THE UNIVERSITY OF CHICAGO
AH ECOLOGICAL SURVEY OF THE PORCUPINE MOUNTAINS
A DISSERTATION SUBMITTED TO THE FACULTY OF TEE OGDEN GRADUATE SCHOOL OF SCIEHCE IH CANDIDACY FOR THE DEGREE OF DOCTOR OF PHILOSOPHY
DEPARTMENT OF BOTANY
CHICAGO .ILLINOIS
NOVEMBER. 1923
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INTRODUCTION
1
EARL IER INVESTIGATIONS III THE PORCUPINE MOUNTAINS - 3
LOCATION AND PHYSIOGRAPHY - - - 5
CLIMaTE OP THE REGION - 7
THE CLIMAX FORMATIONS - 11
I. THE HEMLOCK CLIMAX - 12
A. Aspect of the forest - -- -- -- -- -- -12
B. Composition and dynamics of the forest - - - 16
1. Consideration of individual species - - 17
2. Quadrat studies ------------22
3. Initial physical factors and
competition ------------25
4* Equilibrium at any point --------28
C« Successions leading to the hemlock climax - - 29
1. Primary successions ----------29
a. Physiographic influences ----- 29
b* The shore successions -------31
Types of shore - - '- - v- ----- 34
2* Secondary successions in the Hemlock climax - -----------
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II. THE MAPLE CLIMAX - 38
A. General physiographic features ------- 39
B. Successions relations - -- -- -- — - - 41
I. Xeruroh successions on the first range - 41
(1) Summit of the range -------42
fa) Ecological factors ----- 42 (b) The plant associations - - - 43 fc) Quadrat studies -------47
(2) The escarpment and its asso¬
ciations ----------50
(3) The talus slope ---------53
f4) Forest below the talus ------ 58
II. Hydrarch successions in the valley
of Carp River -----------61
a. Carp River ------------64
b • Carp Lake ------------66
o. Flood plain -----------69
SUMMARY - 71
REFERENCES - 77,78,79,80
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Map showing general position of the Porcupine Moun¬ tains in Ontonagon County, Michigan.
INTRODUCTION
In his classic article on the climax forest of Isle Royale, Lake Superior, Cooper (5) refers to the trans- itional zone between the two great phytogeographic regions - the northeastern conifer forest and the eastern deciduous forest. Certain features of both regions, he says, are found in the southwestern portion of the island; but he did not carry out his first intention of tracing the relat¬ ions between them. On the mainland of Michigan to the south, the maple forest is well developed, especially at certain inland points. Areas near the coast, however, may show many transitional features, such as occur in the Porcupine Mountains, which are about 125 km. south southwest of Isle Royale. These so-called mountains, which are really prominent hills or hilly ridges, represent the highest points of land reached in the Upper Peninsula. As Leverett (20) points out, they are "the most conspicuous features in this entire area, for they rise on their north slope very abruptly from the shore of Lake Superior to a height of 1400 feet above the lake".
The purpose of this ecological survey was to make a careful study of the climax formation of the region, in eluding their relations to each other, and to correlate, if possible, the various plant associations occurring within them.
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The Porcupine Mountains consist roughly of three ranges of hills, paralleling the coast (fig. 1), that nearest the shore b&ing the most rugged. Back of these lies a table¬ land stretching south to the Gogebic Range.
It was not found possible to examine all of this territory; nor does it seem essential to an understanding of the vegeta tional development of the region. Practically all the detail studies were made in connection with the first range, and the valley of Carp River behind it. It must be admitted that this near-shore region received most attention because of its greater accessibility, yet aside from this it seemed of major importance for the following reasons: (1) on account of the pioneer conditions found on the first range, where the summit still remains unclaimed by vegetational development, (2) on account of the proximity of Lake Superior, permitting the observation of various stages of succession along the shore, (3) the proximity of a comparatively high altitude (for the region) to the wind-swept surface of Lake Superior, giving a definiteness to the larger problems of vegetation, (4) a forest covering which gives it unusual value for a study of the relation between two climax formations, (5) opportunity for observing praotically primeval forest conditions.
Field work was carried out in the sunnier of 1922. Headquarters were first established at a point on Union
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Map showing a portion of the Porcupine Mountains.
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Bay (Sec. 16, T. 51 H» H 42 W«). This was found to be the most convenient location for the examination of the shore line and the hemlock forest of the north slope. Later, head¬ quarters were located on the site of an old mining property near Carp Lake. All the work in connection with Carp River valley and the summit of the range was done from this point.
I wish to express my appreciation of the encourage¬ ment and co-operation of Dr. H. C. Cowles of the University of Chicago, under whose direction the work was undertaken.
