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THE BROAD-SCLEROPHYLL VEGETATION 
OF CALIFORNIA 

AN ECOLOGICAL STUDY OF THE CHAPARRAL AND 
ITS RELATED COMMUNITIES 


BY 


WILLIAM S. COOPER 


Published by the Carnegie Institution of Washington 
Washington, October, 1922 


CARNEGIE INSTITUTION OF WASHINGTON 
Publication No. 319 


1 6 192 


TECHNICAL PRESS 
WASHINGTON, D. C. 


CONTENTS. 


Page. 

Introduction ° 

Relations of the chaparral to other 
communities of scrub in North 

America " 

Previous work ' 

Scope of present paper 9 

Acknowledgments 10 

I. Range and center of distribution. ... 11 
Location of greatest differentiation 

of type I 2 

Location of dominance or great 

abundance of individuals 14 

Location of synthetic or closely re- 
lated forms ■ • • • 14 

Location of maximum size of indi- 
viduals IS 

Location of least dependence upon 

a restricted habitat 15 

Location of greatest importance 
of the type in the climax commu- 
nity 16 

Continuity and convergence of 

lines of dispersal 16 

II. Climatic relations 17 

III. The communities 20 

The broad-sclerophyll communities 20 
The broad-sclerophyll forest for- 
mation 21 

The chaparral formation 25 

The climax chaparral associa- 
tion 26 

The conifer forest chaparral 

association 27 

IV. Vegetation and habitat 30 

The locality for intensive study. . . 30 

The Palo Alto region 30 

Jasper Ridge 30 

The vegetation 32 

The habitat 42 

The soil factors 42 


Page. 
IV. Vegetation and habitat— Cont'd. 

Physical character 42 

The soil moisture 43 

The soil temperature 55 

The atmospheric factors 56 

Light 56 

Temperature 57 

Wind 58 

The atmospheric moisture .... 58 

Discussion and correlations 63 

The broad-sclerophylls and their 

habitat 63 

The habitats of the two climaxes 

contrasted 67 

V. Development 72 

The climax regions of California . . 72 

The broad-sclerophyll climax forest 73 

The climax chaparral 75 

Evidence of its climax character 75 
Extent of the chaparral as a true 

climax "6 

Successions leading to the chap- 
arral climax 82 

Primary successions 82 

Secondary successions 86 

VI. Ecological character of the broad- 

sclerophyll shrubs and trees .... 88 

Growth form 88 

Root system 89 

The leaf 92 

The deciduous element 92 

External characters 93 

Internal structure • 97 

Effects of environmental condi- 
tions upon leaf structure 107 

Comparative transpiration-rate . 1 10 
Appendix: Annotated list of broad- 
sclerophylls and accompanying spe- 
cies 113 

Bibliography 122 


I 7 H 3 


THE BROAD-SCLEROPHYLL VEGETATION OF CALIFORNIA. 


By William S. Cooper. 


INTRODUCTION. 

The characteristic vegetation of California west of the high 
Sierra Nevada and the Colorado and Mojave Deserts is of the type 
aptly described by the term "broad-sclerophyll." The use of the 
prefix "broad," which expresses a very general group character, 
in distinction to the needle-leaf of the "narrow-sclerophyll" conifers, 
is not without its disadvantages, since the most important chaparral 
species, Adenostoma fasciculatum, possesses a needle-like leaf. This 
single though important exception seems not to be sufficient cause 
for discarding the very expressive appellation. 

Broad-sclerophyll vegetation is not confined to California, but 
recurs upon other portions of the earth's surface, notably the shores 
of the Mediterranean. The leaf character is the conspicuous and 
diagnostic feature, that organ being thick, stiff, and hard, ordinarily 
flat, and evergreen. Schimper (80) has shown that this vegetation 
type is everywhere correlated with a definite type of climate, namely, 
one with a long, dry summer and a rainy winter. Some of the broad- 
sclerophylls are trees, but most are scrubs. We therefore find 
broad-sclerophyll forest and broad-sclerophyll scrub, the latter 
being the more widespread and important. The present work is 
an ecological study of the broad-sclerophylls of California; of their 
relations to climate and soil and to each other. Being somewhat 
of a pioneer work, many phases of the problem are touched, and 
many lines of investigation have been opened up which could not 
be followed to the end. The field is a fascinating one, and a lifetime 
would not suffice to exhaust its possibilities. 

In the Mediterranean region broad-sclerophyll scrub is known as 
"macchie" and "garigue"; in California it is called "chaparral." It 
has already been noted that the scrub is more important than the forest, 
both scientifically and economically. In fact, the present research 
began as an investigation of the chaparral alone. Because of the close 
relations between them, it was a simple matter to extend the field of 
study to include the trees. The term "chaparral" is of Spanish origin, 
being derived from the word "chaparra," meaning scrub oak. It 
seems to have been applied by the early explorers of California to 
the low, shrubby, dominantly evergreen vegetation which they found 
to be so characteristic of the Coast Ranges and the foothills of the 
Sierras. Locally the term is sometimes restricted to a single species, 
often Ceanothus cuneatus. The term ' ' chamisal ' ' is frequently applied 
to a pure growth of Adenostoma fasciculatum or "chamise." 


6 THE BROAD-SCLEROPHYLL VEGETATION OF CALIFORNIA. 

RELATIONS OF THE CHAPARRAL TO OTHER COMMUNITIES 
OF SCRUB IN NORTH AMERICA. 

It will be well at this point to differentiate between the chaparral 
and the other scrub communities of western North America. The four 
great types may be characterized as follows, no attempt being made to 
describe them minutely or to relate them to environmental conditions. 

The sagebrush type. — The characteristic species, Artemisia triden- 
tata, always makes a large part and frequently grows in purity over 
immense stretches. This is preeminently the type of the Great 
Basin, though extending beyond it more or less in all directions. 
It is sharply differentiated from the chaparral by reason of its abso- 
lutely different leaf-type and by the fact that the two overlap very 
slightly in range. 

The desert scrub.— This is made up of a multitude of species not 
at all uniform superficially in ecological character. The succulents 
are very important, opuntias of both the cylindrical and flat-jointed 
forms being especially prominent. There are also thorny shrubs, 
some of them with soft deciduous leaves. Others, with very small 
leaves, have been well named microphylls. Finally, a few species 
in aspect recall the chaparral, the most important of these being 
Comllea tridentata. The desert scrub ranges from Arizona to Texas 
and southward into Mexico. In ecological character it is sharply 
set off from the chaparral, except for the superficial resemblance 
of Covillea just noted. This species, although it ranges to the very 
border of the chaparral country, mingles with that type practically 
not at all. Cannon (20), moreover, states that "up to this time 
.... all attempts to grow it at the Coastal Laboratory [Carmel, 
Monterey County] have failed." He explains this on the basis of 
less efficient soil temperature, but the value of that factor is of course 
a direct result of climatic causes. There is thus some element in 
the ecological make-up of the species which unfits it for life in the 
chaparral region, in spite of its superficial likeness. Here is a warning 
against the placing of too much reliance in the working out of ecologi- 
cal relationships upon a single conspicuous character, or even upon 
structural characters in general. Vital processes rather than struc- 
ture are fundamental. 

The deciduous thicket type. — Most important here are scrub oaks 
of various species, and the type is a widespread one, occurring from 
the Atlantic to the Pacific and from Canada to Mexico. Great 
stretches of foothills in the central Rockies are densely covered by it. 

This is the closest of the three to the chaparral, both floristically 
and ecologically. In contrast to the first two, the transition between 
this type and the chaparral is gradual. In the Sierras and in northern 
California much of the scrub, dominantly evergreen, has nevertheless 
a large deciduous element, and there are considerable thicket areas 
which are composed entirely of deciduous species. 


THE BROAD-SCLEROPHYLL VEGETATION OF CALIFORNIA. 7 

A few of the Californian sclerophylls, too, extend far beyond the 
average limits of the type. Arctostaphylos pungens ranges eastward 
to southwestern Colorado, where it forms an unimportant part of 
the deciduous thickets. Moreover, Quercus undulata, an important 
member of the Rocky Mountain thickets, itself tends strongly 
toward evergreenness. 

The chaparral— The chaparral may be denned as a scrub com- 
munity, dominated by many species belonging to genera unrelated 
taxonomically, but of a single constant ecological type, the most 
important features of which are the root system, extensive in pro- 
portion to the size of the plant, the dense rigid branching, and pre- 
eminently the leaf, which is small, thick, heavily cutinized, and 
evergreen. This definition might be applied with equal accuracy 
to the macchie of the Mediterranean regions; chaparral and macchie 
appear to be ecologically equivalent. The chaparral is characteris- 
tically, almost exclusively, of California west of the Sierra crest and 
the deserts; in other words, of the region of "Californian" climate. 

Because of its ecological distinctness, the Californian broad- 
sclerophyll scrub is entitled to a name of its own, and the term 
"chaparral," by reason of almost universal usage, is the obvious 
choice. The desert scrub and the deciduous thicket, which have 
been called chaparral by various authors, can easily be provided 
with other names if the ones used here are not satisfactory. Finally, 
it should be emphasized that the chaparral finds its closest ecological 
relative not in any other scrub community, but in the broad-sclero- 
phyll forest, which is a response to the same type of climate. 

PREVIOUS WORK. 

Practically no work of purely ecological nature dealing with the 
chaparral has been published up to the present time. Several 
foresters have written excellent accounts of the aspect and behavior 
of the brush, especially in its relation to the forests which are asso- 
ciated with it. This emphasis is natural, since the chaparral is 
extremely important to the forester whose field of work is in Cali- 
fornia. It is essential for him to determine whether the brush can 
be replaced by a more valuable crop and, if not, how it can best be 
made to perform its important economic function of water-shed 
protection. In addition, there have been taxonomic studies of 
certain genera, and phytogeographic researches of more or less 
general nature, in which the chaparral has been treated. The 
broad-sclerophyll forest has been almost wholly neglected, except in 
its taxonomic aspects. It will be convenient to arrange the following 
brief survey of the literature under four heads, adding a miscellaneous 
group for certain papers that can not be classified under the three 
mentioned above. 

(a) Detailed notices of taxonomic researches are outside the 


8 THE BROAD-SCLEROPHYLL VEGETATION OF CALIFORNIA. 

province of this work. Four papers dealing with difficult genera 
should be mentioned: Abrams on Uva-Ursi [Arctostaphylos] (2), 
Trelease and Brandegee on Ceanothus (89, 10), and Miss Eastwood 
on Garry a (28). 

(6) Papers by foresters may be grouped in two classes: (1) those 
dealing particularly with chaparral; (2) descriptions of various 
forest reserves in which chaparral occurs. One of the former, 
by Plummer (74), purports to be a rather full discussion of the subject 
from both the purely scientific and the economic standpoints. 
It is totally inadequate. All the other papers by foresters deal 
with conditions in more or less restricted localities. Those by Boerker 
(9), Foster (30), Haefner (37), and Sterling (85) treat of northern 
California, where the chaparral is mainly of the temporary kind. 
Naturally the successional relations with the forest trees and the 
effects of fire upon these are treated with considerable detail. Sub- 
division of the general type into communities and subcommunities 
is attempted to some extent, and also the correlation of these in a 
very general way with habitat factors, especially slope exposure. 
The work has been almost wholly observational, with no exact 
habitat measurements and few statistical studies of the vegetation. 
Miller (64), studying the chaparral of northern California as a 
watershed cover, gives some data bearing upon successional relations. 
In the works of more general scope by Barber (6), Leiberg (50-56), 
and Sudworth (86) there is considerable material of value relating 
to the extent, composition, zonation, and successional relations 
of the chaparral in various parts of the State. E. N. Munns has put 
forth three papers (66-68), in which some instrumental habitat 
data are presented. He has also much valuable material, as yet 
unpublished, to which I have had access through his kindness. 

(c) Four papers dealing with the phytogeography of southern 
California must be mentioned. McKenny (60) recognizes in Orange 
County seven formations, two of which (the mountain and the 
foothill formations) are mainly chaparral of various types, which 
are not very clearly distinguished. Hall, in his account of the San 
Jacinto Mountains (38), relates the vegetation to the well-known 
temperature zones of Merriam, and distinguishes two altitudinal 
belts of chaparral, the lower dominated by Adenostoma, the upper 
by Castanopsis and other genera. He also summarizes the obvious 
ecological characteristics of the average chaparral shrub, noting 
reduction of leaf-surface, vertical position, thickness and leathery 
quality, frequency of woolly pubescence (with which I would dis- 
agree), and depth of penetration of root system. Parish (71) 
divides southern California into five phytogeographic areas, and in 
consideration of the cismontane area describes the chaparral in 
general terms. Abrams (1) emphasizes the facts of zonation, ad- 
hering to the Merriam arrangement, and distinguishes three altitudi- 


THE BROAD-SCLEROPHYLL VEGETATION OF CALIFORNIA. 9 

nal belts of chaparral: the lowest, dominated by half-shrubs such 
as Ramona and Eriogonum (not to be classed as chaparral in my 
opinion); the second, in which Adenostoma is most important; and 
the upper, in which Arctostaphylos and other genera are in control. 

The more recent phytogeographic handbooks contain brief descrip- 
tions of Calif ornian vegetation, with more or less accurate references 
to the chaparral. Drude (2G) applies the term to the very different 
desert scrub of western Texas, southern New Mexico, and northern 
Mexico, and has little to offer upon the sclerophyll vegetation of 
California. Engler's treatment (29) is similar. Schimper (80) is 
the first of the European geographers to give an adequate description 
and interpretation of the California sclerophyll vegetation. His 
information is mostly obtained apparently from a paper by Purpus 
(76). He gives a brief but adequate description of the chaparral, 
its general character, leaf-type, and relation to climate, and shows its 
likeness to the vegetation of other regions with winter rains. Warm- 
ing (90) uses the term chaparral in the same sense as Drude does, 
but recognizes the Californian type and its relation to similar ones 
in other regions in the sentence : " In California maqui is known under 
the name of chaparral." Harshberger's account (41) is merely a 
compilation from Drude, Jepson, Parish, and McKenney. Clements 
(22) gives a brief description of the California scrub, treating it as 
the third of three subdivisions of the Chaparral Formation, which 
he conceives very broadly: the Petran (Rocky Mountain), the 
Sub-climax, and the Coastal Chaparral. The first two correspond 
with the "deciduous thicket" of the present work. 

(d) Among miscellaneous papers should be mentioned a local 
descriptive article by Purdy (75); three by Cannon — one (17) 
showing the dependence of the Monterey pine (Pinus radiata) 
upon prevention of soil desiccation by accompanying chaparral, 
and two (18, 19) in which the relation of Quercus agrifolia and other 
trees to soil-moisture is treated; one by Brandegee (12) describing 
the recovery of the chaparral after fires; one of similar scope by Jep- 
son (49) ; and an account of the distribution of species of Eriodictyon 
by Abrams and Smiley (3). Incidental references to various phases 
of the ecology of the chaparral are found in the publications listed 
in the Bibliography as Nos. 24, 27, 33, 34, 35, 44, 45, 46, 61, 62. 

SCOPE OF PRESENT PAPER. 

It will be seen that investigation has progressed to a more or less 
satisfactory degree along the following lines: taxonomy, ranges of 
species, range of type, its subdivisions, relation to similar types in 
other regions, to climate, and to fire. The ecological character 
of the different species has been barely touched; the same is true 
of the mutual relations of vegetation and habitat, and the develop- 
mental phases of the problem have been treated only so far as fire 


10 THE BROAD-SCLEROPHYLL VEGETATION OF CALIFORNIA. 

is a factor in them. These subjects are of great scientific interest 
in themselves. They are also fundamental to a proper understanding 
of the economic relations of the species. The main emphasis in 
this paper is laid upon these three subjects, though new material 
is offered along all the other lines mentioned, except taxonomy. 
The plan of treatment is to pass from the general to the specific. 
The first two chapters deal with phytogeographic relations, the 
next three with local units, their development and relation to habitat, 
and the last treats of the ecological character of the individual plant. 
An annotated list, with much detail that may not interest the average 
reader, has been added as an appendix. 

The field work was of the two usual sorts: intensive instrumental 
and quadrat study, and extensive exploration. The former was 
carried on mainly in the vicinity of Palo Alto from November 
1912 to September 1915, and in the summers of 1916, 1917, and 
1919. The exploration covered the whole extent of the Coast Ranges 
from San Diego to Eureka, and a number of representative localities 
in the Sierras. 

ACKNOWLEDGMENTS. 

I wish to express first my deep appreciation of the very great 
kindness of every one of the faculty of botany at Leland Stanford 
Junior University, who put all the facilities of the department at 
my disposal and who frequently gave me their personal assistance 
in many ways. Mr. S. B. Parish of San Bernardino, Dr. L. R. 
Abrams of Stanford University, and Dr. H. M. Hall and Dr. W. L. 
Jepson of the University of California read the manuscript of the 
floristic portion and made important corrections and suggestions. 
Dr. Charles F. Shaw, of the University of California, furnished 
the mechanical analyses of the soils from Jasper Ridge, and Dr. 
Charles B. Lipman supplied the humus determinations of the same 
samples. Dr. D. T. MacDougal, of the Carnegie Institution of 
Washington, offered valuable advice and encouragement, and 
the Carnegie Institution rendered financial assistance which was 
applied to the purchase of apparatus. Mr. Frank Shaw, of Redwood 
City, gave faithful and efficient assistance in the field work at Palo 
Alto. The photo-micrographic negatives for plate 20 were the 
work of Dr. C. O. Rosendahl, of the University of Minnesota; 
Miss Vinnie A. Pease executed the camera drawings of the leaf- 
sections (figs. 22-43), and Miss Elsa Horn made the multitudinous 
measurements and calculations involved in the studies of leaf char- 
acter in relation to habitat and of transpiration. Miss Horn also 
rendered efficient service in the carrying out of experimental soil 
studies and in making certain drawings. To all these persons I 
wish to express my sincere gratitude. 


THE BROAD-SCLEROPHYLL VEGETATION OF CALIFORNIA. 11 

I. RANGE AND CENTER OF DISTRIBUTION. 

The term "center of distribution" may be understood in two 
ways. It may mean, on the one hand, the region in which one or 
more species have originated and from which they have spread; 
or it may signify the region where a species or a group of species 
attains its greatest development. The present study is not primarily 
concerned with origins and migrations, and therefore the second 
interpretation is the one used. It is true, however, that in most 
cases, and probably in the one here considered, a given center is a 
" center of distribution" in both senses. Transeau, in an important 
paper (88), has expressed the concept as follows: 

"In using the term 'center of distribution' it is not implied that the plants have 
necessarily spread from these centers, but that the complex of climatic factors most 
favorable to the development of this type of vegetation is here localized, and that as 
we depart from such centers we find conditions more and more unfavorable." 

Referring to a particular center he says that "within its limits, 
the plants have a wider range of habitats, attain a greater size, 
and are more abundant than elsewhere." 

Adams (5) gives a list of ten criteria for the determination of 
centers of distribution, which include the three stated by Transeau. 
Six of these are susceptible of use in the present study. They 
are as follows: 

1. Location of greatest differentiation of a type. 

2. Location of dominance or great abundance of individuals. 

3. Location of synthetic or closely related forms. 

4. Location of maximum size of individuals. 

5. Location of least dependence upon a restricted habitat. 

6. Continuity and convergence of lines of dispersal. 

To these I would add another, stated as follows: Location of 
greatest importance of the type in the climax community. There 
is evidence along all of these lines in support of the conclusion about 
to be stated. Another criterion proposed by Adams, and which 
would be of great use were our data sufficient, is worth stating, as a 
suggestion for future study: "Continuity and directness of indi- 
vidual variations or modifications radiating from the center of 
origin along the highways of dispersal." 

From the evidence about to be presented I have reached the con- 
clusion that the center of distribution of the broad-sclerophyll 
vegetation type of the Pacific Coast corresponds with the region 
known popularly as "Southern California," west of the deserts, 
including Ventura and Santa Barbara Counties, and also extending 
an unknown distance into Lower California. The evidence can 
best be stated under seven heads, corresponding with the six criteria 
proposed by Adams and the seventh which I have added. At thi? 


12 THE BROAD-SCLEROPHYLL VEGETATION OF CALIFORNIA. 

point I intend only to establish the location of the center. The 
environmental phases of the problem will be considered later. 

LOCATION OF GREATEST DIFFERENTIATION OF TYPE. 

Our first problem under this head is to discover which part of the 
general region inhabited by the type is richest in species of that type. 
As a corollary to this, the relative number of endemics in the different 
areas may be compared. The former is easily done by plotting the 
ranges of all the species concerned upon a single map and indicating 
by density of shading the numbers of overlapping ranges. The 
results are shown in plate 1, the large map in detail for the State of 
California, the small one in more generalized form for the whole 
region covered. Some practical difficulty was encountered in super- 
posing the ranges of so large a number of species. The problem 
was solved by cutting the ranges from thin cardboard, gluing them 
together in their proper positions, outlining the total extent indicated, 
cutting away all portions where five thicknesses of cardboard or less 
occurred, outlining the remainder, and repeating the process. It is 
scarcely necessary to state that the map must be interpreted broadly 
and that details must be disregarded, since in only a few cases has it 
been possible to draw the ranges with an approach to exactness. 
The species considered are in general those of lists I and II (see 
Appendix), the deciduous ones being excluded. A few of the broad- 
sclerophylls were omitted because of lack of satisfactory knowledge 
of their ranges. The total number of species considered is 71. 

From the small map we see that, broadly speaking, the type has 
its stronghold in California and Lower California. A few species 
extend northward beyond the State line; about 21 into Oregon, many 
of them a short distance only; 11 into Washington, and 8 into British 
Columbia. None occurs north of California which does not enter 
that State, unless we admit Howell's species of Arctostaphylos to 
consideration. The complete list of those ranging northward beyond 
California is as follows 1 : 

Myrica californica.** Ceanothus cuneatus. Arbutus menziesii.** 

Castanopsis chrysophylla.* sanguineus.** Arctostaphylos manzanita. 

sempervirens. thyrsiflorus.* nevadensis.* 

Quercus chrysolepis. velutinus.** patula. 

sadleriana. Garrya elliptica. tomentosa.** 

Pasania densiflora. fremontii. Gaultheria shallon.** 

Umbellularia californica. Rhododendron californicum.** Vaccinium ovatum.** 

Six species extend discontinuously eastward beyond the boundaries 
of California: 

Cercocarpus ledifolius. Ceanothus velutinus. 

Rhamnus californica. Arctostaphylos patula. 

crocea. pungens. 

1 Unstarred species extend into Oregon only; those with a single star (*) into Washington, 
and double-starred (**) species into British Columbia. 


THE BROAD-SCLEROPHYLL VEGETATION OF CALIFORNIA. 13 

Over the great area of the Great Basin and the Rocky Mountains 
covered by the lightest shading, the distribution of the few broad- 
sclerophylls is of course not continuous. The extreme limits of 
the ranges are indicated, detailed mapping in these cases being 
impossible. 

Focusing attention upon the State of California, the following 
facts appear : First of all, it is seen that the Coast Ranges, the lower 
and middle altitudes of the Sierras, and the coastal area of southern 
California are the regions where the broad-sclerophylls are of im- 
portance. In two places they are absent — the Great Valley and 
the alpine regions of the Sierras. Over much of the former occasional 
plants of a number of species occur, and the region might fairly 
be covered by the lightest shading. This problem is discussed 
later (p. 77). 

The development of the type in the Sierras is moderate, the belt 
of maximum number being in the region where the ranges of foothill 
and forest species overlap. 

The zone of deep shading in the Coast Ranges, southward through 
southern California into Lower California, is the outstanding feature. 
Northward this follows the inner ranges, but from Monterey Bay 
south it borders the coast. Two spots of very special abundance 
are seen, one extending from Marin County to the Santa Lucias, 
the other covering the mountains of Santa Barbara and Ventura 
Counties and the San Gabriel and San Bernardino Ranges. Too 
much reliance should not be placed upon these, since both regions 
have been explored and studied with comparative thoroughness. 
It is true, however, that certain portions of these areas have been 
proved to be rich in endemics, and it may well be, therefore, that 
the seeming abundance of species in these spots is not wholly a false 
appearance. 

A division into regions, with lists of species confined to each, will 
supplement the data furnished by the map: 

In the Sierra Nevada 32 species occur, but 15 of these are found 
also in all the other regions and only the 3 following are confined 
to this region alone: 

Ceanothus diversifolius. Ceanothus parvifolius. Arctostaphylos mariposa. 

In the North Coast Ranges (San Francisco Bay being the point 
of division), 38 species occur, and 1 is endemic, Arctostaphylos 
stanfordiana. 1 

In the South Coast Ranges 37 species occur, and the 6 following 
are endemic: 

Ceanothus dentatus. Arctostaphylos andersonii. Arctostaphylos pumila. 2 

papillosus. 2 hookeri. 2 vestita. 2 

1 Here, and in other lists, several species might be added if accurate knowledge concerning 
their validity and range could be obtained. 

2 Members of the group of endemics characteristic of the Monterey region, A. hookeri and 
A. vestita being strictly confined to it. 


14 THE BROAD-SCLEROPHYLL VEGETATION OF CALIFORNIA. 

In Southern California 47 species occur, and the following 13 
are confined to the region or extend into Lower California: 

Quercus engelmanni. Ceanothus crassifolius. Ceanothus oliganthus. 

Adenostoma sparsifolium. megacarpus. Comarostaphylis diversifolia. 

Rhus integrifolia. spinosus. Xylococcus bicolor. 

laurina. verrucosus. Arctostaphylos drupacea. 

ovata. 

Summarizing from the map and the lists just given, we see first 
that California and Lower California are the home of the broad- 
sclerophylls. The number of species diminishes eastward very 
rapidly, and northward along the coast more gradually. Further, 
we see that the greatest number of species occur in the Coast Ranges 
and Southern California. By a division into four areas we discover 
that the Sierras are poorest both in total number of species and in 
endemics; that the north and south Coast Ranges are next, being 
about equal in total numbers, but very unequal in endemics, the 
north portion having one and the south six; and that southern 
California stands highest with respect to both categories. Our 
evidence therefore points to southern California as the center of 
distribution of the broad-sclerophylls, and confirmation of this 
conclusion will be found in the paragraphs following. 

LOCATION OF DOMINANCE OR GREAT ABUNDANCE OF 

INDIVIDUALS. 

It is a matter of easy observation that the chaparral fields have 
their greatest extent and dominance in southern California. We 
have only to cite as examples the mountains of Ventura County 
(plate lie), the lower ridges of the San Gabriel, the San Bernardino 
and San Jacinto Ranges, and the Cuyamaca Mountains (plate 11a). 
Without doubt the same is true of northern Lower California. 
Traveling northward, we find in both Coast Ranges and Sierras 
a gradual decrease in the vegetational importance of the broad- 
sclerophylls. The chaparral areas are more and more restricted, 
and increasingly dominated by species of successional status. In 
the southern Coast Ranges and Sierras the change is not so notable, 
but it intensifies as we reach the central portion of the State. A 
similar decrease is seen, very naturally, as we ascend to higher alti- 
tudes in all parts of the region. In the northern portion of the 
State and beyond its limits, the broad-sclerophylls lose their domi- 
nance altogether and become less and less important vegetationally. 
Eastward the decrease is very sharp, so that beyond the western 
borders of the deserts and the middle forest region of the Sierras 
the type is almost altogether absent as a vegetational entity. 

LOCATION OF SYNTHETIC OR CLOSELY RELATED FORMS. 
It is impossible, in the present state of our knowledge, to obtain 
accurate data upon this point. However, the very confusion which 


THE BROAD-SCLEROPHYLL VEGETATION OF CALIFORNIA. 15 

is so evident in the various taxonomic treatments of certain genera 
is itself evidence after a fashion. The genera Ceanothus and Arcto- 
staphylos are classic examples. In both, the number of species 
proposed has been very large. Many of these fall into definite 
groups having close relationship within themselves, and by some 
authors these groups are treated as single variable species. A case 
in point is the group-species known commonly as Arctostaphylos 
tomentosa. From this Miss Eastwood has segregated three forms, 
all of which grow upon Mount Tamalpais; Abrams refers all to 
A. tomentosa. Howell has described 7 from southwestern Oregon, 
which Abrams reduces to synonymy. In Ceanothus several groups 
of closely related forms or species might be noted (Brandegee, 10), 
and in Rhamnus and Garrya the structure is similar, but on a smaller 
scale. It is evident that variation and hybridization are rampant 
among certain genera of the California sclerophylls. It is impossible 
to locate accurately the geographical area where these processes 
are most active, further than to state that they are less evident in 
the Sierras than in the Coast Ranges and southern California. 

LOCATION OF MAXIMUM SIZE OF INDIVIDUALS. 

In the case of the 9 broad-sclerophyll trees decision is easy; 4 of 
them, Myrica californica, Quercus agrifolia, Q. chrysolepis, and 
Q. wislizeni, attain their largest size in the central Coast Ranges, 
and the last two (according to Sargent) also in the central Sierras; 
4 more, Castanopsis chrysophylla, Pasania densiflora, U?nbellularia 
californica, and Arbutus menziesii, make their best growth in north- 
western California. Quercus engelmanni is confined to southern 
and Lower California. As to the chaparral shrubs, data are scanty 
and unsatisfactory, especially because fire so commonly brings the 
shoots to an untimely end. As to the most important single species, 
Adenostoma fasciculatum, the greatest average size that I have seen 
was in San Benito County, in the south Coast Ranges. Other 
species, ordinarily shrubs, attain respectable tree size in the same 
general region, e. g., Heteromeles arbutifolia and Prunus ilicifolia 
in the vicinity of Palo Alto. The very general statement may be 
made that the broad-sclerophylls attain their greatest size in the 
coastal region — the trees in the north and the shrubs in the south. 

LOCATION OF LEAST DEPENDENCE UPON A RESTRICTED 

HABITAT. 

In southern California we find the broad-sclerophylls least con- 
fined in this respect. East of San Diego the chaparral (mainly 
Adenostoma fasciculatum) covers the gently sloping mesas, and is 
solid on all exposures of the lower Cuyamaca Mountains (plate 11a). 
The same is true, where environmental conditions are undisturbed, 
in certain parts of the Los Angeles and San Bernardino Valleys and 


16 THE BROAD-SCLEROPHYLL VEGETATION OF CALIFORNIA. 

on the foothills surrounding them. Farther north, in Coast Ranges 
and Sierras, the chaparral is more and more restricted to south-facing 
exposures (plate 10, a, b), the opposite slopes being occupied by 
other plants, first by broad-sclerophyll trees, and still farther by 
conifers and broad-leaved deciduous species as well. The same 
changes are noted in ascending the higher mountains in any part of 
the State. 

LOCATION OF GREATEST IMPORTANCE OF THE TYPE IN THE 

CLIMAX COMMUNITY. 

This line of evidence is closely related to the last, since a plant 
community which covers all slopes and exposures with fair uniformity 
is likely to be the climax of that region. In another place (p. 72) 
I will show that in certain regions the climax is dominantly of the 
broad-sclerophyll type; that in others the broad-sclerophylls are 
secondary and successional, and that there are intermediate areas 
where the status of these plants is uncertain; and, finally, that the 
region where the broad-sclerophyll type, and in particular the 
chaparral, is most certainly climactic, is southern California. 

CONTINUITY AND CONVERGENCE OF LINES OF DISPERSAL. 
If we were to select an ideal center from which migrating species 
might most quickly and easily reach all parts of the region where 
broad-sclerophylls occur commonly, we would without fail fix upon 
the vicinity of Ventura County. From this point easy migration 
routes for all the species concerned, which would be mountain ranges 
of moderate altitude, lead in various directions, and nowhere along 
their courses are there barriers of any importance. From the north 
two routes converge, the Coast Ranges, and the Sierras by way of 
the Tehachapi Mountains. Southward are the various ranges 
of southern and Lower California. Surely it is more than coincidence 
that the evidence presented along other lines points to this same 
region and the country immediately southeast of it. 

I have endeavored in this chapter to present a picture of the range 
of the California broad-sclerophyll vegetation-type, principally by 
superposition of the ranges of the individual species; and to show, 
through seven lines of evidence, that the center of distribution of 
that type is in southern California west of the deserts, from the 
Santa Ynez and Sierra Madre Ranges southward into northern 
Lower California. 


THE BROAD-SCLEROPHYLL VEGETATION OF CALIFORNIA. 17 

II. CLIMATIC RELATIONS. 

Schimper (80) has shown clearly the constant relation between 
sclerophyll dominance and climate. He says: 

"The mild temperate districts with winter rain and prolonged summer drought 
are the home of evergreen xerophilous wood}'- plants, which, owing to the stiffness of 
their thick, leathery leaves, may be termed sclerophyllous woody plants. 
Wherever original conditions have not been altered by man the sclerophyllous trees 
and shrubs of districts with a moist winter always form dense and continuous wood- 
land, which in most cases consists principally or exclusively of shrubs, but which 
occasionally becomes true forest, although of low or middle height only." 

As to the advantage of the evergreen habit, he states that the 
vegetation is subject to short but frequent irregular periods of rest, 
sometimes due to cold, sometimes to drought; that short periods 
only afford simultaneously optimum conditions in temperature and 
moisture; the absolute optima for these two factors being entirely 
separate in time. It is therefore decidedly advantageous for the 
plants to be prepared to do their assimilative and vegetative work 
at all times. The regions which possess such a climate and support 
such a vegetation are, according to Schimper, the Mediterranean 
shores, the southwest extremity of Africa, southwestern and much 
of southern Australia, central Chile, and California. More detailed 
and localized works (4, 7, 8, 25, 78, 91) confirm Schimper's conclusions. 

After such a thoroughly adequate, even though brief, treatment 
by the pioneer author, it is necessary here merely to particularize 
somewhat concerning the region under discussion. 

The map (plate 2) is in part adapted from Reed and Kincer (77). 
The iso-lines indicate the percentage of total precipitation occurring 
in the half year April 1 to September 30. By comparing it with 
the map (plate 1) a remarkable correspondence will be at once 
evident between the region where the summer precipitation is less 
than 20 per cent and the region where broad-sclerophyll species 
are numerous. Moreover, the area of less than 10 per cent summer 
precipitation corresponds closely with the center of distribution of 
the sclerophylls, as described in the section devoted to that topic. 
Seasonal distribution alone, however, is not sufficient to explain the 
region of dominance of the broad-sclerophylls ; total precipitation is 
only slightly less important. If the total is very high, or if atmos- 
pheric conditions are such as materially to reduce evaporation during 
the dry season, it may be possible for species that are less xerophytic 
to control; if the total is very low, true desert species will replace 
the broad-sclerophylls. I have therefore plotted, in a generalized 
way, the total precipitation in the area with less than 20 per cent 
summer rainfall. The iso-lines selected are of course arbitrary, but 
they nevertheless mark out in a striking way the areas dominated 
by the three great vegetation types. Where the total precipitation 
is more than 30 inches, the vegetation is conifer forest of some type. 


18 THE BROAD-SCLEROPHYLL VEGETATION OF CALIFORNIA. 

The particular reasons for its presence differ in different places. 
In the Sierras and the isolated mountain areas of southern California 
the dominating cause is high total precipitation, which furnishes a 
sufficient amount of soil-moisture to tide the relatively mesophytic 
vegetation over the unfavorable season. In the higher mountains 
the slowly melting snows are of very great importance. In the 
northern end of the State, in addition to a high total precipitation, 
there is a decrease in the duration of the dry period. Along the 
northwestern coast there is, in addition to the other factors, the 
abundance of summer fog, which is the particular reason for the 
redwood forest. 

The area with 10 to 30 inches of rainfall is the region of broad- 
sclerophyll dominance. The correspondence with the region deter- 
mined upon through other lines of evidence is quite striking, even 
the Sacramento Valley being included (see p. 81). Only the narrow 
strip along the east slope of the Sierras, dominated by the vegetation 
of the Great Basin, must be left out. In the north Coast Ranges 
the broad-sclerophylls, both trees and chaparral, are of great impor- 
tance, as plate 1 indicates. Observation shows, however, that the 
conifers are competing with them on at least equal terms (see p. 73). 
The climatic map, indicating conifer forest conditions for this region, 
is therefore not deceptive. 

Finally, those regions with less than 10 inches of rainfall correspond 
accurately with the deserts — the western portions of the Colorado 
and Mojave Deserts and the Owens Valley region — and in addition 
the southern part of the San Joaquin Valley, which closely approaches 
desert conditions. 

The same points are brought out in another way by table 1. 
The three great regions are seen by the summary to be thoroughly 
distinct in total precipitation, the proportion being approximately: 
desert 1; broad-sclerophyll 6; conifer forest 15. 

The seasonal distribution in conifer forest and broad-sclerophyll 
regions is much alike, the summer precipitation averaging well 
below 20 per cent. In the desert the percentage is distinctly higher, 
because a number of stations east of the 20 per cent line were included 
in order to give a true picture of the California desert region as a 
whole. 

Certain temperature figures are added, though the data are incom- 
plete and their interpretation unsatisfactory. The mean annual 
temperature is of little use; the seasonal extremes, i. e., the means 
of the hottest and coldest months (in nearly every case July and 
January) and the mean maxima and minima of the same months 
are more significant. The mean annual temperature of the broad- 
sclerophyll region is only slightly below that of the desert. The 
mean of the hottest month, on the contrary, is much lower, being 


THE BROAD-SCLEROPHYLL VEGETATION OF CALIFORNIA. 19 

only slightly greater than that of the conifer forest. The striking 
and significant fact is that the seasonal range of temperature is far 
less in the broad-sclerophyll region than in either conifer forest or 
desert, the minima especially being decidedly above the others. 
This fact fits well with Schimper's elucidation of the evergreen 
habit as a means of utilizing short periods of favorable conditions for 
activity at all times of the year. The relatively narrow seasonal 


Table 1. — Climate and vegetation. 


Region. 


Precipitation. 


No. 


sta- 
tions. 


Total 
(inches). 


P. ct. 

May 1 

to 

Oct, 31. 1 


Temperature (° C. ; No. of stations varies). 


Mean 
annual. 


Mean 

of 
hottest 
month. 


Mean 

of 
coldest 
month. 


