclusion that light readings
in the forest are of little value is not in accord with extensive experience in
making and utilizing such readings in ecological studies. On the contrary,
one of the chief difficulties in the correlation of edaphic communities with
their habitats is the absence of measurements of hght intensity. Where
these have been made with care and in large number through several years,
as in the Pike's Peak region of the Rocky Mountains, they have proved
invaluable in the study of reproduction, development, and plant indicators,
as well as in that of leaf adaptation and photosynthetic efficiency. Measure-
ments of light intensity in the forests of the West have been made by Clements
(1905, 1910), E. S. Clements (1905), Pearson (Zon and Graves, 1911:46),
and Bates (1917:233). Studies of the quaUty of forest hght have been
carried on for several years by means of a portable spectrophotometer (Cle-
ments, 1918: 291), but the detailed results have not yet been published.
Site indicators. — The term site, Uke forest type, has a wide range of mean-
ing among foresters. While it is regularly employed to denote the habitat,
it is appUed to all possible divisions of the latter. This is understandable,
since this is the present ecological practice in the case of habitat. But just
as it has proved necessary to distinguish habitats of different character and
350 FOREST INDICATORS.
various degree, so is it desirable to recognize several categories of site. Climax
and serai habitats or sites are fundamentally different, though they are often
found side by side. The habitat of one consociation differs from that of
another of the same association, and mixed areas of the two show subordinate
differences. Finally, the same consociation exhibits marked variations in
growth and density, each corresponding to smaller differences of the factor-
complex.
In practice, the forester has emphasized two of the several categories of
sites. The first is the consociation habitat or the site occupied by a dominant,
and the second the minor sites marked by significant differences in the growth
or density of a particular dominant. The more specialized use of the word
has been in the latter connection (Roth, 1916: 3; 1918: 749; Watson, 1917: 552;
Bates, 1918:383). As a matter of fact, the two types are developmentally
connected, the growth sites, commonly designated as I, II, III, and IV, repre-
senting a sequence of minor habitats within that of the dominant consociation,
such as Pinus ponderosa, Pseudotsuga, etc. The recognition of growth sites
is chiefly important in connection with yield tables and working plans. In
planting operations, consociation sites must first be determined, and then
growth sites may be employed to ascertain the most promising areas.
Growth as an indicator. — As stated in a previous chapter, the presence of a
dominant furnishes one set of indications, and its growth, another. The
latter naturally affords a more sensitive scale of measurement, and hence
indicates the effective differences of the habitat in terms of timber production.
It is obvious that total growth is the most complete indicator, as Bates has
insisted (1918 : 383), though it is equally clear that height-growth or even width-
growth may be used with much success. Since readiness and convenience
are essential in the practical use of indicators, height-growth has received the
most attention at the hands of those interested in the classification of sites.
The whole question of site indicators as well as the advantages of height-growth
in this coimection has been well stated by Frothingham (1918 : 755) :
"Any method of determining forest sites must employ an indicator, whether
this be the probable ultimate forest ('climax type'), the height-growth of one
or more species present, the current annual volume increment of a fully
stocked pure stand, some herb or shrub typical of a locaHty, or merely the
composition of the existing stand. Similar sites are then to be recognized
either by the identification of similar indicators or by determining the simi-
larity of the physical-site factors. These may be measured in precise terms
or simply estimated. Precise measurements appeal to the investigator.
Accepting the permanent type as an indicator, for example, it would only
remain to learn quantitatively the physical factors determining it. These
physical factors wherever found interacting in precisely the same amounts
will always produce, in time, barring accident or design, precisely the same
form of forest. The plan of classification based on physical factors appeals
to the investigator because it is truly fundamental. The apparent difficulties
in deciding what is the permanent type in the isolation and measurement of the
several physical factors, etc., may not be so formidable, after all, and the work
may be simphfied by the discovery that only one or two of the factors are of
particular significance. In many large regions, the permanent forest type is
strikingly apparent. In other places it remains exceedingly obscure. Even
where plainly evident, subdivisions with reference to yield are a necessity
CLIMATIC AND EDAPHIC INDICATORS. 351
from considerations of future as well as present management. This sub-
division of permanent forest types or of any other kind of types can be effected
by the use of an indicator. Indicator plants, volume growth, and height-
growth are means to this end. Under certain circumstances the use of
indicator plants may prove very useful, as experiments by Korstian and others
indicate.
"The use of the current annual increment as a means of determining
site involves the double difficulty of securing a basis and of applying the
measure of the site, when found, to the identification of similar site conditions
elsewhere. As an exact indicator it may prove the last word in refining
previous site determinations in locahties where it can be employed, but as a
general method, suitable for immediate use, it fails to meet the requirements of
simpUcity and widespread utihty previously set forth. The utihty of height —
one of the functions of volume, but far less unwieldy as an index — ought
to be plainly evident to everyone as the logical immediate basis for sub-
division. Height-growth, as a matter of fact, appeals in two ways: First,
as an immediate means of classifying forest sites in general, and second, as a
guide and a short cut in arriving at a possible future classification of sites on a
physical or permanent type basis.
"In conclusion, the principle of height-^owth as a guide to site has the
following features :
"1. It is simple, natural, easily understood, and easily applied in the field.
"2. It is independent of the determination of physical sites producing
definite permanent forms of forest; but the two are not antagonistic; both are
'indicators' and both demand equally a determination, more or less refined,
of the physical factors of site.
"3. The sites determined by height-growth are species sites, not permanent-
type sites; hence they are useful with reference to short-Hved intolerant and
long-Hved tolerant species growing in the same stand.
"4. By adopting one or more index species (intolerant species of wide oc-
currence on a variety of sites) the height-growth of other species can be gauged,
their relative value in each site can be determined, and this value can be ex-
pressed by naming the site in terms of the growth of each species present, and,
by analogy, of other species which do not happen to be present.
"5. It affords a means of comparing the growth of all American species on
the basis of the soil and climate to which each is best suited, as well as in less
favorable sites.
"6. It permits a ready comparison (a) between even-aged second-growth
stands in widely different regions, thereby avoiding such inconsistencies as
those to be found in the pubhshed yield tables for the same species in different
States; and (6) between second-growth and old-growth stands in the same or
different regions.
"7. Since height-growth is sensitive to interferences in the natural Ufe of
the stand (fire, culling, changes in density, etc.) care and judgment are
necessary in the choice of trees to serve as the index; but except for very pre-
cise site determinations, the method, if used with ordinary caution, will
undoubtedly prove serviceable for the majority of wild-woods conditions as
well as for even-aged stands.
"8. As the knowledge of the laws of growth of our species increases, the
refinement of site determination by height-growth can be increased."
The correlation of height-growth with rainfall and other factors has been
made by Pearson (1918:688) for PiniLS ponderosa in Arizona:
" Western yellow pine in northern Arizona makes its height-growth during
the period of lowest precipitation in the year. During this period of high
352 FOREST INDICATORS. *
activity, the trees are dependent almost entirely upon moisture stored in the
soil during the preceding winter and spring. Normally the great bulk, and
in some years all of this moisture, is stored during the winter months, De-
cember to March. When winter precipitation constitutes the sole supply,
height-growth in young saplings is apt to be small. If winter precipitation is
supplemented by 2 inches or more in April and May, a pronounced stimulus
to height-growth results. It may be stated as a general rule for the sites
covered by this study, that 2 inches or more of precipitation between April 1
and May 31 is several times as effective as the same amount in exce^ of the
normal precipitation between December 1 and March 31. Factors reflecting
atmospheric moisture conditions, including evaporation, wind movement,
relative humidity, cloudiness, and length of rainless period, from April 1 to
June 30, show a close, though not entirely consistent, relation to height-
growth. Temperature on the sites studied appears to be important only in
so far as it affects moisture conditions. Since the increase in temperature
results in increased water consumption, height-growth, if, as is usually the
case, there is a shortage of moisture, varies inversely with temperature. Ob-
servations indicate that where moisture is abundant, height-growth increases
directly with temperature. Complete records of soil moisture, if available,
would probably show even a closer relation to height-growth than does pre-
cipitation. "
It is highly probable that water-content is the factor that exerts the primary
control upon height-growth, and width-growth also. However, it seems
practically certain that the competition for water and food between the grow-
ing points and the cambium ring determines that height-growth shall largely
precede width-growth during each year as well as during the Ufe history of the
individual (Mitchell, 1918). The studies of Brewster (1918:869) indicate
that "the height-growth of larch seedUngs does vary in accordance with
variations in weather conditions from year to year, and that the most favor-
able conditions for rapid height-growth are produced in the North Idaho
region by a combination of temperatures somewhat above the average,
coupled with a high percentage of clear days, with an average amount of pre-
cipitation evenly distributed in the form of good rains at intervals of four to
ten days preceded and followed by lighter showers." The greater rainfall,
lower temperature, and greater cloudiness of northern Idaho in comparison
with northern Arizona readily explain the relatively greater importance of
temperature and Ught in height-growth, as well as the difference in the sea-
sonal occurrence. This must be expected for the various climax associations,
for which the task of correlation is primarily one of discovering the limiting
factor by the measurement of the habitat complex.
In the determination and classification of sites, as well as in their discussion,
it will conduce to clearness to recognize that this is almost wholly a matter of
applying the indicator method. While the word site appears to refer to the
physical conditions, it does so only in so far as these are indicated by the
presence or growth of the species concerned. And while it is felt that the
species affords a better measure than instruments do, such a measure is one of
actual growth and not one of the controlling or hmiting factors. Hence, it
must be recognized that height-growth indicates habitat only in a general
way, and that its specific indications apply only to the productiveness of the
area in terms of a particular tree crop.
CLIMATIC AND EDAPHIC INDICATORS. 353
Burn indicators. — It is a general rule that subclimax dominants serve as
the typical indicators of forest burns. This is in conformity with the principle
that almost any consocies and many socies of the subsere may indicate fire
as well as other similar disturbances, the particular initial stage depending
upon the degree of disturbance or the frequency of its repetition. The uni-
versal occurrence of tree and shrub consocies as burn indicators is explained
by the fact that fire not only produces areas temporarily free from the com-
petition of the climax species, but also characterized by conditions favorable
to less exacting species. Their characteristic dominance is chiefly due to the
rapidity and completeness with which they occupy the ground, as a conse-
quence of excessive seed production, the opening of cones by fire, or the abiUty
to produce root-sprouts. The conifers rely almost wholly upon the first
two methods and chiefly the second, while the deciduous trees depend mainly
upon root-sprouts. Among trees, the three types are represented respectively
by Pseudoisuga and Larix, such pines as Pinus contorta and attenuata, and by
aspen, birch, and alder. The scrub indicators owe their character almost
wholly to root-sprouting, reinforced more or less by seed production and
mobihty.
The burn subsere consists of the usual stages of annual and perennial herbs,
grasses, shrubs, and trees. However, the number and distinctness of the stages
and the duration of the subsere depend chiefly upon the severity of the burn.
In the most severe burns the initial community often consists largely or wholly
of mosses and liverworts, Bryum, Funaria, and Marchaniia, and is followed
by one of annuals, and this by one of perennials. The species, and to a less
extent the genera, of these vary with the climax association, but such species
as Agrostis hiemalis, Epilobium spicatum, Achillea millefolium, and Pteris
aguilina are more or less universal. The development of a grass stage is less
regular, since its place is often taken by scrub when the root-sprouting shrubs
are abundant. The scrub is normally replaced by aspen, birch or alder, and
these may yield to a subclimax forest, such as that of lodgepole pine, or be
replaced directly by the climax. It is obvious that fire may sweep through
the scrub, aspen, or lodgepole communities, and initiate new subseres, pro-
ducing an intricate pattern of seres and conamunities. In the great majority
of cases, the succession is more or less telescoped, and often completely so.
The root-sprouting ability of the shrubs and aspen and the release of the seeds
inclosed in cones or buried in the duff enable the shrubs and trees to begin
development the first year, at the same time that the herbs appear. In such
cases practically all the dominants appear at once, but the development still
exhibits many of the features of succession. The stages, though brief, give
character to the area in the normal sequence and each disappears in turn as
the competition of the next one becomes too great for it.