I also wish to thank Dr. Geo. D. Puller of the same institution for suggestions in regard to the method of work. To the follow ing gentlemen, I desire likewise to extend my thanks. Dr. A. J. Grout of New Brighton, II. Y. , for the determination of about 45 species of moss. Dr. Bruce Pink of Miami University, Ohio, for the determination of about 60 species of lichens, and Dr.
E. A. Bessey of the Michigan Agricultural College, for assist¬ ance in various ways. The nomenclature used in connection with the pteridophytea and spermatophytes is that of GRAY'S MANUAL, seventh edition.
EARLIER INVESTIGATIONS IN THE PORCUPINE MOUNTAINS-
The early interest attaching to an exploration of the mountains was based on the prospect of finding copper. Indications of this interest are shown in the abandoned shafts and wordings in various parts of the region. In 1848
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Pig. 1. - Carp Lake from top of fir at range, looking southwest: second and third ranges in the distance: escarp ment of first range extending H. S. W. (extreme right); outlet of lake at far end.
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the mountains were visited by W. D. Whitney (11) acting as botanist on a government expedition in charge of J. W. Foster. The following year, several places on the south shore of Lake Superior were visited - as far west - Whitney says, as the Ontonagon Valley and Carp River, both being in the vicinity of the Porcupines. In the second report on the region (IP) , which was published in 1851, Whitney gives a list of plants seen in the Upper Peninsula, including some from Isle Royale. This list, being very general, gives no clue as to what species were observed in the Porcupine Mountains. In JACKSON'S LAKE SUPERIORS), published in 1849, Bela Hubbard, a geologist, in discussing the origin and character of the soil in the Porcupines, points out that the sugar maple pre¬ dominates throughout the elevated portions, 'while hemlock is the prevailing tree upon the lower lands.
During the next fifty years, apparently little was done in the way of botanical investigation in this region.
In the summer of 1903, F. E. Wright (£8), Assistant State Geologist, continued the work, earlier begun under the direction of Dr. L. L. Hubbard, of preparing data for an accurate geological report and map of the mountains. During a part of this time he was accompanied by Dr. A. G. Ruthven
of the University of Michigan, who became interested in the biological aspects of the country. In 1904 and 1905, the
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University Museum sent purties to northern Michigan to make biological studies in the Porcupine Mountains and in Isle Royale. One party, led by ])r. Ruthven, spent one month in the Porcupines and the remainder of the season on Isle Royale. The report of this expedition fl) came out in 1905* It covers both regions, listing 91 species of plants, and notes the ecological distribution of the more important species.
A list of over 600 plants found in the neighboring county of Gogebic should be mentioned. It was based on work done by Dr. £• ii. Bessey and the writer (10) during portions of the summers of 1919 and 1920.
LOCATION AND PHYSIOGRAPHY.
The Porcupine Mountains are in Ontonagon County in the Northern Peninsula of Michigan, in lat. 47 0., long. 90 w. (see map). Thoir unique position, close to the south shore of Lake Superior, has already been pointod out. Thoy reach a maxi - mum altitude of 616 m. above sea level or 435 tn. above the level of the lake. The top of the first range or ridge comes within 2 km. of tho shore. Its north slope is rather gentle, but becomes increasingly stoop as one approaches the summit, finally reaching a height of 275 m. abovo the lake in sec. 14, T. 51 B. R. 43 W. There is then a sudden descent of about 120 m. to the valley Of Carp River, half of this descent bOfcng, in places, vertical rock face, at tho base of the cliff there
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Pig. 2. - Geological map of a portion of the Porcupine Mountains, showing their relation to the Keweenaw Series to the south. (After Irving).
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i8 a talus slope extending in places several hundred meters down the side of the valley. This great cliff extends for a distance of about 10 km. across T. hi U. R. 43 W. It is interesting to note Poster’s impressions on first seeing this great outcropping of rock in 1848. He says "Suddenly the traveler finds himself on the brink of a precipice five hundred feet deep, at the base of which lies a small laice, so sheltered and hemmed in by the surrounding mountains that the wind rarely ripples its surface. Gloomy evergreens skirt its shores, whose long and pendant branches are so faithfully reflected on the surface that the eye can with difficulty determine where the water ends and the shore begins. Prom this lake flows the Carp River, and the beholder occasionally catches a glimpse of its waters as they wind through the narrow valley towards the great reservoir".