Mean 

maximum 

(hottest 

month). 


Mean 

minimum 

(coldest 

month). 


Conifer forest: 

Redwood region 

North Sierras 

South Sierras 

Transitional: North Coast 

Ranges 

Broad-sclerophyll : 

South Sierra foothills. . . . 

South Coast Ranges 

Cuyamaca Mountains. . . 
Grassland and coastal sage- 
brush : 

Sacramento Valley 

Los Angeles-San Bernar- 
dino Valley 

San Joaquin Valley 

Desert : 

Owens Valley 

Mojave Desert 

Colorado Desert 

Summary: 

Conifer forest 

Broad-sclerophyll 

Desert 


7 

22 

5 

10 

7 
27 
10 


23 

15 
31 

4 
4 

7 

34 
44 
15 


65.83 
60.50 
42.20 

38.08 

29.33 
20.32 
19.92 


21.85 

16.48 
11.21 

4.89 
3.97 
3.11 

58.91 

21.67 

3.82 


14 

14.4 

13.1 

12.4 


13.9 

11 
13.4 

23.9 

28.2 
28.9 

14.2 
11.6 

27 


11.3 
11.1 


14 

16.6 
14.2 
13.7 


16.9 


16.8 
16.9 


14.9 
17.6 


11.2 
14.4 
15.8 


15.5 

20.7 


20.8 

26.9 
19.7 
21.4 


26.8 


29.1 

26.8 


26.1 
29.8 


19.8 
20.9 
27.9 


7.8 
3.3 


7.8 


7.9 


10.5 
7.9 


4.6 
7.4 


4.2 
8.5 
5.5 


33.1 

27.8 
30.7 


33 
36 


33.8 
40.8 


28.8 
36.4 


3.3 
2.7 
1.6 


3.9 
1.7 


•4.0 
1.6 


1 The figures given here were worked out before the publication of the map (77). The difference in date 
of beginning and ending of summer season does not appreciably affect the results. 

temperature range is of course due to the coastal location of the 
great mass of the broad-sclerophyll region, and it is of interest that 
all the other regions dominated by this type of vegetation are coastal 
too. 

Summarizing briefly, we find that the broad-sclerophylls occur 
abundantly in that part of western North America where the summer 
precipitation is less than 20 per cent of the total, but that they 
dominate only that portion of this area where the total precipitation 
lies between 10 and 30 inches, and that the region of their dominance 
is also characterized by very moderate temperature extremes. 


20 THE BROAD-SCLEROPHYLL VEGETATION OF CALIFORNIA. 

III. THE COMMUNITIES. 

The terminology of plant communities is just now in a state 
of flux, and therefore it is too much to hope that the system employed 
in this paper will be satisfactory to every reader. The best that 
the author can do is to define his terms accurately and relate them 
clearly to the uses of other writers. It is therefore necessary to 
submit the following definitions: 

The Formation. The fundamental unit of vegetation : a community 
relatively homogeneous ecologically in the character of its dominants, 
floristically in that its locally varying subdivisions are bound together 
by the common dominance of one or more species or by the equiva- 
lence of species ecologically near of kin, and developmentally in that 
within a given climatic region it has a constant successional role. 

The Association. A vegetation unit of lower rank than the 
formation and contained within it; differing from other associations 
within the same formation with respect to any or all of the bases of 
the formation (ecological character, floristics, development), in 
minor degree, but sufficiently to cause it to stand out as a distinct 
entity. 

These two units are analogous, respectively, to the taxonomic 
units, species, and variety, and one may conveniently refer to the 
range of a formation or association exactly as one speaks of that of a 
species or variety. In naming the formations I would use descriptive 
titles based upon ecological character, and for the associations I 
would employ, when possible, the names of dominants. 

The Consociation, an association with a single dominant, is fre- 
quently a useful term. The word "community" is an indispensable 
addition to the list, being used to designate any vegetation unit 
without specifying its rank. 

These terms must now be related to two recent systems, that of 
Clements (21) and that of Nichols (69). Clements applies the 
term formation to the climax community only; I would extend it to 
successional communities as well. Clements distinguishes between 
the climax units association and consociation and the successional 
associes and consocies; my use of association and consociation includes 
both types of communities. The formation of the present paper 
agrees in substance with the association-type of Nichols; in the use 
of the terms association and consociation we are in essential agreement. 

THE BROAD-SCLEROPHYLL COMMUNITIES. 

There are two Californian formations in which the broad-sclero- 
phylls are the dominating element — the broad-sclerophyll forest 
formation and the chaparral formation. Each is in part climax, 
in part successional. Further, there is a broad-sclerophyll element 
of minor importance in the redwood forest, making a rather large 


THE BROAD-SCLEROPHYLL VEGETATION OF CALIFORNIA. 21 

part of its undergrowth. The grounds upon which the formations 
have been distinguished, and their range, composition, and structure, 
will be given here. Discussion of their relations to climate and to 
other communities is included in other chapters. 

The broad-sclerophyll forest formation is dominated by trees, 
mainly sclerophyllous evergreens, but including a number of decid- 
uous species (30.8 per cent). It is typically climax, but in this phase 
its extent is limited. It is successional where its range overlaps the 
ranges of the conifer formations, and postclimax in its overlap with 
the climax chaparral. 

The chaparral formation is made up of shrubs, the great majority 
being sclerophyllous evergreens. Its climax and successional phases 
are both of great importance. The latter is related developmentally 
to the conifer climaxes and is almost totally distinct floristically from 
the climax phase. 

THE BROAD-SCLEROPHYLL FOREST FORMATION. 

This formation ranges from southern Oregon southward through 
the coast mountains and Sierra foothills into Lower California, 
reaching its limit probably in the region of Mount San Pedro Martir. 
Nowhere, so far as I am aware, does it dominate the country as a 
conifer forest, for instance, commonly does. It occurs rather in 
discontinuous patches, which may, however, be of considerable 
extent. These alternate in the main with patches of chaparral of 
the type which I have designated as climax. Northward the forest 
is the more important of the two, especially in the Coast Ranges, 
while southward the chaparral becomes more and more preponderant. 
In the north there is overlap also with the ranges of the Sequoia 
sempervirens and the Pseudotsuga associations of the Pacific conifer 
formation, and in the Sierras with the formations of the conifer 
forest region. 

The number of dominant species is not large. In the following 
list a single asterisk indicates importance also in the conifer forest 
chaparral; and two asterisks, in both that and the climax chaparral. 

Sclerophylls. 

Myrica californica. Quercus chrysolepis. Pasania densiflora.* 

Castanopsis chrysophylla.* engelmanni. Umbellularia californica. 

Quercus agrifolia. wislizeni.** Arbutus menziesii. 

Deciduous. 
Quercus kelloggii.* Acer macrophyllum Aesculus californica 

lobata 

Several associations occur, easily recognized because of their 
relative constancy and wide distribution. Many individual localities 
would fit into none of them, and therefore in a minute study numerous 
transitional units might be described. 


22 THE BROAD-SCLEROPHYLL VEGETATION OF CALIFORNIA. 

Pasania-Quercus- Arbutus Association. — This community is charac- 
teristic of the lower altitudes of the North Coast Ranges, a region 
very complex and rather difficult to understand vegetationally, 
since two or more types which are climactic nearby meet here and 
overlap, finding conditions that are reasonably favorable to all. 
The redwoods thoroughly dominate the coast. East of them 
Pseudotsuga mucronata is the commanding species, but shares its 
rule with the broad-sclerophyll association about to be described. 
Chaparral and grassland communities also occur, but these are 
plainly successional. The Pasania-Quercus- Arbutus association is 
itself somewhat of a transitional unit between broad-sclerophyll 
and conifer types, for it rarely occurs without at least a sprinkling of 
conifers, especially Pseudotsuga, and its principal species occur 
commonly as an understory of the Pseudotsuga and Sequoia forests. 

The most important species of the formation are Pasania densiflora, 
Quercus chrysolepis, and Arbutus menziesii, and these attain great 
size. Other tree species occurring more or less commonly are 
Quercus kelloggii, Castanopsis chrysophylla, Umbellularia californica, 
Acer macrophyllum, JZsculus californica, and Cornus nuttallii. The 
association ordinarily possesses two layer societies — one of shrubs, 
including Corylus rostrata californica, Vaccinium ovatum, and Gaul- 
theria shallon, and one of herbs and ground-shrubs, a mixture of 
typically oak-forest species and those commonly associated with the 
redwood and douglas fir. 

The transitional phases of the association will be made evident 
by description of two areas, one in the interior of the Coast Ranges, 
where Pseudotsuga is the competing tree, the other on the edge of 
the coastal redwood region. 

The first locality is in Trinity County, on the north-facing slope 
of the Mad-Trinity Divide. The dominant tree, Pseudotsuga, grows 
here magnificently, many specimens attaining a diameter of 2 
meters. Abies concolor and Pinus lambertiana also occur. Beneath 
the conifers there is an understory of broadleaf trees, nearly all 
sclerophylls. Castanopsis chrysophylla is the most abundant, and 
Pasania, Arbutus, and Acer macrophyllum also occur. This assem- 
blage might here be termed a layer society. Corylus rostrata cali- 
fornica, Cornus nuttallii, and Ceanothus integerrimus form a second 
stratum, and a third is composed of herbs and ground shrubs: 
Vancouveria sp., Polystichum muniturn, Berberis sp., Gaultheria 
shallon. 

The other is the valley of the South Fork of the Eel River, in 
Humboldt County. In the vicinity of Garbersville and for several 
kilometers north of it (downstream), the north slopes and ravines 
are forested with Pasania densiflora, Quercus kelloggii, Q. chrysolepis, 
Q. garryana, Arbutus menziesii, Umbellularia californica, Msculus 


THE BROAD-SCLEROPHYLL VEGETATION OF CALIFORNIA. 23 

californica, Acer macrophyllum, and Pseudotsuga, making a rather 
typical specimen of the Pasania-Qucrcus- Arbutus association. The 
first redwoods appear in groups of large trees on the valley bottom, 
with scattered individuals on north slopes (plate 8a). This con- 
tinues for 15 kilometers or more, then for several kilometers there is an 
almost pure forest of Sequoia on north slopes with the Pasania- 
Quercus- Arbutus association on south exposures. Finally the forest 
becomes nearly pure Sequoia on all slopes, the broad-sclerophylls 
gradually disappearing as a distinct community, though remaining 
to some extent as a layer society, particularly Arbutus and Pasania. 

Quercus agrifolia- Arbutus Association. — This unit is coastal, occur- 
ring from the northern limit of Quercus agrifolia in Mendocino County 
to the southern limit of Arbutus in Los Angeles County. It is thus 
characteristic of the outer central Coast Ranges, where it is the 
dominant cover on north-facing slopes. It is particularly well 
developed in the San Francisco Bay region and southward to the 
Santa Lucia Mountains. The character tree is Quercus agrifolia. 1 
Arbutus menziesii is next in importance, but varies greatly in 
abundance in different localities. ^Esculus californica, a deciduous 
species, is usually prominent, and Umbellularia californica is equally 
so. Acer macrophyllum is frequently important in the more meso- 
phytic localities. In areas that are transitional with the Sequoia 
association, Pasania, Quercus chrysolepis, Q. kelloggii, and Sequoia 
itself occur. Since a typical area of this association is described in 
another part of this paper (p. 38), it will be unnecessary to go further 
into details here. Station 7 at Jasper Ridge is representative in 
every respect (plates 14a, 8b). 

Quercus agrifolia Consociation. — South of the southern limit of 
Arbutus (Los Angeles County) the community is continued as a 
consociation dominated by Quercus agrifolia. This is rather promi- 
nent in the lower altitudes of the west slope of the Cuyamaca Moun- 
tains. 

Umbellularia Consociation. — Umbellularia occurs scattered through 
the Quercus agrifolia-Arbutus association, and in others as well, but 
it also forms pure growths, especially in the central Coast Ranges, 
occupying moist ravines and canyon bottoms. These groups of 
Umbellularia stand out strikingly above the other trees, being con- 
spicuous by reason of their light green color and conifer-like form. 
The shade is very dense and undergrowth almost lacking. Umbel- 
lularia itself, however, is able to germinate successfully under such 
conditions. 

Quercus agrifolia-lobata Association (plate 9a). — This is charac- 
teristic of the broad valleys and gentle footslopes of the central 

1 In some places, especially in the inner Coast Ranges, it is replaced by Q. wislizeni, and thus 
another association might be distinguished. 


24 THE BROAD-SCLEROPHYLL VEGETATION OF CALIFORNIA. 

Coast Ranges, being locally of considerable importance in the San 
Francisco Bay region. The dominant species are Quercus agrifolia 
and Q. lobata, the latter being deciduous. The trees as a rule stand 
far apart, producing a park-like landscape, and it is in such places 
that the largest specimens of both species occur. One tree of 
Q. agrifolia near Palo Alto is 2.1 meters in diameter breast-high. 
A specimen of Q. lobata west of Clear Lake is of the same diameter, 
with a spread of branches of 47 meters. Much larger trees of the 
latter have been reported. Other species are of occasional occurrence. 
In the Palo Alto region large specimens of Umbellularia, Arbutus 
and Prunus ilicifolia make a small part of this association. Because 
of the wide scattering of the trees, the ground between is in most 
places under cultivation. Near Palo Alto, however, there are a 
few localities which retain their original vegetation, because they 
have long been included in certain large estates. In such areas one 
finds the two oaks of all sizes from seedlings to large mature trees. 
Most of the young ones occur in indefinite groups in the opener places, 
while the mature specimens completely dominate the ground beneath 
them. Three layer societies occur. The first, of tall shrubs, includes 
Rhamnus californica, Heteromeles arbuiifolia, Sambucus glauca, 
and Rhus diversiloba. The low-shrub society includes Rubus viti- 
folius, Symphoricarpos racemosus, and Solatium umbelliferum. Mic- 
romeria chamissonis is dominant in the ground layer society. Further 
details concerning this very interesting association will be given in a 
future paper upon the communities and successions of the Palo 
Alto region. 

Quercus chrysolepis-kelloggii Association. — The associations so 
far described are distinctly of low altitudes. The present one belongs 
to the higher Coast Ranges and southern California mountains and 
to the middle altitudes of the Sierras. It is preeminently a north- 
slope forest, but localities are common enough where it occurs on 
other exposures as well, seeming like a true climax. The most 
important tree species is the broad-sclerophyll Quercus chrysolepis; 
Q. kelloggii, deciduous, is often a close second. Others are Arbutus, 
Umbellularia, Acer macrophyllum, Pasania, ALsculus. Since the 
association has so great a range, the subordinate vegetation varies 
greatly. It shows broad transition areas with neighboring associa- 
tions. Its close relation to the Pasania-Quercus- Arbutus association 
is at once evident, and it is not strange, therefore, to find areas that 
can not be placed with certainty in either. Again, just as the 
Pasania-Quercus- Arbutus association passes into the Sequoia forest 
as an understory, so also does the Quercus chrysolepis-kelloggii 
association into the pine forests of the high Coast Ranges and the 
Sierras. In fact, in the Sierras it is commoner to find the community 
as an understory beneath Pinus po?iderosa and P. lambertiana than 


THE BROAD-SCLEROPHYLL VEGETATION OF CALIFORNIA. 25 

as a dominating type. In the mountains of southern California 
the group forms a similar understory beneath Pseudotsuga macro- 
carpa. Upon the xerophytic side there is transition to the chaparral. 
Such areas have so individual a stamp that I have been accustomed 
to refer to them as "dwarf forest." An excellent example is found 
upon the north slope of Mount Tamalpais (Marin County), near 
the summit. Quercas chrysolepis and Q. wislizeni, growing in dense 
thickets 3 to 5 meters in height, are dominant, an occasional full- 
sized tree of Q. chrysolepis rising above the general level. With 
them grow other species: Quercus agrifolia, Pasania, Arbutus, 
Umbellularia, Torreya californica, and the chaparral shrubs Arcto- 
staphylos tomentosa [A. glandulosa Eastwood], Ceanothus sorediatus, 
and Castanopsis chrysophylla minor. 

Quercus chrysolepis Consociation (plate 9b). — In the middle 
altitudes of the Sierras, dominated by the pines and Pseudotsuga, 
Quercus chrysolepis growing almost pure has a distinct successional 
role. Upon the great talus accumulations at the bases of the Yo- 
semite cliffs certain chaparral shrubs are the pioneers. These are 
followed by a dense, pure growth of Quercus chrysolepis which seems 
to persist for a long time, as the live-oak forest is the most conspicuous 
feature of such areas. The talus piles that are manifestly oldest, 
with much accumulation of humus, support a mixture of the oak 
and Pseudo suga. 

A few concluding remarks in summary will gather together the 
main points in the discussion of the broad-sclerophyll forest formation. 
It is plain that the group as a whole is the fundamental unit, the 
minor divisions being closely tied together by a number of binding 
species. The transition zones between associations of the formation 
and with other formations are broad, so that accurate delimitation 
is difficult. The broad-sclerophyll communities, wherever they 
adjoin the conifer forest communities, pass into them as layer societies. 
There is a very close habitat relation between the broad-sclerophyll 
forest and the climax chaparral, in that in the main they overspread 
the same range, occupying areas of comparatively slight physical 
differences. The question of climax, therefore, whether one or the 
other or both, is difficult. My conclusions will be given in a later 
section. 

THE CHAPARRAL FORMATION. 

It was pointed out at the beginning of this chapter that the 
chaparral formation, homogeneous in the ecological character of its 
dominants, at least so far as anatomical structure is concerned, 
embraces two associations which are very distinct floristically and 
developmentally. Separate treatment of these will be the best 
method of presentation. 


26 THE BROAD-SCLEROPHYLL VEGETATION OF CALIFORNIA. 


The Climax Chaparral Association. 

The climax chaparral is the dominant community over the whole 
of the southern Coast Ranges and the mountains of southern Cali- 
fornia and northern Lower California. Only the highest summits, 
controlled by conifers, and the more mesophytic north slopes, 
inhabited by broad-sclerophyll forest, must be excepted. North- 
ward in the north Coast Ranges the chaparral shares its control 
more and more with the broad-sclerophyll trees, and opposite the 
northern end of the Sacramento Valley it disappears entirely as a 
dominating community. In the southern Sierras it is of great 
importance, occupying a wide belt in the foothills. In the northern 
Sierras its continuity is broken, and this is not strange, since the 
conifers of the montane forest here reach the valley floor. The 
present range of the climax chaparral is indicated in a very general 
way by the range of its most important species, Adenostoma fas- 
ciculatum (plate 3). In addition, I believe that there are certain 
extensive areas now inhabited by grasses and by half-shrubs that 
climatically and potentially are chaparral regions (p. 76). 

Since the climax chaparral is by far the most widely extended 
and diversified of the broad-sclerophyll communities, it is natural 
that the present list of species should be the longest. The following 
are all evergreen, except that Quercus dumosa is barely so. One 
asterisk (*) indicates that the species is also of importance in the 
conifer forest chaparral; two asterisks (*) that it is important in that 
and also in the broad-sclerophyll forest. 


Castanopsis chrysophylla minor.* 
Quercus chrysolepis.** 

dumosa. 

durata. 

wislizeni frutescens.** 
Dendromecon rigidum. 
Heteromeles arbutifolia. 
Cercocarpus betula?folius. 
Adenostoma fasciculatum. 
sparsifolium. 
Prunus ilicifolia. 
Xylothermia montana. 
Cneoridium dumosum. 
Rhus integrifolia. 


Rhus laurina. 

ovata. 
Rhamnus californica.* 

crocea. 
Ceanothus crassifolius. 

cuneatus. 

dentatus. 

divaricatus. 

hirsutus. 

megacarpus. 

papillosus. 

rigidus. 

sorediatus. 

verrucosus. 


Garrya elliptica. 
Comarostaphylis diversifolia. 
Xylococcus bicolor. 
Arctostaphylos andersonii. 

glauca. 

hookeri. 

manzanita. 

montana. 

pumila. 

stanfordiana. 

tomentosa. 

vestita. 
Eriodictyon californicum. 


With so large a list of species there is naturally great diversity in 
the composition of the association. Anyone given to splitting of 
hairs would easily separate many communities of lower rank. This 
is in part due to slight habitat differences, but also in an important 
degree to the great number of species with restricted range and to 
the frequent occurrence of fires, which result in multitudinous com- 
binations of species, depending upon which are able to survive or to 
repopulate the area burned. It is easy to recognize, however, 
throughout the length and breadth of the region, one striking and 


THE BROAD-SCLEROPHYLL VEGETATION OF CALIFORNIA. 27 


characteristic consociation, for Adenostoma fasciculatum covers 
many hundreds of square miles in practically pure dominance. 
The range of the Adenostoma consociation is indicated on the map 
(plate 3). Other species, too, completely control certain areas, 
but it is far commoner for these to mingle with each other and with 
Adenostoma in an endless number of combinations and proportions. 
In 87 listed localities in all parts of the State, the following occur- 
rences of important and widespread species are noted: 


Adenostoma fasciculatum 75 

Arctostaphylos (all species) 50 

Heteromeles arbutifolia 26 

Ceanothus cuneatus 25 

Quercus dumosa and Q. durata 23 


Cercocarpus betulsefolius 19 

Quercus wislizeni frutescens 11 

Rhamnus calif ornica 10 

Quercus chrysolepis 10 


Such being the condition, it avails little to attempt to distinguish 
minor units within the association. It is more reasonable to express 
the differences by noting the dominance of one or more species in 
particular cases. One fact, however, must be brought forward. 
The genus Arctostaphylos gives its stamp to certain localities in a 
very characteristic way. No one species is dominant throughout. 
Arctostaphylos tomentosa is by far the most important, ranging over 
the whole region. A. glauca is abundant in the southern half of the 
State and A. manzanita in the northern, and several others are 
prominent locally. This phase nearly everywhere accompanies 
the Adenostoma consociation, occupying the less xerophytic north- 
facing slopes where these are not sufficiently moist to permit the 
forest to exist, and at higher altitudes replacing the Adenostoma 
consociation on the south slopes, the north exposures being forested. 
The combination is well shown at Jasper Ridge, described in the 
next chapter. 

The Conifer Forest Chaparral Association. 

The range of this community is nearly coextensive with that of 
the montane conifer forest, spreading to some extent into the region 
of the subalpine conifer forest. Its home is, therefore, in the middle 
altitudes of the Sierras, with extensive colonies throughout the 
higher mountains of northern California and Oregon, the north 
Coast Ranges, and the mountains of southern California. It reaches 
its best development where the forest which controls it is best 
developed, and therefore its true center is in the northern Sierras. 
Accurate altitudinal data are unavailable, and the patchy distribution 
makes close determination impossible, but the lower limit may be 
placed roughly at the lower limit of Pinus ponderosa, which is very 
near to the valley-level at the northern end of the Sierras and rises 
gradually southward. Naturally there is extensive overlap with 
the range of the climax chaparral which dominates the foothill 
region in imperfect manner. The upper limit is equally indefinite. 


28 THE BROAD-SCLEROPHYLL VEGETATION OF CALIFORNIA. 

Above the ranges of the dominant trees of the Montane Forest the 
chaparral species become gradually fewer. At least one (Arctosta- 
phylos nevadensis) reaches timberline in the Yosemite region (39). 

The following list includes those species which are of importance 
in the conifer forest chaparral in various parts of its range. Many 
others, of course, occur occasionally, especially where the range of 
the formation overlaps that of another. Species marked with a 
single asterisk (*) are of importance also in the broad-sclerophyll 
forest, those with two asterisks (**) in the climax chaparral, and 
those with three in both. 

Sclerophylls. 

Castanopsis chrysophylla minor.* Pasania densiflova echinoides.* Arctostaphylos mariposa. 

sempervirens. Rhamnus californica.** 1 nevadensis. 

Quercus ehrysolepis.*** Ceanothus cordulatus. patula. 

sadleriana. velutinus. pungens. 

vaccinifolia. Garrya fremontii. viscida. 

wislizeni.*** Arctostaphylos drupacea. 

Deciduous. 

Corylus rostrata californica. Amelanchier alnifolia. Cercis occidentalis. 

Quercus breweri. Prunus demissa. Acer glabrum. 

garryana. emarginata. Ceanothus integerrimus. 

kelloggii.* subcordata. sanguineus. 

The conifer forest chaparral association is at least as variable as 
the climax chaparral. This is due in part to great variation in habitat 
and also in an important degree to what may be termed accidental 
causes, for since the community owes its existence in large part to 
the frequent destruction of the forest by fire, the population of a 
given area must depend largely upon what species are producing 
seed in its immediate vicinity. The association has been carefully 
studied by the U. S. Forest Service, since its occurrence within the 
belt of merchantable timber gives it great economic importance. 
A number of reports have been published (see introduction) and 
many more are still in manuscript, and to these I have had access 
through the kindness of the officials of District 5 in San Francisco. 

Since the work of the Forest Service upon this community greatly 
outweighs mine, and since more of it is soon to be published, I will 
not attempt detailed subdivision. A few general features are worth 
pointing out, however. In the lower and drier portion of the yellow- 
pine belt of the Sierras one combination is of great importance. 
This is made up of Arctostaphylos viscida and Ceanothus integerrimus, 
the former being especially conspicuous because of its beautiful gray 
foliage. It is particularly widespread in the regions surrounding 
the old placer diggings, where the timber was cat and burned 
off more than half a century ago. In the upper and moister por- 
tion of the pine belt and the lower part of the Subalpine Zone 
the areas of chaparral show greater floristic diversity, and a great 

1 Principally in its two vaiieties, R. c. tomentella and R. c. rubra. The latter is deciduous. 


THE BROAD-SCLEROPHYLL VEGETATION OF CALIFORNIA. 29 

number of consociations and mixtures might be distinguished. 
In the higher northern Sierras half a dozen species are of paramount 
importance. These are Castanopsis sempervirens, Quercus vac- 
cinifolia, Prunus emarginata, Ceanothus cordulatus, C. velutinus, 
Arctostaphylos nevadensis, and A. patula. They occur in all possible 
combinations, so that a classification for one region may not fit 
another at all. We should also mention the thickets of deciduous 
oaks, especially Quercus kelloggii and Q. garryana, which are so 
extensive in the mountains of Trinity County and northward. 
These species, ordinarily trees, here grow in dense masses like the 
chaparral, forming a connecting link ecologically with the deciduous 
oak thickets of the Rocky Mountain foothills. 

The following outline of the broad-sclerophyll communities will 
serve as summary to this chapter, all being climax except those 
specially noted: 

A. Broad-sclerophyll forest formation. 

1. Pasania-Quercus-Arbutus association. 

2. Quercus agrifolia-Arbutus association. 

2a. Quercus agrifolia consociation. 
26. Umbellularia consociation. 

3. Quercus agrifolia-lobata association. 

4. Quercus chrysolepis-kelloggii association. 

4a. Quercus chrysolepis consociation (successional) . 

B. Chaparral formation. 

1. Climax chaparral association. 

la. Adenostoma and other consociat'ons and various mixtures. 

2. Conifer forest chaparral association (successional). 

2a. Numerous vague minor units. 


30 THE BROAD-SCLEROPHYLL VEGETATION OF CALIFORNIA. 

IV. VEGETATION AND HABITAT. 

THE LOCALITY FOR INTENSIVE STUDY. 
THE PALO ALTO REGION. 

For intensive study of vegetation and habitat it was necessary 
to find a spot as nearly representative as possible, affording oppor- 
tunity for comparison of related communities and favorably situated 
with respect to a base of operations. The vicinity of Palo Alto 
satisfied these requirements, the botanical laboratory of Stanford 
University furnishing facilities for indoor work. 

Palo Alto is situated in the central Coast Range region, near the 
southern extremity of San Francisco Bay, from which it is but 
3 km. distant. The lowland upon which it lies extends along the 
southwest shore and is commonly spoken of as a northwestward 
extension of the Santa Clara Valley. Southwestward from the town 
rise the Santa Cruz Mountains, the crest, ranging from 512 to 850 
meters in height, being 11 km. distant. The northeast face of the 
range is a fault scarp, and therefore abrupt. There is, nevertheless, 
a zone of foothills between the main mountain front and the valley, 
in the vicinity of Palo Alto 5 km. broad and attaining a height 
of 246 meters. The altitude of Palo Alto itself is but 17 meters. 

The topographic diversity just outlined, together with the influence 
of the ocean, which is distant from Palo Alto 25 km. over the Santa 
Cruz Range, produces very great climatic differences within short 
distances. Thus, the annual precipitation at Palo Alto is 66 cm., 
while on the mountain summits, only 15 km. away, it is 139 cm. 
(23, p. 186). At the ocean shore the precipitation is again light, 
75 cm. being recorded at one station. The summer fogs, which 
regularly cover the mountains but rarely invade the valley, are also 
of profound climatic importance. 

In correlation with topographic and climatic diversity we find 
equal diversity in the vegetation. The prevailing type in the fog- 
bathed mountains is the redwood forest ; the well-watered mountains 
without fog support a vegetation made up of evergreen oaks, madrono, 
and Douglas fir; the foothills and drier mountain sides are clothed 
with chaparral except where local conditions, such as steep north 
slopes, permit the development of oak forest; the gentle slope from 
foothills to bay was originally covered by chaparral, open oak forest, 
and salt marsh, all of which have been more or less disturbed by 
cultural operations. For an account of the redwoods and their 
relation to rainfall and fog, the reader is referred to a former paper (23). 

JASPER RIDGE. 

The locality chosen for quadrat and instrumental study was one 
of the higher foothills, 7 km. southwest of Palo Alto, known locally 
as Jasper Ridge. It is a hilly mass, approximately 10 km. northwest 


THE BROAD-SCLEROPHYLL VEGETATION OF CALIFORNIA. 31 

and southeast, by half as much in the other dimension. It is nearly 
surrounded by the valleys of San Francisquito, Los Trancos, and 
Corte de Madera Creeks, the floors of which range in altitude from 
60 to 120 meters. The average height of the crest of the ridge is 
approximately 180 meters, and the highest point, near the south- 
eastern end, 246 meters. The mass here has a rather broad, rolling 
summit, but the slopes are considerably dissected by ravines. North- 
ward and northeastward from Jasper Ridge the hills are lower, but 
southwestward, across the valley of Corte de Madera Creek, the 
main front of the Santa Cruz Mountains rises to an altitude of 600 
meters. 

The surface rock of the main part of the ridge is probably the 
Chico sandstone of Upper Cretaceous age (14). There are two 
areas of the Franciscan formation of considerable extent and one 
outcrop of serpentine, but the area studied is entirely within the 
limits of the presumptive Chico. This rock weathers into a uniform 
coarse yellow sand. In most places the layer of residual soil is 
very thin, but on a few level spots there is a greater depth. In 
excavations in such places the sand is seen to merge gradually into 
the undecomposed rock, which is found practically intact at a maxi- 
mum depth of a meter or a little more. On steep hillsides the soil 
is irregular in depth, with rock outcrops alternating with sand 
pockets. The greatest accumulations are naturally at the foot of 
the steepest slopes, where the sand contains many angular fragments 
of considerable size. Of the ten stations studied, eight possess a 
uniform soil of the type just described. The other two show local 
differences which are of sufficient importance to affect considerably 
the vegetation growing on them. 

At first thought it would seem absurd to devote a paragraph to 
the climate of so limited an area as Jasper Ridge, after the climate 
of the region as a whole has been discussed. In California, however, 
such is not the case. One can not assume that the climates of two 
places are alike because they are but a few kilometers apart. Witness 
the great difference in rainfall already noted between Palo Alto 
and the summit of the Santa Cruz Range. In the matter of rainfall, 
Jasper Ridge lies between the above stations, as it does in position. 
The precipitation for a number of stations in the Santa Clara Valley, 
foothills, and Santa Cruz Mountains in the season 1913-14 (a very 
wet year), was as follows (see 23, p. 185): 

cm. 

,, „ ( San Jose 47 . 83 

Valley: | Palo AltQ 62 15 

Foothills: Jasper Ridge 103 .71 

, , . . ( King's Mountain 169 . 25 

Mountains :{ Ben Lomond ; 197 66 

Assuming that the proportion between the stations will hold 
roughly constant for a succession of years, the normal rainfall at 


32 THE BROAD-SCLEROPHYLL VEGETATION OF CALIFORNIA. 


Jasper Ridge, calculated from those of San 
Jose and Ben Lomond Weather Bureau Sta- 
tions, is about 80 cm. 

It seems probable that Jasper Ridge has a 
smaller total of fog than either the valley or the 
mountains. The true ocean fogs rarely reach 
it and the "bay" or "tule fogs," which are 
frequent during the forenoon in the lowland, 
do not ordinarily rise so high. The average 
midday temperature is probably higher than 
in the valley because of the proximity of the 
bay to the latter, and also higher than in the 
mountains because of altitude and fog. Tem- 
perature and fog affect vegetation through their 
influence upon the evaporating power of the 
air, and it is quite certain that the evapora- 
tion-rate is much higher upon Jasper Ridge 
than in the mountains, and almost as certain 
that it is higher than in the valley, because of 
distance from the bay, absence of fog, and prob- 
ably higher mid-day temperature. We there- 
fore conclude that Jasper Ridge is far more 
xerophytic in climate than the mountains and 
perhaps somewhat less so than the valley. It 
may be, however, that the greater rainfall is 
neutralized by the higher evaporation-rate. 
The evidence of the vegetation is that there is 
little climatic difference between the ridge and 
the valley. 

THE VEGETATION. 

The vegetation of Jasper Ridge was orig- 
inally mainly chaparral. Large portions have 
been cleared of the bushy growth, quite cer- 
tainly within a century, and the cleared areas 
are now expanses of wild oats (Avena fatua 
and A. barbata), with scattered oaks, especially 
Quercus douglasii, which is peculiarly charac- 
teristic of such secondary areas. Quercus agri- 
folia and Q. kelloggii are also frequent, and 
there is a considerable scattering of shrubs of 
the species that frequent such cleared areas: 
Ceanothus cuneatus,Heteromeles arbutifolia,Bac- 
charis pilularis, and especially Rhus diversiloba. 

Fig. 1. — Profile of a part of Jasper Ridge, drawn approximately 
to scale, showing topography along trail, distribution 
of plant communities, and location of stations. 


>* 


THE BROAD-SCLEROPHYLL VEGETATION OF CALIFORNIA. 


33 


The original vegetation still remaining is comprised in several 
large patches, the two principal ones being at the northwest and 
southeast extremities of the ridge. It is true that these are mere 
remnants, but they are of sufficient size to show absolutely natural 
conditions, except along the edges. The studies were made in the 
area at the southeast extremity, which covers approximately 2.5 
sq. km. and includes the highest point of the ridge. It possesses 
rather bold relief, including several summits and ravines, one of 
which is decidedly abrupt. The extreme range of altitude is from 
184 meters at the bottom of the deepest ravine to 246 meters at 


A' 


a' 
A 9 A 


A' 


A' 


A 3 


A** A 


A' 


a '5 


A' 


A 5 


A' 


A 


A 1 


A , A 


A' a-5 

A A 


A' 


3 


A' A 


a' a 
, A A 3 
A 2 


A' 


A 


A'r 

.10 


a' A' 


A 3 


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A „2 


A 


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A A n 


/ 


A 

t 


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. C 


A A' 


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12 

Ar 


5 A 

A A 3 
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A 2 

A 6 


A 3 


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A'r A ' 


Fig. 2. — Quadrat at station 1, 5 meters square Note abundance 
of individuals of Adenostoma, which, however, are 
small and do not control the area. For symbols in 
this and succeeding quadrats see footnote, p. 34. 


the highest hilltop. The vegetation of the area is mainly chaparral. 
The Adenostoma consociation covers the south-facing slopes and the 
summits and is by far the most extensive type; Arctostaphylos is 
dominant upon the gentler north-facing slopes; and on the north- 
facing slope of the deepest ravine is a typical area of the Quercus 
agrifolia- Arbutus association of the broad-sclerophyll forest. It is 
thus an ideal place in which to study the various communities of 
broad-sclerophyll vegetation and their relations to habitat and to 
each other. 

For quadrat and instrumental study a series of ten stations was 
determined upon, lying on an approximately north-south line 


34 THE BROAD-SCLEROPHYLL VEGETATION OF CALIFORNIA. 

which crossed all slopes and vegetation types, giving two or more 
examples of each. A trail was cut through the brush connecting 
these with each other and with a nearby road. The distance between 
the extreme stations was approximately 800 meters. 

Stations 7 and 8 represent the forest and the remaining eight the 
chaparral. Of the latter, stations 1, 4, 5, 9, upon south-facing slopes, 
and 2 and 10, on nearly level summits, were in areas of Adenostoma 
dominance, and stations 3 and 6, upon north-facing slopes, in Arc- 
tostaphylos dominance. Quadrats were charted in six of these. 
A number of statistical quadrats confirm the results. 

Station 1. 

This has the poorest vegetation of any. A quadrat 5 meters 
square is represented in figure 2. 1 The species within it are given 
below in order of abundance, with the number of plants of each 
and the number of individual stems. Exact statistical study of 
chaparral vegetation is difficult, because of the common habit of 
growing in clumps and the frequent impossibility of readily deter- 
mining the limits of a single group. The figures given are therefore 
not absolutely accurate. 

Clumps. Stems. 

Adenostoma fasciculatum 81 219 

Arctostaphylos tomentosa 9 60 

Total 90 279 

Heteromeles arbutifolia is occasional nearby. The bushes are all 
small, ranging from 3 to 12 dm. in height, most of them nearer the 
former figure. In spite of the large number of individual plants, 
the ground is poorly controlled, large areas being entirely unshaded. 
Herbaceous growth is practically absent, the quadrat showing not a 
single plant at the time when it was plotted (August 25). There is 
no humus superficially visible, and very scanty litter. 

Station 2. 

This station is on the highest point of Jasper Ridge and there- 
fore most thoroughly exposed to atmospheric agencies. Moreover, 
with station 1, it differs in soil character from the other eight, as 
will be later shown. The vegetation is of better appearance than 
that of station 1, but is still low and scattered, so that it is possible to 
walk between the bushes in many places. No chart quadrat was 

1 The symbols used in this and the following quadrats are given here. Exponents, except 
in figure 6, indicate number of stems in a clump. 