For the reasons just given, the herbs are relatively unimportant indicators
in complete burns, though they are characteristic in the case of Ught ground
fires. The bum subsere is characterized almost wholly by scrub, deciduous
woodland, or subclimax forest, not only because of the duration of the latter,
but also because repeated fires tend to make them relatively permanent. On
account of differences of distribution as well as the general similarity in require-
ments, the three types rarely occur in the same subsere. Two, however, are
frequent, aspen and lodgepole being the most conmion. The rule is that the
354 FOREST INDICATORS.
dominant with the greatest requirements is the subclimax. This is in accord
with the occurrence of lodgepole as the characteristic burn community in the
northern Rocky Mountains, aspen in the southern, and scrub in the Southwest
and in CaUfornia. As burn indicators, they have several features in common,
in spite of their differences in hfe-form. They not only indicate the possibil-
ity of reestabUshing the climax by preventing fire in some cases or by planting
in others where the original cUmax dominants have disappeared. But they
also make it clear that artificial means and fire especially must be resorted
to in areas where it is desirable to maintain the subclimax as a relatively
permanent type (plate 87).
The importance of burn subclimaxes has been emphasized by Clements
(1910: 56) in the case of the lodgepole pine:
" The lodgepole forest is the key to the silvicultural treatment of the forests
of the eastern Rocky Mountains, especially in Colorado and Wyoming. Its
position in a zone between Douglas fir and yellow pine below, and Engelmann
spruce and alpine fir above gives the forester a peculiar advantage. Its
enormous seed-production, the power of the seeds to remain viable in the
cones for years, its preference for soils of moderate water-content, the de-
pendence of reproduction upon sunlight, and its rapid growth are all points
of the greatest value in enabling the forester to accomplish his results. And
it is by means of fire properly developed into a silvicultural method that the
forester will be able to extend or restrict lodgepole reproduction and lodgepole
forests at will. "
The relation of aspen to lodgepole in bum subseres and its role as a tem-
porary type have been dealt with in the same study (20, 47). The significance
of aspen as a burn subclimax and its importance as a temporary type have
been discussed by Pearson (1914: 249), Sampson (1916:86), and Baker (1918:
294, 389). In the Northwest where Pseudotsuga forms a remarkably per-
manent subcUmax in burns of enormous extent, Hofmann (1917:23) has
reached the following conclusions:
"The study of burns and cut-over areas in the Douglas-fir region of the
Pacific Northwest has brought out the following facts : The distance to which
seed trees are capable of restocking the ground is limited to from 150 to 300
feet. They can not, therefore, account for the restocking of the large burned
areas. The irregular dense stands of young growth are due to seed stored in
the forest floor or in cones. This seed retains its viability through the fire
and is responsible for the dense reproduction that springs up after the first
fire. The even-aged stands of reproduction immediately following a fire,
regardless of location of remaining seed-trees, the irregular alternation of
dense stands of reproduction with grass areas, and the failure of reproduction
on areas burned over by a second fire before the stand reaches seeding age, or
by consuming all of the duff and precluding any possibility of seed remaining
after the fire, all point to the seed stored in the duff as the principal source of
seed responsible for the restocking.
"Since the seed must be produced by the stand before it is destroyed, the
age at which the different species begin to produce seed is of the utmost im-
portance. It varies greatly, and this variation alone is often the controlling
factor in determining the composition of the second growth. For example,
when western white pine, Douglas fir, and knobcone pine (Pinus attenuata)
appear in a mixed stand which is destroyed by fire, all of these species may
again appear in the next stand; but if this second growth is destroyed by fire
CLEMENTS
PLATE 87
A. Chatnasbalia foliolosa indicating fire in pine forest, Yosemit« National Park,
California.
B. Ceanolhus velutinus indicating fire in pine forest, Bums, Oregon.
CLEMENTS
PLATE 88 t
^^J^.
A
^:^ '^^Vi^;
A. Anaphalin and Kpilobium indiciiting u rcfcnt burn, Wind Kivcr KxiMTiincnf Siuti on,
Washington.
B. Pteris and Rubus indicating fire following one marked by Arbutus, Prwnus, etc., Pseudo-
tsuga forest, Eugene, Oregon.
CLIMATIC AND EDAPHIC INDICATORS. 355
when it is from 10 to 12 years-old, the next stand will consist principally, if
not wholly, of knobcone pine. The knobcone pine begins producing seed
when it is 6 years old and is producing good crops of seed at 10 years, while the
white pine and Douglas fir bear only occasional cones at ages under 12 years.
Therefore the knobcone pine is the only species which has any seed present to
produce a forest stand following the second fire. Instances of such types are
the knobcone pine types on the Siskiyou National Forest. "
Scrub communities are regularly indicators of fire where they are in contact
with forest. In fact, sagebrush appears to be a fire subcUmax in the pifion-
cedar woodland, as well as in the southern portion of the Coastal chaparral.
Chaparral, however, is the typical scrub indicator of fire in woodland and
forest. This is as true of the subcUmax chaparral along the eastern edge of the
grassland climax as.it is of the Petran and Coastal associations. The most
characteristic development of chaparral as a burn indicator is found in the
montane forest in CaUfornia, where the scrub persists as a more or less com-
plete forest layer (p. 213; cf. Mitchell, 1919: 39; Foster, 1912: 212). Chaparral
owes its importance as a fire indicator to its remarkable abiUty to form root-
sprouts, and hence the form of the dominant shrubs is itself a response to fire.
Fire in chaparral leads to a short subsere, in which the herbaceous stsiges per-
sist for only a few years before the new shoots overtop them. Repeated fires
may produce a subcUmax characterized by Eriodictyum, or by Artemisia,
Salvia, and Eriogonum. In the region of its contact with woodland and forest,
chaparral is an indicator of forest burns, and consequently is subcUmax.
This is true in both associations, but is more marked in the Sierran, perhaps
because of its greater massiveness. Munns (1919:9) has assmned that aU
of the latter is a temporary type due to fire, but this certainly seems not to be
true of the regions with 12 inches or less of rainfall. This assumption is
largely due to a misconception of what constitutes the test of a climax. Both
of the tests used, the successful planting of trees and the existence of scattered
trees and tree stands, would prove the grassland climax to be a temporary
one. The critical processes in the estabUshment of a forest are seed-pro-
duction, dissemination, and ecesis, and artificial planting is powerless to throw
Ught upon the outcome of these. Further studies of the chaparral formation
during the past three years have confirmed the view expressed in 1916 (Plant
Succession, 180) that it constitutes a real climax, though portions of it are
undoubtedly subcUmax. This view is supported by the conclusions of Cooper
(1919), who has made an intensive study of the California chaparral upon the
instrumental and successional basis (plate 88).
Grazing indicators. — With reference to the forest itself, only those grazing
indicators are of importance that indicate overgrazing, and hence actual or
potential damage to the reproduction. The presence of the usual overgraz-
ing indicators would serve this purpose, but these are usually accompanied by
evidences of damage to the seedlings as well. However, while abundant
evidence of this nature denotes overgrazing, it is still a question as to just
when this becomes critical in the reproduction of the forest. In fact, it is
clear that the critical degree of overgrazing depends much upon the nature
of the community, time of year, age of the seedlings, and other factors. Much
Ught has been thrown upon the problem by three careful studies in the national
forests.
356 FOREST INDICATORS.
Hill (1917: 23) has reached the following conclusions with reference to the
damage done to seedUngs in the yellow-pine forests of northern Arizona:
"Of 8,945 trees of a size subject to grazing, observed over a period of three
years, 1,493 or 16.7 per cent were severely damaged each year and 1,222
or 16.1 per cent were moderately damaged. The most injured are the
seedlings, 21 per cent of which are seriously damaged. The damage gradually
decreases with an increase in the size of the trees. Trees above 4.5 feet in
height are free from damage by browsing. The greatest amount of damage
occurs during the latter half of June and the first part of July, or when the
effects of the spring dry period are most pronounced. Under normal con-
ditions of grazing, cattle and horses do an inconsiderable amount of damage
to reproduction. Sheep under the same conditions may be responsible for
severe injury to 11 per cent of the total stand. On overgrazed areas all
classes of stock are apt to damage small trees severely. Cattle and horses
may damage about 10 per cent of all reproduction. Where sheep are grazed
along with them, however, at least 35 per cent of the total stand may be
severely damaged. The amount of palatable feed available during the graz-
ing season, and especially during June and July, has an important bearing on
the amount of damage that grazing will cause to reproduction" (plate 89).
Sparhawk (1918) has shown that the damage to seedlings more than a
year old is negligible in the yellow-pine forests of central Idaho, while the
mortality of seedlings less than a year old averages 20 per cent. He states
that, on the whole —
"More than three times as many seedlings were killed by other causes as
were killed by sheep grazing, and five times as many were injured. As a
general rule, the range should be grazed just enough to remove the greater
part of the palatable forage. Extensive browsing of the least palatable species
or of conifer reproduction is the best evidence that the area is being grazed
too closely not only for the good of the range, but also for the best interest of
the stock. Steep slopes with loose soil, particularly where the seedlings are
less than a foot and a half high, and reproducing burns, clear-cut areas, or
plantations with seedlings up to 5 or 10 years old, depending on the site,
should be grazed rather lightly, especially in the first part of the season or
during a wet period. In many instances it will be desirable to eliminate
grazing entirely from plantations or other areas of seedlings less than three
years old. During a dry season spots where danger of fire is greatest may be
grazed as closely as possible. "
Sampson (1919: 25) has summarized the results of his study of the effect
of grazing upon aspen reproduction as follows :
"The leafage, young twigs, and branches of the reproduction are browsed
with varying degrees of relish by both cattle and sheep. Over 90 per cent of
the damage inflicted by stock is chargeable to browsing, the injury due to
trampling, rubbing, and similar causes being negligible. Sheep are responsible
for severe damage to the reproduction, both as it occurs in standing timber and
on clear cuttings, regardless of the variety and supply of choice forage. Cat-
tle cause some damage, but the extent of injury is usually slight, except where
the lands are overgrazed or where the animals are inclined to congregate for
more or less lengthy periods. The injury and mortality chargeable to the
presence of live stock is roughly proportional to the closeness with which the
lands are grazed. Observations covering a 50-year period in standing timber
on sheep range showed that 27.2 per cent of the reproduction was either in-
CLEMENTS
PLATE 89
A. Pine reproduction in a fenced area, Fort Valley Elxperiment Station, Arixona.
B. Fenced quadrat showing effect of grazing upon reproduction, Cliffs, Arizona.
PLANTING INDICATORS. 357
jured or killed on lightly grazed plots, 31.8 per cent on moderately grazed areas,
and 65 per cent on heavily grazed plots. During 1915 and 1916 the average
percentage of injured and killed sprouts by cattle browsing was 1.6, 2.4, and
26.8 on lightly, moderately, and heavily grazed plots, respectively. On clear-
cut lands, where the reproduction is conspicuous and the stand even, the
annual mortality due to sheep grazing is exceedingly heavy. As a rule, three
years of successive sheep grazing on such lands results in the destruction of
the entire stand. "
Cycle indicators. — Trees, and shrubs also, may serve as indicators of climatic
cycles by virtue of their growth, seed-production, or reproduction. In addi-
tion, there appears to be a certain correlation between the frequence and in-
tensity of forest fires and the dry and wet phases of the cycle. The growth
of trees as recorded in the annual rings is the classic material for the studies of
Douglass, Huntington, and Kapteyn upon chmatic cycles. The width of the
ring indicates the varying rainfall of different years so clearly that Douglass
(1919) has found it possible to cross-identify rings from trees grown many
hundreds of miles apart. He has also found that the yellow pines of central
Arizona often indicate two growing periods in one year by the formation of a
double ring, and Shreve (1917: 706) states that this appears to be regularly
the case with trees at 6,000 feet in the Santa CataUna Mountains. It seems
almost certain that height-growth and volume will likewise show cycle cor-
relations, and this is suggested by Pearson's results in the study of the re-
lation of height-growth to spring precipitation in northern Arizona (p. 351).
The suggestion that seed-production is related to chmatic cycles is based upon
its well-known periodicity (Zon and Tillotson, 1911: 133), as well as upon the
fundamental fact that as a growth response it is controlled primarily by water
and temperature. It seems probable that the seed-production cycle of pines
especially is a response to the interaction of the 11-year cycle and the excess-
deficit cycle of 2 to 3 years.
Reproduction reflects more or less faithfully the variations in rainfall dur-
ing the 2 to 3 year, the 11-year, and the 22-year cycles. This correlation is
clearly seen in the case of woodland and montane forest, especially at the
lower limit, but it is naturally less evident in climaxes with a higher rainfall.