Geologioally , the mountains form a crescent-shaped off -shoot or spur from the main range to the south (fig. 2). This latter extends from Keweenaw Point southwest to Wisconsin, including the well-known iron and copper ranges of the Keweenaw Series. The ranges of the Porcupines consist largely of eruptive rocks with interbedded sandstones and conglomerates, the strata tilted from 30° - 40° . They represent part of a pre-Cambrian upheaval, probably during early Proterozoic time. The present system of hills forms a comparatively small
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Geological sections illustrating the struc
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portion ( fig. 3) of the original land mass, the rest having been removed by erosion during a very long period of time.
At the beginning of the glacial period, the general topography was probably much the same as at present. The mountains were laid bare at a relatively early date, mating a cusp in the ice front, presumably between the Warren and Algon¬ quin stages. According to Lane (19) the water was ponded on the north side of the mountains to a depth of 171 m. above the present surface of Late Superior and on the south side at least 49 m. higher than this, the drainage being toward the Mississippi. Old beach lines on the north slopes show successive stages in the height of the late, where the late level was more or less stationary.
From what has been said, it is evident that the highest level lies bact of the first range, though the latter is much the most rugged. The rough topography is, in general, conditioned by the geologic structure of the region. The main drainage lines are occupied by the Carp and Little Carp rivers, which flow roughly southwest. These parallel the general direction of the ridges, and finally turn northwest, emptying into Lake Superior. A portion of the drainage is also east and southeast into the valley of Iron Eivor.
CLIMATE OF THE HBOIOH.
The following data were obtained through the courtesy of the U. 3. Weather Bureau at East Lansing; see also
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report by Seeley (£4). It is believed that tables I and II taken together give a fair index of the olimatio conditions. Ber gland, representing inland conditions, is about £7 km. south southeast of Carp Lake; it has an elevation of £15 m. above the surface of Lake Superior. Ontonagon is situated at the mouth of the Ontonagon River, 3£ km. east of Bergland. The tables show that the mean temperature for the year is very nearly the same for both places.
-TABLE I-
MEAH TEMPERATURE AT BERGLAHD FOR 11 YEARS
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°C — Jan. |
Feb. |
Mar. |
Apr. |
May |
June |
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-1£.9 |
-11.4 |
-4.1 |
4.1 |
10.5 |
16.3 |
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°C — July |
Aug. |
Sept • |
Oct. |
Uov • |
Dec. Yr. |
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18.6 |
16.9 |
1£.7 |
6.8 |
-0.£ |
-7.7 4.1 |
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-TABLE II- MEaH TEMPERATURE AT Oil TO 1J AG OH |
FOR 7 |
YEARS |
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°C — Jan. |
Feb. |
Mar. |
Apr. |
May |
June |
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-9.3 |
-10.8 |
-3.5 |
3.8 |
9 .£ |
13.5 |
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*C — July |
AUg. |
Sept . |
Oct. |
Hov. |
Dec. Yr. |
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17.8 |
17.4 |
14.0 |
9.4 |
0.7 |
-5.8 4.£ |
di eroriees in "the average monthly temperatures 0f the tm) P^cea indicate the probable moderating influence Ox ^Lq J.arge body of water* ^he average maximum temperature for 5 years at Ontonagon was 34.6° C. and the average minimum -^‘•7 C. The mean monthly temperature at Bergland for 11 ye&iii was above 0 C. for 7 months of the year, beginning with April, and the mean monthly minimum above this for 6 months, beginning with Hay. Tables prepared by the U. 3. Weather Bureau show that the average date of the last killing frost in spring is June 9, while that of the first Killing frost in the fall is 3opt ember 16, giving 89 days as the average length Ox uhe growing season. In this region the isotherms parallel the shore line, and the average temperature of points along the coat is several degrees warmer than inland points a few miles further back. During the hot summer months, however, the isotherms move back from the shore, so that the discrepancy between shore and inland conditions is not so great.
-TABLJ5 III-
AViSRAGiS MONTHLY PRJSC IPITATIOU AT B3RGLABD FOE 11 Y&ARS
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— Jan. |
Feb. |
Mar. |
Apr. |
May |
June |
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cm 4.05 |
3.26 |
4.27 |
4.70 |
7.86 |
8.87 |
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July |
Aug. |
Sopt. |
Oct. |
Ilov. |
Dec. Yr. |
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-TABLE IV-
AV ERASE MONTHLY PRECIPITATION AT ONTONAGON FOR 6 YEARS
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_ Jan- |
Feb. |
liar. |
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May |
June |
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cm -- 6.96 |
4-66 |
3.89 |
2.61 |
6.72 |
6.25 |
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— July |
iH* |
Sept. |
Oot. |
Nov. |
Be o. Yr. |
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cm — 11.37 |
8.42 |
9.27 |
4.37 |
5.86 |
7.02 74.57 |
1.&0 above data, while not extending over as groat a period of time as might be deuxrublo, would seem to indicate that the average yearly rainfall for the region is about 76 cm* The figures show that the average precipitation along the coast during the months from November to February is 305? greater than the precipitation at Bergland 26 ion. bacic from the coast- This may help tc explain certain striking differ¬ ences between the vegetation near the shore and that further inland- Slightly more than one-half the average rainfall occurs during the 5 months of the growing season (from May to September), apparently coming earlier in the season at inland points- The greatest average precipitation was in July.