A. Adenostoma fasciculatum. B. Baccharis pilularis. Qa. Quercus agrifolia. 

Ab. Arbutus menziesii. C. Ceanothus sorediatus. Qd. Quercus durata. 

Ae. ^Esculus californica. D. Diplacus glutinosus. Qw. Quercus wislizeni. 

Ar. Arctostaphylos tomentosa. H. Heteromeles arbutifolia. R. Rhus diversiloba. 

As. Aster radulinus. Ho. Holodiscus discolor. 


THE BROAD-SCLEROPHYLL VEGETATION OF CALIFORNIA. 


35 


made, but a statistical quadrat of 5 meters square gave the following 
results : 

Clumps. 

Adenostoma 98 

Arctostaphylos 4 

Total 102 

Quercus durata is rather frequent in the vicinity and Heteromeles 
arbutifolia and Quercus wislizeni also occur. Undergrowth is hardly 
more noticeable than in station 1 . There is practically no humus and 
very scanty litter. 

Station 3. 

A short distance north of station 2 a moderate slope begins, which 
extends downward for a distance of 75 meters to the bottom of a 
shallow ravine. From the summit for a little distance downward, 


X-Ar 


Qd 


Ar 


Qd 


Ar 

8 i 

H H 


Ar 


Ar < 
A 


Ar 


Qd 


Ar 


A Ar 


Ar 


Ar 


Ar 


Ar 


Ar 


Ar 


Ar 


Ar 


Qd 


Ar 


Fig. 3. — Quadrat at station 3, 5 meters square. Note fewness of 
individuals, mostly Arctostaphylos, which nevertheless 
thoroughly control the area. 

Adenostoma is predominant, but a gradual change is noted, until 
the lower half is seen to be dominated by Arctostaphylos and Quercus 
durata, with Adenostoma a decided minority. The size of the shrubs 
also increases gradually, until near the bottom of the slope they 
average 2 meters in height. The density is such that the ground is 
entirely dominated, and the only way to travel is on one's hands 
and knees below the zone of tightly intertangled branches. The 


36 THE BROAD-SCLEROPHYLL VEGETATION OF CALIFORNIA. 

enormous woody masses which frequently form the bases of the 
Arctostaphylos and Adenostoma clumps are very prominent here, 
occupying a surprising amount of the ground area. The quadrat 
shown in figure 3 gives the following summary: 

Clumps. Stems. 

Adenostoma 7 23 

Arctostaphylos 18 44 

Quercus durata 4 8 

Heteromeles 3 11 

Total 32 86 

An occasional plant of Diplacus glulinosus, a half-shrub, is found 
here, badly off for light. Depauperate specimens of Symphoricarpos 
racemosus are rather frequent. Herbaceous growth occurs, but not 
in great amount. The most abundant is Aster radulinus, which 
produces nothing but basal leaves under the solid chaparral cover. 
The only other is the fern Gymnogramme triangularis. The woody 
bases of the shrubs are covered with mosses and small Cladonias. 
Humus is in fair amount and litter is abundant. Where the trail 
crosses the ravine bottom a single young specimen of Quercus agri- 
folia suggests a tendency toward mesophytic forest conditions. 

Station 4. 

Crossing the ravine, the vegetation is seen to change, with no 
transition zone, to Adenostoma dominance. The striking contrast 
is manifestly related to the sharply angular change of slope at the 
ravine bottom. Station 4 is exactly opposite station 3 and at an 
equal height. The bushes, averaging 1.2 to 1.5 meters, are decidedly 
better in appearance than those of stations 1 and 2, and the ground 
is controlled by them to a much greater degree, though not completely. 
The quadrat (fig. 4) contains the following: 

Clumps. Stems. 

Adenostoma 24 133 

Arctostaphylos 5 42 

Quercus durata 3 4 

Total 32 179 

The undergrowth is exceedingly sparse, including a few individuals 
of Aster radulinus and Gymnogramme triangularis. Humus is 
scanty, but there is considerable litter beneath the shrubs. A plant 
of Quercus wislizeni close to the quadrat has three trunks 2.5 meters 
high, standing well above everything else. 

Station 5. 

Going northward up the gentle slope, we pass through vegetation 
like that of station 4, but becoming lower and less dense. There 
are frequent areas where one may walk between the bushes, many of 
which are of low stature. Adenostoma is everywhere dominant, 
and Arctostaphylos, Heteromeles, Quercus durata, and Q. wislizeni are 
also present. Undergrowth is practically absent, and humus and 
litter are scanty. 


THE BROAD-SCLEROPHYLL VEGETATION OF CALIFORNIA. 37 


Station 6. 

Passing over the second summit, we find Adenostoma still dominant 

and greatly increasing in size and controlling power. Descending 

the steep north slope a short distance, we encounter a gradual change 

to conditions like station 3. Here station 6 was established. The 


Qd 


Qd 

2 


A 


A^ A< 
A J 


A 
A A 


31 


Qd 


; 


Ar 


,* 


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2 

Ar 


A J 


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A £ 


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IB 

, A 
A 

Qw 


7 

A 
a 
A 

A 7 


a' 5 


6 


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A 


Fig. 4. — Quadrat at station 4, 5 meters square. Note relative 
fewness of individuals of Adenostoyna, which control 
the area with fair completeness. The dotted line 
indicates the area dominated by the large clump of 
Arctostraphylos (Ar 34 ). 

shrubs are taller than in any previous station, averaging 1.8 meters, 
and thoroughly control the ground. The summary of a quadrat 
(fig. 5) follows: 

Clumps. Stems. 

Adenostoma 2 8 

Arctostaphylos 20 55 

Quercus durata 2 4 

Heteromeles 1 6 

Total 25 73 

The bases of the stems have the large woody masses noted in 
station 3, and the low shrubby and herbaceous species are the same, 
with a number of new ones, most of which are characteristic of the 
nearby forest. The list follows: 

Micromeria chamissonis. Rosa californica. Chlorogalum pomeridianum. 

Dominant. Trientalis europsea latifolia. Symphoricarpos racemosus. 

Aster radulinus. Domi- Gymnogramme triangularis. Galium californicum. 

nant. Pedicularis densifiora. 

There is considerable litter and a moderate amount of humus. 
Bed rock is exposed in a few places. 


38 THE BROAD-SCLEROPHYLL VEGETATION OF CALIFORNIA. 


Station 7. 

Descending still farther, the slope becomes steeper and we pass 
through a transition zone into the forest which clothes the lower 
part of this north-facing hillside. It is not an extensive area, the 
altitudinal distance covered by it being only 40 meters, but it is 
nevertheless well developed and typical in every way. Two stations 
were located in it. Station 7 is in a representative spot 12 meters 


Fig. 5. — Quadrat at station 6, 5 meters square. Note likeness 
to station 3 (fig. 3). 

above the bottom of the ravine. Since trees are the dominants 
here, it was necessary to increase the size of the quadrat to 10 meters 
on a side. This quadrat, therefore, equals in area 4 of those in other 
localities. A summary, as far as the dominants are concerned, is 
given (fig. 6): 

Clumps. Stems. 

Quercus agrifolia 6 6 

Arbutus menziesii 2 8 

^Esculus californica 2 2 

The specimens of Quercus and JEsculus are all single-stemmed 
individuals. Those of the latter species are of little importance, 
being but 3.8 and 6.3 cm. in diameter. The oaks range in diameter 
from 3.8 to 36 cm., four being 10 cm. or larger. The eight Arbutus 
stems are in two clumps of large stump sprouts, a very common 
habit of the species. The diameters of the individual stems range 
from 10 cm. to 18 cm. The area is shaded and controlled by the 


THE BROAD-SCLEROPHYLL VEGETATION OF CALIFORNIA. 39 

three or four largest oaks and the two Arbutus clumps, together 
with other trees outside the limits of the quadrat. 

If we should make a more general survey of the locality, we 
would find that the quadrat represents average conditions faithfully, 
except that another tree species, Umbellularia calif ornica, occurs 
along the ravine-bottom and in side gulches. None of the trees 
are tall, the mature of all species ranging from 7 to 12 meters in 


Fig. 6. — Quadrat at station 7, 10 meters square. The symbols 
surrounded by double lines indicate trees of the domi- 
nating stratum; the others represent the shrub stra- 
tum; the herbaceous stratum was not charted. 

height. The oaks have mostly single trunks, those toward the 
bottom of the slope being much larger than those above. One 
specimen, 10 meters above the ravine-bottom, had a diameter of 
8 m. The madronos mainly show the clump habit. Seedlings of 
oak occur, but are very rare. No madrono seedlings were found. 
The shade is nearly everywhere dense. 

Unlike the chaparral, the oak-madrono forest shows distinct 
vertical zonation or layering. The dominants are the trees, and 
beneath them there are two subordinate strata, one composed of 
tall shrubs, the other of low shrubs and herbs. The first is few in 
species, but one of these, Rhus diversiloba, is abundant. Others, all 
relatively unimportant, are Berberis pinnata, Holodiscus discolor 
aricefolius, Rosa calif ornica, and Dirca occidentalis. With these 
should be included a few frequenters of disturbed areas, such as 


40 THE BROAD-SCLEROPHYLL VEGETATION OF CALIFORNIA. 

Ceanothus sorediatus, Eriodictyon californicum, and Diplacus glu- 
tinosus, which occur in small numbers in the few openings; also, 
occasional wanderers from the chaparral; and finally, the young 
individuals of the dominant trees. The same quadrat includes the 
following shrubs: 

Rhus diversiloba 59 

Holodiscus discolor 2 

Quercus durata 1 

The herbaceous and ground-shrub vegetation is abundant, both 
in species and in individuals. The following list is nearly complete, 
the three most important being numbered in order of abundance: 

Gymnogramme triangularis. Smilacina amplexicaulis. Cynoglossum grande. 

Adiantum jordani. Ranunculus hebecarpus. Micromeria chamissonis (2). 

Aspidium rigidum ar- Dentaria integrifolia. Pedicularis densiflora. 

gutum (1). Saxifraga californica. Galium aparine. 

Melica imperfecta. Tellima heterophylla. Galium californicum. 

Luzula comosa. Potentilla glandulosa. Symphoricarpos racemosus (3). 

Fritillaria lanceolata. Psoralea physodes. Hieracium albiflorum. 

Trillium sessile gigan- Trientalis europsea lati- Achillea millefolium. 

teum. folia 


As 


c 

5 


1 

a' 5 


A< 
A 4 


Rock 


D 


A 3 


DAs 


Fio. 7. — Quadrat at station 9, 5 meters square. Dominance of 
comparatively few individuals of Adenostoma. 


At all times of the year this vegetation is in marked contrast to 
the bareness of the ground beneath the chaparral. In the spring 
the greenness and luxuriance are especially striking, when such 
plants as Fritillaria, Trillium, Smilacina, Tellima, and Cynoglossum 
are conspicuous. Litter is naturally abundant, and the soil is well 


THE BROAD-SCLEROPHYLL VEGETATION OF CALIFORNIA. 41 

supplied with humus therefrom. The occasional rock outcrops 
bear a fair amount of moss vegetation. 

Station 8. 

This is similar to the last, but is close to the ravine bottom. 
Umbellularia californica is very important, growing in dense groups, 
which cast almost complete shade. Lower vegetation is almost 
absent in such places (although a healthy seedling of Umbellularia 
was found), but elsewhere the herbaceous element is like that 
described above. 

Station 9. 

A sudden change of habitat, due to the sharp V-shaped bottom 
of the ravine, brings about a transition in vegetation that is even 
more abrupt than that between stations 3 and 4. Facing the 
oak-madrofio slope and beginning in full development at the very 
bottom of the ravine, we find a nearly pure growth of Adenostoma. 
The shrubs are larger here than in any previous station dominated 
by that species, averaging 1.5 meters in height. The living and 
dead branches are so densely interlaced that progress even on hands 
and knees is almost impossible. The following summary of the 
quadrat (fig. 7) gives a satisfactory picture of the composition: 

Clumps. Stems. 

Adenostoma 29 175 

Ceanothus sorediatus 1 1 

Total 30 176 

The one specimen of Ceanothus sorediatus overtops everything 
else. The shade is dense, considering the fact that Adenostoma is 
responsible for most of it. Ground-cover is very sparse and consists 
of Aster radulinus, Chlorogalum pomeridianum, and occasional small 
plants of Diplacus glutinosus. Litter and humus are scanty and 
the steep slope shows frequent rock outcrops. 

Station 10. 

This is situated on the gently south-facing slope, 130 meters south 
of the last. It was chosen for special study because it was in the 
only chaparral area where the soil was such that excavation for 
water-content determination could be made in it to the desired 
depth. The fact that the vegetation has been slightly disturbed in 
consequence of its proximity to an old road does not vitiate its 
usefulness for this purpose. Adenosto??ia is dominant and large. 
Arctostaphylos and Quercus durata are both frequent, and Q. wislizeni, 
Heteromeles, and Prunus ilicifolia also occur. Because of disturbance, 
Eriodictyon calij 'ornicum, Helianthemum scoparium, and Diplacus 
glutinosus are frequent, with quite an assemblage of small wet- 
season annuals. Litter and humus are scarce. The uniform sandy 
soil grades evenly into the bed rock, becoming too hard for excavation 
at a depth of a little more than a meter. 


42 THE BROAD-SCLEROPHYLL VEGETATION OF CALIFORNIA. 


THE HABITAT. 

The foregoing description, assisted by the profile (fig. 1), makes 
it plain that superficially the distribution of the various communities 
depends altogether upon the topographic factor slope. This of 
course is a complex of simpler factors and the present study therefore 
resolves itself mainly into an analysis of those factors whose variation 
depends upon differences in direction and angle of surface inclination. 

At this point a summary of the observed angles may well be 
given. 

Table 2. — Direction and angle of slope. 


Station. 


Vegetation. 


Direction. 


Angle. 


Station. 


Vegetation. 


Direction. 


Angle. 


No. 1 
2 
3 
4 
5 


Adenostoma. . . 
Adenostoma. . . 
Arctostaphylos 
Adenostoma. . . 
Adenostoma. . . 


S 

N 
S 

s 


8 


32 

6-14 

5 


No. 6 

7 

8 

9 

10 


Arctostaphylos 

Forest 

Forest 

Adenostoma. . . 
Adenostoma. . . 


N 
N 
N 
S 
S 


30-34 
37 
42 

23-38 

7 


THE SOIL FACTORS. 
Physical Character. 

Samples were taken from a selected series of stations — Nos. 2, 3> 
4, 6, 7, 10 — these being the ones used in the study of water-content- 
From the first four, two each were taken, from 10 cm. and 30 cm. 
depth respectively. In stations 7 and 10 three depths were sampled: 
10 cm., 50 cm., and 100 cm. All of these correspond with the 
depths used in moisture determination in each habitat. Since no 
differences of moment were discovered between samples from a 
single station, these have been combined and averaged in each case. 
The analyses were made by Mr. Alfred Smith, of the University of 
California, through the kindness of Dr. Charles F. Shaw. In the 
first part of table 3 the five grades of sand and gravel have been 
condensed into two. 


Table 


3. — Mechanical analysis. 


Station. 


Gravel. 


Sand. 


Silt. 


Clay. 


Gravel +Sand. 


Silt+Clay. 


2 


2.30 


55.71 


12.66 


28.96 


58.01 


41.62 


3 


2.01 


78.82 


2.42 


16.31 


80.83 


18.73 


4 


5.58 


72.08 


2.01 


19.92 


77.66 


21.93 


6 


1.52 


76.05 


2.04 


20.09 


77.57 


22 . 13 


7 


4.61 


73.21 


12.54 


9.34 


77.82 


21.88 


10 


1.93 


81.73 


7.88 


8.02 


83.66 


15.90 


It is seen that the soils in all but station 2 are closely similar, 
with the proportion of gravel and sand running from 77.57 to 
83.66 per cent. Some, according to Dr. Shaw, would be classed as 
light sands and others as sandy loams. Their similarity would be 


THE BROAD-SCLEROPHYLL VEGETATION OF CALIFORNIA. 43 

assumed from field observation, the only noticeable difference being 
that some are a little more coherent than others. The soil of station 
2 is strikingly different, having much less of the coarser grades and 
a correspondingly larger proportion of silt and clay, especially the 
latter; consequently it is sticky and heavy when wet, is unfavorable 
to water movement (shown by the fact that water stands in holes 
for many hours after a rain), and is very hard and almost rock- 
like when dry. Though still belonging to the sandy-loam class, it 
tends strongly toward clay. This physical character results in 
quite a different set of soil-moisture values, as will appear later, 
and it is therefore not surprising to find the difference in the vege- 
tation which has been noted— a difference, however, entirely in 
relative luxuriance. The importance of the mechanical analysis to 
the present study is that it demonstrates that the soils of most of 
the localities studied do not differ in physical nature (excluding the 
humus portion), and that therefore this factor as a determinant of 
water-content and of vegetation has been excluded, since it is not 
a variable. The stations in which no analyses were made, from 
field observation should be grouped as follows: station 1 like sta- 
tion 2, 5 like 4, 8 like 7, and 9 like 10. 

The same samples were submitted to Dr. Charles B. Lipman, of 
the University of California, for determination of humus. The 
depths are those noted in the last section. T indicates less than 
0.1 per cent. 

Table 4. — Average humus content. 


Station. 


Vegetation. 


At 10 cm. 


At 30 cm. 


At 50 cm. 


At 100 cm. 


Nos. 2,4, 10 
3, 6 

7 


0.11 
0.34 
1.97 


T 
T 


T 
0.85 


0.66 


The importance of this reaction-factor in the surface layer is 
seen, and its penetration to a considerable depth in the forest. 

The Soil Moistuke. 

The determinations of water-content were made in two series. 
In the 'first and more important, two stations were utilized, Nos. 
7 and 10, the object being to contrast the conditions in chaparral 
and forest. Determinations were made weekly for a period of one 
year, and the series was later resumed for a few weeks for a special 
purpose. In the second the stations selected were the six used in 
the evaporation experiments and the same from which the samples 
for mechanical analysis were taken. This series ran parallel to the 
evaporation work, determinations being made at intervals of four 
weeks from June to April. 


44 THE BROAD-SCLEROPHYLL VEGETATION OF CALIFORNIA. 

Series I. 

Station 7 is an altogether favorable spot for the study of the forest 
soil. Station 10 was selected to represent the chaparral because it 
was the only one having a soil in which it would be possible to 
excavate to the desired depth. For the study of conditions surround- 
ing the deep-rooted chaparral species, a knowledge of the water 
conditions in the deeper soil-layers seemed essential. Even here the 
deepest excavation possible did not approach the region reached by 
the longest roots, which, as will be shown (p. 89), penetrate the 
undecomposed sandstone to a considerably greater depth. Extreme 
shallowness of soil is general over the chaparral area in which the 
studies were made. It was felt that this advantage in depth of soil, 
which station 10 possessed, compensated for certain disadvantages — 
lack of slope contrast to station 7, the angle being only 7° southward, 
and slightly disturbed condition, due to proximity to an old road 
and the edge of the chaparral area. 

The series was begun January 21, 1913, and continued for a 
total of 54 weekly observations, ending January 26, 1914. Occa- 
sionally a visit was delayed for a day or two by storms or other 
causes, especially in the winter of 1913-14; otherwise the program 
was carried through without a single break or mishap of any kind. 
Samples were taken in each station at three depths: 10, 50, and 100 
cm. Excavations were made with a spade and samples were col- 
lected in numbered and weighed glass bottles. The sample was 
obtained, whenever conditions permitted, by pushing the mouth of 
the bottle into the freshly exposed soil-surface. When this became 
impossible toward the end of the dry season, especially at the lowest 
level, lumps of soil were cut out and pressed into the bottle, which 
was immediately tightly corked. The first weighings were always 
made within a couple of hours after digging the samples and were 
carried out to 0.01 gram, which is probably greater accuracy than is 
necessary in such determinations. The soils were dried at a tem- 
perature of 105° C, and the water-loss was computed upon the 
basis of dry weight. 

The results have been plotted together in figure 8. The first 
winter was a very dry one, the total precipitation at Palo Alto 
being only 19.49 cm. Assuming a proportional relation at Jasper 
Ridge, the rainfall at the latter locality should have been 32.5 cm. 
The winter of 1913-14 was in great contrast to the preceding one, 
the precipitation at Palo Alto being 62.15 cm. and at Jasper Ridge, 
by actual measurement, 103.71 cm. 

Taking first the three curves representing the soils of station 10, 
in the chaparral, we observe the following facts: The effect of 
rainy and dry seasons is the most conspicuous feature. The highest 
point reached in the first rainy season was 13 per cent, in the second 


THE BROAD-SCLEROPHYLL VEGETATION OF CALIFORNIA. 45 

17.2 per cent. The absolute minimum was 0.5 per cent on October 
31. We next observe the gradual dropping of the three lines, 
beginning with the end of the spring rains, continuing at a constantly 
decreasing rate through the dry season of summer and fall, and 


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Fig. 8. — Soil moisture at weekly intervals for one year, in chaparral (station 10) and broad- 
sclerophyll forest (station 7), at depths of 10, 50, and 100 cm. Jasper Ridge. The 
wilting coefficients for the 10 cm. and 100 cm. depths have been added for each 
station. 


46 


THE BROAD-SCLEROPHYLL VEGETATION OF CALIFORNIA. 


thus approaching a condition of constancy. The sudden rise with 
the first autumn rain is the most striking single feature. Comparing 
the three lines, we see that the 100 cm. level had the highest water- 
content through most of the year, and the 10 cm. level the least. 
The order was suddenly reversed immediately after rains, the 
most striking case being at the beginning of the rainy season of 
1913-14. The first rain occurred on October 31, and was a sudden, 
heavy shower, followed by others at frequent intervals during the 
month of November. From October 31 to November 6, inclusive, 
the precipitation at Palo Alto was 3.5 cm. Figure 8 shows that on 
November 7 the water-content at 10 cm. depth had risen from 0.5 
per cent to 5.2 per cent and on November 14 to 10.2 per cent. 

The lag in the response of the lower levels is interesting. At 
50 cm. depth no effect was observable until November 22, and the 
increase when it came was less sudden. The water had not reached 
100 cm. depth on December 5 and the rise thereafter was still more 
gradual. The slow penetration of the rain-water is not due to 
run-off, since the slope is only 7 per cent, but doubtless, in the main, 
to the air-filled condition of the soil. Table 5 shows roughly the rate 
of penetration in the two stations during this period. No important 
difference between the two stations is seen in this respect, and the rate 
of penetration was approximately uniform as far as it was followed 

Table 5. — Rate of penetration of first rains. 


Depth of penetration in cm., 
first rain October 31. 


Station 7. Station 10. 


Nov. 14 
Nov. 22 
Dec. 13 
Dec. 22 


31 35 
50 to 60 58 
70 to 100+ 90 
75 100 + 


Returning to station 10, we note further the tendency toward 
convergence of the three lines as the dry season progresses. The 
sudden jumps of July 13 and August 31 in the 100-cm. line are 
difficult to explain. They may possibly be due to encountering 
small masses of soil where the clay-content was above the average. 

We may draw the following conclusions concerning the soil- 
moisture conditions in this particular chaparral station during the 
period studied. During the actual continuance of the rainy season 
there is an abundance of water at all depths. This was true even 
in the unusually dry winter of 1912-13. As to the following very 
wet season, the soil at station 10 was frequently so thoroughly 
saturated that the walls of the excavations continually collapsed 
into an almost soupy mass, making it difficult to obtain fair samples 


THE BROAD-SCLEROPHYLL VEGETATION OF CALIFORNIA. 47 

at the lowest depth. During the spring and early summer of 1913 
the water-content steadily decreased, and by mid-July it had reached 
a point beyond which it could not drop much farther, the samples 
when gathered appearing as incoherent air-dry sand. From then 
till the first rains, three and a half months, there was a period of 
extreme deficiency, which is not exceeded in severity by conditions 
as recorded in the desert of Arizona (57). The lag of several weeks 
in the response of the lower strata to the first rains shows that their 
advent does not close the dry season, so far as the soil is concerned. 
In the forest station the general form of the curve is the same, 
but there are nevertheless important differences. The maxima are 
uniformly greater than in the chaparral. Comparing the three 
depths, we find the relative positions of the 10-cm. and 100-cm. 
lines the reverse of those in the chaparral, the 10-cm. depth showing 
nearly always the highest water-content and the 100-cm. depth the 
lowest. Obviously this is to be traced to the effect of the humus on 
water-retaining capacity. The lines, too, during the rainy seasons, 
are much more widely separated than in station 10. During the 
dry season, however, they converge until they are as close together 
as those of the chaparral. The response to the first rains in the 
deeper levels shows a more noticeable lag than appears in the chapar- 
ral, the first certain increase at 100 cm. depth appearing on December 
26, eight weeks after the earliest shower. Comparing equal depths 
in the two stations, we find that at 10 cm. the forest line is uniformly 
higher than that of the chaparral, the reasons being shade and 
humus. The maximum difference between them during the rainy 
season is 14 per cent, and the average for the rainy seasons ap- 
proximately 8 per cent. During the progress of the dry season 
the lines converge, the average difference for the last three and 
a half months being 3 per cent. At 30 cm. depth the forest line is 
still well above that of the chaparral, but the differences are uni- 
formly less in both wet and dry seasons. At 100 cm. no such 
constant differences are seen. During the first winter the chaparral 
soil at this depth was wetter than the forest; during the dry season 
and the second winter the lines cross and recross without revealing 
any differences of importance. 

The points of greatest general import are: (1) the rather striking 
difference in water-content between chaparral and forest during the 
rainy season; (2) the convergence of the six water-content lines to 
minima which at the end of the dry season are not far apart. 

The depletion of the water-content in every case is due to three 
causes. Drainage of the gravity water through the soil takes place 
with great rapidity during the wet season, which is proved by the 
fact that the ravines of Jasper Ridge contain running streams for 
considerable periods. After the rains have ceased, however, it can 


48 THE BROAD-SCLEROPHYLL VEGETATION OF CALIFORNIA. 


not be long before all the gravity water will have been removed from 
the upper meter of depth, so that this cause will no longer be oper- 
ative. The second cause, evaporation directly from the soil, and 
the third, removal by plants, will continue throughout the dry 
season. Evaporation from the soil is undoubtedly higher in the 
chaparral habitat than in the forest, and yet the gradient of depletion, 
as shown by the graph, is decidedly steeper in the latter. This 
seems to show that the most potent cause of water-content depletion 


ZW2 

Oft: 
< *- 

K hi I 


1913 

SEPT. OCT. NOV. 

12 19 26 3 '0 17 24 31 7 14. 22 


1914 
SEPT. 
17 24- I 


OCT. NOV. 

8 15 22 30 5 12 20 


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Fig. 9. — Soil moisture at end of dry and 
beginning of wet season, fall of 1913. 
Jasper Ridge. Wilting coefficients as 
in fig. 8. 


Fig. 10. — Soil moisture at end of dry 
and beginning of wet season, fall 
of 1914. Jasper Ridge. Wilting 
coefficients as in fig. 8. 


is the vegetation itself, since where the plants are largest and most 
abundant, there will be the greatest drain upon the water-supply, 
which statement exactly fits the forest in this case. Measurements 
given in another connection (p. 112) show that the rate of transpira- 
tion in the same species growing in both habitats is much higher in 
the chaparral habitat (in the case of Adenostoma, forest : chap- 
arral : : 1 : 1.92; in the case of Arctostaphylos, 1 : 1.69). However, 
it is reasonable to assume that the far greater bulk of transpiring 
vegetation in the forest, comprising trees of large size and luxuriant 


THE BROAD-SCLEROPHYLL VEGETATION OF CALIFORNIA. 


49 


herbaceous vegetation, will much more than counterbalance the 
greater rapidity of the process in the chaparral. 

The graph (fig. 9) shows dry season conditions after a winter 
of deficient rainfall (1912-13). The following winter was a very wet 
one, and it seemed worth while to resume the soil-moisture deter- 
minations for a few weeks during the critical period of the dry 


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50 THE BROAD-SCLEROPHYLL VEGETATION OF CALIFORNIA. 


season following. The two graphs side by side (figs. 9 and 10) give 
the minima shown in table 6. This shows that there are very 
perceptible differences in water-content at the critical periods 

Table 6. 


Years. 


Chaparral. 


Forest. 


10 cm. 


50 cm. 


100 cm. 


10 cm. 


50 cm. 


100 cm. 


1913 
1914 


0.5 

1.1 


1.1 
1.1 


17 
5.9 


3.7 
5 


1.9 
3.7 


1.8 
3.9 


following winters of deficient and abundant rainfall, and that these 
differences appear especially in the deeper soil-layers. In the 
chaparral, at 100 cm. depth, the minimum percentage after a wet 
winter was more than three times that of the preceding season; 
at the corresponding forest depth the percentage was more than 
twice that of 1913. 

Series II. 

This series was carried out at the same six stations that were 
used for the evaporation studies, and during the same period (June 
15, 1913, to April 17, 1914). There were thus provided three 
examples of Adenostoma chaparral (Nos. 2, 4 and 10), two of 
Arctostaphylos chaparral (Nos. 3 and 6), and one of forest (No. 7). 
The samples were taken at intervals of 4 weeks, and in stations 2, 
3, 4, and 6 at two depths — 10 cm. and 30 cm. In stations 7 and 
10 the figures from Series I were used, the 50-cm. depth being con- 
sidered as parallel to the 30-cm. depth in the other stations. In 
figure 11 the results for the 10-cm. depth are compared. 

The most striking feature is the line representing station 2, the 
highest in water-content and yet the poorest in vegetation. The 
explanation of this apparent paradox is found in the mechanical 
analysis and wilting coefficient. The sudden changes in water- 
content without apparent reason — e. g., the sharp crest on July 13 
and the sudden drop after March 4 — are perhaps due to local soil 
differences, small masses of unusually high or unusually low clay- 
content. The other two Adenostoma stations are consistently the 
lowest and the forest is the highest. Between forest and Adenos- 
toma chaparral are the two Arctostaphylos stations. In figure 12 all 
stations of each type, both depths, have been averaged, station 2 
being omitted. The daily precipitation for the period is also added. 
The Adenostoma community is decidedly the lowest, and the forest 
is highest most of the time, though the Arctostaphylos community is 
not far below. The close approach of all the lines during the dry 
season and their separation during the wet season (seen in Series I) are 


THE BROAD-SCLEROPHYLL VEGETATION OF CALIFORNIA. 51 

evident here also. In general, Series II confirms the results obtained 
in Series I and adds data for the Arctostaphylos community, which is 
seen to be intermediate in water-content between the other two. 


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Water-retaining capacity. — The reasonable way to compute water- 
retaining capacity is upon the basis of dry volume of soil. The 
same is true of water-content, but as yet it is not feasible to make 
moisture determinations in extensive series on the basis of volume. 
For the sake of uniformity, therefore, it is convenient to express the 
water-retaining capacity in terms of dry weight as well as of dry 


52 THE BROAD-SCLEROPHYLL VEGETATION OF CALIFORNIA. 


volume. The method employed was the one which has been in 
general use of late. Circular pans were made having bottoms of 
perforated metal, with sides 1 cm. high and of such an area that the 
capacity, when the soil was smoothed off level with the top, would 
be 100 c. c. The bottoms were covered with cheese-cloth. The soils 
were all prepared — pulverized and compacted — as nearly as possible 
in the same way, and the pans, filled level full, were stood in shallow 
water to permit absorption. After saturation was complete they 
were allowed to drain until all the gravity water had passed off. 
The percentage of water retained was then calculated upon the 
basis of dry weight and also of dry volume. In each case the average 
of five tests was used. The shortcomings of the method are fully 
realized, prominent among them being the unnatural condition of 
the soils when tested. The results, however, although they do not 
give a true picture of the behavior of a given soil under natural 
conditions, do give data whereby fair comparison may be made 
between different ones. Samples were taken from the three depths 
in stations 7 and 10 for comparison of conditions in forest and 
chaparral, and from station 2 because of its peculiar qualities. 

Table 7. — Water-retaining capacity, percentages. 


Station. 


At 10 cm. 


At 10 to 
30 cm. 


At 50 cm. 


At 100 cm. 


Average 
all depths. 


Ratio. 


By dry weight: 

No. 10, chaparral. . 

No. 7, forest 

No. 2 


20.6 
30.5 

38.5 
49.3 


46.4 
71.4 


17.9 
24.9 

36.7 
47.3 


21.4 
16.3 

39.4 
32.5 


20 

23.9 

46.4 

38.2 
43.0 
71.4 


1 

1.20 

2.32 

1 
1.13 

1.87 


By dry volume: 
No. 10, chaparral. . 

No. 7, forest 

No. 2 


Considering the dry-volume figures, which give the truest picture 
of the soil qualities, we note that there are no differences of im- 
portance among the various depths in station 10. The high water- 
retaining capacity in station 7 at 10 cm. depth is plainly due to the 
large humus content. The high figure for station 7, 50 cm. depth, 
as compared with the low one for 100 cm., is difficult to explain. 
Mechanical analysis offers no clue; nor does humus content, since 
50 cm. and 100 cm. are more like to each other than to 10 cm. depth. 
Station 2 shows striking originality in this feature as in others, and 
the reason is plain — the high percentage of clay and silt. Sum- 
marizing, we find that the comparative water-retaining capacities 
of stations 10, 7, and 2, representing chaparral, forest, and a par- 
ticularly unfavorable chaparral station, may be expressed by the 
ratio 1 : 1.13 : 1.87. 


THE BROAD-SCLEROPHYLL VEGETATION OF CALIFORNIA. 53 

A second series of determinations was made at a later time. The 
percentages are somewhat higher, but the relative values are very 
similar in most cases, which is the important thing. The series 
given here is the more valuable, since the soils used were composites 
of many individual samples. 

Wilting coefficient. — The method developed by Briggs and Shantz 
(15) was followed, and the soils to be tested were brought from Jasper 
Ridge to the University of Minnesota. The experiment was carried 
on in the university greenhouse, in a room where the relative 
humidity averages 30 to 40 per cent during the middle of the day. 
An atmometer was kept in operation close to the jars during most 
of the period of growth and wilting. The average daily evaporation 
recorded, reduced to the usual standard, was 10.2 c. c. The extremes 
were 14.7 c. c. and 3.1 c. c. Glass tumblers were used for containers 
and a constant soil temperature was maintained by immersing them 
almost to the top in slowly running water. Kubanka wheat, 
obtained through the kindness of Dr. Briggs and Dr. Shantz, was 
used as the indicator plant. 

The constant termed the "wilting coefficient" has been variously 
interpreted. The latest and most reasonable conception, due to 
Shull (82) and Moore (65), is that it is purely a function of the 
soil, "a point in the water-content of the soil at which the water 
practically ceases to move along the film (on the soil particle), no 
matter how sharp the gradient at the edge of the film," and not a 
matter of "balance between the 'back-pull' of the soil and the pull 
of the plant." If this be true, one plant is as good as another for 
indicator use, and Kubanka wheat will furnish just as serviceable 
results as would Adenostoma. This is fortunate, since difficulty has 
been encountered in bringing about germination of the chaparral 
species under artificial conditions. The one chief essential to 
success seems to be the maintenance of uniform environmental 
conditions during the period of the experiment, especially those 
affecting the evaporation-rate. It must never be forgotten that 
the wilting coefficient is the ultimate point at which plants must 
wilt, but that under certain conditions wilting may take place 
before that point is reached. Its usefulness in the investigation of 
different soils with regard to their effect upon plant life is obvious. 

Comparison was made primarily between the soils of two stations, 
Nos. 7 and 10, representative of forest and chaparral respectively. 
In each case two depths were considered, 10 and 100 cm. Station 2 
was added because of the interesting singularity apparent in its 
other characteristics. The figures in table 8 are each an average 
of seven unimpeachable determinations. 

The figures are about what one would expect after study of the 
physical character of the soils and their water-retaining capacities. 


54 THE BROAD-SCLEROPHYLL VEGETATION OF CALIFORNIA. 

Station 10, almost a pure sand, has a very low wilting coefficient, 
with no difference of moment between the two depths, since the 
surface layer has but a very slight admixture of humus. In station 7 
the effect of surface humus in raising the wilting coefficient is very 
evident. In station 2 the large percentage of silt and clay is respon- 
sible for a strikingly high figure. 

Table 8. — Wilting coefficient in stations 10, 7, and 2. 


Depth. 


Station 10. 


Station 7. 


Station 2. 


10 cm. . . 

100 cm. . . 


p. ct. 
1.5 
1.7 


p. ct. 
4.5 
2.3 


p. ct. 
16.1 


It has been customary to draw a line to indicate the wilting 
coefficient upon the graph representing the seasonal march of soil- 
moisture. Accepting the interpretation of the wilting coefficient 
presented by Shantz and Moore, we are justified in drawing this 
line, and in assuming that, when the water-content line falls below 
that of the wilting coefficient, the vegetation can extract no moisture 
from the soil. Referring to figure 8, then, we find that in station 
10 (chaparral) there was at 10 cm. depth no available water from 
July 1 to November 1. At 100 cm. depth the water-content line, 
though it is not far above the wilting coefficient, actually touches 
it but once. In station 7 (forest) conditions at 10 cm. depth were 
only slightly better than in station 10, water-content and wilting 
coefficient lines both being relatively and equally high. The period 
of unavailable water was shorter by the first two weeks of July. 
At 100 cm. depth conditions were actually less favorable than in 
station 10, since three times the water-content line descends below 
that of the wilting coefficient. With regard to the relation between 
water-content and wilting coefficient, it would seem that there is 
no striking difference between stations 10 and 7; that soil-moisture 
conditions, as indicated by these two factors, are about equally 
severe during the critical period. 

The dry season of 1913 was of unusual severity. That the 
conditions recorded are extreme is indicated by figure 10, presenting 
the soil-moisture in relation to the wilting coefficient at the critical 
period of 1914, which followed a very wet winter. Except for 
station 10, at 10 cm. depth, the water-content was everywhere 
well above the wilting coefficient, and the abundance of available 
water at 100 cm. depth in station 10 is noteworthy. Very likely 
the average condition is somewhere between the extremes of 1913 
and 1914, but the special importance of seasons of unusual severity 


THE BROAD-SCLEROPHYLL VEGETATION OF CALIFORNIA. 55 

(like that of 1913), which recur every few years with tolerable 
regularity, is fundamental. 