It is most striking where woodland or forest is in contact with a conununity
of lower water requirements, such as grassland, sagebrush, or chaparral, and
shows less in the reproduction on the forest floor. All the cases of tree savan-
nah and "natural parks" so far investigated warrant the working hypothesis
that reproduction in such areas is cycHc and corresponds as a rule to the
11-year cycle, though minor variations conform to the 2 to 3 year cycle.
There is also considerable evidence that the success or failure of planting
operations has often been determined by their accidental coincidence with the
wet or dry phases of the 1 1-year cycle, while it is obvious that in the future
planting should be carried out with reference to the phases of the 2 to 3 year
and 11-year cycles (plate 90).
PLANTING INDICATORS.
Kinds. — Indicators of sites for planting are of two kinds: (1) those that
indicate the former presence of forest; (2) those that suggest the possibility
of developing forest in grassland or scrub areas. The first are indicators of
reforestation, the second of afiforestation. The obvious indicators of reforesta-
358 FOREST INDICATORS.
tion are relict survivors, or trunks and stumps. Less obvious but equally
conclusive are charred fragments or pieces of charcoal in the soil. In those
cases where there is no direct evidence of the original forest, the desired clues
are readily afforded by indicator communities which bear a definite relation
to the forest. Such are serai and especially subclimax communities which
exhibit a successional relation to the forest cUmax, and societies of shrubs or
herbs which formed layers in it. WhiJe the latter are frequent in burns and
clearings, they are usually accompanied by tree relicts which furnish more
direct evidence. In some cases, however, they are the sole indicators of the
former existence of forest in a particular spot. Subclimaxes are by all odds
the best indicator communities of forest cHmaxes, since they show that the
habitat has reached the condition in which the chmax dominants can thrive.
The earlier communities of a subsere have nearly the same value, since the
habitat undergoes relatively slight change. In the case of a prisere, only the
grass and scrub stages indicate that the slow reaction upon the originally bare
area has reached a point in which remaining changes may be compensated by
planting operations. Afforestation indicators are savannah, chaparral, or
grassland of tall-grasses, in which the water requirements are sufficiently near
those of trees that the gap may be bridged by planting methods, and espe-
cially by making use of the increased rainfall of the wet phase of the climatic
cycle.
Furthermore, the indicators of sites for planting or sowing serve also to
indicate the preferred species. In the case of reforestation, the general rule
is that these are the climax trees that were in possession, but reasons of manage-
ment may make it desirable to employ a subclimax dominant, such as lodge-
pole pine. Similarly, the growth-form best adapted for planting in a region
is the one developed by that region, as the Forest Service has repeatedly
demonstrated at its experiment stations. In the case of afforestation, the
indications as to species must be derived from tree communities somewhere in
contact with the grassland or scrub, as from pine in the case of the sandhills of
Nebraska, from the indications of an intermediate conamunity, such as scrub,
or from the comparative study of habitats.
Prerequisites for planting and sowing. — The critical part played by rodents
and by competition in natural reproduction was recognized more than a
decade ago (Clements, 1910). Extensive tests of sowing in many national
forests by the Forest Service has shown that destruction or control of the
rodents is imperative (Tillotson, 1917:50). In fact, it seems evident that
for practically all regions rodents are the most serious enemies of both natural
and artificial reproduction, and that they should be systematically and
permanently cleared out of all areas in which reproduction is important. Com-
petition is a process which is less readily controlled on a large scale. Com-
petition for water is much more decisive as a rule than for light, the latter
usually becoming critical only in dense scrub or similar communities. The
disturbance of the soil involved in planting seedUngs or in sowing by the seed-
spot method usually suffices to reduce water competition sufficiently, except in
a grass sod. The latter is usually encountered in clearings and in grassland
associations in which afforestation is the method to be employed. In climax
grassland, where the annual rainfall is less than 25 inches, the grasses use all
of the water-content during the drier portions of the season. As a consequence
CLEMENTS
A. Reproduction cycle of I'icea cngclmanni, I'ncoiiipahnre Plateau, Colorado.
B. Extension of Juniperun into sagcbnish (iuriuK wet phase of cycle. Miiford, Utah.
PLANTING INDICATORS. 359
seedlings or transplants have little chance of survival unless the sod is de-
stroyed about them, or unless planting is done during a period of unusual rain-
fall. As a desirable precaution under all conditions, the competition of the
grass cover should be decreased by such treatment as the density of the sod
and the nature of the soil will permit (Bates and Pierce, 1913:43). By far
the most important practice in this connection, however, is the utilization of
climatic and seasonal cycles to evade serious drought during the first few
years (Hofmann, 1919).
Use of climatic cycles. — The critical importance of wet and dry periods for
planting plans is strikingly shown by the variations in rainfall for the two
areas in which afforestation has been tried on a large scale. The lowest rain-
fall at Valentine, on the northern edge of the sandhill region of Nebraska, was
10 inches in 1894; the highest was 28 inches in 1905. The lowest rainfall at
Garden City, in the sandhill region of Kansas, was 9 inches in 1893; the
highest was 29 inches in 1898. In both cases the rainfall of the wettest year
was practically 3 times that of the driest, and the wettest and driest years
departed practically 10 inches from the normal. A somewhat similar con-
dition is shown at higher altitudes, where most of the reforestation planting
and sowing is done. The base of Long's Peak, altitude 8,700 feet, shows a
variation from 14 to 30 inches, while Pike's Peak, altitude 14,100 feet, exhibits
a range of 9 to 44 inches. In all of these, the minimum rainfall occurred at
the maximum of the 11-year sun-spot cycle, while the maximum rainfall either
occurred at the sun-spot minimum or was related to it through the excess-
deficit cycle of 2 to 3 years. In planting operations, the minimum is to be
avoided at all costs, and this can be done almost certainly by utilizing the
date of the maximum of the sun-spot cycle of 11 years. It is almost as im-
portant to anticipate a period of several wet years. The correspondence of
the wet phase with the sun-spot minimum is not so good as that of the dry
phase with the maximum, but it is sufficiently close in time and amount to
make a great improvement over present methods. When the excess-deficit
cycle is taken into account, the correspondence becomes so close as to warrant
the assumption that planting can be planned in such a way as to avoid dry
periods and to coincide with wet ones. As already shown in Chapter V, it is
necessary to determine the operation of the climatic cycle in the particular
region concerned.
Reforestation indicators. — The first definite proposal to use native plants as
indicators of specific planting sites appears to have been made by Zon (1915) :
"The selection of sites suitable for planting in a region which has been
stripped of its natural timber is among the most perplexing problems. As
long as there is a remnant of the virgin forest left, the latter may serve as a
guide in selecting the species to plant on the given site.
"When, however, as is the case of the Ephraim Canyon and several other
canyons on the Manti Forest, the original virgin timber has nearly disappeared
altogether, both as the result of severe bums and grazing, and has been re-
placed by shrubs, herbaceous vegetation, and wide stretches of aspen cover
extending over an area originally occupied by several forest types, the ques-
tion of deciding what species to plant on a given site becomes very difficult
indeed. In such cases the shrubs and the herbaceous vegetation which occur
throughout the canyon can be used to advantage as an indicator of the mois-
360 FOREST INDICATORS.
ture content of the different sites and therefore for prognosticating the kind
of timber the site can best support. The native shrubs and herbaceous
vegetation, since they are not merely forerunners of the forest type that will
eventually develop on a given site, but are also associates and are characteris-
tic of different types as their typical undergrowth, are useful in deciding upon
the species to plant. This is true not only where the original forest has en-
tirely disappeared, but also on sites where there are still some traces of the
original stand but which, because of the change in the physical condition of
the site brought about by clear-cutting or burning, may better support a
species which naturally grows at a somewhat lower elevation.
"For the purpose of artificial reforestation, Ephraim Canyon may be di-
vided into five vegetation belts. The upper and lower limits of these vegeta-
tion belts vajy, of course, on the southern and northern exposures; on the
southern slopes the upper limits of each vegetation belt will extend to a higher
elevation than on the northerly slopes, but wherever a certain vegetation is
found it may be indicative of one or another natural timber belt, irrespective
of the altitude or exposure. These five belts are as follows: (1) the lower
timberless belt; (2) the yellow-pine belt; (3) the Douglas-fir belt; (4) the
Engelmann-spruce belt; and (5) the upper timberless belt."
The indicators of the various zones are shown in figure 25.
Tillotson (1917:53) has pointed out the importance of indicators in the
selection of planting sites (plate 91) :
"The suitabihty of an area is very strongly indicated by the natural growth
present. This is a pretty fair criterion of the quahty of the site, and it points
out the species which are most hkely to succeed — either those which naturally
occupy the area or others whose demands upon soil and chmate are quite
similar. A heavy growth of trees on similar adjacent sites will indicate that
the area is quite probably suitable for sowing or planting; while a sparse growth
of a drought-resistant species of tree on such sites will indicate that the area is
only suited to reforesting' with very drought-resistant species and that even
then success will be uncertain."
He has also given a detailed summary of the planting indicators for the
various regions and the most important species of the West. The nature and
importance of his account may be gained from the following extract, which
gives the indicators for Utah and southern Idaho:
"Western yellow pine in Utah: (1) Burned-over areas in the natural yel-
low-pine types; (2) areas covered with brush, mainly of oak, maple, and
service berry; (3) areas covered with open stands of scrubby aspen; (4) sage-
brush areas.
"Western yellow pine in southern Idaho: (1) Those sites producing yellow
pine naturally; (2) brush areas withjn the limits of yellow pine and adjoining
stands of that species; (3) open grassy areas in the neighborhood of timber
stands.
"Douglas fir: (1) Bums within the fir type; (2) sites covered with aspen
of moderate density; (3) bums in the Engelmann spmce type; (4) areas
covered with bmsh of oak, maple, service berry, cherry, and other deciduous
species; (5) open grassland and mountain meadows. The planting of this
species naturally centers mainly around the aspen type, particularly in Utah.
The last two sites are not considered favorably for planting at present.
"Engelmann spmce: (1) Bumed-over, non-restocking Engelmann spmce
and balsam-fir cuttings; (2) the denser and better stands of aspen occurring
at high altitudes; (3) lodgepole-pine bums.
CLEMENTS
A. Arbulun indicator of reforestation sites, Pmiulotsuya forest, Kugene, On'gon.
B. ReprotkictioD of Pseudotnuga from seed stored in soil, Wind River Kxi)eriment Station,
Washington.
PLANTING INDICATORS.
361
"Lodgepole pine: (1) Lodgepole-pine burns which are non-restocking;
(2) non-restocking Engehnann-spruce burns; (3) aspen-covered areas at
higher altitudes. This species is not thought suitable for planting on brush
areas nor on open grassy land where sheltering objects are missing."
10,000;
PROTECTION' PLANTING
ELDER. GOOSEBERRY,
ALPINE FIR
ENOELMANN
SPRITCE SITES
LODGEPOLE
PINE SITES
Abiei lasiocarpa - 100
Pachyiitigrma myrsiniteg-lO
Rudbeckia occidentalii -10
Sambucui inicrolKitrys-lOO
Pachygtifrtna myrsinitc8-60
Populus tremuloide8'60 (Aspen)
Abies lagiocarpa-100 (Alpine fir)
Rudbeckia occidentalig- 100 (Cone flower)
Ribes inebrians-lOO (Mt. Currant)
Symphoricarpug occidentalig-SO
Opulagter malvaceug -10 (Nine bark)
Pinui flcTcilir
A.lagiocarpa (gbrab)
Chrysothamnus ip.
Salix glaucopt
DOUGLAS FIR
SITK9
Symphoricarpus occidentalig-lOO (Deer brush)
Populus tremuloideg-lOO (Agpen)
Pachygti^ma myrginites-lOO (Mt.Myrtle)
Lonicera involucrata (Honeyguckle)
Ribeg gp.- 10 (Wild Gooseberry)
Sarabucus microbotryg-60 (MtElder)
Berberis repens -100 (Barberry)
YELLOW PINE
SITES
Quercua grambellii-lOO(Oak) Khas trilobata-10(8nm«c)
Purshia tridentata- lOO Cercocarpu* parvifoUua-100 (UUMaho^nj)
' Betula fontinalis-lOOCDirch)
'Berberis repeoa-SO (Barberry)
Arctostapbylua pungrens- 100 (Manzanita')
Symphorirarpua occldentalU-lO (Deer bruali)
Rosa f endleri ■ 100 (Rosebush)
Amelanchier alnifolia 50 (Juneberry)
NO TREE
PLANTING
Rosa fendieri (Rose bush)
Amelanchier alnifolia (Juneberry)
Pinus edulig (Pinon) Juniperus utabensig (C^edar)
'Artemisia tridentata (Sagebrush)
Chrysothamnus nauseosus (Rabbit brush)
Peraphyllum ramosissitnum (Wild apple)
Bromus tectorum (Cheat brome)
Fio. 25.-
-Indicators of planting sites in the various zones, Utah Experiment Station,
Ephraim. After Zon.