The average number of cloudy days per month for 5
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Fig* 4. - iSxfJorior view of hemlock climax along a "forty” lino where the timber hue been cut: two eugar maples to the right, largo hemlock in the background, salmon berry and three email hemlocks in the fore¬ ground; elevation about 100 m. above Lake Superior.
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years at Ontonagon was 14, and partly cloudy 5, leaving an average of 137 clear days for the year. The prevailing direction of the wind at the same station is from the northwest, often veering around from the west.
The extent and ruggednesa of the Porcupines allow for much local variation. The above climatic data axe not meant to be more than general. Their character accords with the general mesophytic character of the vegetation in its larger aspects.
THE CLIMAX FORMATIONS.
There are two climax plant formations covering the ranges of the Porcupine Mountains. On the north slope of the first range occurs a typical hemlock: forest. This gradually merges into a maple forest near the top of the slope. From this point maple forms the climax formation on the ranges to the south, though scattered patches of hemlock: occur on the lower slopes. Any interpretation of the vegetation of the region must take into account the relation between these two formations, their relative position with respect to the larger physiographic features and the successions leading up to them. In this paper the hemlock climax will be considered first.
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I. Tim HJ&ILOCiC CL mAX
This is apparently the most mesophytic formation of the region. Its most typical development is on the lower half of the north slope of the first range. It is composed largely of three tree species: Tsuga canadonsi s (L.) Carr, (hemlock) , Acer ^accharum Harsh, (sugar maple) and Betula lutea Michx. f. (yellow birch). At the lower levels near the lake shore, the forest is almost entirely hemlock:, while near the top of the ridge it mergest into the less mosophytic maple forest.
Intensive studies were made at various points in the forest with a view to determining the relations between the three principal species. The life habits of each, from the seedling stage up, were studied as closely as time permitted. Interrelations of the species were also studied by means of quadrats and windfall areas.
A. Aspect of the Forest.
At first sight the forest appears to be almost a pure stand of hemlock. The boles are conspicuous below, but the upper portions of the trees, which are 25-30 m. or mere tall, form a dense mass of interlaced foliage, with a ragged skyline. Here and there are occasional trees of yellow birch, with more open tops; also a few tall spindling maples, devoid of foliage, excepting near the summit, and
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Pig. 5. - Showa distribution of yellow birch and maple, the conifers being r amoved; trees in the foreground are mostly maples; looking northeast toward Lake Superior; edge of forest to left; note abundant growth of aalmon berry aa a ground cover.
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often indicating by the presence of dead twigg, the com¬ petition to which they are subjected.
In section 16, T* 51 K* R. 42 W. , the hemlock: had been removed from certain "forties", making it possible to obtain a view of the general composition of the forest from the outside. This is shown in fig* 4. The three species mentioned are practically the only ones in evidence from an exterior view of a soction made in this part of the forest. Other large tree species, of less common occurrence, will be considered later.
In the area cut over, referred to above, only the conifers had been removed, leaving the two principal deciduous species standing, as shown in fig* 5* This gave an opportunity to estimate the relative distribution and character of the latter. An estimate was also made of the comparative number of species in the forest having a diameter not less than 1.5 dm. This was done by listing the individuals in a belt transect 220 m. long and 10 m. wide. It resulted In the following data so far as the principal species is concerned: hemlock, 80.5$; maple, 13.6$; yellow birch, 4.5$; basswood,
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On entering tho forest, one is impressed with the apparent age and maturity of the trees (fig* 6). The light is much reduced by the dense canopy above, formed principally
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Fig. 6. - Interior view of Liosophytio forest (see. 16, T. 61 K* R. 42 W#): trees mostly hemlook; a largo yellow biroh in foreground at left; a portion of the orown of a maple at the right; looking north to¬ ward Lake Superior; note gentlo slope.
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by the fine spray of the hemlocks. An examination over a large area shows considerable diversity in regard to light conditions, the differences boing due to more or less open areas caused by windfalls of varying ages. In reality the forest may be considered as a patchwork of these windfalls, which are ever appearing, maturing their growth and con¬ sequently producing a general shift in the position of the better lighted areas.