In station 2, the constantly high water-content is rendered in- 
effective by the high wilting coefficient. At 10 cm. depth, during 
the period from June 15, 1913, to April 17, 1914, the soil furnished 
available water only from November 1 to April 1. It seems un- 
necessary to seek further for the explanation of the poverty of the 
vegetation in that station and its vicinity. 

The Soil Temperature. 

In making determinations of soil temperature, the simplest 
method seemed the best — the plunging of a chemical thermometer 
into the freshly cut surface at the time of taking water-content 
samples. During the dry season it was found necessary at the 
lowest level to bore a hole with a small auger. The observations 
were made in the two stations of water-content Series I, at all 
depths used in that series. They were begun March 25, 1913, and 
with a few minor interruptions continued to January 26, 1914, the 
closing date for the soil-moisture work. During much of the period 
the temperature of the surface was also observed, in shade in 
station 7 and in sun and shade in station 10. In these cases the 
bulb of the thermometer was covered with a thin layer of soil or 
litter. The results are plotted in figure 13. 

The first point to note is that during the dry season the soil 
temperatures in the two stations are widely different, the three 
lines representing station 10 being all of them regularly below those 
of station 7. With the arrival of the wet season they all descend 
and at the same time converge, the differences between them almost 
disappearing. This is exactly the reverse of the soil-moisture's 
behavior, where convergence takes place in the dry season. It is 
due of course to the greatly increased water-content of both soils. 
The surface temperatures, naturally the highest in each station 
through most of the period, show the same tendency, and in the 
case of station 7 the line actually drops below those representing 
the subterranean temperatures. 

Comparing the lines of a single habitat, we find that in station 7, 
during the dry season, the temperatures vary inversely with the 
depth, the order being, from highest to lowest, surface, 10 cm., 
50 cm., 100 cm. During the wet season the order is roughly the 
reverse, the order most of the time being 100 cm., 50 cm., 10 cm., 
surface. In station 10 the case is the same, except that the shaded 
surface and 10 cm. lines do not greatly differ, because of the lack of 
cover, and in the wet-season portion the lines do not hold constant 
relative positions. In both stations the greatest fluctuations occur 
at the surface and at 10 cm. depth, and the greatest uniformity at 
100 cm. depth. 


56 THE BROAD-SCLEROPHYLL VEGETATION OF CALIFORNIA. 

THE ATMOSPHERIC FACTORS. 
Light. 

On August 17, 1917, a series of observations was made to determine 
the relative light values at the different stations. The apparatus 
used was the Clements photometer. The observations were made 
as rapidly as possible in the course of a trip over the trail from 
station 1 to station 10. The first was made at 2 h 30 ra p. m. and the 


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THE BROAD-SCLEROPHYLL VEGETATION OF CALIFORNIA. 57 

last at 3 h 15 m . Those toward the end are therefore comparatively 
a trifle too low. In the computation the highest value obtained 
(at station 5) is taken as unity and the others are reduced to decimals 
in proportion. In the observations of sun intensity the instrument 
was pointed directly toward the sun. In the spotty shade of the 
chaparral it was moved about continually during the exposure, so 
that an average figure was obtained. 

Table 9. — Light intensity at stations 1 to 10. 


Stations. 


Sun. 


Shade. 


Stations. 


Sun. 


Shade. 


Summary. 


Sun. 


Shade. 


Proportion. 


No. 1 


0.94 


0.20 


No. 6 


0.69 


0.10 


Adenostoma. . . 


0.84 


0.17 


100 to 20 


2 


.75 


.17 


7 


.56 


.07 


Arctostaphylos 


.69 


.07 


100 to 10 


3 


.69 


.04 


8 


.05 


Forest 


.56 


.06 


100 to 11 


4 


.75 


.21 


9 


.11 


5 


1.00 


.23 


10 


.75 


.07 


The great differences in the direct sunlight intensities are appar- 
ently due to differences in amount of reflected and diffused light, 
the chaparral stations, with much bare light-colored soil naturally 
being the highest, and the forest, with dark soil and much vegetation, 
the lowest. The shade differences are less than might be expected. 

Temper attjee. 

In the matter of atmospheric temperature there is an unfortunate 
shortage of data. Isolated observations of so variable a factor, 
even though numerous, are of little value. The thermograph is the 
only satisfactory apparatus for habitat study, and no thermographs 
were available for the work. Some knowledge of comparative 
temperature values during the dry season may be gained from two 
series of observations (table 10), obtained during trips over the 
trail connecting the stations. The first was made during the middle 
of the day, the second between 3 and 4 p. m. The readings were 
made from the dry bulb of the cog psychrometer in the process of 
measuring relative humidity. 

The outstanding feature is the uniformity of temperature. No 
differences of moment occur between any of the stations, nor be- 
tween sun and shade. The latter would, of course, not be true if 
the sun had been allowed to shine on a stationary bulb. The 
probable effect in such a case is roughly indicated by the high sun 
temperatures recorded in the surface lines of the soil temperature 
graph (fig. 13). As the air readings stand, the shade temperature 
in the Adenostoma stations is in nearly every case higher than the 
sun temperatures, while in the other stations the reverse is true. 
The reason in the former case is not clear. 


58 THE BROAD-SCLEROPHYLL VEGETATION OF CALIFORNIA. 

The maxima during the dry season would often be considerably 
higher than those recorded here. Even in winter the day tem- 
peratures are frequently quite high. Frosts are rare and slight. 
During the winter of 1913-14 no atmometers were broken from this 
cause — and these instruments are very sensitive to that danger. 

Table 10. — Atmospheric temperature. 


July 4 


, 1916. 


Aug. 16, 1917. 


Sun. 


Shade. 


Sun. 


Shade. 


Station No. 1 . . . 


27.5 


30 


22.8 


24.4 


2. . . 


25 


28.5 


22.5 


23.9 


3. .. 


27.7 


25.5 


21.7 


20.3 


4. .. 


30 


29.5 


23.6 


23.4 


5. . . 


29.5 


30 


23.9 


25.0 


6. . . 


28 


25.7 


22.8 


21.1 


7. . . 


27 


26 


20.8 


18.9 


8. .. 


28 


25.6 


20 


19.4 


9. . . 


26.3 


27.5 


21.7 


20.6 


10. . . 


26.6 


26 


20.6 


21.7 


Summary : 


Adenostoma. . . 


27.5 


28.6 


22.5 


23.2 


Arctostaphylos . 


27.8 


25.6 


22.2 


20.7 


Forest 


27.5 


25.8 


20.4 


19.1 


Wind. 

I have no data for Jasper Ridge, but a statement as to the sur- 
rounding region as a whole will be of value. Throughout the Santa 
Cruz Peninsula and northern Santa Clara Valley, except where 
topography produces local differences, the prevailing direction of 
wind is northwest. During the dry season this is almost universally 
true. During the wet season the direction is much more variable. 
Northwest winds are still the commonest, but the severe storms 
that bring the rains are usually accompanied by gales from the 
southwest. The north-facing slopes, therefore, receive most of the 
dry summer winds, while the south-facing slopes receive the full 
force of the rain-bearing winter gales. That the former may be 
very severe in their effects I have shown in another paper (23, 
p. 187). The actual vegetation cover of the north- and south- 
facing slopes is evidence that in general the prevailing winds are 
not important as locally controlling factors. 

The Atmospheric Moisture. 

Rainfall, cloud, and jog. — These topics have already been treated 
(p. 31). They are of interest in consideration of the locality as 
a unit, but have little influence upon the distribution of the plant 
communities as determined by slope exposure. 

Relative humidity.— The effects of relative humidity upon veg- 


THE BROAD-SCLEROPHYLL VEGETATION OF CALIFORNIA. 59 

etation are included when the evaporating power of the air is 
measured, as are also in part the effects of temperature, wind, and 
light. The two series of observations shown in table 11 are of 
interest, however, in illustrating the values of this simple factor in 
the various stations. The readings were made with a cog psy- 
chrometer, breast-high, except where dense chaparral made a 
lower level necessary. 

Table 11. — Relative humidity, percentages. 


July 4 


, 1916. 


Aug. 16, 1917. 


Sun. 


Shade. 


Sun. 


Shade. 


Station No. 1 . . . 


48 


43 


53 


51 


2. . . 


57 


46 


59 


54 


3... 


48 


49 


60 


60 


4. .. 


44 


42 


56 


52 


5... 


42 


39 


54 


48 


6... 


45 


49 


57 


59 


7... 


49 


48 


61 


66 


8. . . 


45 


47 


62 


66 


9. . . 


46 


42 


60 


63 


10. .. 


54 


48 


63 


60 


Summary : 


Adenostoma. . . 


48.5 


43.3 


57.5 


54.7 


Arctostaphylos . 


46.5 


49 


58.5 


59.5 


Forest 


47 


47.5 


61.5 


66 


The percentages given in table 11 do not approach to what we 
are accustomed to think of as xerophytic values. It may be that 
they do not represent average dry-season conditions, though there 
is ample reason in the proximity of the bay and the ocean for 
relatively high humidity. Other chaparral localities would cer- 
tainly show a much lower average. The sun humidities in the 
Adenostoma habitats are higher than those in the shade; in the other 
stations the order is reversed. 

Evaporation. — Observations were made by means of the Livingston 
cylindrical porous-cup atmometer, standardized at the beginning and 
end of their use by the Plant World Company. For dry-season 
study instruments were set out in all the stations except No. 10, 
two per station, one at the level of the ground, and one near the top 
of the vegetation in the region of most abundant foliage. The 
instruments at the ground-level were set in small excavations, so 
that the tops of the porous cups were about 2 dm. above the surface. 
Those at the upper levels were set upon posts of proper height, 
ranging from 0.7 meter in station 1 to 2.5 meters in station 6. In 
the forest stations, No. 7 and 8, it was necessary to construct wire 
trolleys running to the tops of trees, so that the instruments could 
be lowered for measurement. 


60 THE BROAD-SCLEROPHYLL VEGETATION OF CALIFORNIA. 

Considerable trouble was encountered by reason of the depreda- 
tions of thirsty animals, and several of the surface cups were de- 
stroyed, so that the lower series is incomplete. The dry-season 
study was carried on from June 8 to October 17, 1913, and readings 
were taken at weekly intervals, with a few irregularities. For the 
investigation of rainy-season conditions, stations 3, 4, and 7 were 


<* <t <* <* c 

A VCD d3d Sy3-L3tMUN3D 31803 'NO UVd0dVA3 


THE BROAD-SCLEROPHYLL VEGETATION OF CALIFORNIA. 61 

selected, representing the Adenostojna, Arctostaphylos, and forest 
habitats, and rain-correcting atmometers were substituted for the 
ordinary kind. The surface instruments were surrounded with 
chicken wire, which proved an adequate defense. Readings were 
taken weekly until the close of the soil-moisture observations on 
January 16, 1914, and at intervals of approximately four weeks 

AVERAGE DAILY EVAPORATION IN CUBIC CENTIMETERS 

Dry season Wet season 

131 days, June 8 to October 17, 1913 114- days, November 10, 

' 1913 to March 4-, 1914 

Sta.l. 5outh slope 
Adenostoma 30.4 


Sta. 2. Summit 
Adenostoma 


Sta. 3. North slope 
Arctostaphylos 


Sta.4. South slope 
Adenostoma 


Sta 5 South slope 
Adenostoma 


Sta 6. North slope 
Arcrostapriylos 


Sta 7. North slope 
Forest 


Sta. 8. North slope 
Forest 25.3 

Sta.9. South slope 
Adenostoma 27.7 


Summary, dry season 
All Adenostoma 

All Arctostaphylos 


28.2 


Maximum daily evaporation. week ending September 19 
Sta.l 


49.6 


Sta. 2 


51.4 


Sta. 3 


48 


Sta. 4 


49.5 


Sta. S 


48.2 


Sta. 6 


47.6 


Sta. 7 38.6 


Sta 8 


47.4 


Sta. 9 44.2 


Fig. 15. — Average daily evaporation in cubic centimeters in 
stations 1 to 9 at Jasper Ridge, for the dry season 
of 1913 and the succeeding wet season; also the 
maximum daily rate (week ending Sept. 19). 

thereafter until April 17, when the series was closed. We thus 
have records of one complete dry season, following a winter of 
deficient rainfall, and of one complete wet season — an unusually 
rainy one — fair samples of extremes in both directions. The dry- 
season series is complete for nine stations at the upper level and 
incomplete for the lower; the wet-season series is practically com- 
plete for the representative stations at both levels. 

The results have been summarized in three figures. In figure 14 
the upper-level series is used, and the water-losses for three rep- 


62 THE BROAD-SCLEROPHYLL VEGETATION OF CALIFORNIA. 

resentative stations (Nos. 2, 3, and 7) are given. These, as pre- 
sented, denote the average daily evaporation in cubic centimeters 
for each observation period, reduced to the official standard main- 
tained by the Laboratory of Plant Physiology of Johns Hopkins 
University. The conclusions may be very simply stated. The high 
rate of evaporation for the dry season and the low for the rainy 
season are immediately evident. A rainless period in December 
caused a sharp rise. The relative positions of the three lines are 
maintained throughout the period of observation almost without 
change, the Adenostoma habitats having the highest rates and the 
forest the lowest. The absolute maximum attained was 51.4 c. c. 
in station 2, Adenostoma chaparral, for the week ending September 
19. This period included some of the hottest days recorded for the 
region. The absolute minimum was attained on January 9, 3 c. c. 
daily evaporation for the period of 6 days preceding. 

Evaporation 

R +* J To P °* Vegetation CUnity) 
Katl ° V Surface of Ground 
Dry Season Wet Season 
49 days 114 days 
June 8 to July 27 7 Nov. 10, 1913, to 
1913 March 4, 1914 
Sta. 2 Adenostoma 
I J 


".92 


Sta.3 
1 


.73 


Sta. 7 
1 


.82 


.53 


Arctostaphylos 

Forest 

J 


.69 


Fig. 16. — Ratio between evaporation at top of vegetation and at surface of ground, 
in three representative stations at Jasper Ridge. 

In figure 15 the average daily evaporation for each station is 
given, for both wet and dry seasons, readings from the upper series 
of instruments being used. During the dry season the Adenostoma 
stations have regularly the highest rates. Station 2, located on 
the topmost point of Jasper Ridge, exposed to winds from every 
direction, naturally has the highest of all. Stations 1, 4, and 5, 
on gentle south-facing slopes, come next, and station 9, on the 
steep south-facing slope of an abrupt ravine, is last, falling slightly 
below the Arctostaphylos stations. The latter (stations 3 and 6) 
are closely alike, and fall between the Adenostoma and the forest 
stations, but nearer the former. The forest stations are decidedly 
below the others. Evaporation during the wet season averages 
about 30 per cent of the dry-season rate in the stations studied. 
The figure also shows rates of evaporation during the most extreme 
conditions of the year. The figure for station 8 seems abnormal. 


THE BROAD-SCLEROPHYLL VEGETATION OF CALIFORNIA. 63 

Figure 16 presents the ratio between evaporation at the top of 
the vegetation and at the surface of the ground. Stations 2, 3, and 
7 were selected, since they were continued through both wet and 
dry seasons, and the average daily losses for the period are used 
in computing the ratios. During the dry season the rates at the 
two levels did not differ very greatly, while during the wet season 
the differences were considerable, especially in the chaparral stations. 
This suggests that during the latter period there is a surface stratum 
of moist air due to evaporation from the saturated soil, and that 
the contrast between it and the upper air layers is greater in the 
chaparral stations than in the forest because of freer circulation. 

DISCUSSION AND CORRELATIONS. 

It is very easy and pleasant to describe the vegetation of a locality, 
to mark it out into communities, and to name the dominant and 
secondary species thereof, and even to present quadrats of the same. 
It is not so easy completely to analyze the habitat. With our 
present methods of investigation certain factors elude us almost 
altogether, and much of the data, even when obtained, is difficult to 
utilize. It is most difficult satisfactorily to link vegetation and the 
measured factors of the habitat in the relation of cause and effect. 
The present chapter has so far been devoted to description of veg- 
etation and analysis of habitat. Some correlations of the two will 
now be attempted. 

THE BROAD-SCLEROPHYLLS AND THEIR HABITAT. 

After the analytical treatment that has preceded, it is proper 
first to synthesize the various elements into a whole, to characterize 
the broad-sclerophyll habitat as a unit, so far as we fairly may from 
the data in hand. Afterward it will be in order to consider habitat 
differences and community differences and their correlation. 

To describe the broad-sclerophyll habitat in the large is merely 
to describe the climate of California west of the Sierras and its 
effects upon the soil factors. Emphasis must be placed upon the 
complete seasonal march of the factors, since vegetative activity of 
some sort and degree may here take place the whole year through. 

Of direct and fundamental importance is soil-moisture. Its 
great abundance during the winter months makes ample provision 
for growth during that time. The supply is made more completely 
available by the low air-temperature and low evaporation-rate 
during the period. The cessation of the rains at some time during 
the spring is followed by gradual depletion of the water-content, 
due to failure of the renewal supply, gravity drainage, evaporation 
from the soil, and absorption by the vegetation itself. These 
partial causes will vary in importance in various places. In a 


64 THE BROAD-SCLEROPHYLL VEGETATION OF CALIFORNIA. 

region of relatively heavy rainfall, the dry season is likely to be 
shorter and the supply will dwindle less rapidly. A soil with a 
high water-retaining capacity will lose less through gravity. If the 
evaporation-rate is high, more will be lost thereby, and forest 
vegetation will extract a far greater quantity than will scrub. But 
whatever the difference in rate due to these separate elements, the 
depletion goes on, and the water-content approaches the wilting 
coefficient. In some places at least, and in some years, it actually 
drops below for a considerable period. The Jasper Ridge observa- 
tions demonstrate this; moreover, the general conditions of moisture 
here are much less severe than in other regions where broad- 
sclerophylls are even more thoroughly in control. When the autumn 
rains finally arrive there is still, in some soils at least, a period of 
several weeks before the water forces its way into the deeper layers 
of the air-dry soil. The importance of this delay is lessened some- 
what by the fact that much of the root system is contained within 
the first half-meter of depth. There is probably but small delay 
in the production of new absorption apparatus from the old dormant 
roots, once the moisture touches them. 

As the store of soil-moisture decreases, the evaporation-rate rises 
and water-loss from the leaves must increase. Thus the water- 
balance is affected unfavorably at both ends at the same time, and 
the late summer and early autumn, therefore, constitute the time 
of greatest danger. The deeply penetrating roots and the effectively 
guarded leaves are the answer. 

Air-temperature and, in response, soil-temperature, at a minimum 
during the months of abundant moisture, rise as water-content 
decreases. This combination is altogether unfavorable for veg- 
etative activity. When moisture is abundant, the low soil-tem- 
perature makes absorption difficult and root-growth slow, and the 
low air-temperature is unfavorable to photosynthesis and the other 
growth activities. When the soil-temperature is favorable for 
root-growth and absorption, the water-content is scanty or neg- 
ligible. When air-temperature is favorable to rapid photosynthesis, 
the water supply necessary to that process and to vigorous growth 
is insufficient. High temperature is now itself a danger, in that it 
raises the evaporation-rate and thus increases the depletion of the 
scanty moisture supply, both in plant and soil. 

The seasonal development of the broad-sclerophylls is accurately 
adjusted to the peculiar seasonal march of the factors just outlined. 
With the beginning of the heavy rains (usually December, sometimes 
earlier or later), growth starts in most of the species. The history 
in detail presents many variations. For instance, Arctostaphylos 
flowers immediately from buds already formed, then proceeds to 
put forth new leaf-shoots, which terminate with next year's flower- 


THE BROAD-SCLEROPHYLL VEGETATION OF CALIFORNIA. 65 

buds. When these are fully formed (about May), growth for the 
year practically ceases. In Adenostoma the procedure is exactly the 
reverse. This species begins its activity with the formation of its 
vegetative shoots, and its flowers, borne on these, open in June and 
close the period of active growth. All agree in making the fullest 
utilization of the relatively short period when both moisture and 
temperature conditions come nearest to combining for the general 
good, i. e., in the spring months, when soil-moisture is still abundant 
and air and soil temperatures are on the increase. April, in the 
Palo Alto region, is the month of greatest vegetative activity among 
the broad-sclerophylls and other types of plants as well. An 
additional advantage which many of the former show at this time 
is the possession of an increased photosynthetic apparatus, since 
the last year's Leaves have not yet fallen and the new ones have 
reached or are approaching maturity. It is doubtless at this period 
that the superficial roots described on page 91 have their greatest 
extension. A glance at figure 8 will reveal the interesting fact that it 
was in April that the soil-moisture suffered the most rapid depletion — 
a fact that may reasonably be referred to the abundant use of water 
by the vegetation at this time. 

Soon after the period of maximum activity, the decreasing water- 
supply makes a limitation of growth inevitable and necessary, and 
it is surely more than a coincidence that a number of the species 
drop their oldest leaves rather regularly during the month of June. 
This phenomenon is sometimes so constant and definite that the 
chaparral may take on a distinctly yellowish hue for a few days, 
resuming its normal tone after the old leaves have dropped off. The 
same is strikingly true of the broad-sclerophyll tree Arbutus, which 
passes through a period in June when dead leaves are its most 
conspicuous feature. It is of interest to note further that Msculus 
californica, not an evergreen, has a corresponding habit, dropping 
its leaves gradually during the summer, apparently as a response to 
the decreasing water-supply, until it is often nearly leafless before 
autumn. After the period of leaf fall the broad-sclerophylls enter 
a state bordering upon dormancy, growing very little, merely main- 
taining themselves through the scanty supply of water absorbed 
by the few roots that penetrate the deeper soil layers. 

That water lack is the reason for the stoppage of growth activity 
is shown by the behavior of stump sprouts. If the aerial portions 
of a shrub are removed during the dry season, even in the most 
severe part of it, sprouts are immediately put forth which grow 
with amazing rapidity. On Mount Tamalpais, three weeks after 
a severe fire, I found sprouts of scrub oak 45 cm. high. Visiting the 
scene of the Ojai Valley fire of June 1917, six weeks after the event, 
sprouts of 90 cm. were found. In such cases the water-supply of 


66 THE BROAD-SCLEROPHYLL VEGETATION OF CALIFORNIA. 


a whole clump of shoots is suddenly concentrated upon a few small 
sprouts. Moisture and temperature are both favorable to the 
utmost, and strikingly rapid growth is the result. 

The meaning of the evergreen sclerophyll is plain enough when the 
seasonal factor-march is thus considered. It is a compromise which 
enables the plant to meet the lack of agreement in time between 


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THE BROAD-SCLEROPHYLL VEGETATION OF CALIFORNIA. 67 

moisture and temperature optima. The prominent cuticle and the 
other features that are effective in limiting water-loss enable the 
plant to exist through the critical period of late summer and autumn. 
The evergreen habit permits it to make use of the spring period, 
when growth conditions average best — a time when an ordinary 
summer-green plant would be putting all its energies into the build- 
ing of a new photosynthetic apparatus — as well as the rather frequent 
periods during the winter months when the temperature is high 
enough for effective photosynthesis. This explanation has been 
advanced by Guttenberg (36) for the broad sclerophylls of the 
Mediterranean region, and by Schimper (80) for the type in general. 
It seems entirely adequate for the Californian species. It might 
be added, however, that possibly in JEsculus californica we have 
a still more effective and economical way — the quick production 
of thin, deciduous leaves for use during the favorable period and 
their gradual elimination as unfavorable moisture conditions render 
them dangerous rather than useful. 

In figure 17 I have combined the principal factors of the broad- 
sclerophyll habitat in a way that gives a vivid impression of the 
whole — rainy and dry season, decreasing summer water-content, 
with increasing temperatures and evaporation. 

THE HABITATS OF THE TWO CLIMAXES CONTRASTED. 

The topic that naturally follows is comparison of the respective 
habitats of the two broad-sclerophyll climaxes, forest and chaparral. 
Both communities are typically represented on Jasper Ridge, 
occupying opposite sides of the same ravines, and two subcommunities 
of the chaparral as well. Care must be exercised in extending the 
conclusions here drawn to the two climaxes in general, for it is of 
course true that the factor values noted upon the slopes of a single 
hill do not in detail perfectly represent the averages that characterize 
great regions. It may be said, moreover, that given freedom from 
disturbing agencies, the more xerophytic community, through the 
reactive influence of the vegetation, might continue its mesotropic 
development until forest replaced chaparral. Certain determination 
of this point in any single given case is very difficult. Detailed 
examination of the tension areas at Jasper Ridge failed to produce 
satisfactory evidence, either positive or negative. For the present 
purpose, the question may be settled with sufficient certainty by 
treatment in line with the discussion upon page 74. 

Theoretically, there must be a region intermediate between those 
clearly dominated by forest and by chaparral where the control is 
in suspense, and here any decided local variation in habitat toward 
xerophytism or mesophytism, as would result from opposite hill or 
ravine slopes, would bring about permanent control of a limited 


68 THE BROAD-SCLEROPHYLL VEGETATION OF CALIFORNIA. 

area by one or the other climax. All the evidence points toward the 
southern Coast Ranges as a region of this nature, and it therefore 
seems safe to make use of the data obtained at Jasper Ridge in 
illustrating the differences between the larger units. Further, the 
differences here are likely to be close to the minimum in degree 
which are able to bring about the differentiation of climaxes, and 
are of special interest on that account. Such a comparative evaluation 
must of necessity include the reactional effects of vegetation upon 
habitat, accumulated through a long period of development. This 
is as it should be, since in the interplay of primary and reactive 
factors we find the "continuing causes" of the vegetation. 

Summarizing and commenting upon the differences between 
forest and chaparral habitats, we attain the following results: 

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 is contained 
therein. It is here, too, that the water-content differences mainly 
show themselves, being practically negligible at the depth of 1 
meter. As the dry season advances, water-content values in both 
communities 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 coefficient 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, we may dismiss rainfall, cloud, fog, 
and wind as immaterial 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 trans- 
mission and the 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 Arctostaphylos is practically the same as 
in the forest indicates that the leaf character is determinative — the 
sparse needle foliage vs. the broad leaves of the other shrubs and the 
trees. Temperature and relative humidity data are unsatisfactory, 
but their effects relative to the present purpose are largely included 


THE BROAD-SCLEROPHYLL VEGETATION OF CALIFORNIA. 


69 


in evaporation. The differences in this factor, though not strikingly 
great, are constant throughout the year, the Adenostoma chaparral 
being the highest and the Arctostaphylos 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 
differences of import to the problem in hand. 

It may be objected that the evaporation values used here are 
affected to an unknown degree by the presence of abundant vegeta- 
tion. In order to discover something of the actual comparative 


SLOPE PROFILES 


N. 

rSta.I 


S. 
Sta.lly 


N. 
\,Sta.lV 


S. 
Sta.lII 


^y^. 


-M—^** 


^pV. 


^i? 


50 


ioo Meters 


JULY 
7 16 23 29 


AUG. 
12 19 26 


JULY 
7 16 23 29 


AUG. 
7 12 19 26 


\ 


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1 


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^ 


/ 


1 


f 


\ 


/ 


\ 


/ 


1 


Sta.I (S-facing) 
Sta.lI(N-facing) 


Sta. IV (S- facing) 
Sta.lII (N-facing) 


Fig. 18. — Evaporation during the dry season of 1915 on opposite 
north- and south-facing bare slopes. Foothills of the 
Santa Cruz Mountains, near Palo Alto. 


values upon opposing north and south slopes, uncomplicated by 
reaction, a short study was made in the hills near Stanford Uni- 
versity in the summer of 1915, an account of which is inserted here. 
Evaporation was measured upon the contrasting north- and south- 
facing slopes of two ravines, distant about 5 km. from Jasper Ridge. 
The profiles of these are shown in figure 18. Stations 1 and 2 
were 15 meters, and stations 3 and 4 were 18 and 15 meters, re- 
spectively, above the valley floors. The slopes were bare of shrubs 
and trees, the vegetation being largely wild oats, which, with the 
other herbaceous plants, were dead and brown at the time of the 


70 THE BROAD-SCLEROPHYLL VEGETATION OF CALIFORNIA. 

study. The stalks were cleared from the vicinity of the instruments 
and the effects of vegetation were thus eliminated. The atmometers 
were installed July 1, and were visited at approximately weekly 
intervals until August 26. Unfortunately, three readings at station 
1 were lost through interference by cattle, which did not respect 
the chicken-wire defenses. Except for one reading in stations 3 
and 4, the south-facing slopes show the higher evaporation-rate. 
The reversal on July 29 is hard to understand, but may possibly be 
due to experimental error. Omitting the figures in station 2, which 
have no corresponding south-facing slope values, we find the following 
average evaporation-rates : 

For the first pair, south-facing : north-facing : : 100 : 85. 

For the second pair, south-facing : north-facing : : 100 : 79. 

For the 13 complete readings afforded by the two, south-facing : north-facing : : 100:82 

There is, then, a distinct difference in evaporation-rate between 
opposing north and south slopes, when uncomplicated by vegetation. 
In these open ravines with comparatively gentle slopes the average 
rates were as 4 to 5. If they had been as steep-sided as certain ravines 
at Jasper Ridge, the contrast would doubtless have been greater. 

We have here sufficient data to explain the greater size and 
luxuriance of the plants growing upon the north-facing slopes, and 
the absence of the more mesophytic species from the south-facing 
exposures. Many factors are indirectly involved, but fundamentally 
the problem is one of water-balance. During the height of the 
rainy season there is in both habitats an abundance of soil-moisture 
and a minimum of evaporation. But the air and soil temperatures 
are low, and there is consequently little growth. As the temperature 
rises, the rate of growth increases accordingly, but at the same time 
the rains are diminishing in frequency and amount, finally ceasing 
entirely, and the evaporation-rate is going up. It has already been 
stated that the period when most of the growth occurs is in the 
spring months, culminating in April. The amount of actual growth 
during this time, other things being equal, will depend upon the 
ratio of water-supply to water-loss, and plainly this water-balance 
is more favorable upon the north-facing slope inhabited by forest. 
The size of the full-grown plant of a given species depends largely 
upon the turgor of the growing cells, and a healthy condition of 
turgor is conditioned upon a water-supply that will more than 
compensate for the loss by evaporation. If the supply is so scant 
or the loss so severe that the water-balance is barely maintained at 
equality, the plant and its organs will be small. If either member of 
the system varies in such a way that the supply is well in excess of 
the loss, rapid growth will result. The ever useful example of the 
stump sprout illustrates this point. The water-supply which 
formerly fed a full-sized shrub is concentrated upon a few small 


THE BROAD-SCLEROPHYLL VEGETATION OF CALIFORNIA. 71 

shoots, which grow for a time with surprising rapidity (see p. 86), 
although no decrease has occurred in the rate of loss. The size 
and luxuriance of the plants are therefore greater upon north-facing 
slopes, where soil-moisture is more abundant and evaporation less 
rapid during the growing-period. 

To account for the absence of the more mesophytic species from 
the south-facing slopes, we must appeal to the dry season. It has 
been shown that the soil-moisture contents of the two slopes, con- 
sidered in relation to the wilting coefficient, are about equally unfavor- 
able during the critical period. This is not true, however, of the 
evaporation-rate, which is considerably higher in the chaparral 
community. A seedling of a mesophytic forest species, which might 
conceivably obtain a start during the spring months, though not 
making much increase in size, in the chaparral habitat, would be 
very likely to succumb during the ensuing critical period, when the 
high evaporation-rate had made the water-balance still less favorable. 

Since the plants of the forest, because of their size and abundance, 
use more water than the chaparral species as food material and lose 
more through their enormously great expanse of foliage, more is 
withdrawn by them from the soil. The much more rapid depletion 
of the water-content during the spring months, resulting from this, 
is perfectly evident in figure 8. Thus the very luxuriance of the forest 
vegetation is itself the prime cause of the reduction of water-content 
practically to the low level of the chaparral. 

Our conclusion, then, extended to the larger vegetation units, 
is that the fundamental distinguishing difference between the two 
broad-sclerophyll climaxes — their continuing cause, so to speak — is in 
the water-balance and its variations, whatever the indirect factors 
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. 


72 THE BROAD-SCLEROPHYLL VEGETATION OF CALIFORNIA. 

V. DEVELOPMENT. 

THE CLIMAX REGIONS OF CALIFORNIA. 

In a region of slight relief and uniform climate, such as the Missis- 
sippi Basin or the Great Plains, a single climax extends for hundreds 
or even thousands of miles. In California the case is very different. 
The extremes of latitude and altitude, the proximity of the ocean, 
and the barrier influence of high mountains upon moisture-bearing 
winds all operate to bring about great and abrupt climatic differences, 
and therefore great vegetational complexity. Instead of a single 
climax community there are a half dozen, each, though limited in 
area, comparable to such a community as the Great Plains grassland 
or the eastern deciduous forest. Successional investigation has not 
proceeded far enough to enable us to define these climaxes with 
accuracy. The following outline is tentative, and is given merely 
that we may properly place the communities with which we are 
dealing. 

The conifer-forest climaxes are three in number, and the first two 
have important contact relations with the broad-sclerophyll com- 
munities. The Pacific Conifer Climax Formation, which includes 
the forests of the coastal region from California to Alaska, is repre- 
sented in northwestern California by two associations: (1) The 
Sequoia sempervirens association ranges from the northern boundary 
of the State, in the immediate vicinity of the coast, southward to 
San Luis Obispo County. South of San Francisco Bay its continuity 
is much broken. (2) The Pseudotsuga association, which has its 
center in the Puget Sound region, is poorly represented in California, 
occurring in the interior of the north Coast Ranges. It is confused 
with other communities, especially the broad-sclerophyll forest, 
so that the portion included within the State should probably be 
considered as transitional. 

The Montane Conifer Climax Formation covers the middle altitudes 
of the interior mountain region of western America, and the character 
tree everywhere is Pinus ponderosa. In California it is represented 
by the Pinus ponder osa-lambertiana association, which occurs in the 
middle altitudes of the west slope of the Sierras and on the higher 
Coast Ranges and the mountains of southern California. 

The Subalpine Conifer Climax Formation is practically coextensive 
with the preceding in general range, but lies above it altitudinally. 
I will not apply a designation to the California subdivision, as it is 
rather complex, and no successional work has been done within it. 
It occurs in the higher Sierras and there are isolated outliers else- 
where. The character trees are Abies magnifica and Pinus monticola 
in the lower part, and Pinus albicaulis and Tsuga mertensiana near 
timberline. 


THE BROAD-SCLEROPHYLL VEGETATION OF CALIFORNIA. 73 

The broad-sclerophyll climaxes, including the broad-sclerophyll 
forest and the climax chaparral, will shortly be treated in detail. 
The alpine meadow climax belongs to the highest summits of the 
Sierras. The desert climax occurs east of the Sierras and the moun- 
tains of southern California. The basin sagebrush climax enters 
the eastern part of the State to some extent, and the coastal sagebrush 
is locally important in the interior valleys of the south. It is possible 
that the Great Valley or a part of it is climax grassland. The 
coastal sagebrush and the grassland are in extended contact with the 
climax chaparral. 

THE BROAD-SCLEROPHYLL CLIMAX FOREST. 

Discussion of the climax nature of the broad-sclerophyll forest 
involves considerable difficulty. Its distribution is patchy, i. e., 
no extensive area is completely dominated by it. In parts of the 
region elements of other vegetation types are mingled with it, giving 
the appearance of a transitional type. Its natural distribution has 
plainly been restricted somewhat, especially by fire. 

The range of the broad-sclerophyll forest is practically coextensive 
with that of the climax chaparral, and over most of the region there 
is sharp alternation between the two. The forest is least important 
southward. In the Cuyamaca Mountains the chaparral covers all 
slopes of the lower altitudes, the forest being confined to the steepest 
ravines and similar situations where the moisture conditions are 
unusually favorable. As we go northward, or upward in the moun- 
tains, we find the forest increasing in importance. In the central 
Coast Ranges it is the regular covering of the steeper north-facing 
slopes, the chaparral being confined to south slopes and summits. 
In the San Francisco Bay region the two are roughly equal in impor- 
tance, and still farther northward the forest continues to gain. 
Here, however, a new complication arises. Pseudotsuga mucronata 
is present in the most mesophytic situations and rapidly increases 
in importance northward. In some places it forms pure growth, but 
oftener occurs in mixture with the broad-sclerophyll trees, the chapar- 
ral still holding the south slopes, but steadily decreasing in impor- 
tance. Finally, we encounter a clear dominance of Pseudotsuga, 
with the broad-sclerophyll trees forming an understory. Ascending 
one of the southern mountain ranges, we meet with a similar tran- 
sition, the broad-sclerophyll forest gaining over the chaparral and 
finally merging with a forest of Pseudotsuga, the species of the last 
being different (P. macrocarpa) , but to a degree ecologically equiva- 
lent to the northern one. In short, the broad-sclerophyll forest is 
plainly unable to control in the south; it increases in relative impor- 
tance northward and upward, but just as it begins to show decided 
signs of dominance over the chaparral, it comes into competition 
with a coniferous element, to which it soon becomes subsidiary. 


74 THE BROAD-SCLEROPHYLL VEGETATION OF CALIFORNIA. 

Before proceeding to interpretation, certain definitions are neces- 
sary. The climax is here considered to be the most mesophytic 
community which a region as a whole, under present climatic con- 
ditions, is able to support. Regions nearby have different climaxes, 
more mesophytic or less so, according to whether the climates are 
more or less humid, and the climax of the first region might be 
succeeded by one or another of these, should the climate change in 
the appropriate direction. The neighboring climaxes are thus 
potential climaxes for the region under discussion (Clements, 21, 
p. 108). A potential climax is a postclimax if it is more mesophytic 
than the existing one, and a preclimax if less so (1. c, p. 109). Fre- 
quently a potential climax is actually present in a region, in situations 
of unusually favorable or unfavorable moisture conditions. An 
excellent example of a postclimax is the forest which follows the 
river valleys far westward into the Great Plains region. 