Korstian (1917: 281) has made use of the herbaceous and shrubby species
in distinguishing between Sites I and II for yellow pine in the Datil National
Forest in New Mexico.
"A perusal of the list shows marked differences in the individuahty of the
vegetation of the two sites. Site I is shown to produce such typical meso-
phytes as Mnium sp., Agrosiia hiemalia, Bromus polyanthus, Muhlenbergia
wrightii, Populus tremuloides, Arenaria conjusa, Cerastium longipedunculatum,
Silene laciniata, Aquilegia chrysantha, Thalidrum wrightii, Draba helleriana,
Potentilla atrorubens, P. criniia, Rosa fendieri, Geranium richardsonii, Viola
neomexicana, Amarella scopulorum, Gentiana bigelowii. Prunella vulgaris,
Mimulus langsdorfii, Penstemon virgatus. Campanula petiolata, and Solidago
neomexicana. Site II bears such transitory species and xerophytes as Poa
rupicola, Commelina dianthifolia, Yv^ca sp., Quercus grisea, Portulaca oleracea,
Heterothrix longifolia, Cercocarpua brevifiorus and Hymenopappus radiatus.
362 FOREST INDICATORS.
The moss {Mnium sp.) was found only in cool, moist, and shaded situations,
thereby indicating unusually favorable site conditions. The monkey flower
{Mimulus langsdorfii) was the only plant which was confined to the proximity
of water, indicating excessive soil moisture conditions.
" Practically all of the species listed a.s occurring entirely on Site II, which
do not overlap on other sites, were found in hot, dry, and unshaded situations
and might be regarded tentatively as indicators of poor western yellow-pine
sites in the San Mateo Mountains. The mesophytes listed as possible Site I
indidators were not found on poorer sites in this locality. However, it may be
true that further detailed studies in the San Mateo Mountains might require
a different listing of the vegetation than that here given. A number of the
species listed as occurring on only one site are, to the writer's personal knowl-
edge, known to occur on different sites in other parts of the Southwest. The
vegetation on Site II was comparatively sparse and more open than on Site I
where it was also more luxuriant and vigorous. Those species which were
found to overlap on both sites normally made their optimum development on
Site I. Approximately twice as many species were found on Site I as on Site
II."
Afforestation indicators. — As already stated, the indicators of the pos-
sibility of forest production in grassland and scrub climaxes are either such
extra-regional communities of trees as are found in savannah or in the fring-
ing woods of river valleys, or such grasses and shrubs as indicate an approach
to the water requirements of trees. As a matter of fact, practical afforesta-
tion has been confined chiefly to the sandhill regions of Nebraska and Kansas,
in the first of which all four of these indicators have been present in some degree.
Indeed, the success of planting in Nebraska and its failure in Kansas are related
to the fact that these indicators were present in the one State and largely
lacking in the other. While it is clear that no sharp line can be drawn be-
tween reforestation and afforestation, the latter is regarded as having to do only
with those climaxes, grassland and scrub, in which trees occur at the margins
or in valleys. While pine savannah and valley woodland were doubtless more
extensive in the sandhills of Nebraska during the wet phases of some of the
major climatic cycles of the present geological period, it is practically certain
that this region has belonged to the grassland formation since the Miocene
at least (plate 92).
Bessey (1887, 1895) was the first to point out the evidence which indicated
that the sandhills of Nebraska could be forested, or reforested as he regarded it.
This evidence consisted wholly of valley and canyon reUcts of woodland,
chiefly yellow pine. It was summarized as follows :
"There are many isolated canyons which contain trees; there are western
as well as ea.stem trees and shrubs in these canyons; the yellow pine of the
Rocky Mountains now grows with other trees upon the hills of Pine Ridge
from the Wyoming hne in Sioux County to the Dakota line in Sheridan County ;
the yellow pine is now to be found in the canyons of the Niobrara River and
its tributaries as far east as the border of Holt County ; it extended eastward
along the North Platte River and Lodge Pole Creek to Deuel County until the
pioneers destroyed it, forty or fifty years ago ; it grew in considerable quanti-
ties in at least one station on the Republican River until destroyed by the
early settlers; in the Loup Valley there are yellow pines on the South, Middle,
and North Loup Rivers; logs and fragments of pine trees occur here and there
in the sandhills."
CLEMENTS
PLATE 02 4
A. Salix ami Ceatwlhua iudicaliaii plaiiliug hilt; in sandhills, Halsey, Nebraska.
B. Ihree-year old plantation of jack pine (Finm divaricata) in sandhills,
Halsey, Nebraska.
C. Jack pines 10 years after transplanting, Halsey, Nebraska.
PLANTING INDICATORS. 363
Pool (1914: 267) has considered in some detail the sandhill communities of
shrubs which show the close approach to the water requirements of trees,
among the most important of which are Celtis, Prunus, and Salix.
Bates and Pierce (1913: 15) have discussed the sandhill shrubs in their
general relation as indicators of forestation and of planting sites:
"Of the numerous woody undershrubs the yucca, or soap- weed (Yucca
glauca), is probably the most striking plant of the sandhill region and is least
abundant where the soil is the most stable and firm. Other shrubs, most of
which are more or less gregarious and form clumps or mats on the ground, are
the sandhill willow (Salix humilis), very common on north slopes and indic-
ative of good moisture conditions, the redroot or New Jersey tea (Ceanothus
ovatus), typical of sandy hilltops; the sand cherry (Prunus besseyi), found in
almost any site, but especially in the loose sand around blow-outs; and the
shoe-string bush (Amorpha canescens). Wolf berry (Symphoricarpos occi-
dentalis), choke-cherry, and wild plum frequently form thickets on the slopes
of pockets facing the southeast, where they are favored by the moisture from
snowdrifts. The first-named seldom becomes more than 2^ feet high, the
other two frequently 15 feet.
"From the standpoint of forestry one of the most important of the woody
plants is the low bearberry or kinnikinnik (Arctostaphyhs uva-ursi). While
this grows in only a few limited localities, on moist north slopes, it is thought
to be indicative of conditions favorable for western yellow pine, since it is an
almost invariable associate of that tree in the Rocky Mountains.
"Typical of the stream valleys in both Kansas and Nebraska are the false
indigo (Amorpha fruticosa), the buffalo berry, peach-leafed willow, sand-bar
willow, wolfberry, plum, and chokeberry. The diamond willow, one of the
Nebraska sandhills' most valuable small trees, is not found in Kansas. On
the whole, shrubby growth is much more typical of the Nebraska than the
Kansas sandhills, which usually have a heavy grass sod that does not permit
the growth of shrubs."
>l
A
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INDEX
Abies 208. 209. 210. 218. 220, 221. 222. 223.
224. 225, 226
amabilis 214. 217. 218. 223. 227
concolor 197. 205. 207. 208, 211. 212, 213,
223. 346
grandis 214, 215. 217, 218, 219, 220, 221
lastocarpa 216, 221, 222, 223, 224. 225. 226.
227, 228
magnifica 223, 224. 227, 228
shastensis 227
nobilia 217, 218, 223. 227
Acacia 162. 163. 164, 165. 166, 168, 169, 170,
172. 173, 277, 301
catechu 16
constricta 164, 168, 169, 171. 172, 174
greggii 164, 168, 169. 171, 172, 173, 174
Acanthaceae 60
Acer circinatum 219
glabrum 210. 219. 228
negiindo 42, 188
saccharinum 42
Acerales 178
AchiUea millefolium 15. 68. 93. 130. 152. 160,
187, 193, 214, 234, 299, 353
lanulosa 56
Acnida tamariscina 262
Aconitum columbianum 221
Actaea rubra 210
spicata arguta 219, 221
Actinella acaulis 199
floribimda 160
Actinolepis lanosa 176
Adelia phyllarioides 171
Adenium 61
Adenocaulum bicolor 214, 219. 221
Adenostoma 160, 161, 177, 181, 183, 191, 192,
301
fasciculatum 182, 191, 192
sparsifolium 191
Adolphia califomica 191
Adoxa moschatellina 226
Agaricua tabularis 12
Agave 61, 165. 167, 171, 300
lechugmlla 291
Agoseris aurantiaca 234, 236
cuspidata 130
grandiflora 152, 193
heterophylla 152
retrorsa 193
Agropyrum 31, 39, 48, 50. 96, 98, 106, 107,
115, 116, 119, 120. 121, 122, 123, 124.
126. 135. 136, 137, 138, HO. 142, 149,
150, 151, 152, 154, 156, 231, 266, 258,
273, 275, 279, 281, 285, 298, 301. 308.
309. 313
eaoinum 187, 287
^auc\un 38, 39, 49. 107. 119. 122, 125, 132,
137, 149, 150, 151, 155, 160, 259, 285,
287
scribneri 287
apicatum 39. 49, 115, 119, 150, 151, 155, 156,
160, 285, 287, 304
Agrostia 230, 234
alba 287
hiemalia 14. 93, 287, 353, 361
geminata 235
humilia 235
rosaa* 235
Alchemilla 60
Ali8ma39, 87, 110
Allenrolfea 12, 159
Allionia incamata 176
linearia 302
Allium 59, 61
acimiinatum 199
canadenae 299
cemuum 160, 210
mutabile 130
reticulatum 187, 234
Aloe 61
Alaine baicalenaia 226
Amarantus &mbriatus 262
hybridua 262
palmeri 176, 262
powellii 262
retroflezua 262
torreyi 262
wrightii 262
Amarella scopulorum 361
Ambrosia artemiaifolia 94, 302
Amelanchier 25, 178. 180, 183, 184. 185, 186,
191
alnifolia 178, 182, 183, 185. 186. 188, 191.
213. 290
Ammophila 60, 110
Amorpha 50, 105, 107
caneacena 39, 46, 120, 127. 130. 299, 363
fruticoaa 363
nana 130. 299
Amainckia intermedia 94, 176
teaaellata 176, 303
Anaphalia margaritacea 15, 93, 219
Andreaea 61
Andromeda 45, 87
Andropogon 19. 20. 61. 106. 118. 121, 123. 124.
126. 131. 132. 133. 138. 140. 142, 147.
197. 256. 258. 259. 273. 275. 278. 281,
286. 306. 308. 309. 321
contortua 17
furcatua 106. 121. 123. 124. 132. 133. 134. 287
hallii 133. 134. 281. 285. 287
nutena 123. 132. 133. 134. 287
aaccharoidea 132. 133, 134. 144. 146. 287. 323
acopariua 38. 40. 45. 106. 115. 119. 121. 122,
123. 132. 133. 134. 144. 202. 281, 285,
287
aorghimi halepenae 287
Androaace chamaejasme 234
occidentalia 130, 302
aeptentrionalia 210, 226, 234
Anemone 45, 60, 129
canadensis 130, 138, 190
caroliniana 51, 130
cylindrica 130, 190
875
376
INDEX.
Anemone — continued.
globosa 160
bepatica 58
naroissiflora 234
nemorosa 60
oregana 219
patens 130, 160, 187
quinquefolia 219, 221
Aneura 61
Angelica grayi 234
Anogra albicaulis 94
Antennaria alpina 234, 236
argentea 214
diocca 51. 130, 148. 160. 234. 236, 299
racemosa 219
Anthistiria gigantea arundinacea 16, 17
villosa 16
Apocynxim androsaemifolium 219
Aquilegia 45
chrysantha 361
coerulea 210, 226
fonnosa 219
Arabia drummondii 199, 226
holboellii 187
Araceae 60
Aragalus deflexus 160, 226
lamberti 120. 130, 187. 299, 317
speciosus 160
Aralia nudicaulis 190, 210
Arbutus 212
menziesii 205, 211, 216
Arctostaphylus 178, 183. 186, 191, 192, 301
bicolor 191
drupacea 213
glauca 191. 192
mansanita 191
nevadensis 228
patula 213
pringlei 192
pungens 178, 181. 182. 183, 185. 186. 190. 191
tomentosa 182, 183, 191
uva-ursi 60, 210, 363
Arenaria biflora 234. 236
confusa 361
fendleri 187
hookeri 290
Argemone platyceras 149, 302
Aristida 19, 41, 48, 119, 120, 121, 126. 140. 144.