The forest floor is rather uneven and on the whole well drained, the general direction of the gullies being north (towards Lake Superior). A few of these gullies are occupied by small streams, even during the summer months, while others contain no running water* but are very moist, so that the moisture content of the soil is quite variable for different portions of the forest. This seems to be the controlling factor in causing certain departures from the ordinary composition of the forest (fig. 7).
There is comparatively little shrubby vegetation in the dense hemlock forest. Of the few shrubs found, probably Lonicera canadensis Harsh, (bush honeysuckle) is the most shade tolerant. The most important ecologically is Rub us parvlflorus Ifutt. (salmon berry), which is very quick to appear where an opening admits even a little more light to the forest floor. The bottoms of shallow draws
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Pig* V. - Shows a *78 1 tor, more open por¬ tion of the forest, in which tho predominant large tree is arbor vitae: in the foreground, salmon borry, and 30 idlings of maple, balsam, and white spruce; other tree seedlings ob¬ served vjere yellow birch, basswood, and whito
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are sometimes covered with it, evon when partially shaded.
Large numbers of woody sugar maple seedlings from 2-6 dm. tall often form a shrubby growth of considerable ecological importance. Other shrubs and shrubby trees found more or lees frequently in or near the border of windfall areas are: Acer spicatum Lem. (mountain maple) , Amelanchier canadensis (L. ) lledie. (June berry), Salix rostrata Richards (Bebbfs 7,/illow) , Prunus Virginians L. (choke cherry), Cornus alternifolia L. f. (alternate -leaved dogwood) , and Corylus rostrata Ait. (beaked hazelnut ) .
In general, tfte herbaceous vegetation forms a closer index to the moisture content of the surface soil than the woody vegetation. . The most widely spread and shade-tolerant species of the hemlock forest is Aral la nudicaulis L. (wild sarsaoarilla) • Others of rather general distribution are:
Galium triflorum Kichx. (bed straw) , Aster macro phyll us L. (large-leaved aster), Clintonia borealis (Ait) Raf . , Pitched! a repens L. (partridge-berry) , Ox alia Acotosolla L. (wood sorrel^, Trientalis americana (Pers.) Pursh. ( star-f lower ) , Lycop odium ennotinum L. (stiff club moss) and Aspidium spinulosum (0. F. Mtlller) Sw- var. intermedium (Muhl.) P. C. Eaton. The follow¬ ing list is not so characteristic, but it includes some which are frequently found along water courses or low ground:
Asplenium Pilix-f emina (L.) Bernh. (lady fern), Onocloa
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?%. Q. - Stand of sugar muplo, approximately 7a m.
north of the summit of the ridgo in see. 14. hi n. H. 43 tho trees here aro somewhat larger than is typioal; note comparatively dear forest floor; maple seedlings
in tho foreground.
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Struthiopteris (L. ) Hoff, (ostrich fern), Phegopteris poly- podioidea Fee (beech fern), Circaoa alp in a L. (enchanter's nightshade), Solidago latifolia L. (broad-loaved goldenrod), Mitella nuda L. (bishop's cap), Stroptopus roseus Itichx. (twisted-stalk), Cornua canadensis L. (dwarf cornel),
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Chinaphlla uribellata (L. ) Hutt. (pipsiosowa) , Pronanthea alba L. (rattlesnake-root). Aster paniculatus Lam., Kununculua recurvatus Poir. (rough cinquefoil).
Several species of moss and lichens lend color to the general aspect of the forest. One of the most conspicuous is Ileokera pennata (L.) Hedw. , forming green mats on the sides of the trees and oft on extending several meters up. On rotting logs in windfalls and along small crooks occur such moss species as Brachy thee ium salebrosum (Hof fin.) Bryol., Plagiothecium turfaceura lindb., Kypnum Crist a-Custrensis L. , and the lichen 3ticta pulmonariu (L.) Schaer.
B. Composition and dynamics of the forest.
As before indicated, one of the major problems in connection with the forest of the north slope, is to account for its composition, especially as regards the relation be¬ tween the hemlock and maple. As one ascends the slope the maple contingent becomes greater and the hemlock less, so that finally there appears to be at first sight an almost pure stand
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of maple (fig* 8).
The fact that the most conspicuous stand of almost pure hemlock forest is to be found on the north slope of the first range within about 10G0 m- of the shore is probably to be accounted for by climatic conditions, rather than by differences in character of soil. The present composition of the hemlock climax has undoubtedly existed for centuries. In other words, the forest as a whole is in equilibrium as regards the relative numbers of the component tree species at a given altitude. A casual observation of the stages of succession in a windfall area, might lead one to think that maple should be the predominant tree (fig. 9). For this reason it seemed necessary to consider carefully such questions as the rate of growth, habit, shade tolerance, etc. of the more important species, and the relationship of their development, as shown by quadrat studies.