In the light of these definitions it is evident that the broad-sclero- 
phyll forest is postclimax in Southern California. The chaparral 
is plainly in control, although it is certain that its dominance has 
been extended somewhat by fire. In central California, where the 
two are rather evenly balanced, the question is difficult, but the 
tendency of the forest northward to increase its dominance is plain. 
In such a transitional region, where the actual control is uncertain, 
the spatial relations of the competing communities depend upon the 
nature of the topography. In a level country the change is usually 
seen in a gradual mingling of the species of the two impinging regions. 
In a broken country, where steep slopes with various exposures are 
the rule, the situation is otherwise. The differences in atmospheric 
factors resulting from contrasting slope exposures are in such a region 
no greater than elsewhere; but because there is here a zone in which 
the general conditions permit both groups of species to flourish, 
the relatively slight differentiation of habitat due to the factor of 
slope exposure exerts a maximum apparent effect upon the vegetation, 
a sifting of the species into two groups. We therefore find the 
two communities sharply set off from one another, each in permanent 
control of its area, with no successional relations between them. 
Each is the climax within its own little sphere of influence. Such is 
the relation of broad-sclerophyll forest and chaparral in the central 
Coast Ranges, the forest permanently controlling the north slopes, 
the chaparral the south. Passing into the north Coast Ranges, 
we would expect to find the broad-sclerophyll forest finally attaining 
a true climactic status, and there is an undoubted tendency in this 
direction. The effect is spoiled by the competition of Pseudotsuga, 
the addition of which produces a mixed broad-sclerophyll-conifer 
community, which is apparently the climax of the region in which it 
occurs. Farther north, the broad-sclerophyll element loses all 


THE BROAD-SCLEROPHYLL VEGETATION OF CALIFORNIA. 75 

claim to dominance, becoming a subordinate part of the conifer 
forest, and possibly a successional stage in its development. 

In way of summary, we may say that although no extensive region 
is completely dominated by broad-sclerophyll forest, nevertheless it 
must be considered a climax, since it represents a degree of meso- 
phytism between that of the chaparral and the conifer forest, and 
because it shows plainly a tendency to gain dominance over the 
chaparral, attainment of which is hindered only by the competition 
of a still more mesophytic type. 

THE CLIMAX CHAPARRAL. 
EVIDENCE OF ITS CLIMAX CHARACTER. 

The evidence of the climax nature of that type of chaparral that 
I have designated as such is presumptive and direct. Under the 
first head four points may be made. 

Dominance. — The very fact that the chaparral is by far the most 
widespread of all the communities within its range (this being espe- 
cially true in the region of its center of distribution) in itself creates 
the presumption that the chaparral is the climax. Bearing in mind 
that there are cases in which an important and widespread community 
is not the climax of its region, for instance, the Pinus murrayana 
forest of the central Rockies, whose temporary dominance is due to 
fire, we can not accept this evidence without confirmation. 

Stability. — In most areas the chaparral has obviously been in 
control for a long period of time — so long that there is no evidence 
existing of previous vegetation of other type. This is not universal, 
and in any case is not entirely conclusive. 

Occurrence on diverse sites as to soil and topography. — The fact 
that a community is not restricted to a single topographic situation 
or soil type, but occurs on many, is good evidence of climax nature. 
This is true of the chaparral in the region where other evidence 
indicates its climactic character, i. e., its center of distribution. 

Adjustment to climate. — In every region there are many plants 
which are plainly in adjustment with some very special habitat. 
Such are aquatic plants, halophytes, and species of rock crevices. 
All of these occur in the chaparral region. But the species of the 
chaparral itself possess a constant and much specialized character 
which is plainly a response to a very particular type of climate. 
The correspondence in area covered by climate and vegetation type 
has already been shown. If further evidence be desired, it may 
be derived from the ecologically equivalent "macchie" of the 
Mediterranean region and its relation to a climate which is almost 
identical with that of California. It is difficult to escape the con- 
clusion that a vegetation type which is so perfectly adjusted to the 
climate of its region must be the ultimate or climax type, in that 
area at least where it reaches its most perfect development. 


76 THE BROAD-SCLEROPHYLL VEGETATION OF CALIFORNIA. 

The direct evidence for the climax nature of the chaparral is 
derived from a study of the successions themselves, in which we 
find that all that have been investigated in a rather widely extended 
exploration culminate in the establishment of this community, and 
that over much of the region there is no evidence that any other 
community is superseding it. Detailed consideration of the succes- 
sions is reserved for a separate section. 

EXTENT OF THE CHAPARRAL AS A TRUE CLIMAX. 

Because of widespread disturbance by various agents of destruc- 
tion, it is impossible to set definite and certain limits to the region 
of true chaparral dominance. Fire occurring in the transition zone 
between two formations seriously alters the normal relations due to 
climatic control. Another source of difficulty lies in the fact that 
much of the original vegetation of the economically more useful land 
has been totally destroyed by the invading white man, so that it is 
necessary to reconstruct the original picture from fragments. Certain 
areas, however, may be fixed upon as chaparral climax which will 
not be questioned. 

The foothills and low mountains of southern California and certain 
parts of the valleys and mesas are the most certain, and it is probable 
that exploration of northern Lower California would add a large 
extent of country to the range of the chaparral climax. In these 
places Adenostoma is usually the dominant species, or if cultivation 
has largely destroyed the native vegetation, remnants show it to 
have been so at a former time. Such is the case in portions of the 
Los Angeles and San Bernardino Valleys and on the broad mesas 
east of San Diego. As we ascend the higher mountain ranges of 
southern California, the evidences of climactic character in the 
chaparral become less and less convincing. Species which belong 
to the conifer-forest chaparral appear, and there is more and more 
alternation with patchy areas of broad-sclerophyll and of conifer 
forest, in which Pseudotsuga macrocarpa is the first to attain impor- 
tance. In this region there has plainly been an increase of the chapar- 
ral areas at the expense of the forest, due to the fact that repeated 
fires in a transition zone favor the extension of the more xerophytic 
community. Passing northward in the Coast Ranges, we encounter 
a similar transition, except that there is practically no admixture 
of conifer-forest chaparral species until we are well north of San 
Francisco Bay, and that the alternation is with broad-sclerophyll 
tree species alone. Here, too, the forest areas show frequent evidence 
of fire restriction. In the southern Sierras there is a belt along the 
lower foothills where Adenostoma and other chaparral species are 
of great importance, alternating, however, with much broad-sclero- 
phyll forest. As we go northward, the yellow pine zone, with its 
accompanying temporary chaparral, approaches more and more 


THE BROAD-SCLEROPHYLL VEGETATION OF CALIFORNIA. 77 

closely to the Great Valley, so that roughly from the latitude of 
Sacramento northward the climax chaparral is excluded from the 
mountains and foothills proper, such scrub species as occur being 
of the conifer-forest group. It is an interesting fact that in this 
stretch of the Sierras Adenostoma is almost absent. North of Auburn 
I have failed to find it in four crossings of the foothills and have 
been able to discover but one record of its occurrence, noted by Dr. 
Jepson northeast of Chico. 

The relations between chaparral and grassland present certain 
problems difficult and perhaps impossible of full solution. The 
fact of the greater extension of the chaparral in the past is certain; 
the magnitude of that extension is the point of difficulty. The 
very general statement may be made, subject to qualifications 
about to be indicated, that in central California the lower mountains 
are controlled by chaparral and the plains by grasses. The character 
of the transition zone between the two types is as follows: 

The first hills are as a rule entirely grass-covered, though even 
on these, and occasionally out upon the valley-floor, are patches 
of chaparral. These show absolutely no correlation with altitude, 
slope-exposure, or soil-type. Their edges are sharp and the shrubs 
are uniformly developed throughout. They are obviously remnants. 
Penetrating farther into the mountain mass, the chaparral patches 
become more and more numerous, but are still arranged purely in 
hit-and-miss fashion. Farther still, the chaparral controls the 
greater area, and the grassland forms the patches, which in summer 
appear like tan-colored inlays set into the green of the scrub. Finally, 
the grassland disappears, leaving the chaparral in complete control. 
In such a journey we do not necessarily encounter continually higher 
altitudes; we are merely penetrating more and more deeply into a 
mountain complex in which the ridges may all be of similar height. 
In short, everywhere near the valleys and plains the hills are grassy, 
while in the depths of the ranges they are covered with scrub. The 
larger the extent of the mountain mass the greater is the central 
area of chaparral. Conversely, a small isolated area of hills, though 
of considerable altitude, may have none. This arrangement is so 
nearly universal where chaparral and grassland meet that specific 
examples are hardly necessary, and yet perhaps a graduated series will 
be of interest. 

The Marysville Buttes in the Sacramento Valley are excellent 
examples of the isolated hill with practically no brush. The highest 
summit is 630 meters and the slopes are everywhere covered with 
the typical annual vegetation of the plains. Even here, however, 
there are suggestions ol the chaparral in the presence in small numbers 
of Quercus dumosa, Q. wislizeni, and Heteromeles arbutifolia (44). 

Mount Diablo is also an isolated mass, but of greater extent and 
height than the Marysville Buttes. Its lower flanks and the sur- 


78 THE BROAD-SCLEROPHYLL VEGETATION OF CALIFORNIA. 

rounding hills are grassy, with patchwork of scrub, and the upper 
300 meters are fairly solid chaparral, in which Adenostoma is greatly 
predominant. In the Mount Hamilton Range we have an extensive 
complex system made up of ridges of similar height. Penetrating 
the mass at the point where Coyote Creek debouches into the 
Santa Clara Valley, we encounter grassy hills, but on the first series, 
and even on the footslope itself, are patchy remnants of chaparral, 
mainly Adenostoma. North slopes are well forested with broad- 
sclerophyll trees, and this is entirely natural, since these would 
resist destruction by fire to a far greater degree than would the chapar- 
ral, both by reason of their greater size and the better moisture 
conditions of their habitat. Grassland is nearly continuous over 
most of the slopes up to the summit of the first main ridge, where 
there is a very thin forest of Pinus ponderosa, with the same meadow 
vegetation under the trees. Eastward from here we look into the 
heart of the mountain system, where numerous ridges are covered 
with an irregular mosaic of chaparral and grassland. The Santa 
Lucia Range and the mountains of San Benito County may be cited 
as examples of the many systems in which one finally penetrates 
to a central region of solid chaparral. 

The most convincing proofs of former control of present-day 
grassland by chaparral are the frequent remnants that painstaking 
search brings to light. The sharply limited patches in the midst of 
other vegetation, in which Adenostoma is usually most prominent, 
have already been described. Experience has shown that even a 
single mature specimen of this plant is almost certainly a relict and 
not a fresh arrival, since when its mass control is once thoroughly 
destroyed it reestablishes itself with the utmost difficulty, probably 
because of special conditions necessary for successful germination, 
as yet undiscovered. It is fairly safe, therefore, to assume that 
wherever mature individuals of Adenostoma remain, either isolated 
or in patches, that that species was formerly dominant. Fence-rows, 
pieces of rocky or unused ground, ravines, etc., are the sort of places 
where one looks for such evidence. Using this method, which has 
in some cases been corroborated by historical testimony, it has been 
possible to demonstrate that dense chaparral once covered extensive 
areas which are now grassland or under cultivation. For example, 
the floor of the Santa Clara Valley southeast of Palo Alto, which is 
to-day one of the great orchard regions of the State, was less than 
half a century ago solid chaparral. The bare, grassy hills nearby, 
with their thin young growth of oaks, were similar. Scattered but 
full-sized individuals of Adenostoma along fences and occasional 
patches of uncleared ground suggest this, but in the present case 
we have direct historical evidence of the fact. 

Mr. G. F. Beardsley, a retired mining engineer now living in 
Carmel, California, spent several years of his boyhood in this vicinity, 


THE BROAD-SCLEROPHYLL VEGETATION OF CALIFORNIA. 79 

and is able to recall with considerable accuracy the general character 
of the vegetation at that time. About 1870, according to Mr. 
Beardsley, the present orchard land between Palo Alto and San Jose 
was solid chaparral, and patches of the scrub occurred on the floor 
of the valley between San Jose and Gilroy. A demand arose in 
San Francisco for the massive woody "roots" of the shrubs for fuel, 
which made it profitable to clear the chaparral from valley and foot- 
hills and ship it to the city. Later the value of the land for fruit and 
grape culture was discovered, which resulted in the almost complete 
destruction of the brush. Those cleared areas which are not under 
cultivation are to-day typical California grassland, sometimes with 
young oaks scattered through them. 

A very interesting and significant bit of relict evidence is the 
occurrence of a typical area of chaparral well out in the Sacramento 
Valley. This locality, in Colusa County, between Hershey and 
Arbuckle, was brought to my attention by Dr. H. M. Hall, of the 
University of California. Here are several sharply defined patches, 
typical remnants. One occupies a shallow draw running through 
a cultivated field; another, in an uncultivated piece of level ground, 
ends abruptly at a fence. In all, Adenostoma is by far the most 
abundant species; it is of very large size (3 meters) and apparently 
perfectly content with its home. Other species seen are Arctosta- 
phylos manzanita, A. tomentosa, Heteromeles arbutifolia, and Rhamnus 
crocea. Some scattered trees of Quercus douglasii grow where the 
chaparral has been partially destroyed. These localities are 5 to 
8 km. distant from the foothills of the Coast Range. 

A few words should be added concerning the trees which occur in 
scattering growth with the grasses. These are deciduous oaks, 
especially Quercus douglasii, and Pinus sabiniana. Typical stands 
of young Q. douglasii have been seen where it is certain that chaparral 
was formerly in control. In some places remnants of chaparral 
are mingled with the oaks. The habits of this species, moreover, 
fit it admirably for such a life. It is an abundant seeder, withstands 
severe drought, and is one of the least shade-tolerant of the Cali- 
fornia trees. Pinus sabiniana is similar in habitat requirements 
and frequently occurs in chaparral, especially with Adenostoma. 
It is at least a reasonable supposition that the thin woodlands of 
Quercus douglasii and Pinus sabiniana which cover great areas in 
the Coast Ranges and Sierra foothills, often forming a wide zone 
between the grassland of the plains and the chaparral of the moun- 
tains, are secondary, occupying areas which would support climax 
chaparral but for agencies of disturbance. 

It remains to account for the absence of the chaparral in these 
areas of grassland, where it is hypothetically the climax. Several 
agencies have operated to bring this about, some of which have 


80 THE BROAD-SCLEROPHYLL VEGETATION OF CALIFORNIA. 

already been suggested. Clearing for firewood has been locally 
effective; clearing for cultivation much more so. By far the most 
important cause of destruction has been fire. It has been stated 
that fire favors the extension of the chaparral at the expense of the 
forest. It is also true that fire, if it occurs with great frequency, 
favors grassland at the expense of the chaparral. A single burning 
of chaparral will result merely in a crop of stump sprouts and greater 
density than before, but yearly burning will inevitably destroy the 
brush completely or prevent invasion by it. Cattlemen and sheep- 
men in the early days, according to unpublished Forest Service 
reports, were accustomed to fire the brush annually in the foothills to 
destroy it and thereby improve the grazing conditions. This resulted 
in a great increase of grassland at the expense of the chaparral. 
Such recent events, however, are of small importance compared 
with the effects produced by the aboriginal population. The 
following quotation from Jepson (47) is of interest in this connection : 

"The herbaceous vegetation [in the Great Valley] in aboriginal days grew with 
the utmost rankness, so rank as to excite the wonderment of the first whites. ■ • • • 
This dense growth was usually burned each year by the native tribes, making a quick 
hot fire sufficiently destructive to kill seedlings, although doing little injury to estab- 
lished or even quite young trees." 

Dr. Jepson writes concerning the sources of his information : 

"The statement made in the Silva re periodical burning rests upon evidence gath- 
ered by myself from members of the Nyah, Hupa, Porno and other tribes; also from 
verbal relations of early Californians." 

It may be added that Merriam estimates the Indian population 
of California west of the Great Basin at its maximum to have been 
250,000. Here we have suggested the cause of destruction of the 
chaparral, or the prevention of its establishment. It is easy to 
conceive of the possibility of an occasional area escaping disaster, 
which would account for the fragments near Hershey and others like 
it. The reason for the scattering woodland of Quercus douglasii 
and other species is also apparent; an occasional year without burning 
or a succession of such years would permit the successful germination 
of young trees, which once established would resist the attacks of 
fire. The patchy transition between grassland and chaparral is 
also explained, for fires started in the valleys, where most of the 
Indian population lived, would spread into the surrounding ranges, 
in various directions and to varying distances. Certain areas would 
escape, and these would be larger and more numerous toward the 
interiors of the mountain systems, where paucity of population 
would reduce the starting of fires to a minimum. The reasons for 
the burning I have not been able to discover. 

It is certain, therefore, that extensive areas which are now domi- 
nated by grasses or thin forest of xerophytic trees were formerly 


THE BROAD-SCLEROPHYLL VEGETATION OF CALIFORNIA. 81 

controlled by chaparral or would come to support chaparral if 
destructive agencies were eliminated; and the principal causes of 
the destruction of the chaparral or prevention of its establishment 
have been clearing and repeated fires. 

As to the exact extent of former chaparral dominance we can not 
set limits with any degree of assurance. Some areas are made certain 
by historical testimony and others almost equally so by relict evi- 
dence. We are thus led to admit the extreme probability that the 
great mass of the Coast Ranges, the foothills of the Sierras, and such 
minor valleys as the Santa Clara were originally dominated by broad- 
sclerophylls; that areas now inhabited by grasses or xerophytic 
trees, occurring as isolated patches surrounded by chaparral or 
forming a more or less continuous zone upon the foothills bordering 
the major valleys, are such by reason of clearing or repeated fires. 
It may be necessary to except from this category the ridges of Coast 
Range and Sierras that immediately surround the southern end of the 
San Joaquin Valley, which, with the inclosed plains, are desertlike. 

There is a possibility, further, that the northern end of the Great 
Valley itself may once have been dominated by chaparral. The 
evidence for this is not absolutely conclusive, but is of sufficient 
weight to justify presentation. The remnant near Hershey, in 
the Sacramento Valley, shows that the chaparral species are able to 
grow to their maximum size and to form a solid cover under typical 
valley conditions. The practical absence of typical chaparral along 
the northeastern border of the valley (p. 77)— the only break of 
importance in the whole circle of surrounding foothills — suggests 
the probability of a former connection across the valley floor. The 
climax chaparral has apparently been pinched out between the 
invading mass of the fire-favored grassland and the relatively resistant 
barrier of the conifer forest. 

So far as available data show, there are no constant efficient 
climatic differences between the areas dominated to-day by chaparral 
and the Sacramento Valley. Referring to table 1 (p. 19) we find 
that 44 stations in the southern Coast Ranges, southern Sierra 
foothills, and Cuyamaca Mountains, which are the regions most 
certainly controlled by chaparral, give an average of 21.67 inches of 
precipitation, while 23 stations in the Sacramento Valley average 
21.85 inches. Neither is the seasonal distribution notably different, 
the proportion of total precipitation occurring in the months May 
to October being, in the case of the chaparral regions, 11.6 per cent, 
and in the Sacramento Valley 13.9 per cent. Available temperature 
data are unsatisfactory, as there are no records of mean summer 
maxima for the Sacramento Valley. 

Clements (22, p. 150) has advanced the theory that the Great 
Valley of California, "from Bakersfield to Mount Shasta and from 
the foothills of the Sierra Nevada and Cascade Mountains, through 


82 THE BROAD-SCLEROPHYLL VEGETATION OF CALIFORNIA. 

and over much of the Coast Range" was originally grassland of the 
bunch-grass type, Stipa being the most important genus, which has 
been almost entirely replaced by the introduced annual grasses 
(Avena fatua and A. barbata) that are so prominent to-day. He 
admits the unlikeness of the climate, especially in seasonal distribu- 
tion of precipitation, to that of other regions of grassland climax, 
but rightly affirms that the climax plant community is itself the 
best available indicator of climate. The decision rests, therefore, 
upon correct identification of the climax community. Clements's 
evidence of grassland dominance is based upon assumed relicts, 
and my evidence of chaparral dominance is of the same nature. 
In an area where individuals and patches of both types occur today, 
the weight of probability would, in my opinion, favor the chaparral 
plants as being the survivors of the true regional climax. It has 
already been stated that most of the species of the climax chaparral, 
notably Adenostoma, reestablish themselves with the utmost difficulty 
once their mass control has been destroyed, and that therefore thor- 
oughly isolated individuals or patches of such plants are almost 
certainly relicts of former dominance rather than centers of recent 
colonization. The same is not true in the case of grasses, even the 
perennial species which make the grassland climaxes. With these, 
greater mobility and ease of germination bring about a wide scattering 
of individuals, and the acceptance of isolated plants or patches as 
true relicts is therefore rather hazardous. 

The acceptance of my conclusions as to former control of certain 
regions (the main mass of the Coast Ranges with its minor valleys, 
the foothills of the southern Sierras, and perhaps the northern end 
of the Sacramento Valley) by chaparral does not necessarily preclude 
the possibility of climatic grassland over much of the Great Valley. 

In southern California the contact between chaparral and coastal 
sagebrush resembles that between the former and the grassland in 
the central part of the state. The sagebrush, which is undoubtedly 
climax in certain portions of the interior valleys, has extended its 
area of dominance at the expense of the chaparral, because of fire. 

In conclusion, then, the climax chaparral has transgressed its 
normal climatic limits along its mesophytic border through its 
invasion of the forest, fire being the causative agent; on its xerophytic 
border it has been pushed back a considerable distance by the grasses 
and xerophytic forest in the north, and by the coastal sagebrush 
in the south. 

SUCCESSIONS LEADING TO THE CHAPARRAL CLIMAX. 

Primary Successions. 

The areas where primary succession may be observed are limited, 
the bulk of the area having reached its final stage or being in process 
of secondary development. Naturally most of the successions are 


THE BROAD-SCLEROPHYLL VEGETATION OF CALIFORNIA. 83 

of the xerarch class. Three distinct lines of development have been 
observed upon primary areas, corresponding with three common 
modes of soil formation. These are the successions on rock surfaces, 
on washes and alluvial fans, and on coastal dunes. In dealing with 
such an extensive and varied region the treatment can not be com- 
plete, and there is here a fruitful field for further study. 

Development on rock surfaces. — Though most of the chaparral- 
covered mountains have a uniform, unbroken mantle of vegetation, 
there are locally extensive areas where bare rock is being invaded. 
Such successions are much the same in character wherever they occur. 
The usual lichens and xerophytic mosses cover the surfaces and 
their establishment is assisted by the abundant scaling of the rock 
due to sudden temperature changes. Crevice plants as usual are 
of supreme importance. Among the herbaceous species, Pellcea 
mucronata and Selaginella bigelovii are frequent. The most impor- 
tant pioneers are the chaparral shrubs themselves, the successional 
stages thus being greatly telescoped. Adenostoma is perhaps most 
important among these. Yucca whipplei is common in such places 
in the southern part of the State. Dead remains of shrubs anchored 
in the crevices show that permanent establishment may be a matter 
of many generations. Gradually the rock disintegrates and the 
chaparral shrubs increase in number. It is not uncommon, however, 
to find a solid cover of chaparral concealing and growing entirely 
from the crevices of a rock-layer whose surface is barely at all dis- 
integrated. Thus, through a process long in point of time but com- 
prising few stages, the climax community comes to control the bare 
rock areas. 

Development on alluvial fans and washes. — Because of frequent 
production of fresh surfaces due to erosion and deposition by periodic 
torrents, there is excellent opportunity for the study of such succes- 
sions. Alluvial fans and continuous piedmont slopes occur through- 
out the State, but they are especially well developed in the Los 
Angeles and San Bernardino Valleys, bordering the high ranges to 
the north. The physiographic processes involved in their formation 
are a complex combination of erosion and deposition. The periodic 
torrents from the mountain canyons and ravines are continually 
changing their courses, depositing material now here, now there, 
cutting into deposits already made, and forming new surfaces through 
both processes. If the cutting goes deep enough terraces are formed 
whose surfaces are thereafter free from further direct disturbance. 

Certain ancient fans now in process of dissection show all stages 
in the physiographic cycle. There is a very remarkable example 
south of San Timoteo Canyon which may be viewed to excellent 
advantage from Smiley Heights, near Redlands. V -shaped ravines, 
cut sharply into the original smoothly sloping surface of the fan, 


84 THE BROAD-SCLEROPHYLL VEGETATION OF CALIFORNIA. 

represent extreme youth. Wider ravines with graded floors approach 
maturity, and extensive base-leveled areas with occasional monad- 
nocks have reached old age. With such a series it is an easy matter 
to correlate vegetational development with physiographic age. 
Invariably upon the flat surfaces of the terraces and uneroded 
remnants the vegetation is well-developed chaparral, in which 
Adenostoma is commonly dominant, either solid or represented 
by relict masses. Chaparral covers the newer base-leveled areas 
also, except where streams have recently coursed over them. In 
other words, the stable areas, which have had a chance for a relatively 
long period of vegetational development, support the chaparral 
community. Further, the composition of the vegetation of oldest 
terrace-tops and youngest base-levels is practically identical. Since 
the terrace-tops, with their vastly greater age, have not advanced 
beyond the stage reached by the recent base-levels, it is plain that 
that stage is the climax. 

The species that inhabit the unstable eroding slopes and the 
recently formed washes make a very different assemblage. They 
are mainly short-lived half-shrubs which germinate readily and are 
able to exist in the unfavorable conditions which such habitats offer. 
Clements (22) regards this well-marked community as the western- 
most association of the sagebrush formation, because of the impor- 
tance in it of Artemisia californica, and gives it climactic rank. 
His appellation is here tentatively accepted. The area of coastal 
sagebrush dominance has not been accurately determined, but 
roughly it covers the plains and low interior valleys of southern 
California from the Santa Ana Range to the San Jacinto Mountains. 
Within the climax chaparral it is successional, occurring in both the 
primary and secondary series. A number of the species extend 
northward for varying distances, a few as far as the San Francisco 
Bay region. 

A list of the most important species follows, those particularly 
characteristic of the southern California group being marked with 
an asterisk (*) : 

Eriogonum fasciculatum.* Ramona stachyoides. Baccharis pilularis. 

Syrmatium glabrum. Sphacele calycina. Encelia farinosa.* 

Helianthemum scoparium. Diplacus glutinosus. Eriophyllum confertiflorum. 

Malacothamnus fasciculatus.* longiflorus. Lepidospartum squamatum.* 

Ramona clevelandi.* puniceus.* Artemisia californica. 

nivea.* Ericameria pinifolia.* Senecio douglasii. 

polystachya.* 

Two or three brief descriptions of individual localities will be of 
interest. The eroding southwest slope of Smiley Heights, apparently 
a remnant of an ancient fan, near Redlands, is steep and unstable. 
The species are Eriogonum, Encelia, Ramona stachyoides, and Arte- 
misia. The bluff is much dissected into gullies and ridges which 


THE BROAD-SCLEROPHYLL VEGETATION OF CALIFORNIA. 85 

present alternating southeast and northwest slopes, and there is 
sharp vegetational alternation corresponding with the slope-exposure 
differences. The first two species occupy the slightly moister north- 
west slopes in relatively close formation, and the last two make a 
sparse covering on the opposite hot, dry exposures. The alternation 
is very conspicuous when viewed from a distance. There are thus 
degrees of xerophytism among the coastal sagebrush species, giving 
rise to additional successional stages where delicate differentiation 
of habitats exists. Remnants indicate that the original vegetation 
of the level summit of Smiley Heights was Adenostoma chaparral. 

Three successional stages were revealed by study of the dry 
washes of Mill and Santa Ana Creeks, at the southern base of the 
San Bernardino Mountains, and of other similar localities. The 
plants upon the areas which had most recently been water-swept 
were Baccharis viminea, Salix argophylla, S. lasiolepis, and Populus 
fremoniii, suggesting the inception of a stream-bank community, 
which can survive only as long as the stream holds its course. The 
second group, a few individuals of which enter with the first, are 
the coastal sagebrush species. The pioneer of this stage is the almost 
leafless composite Lepidospartum squamatum. Others gradually 
arrive, until a typical half-shrub community is established. Most 
important on these washes are the following: 

Syrmatium glabrum. Ramona stachyoides. Opuntia covillei. 
Eriogonum fasciculatum. polystachya. bernardina. 

Artemisia californica. Malacothamnus fasciculatus Yucca mohavensis. 

Ericameria pinifolia. splendidus. Encelia farinosa. 

Senecio douglasii. 

The last is confined to the region from San Bernardino to Elsinore, 
so far as southern California west of the deserts is concerned, and 
Opuntia covillei is replaced by 0. occidentalis farther west; otherwise 
the list is representative of the whole. Selaginella bigelovii covers 
large areas of cobbles and sand with dense growth. The third and 
final stage comes with the establishment of Adenostoma. In the 
younger areas we find it scattered, with many of the above list mingled 
with it. On the areas longer undisturbed, as well as on the higher 
terraces nearby, it forms an almost pure growth. Frequently an 
uneroded island is seen, surrounded by bare water-swept cobbles. 
Such an area is likely to possess a remnant of pure Adenostoma. 

In central California, washes, fans, and terraces are not such 
striking topographic features, perhaps because the mountain fronts 
are less abrupt and torrential erosion is therefore less powerful. 
Still, they do occur, and the same developmental stages and the same 
Adenostoma climax are present, though the successional species 
are somewhat different. 

Development on coastal dunes. — A comprehensive study of the 
strand vegetation of the Pacific Coast is now in progress. A very 


86 THE BROAD-SCLEROPHYLL VEGETATION OF CALIFORNIA. 

brief sketch must here suffice. The pioneers upon beach and dune are 
mainly strand-succulents, such as Abronia latifolia, A. maritima, 
A. urnbellata, Mesembryanthemum cequilaterale, Convolvulus soldanella, 
and Franseria bipinnatifida. These are followed by a group of 
half-shrubs, including Eriogonum parvifolium, Lupinus chamissonis, 
Ericameria ericoides, and Eriophyllum stcechadifolium. In the 
Monterey region, on an area of very ancient dunes, the succession 
may be traced farther. Adenostoma and Arctostaphylos pumila follow 
the half-shrubs and are themselves succeeded by Arctostaphylos vestita 
and other relatively less xerophytic chaparral species. This commu- 
nity is displaced by a low forest of Quercus arjrifolia, to which, on 
the Monterey Peninsula, is added Pinus radiaia. This is the local 
climax, more mesophytic in type than in the regions adjacent, 
probably because of more favorable moisture conditions. 

Secondary Successions. 

Two classes of secondary successions may be distinguished — those 
after occasional burning or clearing (where the basal portions of the 
shrubs are left to sprout) and those after thorough destruction of 
the original vegetation, either by the grubbing out of the underground 
parts or by burning at very frequent intervals. 

In the first case the succession is a short one, bringing a return 
practically to the original state in a very few years. The composition 
of the new chaparral is for a time somewhat different from what it 
was formerly because of the persistence of some of the plants which 
came in after the fire. The following outline gives the general features 
of the development as determined by a quadrat study near Palo 
Alto and observation elsewhere. Most of the species sprout readily 
from the stump, and the new shoots grow with astonishing rapidity, 
even in the driest part of the dry season. Six weeks after the Ojai 
Valley fire of June 1917, sprouts were found which had attained a 
height of nearly a meter. The sprouts therefore have a tremendous 
advantage over any seedlings that may start, especially if the fire 
occurs early in the dry season, since germination can not take place 
until the rains begin. With the first rains, seeds which have blown in 
or lain dormant germinate in enormous number and great variety. 
Among these are many of the shrub species, which gradually decline 
in number as the years pass. In a permanent quadrat 5 meters 
square, near Palo Alto, 562 shrub seedlings appeared during the 
first rainy season. Seven years later the number of survivors (in- 
cluding some new germinations) was 189. Of the first arrivals, 13 
per cent were Adenostoma and 62 per cent Ceanothus cuneatus, 
although the original growth was nearly pure Adenostoma. The 
greatest number of herbs appeared during the second rainy season. 
The 2,841 recognizable individuals comprised 28 species, of which all 
but half a dozen were annuals. Of this large number, only 13 


THE BROAD-SCLEROPHYLL VEGETATION OF CALIFORNIA. 87 

individuals survived until the following November. There is 
thus a yearly crop of annuals, smaller each season because of com- 
petition with plants of greater stature. The shrub seedlings suffer 
also in competition with the sprouts, which finally dominate the 
area. A few of the seedlings survive, however, especially those of 
Ceanothus, and form an important part of the stand for a number 
of years. Ceanothi of several species, when present in large numbers, 
seem to be indicators of recent disturbance — in other words, chaparral 
with a large proportion of Ceanothus is likely to be a penultimate 
stage in a secondary succession. 

When the chaparral is utterly destroyed, whatever the cause, 
the course of development leading to its reestablishment is usually 
an exceedingly long one. Often a community of a very different 
stamp takes possession, which, if the disturbing agency frequently 
repeats its work, may last indefinitely and simulate a true climax. 
I have already stated my conviction that the grassland of central 
California is in part a stage in a secondary succession within the region 
of the chaparral climax, and that certain trees which habitually 
grow with the grasses, notably Q. douglasii, have a role in the same 
process. If such grassland be kept moderately free from grazing 
and fire, a rough, thick growth of shrubs and half-shrubs often occu- 
pies it. These are Rhus diversiloba, Sphacele calycina, Diplacus 
glutinosus, Baccharis pilularis; and they may represent a further 
stage in the reestablishment of the climax. 

In southern California the coastal sagebrush plays an even more 
important part in the secondary successions than in the primary. 
Great areas of it cover the mesas and lower foothills, and its spatial 
relation to the chaparral is usually exactly analogous to that of the 
grassland of central California. There is the same patchy alternation 
between the two, with decrease of the half-shrubs and increase of 
chaparral as one penetrates a mountain mass. No relation to at- 
mospheric, soil, or slope factors can be made out, and the inevitable 
conclusion is that it has replaced the chaparral because of the destruc- 
tion of the latter by repeated fires which, starting in the valleys, the 
centers of human habitation, have spread varying distances into the 
foothills. Here again we find the chaparral following the forest into 
the mountains, itself followed by the coastal sagebrush, fire favoring 
the more xerophytic community in each case. The most important 
species in the secondary coastal sagebrush are Eriogonum fascicu- 
latum, Ramona nivea, R. stachyoides, and Artemisia calif ornica. 
Often they are mixed, but sometimes one encounters great stretches 
of a single species almost pure. The last two are characteristic 
secondary species as far north as Monterey Bay. In the valley of 
the Carmel River I found a deserted vineyard that was thickly 
grown up to these two species — excellent evidence of their role in 
secondary development. 


88 THE BROAD-SCLEROPHYLL VEGETATION OF CALIFORNIA. 

VI. ECOLOGICAL CHARACTER OF THE BROAD-SCLERO- 
PHYLL SHRUBS AND TREES. 

As a text for this chapter I will quote a paragraph from the pioneer 
of physiological plant geography. He is characterizing the broad- 
sclerophyll type in general (80, p. 510). 

"The trees are usually low, their stems generally massive, and the branches 
gnarled. The leaves are at most of moderate size, about as large as the leaves of 
laurel or oleander, usually smaller, or even very small; they are scarcely ever com- 
pound, as a rule narrow, lanceolate or linear to acicular; their margins are usually 
entire. The leaves are not generally placed with their flat surfaces perpendicular to 
the strongest light, but usually avoid it by assuming an oblique or parallel position. 
They are either destitute of an air-containing tomentum, or this is confined to their 
under-surface; on the other hand glandular hairs are not uncommon on both leaf- 
surfaces. Even when there is no tomentum the leaves comparatively speaking are 
seldom shiny, but more frequently, even if smooth on the surface, are dull, perhaps 
owing to exudations of resin, and often bluish. Histologically the foliage is character- 
ized by the thickness of the walls of all the cells, including even the parenchymatous 
ones, by the abundance of sclerenchyma, by the strong development of cuticle, and 
by the diminution of the intercellular spaces; these qualities in the aggregate give the 
leaf its characteristic, stiff, leathery consistency." 

In the large, this is an adequate brief characterization of the 
California broad-sclerophylls. The following detailed analysis will 
confirm Schimper's statements in the main, at the same time pointing 
out features in which the California species diverge from his generali- 
zations. 

GROWTH FORM. 

A very great majority of the California broad-sclerophylls (88 
per cent) are shrubs. In Raunkiar's scheme (83) they would be 
classed as nanophanerophytes. The height of mature individuals 
is naturally variable. Adenostoma may be found, under various 
conditions, 3 dm. high to 4 meters high. The average for all shrubby 
species, for the region as a whole, may fairly be placed between 
1.5 and 2 meters. In a single locality the height of the individuals 
of all species is usually remarkably uniform. A few species, which 
do not usually occur in abundance, habitually rise above their 
neighbors. Such are Heteromeles arbutifolia and Garry a elliptica 
and those which are potential trees. The broad-sclerophyll trees 
come mainly under Raunkiar's class of mesophanerophytes (8 to 30 
meters). Castanopsis occasionally attains a greater height, and 
probably Pasania and Arbutus also. Most of the trees reach great 
size under favorable conditions. The diameters of the largest speci- 
mens that I have measured are as follows: Quercus agrifolia, 2.1 
meters; Quercus chrysolepis, 1.8 meters; Arbutus menziesii, 1.5 meters. 
Greater diameters have been reported for these species, and Sargent 
(79) reports 3 meters as the maximum for Castanopsis, 1.8 meters 
for Pasania, and 1.5 meters for Unibellularia. 


THE BROAD-SCLEROPHYLL VEGETATION OF CALIFORNIA. 89 

The branching of the shrub species is notoriously close and intri- 
cate, and the clump habit is almost universal, partly but not wholly 
due to fire. Many of the tree species show a similar manner of 
growth— several stems from a single base (often because of fire) — and 
contorted assurgent or horizontal branches. Quercus agrifolia is a 
notable instance, with its branches of enormous size frequently 
resting on the ground. Most of the trees are marked by great 
spread of branches rather than by height. A specimen of Quercus 
agrifolia near Palo Alto shades an area 30 meters in diameter, and 
this is not an extreme case. The deliquescent mode of branching 
is the rule. Even when there is a distinct trunk, it is soon lost in 
the branches. Pasania and Castanopsis exhibit the closest approach 
to the excurrent type, maintaining a distinguishable trunk almost 
throughout. Young specimens of Umbellularia show the same form 
very perfectly, so that one frequently takes them at a distance to 
be conifers. Large trees of this species are usually branched near 
the base, but the separate stems maintain the excurrent form. 