145, 146. 148. 280. 286. 298. 299, 300
americana 176
ariionica 119, 145, 146, 147
baairamea 287, 307
bromoides 303
californica 119, 145, 146, 147. 287. 316
divaricata 119. 145, 146. 147, 148, 177, 287,
316
micrantha 287
purpurea 95, 106, 108. 115. 119. 121. 140,
142. 144. 145. 146. 147, 148, 149. 160.
307
longiseta 287
Arnica cordifolia 15. 93, 152. 210. 221. 226.
234, 236
Artemisia 12, 31, 41, 60, 61, 95, 106, 153, 154,
156, 157, 158, 159. 160, 243, 244, 286,
299. 300, 301. 306. 316, 321, 323, 355
arbuacula 157. 159, 301
californica 154, 156. 161. 192. 301
eana 154. 157, 158. 301
Artemisia — contintitd.
canadensis 160, 299
discolor 199
dracunculoides 130, 299
filifolia 140, 161. 170, 189. 301
frigida 31, 94, 95, 110, 120, 128, 130. 134,
140, 160, 187. 199. 299
gnaphalodes 128. 130. 149. 187, 190, 202,
299
heterophylla 193
norvegica 228
rigida 157. 290. 301
scopulorum 234
spinescens 157. 158, 301
tridentata 84. 91, 96, 152, 163. 154, 156. 157,
158. 160. 161, 257, 282, 290. 301
trifida 154. 157, 159. 301
Asarum caudatum 219, 221
Asclepias verticillata 299
Asperula 14
Aspidium 61
rigidum 214
Aster 129
alpinus 234
azureus 130
bigelovii 160, 187, 199
campestris 290
canescens 302
cricoides 149, 199
fremontii 152
levis 190
levis geyeri 152
multiflorus 128, 130, 299
novae-angliae 130
oblongifolius 130, 299
paniculatus 130
sericeus 128. 130. 299
spinosus 176
tanacetifolius 148, 302
Asteraceae 152, 162
Astragalus 50, 56, 106
alpinus 234
arrectus 152
bigelovii 148
bisulcatus 289, 299
carolinianus 289
collinus 152
crassicarpus 50, 120, 130, 160, 299
crotalariae 193
drummondii 160
flexuosus 160, 199
leucopsis 193
moUiasimus 299
nuttallianua 176
racemosus 299
spaldingii 152
Ataenia gnirdneri 290, 292
Athyrium cyclosorum 221
Atriplex 41, 84, 153. 154, 156, 159, 162, 165.
166. 168, 169, 171, 172. 257. 281. 282
canescens 95, 153, 154. 156. 157. 158. 169,
161, 164, 165, 168, 170, 171. 172, 174,
290
confertifolia 84, 96, 153, 156, 167, 158, 169,
257, 282, 290
corrugata 97, 159, 282
elegans 176
expansa 262
INDEX.
377
Atiiplex — continued.
nuttallii 97. 159. 281, 290
pabularis 282
polycarpa 170, 171. 172, 174
rosea 262
semibaccata 290
texana 176
volutans 290
Avena 156. 203. 279. 282, 283. 301. 304, 321
fatua 279, 282, 287, 301, 303, 304, 321
Axolla 61
Azorella 58, 60
Baccharis 172
wriKhtii 171, 300
Bacteris 61
Baeria gracilis 176, 303
Bahia absinthifolia 176
Baileya multiradiata 176
Balsamorhiza 120
deltoidea 160, 299
sagittata 152, 160, 290, 292, 299
Bambusa 61
Baptisia leucophaea 130, 138, 299
Bebbia juncea 171, 300
Berberis 187
aqiiifoliutn 219
nervosa 219
trifoliata 189
Besseya alpina 234
plantagioea 210
Betula92, 110
occidentalis 210
papyrifera 92
Bidens tenuisecta 187
Blechnum spicant 219
Boerhavia intermedia 303
torreyana 283, 303
viscosa oligadena 176
Bouteloua 41, 47, 48, 98, 106, 107, 109, 115,
116, 119, 120, 121, 123. 124, 126, 132,
135, 136, 137, 138, 140, 141, 142, 144,
145, 146, 148, 150, 154, 156, 163. 197,
272, 273, 275, 279, 281, 282, 286, 298,
300, 308, 313, 316, 317
aristidoides 176, 287, 303
bromoides 144, 145, 146. 147, 148, 287
ciliatus 287
ctirtipendula 323
eriopoda 119, 142, 144. 145. 146. 147. 148,
285, 287, 316
gracilis 27, 35, 38, 45, 47, 48, 106, 107, 116,
118, 119, 120, 121, 124, 125, 137, 138.
140. 142, 143, 144, 145, 146, 147, 148.
149, 155, 160, 268, 285, 287, 309, 316,
323
hirmita 119. 140, 141, 143. 144, 145, 146, 147.
148, 287, 323
oligostachya 305, 323
polystachya 176. 287. 303
raeemosa 45. 106. 119, 132, 133. 134. 138.
141. 144. 145, 146. 147. 148. 202, 287.
323
Tothrockii 119, 144, 145. 146. 147. 148. 177,
285. 287, 316, 317, 323
vesiita323
Bowlefda lobata 176, 303
Brasaica arvenris 290
nigra 45, 94, 262
Brauneria 121, 127
palUda 46, 127, 130, 299
Brickeliia grandiflora 187
Brodiaea capitata 193
oongesta 193
crandiflora 193
minor 193
Bromelia 61
Bromus 156. 203. 282. 283. 301, 304
brisaeformis 25
ciliatus 187
hordeaceus 25, 287, 303, 304
inermis 287
marginatus 42. 287. 292
maximus 94, 287, 304
Russoni 303
I>olyanthu8 361
nibens 282, 289, 304
tectorum 25, 160, 282, 287, 304, 321
Bryum 353
argenteum 15, 93
Buchloe dactyloides 305
BulbiUs 19, 48, 106, 107, 115, 116. 120. 121.
125. 126. 135. 136. 137. 138, 140, 141,
142, 143. 146. 149, 163, 258, 272, 273.
275, 281. 283, 285, 306, 308, 309, 313
dactyloidea 107, 120, 121, 137, 140, 141. 144.
287. 305. 326
Bulbophyllum 61
Butea frondosa 16
Buteo b. calurus 56
Cactaceae 60, 61
Calamagrostis 230
canadensis 287
langsdorfii 235
piiTpurascens 287
vaseyi 235
Calamovilfa 138. 256, 281
longifoUa 40, 115, 287
Calamus 61
Calandrinia menziesii 303
Calliandra eriophylla 148, 171, 300
Callirrhoe alcaeoides 130
involucrata 130
Calluna 14, 61
v\ilgaris 14
Caloehortus gunnisonii 160. 187
luteus 193
splendens 193
venustus 193
Calvatia 12
Calypso borealis 219
Campanula parryi 160
petiolata 361
rotundifolia 160, 187
alpina 234, 236
uniflora 234
Canotia holacantha 171
Carex 58, 60, 61, 96, 102, 106, 115, 135. 138,
230, 232. 233, 234. 235. 273
ablata 235
alpina 232
aquatilis 289
aristeta 289
atrata 232. 233. 235. 289
bella 233. 289
breweri 235
capillaris 232
concolor 232
douglaaii 289
engelmanni 232, 233
festiva 232. 233, 235, 289
378
INDEX.
Carez — continued.
glifolia 107, 120. 121. 137, 138, 231. 232. 233.
235
geyeri 152
iUota 232. 235
lanugiDoaa 289
marcida 289
nardina 232, 235
nigricana 232, 233, 235
nova 232, 233. 289
obtusata 231
pennsylvanica 130, 289
petaaata 232
phaeocepbala 235
pyrenaioa 232, 235
roasii 15
rupestria 231. 232. 233. 289
scirpoidea 235
siccata 289
apectabilia 235
Btenophylla 107, 120. 121. 137. 138
straminea 289
■tricta 289
tolmiei 232. 233
utriculata 289
vemacxila 235
vtilpinoidea 289
Carduua 93, 95, 120
folioaue 152
gardneri 152
hookerianua 226
palouaensis 152
plattenaia 160
undulatuB 120, 130, 149, 160, 299
Camegiea gigantea 41
Cania cbamaecriata 302
Castanopsia chryaopbylla minor 213
sempervirena 213
Castilleia affinia 193
ciilbertaonii 236
foliolosa 193
Integra 187
lutescena 152
miniata 160, 187, 210. 226. 290. 292
nevadenais 290
oreopola 236
pallida 236
occidentalis 234
parviflora 214 .
aessiliflora 130. 299
Casiiarina 61
Catastoma 12
Ceanothua 106, 161. 163. 177, 178, 180, 183.
185. 189, 195
eordulatua 213, 228
cuneatua 178, 181, 182. 183. 186. 186. 191
greggii 178. 182. 190
dentatua 191
divaricatua 182. 191, 192
hirautua 191
integerrimua 213
ovatua 189. 363
parviflorua 213
proatratua 213
Borediatua 191
vdutinua 45. 213
verruooflua 191
Cedrela toona 16
Oltia 90. 172, 189. 301. 363
oeddentalia 188
palUda 90. 171. 172
Cenchrua tribuloidea 94, 287
Centauroa cyanua 304
melitensia 303, 304
Cephalanthua occidentalia 189
Ceraatium arvenae 234. 236
longipedunculatum 361
Cercia 189
canadenaia 189
percocarpua 106, 177, 178, 180, 182, 183. 184,
185. 186. 188. 191. 195
breviflorua 361
ledifoliua 178. 182. 185. 186. 187. 191
montanua 25
parvifoliua 45, 178, 182. 183, 184. 185. 186,
187, 191. 192
Cereua 165, 166, 167. 172. 175. 197. 300
giganteua 91. 171. 172, 291
tiiurberi 171
Cetraria 61
Chaenactia douglasii 160. 214
Btevioidea 176
Chamaebatia folioloaa 213
Chamaecyparis 227
lawaoniana 217. 218
nootkatenaia 214. 217, 218, 223, 227
Chamaedaphne 45
Chamaenerium 45
angustifolium 14
Cheilanthea fendleri 202
Chenopodiaceae 152, 162
Chenopodium 61
album 94, 262
fremontii 176, 187, 199
leptophylliun 199, 302
Chilopsia 172
Chimaphila umbellata 219, 221
Chionophila jameaii 234
Chloria elegana 176, 287, 303
Chrysoma laricifolia 168, 171, 300
Chryaopsia villoaa 148, 199, 299
Chryaothamnua 12, 41, 157, 158
nauaecsua 153, 154. 157. 159, 161
glabratua 159
viscidifloruB 157. 158. 159
Circaea 61
pacifica 221
Ciraium arvenae 59
Citellua t. parvua 56
Cladonia 61
Cladothrix lanuginoea 176, 303
Clay tenia aaarifolia 221
linearia 152
megarhiza 234
Cleome integrifolia 290
Clintonia uniSora 219, 221
Colaptea chrysoidea 91
Coleogyne 181, 182, 183. 186
ramoaiaaima 182. 185
Coleua 86
Collinfiia parviflora 152
CoUomia linearia 302
Comandra umbellata 130. 160, 187. 202
Commelina dianthifolia 361
Condalia 165, 166. 169, 170
lycioidea 168, 171, 172, 174
apathulata 171
Convallaria majalia 58
Convolvulua occidentalia 193, 221
Corallorhiza 61
multiflora 214
Cordylanthua wrightii 160, 199, 202
INDEX.