1. COlf SID .SHAT ION OF INDIVIDUAL SPSCIiiS.
T3UGA CANADi&NSIS (hemlock).- This species continues to grow in diameter many years after its top has leached the crown of the forest, the result being that the stand consists of individuals with great diversity in their ages. Sapling stages are quite common, though their growth is often vory slow. The tolerance of all stages for weak light explains
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Pig* 9. - Seedlings of sugar maple in hemlock forest: thooo pioturod ara 1*5 • S.O dm* high, there being approximately 40 in¬ dividuals per square meter*
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the dominance of the species over maple, its nearest com- petltor in the forest. On account of this tolerance, suppression at eome stage of its earlier growth is the rule rather than the exception.
The tree usually seeds at intervals of every & or 3 years, and in spite of reduced fertility, many more seedlings start than are able to mature, even though they are not notice¬ ably abundant, us in the case of the maple. The production of seeds and seedlings is therefore not the critical fuetor in the regeneration of either species.
The species is extremely sensitive to sudden changes in the density of the forest, and seedlings respond quickly in rate of growth to alight increases in the amount of light admitted, but they are killed by too much light, and therefore the tree will not take a central position in an open vyiridfall unless it is sheltered by fast'er growing species. On account of its shallow root system, it is very susceptible to surface fires.
ACKR SACCHaKUM (sugar maple). - This species, as it occurs in the hemlock climaK, is tall and slim and free of limbs except near the top. The trees are apparently healthy, though all of them have undoubtedly suffered more or lees suppression. As al ready noted, the seedlings occur in such numbers that a superficial observation might lead one to
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Pig. 10. - View along an old wood road, which here acta ae an artificial •windfall: on each aide of the road there ie a donee growth of young maplee, E - 6 ra« high; ualmon berry in the foreground.
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conelude that the forest would, in a few generations, be¬ come a pure stand of maple. Closer observation soon shows that a very small percentage of these ever mature* Accord¬ ing to Fro thingham (13) the trees seed every 3-5 years under forest conditions; and oven-aged groups of very close- standing seedlings are of common occurrence* They prefer mapia leaf -mold and avoid areas covered with hemlock needles* The close and abundant growth of the seedlings results in such severe competition that the individuals are weakened and most of them succumb to suppresion or disease. However, the seedlings are very tolerant of shade conditions, arid a few here and there are able to persist, and take advantage of the increased light occasioned by a windfall* Indeed, the relative stand of maple and other hardwoods in the hemlock climax seems mainly to be conditioned by the number of windfall areas. In such areas. Hub us parviflorus often forms a ground cover, affording more or less protection to young seedlings which are exposed to strong sunlight.
BKTULA LUSHA (yellow birch). - This tree, coming next to maple in its distribution, is an important element in the climax formation. In the forest it becomes slim and tall with a clean bole, having limbs only near the top. A specimen was observed along a woods road about 30 m. tall, ivith a broad crown, occupying half the height; this tree was
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5*6 d m* in diameter and was fruiting heavily. It grows more rapidly than the maple end in its earlier stages requires muoh nore light* Seedlings are comparatively rare in the hemlock forest; when found, they are apt to occur in well- lighted windfalls* Sometimes they arc; very numerous on a email area in full sunlight • They occur also on rotting logs with hemlock and other seedlings, and are apparently free from disease. The natural point of regeneration for the apscics is in vindfall ureas* Where an area has been slightly burned over, the seedlings are sometimes very numerous* At one point, where the forest had been cut away, the mature specimens cf birch seemed nore prone to rot than the maple, apparently suffering from a sudden influx of bright sunlight; in other words, maple seems to be u less critical tree in most cf its stages, than the birch* The latter is a much less aggressive reproducer than the maple, in spite of the fact that it seeds mere often* It may and often does become extensive in its habit (Prothingham 13), producing largo stands of even-aged trees, which shows that its seed production has a high enough "factor of safety" to be vvell within the limits reouired by nature* Besides reproduction by seeds, this species readily sprouts from the stump* It seems clear that its relative distribution in the hemlock: climax is net based cn the perform¬ ance of its seeds, but on its less tolerance for shade con-
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ditions than the maple and hemlock*
omm SPiiCIKS OF TRKi$8 III TKK IDmOCK: FOREST. - Several other tree species occur, hut they are of less Importance eco¬ logically than those mentioned. One of those of occasional occur¬ rence is basswood (Tilia amor lean a L«). It gets to be a large tree, with a clear hole nearly up to the forest crown. Seedlings were frequently found, having a distinctly prostrate habit, the leaves becoming very large in the shade. (Thuja occidental is L. (arbor
vitas) occurs in low spots but is not a tree of general die-
%
tribution. As a forest tree it often becomes very large. Its presence along the shore line will be discussed litter. Pinus St rob us L. (white pine) is occasionally found as a very large tree, towering above the rest of the forest. My observations seamed to indicate that where one was found, several others were likely to occur in the some neighborhood. Abies bal Samoa (L. )
Mill, (balsam) is not common. It is rarely found as a mature tree in the hemlock forest, though seedlings are often frequent in windfall openings, and occasionally colonies of young trees are found in like situations. Whether this species will mature in competition with others evidently depends on the size of the forest opening; in most cases it is suppressed by the more shade- tclerant trees, \7hen it occurs as a mature tree in the forest, it is safe to infer that the opening was well lighted for a considerable length of time. Its beha\rior in this respect bears
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out the findings of Cooper (Z>) on Isle Royal 0, where he showed that the birth-rate of this species Is balanced by a high rate
of mortality when in competition with certain other species.