This seems an appropriate place to mention the small but con- 
spicuous group of species which have more or less spinescent branches. 
These are Xylothermia montana, Ceanothus cordulatus, C. divaricatus, 

and C. incanus. 

ROOT SYSTEM. 

Somewhat scanty evidence indicates that the root systems of 
the chaparral shrubs, when growing in loose soil, are prevailingly 
of the "dual type" described by Cannon (19). Such root systems 
are in part deeply penetrating and in part superficial, the latter 
making up the greater bulk. Cannon states that the sclerophyll 
Quercus agrifolia and the deciduous Q. douglasii and ALsculus cali- 
fornica are of this type, and suggests that the deeply penetrating 
roots, which may reach to the neighborhood of the water-table, 
are formed in youth, while the more numerous superficial roots 
are developed later. 

The root system of a large specimen of Adenostoma growing on 
Jasper Ridge near Palo Alto was carefully excavated and charted 
(fig. 19). This plant grew in a spot where the soil was pure sand, 
gradually compacted downward into undecomposed sandstone. 
It was impossible to trace the roots to a greater depth than a meter, 
and this was the only locality on the ridge where excavation was 
feasible at all. The plant grew close to station 10 of the habitat 
study series. Its root system was decidedly of the dual type. 
Figure 19 (lower), drawn as if the roots grew all in one plane, exhibits 
their vertical distribution. It is very common for a large root, at 
first horizontal, to bend suddenly downward. Several such, lost at a 
depth of a meter, were 6 to 7 mm. thick at that point. No tap-root 
or anything approaching it was found, though every seedling possesses 


90 THE BROAD-SCLEROPHYLL VEGETATION OF CALIFORNIA. 


a well-developed one. Small branches of 1 mm. or less diameter 
were given off rather regularly, but at long intervals, all along the 
main roots. These terminated in groups of mycorhizal rootlets 
which were embedded in masses of sand-grains held loosely together 
by hyphae. 


Fig. 19. — Root system of Adenostoma fasciculatum: upper drawing shows hori- 
zontal, lower shows vertical distribution. In the latter case the roots 
are arbitrarily drawn as if growing in one plane. 

Another excavation of considerable extent was made nearby to 
learn something of the subterranean relations between the chaparral 
shrubs and the lower plants that accompany them. The dominants 
here were Adenostoma fasciculatum, Quercus durata, and Arctostaphylos 
tomentosa. The individuals grew rather far apart, and therefore 
the accompanying species were more numerous than usual. A second 
stratum included Eriodictyon californicum, Rosa californica, Helian- 
themum scopariu?n, Diplacus glutinosus, and Syrmatium glabrum, 
low shrubs and half-shrubs. A third stratum comprised Micromeria 
chamissonis, Gymnogramme triangularis, and a few grasses. Below 
the surface only two strata were distinguishable. The upper one, 
about 20 cm. in depth, with some humus, was fairly well filled with 
the roots from the second and third aerial strata, together with great 
numbers belonging to the dominants, which were most conspicuous 
because of their large size. Below 20 cm. were found only the scat- 
tered, deeply penetrating roots of the dominants. 


THE BROAD-SCLEROPHYLL VEGETATION OF CALIFORNIA. 91 

General observation shows that the three principal species of 
Jasper Ridge, Adenostoma, Quercus, and Arctostaphylos, all possess 
the dual root system. Its usefulness is apparent. During the winter 
and spring, when most of the year's growth is accomplished, the 
abundant superficial roots absorb large quantities of water. The 
humus in this stratum both increases water-retaining capacity and 
adds to the supply of other food materials. During the dry summer 
the deeply penetrating roots supply the plant with the minimum 
amount of water necessary to tide it over the critical period. It is 
inevitable, when one recalls the extreme desiccation of the surface 
soils, that the superficial roots cease functioning during the dry 
season. The dual system is of course apparent only in plants growing 
in ordinary soil. Where the rock is at the surface, which is very fre- 
quently the case, the roots penetrate the crevices wherever they can, 
without observable system. 

Eriodictyon californicum has a very different root plan (fig. 20). 
The main roots are few, and they travel close to the surface, often 
from 1 to 6 cm. below it, and occasionally one turns abruptly down- 


Fig. 20. — Root system of Eriodictyon californicum. For explanation, see fig. 19. 

ward to the deeper soil-layers. From the horizontal portions 
sucker shoots appear, so that a number of apparently independent 
plants are often found to be connected below ground. Whenever 
the roots are exposed, as by erosion, they produce shoots abundantly. 
The roots of Eriodictyon are useful, therefore, for propagation as well 
as for absorption. 

The three principal chaparral species of Jasper Ridge, Adenostorna 
fasciculatum, Quercus durata, and Arctostaphylos tomentosa, have 
been proved to be mycorhizal. In the excavations no normal root- 
hairs were seen, but it is hardly reasonable that the most deeply 
penetrating roots should be associated with fungi. The mycorhizas 


92 THE BROAD-SCLEROPHYLL VEGETATION OF CALIFORNIA. 

are most abundant naturally in the upper soil layers, where there is 
most humus. Pockets of nearly pure humus were occasionally 
found, probably derived from rotted roots, which were thoroughly 
penetrated by the coralloid rootlets. The mycorhizas were by no 
means confined to the regions of abundant humus, however. The 
roots which penetrated the pure sand below the humus layer were 
almost as well supplied with the fungi. In station 2, where the soil 
is merely a slightly decomposed clayey sandstone, well-developed 
mycorhizal roots of Arctostaphylos were taken from tight crevices 
between the fragments. 

The best material for study was obtained from Quercus durata. 
The last few centimeters of the roots were found to branch freely, 
giving off numerous clumps of blunt-tipped coralloid rootlets, each 
clump firmly embedded in a mass of sand-grains bound together by a 
network of fungal hyphse. The hyphse were of two kinds: (1) very 
small, transparent, branched, quite certainly non-septate, much 
more abundant than (2), doing most of the sand-binding; (2) diameter 
twice or thrice that of (1), branched, very dark brown, some opaque, 
others only partially so, plainly septate. What appeared to be 
tight bundles of hyphse of the septate type were seen, simulating 
rootlets. A cross-section of a mycorhizal root of this species is 
given in plate 20a. The dense felt of mycelium completely sheathing 
the root is well shown, and the hyphse are seen to penetrate between 
the cells of the cortex, so that some of the outer ones are apparently 
isolated from their neighbors. The strands which originally extended 
out into the soil have, of course, been lost in the process of slide- 
making. 

THE LEAF. 
THE DECIDUOUS ELEMENT. 

Of the 91 species listed on pages 113 to 120 as being included in the 
broad-sclerophyll communities as dominants, 18 or 19.8 per cent 
are deciduous. These are as follows (two or three species which lose 
their leaves in late winter or spring are classed as evergreens) : 

Corylus rostrata californica.* Amelanchier alnifolia.* Acer macrophyllum.* 

Quercus brewed. Prunus demissa.* ^Esculus californica. 

douglasii. emarginata.* Ceanothus integerrimus. 

garryana.* subcordata. parryi. 

kelloggii. Cercis occidentalis. parvifolius. 

lobata. Acer glabrum.* sanguineus.* 

Omitting those which are not characteristically Californian 
(marked by asterisk), the number is reduced to 10, or 11 per cent. 
The relation of the evergreen habit to the Californian habitat is 
further shown bjr a comparison of the three communities. The 
climax chaparral, most characteristically Californian, with a total 
of 44 dominant species, has no deciduous dominants, the broad- 
sclerophjdl forest, with the small total of 13, has 4 deciduous, or 


THE BROAD-SCLEROPHYLL VEGETATION OF CALIFORNIA. 93 

30.8 per cent, the conifer forest chaparral, with 29 dominants, has 
12 deciduous, or 41.4 per cent. Of these 12, 7 are not characteristic- 
ally Californian, ranging far beyond the boundaries of the State. 
It is thus evident that the most characteristically Californian com- 
munity is made up entirely of evergreens, so far as its dominants are 
concerned, and that the community which has the greatest proportion 
of deciduous species is also the least characteristically Californian. 
Further discussion of the leaf will be confined to the evergreen species, 
or, in other words, to the broad-sclerophylls. 

EXTERNAL CHARACTERS. 

Compound leaves. — Of the 74 broad-sclerophyll species, only 2 
have compound leaves. These are Berberis pinnata and Xylothermia 
montana. The leaves of the first are pinnate, with 5 to 9 leaflets, 
and the second palmate, ordinarily with 3 leaflets. In the measure- 
ments to follow, the individual leaflet of these species has been taken 
as the unit. 

Form. — Lobing is still rarer. Fremontodendron californicum is 
the only species, and even in this many of the leaves are unlobed. 
In shape there is great uniformity. Of the 71 species which are 
neither compound nor lobed, 54 are of the oval tj^pe, ranging from 
orbicular through elliptic to ovate, the great majority being elliptic. 
Ten are distinctly obovate, 5 are lanceolate or oblanceolate, and 2 
(genus Adenostoma) are linear and terete. Adenostoma fasciculatuw. , 
the most important single species, is not a frroad-sclerophyll at all, 
but, as already suggested, this is hardly sufficient ground for dis- 
carding for the whole type that very satisfactory appellation. 

Size. — It is well known that leaf-size is a fairly trustworthy measure 
of habitat, especially of the moisture element. Raunkiar has pro- 
posed an ecological classification of plants upon the basis of this 
character, which has been recently brought to our attention in the 
translation by Fuller and Bakke (31). He has established several 
size-classes based upon the surface area, the upper limits of which are 
as follows: 

sq. mm. 

1 . Leptophyll 25 

2. Nanophyll (9 by 25 sq. mm.) 225 

3. Microphyll (9 2 by 25 sq. mm.) 2,025 

4. Mesophyll (9 3 by 25 sq. mm.) 18,225 

5. Macrophyll (9 4 by 25 sq. mm.) 164,025 

6. Megaphyll 

Some other delimitation of the classes would have served much 
better for the broad-sclerophylls of California, since most of the 
leaves seem to group themselves about the division-lines, but for 
the sake of comparison with other regions it is better to hold to the 
system that Raunkiar has established. All the leaves to be classified 
here come under the first four classes, and it may be helpful to state 


94 THE BROAD-SCLEROPHYLL VEGETATION OF CALIFORNIA. 


that a leptophyll, if of the common elliptic form, will be about 9 mm. 
or less in length, and that the upper length limits of the next three 
classes, assuming the same leaf -form, will be approximately 27 mm., 
81 mm., and 243 mm. The sizes of the leaves were determined by a 
study of the specimens in the herbarium of the University of Minne- 
sota, which has an excellent representation of the Californian flora. 
To provide for cases in which a species overlaps two classes, three 


36 


34 


32 


30 


28 


26 


io24 


Id 


U 22 


Id 


$20 


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or 16 


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* 14 


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I i 


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\ \ 


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/ / 
/ / 
/ / 


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10 


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/ * 

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/ i 


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LN 


N 
Total 


NMi 


Mi 


MiMe Me 


Climax Chaparral 

Conifer Forest Chaparral 

Broad-sclerophyll Forest 

Fig. 21. — Leaf size in the broad-sclerophyll communi- 
ties. See text. 

intermediate categories were made. Because such a large number 
were found to cluster around the division-lines, it was thought best 
to include also in the intermediate classes those which were con- 
sistently very close to the limit, though not actually crossing it, so 
far as was shown by the specimens examined. 

Figure 21 gives the results of the study. The generally small size 
of leaf is manifest, all but 1 1 of the 74 species falling within the three 
lowest classes — leptophylls, nanophylls, and microphylls. Further- 


THE BROAD-SCLEROPHYLL VEGETATION OF CALIFORNIA. 95 

more, there is a very decided maximum in the NMi region, practically 
half of all being in this class. Species with very small leaves are 
scarce, though it must not be forgotten that Adenostoma fasciculatum, 
most important of all, is one of these. Considering the vegetation 
by communities, we find that of 42 important species of the climax 
chaparral nearly half are of the NMi class, with the rest well dis- 
tributed on both sides of it. Of 17 species of the conifer forest 
chaparral, those of class NMi compose nearly one-half, but the 
others are all of larger classes. Of the 9 broad-sclerophyll forest 
species, none are smaller than Mi and the maximum lies in the class 
MiMe. There is thus shown a relation between leaf-size and habitat, 
the community living in the driest habitat having the largest pro- 
portion of small leaves. There is also a correlation between size of 
leaf and size of plant, since the trees of the broad-sclerophyll forest 
show consistently greater leaf-size than the shrubs of either of the 
two chaparral communities. 

Attitude. — In the majority of species the leaves lie horizontally, 
but there is a small group with vertically placed leaves. Certain 
species of Arctostaphylos are prominent here, especially A. glauca, 
A. hookeri, and A. viscida. In many others there is a more or less 
prevalent tendency toward the vertical position. Dendromecon 
rigidum has leaves that are ordinarily vertical, but, as in many other 
cases, they are horizontal in the more mesophytic situations. 

Margin. — A majority of the 74 species (58.1 per cent) have entire- 
margined leaves, although a number of these may show occasional 
dentation, especially on stump sprouts. 24.3 per cent have leaves 
that are more or less toothed in the normal fashion; they are serrate, 
dentate, or crenate. In nearly every case the teeth are shallow. A 
smaller but conspicuous and characteristic class (17.6 per cent) 
have notably spiny-toothed leaves that may be aptly described as of 
the holly type. The resemblance in leaf character between the 
various species of this group is often striking. This is particularly 
true of Prunus ilicifolia and Rhamnus crocea, whose leaves are 
frequently so similar as to require very minute examination to dis- 
tinguish them. Eight species (10.8 per cent) have leaves with notably 
revolute edges. This character appears inconstantly in a number of 
others. 

Pubescence. — Pubescence is not a prominent feature of the broad- 
sclerophylls. Of the 74 species, 48.7 per cent have more or less 
pubescent leaves, but in only 17.6 per cent are thej r pubescent on 
both surfaces, and often the covering is sparse. The leaves with 
hair-filled cavities are not considered here unless the hairiness is 
evident to superficial examination. 

Miscellaneous. — Two species, Eriodictyon californicum and Ceano- 
thus velutinus, have leaves that are varnished and glutinous on the 


96 THE BROAD-SCLEROPHYLL VEGETATION OF CALIFORNIA. 


upper surface. In both they are pubescent below. A few species of 
Ceanothus and Arctostaphylos have more or less sticky-glandular 
leaves. Three species commend themselves to the sense of smell — 
Myrica calif ornica, Umbellularia californica, and Eriodictyon cali- 
fornicum. The last two are widespread and common, and thus give 
the broad-sclerophyll vegetation a reputation for odoriferousness 
which it hardly deserves. 

The external characteristics of the 74 species are presented in 
detail in table 12. 

Table 12. — External leaf character. 


Corn-pound (2.7 p. ct.): 
Berberis pinnata. 
Xylothermia montana. 
Lobed (1.4 p. ct.): 

Fremontodendron califor- 

nicum. 
Size: 

Leptophylls (4.1 p. ct.): 

Adenostoma fascicu- 
latum. 

A. sparsifolium. 

Ceanothus dentatus. 
Nano-leptophylls(2.7p.ct.) : 

Ceanothus foliosus. 

C. rigidus. 
Nanophylls (9.5 p. ct.): 

Cneoridium dumosum. 

Ceanothus cuneatus. 

C. pinetorum. 

C. prostratus. 

C. verrucosus. 

Arctostaphylos myrti- 
folia. 

A. nummularia. 
Nano-microphylls (45.9 
p. ct.): 

Quercus dumosa. 

Q. durata. 

Q. vaccinifolia. 

Cercocarpus betulse- 
folius. 

C. ledifolius. 

Xylothermia montana. 

Rhamnus crocea. 

Ceanothus cordulatus. 

C. crassifolius. 

C. divaricatus. 

C. diversifolius. 

C. hirsutus. 

C. incanus. 

C. megacarpus. 

C. papillosus. 

C. sorediatus. 

C. spinosus. 

C. thyrsiflorus. 

C. tomentosus. 

Arctostaphylos drupacea. 

A. glauca. 

A. hookeri. 

A. manzanita. 

A. mariposa. 

A. montana. 


Size— Cont'd. 
Nano-microphylls (45.9 

p. ct.) Cont'd. 
A. nevadensis. 
A. parryana. 
A. patula. 
A. pumila. 
A. pungens. 
A. stanfordiana. 
A. tomentosa. 
A. vestita. 
A. viscida. 
Microphylls (20.3 p. ct.): 
Castanopsis semper- 

virens. 
Quercus chrysolepis. 
Q. engelmanni. 
Q. wislizeni. 
Berberis pinnata. 
Dendromecon rigidum. 
Prunus ilicifolia. 
Rhamnus californica. 
Ceanothus palmeri. 
Fremontodendron cali- 

fornicum. 
Garrya elliptica. 
G. fremontii. 
Comarostaphylis diver- 

sifolia. 
Xylococcus bicolor. 
Arctostaphylos ander- 

sonii. 
Micro-mesophylls (14.9 p. ct.) 
Myrica californica. 
Castanopsis chryso- 

phylla. 
Quercus agrifolia. 
Pasania densifiora. 
Umbellularia californica. 
Heteromeles arbutifolia. 
Rhus integrifolia. 
R. laurina. 
R. ovata. 

Ceanothus velutinus. 
Eriodictyon calif ornicum. 
Mesophylls (2.7 p. ct.): 
Quercus sadleriana. 
Arbutus menziesii. 
Margin: 

Entire (58.1 p. ct.): 

Castanopsis chrysophylla. 
C. sempervirens. 


Margin — Cont'd. 

Entire (58.1 p. ct.) Cont'd. 
Quercus vaccinifolia. 
Umbellularia californica. 
Dendromecon rigidum. 
Cercocarpus ledifolius. 
Adenostoma fascicu- 

latum. 
A. sparsifolium. 
Xylothermia montana. 
Cneoridium dumosum. 
Rhus integrifolia. 
R. laurina. 
R. ovata. 

Rhamnus californica. 
Ceanothus cordulatus. 
C. cuneatus. 
C. divaricatus. 
C. hirsutus. 
C. incanus. 
C. megacarpus. 
C. palmeri. 
C. spinosus. 
Garrya elliptica. 
G. fremontii. 
Arbutus menziesii. 
Xylococcus bicolor. 
Arctostaphylos drupa- 
cea. 
A. glauca. 
A. hookeri. 
A. manzanita. 
A. mariposa. 
A. montana. 
A. myrtifolia. 
A. nevadensis. 
A. nummularia. 
A. parryana. 
A. patula. 
A. pumila. 
A. pungens. 
A. stanfordiana. 
A. tomentosa. 
A. vestita. 
A. viscida. 
Toothed (24.3 p. ct.): 
Myrica californica. 
Quercus engelmanni. 
Q. sadleriana. 
Pasania densifiora. 
Cercocarpus betula?- 
folius. 


Species- density of broad-sclerophylls, shown by depth of shading, in California and in western North America. 


,3^ 


3 Ml 


* 70* x\ ( 


~\ .'s 1 xes^ — \ ~~i 


/ L 
X / ■= 

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-TOTAL PRECIPITATION 


|k 


4 7. O^hM 

p>escott r^-. 

\ K \ 

^^HOENIX yl 


' j / .ci 

¥ J i 


1VL— T 


Less than 10 in. 
I0to30in. 

. More than 30ln. 


c zo^Cr \ A. 

V %. /30T-~^J \ / \ 


s US 1 1 

xJ\t e x ^f 
c o l\ \_>-^v 


100 


200 300 *00 500 MILES 


distribution of invcipihition in western Nurth America, and average total sea^jmil precipitation in region with \v 
than 20 per cent summer precipitation. 


Distribution of Adenostoma fascicuiatum: dots show autnentic localities; solid black, areas where it has been accurately mapped 
as dominant; crosses show localities which are doubtful or where it probably does not exist at the present time. 


COOPER 


A. Subalpine forest zone in the northern Sierras: conifer-forest chaparral m 

foreground; Mount Lassen in the distance. 

B. Secondary thicket growth of Quercus kelloggii and (J. garryana, with relicts 

of Pinus ponderosa and Pseudotsuga mucronata. South Fork Mountain. 
Trinity County. 

C. Conifer-forest chaparral association: Arctostaphylos patida, A. nevadensis, 

Castanopsis sempervirens, Ceanothus velutinus, Quercus vaccinifolia, Amel- 
anchier alnifolia; remnants of climax forest. Near Mount Lassen, northern 
Sierras. 


A. Transition between broad-sclerophyll and redwood forests: a group of redwoods on 

flood-plain in left center; broad-sclerophvll forest (Pasania-Quercus-Arbutus associa- 
tion) at right, with admixture of Pseudotsuga. South Fork of Eel River, Humboldt 
Count v. 

B. Undergrowth of Quercus agrifolia-Arbutu* association: Symphoricarpox racemosus 

most abundant. Near Palo Alto. Santa Clara County. 


A 


A Quercus agrifolia-lobata association on alluvial fan: winter aspect, the (J. lobat., leaf- 
less. Atherton, San Mateo County. 
H Quercus chrysolepis consociation fsuccessional) on talus. Yosemite Valley. 


A. Alternation of chaparral (Adenostoma consociation) and broad-selerophvll forest 

correlated with south and north-facing slopes. The trees in the immediate foreground 
are secondary oaks in a grassy area. Santa Lucia Mountains, Monterey County. 

B. Alternation of chaparral (Adenostoma consociation) and broad-sclerophyll forest 

(Quercus agrifolia-Arbutus association), corresponding with south and north facing 
slopes; Quercus agrifolia, Q. kelloggii, Arbutus menziesii, and Umbellvlaria californica 
(conical form) prominent in the latter; chaparral somewhat disturbed. Chaparral 
(Arctostaphylos dominance) at the top of the north facing slope; also a clearing. 
Permanente Canon, east slope of Santa Cruz Mountains, near Black Mountain. 


A. Vegetation cover of lower Cuyamaca Mountains: chaparral on all slopes; 

occasional broad-sclerophyll trees. Viejas Grade, San Diego County. 

B. Chaparral cover of Santa Lucia Mountains: Adenostoma most abundant; 

Arctostaphylos glauca (light tone) at left; Quercus agrifolia in ravine ai 
right; occasional dead stalks of Yucca whipplei; secondary grassy areas. 
Near Tassajara Springs, Monterey County. 

C. Mountains of Ventura County, solidly clothed with chaparral. Near Wheeler 

Hot Springs. 


A. Chaparral of Adenostoma fasdcvlatum and Ceanothus crassifolius (light), 

a common combination in southern California. Near Wheeler Hot Springs, 
Ventura County. 

B. Ground cover at Station 3, Jasper Ridge; relatively abundant litter beneath 

Arctostaphylos. 
C Station 2, Jasper Ridge, showing atmometers in position. 


A. Ja •!>■!' Ridge: vicinity of Station 3 from Station t: Arcto i and 

(jut reus durata. 

B. South-facing slope at Jasper Elidge upon which Stations4 and 5 are located; from vicinity 

of Station 3. 


W^rm 


# 


SigP 


j»^. 

%£ 


A 


A. Quercus agrifolia-Arbutus association on north slope at Jasper Ridge; Stations 7 and S 

are in the area of the picture; chaparral at ridge top. 

B. Typical scenerv of the interior north Coast Ranges, where the dominating vegetation 

is a mixture of broad-sclerophylls and conifers, especially Psetidotsuga mucronata: 
secondary grassy areas; Mount St. Helena. 


A. Remnant of chaparral (Adenostoma consociation on the floor of the Sacramento 

Valley, in Colusa County, south of Arbuckle; Coast Range in the distance. 

B. Adenostoma consociation on cast slope of north Coast Ranges: clearing and 

secondary grassland with Finns sabiniana and Quercus douglasii growing with 
the latter; Pinus ponderosa on distant ridges. Beegum, Tehama County. 

C. R< mnant of original chaparral cover on the slope of an isolated mountain; sec- 

ondary grassland, with abundant cattle trails; live oaks in ravines. Mount 
Diablo, Contra Costa County- 


A. Primary succession in the climax chaparral region: lichens and mosses 

on rock surface; Adenostoma, Arctostaphylos, and Yucca as crevice 
pioneers. Cuyamaca Mountains, San Diego County. 

B. Later stage of succession, showing the preeminent importance of the 

crevices. Same locality as the last. 

C. Fully developed chaparral (Adenostoma consociation) with Yucca 

whipplei. Same locality as the last. 


.dj% 


A 


Primary succession on alluvial fan: recent wash with scattered pioneers ol 
numerous species; low terrace at right with partially developed Adenostoma 
climax; uneroded remnant at left with Adenostoma. Mill Creek Wash, south 
base of San Bernardino Mountains. 

B. Primary succession on alluvia! fan: coastal sagebrush on old wash; Syrmahum 

glabrum, Eriogonum fascicvlatum, and others; Adenostoma climax on terrace. 
Mill Creek Wash, south base of San Bernardino Mountains. 

C. Coastal sagebrush on south-facing unstable slope: Ramona stachyoides, 

Artemisia californica, Eriogonum fasciculaium, Eneelia farinosa. Smiley 
Heights, near Hedlands. 


•it: .. ■■ . 


■>-.■■ «r ■•-Jft* 


A 


* . s 


Young stump sprouts of Adenostoma fascictdatum. 

Destruction of chaparral bv the Ojai Valley fire of June 1917; underground parts 
killed in many cases; edge of burned area at top of ridge. Near Wheeler Hot Springs 


A. Chaparral-covered mountains north of Arrowhead Springs. San Bernardino Mountains; 

fire-restricted remnants of Pseudotsuga macrocarpa. 

B. Rebel patches of chaparral (Adenostoma consociation'; secondary grassland on ridge 

top; secondary coastal sagebrush on slopes too steep for grazing. ° San .lose Canon. 
Monterey County. 


A 


^ 


A. Quercus durata: cross-section of mycorhizal rootlet; note the thick external felt of 

mycelium, and the hyphae penetrating between the cells of the cortex. X 170. 

B. AdenoatomafasciLulaliun: cross-section of normal leaf. X 75. 

C. Adenostoma fascicvlatum: cross-section of leaf from stump sprout. X 70. 

D. Adenostoma fasciculatum: cross-section of leaf from seedling. X 70. 


a 


\ ) \ \t ( 


B 


A. Adenostoma fascicvlatum: a is the normal xerophytic type; 6 is from 
a shady mesophytic situation (Station 7 at Jasper Ridge). 

15. Adenostoma fasciculatum: upper row, normal leaves; middle, leaves 
from a stump sprout; lower, from seedlings. 


THE BROAD-SCLEROPHYLL VEGETATION OF CALIFORNIA. 97 


Table 12. — External leaf character — Continued. 


Margin — Cont'd. 
Toothed — Cont'd. 

Ceanothus dentatus. 

C. diversifolius. 

C. foliosus. 

C. papillosum. 

C. sorediatus. 

C. thyrsiflorus. 

C. tomentosus. 

C. velutinus. 

C. verrucosus. 

Fremontodendron cali- 

fornicum. 
Comarostaphylis diver- 

sifolia. 
Arctostaphylos ander- 

sonii. 
Eriodictyon calif ornicum. 
Spiny-toothed (17.6 p. ct.): 
Quercus agrifolia. 
Q. chrysolepis. 
Q. dumosa. 
Q. durata. 
Q. wislizeni. 
Berberis pinnata. 
Heteromeles arbutifolia. 
Prunus ilicifolia. 
Rhamnus crocea. 
Ceanothus crassifolius. 
C. pinetorun. 
C. prostratus. 
C. rigidus. 
Revolute (10.8 p. ct.): 
Quercus durata. 
Cercocarpus ledifolius. 
Rhamnus californica. 
Ceanothus crassifolius. 
C. dentatus. 
C. papillosus. 
Garrya elliptica. 
Xylococcus bicolor. 
Surface: 

Glabrous (52.7 p. ct.) : 
Myrica californica. 
Quercus agrifolia. 
Q. vaccinifolia. 


Surface — Cont'd. 

Glabrous (52.7 p. ct.) Cont'd. 

Q. wislizeni. 

Umbellularia califor- 
nica. 

Berberis pinnata. 

Dendromecon rigidum. 

Heteromeles arbuti- 
folia. 

Adenostoma fascicu- 
latum. 

A. sparsifolium. 

Prunus ilicifolia. 

Xylothermia montana. 

Cneoridium dumosum. 

Rhus integi ifolia. 

R. laurina. 

R. ovata. 

Rhamnus crocea. 

Ceanothus cordulatus. 

C. divaricatus. 

C. foliosus. 

C. palmeri. 

C. pinetorum. 

C. prostratus. 

C. spinosus. 

C. thyrsiflorus. 

C. verrucosus. 

Arbutus menziesii. 

Arctostaphylos drupa- 
cea. 

A. glauca. 

A. hookeri. 

A. manzanita. 

A. myrtifolia. 

A. nevadensis. 

A. nummularia. 

A. parry ana. 

A. patula. 

A. pungens. 

A. stanfordiana. 

A. viscida. 
Lower surface pubescent 
(31.1 p. ct.): 

Castanopsis chryso- 
phylla. 

INTERNAL STRUCTURE. 


Surface — Cont'd. 

Lower surface pubescent 

(31.1 p. ct.) Cont'd. 
C. sempervirens. 
Quercus chrysolepis. 
Q. dumosa. 
Q. engelmanni. 
Q. sadleriana. 
Pasania densifiora. 
Cercocarpus betulae- 

folius. 
C. ledifolius. 
Ceanothus crassifolius. 
C. cuneatus. 
C. incanus. 
C. megacarpus. 
C. rigidus. 
C. sorediatus. 
C. velutinus. 
Garrya elliptica. 
G. fremontii. 
Comarostaphylis diver- 

sifolia. 
Xylococcus bicolor. 
Arctostaphylos ander- 

sonii. 
A. pumila. 
Eriodictyon californi- 

cum. 
Both surfaces pubescent 

(16.2 p. ct.): 
Quercus durata. 
Rhamnus californica. 
Ceanothus dentatus. 
C. diversifolius. 
C. hirsutus. 
C. papillosus. 
C. tomentosus. 
Fremontodendron cali- 

f ornicum. 
Arctostaphylos mari- 

posa. 
A. montana. 
A. tomentosa. 
A. vestita. 


I have examined the leaves of 26 of the representative broad- 
sclerophyll species of the central Coast Ranges. 7 are trees of the 
broad-sclerophyll forest and the others are shrubs of the climax 
chaparral. All the important genera are well represented, and it is 
reasonable to assume that the selection presented here gives a true 
picture of Californian broad-sclerophyll structure. The material 
was collected near Palo Alto and in the Monterey region. It was 
killed and preserved in formalin-alcohol, cut in celloidin, and stained 
with safranin and aniline blue. 17 species have been selected for 
illustration by means of drawings executed by Miss Vinnie A. Pease, 
of the University of Minnesota. In addition to the general study, 


98 THE BROAD-SCLEROPHYLL VEGETATION OF CALIFORNIA. 


measurements were made of thickness of leaf and of upper and lower 
cuticle in each species (table 13). For the sake of comparison, a 
group of two sclerophyll species of the redwood-forest undergrowth 
and one of 5 native deciduous trees have been added. The figures 
given in the table are averages of 10 measurements, made in nearly 

Table 13. — Thickness of leaf and cuticle. 


Broad-sclerophyll forest: 

Myrica californica 

Castanopsis chrysophylla 

Quercus agrifolia 

Q. chrysolepis 

Pasania densiflora 

Umbellularia californica 

Arbutus menziesii 

Climax chaparral: 

Quercus durata 

Berberis pinnata 

Dendromecon rigidum 

Heteromeles arbutifolia 

Adenostoma fasciculatum 

Prunus ilicifolia 

Xylothermia montana 

Rhamnus californica 

R. crocea 

Ceanothus cuneatus 

C. papillosus 

C. rigidus 

C. sorediatus 

Garrya elliptica 

Arctostaphylos hookeri 

A. pumila 

A. tomentosa 

A. vestita 

Eriodictyon californicum 

Redwood-forest undergrowth : 

Gaultheria shallon 

Vaccinium ovatum 

Deciduous species: 

Salix lasiolepis 

Alnus rhombifolia 

Quercus lobata 

Platanus racemosa 

Acer macrophyllum 

Summaiy: 

1. Broad-sclerophyll forest 

2. Climax chaparral 

3. Average of classes 1 and 2. . . 

4. Redwood-forest undergrowth. 

5. Deciduous species 


Leaf. 


microns. 
80 
254 
314 
219 
217 
208 
264 

205 
178 
371 
339 
562 
345 
385 
265 
246 
462 
214 
472 
224 
365 
398 
362 
355 
264 
345 

432 
365 

111 

111 
160 
149 
106 

222 
336 
314 
398 
127 


Upper 
cuticle. 


microns. 
3.08 
2.63 
3.75 
3.75 
2.85 
5.58 
2.96 

2.94 
3.82 
4.20 

11.58 
9.73 
3.98 
5.85 
8.25 
5.28 
4.65 
2.25 
6.86 
1.12 

17.25 

11.82 
8.85 
9.89 

12.10 
1.24 


05 

.57 

35 
12 
06 
21 
16 


3.52 
6.36 
5.69 
4.31 

1.58 


Lower 

cuticle. 


microns. 
1.84 
1.39 
1.80 
2.59 
2.06 
3.78 
1.80 

3.21 

2.81 
2.67 
7.57 
9.66 

2.81 


68 
49 
17 
96 
08 
50 
12 
52 


11.63 

5.77 

11.32 

11.44 

1.05 

2.51 
1.61 

6.37 

7.50 

12.75 

12.00 

6.75 

2.04 
5.23 
4.43 
2.06 
.91 


every case upon 10 separate leaves, except in Adenostoma fasci- 
culatum, Arctostaphylos tomentosa, and Quercus durata, where the 
averages are of 40 to 50 separate leaves. 

The following order has been determined upon in the descriptions : 
(1) general; (2) mesophyll; (3) epiderm; (4) stomata; (5) special 
features. 


THE BROAD-SCLEROPHYLL VEGETATION OF CALIFORNIA. 99 


Broad-sclerophyll Forest. 

Myrica californica.-(l) The thinnest of all the leaves studied. (2) Bifacial. Pali- 
sade tissue of one complete and one partial layer, occupying one-third of the mesophyll; 
in some places a suggestion of palisade layer next to the lower epiderm; sponge very loose. 
(4) Stomata on lower side only, slightly elevated. (5) A sheath of tannin-filled cells 
surrounds the bundles; occasional peltate glands in depressions on both surfaces. 

Castanopsis chrysophylla (fig. 22).— (1) The specimens examined are of var. minor, from 
Monterey, and the leaves are probably somewhat more xerophytic in structure than those 
of the typical tree-form of the northern Coast Ranges. (2) Bifacial. Mesophyll dense; 
palisade tissue about four layers deep, occupying a little less than half the mesophyll, 
composed of rather crowded oval or nearly globular cells. (3) Epiderm, no special fea- 


Fig. 22. — Castanopsis chrysophylla: section of leaf . X125. 

Fig. 23. — Quercus agrifolia: section of leaf. X125. 

Fig. 24. — Umbellularia californica: section of leaf. X125. 


25 


26 


Fig. 25. — Arbutus menziesii: section of leaf. X 125. 
Fig. 26. — Quercus durata: section of leaf. X125. 

tures; incomplete hypoderm on both sides, mainly related to veins. (4) Stomata on lower 
side only, slightly elevated, surrounded by collar-like ridges. (5) Tannin in cells sur- 
rounding bundles and in hypoderm; struts of mechanical tissue from epiderm to epiderm, 
following veins; multicellular trichomes covering lower surface, producing a golden fuzz. 
Quercus agrifolia (fig. 23).— (2) Leaf bifacial but not perfectly so. Palisade tissue about 
three to four layers deep, occupying about half the mesophyll and merging gradually into 
the sponge, the cells of which are mostly elongated perpendicularly to the surface, thus 
possessing palisade character; one or two incomplete palisade layers on lower side also. 
(4) Stomata on lower side only. (5) Struts of mechanical tissue as in Castanopsis, but 
more pronounced. 


100 THE BROAD-SCLEROPHYLL VEGETATION OF CALIFORNIA. 

Quercus chrysolepis. — The specimens are from the shrubby chaparral form. Even so, 
they exhibit less of xerophytic character than the last, in that they are more perfectly 
bifacial and that the sponge is more typical. Otherwise they are essentially like those of 
Q. agrifolia. 

Pasania de>mflora.—(2) Bifacial. Palisade tissue about two layers in depth, occupy- 
ing less than half the mesophyll; sponge not abundant, most of the space being taken up 
by groups of large, thin-walled parenchyma cells, apparently water-storage tissue. (3) A 
complete layer of hypoderm beneath the upper epiderm and resembling it; lower epiderm 
papillate. (4) Stomata on lower side only. (5) Struts of mechanical tissue like those of 
the other members of the family. 

Umbellularia calif ornica (fig. 24).— (2) Imperfectly bifacial. Palisade tissue two layers 
in depth, occupying half the mesophyll, and an imperfect layer next to the lower epiderm; 
large oil-cells in both palisade and sponge, many of those on the lower side being enlarged 
elements of the epiderm (84, p. 703). (4) Stomata on lower side only. 

Arbutus menziesii (fig. 25). — (2) Bifacial. Palisade tissue of two complete rows, occu- 
pying^one-third orjmore of the mesophyll. (3) Lower epiderm minutely papillate. (4) 
Stomata on lower 'side only, with small exterior chamber formed by a collar-like ridge. 
(5) Tannin very abundant, almost throughout the mesophyll. 


Fig. 27. — Dendromecon rigidum: section of leaf. 
Fio. 28. — Dendromecon rigidum: stoma. X375. 

Climax Chaparral. 

Quercus durata (fig. 26).— (2) Imperfectly bifacial. Palisade tissue about three layers 
deep, making half the mesophyll; sponge rather loose, but cells palisade-like. (3) Lower 
epiderm papillate. (4) Stomata on lower side only. (5) Tannin in lower epiderm and to 
some extent in upper; struts of mechanical tissue as in Q. agrifolia. 