379
Coreopsis palmata 130
tinctoria 94, 302
Corethrogyne filaginifolia 193
Corispermum hyssopifolium 262
Cornua 180
amomum 189, 210
asperifolia 189
canadensis 219
Duttallii 219
stolonifera 182, 188
Corj'lus americana 188
rostrata 189, 213
Cowania 181, 182
mexicana 181, 182, 183, 185, 186
Crassulaceae 60
Crataegus coccinea 188
Crepis intermedia 214, 290. 292
occiden talis 214
Cresaa 257
truxillensia 84
Ciocus 60
Crotolaria lupulina 202
Croton corymbulosus 303
texensis 302
Cryptanthe angustifolia 176
pterocarya 176
Cupressus 205
goveniana 211
Cuscuta 61
Cyanocitta s. frontalis 56
Cyathea 61
Cycas 61
Cyclamen 59, 60, 61
Cycloloma platyphyllum 94, 262
Cyperaceae 230
Cyperus alternifolius 88
Dactylis glomerata 287
Dalbergia sissoo 16
Dalea 166, 171
emoryi 171
laxiflora 130, 148, 299
schottii 171
scoparia 170
spinosa 90, 171, 174
Danthonia 230, 303
californica 287
intermedia 287
Dasjlirium 165, 167, 171, 286, 300, 328
texanum 291
wheel eri 291
Daucus puaillus 176, 303
Delphinium carolinianum 51
dedonim 214
hesperium 193
parry i 193
penardi 109
scaposiim 176
scopulorum 160, 187
Dendromecum rigidum 191
Deschampoia oaeapitosa 230, 232, 287
Desmanthufl jamesii 149
Desmodium batocaule 202
Dicentra formosa 219
DioBOorea 61
Dipodomys deserti 90
Disporum majus 221
smithii 219
Distichlis 12, 84, 257
spicata 84. 170, 287
Dodecatheon alpinus 236
clevelandii 193
Dondia 110, 172
moquinii 84, 170
sufTrutescens 84
Douglaaia nivalis 234, 236
Draba aurea 187, 226, 236
breweri 234
caroliniana 130, 199, 302
helleriana 361
nivalis 234, 236
streptocarpa 226, 234
Dracaena 60
Draperia systyla 214
Dry as 61
octopetala 234, 236
Dugaldia hoopesii 25
Dyssodia papposa 302
Echinochloa crus-galli 287
Echinopanax horridum 219
Eichhornia 61
Elaeagnus 189
argentea 181, 182, 188
Elymus 110, 133. 134. 256, 281
canadensis 132. 134, 287
condensatus 151, 160, 287
sitanion 115. 149. 150, 151, 160, 287
triticoides 187, 287
virgin icua 190
Elyna 230, 232
bellardi 232, 233, 235
Empetrum 58
Encelia 165. 166
farinosft 171, 172, 300
frutescens 171
Ephedra 61, 162, 164, 166, 166, 168, 170, 174.
277
nevadensis 171
torreyana 168, 169, 170
trifurca 171
Epilobium 93
alpinum 236
anagallidifolium 236
homemannii 236
paniculatum 187, 304
spicatum 93, 219, 353
Equisetum 28, 44, 59, 61, 87
arvense 79. 130
hiemale 130
levigatum 130, 289
Eragrostis 61
cynosuroides 17
major 287, 302
neo-mexicana 176
pectinacea 94
pilosa 176, 287, 302, 303
Eremiastnun bellidioidea 176
EremocarpuB setigerus 94, 304
Eriantlius ravennae 16
Erigeron 50, 106, 129
acris 93
asper 187, 210
breweri 214
canadensis 27, 94. 187, 262, 302
canus 160
compositus 234
corymbosus 152
divergens 302
elatior 226
flagellaris 109, 187
glandulosuB 187. 210
leionterus 234
pumilus 160
380
INDEX.
Erigeron — continued.
radios tus 234. 236
ramomu 129, 130, 299, 302
ealsusinosus 226, 236
uniflurus 234, 236
Eriocaulscese 60
Eriochloa punctata 176
Eriocoma ctispidata 133, 149, 151, 160. 287
Eriodiotj-um 355
californicum 191
Eriogonum 106, 161. 355
abertianum 148. 176. 303
annuum 94, 120, 302
cernuum 302
compositum 193
deflexum 176
faacioilatum 154. 156, 160, 161, 192
polifolium 161, 162
jamesii 300
marifoliiun 228
microthecum 299
effusum 209
nudum 193, 304
polycladum 148, 303
racemosum 160
trichopodum 176
umbellatum 160, 199. 214
ursinum 228
vimineum 304
wrightii 148, 300
Eriophyllum confertiflonim 193
lanatum 152, 193
Eritrichium argenteum 234
Erodium 304
cicutarium 290, 303, 304, 322
moschatum 303, 304
texanum 303
Eo'ngium vaseyi 304
Erysimum aaperum 187, 214, 228
parviflorum 160. 199
Erythronium grandiflonim 152, 236
Eschscholtzia californica 94, 193
mexicana 148. 176. 302, 303
Eupatorium altissimum 130
Euphorbia 95
sJboraarginata 176
capitellata 176
coroUata 130, 299
geyeri 94
marginata 94. 302
montana 187
preslii 176
Eurotia 154. 158. 159
lanata 153. 157, 290
Evax caulescens 176
Evolviilus argenteus 139, 149
Fagales 178
Fallugia 181, 182. 183. 185
paradoxa 182. 185, 186
Fendlera 181. 183. 185. 186
rupicola 182. 185
Festuca 150. 151, 152, 230. 231. 277. 303
brachyphylla 232. 233
confusa 25
megalura 25. 287
microstachys 25
myunu 303. 304
octoflora 176, 287, 302, 303
ovina 150, 155, 160. 226. 287
Bupina 235
■cabreUa287
Flourensia 146. 162. 163, 165, 166. 167, 168,
169, 170. 300
cernua 168
Fontinalis 61
Fouquiera 165. 166, 167, 169, 172, 173, 176
splendens 164, 168. 171, 172
Fragaria 58, 60
vesca 190. 210. 219. 221, 226
virginiana 130, 190, 214
Trankenia 257
grandifolia campestris 84
Franseria 162, 165, 166, 167, 171, 173, 283, 300
deltoidea 171, 172, 175, 300
discolor 262, 290
dumosa 171, 175. 300
tenuifolia 176, 262
FraxinuB 172. 174
lanceolata 42
viridis 181, 182, 188
Fritillaria pudica 152
Frullania 61
Funaria 353
hygrometrica 15, 93
Gaillardia aristata 148, 152
Galium 61
andrewsii 193
aparine 59, 190
boreale 152, 160. 187, 190, 210
scias 56
triflonun 210
Garrya 181
Gaultheria shallon 219
Gaura coccinea 160
suffulta 202
Geutiana affinis 210
amarella 226, 234, 236
bigelovii 361
calycosa 236
frigida 226. 234
newberryi 236
oregana 152
Georgia 61
Geranium 86
caespitosum 160, 187, 210
richardsonii 210, 361
viscosissimum 152
Geum 60
Gilia aggregata 120, 187. 199
filifolia 176
gracilis 303
Glycyrhiza lepidota 39, 120, 130, 299
Gnaphalium bicolor 193
decurrens 193
Gnetaceae 162
Goodyera 109
Grayia 158, 159, 282
spinosa 157
Grindelia 94, 95, 140
squarrosa 25, 130, 134, 149. 160. 199. 299
Gutierrezia 31. 94. 98, 110, 140, 154. 157, 158,
159, 162, 164, 165, 166, 168. 169. 243,
244, 280. 298, 299, 300. 320
microcephala 176
sarothrae 25. 95, 108. 130, 134, 149, 153. 157,
168, 171, 193, 199. 299
Gymnolomia multiflora 187, 199, 202
Haplopappus gracilis 148, 202, 303
linearifolius 193
macronema 228
parryi 210
pygmaeus 234
INDEX.
381
Haplopappus — continued.
spinulosus 299
Bxiffruticosus 228
Harpagonella palmeri 176
Hedeoma drummondii 187, 190
hispida 302
Hedysarum philoscia 289
Heleocharis 39, 87, 110
acuminata 289
obtusa 289
palustris 289
Heleodytcs bninneicapillus 91
Helianthella douglaaii 152
uniflora 290
Helianthus 28, 94. 282
annuus 42, 45, 79, 94, 176, 262, 302
grosse-seiratus 130
maximiliani 130
petiolaris 94, 176, 262, 302
rigidus 120, 130, 299
Heliopsis scabra 130, 190
Hemizonia clevelandii 304
fitchii 304
Hepatica 60
Heracleum lanatum 210
Heteromeles arbutifolia 191
Heteropogon 286
contortus 288, 323
Het«rotheca subaxillaris 176
Heterothrix longifolia 361
Heuchera 109
parvifolia 160. 187, 210
Hieracium 58
albiflorum 214
gracile detonsum 228
Bcouleri 152
Hilaria 19. 141. 146, 147. 148, 154, 162, 163,
166. 283, 306, 323
cenchroides 142, 144. 145, 146, 147, 148, 288,
326
jamesii 140. 143. 144, 156, 160, 282, 288
mutica 142, 146, 283, 288
rigida 144, 162. 171, 175, 300
Hippiiris 59, 60
Hoffmannseggia drepanocarpa 176
jamesii 176
stricta 149. 176
Holacantha emoryi 171
Holodiscus 181, 186, 187, 191
discolor 178. 182. 185. 191. 213
Hoorebekia racemosa 152
Hordeum jubatima 108. 288, 302
maritimum 288
gussoneanum 303, 304
murinum 288. 303, 304
nodosum 288
Horkelia gordonii 236
Hosackia americana 130
decumbens nevadensis 214
glabra 193
Houstonia angustifolia 130
Hydrophyllum occidentale 214
Hymenoclea 171, 172
salaola 171. 300
Hymenopappus filifoliua 148, 199
mexicanufl 202
radiatua 361
tenuifolius 299
H>'TOenothrix wrightii 202
Hypericum concinnum 193
Hypnum 61
Hypochaeris glabra 303. 304
radicata 304
Hypoxia hinnita 130
ImpatienB 14. 86
Imperata arundinaoea 17
Ipomoca 61
leptophylla 140
Iris 61
bartwegii 214
Ischaemum angustifolium 17
Isocoma 98, 162, 164, 166, 168, 169. 175, 300.
320
ooronopifolia 171, 172, 300
bartwegii 149, 168, 171
veneta 171
Isoetes 61
Iva axillaris 262, 290
xanthifolia 94. 262
Jamesia americana 210
Juglans 172
Juncaceae 230
Juncodes 230. 232
divaricatum 235
parviflonun 289
spicatum 232, 233. 235, 289
Juncus 61, 87, 102. 230. 233
balticus 289
castaneus 232
mertensianus 289
Dodosus 289
parryi 235. 289
tenuis 289
triglumis 232
Jimgermannia 61
Juniperus 193. 194, 195, 196, 197. 198. 200, 201,
346
califomica 195, 197, 200, 202, 203. 204
utahensis 196, 198. 203
communis 228
flaccida 196, 200
occidentalis 195, 196. 203, 204
monosperma 196, 198, 199, 200, 201
pachyphloea 196. 197. 200. 201
sabinoides 196, 200, 201
utahensis 196, 198. 199, 204
virginiana 196
scopulorum 196. 198. 199, 200
Eallstroemia brachyatylis 176, 303
grandiflora 176, 303
hirsutissima 303
parvifiora 303
Kalmia 87
Kelloggia galioides 214
Kobresia 230
bipartita 235
Kochia 159
vestita 84, 257
Koeberlinia 162, 166, 169, 174
spinosa 168, 171. 172
Koeleria 47. 48. 106. 109. 115. 119. 121. 122,
123, 124. 125, 127, 131. 132, 134. 135.
137, 138. 150, 151, 281, 286
cristaU38. 107, 119. 122. 132. 134, 137. 149.
150. 160, 288
Koenigia 61
Krameria 164, 166. 168. 100
glandulosa 168, 171, 175, 300
■ecundiflora 148
Krynitskia virgata 160
Kuhnia glutinoaa 130, 187, 290
rosmarinifolia 140
382
INDEX.
Ktuuia tridentata 202
Labiatae 58
Lactuca ludoviciana 290
pulchella 187
Lagophylla ramoaissima 304
Lamarckia aurea 288, 304
Lamiaceae 152
Lappula redowskii 176
texana 187, 302, 303
Larix 216, 210, 220, 221, 223, 228, 283, 353
lyaUii 223, 224, 225, 227, 228
oocidentalis 93, 215, 216, 219, 220, 221
Larrea 41, 90, 97, 145, 146, 157, 160, 161, 162.