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Other tree species occasionally found in the hemlook climax are 2i eea canadensis (Mill.) BSP (white spruce), Quorcus rubra L. (red oak) , Fraxinua amerlcana L. (white ash) , and 0 atrya virgin 1 ana (Mill.) K. Jfoch (hop hornbeam).
B . QUADRAT STUD IBS .
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This method was found useful in connection with the study of forest regeneration, and the distribution of the principal species. 7/hare it became necessary to determine the average ages of the trees, this v?us done by means of tables prepared by Frothinghan (IS). The trees were too large to maxe felling practicable for this work. Besides the quadrat studies every other means that suggested itself was used for gaining a knowledge of the dynamics of the forest. The quadrats were 10 ns. square.
QUADRAT 1 (fig. II). - This quadrat shows the distribution of trees in the typical hemlock climax shown in fig. 6. It represents a condi tion of mature growth. Most of the trees here stand at w average distance of from £ to 3 m. It is noticeable, hovievur, that practically half of this quadrat is occupied by a giant hemlock 300 years old, -whose
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Fig. 11. - Quadrat 1 (see fig. 6 for locution): the numerals indi¬ cate the approximate ages of the
treos: the quadrat is 10 m* square.
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sjajiere of influence lias undoubtedly extended much further than the younger trees. The f or oat floor here was free of large shrubs; of small woody plants, 60 specimens of Rubus Parvlflorus wore counted, 14 of Lonlcera canadensis and at least 30u seedlings of Acer saccharum. The most conspicuous herbaceous plant was Aralia nudicaulis. Other herbaceous plants noted were Pliego p tor is Dryopteris, Cllntonia boreal is, Galium trifloruia, Mitch el la repons. I it ell a nuda. Cornus canadenai s. and Dyco podium annotlnun. In fact, both the woody and herbaceous vegetation were typical of a well-drained portion of the dense hemlock forest.
QUADRAT 2 (fig* 12). - This was taken in a windfall. It consists of comparatively young growth. The oldest standing specimens consist of a hemlock 130 years old, a white spruce 110, and a sugar maple 90 years old; and none of these had reached their full growth. The dominating influence of this hamlocK is clearly shown in the diagram.
Its dense spray is more effective in causing suppression than that of the maple or even of the white spruce. The best- lighted area of the quadrat is occupied by the younger growth, nearly one-third of which consists of balsam. The maple,
100 years old, shown near the top of the quadrat, was broken off several feet above the base by a secondary windfall, and in falling apparently leveled four other trees as shown.
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Abies baj s a.mea. &b Picea. ca.na.den & is pc.
Jietula. hjtea. bl Popu) us gran di dentata. pg
Fa.! ten tree. •—
Fig* 12. - Quadrat 2: taken In a windfall area in the hemlock climax
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consisting of two balsams, a yellow-birch, and a specimen of large-toothed aspen (Populua grand id entata ) . The last three species named are all faeter-grcwing than hemlock or maple. Of the 14 trees which are standing, 5 are balsams,
a hemlocks, Z maples and 1 shite aprftco. The oldest balsam is 50 years, and it is certain the other balsams will be
suppressed, probably before any one of them reaches loO. White spruce (l3icea canadensis ) is very rare in the hemlock forest, and it is likely that this single specimen will eventually disappear before the maturing hemlocks. This leaves the struggle between the 5 hemlocks and the 2 maples, and typifies the final stage in any windfall. It is vory suggestive as to the light it sheds on the ultimate com¬ position of the forest at this point.