Berberis pinnata.—(2) Completely bifacial. Palisade tissue two layers deep, occupying 
half the mesophyll; sponge fairly typical. (4) Stomata on lower side only. (5) Struts 
of mechanical tissue associated with veins. 

Dendromecon rigidum (figs. 27, 28).— (2) Almost perfectly isolateral, in correlation with 
its vertical placement. Palisade tissue on both sides of leaf, two perfect rows above, two 
imperfect ones below, rather loose; sponge central, occupying one-third of the mesophyll, 
loose. (3) Both upper and lower epiderm strikingly papillate. (4) Stomata numerous 
and large, on both surfaces, sunken in pits to the depth of the thickness of the epiderm. 
(5) Struts of mechanical tissue associated with veins. 

Heteromeles arbutifolia.—{2) Bifacial. Palisade tissue about three layers deep, making 
less than half the mesophyll; sponge abundant, rather typical. (3) Lower epiderm papil- 


THE BROAD-SCLEROPHYLL VEGETATION OF CALIFORNIA. 101 

late. (4) Stomata on lower side only, slightly sunken, with a small exterior chamber 
formed by a collar-like ring. (5) Tannin in bundle-sheath and almost throughout the 
mesophyll, abundant. Hypoderm has been reported by Gerard (see Solereder, 84, p. 303), 
but I have been unable to find any. 

Adenostoma fasciculatum (plates 20b, 21a).— (1) Leaves needle-shaped, nearly terete, 
the morphologically upper side flattish, the lower roughly semicircular in cross-section ; 
bundles arranged in a rough circle, the main one being opposite the middle of the upper side. 
(2) Palisade tissue about three layers in depth, equally developed on all sides, with wide 
gaps below the stomata; sponge central, loose, sharply differentiated from the palisade. 


29 


Fig. 29. — Xylothermia montana: section of leaf. X125. 
Fig. 30. — Xylothermia montana: stoma. X375. 
Fig. 31. — Rhamnus crocea: section of leaf. X125. 


Fig. 32. — Ceanothus cuneatus: section of leaf; black indicates distribution of 

tannin. X75. 


(3) Cuticle very thick, equally so on all sides. (4) Stomata on all sides, with exterior 
chambers of the depth of the cuticle, almost closed at the mouth and containing plugs of 
granular material. (5) Veins surrounded by heavy sheaths of large cells which are filled 
with tannin. Leaves from seedlings and sprouts are very different. These will be de- 
scribed in another section (p. 109). 

Primus ilicifolia.—(2) Imperfectly bifacial. Palisade tissue about four layers deep, 
making half the mesophyll, with one or two incomplete layers next to the lower epiderm; 
sponge scanty. (4) Stomata on lower side only. (5) Abundant tannin in bundle sheath. 

Xylothermia montana (figs. 29, 30).— (2) A bifacial leaf of a novel type. Immediately 
below the upper epiderm is a single layer of enormous cells elongated perpendicularly to 
the surface, and extending from two-thirds to three-fourths of the distance to the lower 
epiderm. They resemble palisade tissue both in profile and cross-section, and may perhaps 
be regarded as a modified layer of such. They contain dense masses of tannin which com- 
pletely fill the cavities, and which frequently come out whole or in pieces in the process 


102 THE BROAD-SCLEROPHYLL VEGETATION OF CALIFORNIA. 


of sectioning. According to authors quoted by Solereder (84, pp. 259-260), similar sacs 
in other members of the family may contain protein and other substances in addition to 
the tannin. Between the tapering lower ends of the tannin sacs are found the true pali- 
sade cells, which never reach the upper epiderm. Nearly all of the true mesophyll is 
palisade-like in character, the only differentiation being moderate looseness and irregularity 
near the lower epiderm. (3) Lower epiderm papillate and upper slightly so. (4) Stomata 
on lower side only, sunken to the depth of the epiderm, with small exterior chambers. 
(5) Tannin sacs: see above. 

Rhamnus californica. — (2) Bifacial. Palisade tissue three to four layers deep, occupy- 
ing slightly more than half the mesophyll; sponge loose. (3) Some cells of upper epiderm 
doubled, and occasionally one with an apparently gelatinized inner wall, as reported by 
Herzog (42). (4) Stomata on lower side only, not specialized. (5) Tannin in bundle- 
sheath; a rather thick covering of clustered hairs on lower surface. 

Rhamnus crocea (fig. 31). — (2) Bifacial. Palisade tissue two to three layers deep, occu- 
pying half the mesophyll; sponge very loose. (3) Lower epiderm two to three times as 
thick as the upper, composed of cells elongated perpendicularly to the surface of the leaf, 
many of them being doubled; appearing like weakly developed water-storage tissue. (4) 
Stomata on lower side only, barely sunken. (5) Tannin in bundle-sheath. 


33 


34 35 

Fig. 33. — Ceanothus papillosus: diagrammatic section of leaf. X15. 
Fio. 34. — Ceanothus rigidus: section of leaf, showing a single cavity 

and its surroundings; general features are like those of 

C. cuneatus (fig. 32). X125. 
Fio. 35. — Ceanothus sorediatus: section of leaf. X125. 

Ceanothus cuneatus (fig. 32).— (1) One of the thickest of the leaves studied. (2) Bi- 
facial. Mesophyll very complex (Solereder, p. 886; Gemoll, 32). Palisade tissue about six 
layers deep, not continuous horizontally, occupying the areolae between the closely anasto- 
mosing veins, the courses of which are prominently marked by strands of tannin cells; 
dense, but becoming looser and simulating sponge in center of leaf. Mesophyll extends 
to lower surface around the cavities (see below), in the lower half being of rather dense 
sponge nature, with a tendency toward palisade-form near the epiderm. (3) Upper epi- 
derm partially and irregularly double, the inner cells mostly large. 1 Lower epiderm, 

1 Gemoll (32) states that all the cells of the upper epiderm have gelatinized inner walls, and 
says nothing of doubling. The interpretation given here seems not to be open to doubt, however. 
My material was killed and preserved in formalin-alcohol and cut by the celloidin method, while 
Gemoll obtained his from dried herbarium specimens. 


THE BROAD-SCLEROPHYLL VEGETATION OF CALIFORNIA. 


103 


between cavities, with one or two layers of thick-walled hypoderm behind it, the cuticle 
papillate. In the areolae between the veins the lower epiderm is deeply invaginated to form 
cavities, extending through half the thickness of the leaf and frequently compound, whose 
entrances are often smaller than their interior diameters. The epiderm lining these is 
very thin, not cuticularized, and bears an abundance of hairs, which fill the cavities with 


Fig. 36. — Arctostaphylos hookeri: section of leaf. 
Fiq. 37. — Arctostaphylos vestita: section of leaf. 


X125. 
X125. 


Fig. 38. — Eriodictyon californicum: section of leaf. X75. 


a dense felt. (4) The stomata are found within the cavities, and are raised above their 
immediate surroundings. (5) Tannin is very abundant: in sheath surrounding bundles 
and filling very large cells which in the region of the bundles are massed from epiderm to 
epiderm, the individual cells being many times larger than the palisades; also in the cells 
of the lower epiderm, where it lines the cavities, and in an occasional cell of the upper 
layer of the palisade tissue. 


104 THE BROAD-SCLEROPHYLL VEGETATION OF CALIFORNIA. 

Ceanothus papillosus 1 (fig. 33). —(1) Leaf strikingly revolute. (2) Bifacial. Palisade 
tissue two to three layers deep, occupying one-half the mesophyll; sponge rather loose, 
and many of the cells palisade-like. (3) Upper epiderm making one-sixth to one-fifth the 
thickness of the leaf, composed of large cells filled with tannin; lower epiderm much thin- 
ner, undulate, the cells also containing tannin. (4) Tannin in bundle-sheath, collenchyma 
of midrib, and epiderm; sparse scattering of single hairs on both sides. 

Ceanothus rigid™ (fig. 34). — The description of C. cuneatus will answer for this species 
in almost every particular. The slight differences noted are the smaller proportional size 
of the entrances to the cavities and the greater elevation of the stomata above their imme- 
diate surroundings. Gemoll (32) gives an illustration of the cross-section of the leaf of 
C. crassifolius. It is very similar to C. cuneatus and C. rigidus. Probably all the species 
of the subgenus Cerastes have leaves of the same general character. 

Ceanothus sorediatus (fig. 35).— (2) Bifacial. Palisade tissue two layers deep, occupying 
half the mesophyll; sponge rather loose. (3) Epiderm much like that of C. papillosus, 
but the upper is even more prominent, making from one-fourth to one-third the thickness 
of the leaf. (4) Stomata on lower side only. (5) Tannin abundant in bundle-sheath, 
collenchyma of midrib, upper and lower epiderm, and occasional palisade cells; very sparse 
hairy covering on lower surface. 

Garrya elliptica.—(2) Bifacial. Palisade tissue about three layers deep, occupying half 
the mesophyll, the uppermost layer composed of cells that are shorter than the others 
and of twice the diameter;* sponge loose. (3) Upper and lower epiderm papillate; upper 
cuticle by far the thickest of all those examined. (4) Stomata on lower side only, very 
numerous and large, each surrounded by an imposing collar-like ridge. (5) Dense hairy 
covering on lower surface; isolated sclerenchymatous cells of various shapes in the meso- 
phyll. 

Arctostaphylos hookeri (fig. 36).— (2) Almost perfectly isolateral. Mesophyll composed 
entirely of palisade tissue— about seven layers— slightly denser on the morphologically 
upper side. (3) Cuticle very slightly thinner on the lower side. (4) Stomata on both 
surfaces, sunken to the depth of the epiderm, with a small exterior chamber nearly closed 
at the mouth. (5) Tannin almost throughout the mesophyll. 

Arctostaphylos pumila. — Very similar to the last, but not so perfectly isolateral; palisade 
less dense in the lower half; stomata on lower side only. 

Arctostaphylos tomentosa. — Essentially like A. pumila. According to Niedenzu (70), the 
stomata occur on both surfaces. My material does not confirm this, but such a difference 
would not be strange in so variable a species. 

Arctostaphylos vestita (fig. 37).— Essentially like A. pumila; cuticle distinctly stratified. 

Eriodictyon calif ornicum (fig. 38).— (2) Bifacial. Palisade tissue very sharply differen- 
tiated, about four layers in depth, occupying half or a little more than half of the meso- 
phyll; sponge loose. (3) Upper epiderm papillate, with an exceedingly thin cuticle; lower 
epiderm moderately invaginated between the veins, very thin here, not perceptibly cuticu- 
larized, on the ridges opposite the veins resembling the upper epiderm; a very deep invagi- 
nation on each side of the very large midrib. (4) Stomata on lower side only, confined 
to the invaginated portions, slightly raised above their immediate surroundings. (5) A 
dense hairy covering on lower surface, not confined to the furrows, but best developed there. 

Two species which belong to the broad-sclerophyll element of the 
redwood-forest undergrowth have been studied for the sake of com- 
parison. These, with the other members of the group, range far 
north of California into the conifer forests of the Puget Sound region. 

Gaultheria shallon.—(l) Much like species of Arctostaphylos in general appearance, but 
distinctly bifacial. (2) Palisade tissue one to two layers in depth, occupying one-third or 
a little more of the mesophyll; sponge rather typical, very loose. (3) Upper cuticle moder- 
ately thick, lower thin. (4) Stomata on lower side only, with a small exterior chamber 
with constricted opening. (5) Tannin in bundle-sheath, almost throughout mesophyll, and 
in upper and lower epiderm. 

1 A recent visit to the locality of collection seems to indicate that the material studied is 
Ceanothus dentatus rather than C. papillosus. The two species are closely related. 

2 Apparently interpreted as hypoderm by Sertorius (see Solereder, 84, p. 433) ; but the cells 
contain chloroplasts and are plainly a part of the palisade. 


THE BROAD-SCLEROPHYLL VEGETATION OF CALIFORNIA. 105 


V actinium ovatum (fig. 39).— (2) Bifacial. Palisade tissue two layers in depth, occu- 
pying one-third or less of the mesophyll, its cells very short and rounded; sponge very 
loose. (3) Cells of upper epiderm large, with a moderately thick cuticle; lower cuticle 
very thin. (4) Stomata on lower side only, very slightly elevated. (5) Tannin in bundle 
sheath and in the mesophyll, mainly the sponge-cells. 

Table 14. — Summary of structural characters. 


Leaf more than 300 microns thick . . 
Mesophyll: 

Bifacial 

Imperfectly bifacial 

Isolateral 

Entirely palisade 

More than 2 layers of palisade . 

Sponge central 

Water-storage tissue 

Epiderm: 

Partially double: 

Upper 

Lower 

Lower epiderm invaginated 
Papillate : 

Upper 

Lower 

Upper cuticle more than 4 mi- 
crons thick 

Hypoderm: 

Upper side 

Lower side 

Stomata: 

Lower surface only 

Both surfaces 

Sunken 

With exterior chamber 

In furrows or cavities 

Tannin: 

In bundle-sheath 

In mesophyll 

In epiderm 

Mechanical tissue (struts) 


Broad- 

sclerophyll 

forest 

(7 species). 


Climax 

chaparral 

(19 species). 


12 

12 

4 

3 

2 

15 

2 


3 
1 
3 

4 
8 

13 


15 
4 
6 
6 
3 

9 
8 
5 
3 


Total 
(26 species). 


13 

16 

7 

3 

2 

18 


3 
1 
3 

4 
10 

14 

2 
3 

22 
4 
6 

7 
3 

11 
9 
5 
7 


Redwood 

undergrowth 

(2 species). 


The principal structural characters of the species described are 
summarized in table 14 by communities. From the data given, 
we may characterize the average Californian broad-sclerophyll leaf 
as follows : 

It is moderately small (averaging 2 to 3 cm. in length), simple, 
unlobed, elliptic, and in a majority of cases entire and glabrous. 
Important groups are toothed, spiny-toothed, revolute, or pubescent 
on the lower or on both surfaces. The leaf is thick, averaging 
314 microns, while the deciduous species studied average only 
127 microns. The mesophyll is most commonly bifacial, though often 
imperfectly so, but a few are isolateral. The palisade tissue is 


106 THE BROAD-SCLEROPHYLL VEGETATION OF CALIFORNIA. 


several layers deep. The epiderm is nearly always single, and often 
papillate. The cuticle is very thick, the upper averaging 5.69 
microns as against 1.58 microns in the deciduous species. In the 
case of the lower the difference is still greater: 4.43 microns and 
0.91 microns. The stomata in a large majority are on the lower 
surface only. Many special features occur in their structure and 
distribution that are effective in decreasing water-loss. Tannin is 
abundant and widespread in bundle-sheath, mesophyll, and epiderm. 
Divergences from Schimper's generalizations, quoted at the 
beginning of the chapter, are unimportant. The average Californian 
leaf is smaller than his statement implies; it tends toward the oval 
rather than the lanceolate in form, and vertical placement is less 
pronounced. Many special features are here described which do 
not appear in his account. 

Comparing the two communities, we find that the broad-sclerophyll 
forest has uniformly much larger leaves, which are less often entire. 

The climax chaparral leaf averages 
50 per cent thicker than the forest 
leaf; it includes all the isolateral 
and the majority of the imper- 
fectly bifacial leaves, and its pali- 
sade tissue is more prominent, 
averaging 4 to 5 layers and 66 per 
cent of the mesophyll as against 
2 to 3 layers and 43 per cent in 
the forest species. The chaparral 
leaves have a much thicker cuticle 
than those of the forest — nearly 
100 per cent greater on the upper 
side and more than 150 per cent 
greater on the lower. The species with stomata on both surfaces, 
which are those with isolateral vertical leaves, are all of the chaparral. 
Special features protective against water-loss are almost entirely 
confined to the chaparral. 

We see thus that the broad-sclerophylls, as compared with decid- 
uous species, have a wealth of features of the kind that have been 
assumed to be a response to the moisture conditions of the habitat, 
and which are certainly effective in decreasing water-loss. Certain 
of the characteristics, such as spiny teeth, papillate epiderm, and 
presence of tannin, have no obvious relation to this or to any other 
habitat factor, either as to cause and effect or advantage. We see 
further that the chaparral species are in every way more fully provided 
with transpiration-decreasing features than are the forest species. 
The group from the redwood undergrowth is rather puzzling. In 
thickness of leaf the two species studied are surpassed by but three 


Fig. 39. — Vaccinium ovatum: section of leaf. 
X125. 


THE BROAD-SCLEROPHYLL VEGETATION OF CALIFORNIA. 107 

species of the chaparral; in thickness of cuticle they are superior to 
all the species of the forest and to many of the chaparral. The 
mesophyll, however, is decidedly suggestive of mesophytic influences. 
The habitat of these plants is far more mesophytic than that of the 
other broad-sclerophylls, and the xeromorphic construction of their 
leaves is a warning against the determination of the essential ecolog- 
ical nature of a plant by one structure alone. The commonness of 
this type of leaf in the family Ericaceae, apparently regardless of 
habitat, is too well known to require comment. 

EFFECTS OF ENVIRONMENTAL CONDITIONS UPON LEAF STRUCTURE. 

It is commonly assumed that moisture and light influence power- 
fully the structure of leaves, especially the thickness and character 
of the mesophyll and epiderm. Many have essayed to separate 
the effects of the two factors, not always with success. While it is 
impossible in such a field study as the present to make a close analysis 
of cause and effect, any correlation of structural differences with 
accurately measured habitat factors is of value, and therefore the 
following brief study is presented. 

Three stations in the series at Jasper Ridge (p. 33) were selected, 
Nos. 4, 3, and 7 representing respectively the Adenostoma, the 
Arctostaphylos, and the Quercus agrifolia-Arbuius communities. 
A summary of the moisture and light conditions of each station is 
presented in table 15. The figures are derived from the data given 
in an earlier section (p. 42). Soil-moisture is expressed in per cent 
of dry-soil weight, and the figure is an average of a series of six 
monthly determinations at two depths (10 cm. and 30 to 50 cm.) 
during the dry season from June 15 to October 31, 1913. Evapora- 
tion is given in cubic centimeters of daily loss from a standard 
atmometer, determined weekly, and averaged for practically the same 
period as the soil-moisture readings. Light is expressed as a decimal 
of the full illumination. The readings were made as close together 
as possible in time, at midday of August 17, 1917. The species 
chosen for study were the three most prominent chaparral shrubs of 
the vicinity, Adenostoma fasciculatum, Arctostaphylos tomentosa, and 
Quercus durata. The natural habitat of these species is of the character 
of stations 4 and 3, but they grow occasionally as interlopers in the 
forest, which is represented by station 7, and thus give opportunity 
for comparison. The material was collected from widely separated 
plants within a given association, preserved in formalin-alcohol and 
cut in paraffin. In making the measurements, 10 separate leaves 
were used and 5 measurements made upon each leaf. Every figure 
given is therefore an average of 50 separate measurements. 

The habitat analysis shows that the stations, in the order as given, 
are progressively more favorable as regards moisture conditions, 
both in water-content and in evaporation, and progressively more 


108 THE BROAD-SCLEROPHYLL VEGETATION OF CALIFORNIA. 


deficient in light. Stations 3 and 4, however, are rather similar in 
every factor, while station 7 is quite different. It is not surprising, 
therefore, to find striking structural divergence between stations 
3 and 4 on the one hand and station 7 on the other, and far less 
consistent differences between stations 3 and 4. The leaf is thinnest 

Table 15. — Effect of habitat upon leaf structure. 


Station 4. 

Adenostoma 

chaparral. 


Station 3. 

Arctostaphylos 

chaparral. 


Station 7. 

Quercus agrifolia- 

Arbutus forest. 


Habitat: 
Light: 

Sun 


0.75 
0.21 
3.24 
30.1 

541 
10.10 
10.26 

371 
9.77 
9.36 

233 

3.38 
4.05 


0.69 
0.04 
3.38 
28.4 

574 
10.65 
11.00 

366 
9.06 
14.30 

198 
2.77 
3.23 


0.56 
0.07 
3.81 
22.7 

475 
11.00 
4.64 

250 
6.94 
7.67 

193 

2.55 
2.66 


Leaf -structure: 

Adenostoma f asciculatum : 


Upper cuticle, microns 

Lower cuticle, microns 

Arctostaphylos tomentosa: 


Upper cuticle, microns 

Lower cuticle, microns 

Quercus durata: 


Upper cuticle, microns 

Lower cuticle, microns 


in station 7, and the same is true of the lower cuticle, the differences 
in the latter case being especially noticeable. In the case of the 
upper cuticle the differences in Arctostaphylos and Quercus are less, 
and in Adenostoma there is reversal, the mesophytic station 7 showing 
a cuticle slightly thicker than the others. There are also differences 
apparent in the mesophyll, especially in Arctostaphylos. In this 
species the sections from stations 3 and 4 are barely distinguishable, 
but these two differ strikingly from station 7. Such differences 
can not be expressed numerically, but are very evident in drawings 
(figs. 40 and 41). In the leaf from station 4, the dense palisade extends 
from epiderm to epiderm, being slightly looser below, with here and 
there a tendency toward sponge character. In that from station 7 
the palisade is but two layers deep, and there is a distinct region of 
sponge tissue. Quercus and Adenostoma from the three stations show 
far less striking differences. 

We conclude, therefore, that increased thickness of leaf and of 
cuticle, increased development of palisade tissue, and decrease of 
sponge coincide with decrease of moisture and increase of light. 
Further than this we can not certainly go. The natural assumption 
is that moisture is the controlling factor rather than light, which 
may have an indirect effect. 


THE BROAD-SCLEROPHYLL VEGETATION OF CALIFORNIA. 109 


Evidence that this assumption is well founded may be obtained 
from that unusually interesting plant Adenostoma fasciculatum, in 
the remarkable type of leaf that is found upon seedlings and stump 
sprouts and to a slight degree on mature plants growing in meso- 
phytic situations. Prints of these, with the ordinary type for com- 
parison, are given in plate 21b. The differences in structure are no 
less striking than in form (plate 20, b, c, d). The sprout or seedling 


Fig. 40. — Arctostaphylos tomentosa: section of leaf from a xerophytic habitat (station 4, 

Jasper Ridge). X125. 
Fig. 41. — Ardostaphylos tomentosa: section of leaf from a mesophytic habitat (station 7, 

Jasper Ridge). X125. 
Fig. 42. — Adenostoma fasciculatum: stoma of normal xerophytic specimen. X375. 
Fig. 43. — Adenostoma fasciculatum: stoma of leaf from stump sprout. X375. 

leaf is a flat isolateral structure, averaging 300 microns in thickness, 
with the veins in a single plane after the manner of ordinary leaves. 
The mesophyll is loose, especially the central sponge, and both 
palisade and sponge cells are short and rounded. The epidermal 
cells are very large, thin-walled, and turgid. The cuticle is very 
thin — 1.5 microns as contrasted with 9.73 microns in the ordinary 
leaf of the species. The stomata occur on both surfaces. They still 
possess the exterior chamber, but this is very shallow and open- 
mouthed (figs. 42, 43). 

We may explain these remarkable structural changes — broadening 
of the leaf to form a flat blade, loosening of the mesophyll, loss of 
character in the palisade, reduction of cuticle — after a fashion by 


110 THE BROAD-SCLEROPHYLL VEGETATION OF CALIFORNIA. 

stating that the abnormal leaf type is an ancestral character to which 
the plant reverts in its juvenile stage. This in itself is begging the 
question, and doubt is cast upon its adequacy by the fact that the 
flat leaf sometimes appears in mature individuals in mesophytic 
situations (plate 21a, 6). Light can not be operative here, since it 
is at maximum intensity where sprouts and seedlings are found, and 
observed changes due to increased intensity are invariably in the 
opposite direction. Moisture as the governing factor seems entirely 
adequate. New stump sprouts, even in the midst of the dry season, 
have an exceptional advantage as to water, since they may draw 
upon an absorbing system which formerly supplied a complete 
mature shrub. The large size of leaves upon stump sprouts and 
their mesophytic structure are well-known phenomena, and are 
characteristic of other chaparral species besides Adenostoma. As 
to seedlings, germination and early growth take place at a time of 
year when soil-moisture is abundant and evaporation low, and the 
plant supplements this advantage by immediately sending down a 
taproot to a considerable depth. The occasional occurrence of the 
flat leaf upon mature individuals in mesophytic situations is the 
final argument. It may well be that the mesophytic leaf with its 
distinctive form and structure points back to a mesophytic ancestry 
for the species, which would help to bring it into harmony with the 
majority of the members of its family, among which it is decidedly 
an anomaly. Finally, since moisture seems adequate as a cause of 
variation in the form and thickness of the leaf of Adenostoma and 
in the character of its mesophyll and cuticle, it is reasonable to assume 
that it is the controlling factor in the other species where the same 
differences are present but less striking. 

COMPARATIVE TRANSPIRATION-RATE. 

In the summer of 1917 I made a brief study to determine the actual 
transpiration-rate of two or three of the important broad-sclerophyll 
species. The results were somewhat puzzling, though consistent 
enough among themselves, and it is therefore the better part of valor 
to withhold them in the main for further investigation. One or two 
points were clearly brought out, however, which are worth stating 
here. 

The study was made by the simple potometer method — the placing 
of branches in bottles of water, which were weighed at the beginning 
and end of the experiment. The mouths of the bottles were plugged 
with cotton, which was kept perfectly dry. One or two which became 
wet during the experiment were discarded. The species used were 
Adenostoma fasciculatum , Arctostaphylos tomentosa, and Arbutus 
menziesii. Ten shoots of each of the first two were cut in station 10 
{Adenostoma consociation; see p. 41 for environment), placed in 


THE BROAD-SCLEROPHYLL VEGETATION OF CALIFORNIA. Ill 

bottles and weighed. Five of each species were left in station 10 
and the rest were placed in station 7 (Quercus agrifolia- Arbutus associa- 
tion, p. 38). In station 7, 10 branches each of the same species 
were cut, and in addition 10 of Arbutus menzicsii, and half of each 
set were left in station 7 and the others taken to station 10. The 
experiment was allowed to run for about 48 hours, from August 24 
to August 26. The branches were pressed between driers, and the 
areas of the leaves of Arctostaphylos and Arbutus were later deter- 
mined with a planimeter. In the case of Adenostoma, with its 
terete leaves, a different and less exact method was necessary. Each 
branch was stripped of its leaves and these counted. Then 20 were 
selected at random, placed in boiling water to restore them approxi- 
mately to their original size, and measured accurately as to length and 
diameter. The area was computed as a cylindrical surface, the 
average of the 20 taken, and this applied to the total number of 
leaves on the shoot. The total losses recorded for each shoot were 
reduced to the amount per square decimeter of surface. So much of 
the results as are worth giving at present are seen in tables 16, 
17, and 18. 

Table 16. — Loss per square decimeter, station 10. 

c. c. 

Adenostoma (average of 5 shoots) 5 32 

Arctostaphylos (average of 5 shoots) 6 . 68 

Arctostaphylos (both surfaces considered) 3.34 

It is shown that when the stoma-bearing surface alone is con- 
sidered, the loss per unit is less in Adenostoma; but if both surfaces 
of the leaf are considered in Arctostaphylos, as we must fairly do, 
the relation is reversed. It would seem, therefore, that the Adeno- 
stoma leaf is the more effective in reducing water-loss so far as the 
actual stoma-bearing surface is concerned, but that Arctostaphylos 
compensates for this by the entire absence of stomata (at least in 
the plants studied; see p. 104) over half its leaf-surface. The more 
perfect xerophytism of Adenostoma can not be explained, therefore, 
upon the basis of cuticular and stomatal regulation; and this is 
confirmed by the descriptions presented in the last section, in which 
these structures are seen to be very similar in the two species. We 
may fall back upon the hypothesis that the total leaf-area is less 
in Adenostoma than in Arctostaphylos, plants of equal size being con- 
sidered; individuals of the two species are apt to be so when growing 
together. The general appearance would indicate this, especially 
the small size of the leaves of Adenostoma, and confirmation is ob- 
tained from the fact that the average leaf-area of the shoots used in 
the experiment (both surfaces considered in Arctostaphylos) was 
75 per cent greater in Arctostaphylos. Of course, this is merely a 
rough approximation, but since care was taken to select branches 
as nearly alike as possible, it doubtless indicates the truth. 


112 THE BROAD-SCLEROPHYLL VEGETATION OF CALIFORNIA. 

For comparison with Arbutus it is necessary to use the shoots of all 
species that were cut in station 7 and left there (table 17). 

Table 17. — Loss per square decimeter, station 7. 

e. e. 

Adenostoma (average of 5 shoots) 2 . 77 

Arctostaphylos (average of 5 shoots) 3 96 

Arctostaphylos (both surfaces considered) 1 . 98 

Arbutus (average of 5 shoots) 3 . 69 

Arbutus (both surfaces considered) 1-85 

The two shrubs show the same relations here as in station 10. 
Arbutus seems to be slightly more effective in reducing water-loss 
than Arctostaphylos, and therefore more effective than Adenostoma 
per unit total surface. However, the average total leaf-surface 
per shoot was 38 per cent greater than Arctostaphylos and thus far 
greater than Adenostoma, indicating that even for a plant of equal 
size the total leaf-surface would be greater; and there is the further 
fact of the tree stature of Arbutus. The conclusion seems to be 
that it is not so much differences in cuticular or stomatal effectiveness 
that make the difference in drought resistance as it is the total leaf- 
area exposed in plants of approximately equal size, the separate 
elements in this character being number and size of leaves. 

One other point may be brought out. Table 18 exhibits the 
difference in evaporation-rate which appears in the same species 
growing in the two habitats, due fundamentally to differences in 
the environmental conditions. 

Table 18. — Loss per square decimeter, station 7. 

c. c 

Adenostoma (station 7) 2 . 77 

Adenostoma (station 10) 5 . 32 

Arctostaphylos (station 7) 1-98 

Arctostaphylos (station 10) 3 .34 

In Arctostaphylos the rate in the xerophytic station is 70 per cent 
greater than in the other, while in Adenostoma the difference is 
nearly 100 per cent. The study of the transpiration of these plants 
is one of the most promising fields for further investigation. 


THE BROAD-SCLEROPHYLL VEGETATION OF CALIFORNIA. 113 

APPENDIX. 

ANNOTATED LIST OF BROAD-SCLEROPHYLLS AND ACCOMPANYING 

SPECIES. 

In listing the species which make up the broad-sclerophyll vegeta- 
tion of California, a separation into groups will be convenient. The 
first great division is into dominants and secondary species; both 
classes may conveniently be subdivided. 

THE DOMINANTS. 

Under this head I would include all the true forest and brush- 
forming species — those which give to the type its characteristic 
physiognomy. Although the majority are strikingly similar in 
ecological character, they present great floristic diversity. The 
first two lists include 74 broad-sclerophylls, representing 23 genera 
and 13 families. In all lists species restricted to the Calif ornian 
islands have been excluded. Another group of broad-sclerophylls, 
mentioned in the last chapter, comprises the half-dozen species 
which form an important part of the undergrowth of the northwestern 
conifer forests. These are Berberis nervosa Pursh, Pachystima 
myrsinites Raf., Rhododendron californicum Hook., Gaultheria shallon 
Pursh, and V actinium ovatum Pursh. 

The following list includes all the species that are of importance 
in the composition of the broad-sclerophyll forest. They are few 
in number, and most are of wide range within the Californian region. 
Some are themselves not broad-sclerophylls, but are deciduous; 
these have been grouped together at the end of the list. A number 
of the species, too, when growing in relatively unfavorable situations, 
take the shrub form and in some cases are more important thus than 
as trees. In a few instances the shrubby form has been separated 
by taxonomists as a variety. 

List I. — Arborescent Species. 
EVERGREEN. 

1. Myrica californica Chamisso. Wax myrtle. Immediate coastal region from Puget 
Sound to Los Angeles County. Of subordinate importance as a forest tree. 

2. Castanopsis chrysophylla (Hook.) A. DC. Golden chinquapin. As a forest tree it 
occurs in western Oregon and in the mountains of northwestern California southward to 
Mendocino County. In the latter region it is a member of the mixed broad-sclerophyll- 
conifer forest. It is also frequently associated with the redwood. Var. minor A. DC. is a 
shrub closely resembling C. sempervirens (see No. 17). It is characteristic of the Coast 
Ranges, extending southward to Monterey, while C. semperrirens belongs rather to the 
Sierras. It is a frequent member of the conifer forest chaparral in the north Coast Ranges, 
and appears also in the climax chaparral. 

3. Quercus agrifolia Nee. Coast live oak. Outer Coast Ranges and valleys near the 
coast, from Mendocino County to Mount San Pedro Martir in Lower California. The 
most important live oak, and probably the most important of the genus, within its range. 
Covers hillsides, especially north-facing slopes, with dense forest; also commonly in open 
park-like growth in valleys of the coast range; in such places attaining its largest size, and 
frequently associated with Q. lobata. Almost invariably tree-like in form, the only notable 
exceptions being the bushy contorted specimens in exposed situations near the shore. 


114 THE BROAD-SCLEROPHYLL VEGETATION OF CALIFORNIA. 

4. Quercus chrysolepis Liebm. Mountain live oak. In southwestern Oregon and 
throughout the California mountains west of the high Sierras and the desert, except the 
lowest foothills; south to Mount San Pedro Martir in Lower California. The most widely 
distributed and most important of the live oaks of California, being the dominant member 
or one of two or three dominants in the broad-sclerophyll forest wherever it occurs. Very 
frequent in chaparral form, sometimes in rather tall pure growth on north slopes, forming 

1 dwarf for est." 

5. Quercus engelmanni Greene. Engelmann oak. Of limited range; in southern Cali- 
fornia from Los Angeles County to the Mexican boundary, occupying a belt 80 km. wide, 
distant 25 to 30 km. from the coast. Important within its limited range. Barely ever- 
green. 

6. Quercus wislizeni A. DC. Interior live oak. From Mount Shasta southward through 
the Sierra foothills and the Coast Ranges to Mount San Pedro Martir in Lower California; 
rarely, though occasionally, near the coast. Much less important as a forest tree than 
Q. chrysolepis, and characteristic of less mesophytic situations; occurs frequently in open 
growth with Q. douglasii on the lowest foothills. The shrubby form, var. frutescens Engelm., 
is very common in the climax chaparral. 

7. Pasania densiflora Oerst. Tan-bark oak. Southwestern Oregon to the Santa 
Ynez Mountains in the Coast Ranges, and to Mariposa County in the Sierras. Character- 
istic of the mixed forest of the interior mountains of northern California; also commonly 
associated with the redwoods. The shrubby form, var. echinoides Jepson, is a member of 
the conifer-forest chaparral in northern California. 

8. Umbellularia calif ornica (H. and A.) Nutt. California laurel. Southwestern Ore- 
gon, southward through the Coast Ranges and Sierras to southern California. Character- 
istically a tree of the mesophytic forests, especially addicted to steep north slopes, ravines, 
and stream-banks. Sometimes shrubby, forming an unimportant part of the chaparral in 
the more mesophytic situations, especially in the extreme southern portion of its range. 

9. Arbutus menziesii Pursh. Madrono. Southwestern British Columbia; through the 
coast region of Washington and Oregon; mountains of northern California; southward in 
the Sierras to Tuolumne County, and in the Coast Ranges to Los Angeles County. An ex- 
ceedingly important tree of the broad-sclerophyll forest. Largest in northwestern Cali- 
fornia, where it accompanies the redwoods; in the central Coast Ranges second in impor- 
tance to the live oaks, with them forming the bulk of the north-slope forests; decreasing 
southward in size and abundance, both in Coast Ranges and Sierras. 

DECIDUOUS. 

10. Quercus douglasii H. and A. Blue oak. Low foothills and valleys from Mendocino 
County to the upper Sacramento Valley, southward to the Liebre Mountains and the San 
Fernando Valley. Usually in open growth on the lowest foothills; sometimes pure, some- 
times with Pinus sabiniana or Quercus wislizeni. Rarely associated with the broad- 
sclerophyll trees; the most xerophytic of the California oaks. Its relation to the chaparral 
is treated on page 79. 

11. Quercus garryana Dougl. Garry oak. North Pacific States, extending southward 
in California along the Coast Ranges; abundant as far as Trinity County; occasional to 
the Santa Cruz Mountains. Not very important in California as a forest tree. In the 
northwestern portion, however, it forms dense pure thickets 2 or 3 meters high in the 
forest region. 

12. Quercus kelloggii Newb. California black oak. Corresponding in range rather 
closely to Quercus chrysolepis, and a common companion to it in the forest. Occasionally, 
in shrub form, it makes a part of the conifer-forest chaparral. 

13. Quercus lobata Nee. Valley oak. Valleys and foothills from Shasta County to 
Los Angeles County. Included here because it frequently forms park-like mixed forest 
with Q. agrifolia. 

14. Acer macrophyllum Pursh. Broadleaf maple. Coast Ranges and Sierras, south to 
the San Bernardino Mountains. A frequent companion to the broad-sclerophyll trees in 
the more mesophytic localities. 

15. ^sculus calif ornica Nutt. California buckeye. Coast Ranges from Mendocino 
County to San Luis Obispo County; Sierra foothills. A common inhabitant of north- 
facing slopes in the foothills, growing with the live oaks; sometimes forming dense pure 
thickets. 


THE BROAD-SCLEROPHYLL VEGETATION OF CALIFORNIA. 115 

The species of the next list are the shrubs that make up the chapar- 
ral, which in extent and in number of species and of individuals 
is far more important than the broad-sclerophyll forest. A further 
point of contrast is the far greater number of species in the chaparral 
which have a decidedly restricted range. To complete the picture, 
the following species from List I should be added, since in shrub form 
they have a more or less important place in the chaparral : 

Castanopsis chrysophylla minor. Quercus wislizeni frutescena. 

Quercus chrysolepis. Pasania densiflora echinoides. 

Quercus garryana. 