163, 165, 166, 167, 168, 169, 170, 171,
172, 173, 174. 175, 177, 300
mexicana 164, 168, 171, 172
Lathynia coriaceus 289, 292
polyphyllus 219
splendens 193
sulphureiis 214
vestitua 193
Lecanora 61
Ledum 45, 87
Leguminosae 162
Lemna 61
Lepachys columQaris 120, 130. 148, 190, 299
Lepidium 304
alyssoides 302
intermedium 302
lasiocarpum 176, 302, 303
perfoliatum 160, 304
ramosum 302
thurberi 176
Lepiota 12
Leptochloa dubia 323
viscida 176
Leptotaenia multifida 152, 290. 292
Lepus c. melanotia 56
Lespedeza capitata 130
Lesquerella argentea 199
fendleri 149
gordoni 176, 302. 303
Leucobryum 61
Liatris 129
punctata 128. 129. 130, 149, 299
pycnostachya 128, 129, 130, 299
scariosa 128, 129, 130, 299
spicata 299
Libocedrus 212, 213
decurrens 70, 211, 212, 213
Ligusticum porteri 226
Liliaceae 60, 162
Lilium 59
parviflorum 219
Limnorchis stricta 210
Linaria 58
Linnaea 58, 60, 61
borealis 219, 226
longiflora 221
Linum perenne 160
rigidum 148
sulcatum 130
Lippia wrightii 171
Lithospermum canescena 130
hirtum 130. 190
linearifolium 130. 148
multiflonmi 187
ruderale 304
Lloydia eerotina 234
Lobelia 61
Lomatium foeniculaceum 130
tomentosum 193
Lonicera conjugialis 228
involucrata 226
utahensia 221
Loranthua 61
Lotus americanus 289, 302
hiuniatratua 176, 303
mollis 149
^ strigosua 304
Lupinus affinis 304
albua 27
argenteua 160, 289
fomioaus 193
grayi 214
holosericeus 289
lepidus 219
leptophyllus 176
leucophyllus 152, 289
lyallii 236, 289
micranthua 304
ornatus 152, 214
plattensia 289, 299
puaillus 187, 302
rivxilaris 219. 289
sellulus 292
sericeus 152
aparaiflorus 303
subalpinus 236
truncatua 304
volcanicua 236
wyethii 152
Lycium 171
Lycoperdon 12
Lycopodium clavatum 60
Lygodesmia juncea 299
Machaeranthera parvifolia 176
tanacetifolia 176
Madia 25
dissitiilora 304
exigua 304
Malacothrix fendleri 148. 303
glabrata 176
aonchoides 176, 303
Malvastrum coccineum 148, 160, 199. 299
exile 176
Maraamius 12 *
Marchantia 61. 353
polymorpha 93
Marailea 61
Medicago 58
denticulata 303, 304
luptilina 304
Bativa 290
Megachile 91
Melica 303
Melilotua 282
alba 45, 262. 290
indica 304
ofScinalis 290
Mentzelia albicaulis 176
Menyanthea 60
Menziesia femiginea 219, 221
Meriolix aemilata 51, 148
Mertenaia alpina 234
lanceolata 18,7
polyphylla 226
pratenais 210
Meaembryanthemum 61
INDEX.
383
MicrorhamnuB 166
ericoides 168
Microseris linearifolia 176
nutans 214
Mimosa biuncifera 171
Mimosaceac 162
Mimulus langsdorfii 361, 362
primuloides 236
Mirabilis oxybaphoides 187
Mitella pentandra 226
trifida 219, 221, 226
Mnium 361, 362
Monarda citriodora 202
fistulosa 130, 187, 190, 299
Monardella odoratissima 214
Moneses 59
uniflora 219
Monolepis nuttalliana 176
Monotropa 61
Moustera 61
Muhlenbergia 110, 141, 143, 146, 148, 281, 282
afRnis 202
gracilis 288
gracillima 140, 146, 288
porteri 145. 146, 147, 148, 177, 288
wrightii 361
Munroa squarrosa 288, 302
Musa 61
Myosotis alpestris 234
Myosurus minimus 302
Myrmecodia 61
Myrtillus 14
nigra 14
Nabalus asper 130
Navarretia leucophaea 304
Nelumbo 61
Neotoma 91
Nepeta cataria 187
Nipa 61
Nolina 286, 300, 328
enmipens 291
microcarpa 291
NjTnphaea69, 61, 110
polysepala 68
Nymphaeaceae 55
Oenothera primaveris 303
rhombipetala 94
Olneya 171, 174
tesota 171, 172
Ophrydeae 60
Opulaster 180, 181, 185, 187, 221
opulifolius 182, 185. 186, 210
Opuntia91,95, 162, 165, 167, 175,298,300,317
arborescens 168, 300
arbuscula 171, 300
basilaris 193
bigelovii 300
chlorotica 168, 171, 300
discata 171, 175, 300
engelmannii 171, 193, 291, 300
fulgida 167, 171, 172, 174, 291, 300
mamillata 171, 174, 300
lindheimeri 291
mesacantha 160, 199, 300, 320
phaeaoantha 168, 171, 300
polyacantha 120, 160, 300, 320
robust a 291
spinosior 167, 171, 172, 174, 291, 300
versicolor 167, 171, 172, 300
Orchis, 59 61
Oreoaooptea montanus 91
Oreoxia alpina 234
humilis 234
OrthocarpuB luteua 302
pilosua 228
purpurasoens 176, 304
purpxireuB albus 160
Ozalis 14. 61
acetosella 14
comiculata 193
oregana 219
pumila 219
stricta 130, 190
Pachylophus caespitosus 187
PaAhystigma 187
myrsinites 219, 221. 226
Paeonia brownii 193
Panicum 133, 134, 281
capillare 94, 288
hirticaulum 176
lachnanthum 288
scoparium 133, 134
texanum 322
virgatum 132, 133, 134, 288
Pappophonim wrightii 176
Parkinsonia 162, 165. 166, 167, 171, 172, 173,
175, 197, 300
aculeata 171
microphylla 171, 172, 175
torreyana 171, 172, 173, 174
Parnassia fimbriata 226
Parthenium 162, 166, 169
incanum 168, 171
Pasania densiflora echinoides 213
Pectis angustifolia 302, 303
papposa 176
prostrata 176, 303
Pectocarya 176
linearis 302
penicillata 176
Pedicularis centranthera 199
flammea 234
lanata 234
oederi 234
parryi 234
racemosa 226
Bcopulorum 234
semibarbata 214
wrightiana 202
Pentstemon 110
azureus 193
barbatus 187, 199
bridgesii 214
coeruleus 187, 199
confertus 152, 160, 236
deustus 214
glaucus 226, 234
gracilentuB 214
gracilis 130, 210
grandiflorus 130
haUii 234
beterophyllus 193
labrosus 214
linarioides 199
procerus 290
secundiflorufl 187, 210
Btrictus 160, 187
unilateraliB 160, 187
virgatuB 361
wrightii 176
384
INDEX.
Peramium ophioides 210
Peraphylluni 180. 181. 183. 185, 186, 187
ramoaisaimiun 182, 185
PetalostemoD 50. 95, 106, 107, 128. 281
csndidus39. 120, 127, 128, 129. 130, 148. 299
purpureus 30. 120. 127. 128. 130. 148. 299
Petaait«s58
Peucedanum 61
Phacdia alpina 234
crenulata 176, 303
diatans 176, 303
heterophylla 302, 304
hydrophylloides 228
lyaUii234
ramoaiasima 193, 214
serioea 234, 236
Phalaris caroliniana 176
Phaseolus 28, 86
vulgaris 27, 79
Philadelphus 181, 185, 186, 187, 191
Kordonianus 178, 182. 185
Philibertella hartwegii heterophylla 176
Philotria 86
Phippsia 230
Phleum alpinum 288
pratense 288
Phlox condensata 234, 236
pilosa 130, 138
speciosa 152
Phragmites 39, 50, 60, 101, 102
communis 110, 288
Physalis angulata linkiana 176
lobata 302
Physaria didymocarpa 199
Picea 205, 215, 217, 218, 222, 223, 224, 225, 226,
228
breweriana 211
engelmanni 46. 80, 209, 215, 216. 219. 220,
221, 222, 223, 224, 225, 227, 228, 348
mariana 216
pungens 208, 209. 210
sitchensis 214, 216, 217, 218, 219
Pinus 193, 194, 195, 196. 197, 198. 201. 202,
205, 207, 211, 216, 219, 220. 221
aristata 222. 224, 225, 226
balfouriana 224, 227, 228
arizonica 205. 208, 209
attenuata 93. 211, 212. 213, 283, 353, 354
cembroides 196. 200. 203, 204
chihuahuana 205. 208
contorta93, 205. 207, 208, 209, 210, 215. 216,
219, 220, 221, 222, 223, 225, 227, 228,
283, 353
coulteri 211, 213
divaricata 93, 216
edulis 195, 196, 198. 199, 200. 201
monophylla 196, 197, 198. 200, 202, 203,
204
quadrifolia 196, 200, 203, 204
flexilis 205. 207. 208. 210, 222, 224, 225. 226.
227, 228
albicaulia 205, 207, 208, 224, 225, 227, 228
lambertiana 211, 212, 213
monticola 215. 216, 219, 220. 221, 223, 227,
228
ponderoaa 17, 25. 45, 184, 197. 204. 205. 207.
208, 209, 210. 211. 212. 213. 215. 216,
219, 220, 221, 346, 348, 350, 351
jeffreyi 211, 212, 213, 223
sabiniana 196. 202, 203, 204
Pinus — continued.
acopulorum 205
strobiformis 208
Pirola 109
chlorantha 210
minor 226
picta 214, 219, 221
secunda 210
^ uliginosa 210
Pints diversifolia 219
sitchensis 221
Pistia 61
Pisum arvense 42
Plagiobothrys arisonicus 176. 303
Plahtago 60. 324
elata 148
fastigiata 176, 302, 303
ignota 176
major 58
patagonica 283, 302, 304
Poa 61, 151. 230. 232, 282, 283, 303
alpicola 232
alpina 232, 235
arctica 232, 235, 288
arida 288
compressa 288
crocata 232
cusickii 235
epilis 232
grayana 232
lettennani 232, 233
nemoralis 28S
nevadensis 288
paddensis 235
pattersoni 232
pratensis 133, 134. 190, 226, 282. 288
rupicola 232, 235, 288, 361
sandbergii 288, 292
aaxatilia 235
Buksdorfii 235
tenuifolia 150, 288
Poaceae 162, 230
Podoatemaceae 61
Polemonium confertum 234
pulchellum 226, 234
viacosum 234
Polygala alba 202, 299
californica 193
Polygonaceae 152
Polygonatum 59, 60
Polygonum 25
aviculare 283, 290, 302
biatorta 234
convolvulua 187
daviaiae 228
douglaaii 187
erectum 290
pennsylvanicum 94
ramosiasimum 290, 302
viviparum 234, 236
Polypogon monapelienaia 176, 288, 304
Polytrichum 61
Polystichum munitum 214, 219
Populus92, 110, 172
tremuloidea 25, 92. 110, 205, 209, 223, 225.
361
Portulaca oleracea 283, 303, 361
Potamogeton 27. 59. 61. 110
Potentilla anaerina 60
arguta 160, 187, 190.
INDEX
385
Potentilla — continued.
atronibens 361
blaschkeana 152
breweri 228
convallaria 152
crinita 361
flabeUifolia 236
fruticosa 228
glandulosa 210
gracilis 160, 187
hippiana 160
nivea 234
I)€nn8ylvanica 160
saximontana 234
Primula 58, 60
angustifolia 234
panyi 234
Pronuba 91
Prosopia 41. 90, 95, 97, 145, 157, 162, 163, 165,
166, 167, 168, 169, 170. 171, 172, 173.
174, 175, 197, 300, 301
iuliflora 164, 168, 171, 172, 277
pubeacens 171
Prunella vulgaris 361
Prunus 106. 178, 179, 180, 183, 184, 185, 186,
187. 363
americana 181. 182, 188
besseyi 188. 363
demissa 178, 182, 183, 184, 185. 186. 188,
191. 213. 290
emarginata 213, 219
ilicifolia 191
pennsylvanica 210
eerotina 42
Pseudocymopterus montanus 210, 226,234
Pseudotsuga 42. 46, 186, 205, 206, 207, 208,
209, 210. 211, 213, 216, 217, 218, 219,
220, 221. 283, 350. 353, 354
mucronata 45. 93. 197. 204. 207. 208, 211,
212, 213, 215, 217, 218, 219, 220. 221
macrocarpa 211, 212, 213
taxifolia 346
Psilostrophe cooperi 148. 168. 171. 175. 300
Psoralea 50, 95. 105, 106, 107, 128, 129, 281
argophylla 39, 108, 126, 127, 128, 130, 299
lanceolata 262
tenuiflora39, 46, 108, 120, 128. 127. 128. 129.