Considering the region as a whole, 4 genera, representing as many 
families, are of paramount importance in the chaparral. These 
are Quercus, Adenostoma, Ceanothus, and Arctostaphylos. They 
are widely different in the number of species representing them. 
Adenostoma, with the" most important single species, includes 2; 
Quercus has 6 that are strictly chaparral forms; while in Arctosta- 
phylos and Ceanothus I have listed 18 and 25, respectively. The 
treatment of the last two genera is of necessity unsatisfactory, since 
there is disagreement among taxonomists upon the fundamental 
questions of specific limits and relationships. In both genera there 
are groups of forms which are regarded by some authors as constitut- 
ing single variable species. Within a group there are several forms 
which may be species, varieties, or merely ecological variants. ^ It 
seems better for the present purpose, in doubtful cases, to consider 
the larger unit as the species, rather than to attempt to maintain a 
number of so-called species, sometimes poorly defined, of uncertain 
range, often known only from the type locality. It is not denied 
that these variant forms are of the greatest ecological interest and 
importance. At the present time, however, our knowledge of them 
is in every way insufficient to make adequate discussion possible. 
In the treatment of each genus I have, so far as possible, followed 
the author who has given the most recent and complete taxonomic 
account of the group concerned. These are Trelease (89) in Ceano- 
thus and Abrams (2) in Arctostaphylos. In both cases I have omitted 
a number of species of uncertain validity or range. 

In the list below I have attempted to indicate as accurately as 
has been possible to determine, from personal observation, literature, 
and herbaria, the range and degree of importance of each species of 
the chaparral. In the case of the most important one, Adenostoma 
fasciculatum, the range has been plotted on a map (plate 3). This is 
fairly accurate, since it is based on a careful and widely extended 
field study, supplemented by examination of literature and herbarium 
records, and by notes from a number of persons possessing a wide 
acquaintance with the vegetation of California. These sources 
together yielded a total of about 250 known localities. 


116 THE BROAD-SCLEROPHYLL VEGETATION OF CALIFORNIA. 

List II. — Obligate Shrubs. 
BETULACEjE. 

16. Corylus rostrata Ait. var. californica A. DC. Hazelnut. Central and northern 
Coast Ranges and Sierra Nevada. A rather unimportant constituent of the conifer-forest 
chaparral; occurs more commonly as undergrowth in mesophytic forest. Deciduous. 1 

17. Castanopsis sempervirens (Kellogg) Dudley. Golden chinquapin. From the south- 
ern Cascades along the Sierras, southward to Mount San Jacinto. Characteristic of the 
conifer-forest chaparral of the higher altitudes. 

18. Quercus breweri Engelm. Brewer oak. Inner Coast Ranges from Mount Yolo 
Bolly north; Sierra Nevada to the Kern River region. Forms extensive thickets at middle 
altitudes. A member of the conifer-forest chaparral. Deciduous. 

19. Quercus dumosa Nutt. Scrub oak. From the region of Mount Shasta to Lower 
California (lat. 31°); on the Coast Ranges and Sierra Nevada. Most abundant in the 
coastal region of southern California. A very important member of the climax chaparral, 
ranking with certain species of Arctostaphylos and Ceanothus, next to Adenostoma. Barely 
evergreen. 

20. Quercus durata Jepson. Scrub oak. Closely related to the last. Range not satis- 
factorily determined, but apparently covering the middle Coast Ranges from the Santa 
Lucia Mountains north to Mendocino County and the Napa Range, and probably to the 
Trinity Mountains. Reported from Stanislaus National Forest in the Sierra Nevada. 
Similar in status to the last. 

21. Quercus sadleriana R. Br. Confined to the mountains of southwestern Oregon and 
northwestern California. Forms pure thickets, probably successional. Barely evergreen. 

22. Quercus vaccinifolia Kellogg. Huckleberry oak. Inner north Coast Ranges from 
Mount Shasta to Trinity County; throughout the higher forest region of the Sierra Nevada. 
A member of the conifer-forest chaparral; also occurring as undergrowth in the subalpine 

TOT*PSts 

BERBERIDACE^l. 

23. Berberis pinnata Lag. California barberry. Central Coast Ranges. Sometimes 
in the chaparral; occasionally in the oak forests. Unimportant. 

PAPAVERACEjE. 

24. Dendromecon rigidum Benth. Bush poppy. Of general distribution; from Shasta 
National Forest southward through Coast Ranges and Sierras, reaching Mount San Pedro 
Martir in Lower California; records scarce north of Sonoma and Napa Counties. A 
widely distributed and characteristic member of the climax chaparral, though nowhere 
abundant; its bright yellow flowers contribute a pleasing touch of color here and there. 

ROSACEA. 

25. Heteromeles arbutifolia (Poir.) Roem. Christmas berry; California holly; tollon 
(pronounced "toyon"). Coast Ranges and Sierra Nevada, and through southern Califor- 
nia and Lower California to the Cape region. A characteristic member of the climax 
chaparral; not often abundant, but seemingly so because of its fine clusters of red berries 
and because it usually overtops its neighbors. Sometimes attains tree stature, but retains 
its shrub form. More tolerant of shade than most of its chaparral companions; therefore 
frequently found in the oak forest. 

26. Arnelanchier alnifolia Nutt. Service berry. Has the widest distribution of all the 
species occurring in the chaparral, ranging from Alaska to Mount San Pedro Martir in 
Lower California, east to Michigan, Nebraska, Colorado, and New Mexico; in California 
occurring in the Coast Ranges from San Francisco Bay northward, in the Sierras and the 
higher mountains of southern California. A rather frequent member of the conifer-forest 
chaparral. Deciduous. 

27. Cercocarpus betuloefolius Nutt. Birch-leaf mahogany. Throughout the foothills 
and lower mountains of California. A common and frequently abundant member of the 
climax chaparral, especially in the more mesophytic situations. Often gregarious on north 
slopes, the groups in seed time showing from a distance as white patches. 

1 Unless otherwise'notcd, species are evergreen in leaf habit. 


THE BROAD-SCLEROPHYLL VEGETATION OF CALIFORNIA. 117 

28. Cercocarpus ledifolius Nutt. Mountain mahogany. Ranging widely over the west- 
ern States, but not important as a member of the chaparral. Occurs sparingly in the 
chaparral of the San Bernardino Mountains and other southern California ranges, and in 
the Sierras, but mainly on the east slope. 

29. Adenostoma fasciculatum H. and A. Chamise; grease-wood (the latter name, 
though frequent, is unfortunate, as it has been commonly applied to other shrubs, totally 
unrelated, of the western United States). Range shown in detail on map (plate 3). Its 
occurrence near Hershey in the Sacramento Valley, and other facts, seem to indicate that 
it formerly had a more widely extended range (see p. 79). The most abundant species and 
most important in every way of the shrubs of the climax chaparral. Usually in pure 
growth or nearly so over extensive areas, occupying the less mesophytic situations, which 
greatly predominate in the chaparral region. Pure growth is commonly known as "cha- 
misal." Easily recognized at a distance, when growing in mass, by its characteristic 
color-tone, which varies according to the time of year. Its general shade is gray-green, 
but in June this is whitened by the profusion of spiraea-like flower panicles, and through 
the remainder of the summer and autumn turned to rich brown by the equally abundant 
clusters of withered flowers and achenes. 

30. Adenostoma sparsifolium Torr. Yerba del Pasmo. San Jacinto and Santa Monica 
Mountains to Lower California; also in Santa Ynez Mountains. An interesting and hand- 
some species of limited range and abundance; occurs in the same sort of situations as the 
last. 

31. Prunua demissa (Nutt.) Walp. Western choke cherry. Rocky Mountains to the 
Pacific States and British Columbia. In California, a widely distributed but unimportant 
member of the conifer-forest chaparral; commoner in stream-bank thickets. Deciduous. 

32. Prunus emarginata (Dougl.) Walp. Bitter cherry. Range similar to last; not so 
far eastward, but extending south to Mount San Pedro Martir in Lower California. In 
California an important member of the conifer-forest chaparral, frequently forming exten- 
sive thickets. Deciduous. 

33. Prunus ilicifolia (Nutt.) Walp. Holly-leaf cherry; islay. South Coast Ranges, 
from the region of San Francisco Bay to Lower California. A frequent member of the 
climax chaparral; when shrubby closely resembling Rhamnus crocea. In more mesophytic 
situations it often attains small tree size, with a trunk 3 dm. thick, in such cases resembling 
Quercus agrifolia so closely in habit and leaf-form as to be distinguishable with difficulty. 

34. Prunus subcordata Benth. Western plum. Southern Oregon southward, in the 
Coast Ranges to the Mount Hamilton Range, in the Sierras to the Kern River region. An 
unimportant member of the conifer-forest chaparral. Deciduous. 

CESALPINACEiE. 

35. Cercis occidentalis Torr. Redbud. Foothills of Sierras and Coast Ranges south- 
ward to San Diego County, eastward to western Texas. Frequently a stream-bank shrub; 
occasionally a member of the chaparral; in the Cuyamaca Mountains seen in pure thicket 
growth on a northeast slope. Deciduous. 

LEGUMINOSiE. 

36. Xylothermia montana (Nutt.) Greene [Pickeringia montana Nutt.]. Chaparral pea. 
Coast Ranges from Mendocino and Lake Counties southward; Sierra Nevada, from Mari- 
posa County southward; var. tomentosa Abrams in mountains of southern California and 
Lower California. A widely distributed but not abundant member of the climax chaparral. 

RUTACE^E. 

37. Cneoridium dumosum (Nutt.) Hook. f. San Diego County and northern Lower 
California. Climax chaparral. 

ANACARDIACEjE. 

38. Rhus integrifolia (Nutt.) B. and H. Mahogany sumach. Santa Barbara to Mount 
San Pedro Martir and Magdalena Bay, extending eastward to the desert slopes of the 
Cuyamaca Mountains. 

39. Rhus laurina Nutt, Laurel-leaf sumach. Santa Ynez Mountains to the San Ga- 
briel Range, southward to northwestern Lower California, mainly near the coast. Usually 
not abundant, but conspicuous by reason of its light-green foliage. 

40. Rhus ovata Wats. Ovate-leaved sumach. Santa Ynez Mountains to San Bernar- 
dino and San Jacinto Ranges, south to Mount San Pedro Martir in Lower California. 


118 THE BROAD-SCLEROPHYLL VEGETATION OF CALIFORNIA. 

ACERACE.E. 

41. Acer glabrum Torr. Dwarf maple. Southeastern Alaska to Montana, Colorado, 
western Nebraska, New Mexico; west to California, where it ranges from the Oregon line 
southward to northern Trinity County, throughout the middle altitudes of the Sierras, and 
in the San Bernardino and San Jacinto Ranges. A mesophytic shrub, sometimes forming 
an unimportant part of the conifer-forest chaparral. Deciduous. 

RHAMNACE^l. 

42. Rhamnus californica Esch. (including var. rubra Trelease and var. tomentella Brew, 
and Wats.). Coffeeberry. Coast Ranges and Sierra Nevada, south to Mount San Pedro 
Martir in Lower California. A frequent member of the climax chaparral, occurring also 
in more mesophytic situations such as the oak forest. Var. tomentella extends eastward into 
Arizona and New Mexico; var. rubra is deciduous, belonging rather to the conifer-forest 
chaparral. 

43. Rhamnus crocea Nutt. (including R. ilicifolia Kellogg). Evergreen buckthorn; red- 
berry. Siskiyou County southward in the Coast Ranges and Sierra Nevada, extending to 
Mount San Pedro Martir in Lower California; eastward to Providence Mountains, Cali- 
fornia, and into Mexico and Arizona. A frequent member of the climax chaparral. 

44. Ceanoihus cordulatus Kellogg. Snowbrush. Forested northern Coast Ranges and 
throughout the higher Sierra Nevada forest regions; higher mountains of southern Cali- 
fornia and Lower California to Mount San Pedro Martir; mountains of Nevada according 
to Mrs. Brandegee (10). One of the most important constituents of the conifer-forest 
chaparral, covering extensive areas pure or mixed with other species. As is natural, con- 
sidering its successional status, it is also found abundantly as undergrowth in the coniferous 

45. Ceanothus crassifolius Torr. Santa Ynez Mountains to the San Gabriel and San 
Bernardino Ranges, south to northern Lower California. An important constituent in its 
range of the climax chaparral, conspicuous because of its grayish-green foliage. 

46. Ceanothus cuneatus Nutt. Wedge-leaf ceanothus. Omnipresent in the lower alti- 
tudes of the California mountains; extending northward into southern Oregon and prob- 
ably southward into Lower California. One of the three or four most abundant species 
in the climax chaparral region. It comes up in great numbers after fire, and its presence 
in abundance usually indicates recent disturbance. 

47. Ceanothus dentatus T. and G. Outer Coast Ranges from the Santa Cruz Mountains 
to Santa Barbara County. 

48. Ceanothus divaricatus Nutt. (including var. eglandulosus Torr.). Monterey County 
south to the San Bernardino Range, Cuyamaca Mountains, and Lower California; also 
in the central and southern Sierras. An important shrub in the climax chaparral of the 
southern California mountains. 

49. Ceanothus diversifolius Kellogg. Central Sierras, in the yellow pine belt. A creep- 
ing shrub, growing beneath the pines, not forming brush. 

50. Ceanothus foliosus Parry. Coast Ranges north of San Francisco Bay, to the red- 
wood region of Mendocino County. 

51. Ceanothus hirsutus Nutt. (including C. oliganthus Nutt.). Range uncertain; south- 
ern Coast Ranges; perhaps southward into Lower California. 

52. Ceanothus incanus T. and G. Coast Ranges from Humboldt County to the Santa 
Cruz Mountains, mainly in the redwood region. 

53. Ceanothus integerrimus H. and A. Deerbrush. Mount Shasta region, south in the 
Coast Ranges to the Santa Cruz Mountains; lower yellow pine belt of Sierra Nevada; var. 
puberulus (Greene) Abrams, in the mountains of southern California. According to Mrs. 
Brandegee (10, p. 184), the species ranges southeastward to southern Arizona. An impor- 
tant species in chaparral and as undergrowth in coniferous forest. Deciduous. 

54. Ceanothus megacarpus Nutt. Near the coast, Santa Ynez to Santa Ana Mountains. 

55. Ceanothus Palmeri Trelease. Ventura County to the Cuyamaca Mountains and 
perhaps farther south. 

56. Ceanothus papillosum T. and G. Of limited range; Santa Cruz Mountains to Santa 
Lucia Mountains. Grows in the Monterey region with an interesting group of endemics 
and species of restricted range, including C. rigidus, Arctostaphylos hookeri, A. pumila, and 

A fjPstitd 

57. Ceanothus parryi Trelease. Coast Ranges; Napa and Solano Counties northward 
to the redwood region of western Mendocino and Humboldt Counties. Deciduous. 


THE BROAD-SCLEROPHYLL VEGETATION OF CALIFORNIA. 119 

58. Ceanothus parvifolius (Wats.) Trelease. Central and southern Sierras; conifer-forest 
chaparral. Deciduous. 

59. Ceanothus pinetorum Coville (including C. jepsonii Greene). Coast Ranges; Lake 
County to Mount Tamalpais; also in the southern Sierras (Tulare County). 

60. Ceanothus prostratus Benth. Squaw carpet; mahala mats. North Coast Ranges, 
Mount Shasta to the San Francisco Bay region; pine belt of the Sierra Nevada. Habit 
and habitat of C. diver sifolius, except that toward its southern limit in the Coast Ranges it 
tends to become erect (var. divergent K. Brandegee) . 

61. Ceanothus rigidus Nutt. Limited in range; Marin County to Monterey. (See No. 
56.) 

62. Ceanothus sanguineus Pursh. A northern species reaching the Siskiyou Mountains 
in northern California; conifer-forest chaparral. Deciduous. 

63. Ceanothus sorediatus H. and A. Coast Ranges; Napa and Solano Counties to north- 
ern Santa Barbara County. Somewhat like C. cuneatus in its habits, but preferring more 
mesophytic situations; coming up thickly like C. thyrsiflorus after fire in the redwood 
forest. 

64. Ceanothus spinosus Nutt. Coast region of southern California from Santa Barbara 
County to Orange County. One of the largest members of the genus, sometimes arbor- 
escent. Partly evergreen. 

65. Ceanothus thyrsiflorus Esch. Blue-blossom; California lilac. An abundant spe- 
cies of the redwood region from the northern boundary of the State to the Santa Lucia 
Mountains; temporary, forming dense thickets after fires. 

66. Ceanothus tomentosus Parry. Sierras (Amador County) southward to the San 
Bernardino Mountains and San Diego. 

67. Ceanothus velutinus Dougl. British Columbia to California; south in the Coast 
Ranges to Marin County, and in the Sierras to Kern County; eastward to the Rocky Moun- 
tains. A very important species of the conifer-forest chaparral, with its companions form- 
ing forest undergrowth as well. 

68. Ceanothus verrucosus Nutt. Vicinity of San Diego, southward into northern Lower 
California. 

CORNACE.E. 

69. Garrya elliptica Dougl. Quinine bush. Coast Ranges from Oregon to the Santa 
Lucia Mountains. Usually present in small number in the climax chaparral; seldom abun- 
dant. 

70. Garrya fremontii Torr. Inner Coast Ranges and Sierra Nevada to San Jacinto 
Mountains. More closely identified with the conifer forest than with the climax chaparral. 

ERICACEAE. 

71. Comarostaphylis diversifolia (Parry) Greene. Southern California and northern 
Lower California. Representative of a genus almost entirely Mexican and Central Amer- 
ican. 

72. Xylococcus bicolor Nutt. Near the coast; San Diego County and northern Lower 
California. A rather important climax species within its limited range. 

73. Arctostaphylos andersonii A. Gray. Manzanita. 1 Of local distribution; Oakland 
Hills and Santa Cruz Mountains. 

74. Arctostaphylos drupacea (Parry) n. comb. [A. pringlei var. drupacea Parry: Uva- 
ursi drupacea (Parry) Abrams]. San Bernardino Mountains to northern Lower California. 
Belongs to the forest region of the higher mountains. 

75. Arctostaphylos glauca Lindl. From the San Francisco Bay region and Stanislaus 
County to Mount San Pedro Martir in Lower California. One of the most characteristic 
and conspicuous members of the climax chaparral of the southern half of the State. Gen- 
erally scattered among other shrubs, often Adenostoma, and standing out conspicuously 
by reason of its large size, smooth rounded form, and light gray foliage. Probably attains 
a larger size than any other species of manzanita. 

76. Arcloslaphrjlos liookeri Don. Near the coast, from San Francisco to San Luis 
Obispo County; in the Monterey region growing with other species of restricted range. 
(See No. 56.) 


'The name "Manzanita" is applied to all the species indiscriminately; also to the closely 
related Nos. 71 and 72. 


120 THE BROAD-SCLEROPHYLL VEGETATION OF CALIFORNIA. 

77. Arctostaphylos manzanita Parry. Mountains of the northern half of the State, from 
the region of San Francisco Bay and Stanislaus County into Oregon; almost complementary 
in range to A. glauca, and of equal or greater importance in the climax chaparral. 

78. Arctostaphylos mariposa Dudley. Sierra foothills and to some extent in the forest 
region. Of considerable importance where it occurs. 

79. Arctostaphylos montana Eastwood. Central Coast Ranges, very local; on Mount 
Tamalpais, where it is apparently confined to the outcrops of serpentine, which are avoided 
by other species of the genus growing on the mountain. 

80. Arctostaphylos myrtifolia Parry. Near lone, Amador County. Known only from 
the type locality. 

81. Arctostaphylos nevadensis A. Gray. Upper forest region of the Sierra Nevada; ex- 
treme northern California, the mountains of Trinity County, and in the Cascades of Oregon. 
A very low, spreading shrub, of considerable importance successionally in the high mountain 
forest regions. 

82. Arctostaphylos nummvlaria A. Gray. Outer north Coast Ranges; Santa Cruz 
Mountains; Mount Tamalpais to Mendocino County. Characteristic of the Mendocino 
"white plains;" not important in the chaparral. 

83. Arctostaphylos parryana Lemmon. Southern Sierras and Mount Pinos to the San 
Bernardino Range. 

84. Arctostaphylos patvla Greene. Cascades of Oregon; eastward to the Blue Moun- 
tains (northeastern Oregon) and Utah; south in California to Trinity County in the Coast 
Ranges, throughout the middle altitudes of the Sierras, extending to Mount San Jacinto. 
The most important species of the genus in the upper conifer-forest chaparral. 

85. Arctostaphylos pumila Nutt. Endemic in the Monterey region, growing with other 
local species already noted (see No. 56). A low, spreading shrub, resembling A. nevadensis 
in habit; an important sand-binder on the dunes of Monterey Bay. 

86. Arctostaphylos pungens H. B. K. Southern California (San Bernardino and Cuya- 
maca Mountains) and Lower California to southwestern Colorado, Arizona, and Central 
Mexico. Conifer-forest chaparral. An important species in the dilute chaparral of the 
Santa Catalina Mountains in Arizona. 

87. Arctostaphylos stanfordiana Parry. Of limited range in the inner north Coast 
Ranges from Mount Diablo to Mendocino County. A rather rare species of the climax 
chaparral, conspicuous by reason of its yellow-green foliage. 

88. Arctostaphylos tomentosa (Pursh) Dougl. Southern British Columbia through west- 
ern Washington and Oregon and the Coast Ranges and Sierras of California to Lower 
California. Probably the most widely distributed member of the genus except A. uva- 
ursi and possibly A. pungens. Extremely variable; several more or less well marked species 
have been segregated, and the synonymy of the group is confused. An important member 
of the chaparral, mainly in the climax type; frequently the only manzanita present, and 
in such cases forming the bulk of the growth of the less xerophytic situations. 

89. Arctostaphylos vestita Eastwood. Endemic in the Monterey region, growing with 
other local species already noted (see No. 56). 

90. Arctostaphylos uiscida Parry. East slopes of the inner north Coast Ranges and the 
Sierra foothills; northward to southern Oregon. An important member of the chaparral 
of the digger and lower yellow pine zones; forming a very beautiful gray-green cover when 
in pure growth. 

HYDROPHYLLACE.E. 

91. Eriodiclyon californicum (H. and A.) Torr. Yerba santa. Coast Ranges and lower 
Sierras. Belongs mainly with the climax chaparral; infrequent, however, in dense brush; 
characteristic where climax conditions have been disturbed; frequent along roads and 
trails in the chaparral. Three other species of Eriodictyon occasionally occur in the chap- 
arral, but have been excluded from the category of dominants. 

The Secondary Species. 

In the following paragraphs the normal undergrowth of the 
broad-sclerophyll forest and the climax chaparral is presented. 
In addition a list of incidental species might be compiled and extended 
indefinitely. Some of these are of considerable importance, one 


THE BROAD-SCLEROPHYLL VEGETATION OF CALIFORNIA. 121 

group particularly so. This includes species that belong properly 
to the early stages of primary and secondary successions, remaining 
as relicts in the climax or subclimax. They have been considered 
at some length in the section dealing with development. 

A complete list of the forest undergrowth is here impracticable, 
since the flora is so different in various parts of the State. This is 
especially true in the outer Coast Ranges, where a large element of 
the herbaceous flora of the redwood forest would have to be included. 
In the central Coast Ranges, away from redwood dominance, the 
following shrubs are important as undergrowth: 

Holodiscus discolor Rubus vitifoliua C. and S. 

var. ariasfolius (Wats.) Jepson. Symphoricarpos racemosus Michx. 

In the lowest stratum Aspidium rigidum var. arguium Eat. and 
Micromeria chamissonis (Benth.) Greene are prominent throughout 
the year, and species of Fritillaria, Calochortus, Trillium, Smilacina, 
and other spring-flowering genera are conspicuous for a brief time. 
A complete list from a single typical locality is given on page 38. 

The herbaceous vegetation of the normal undisturbed chaparral 
is exceedingly scanty, both in number of species and of individuals. 
Further, few of the species that do occur can be considered as peculiar 
to the chaparral. All of them could without serious inaccuracy 
be consigned to the category of incidentals. However, a few have 
been selected which seem to be more characteristic of the chaparral 
than of any other community. All of these are perennials. Naturally 
they are more abundant in the less xerophytic situations. This list 
is fairly complete only for the localities with which I am most familiar. 
Doubtless other species would be added with more extended obser- 
vation. Several have the peculiar habit described under Zygadenus 
fremontii. 

List III. — Herbaceous Species of the Chaparral. 

92. Gymnogramme triangularis Kaulf. Gold-back fern. Rather frequent in the more 
mesophytic situations. 

93. Pellaea mucronala (Eaton) Maxon [P. ornithopus Hook.]. Bird-foot fern. Char- 
acteristic of especially dry situations, often where the chaparral is thin. 

94. Zygadenus fremontii Torr. Frequent under the chaparral bushes in suppressed 
condition, not flowering in such state; conspicuous after fire or clearing, flowering freely 
and seemingly suddenly increasing in abundance. 

95. Xerophyllum tenax Nutt. Turkey-beard. Decidedly infrequent, but very con- 
spicuous after fires. 

96. Chlorogalum pomeridianum (Ker.) Smith. Soapweed. Similar in habits to the last. 

97. Brodi&a californica Jepson. Twining brodiaea. An anomalous member of the 
genus in its climbing habit; straggling and weakly twining upon chaparral bushes; lower 
altitudes of the Sierra Nevada. 

98. Lilium washingtonianum Kellogg. Washington lily; chaparral lily. In the chapar- 
ral of the Sierras and in the mountains of northern California, and northward to the Colum- 
bia River. 

99. Aster radulinus A. Gray. Growing in suppressed condition; flowers after clearing. 


BIBLIOGRAPHY. 

(1) Abrams, L. R. 1910. A phytogeographic and taxonomic study of the southern 

California trees and shrubs. Bull. N. Y. Bot. Gard. 6; No. 21: 300-485. 

(2) 1914. Uva-ursi. In North American Flora, vol. 29, pt. 1: 92-101. New 

York Botanical Garden. 

(3) and F. J. Smiley. 1915. Taxonomy and distribution of Eriodictyon. 

Bot. Gaz. 60: 115-133. 

(4) Adamovic, Lujo. 1909. Die Vegetations-verhaltnisse der Balkanlander. Engler 

und Drude: Die Vegetation der Erde, XI. 

(5) Adams, C. C. 1902. Southeastern United States as a center of geographical dis- 

tribution of flora and fauna. Biol. Bull. 3, No. 3. 

(6) Barber, J. H. 1898. A glimpse of the San Gabriel forest reservation. The For- 

ester, 4: 240-242. 

(7) Beck von Mannagetta, G. R. 1901. Die Vegetations-verhaltnisse der illyrischen 

Lander. Engler und Drude: Die Vegetation der Erde, IV. 

(8) Bergen, J. Y. 1903. The macchie of the Neapolitan coast region. Bot. Gaz. 35: 

350-362; 416-426. 

(9) Boerker, R. H. 1915. The reforestation of brush fields in northern California. 

Proc. Soc. Amer. Foresters 10: 284-293; also For. Quart. 13: 15-24. 

(10) Brandegee, K. 1894. Studies in Ceanothus. Proc. Calif. Acad. Sci., ser. 2, vol. 

4: 173-222. 

(11) Brandegee, T. S. 1889. Plants from Baja California. Proc. Calif. Acad. Sci., 

ser. 2, vol. 2: 117-216. 

(12) 1891-92. The vegetation of "burns." Zoe 2: 118-122. 

(13) 1893-94. The southern extension of the Calif ornian flora. Zoe 4: 199-210. 

(14) Branner, J. C. 1909. Santa Cruz folio. U. S. Geol. Sur., Geol. Folio No. 163. 

(15) Briggs, L. J., and H. L. Shantz. 1911. A wax seal method for determining the 

lower limit of available soil moisture. Bot. Gaz. 51: 210-219. 

(16) Cannon, W. A. 1911. The root habits of desert plants. Carnegie Inst. Wash. 

Pub. No. 131. 

(17) 1913. A note on a chaparral-forest relation at Carmel, California. Plant 

World 16: 36-38. 

(18) 1914. Specialization in vegetation and in environment in California. 

Plant World 17: 223-237. 

(19) 1914. Tree distribution in central California. Pop. Sci. Mo. 85: 417-424. 

(20) 1918. The evaluation of the soil-temperature factor in root growth. Plant 

World 21: 64-67. 

(21) Clements, F. E. 1916. Plant succession. Carnegie Inst. Wash. Pub. No. 242. 

(22) 1920. Plant Indicators: The relation of plant communities to process 

and practice. Carnegie Inst. Wash. Pub. No. 290. 

(23) Cooper, W. S. 1917. Redwoods, rainfall, and fog. Plant World 20: 179-189. 

(24) Davy, J. B. 1902. Stock ranges of northwestern California. U. S. Dept. Agr., 

Bur. Plant Ind. Bull. 12. 

(25) Diels, L. 1906. Die Pflanzenwelt von west-Australien sudlich des Wendekreises. 

Engler und Drude: Die Vegetation der Erde, VII. 

(26) Drude, O. 1890. Handbuch der Pflanzengeographie. 

(27) Dudley, W. R. 1901. Zonal distribution of trees and shrubs in the southern 

Sierra. Sierra Club Bull. 3, No. 24: 298-312. 

(28) Eastwood, Alice. 1903. Notes on Garrya, with descriptions of new species and 

key. Bot. Gaz. 36: 456-463. 

(29) Engler, A. 1902. Die pflanzengeographische Gliederung Nordamerikas. Ab- 

druck, aus dem Notizblatt des konigl. bot. Gart. Appendix IX. 

(30) Foster, H. D. 1912. Interrelation between brush and tree growth on the Crater 

National Forest, Oregon. Proc. Soc. Amer. Foresters, vol. 7, No. 2: 212-225. 

122 


BIBLIOGRAPHY. 123 

(31) Fuller, G. D., and A. L. Bakke. 1918. Raunkiaer's "life forms," "leaf-size 

classes," and statistical methods. Plant World 21: 25-37. 

(32) Gemoll, Kurt. 1902. Anatomisch-systematische Untersuchung des Blattes aus 

den Triben: Rhamneen, Colletieen und Gouanieen. Beih. zu Bot. Cent. 12: 
351^24. 

(33) Greene. E. L. 1893. Vegetation of the summit of Mount Hamilton. Erythea 1: 

77-97. 

(34) 1893. Vegetation of Mount Diablo. Erythea 1: 166-179. 

(35) Grinnell, Joseph. 1908. The biota of the San Bernardino Mountains. Univ. 

Calif. Pub. in Zool. 5: 1-170. 

(36) Guttenberg, Hermann RiTTER von. 1907. Anatomisch-physiologische Unter- 

suchungen liber das immergrune Laubblatt der Mediterranflora. Eng. Bot. 
Jahrb. 38: 383-444. 

(37) Haefner, H. E. 1912. Chaparral areas on the Siskiyou National Forest. Proc. 

Soc. Amer. Foresters 7: 82-95. 

(38) Hall, H. M. 1902. A botanical survey of San Jacinto Mountain. Univ. Calif. 

Pub. in Bot. 1: 1-144. 

(39) 1912. A Yosemite flora. 

(40) Hansen, George. 1897. Ceanothus in landscape of the Sierra Nevada. Garden 

and Forest 10: 102-103. 

(41) Harshberger, J. W. 1911. Phytogeographic survey of North America. Engler 

und Drude; Die Vegetation der Erde, XIII. 

(42) Herzog, Theodor. 1903. Anatomisch-systematische Untersuchung des Blattes 

der Rhamneen aus den Triben: Ventilagineen, Zizypheen und Rhamneen. 
Beih. zu Bot. Cent. 15: 95-207. 

(43) Howell, Thomas. 1903. Flora of Northwest America. 

(44) Jepson, W. L. 1891. Botany of the Marysville Buttes, Sacramento Valley. Bull. 

Torr. Bot. Club 18: 317-327. 

(45) 1893. The mountain region of Clear Lake. Erythea 1: 10-16. 

(46) 1899. Vegetation of the summit of Mount St. Helena. Erythea 7: 105-113. 

(47) 1910. The silva of California. University Press, Berkeley. 

(48) 1911. Flora of western middle California. 2d edition. 

(49) (Date?) Regeneration in manzanita. Madrono 1: 3-11. 

(50) Leiberg, J. B. 1899. San Bernardino Forest Reserve. U. S. Geol. Sur., 19th 

Ann. Rep., pt. 5: 359-365. 

(51) 1899. San Gabriel Forest Reserve. U. S. Geol. Sur., 19th Ann. Rep., 

pt. 5: 367-371. 

(52) 1899. San Jacinto Forest Reserve. U. S. Geol. Sur., 19th Ann. Rep., 

pt. 5: 351-357. 

(53) 1900. San Bernardino Forest Reserve. U. S. Geol. Sur., 20th Ann. Rep., 

pt. 5: 429-454. 

(54) 1900. San Jacinto Forest Reserve. U. S. Geol. Sur., 20th Ann. Rep., 

pt. 5: 455-478. 

(55) 1900. San Gabriel Forest Reserve. U. S. Geol. Sur., 20th Ann. Rep., 

pt. 5: 409-428. 

(56) 1902. Forest conditions in the northern Sierra Nevada, California. U. S. 

Geol. Sur., Prof. Paper 8. 

(57) Livingston, B. E. 1910. Relation of soil moisture to desert vegetation. Bot. 

Gaz. 50: 241-256. 

(58) McAdie, A. G. 1902. Wet and dry seasons in California. U. S. Dept. Agr. Year 

Book, 1902: 187-204. 

(59) 1903. Climatology of California. U. S. Weather Bur. Bull. L. 

(60) McKenney, R. E. B. 1901. Notes on plant distribution in southern California. 

Beih. zu Bot. Cent. 10: 166-178. 

(61) Merriam, C. Hart. 1893. Notes on the distribution of trees and shrubs in the 

deserts and desert ranges of southern California, southern Nevada, north- 
western Arizona, and southwestern Utah. U. S. Dept. Agr., Div. Biol. 
Surv., N. A. Fauna No. 7: 285-343. 

(62) 1899. Results of a biological survey of Mount Shasta, California. U. S. 

Dept. Agr., Div. Biol. Surv., N. A. Fauna No. 16. 


124 BIBLIOGRAPHY. 

(63) Merriam, C. Hart. 1905. The Indian population of California. Amer. Anthrop., 

n. s., 7: 596-606. 

(64) Miller, L. C. 1906. Chaparral as a watershed cover in southern California. 

Proc. Soc. Amer. Foresters 1: 147-157. 

(65) Moore, Barrington. 1917. The moisture withholding power of soils. Jour. 

For. 15: 110-117. 

(66) Munns, E. N. 1916. Results of the effect of chaparral and forest cover on meteoro- 

logical conditions. Sci. 44: 759-760. 
(g7) 1919. Some biological and economic aspects of chaparral. Jour, of For- 
estry 17: 9-14. 

(68) 1920. Chaparral cover, run-off, and erosion. Jour, of Forestry 18: 806-814. 

(69) Nichols, G. E. A working basis for the ecological classification of plant com- 

munities. Ecology: in press. 

(70) Niedenzu, Franz. 1890. Tiber der anatomischen Bau der Laubblatter der Arbu- 

toidese und Vaccinioidese in Beziehung zu ihrer systematischen Gruppierung 
und geographischen Verbreitung. Eng. Bot. Jahrb. 11: 134-263. 

(71) Parish, S. B. 1903. A sketch of the flora of southern California. Bot. Gaz. 36 

203-222; 259-279. 

(72) 1917. An enumeration of the pteridophytes and spermatophytes of the 

San Bernardino Mountains, California. Plant World 20: 163-178; 208-223; 
245-259. 

(73) Piper, C. V., and R. K. Beattie. 1915. Flora of the Northwest Coast. State 

College, Pullman, Wash. 

(74) Pltjmmer, F. G. 1911. Chaparral. U. S. Dept. Agr., For. Serv. Bull. 85. 

(75) Purdy, Carl. 1897. The chemise world. Garden and Forest 10: 72; 83. 

(76) Purpus, C. A. T. 1897. Die Chaparral-region der siidwestlichen Sierra Nevada 

von Californien. Mitt. d. deutsche dendrol. Ges. No. 6. 

(77) Reed, W. G., and J. B. Kincer. 1917. Average annual precipitation map of the 

United States. Mo. Wea. Rev. 45, No. 7. 

(78) Reiche, K. 1907. Grundzuge der Pflanzenverbreitung in Chile. Engler und 

Drude: Die Vegetation der Erde, VIII. 

(79) Sargent, C. S. 1905. Manual of the trees of North America. 

(80) Schimper, A. F. W. 1903. Plant geography upon a physiological basis. Transl. 

by Groom and Balfour. 

(81) Shreve, Forrest. 1915. The vegetation of a desert mountain range as conditioned 

by climatic factors. Carnegie Inst. Wash. Pub. No. 217. 

(82) Shull, C. A. 1916. Measurement of the surface forces in soils. Bot. Gaz. 62: 

1-31. 

(83) Smith, W. G. 1913. Raunkiaer's "life-forms" and statistical methods. Jour. 

Ecol. 1: 16-26. 

(84) Solereder, Hans. 1908. Systematic anatomy of the dicotyledons. Transl. by 

Boodle and Frisch. 

(85) Sterling, E. A. 1904. Chaparral in northern California. For. Quart. 2: 209-214. 

(86) Sudworth, G. B. 1900. Stanislaus and Lake Tahoe Forest Reserves and adjacent 

territory. U. S. Geol. Sur., 21st Ann. Rep., pt. 5: 499-561. 

(87) 1908. Forest trees of the Pacific Slope. U. S. For. Serv. 

(88) Transeau, E. N. 1905. Forest centers of eastern America. Amer. Nat. 39 : 875-889. 

(89) Trelease, W. 1895-97. Rhamnaceae. In Asa Gray; Synoptical flora of North 

America: 401-419. 

(90) Warming, E. 1909. (Ecology of Plants. Trans, by Groom and Balfour. 

(91) Wilkomm, M. 1896. Grundzuge der Pflanzenverbreitung auf der iberischen Halb- 

insel. Engler und Drude: Die Vegetation der Erde I. 


THE BROAD-SCLEROPHYLL VEGETATION 
OF CALIFORNIA 

AN ECOLOGICAL STUDY OF THE CHAPARRAL AND 
ITS RELATED COMMUNITIES 


BY 
WILLIAM S. COOPER 


Published by the Carnegie Institution op Washington 
Washington. October, 1922