130, 140, 148, 299
Pteris aquilina 93. 202. 214. 219, 353
Pterocarya linearis 303
Ptilonella scabra 304
Pulsatilla 61
occidentalis 236
Purshia 180, 181, 185. 186. 187. 191. 195
tridentata 107, 182, 185, 186, 290
Pycnanthemum ianccolatum 130
Pyronema confluena 93
Quercus 106, 163. 177, 178, 180, 182, 183. 184.
185, 186, 188, 194, 195, 196. 197, 198.
200, 202, 274, 301
breviloba 189, 301
breweri 213
californica 204, 205, 211, 212, 216
chrysolepis vaccinifolia 213
doudasii 196. 200. 202. 203
dumosa 181, 182. 183, 190. 191. 102
emoryi 196. 200, 201. 203
garryana 182, 204. 211, 212
grisea 361
hypoleuca 200, 201. 203
Quercus — continued.
macrocarpa 181, 182, 188
reticulata 196, 200, 201
arisonica 196, 200, 201
oblongifolia 196, 200, 201
sadleriana 213
undulate 178, 180. 182. 183, 184. 185. 186.
188, 189, 301
gambelii 25, 184, 186
virens 182, 188, 189, 301
wisllEenii 196, 203, 204
Ranunculus 68
adoneus 234
alismifolius 228
eschscholtsii 234, 236
f . reptans 56
glaberrimus 152
hyperboreus 234
macaxileyi 234
nivalis 234
occidentalis 219
oreganus 219
ovalis 130
pygmaeus 234
raphanistnim 304
sceleratus 68, 86
Raphanus sativus 94
Raoulia 58. 61
Redfieldia 110. 281
Rhamnaceae 162
Rhamnus californica 191, 213
crocea 191
purshiana 213
Rhododendrum ellipticum 219
Rha'j41, 106, 166, 178, 180, 183, 184, 185. 186.
187, 189, 195
diversiloba 191, 213
glabra 181, 182, 188
integrifolia 191
laurina 191
ovata 191
radicans 187, 189, 202
trilobata 45, 178, 182, 183. 185. 186, 188
mollis 202
Ribes 25, 41, 180, 187
aureum 182, 188
bracteosum 219
cereum 182, 185, 186. 188, 290
lacustre 210, 219. 221, 226
laxiflorum 219
montigenum 228
nevadense 213
sanguineum 219
viscosissimum 221, 228
Robinia 181
neomexicana 182, 185, 186
Rosa 41, 178, 179, 180. 189
acicularis 182, 185, 186. 187, 210
arkansana 42, 130. 181. 182. 188. 290
fendleri 361
pisocarpa 221, 200
Resales 178
Rubu8 46
idaeus 60
parviflonu 213, 210. 221
spectebilis 210
stri^sus 15, 45, 46
Rudbeckia hirta 130
occidentalis 25
Rumex hymenosepalus 176
386
INDEX
RuBCUS 61
Ruta61
Rydbergia grandlflora 234
8abiJ61
Saooharum munja 16, 17
narenga 16, 17
epontaneum 17
Sagittaria 27, 39, 59, 61, 87, 110
Salaxaria mexicana 161, 171
Salicornia 12, 84, 257
BaUx 26. 86. 290, 363
arotica 234. 236
humilia 189, 363
nivaUs 234. 236
Duttallii 226
reticulata 234, 236
Bcouleriana 219
Balsola 94, 262. 282
kali 262, 302
Salvia 60, 163, 166, 160, 161, 365
apiana 160. 162
aiurea 130. 299
earnosa 161
columbariae 176, 303
lanceolata 187. 302
leucophylla 161
mellifera 154. 161. 192
Sambucus callicarpa 219
eanadeDsis 189
jndanocarpa 221
Banicula bipinnata 193
bipinnatifida 193
marilandica 190
Sapindus 172, 174
Saponaria 58
Sarcobatus 84, 158, 159, 257. 282
vermiculatus 84. 158. 163
Barcodes sanguinea 214
Baxifraga 58
broDchialia 210. 234
chrysantha 234
flagellaris 234
nivalis 234
Bcapania 61
Schedonnardus tezanus 288. 302
8cirp\ia 39, 49, 50, 59, 61. 87, 102, 110
atrovirens 289
fiuviatilis 289
lacustris44, 110. 289
pungens 289
Scleropogon 146, 147. 283
brcvifolius 146. 283, 288
Bcrophularia californica 193
Scutellaria resinosa 187
Seduin68
rhodiola 68
roseum 234. 236
stenopetalum 236
Selaginella rupestris 231, 234
Sempervivum 61
Senecio 93
aureus 130. 187. 299
borealis 236
cernuus 210
douRlaflii 193, 299
eremophilus 25
fendleri 160, 187, 190
lugens 214
■erra 290
triangularis 290
Sequoia 215, 217
gi8antea211. 212
sempervirens 214. 217, 218
Setaria composita 176
glauca 288
italica 288
viridis 288
Shepherdia 178
argentea 182, 188
canadensis 226
Shorea robusta 16
Bibbaldia procumbens 228. 234. 236
Sida lepidota sagittifolia 176
Bidalcea malviflora 193
oregana 152
Sieversia ciliata 130. 160
turbinata 234, 236
Bilene acaulis 60, 61, 234. 236
californica 214
inflata60
laciniata 361
lemmonii 214
Bilphium integrifolium 130
laciniatum 30, 130
Bimmondsia californica 171. 172, 191
Sisymbrium 304
altissimum 94, 160, 304
incisum 187, 199
Bisyrinchium angustifolium 130
bellum 193
grandiflorum 152
Smelowskia calycina 234
Bmilacina amplei^caulis 219. 221
Btellata 187. 190. 210
Bmilax 61
Solanum elaeagnifolium 176. 303
rostratum 302
triflonmi 302
Bolidago 93, 95, 105, 106, 120, 129, 286
californica 193
canadensis 130. 190, 299
humilis 226
nana 234
missouriensis 128. 130. 152, 187. 299
mollis 299
multiradiata 236
nemoralis 130
neomexicana 361
oreophila 210
rigida 120. 128. 130, 190, 299
serotina 130, 152
epeciosa 130. 187. 202. 299
Sophia incisa 25, 176
pinnata 176. 302. 303
Sparganium 87
angustifolium 68
Bpartina 133. 134. 256. 281
cynosuroides 132, 134, 288
gracilis 288
Bpartium 61
Bphaeralcea cuspidata 176
Sphagnum 61
Spiraea menziesii 210
Spirogyra 86
Spirostachys 84. 110, 257
occidentalis 84, 170
Sporobolus 12. 84
airoides 84. 119. 170, 267, 282, 288
asperifolius 288
auriculatus 283, 288
INDEX
387
Sporobolus — continued.
brevifolius 288
confusus 202
cryptandrua 147. 288
Bexuosus 146. 147, 288
wriKhtii 288
Stanleya pinnata 160
Stapelia 60
St«ironema ciliatum 130
Stereospermum suaveolens 16
8tipa46, 47. 48. 50, 96. 106. 107. 109. 115, 116.
119. 120. 121. 122. 123. 125. 127. 131.
132. 134. 135. 136. 137. 138. 140. 141,
149. 150. 152. 156. 160. 161. 193, 203.
273. 275. 279. 281. 285. 286. 298, 301,
303, 309, 313. 323
comata 38. 39. 45. 48. 49, 107, 119. 121. 122,
123. 124. 136. 137. 138. 149. 160. 151,
155. 160. 187. 285. 288, 308
eminena 115. 119. 150. 151, 288
pennata neomexicana 136
setigera 115. 119. 150. 151. 288
spartea 38. 39. 49. 107, 119, 121, 122, 123,
124. 126. 132, 134, 259, 285, 288, 308
speciosa 151
vaseyi 288
viridula 119. 137. 138. 149. 160, 288
Streptanthus arizonicus 176
Streptopus amplexifolius 210
majus 221.
roseus 219
Suaeda 257
moquinii 159
Swertia perennis 234
Symphoricarpu8 41, 178. 180. 183. 185, 189, 221
albus 178. 182. 183, 185. 186
mollis 213
occidentalis 181. 182, 187, 188, 363
oreophilus 25, 213
Synthyris rubra 152
Taraxacum 58. 60
Tellima grandiflora 219
Terminalia 16
Tetradymia 158
spinosa 157. 159
Teucrium canadenae 130, 190
cubense 176
occidentale 130
Thalictrum alpinum 234, 236
fendleri 107, 187. 210. 226
occidentale 221
purpurascens 130
wrightii 361
Thelesperma gracile 148, 187
Thelypodium lasiophyllum 176. 303
Thermopaia divaricarpa 289
montana 187
Thlaapi arvenae 59
Thuja 214. 215. 216. 217. 218. 219, 220, 221
plicata 214, 215, 217, 218, 219, 220, 221
Thymus 60
Thyaanocarpus curvipes 303
Tiarella trifoliata 219
unifoliata 221
Tilia aroericana 188
Tradescantia virginiana 130, 187, 299
Trianthema portulacaatrum 176
Tribulus terrestria 303
Trichostema lanatum 161
lanceolatum 304
Tricn talis latifolia 219
Trifolium amplectens 304
breweri 214
daayphyllum 234. 289
gracilcntum 3(94
hybridum 290
incarnatum 290
microcephalum 304
monanthum 236. 289
nanum 234
parryi 234. 289
pratenae 58. 290
repena 58. 290
tridentatum 304
Triglochin maritima 290
Trillium ovatum 219, 221
Triodia mutica 176
pulchella 176
Trisetum 230, 232
aubapicatum 232. 235, 288
Triticum 258
durum 42
Trixia calif ornica 171
TroUius laxus 234, 236
Tsuga 214, 215. 216, 217, 218, 219, 220, 221.
223. 227. 228
heterophylla 214. 215, 216, 217, 218, 219,
220, 221
mertensiana 223. 224, 227, 228
Tumboa 61
Typha 39, 42, 49, 50. 59, 102, 110
angustifolia 110
latifolia 110
Ulmua americana 42, 188
Umbilicaria 61
Urtica 58
gracilia 190
Uanea 61
Utricularia 61
Vaccinium 45, 87
caeapitoaum 226. 228
macrophyllum 219, 221
myrtillus 60, 226
occidentale 228
oreophilum 14
ovatum 219
parvifolium 219
Valeriana silvatica 210
sitchcnaia 236
Vancouveria hexandra 219
Verbascum 61
Verbena 58. 95. 286
bracteosa 302
ciliata 176
haatata 130. 299
prostrata 193
stricta 130. 193. 299
Verbeaina encelioidea 148, 176, 302
Vernonia 95. 129
baldwinii 130. 149. 299
faaoiculata 130, 299
Veronica alpina 236
peregrina 176
virginica 130
Vetiveria xixanoidea 17
388
INDEX
Viburnum cUipticum 219
pauciflorum 210
Vicia americana 130. 187, 190
linearis 289
Viola 129
adunca 152
hiflora 210
blanda 210
cucuUata 130, 190
Klabella 221
howellii 219
lobata 214
neomexicana 361
orbiculata 221
pedata 130
pedatifida 130
pedunculata 193
eempervirens 219
WashinKtonia divaricata 219, 221
nuda 214
obtusa 210
Whitneya dealbata 228
Wislizenia refracta 176
Wyethia amplexicaulis 152, 160, 290
angustifolia 193
arizonica 160
glabra 193
Wyethia — continued.
helenioides 193
helianthoides 160
mollis 290, 292
Bcabra 160
Xanthoxylum americanum 188
Xyloscopa 91
Yucca 60, 61, 91, 161, 162, 163. 164, 165. 166,
167, 168, 174, 204, 277. 286, 301, 317,
328, 361
arborescens 203, 204, 317
baccata 148, 171, 199. 291
glauca 189, 291, 299, 363
macrocarpa 164, 167. 168, 169, 204, 291, 301
radiosa 148, 163, 164, 165, 167, 168, 169, 170,
171, 172. 204,291,301, 317
Zauschneria californica 193
Zea mays 288
Zinnia 164, 166, 168, 169
pumila 148, 168, 171, 172, 175, 300
Zizania 50
aquatica 110
Zizia aurea 130
Zostera 59, 61
Zygadenus 318, 319
elegans 226, 234
Zygophyllaceae 162
B391
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Understanding 9/11