Salmonberry and largo seedlings of mountain maple and sugar maple formed a low woody growth that acted as a screen for the usual herbaceous vegetation. The quadrat contained several hundred sugar maple seedlings, the oldest being about 5 years. These latter were very much affected by anthracnose leaf spot and by an insect disease. Ninety hemlock seedlings were counted, mostly growing on rotting logs in the shadier part of the quadrat. Large-toothed aspen was represented by 15 seedlings; the largest in¬ dividuals, though only 3 years old, were twice as tall as
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tho 5-ycur seedlings of sugar maple* Balsam seedlings wore found in the suimier parts of the quadrat, Zb individuals being counted* Several species of moss, already mentioned, were found on rotting logs in or near this quadrat* They are often of considerable ecological importance in the formation of seod beds*
In tho quadrat studies above described, certain conclusions in regard to shade tolerance and its effect in the distribution of the species, seem inevitable* This will bo considered in what follows*
3. IUITIiiL PHYSICAL FACTORS AND COMPETITION.
I<; is evident that a great many factors enter in to the dynamics of the forest* a few of those have been pointed out as thoy affect the life history and occurrence of the dominant species of troes* In a consideration of the composition of the hemlock climax on the north slopo, two questions arise* First, what cutises tho variation in com¬ position from tho base of tho elope to tho top of the ridgo, a difference in elevation of approximately 300 m.? Second, what is the most effective factor governing tho composition at any one point? Frothingham has pointed out that there are two sets of factors influencing the distribution and dominance of trees in tho natural forest, namely, physical, including soil, humidity, li^ht, etc. and physiological (biotic) including
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aggressiveness in reproduction, tolerance of shade, rate of growth, form, size, longevity, and resistance to injury and disease. The first question seems to he answered hy a consideration of the physical factors of moisture and light. Soil evidently has little to do with it; if all the hem¬ locks were removed from the north slope, maple oould easily take possession, as is evident from its regeneration in windfalls, and its prominence in the ranges further south. Hemlock, rather than maple, is thus the critical tree on the north side of the first range. This species is known to prefer cool, moist slopes, where the drainage is f&ir. Good drainage, however, may he left out of consideration here, as it occurs on the ranges farther south where hemlock is not prominent. The greatest humidity lies low along the lake shore. Here dense fogs are frequent even in the earlier part of the growing season. The smaller ratio of humidity at the higher elevations allows a corresponding increase in the intensity of the light near the top of the ridge. As before noted, hemlock is known to he very sensitive in its response to light; it is also known to he more shade tolerant than maple. Thus it seems clear that the dominance of hemlock at lower elevations on the north slope, and its absence as a dense stand on higher elevations and on the ranges further south, is correlated with the physical factors of moisture
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and light.
The answer to the second question involves the consideration of the relative physiological response of other species, especially maple and yellow birch, to the conditions imposed by the dominant hemlock. Hemlock and sugar maple, are the most conspicuous examples in the lake Region of what Fro thing ham calls intensive reproducers, i.e., species which are more aggressive inside than outside the forest. The effective aggressiveness of each species i3 due to a oonbination of factors. Both species, when growing under forest conditions, are likely to have a suppressed period of growth for at least the first 50 years. Quadrat studies show a great variation in age of individ¬ uals, even among the adult trees forming the forest crown, mature trees varying from 100 to 300 years or more. One hemlock, measuring about 1 m. in diameter, was estimated at over 400 years. The greatest tolerance of maple, how¬ ever, seems to be in the seedling stage, quadrat studies often showing hundreds of seedlings in the dense shade of the hemlocks. On the other hand, the seedlings of hemlock are rather critical in their light requirements, being killed by too much or too little shade. In general, they grow more abundantly in the more open part of the forest, but not necessarily in a windfall.
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4. EQUILIBRIUM AT ARY POINT.
Though the different tree species vary widely as to their relative production of seeds and seedlings, it seems certain that all are productive enough to be well within the limits required by nature. It has been pointed out by various observers that the "factor of safety” in seed and seedling production is very large and that there is an enormous wastage In all cases. While this larger seed production may be important on denuded areas, it seems clear that it has little to do with the relative number of in¬ dividuals of different species, where the dominant species are intensive, and where a balance has long been reached and maintained. This balance is changed little if any by excessive seed production of any species. It is conditioned by something more invariable than seed production. The true explanation seems to be the relative tolerance of the species for each other under the conditions imposed by the physical factors at that point. For example, the population of the yellow birch, which forms approximately 5^ of the total tree population half way up the north slope, is a measure of its relative response to the conditions imposed by the hemlock and maple. Since the equilibrium of the forest represents the result of the effective response of each species, the balance may be shown diagrammatically as
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hemlock magpie yellow birch a.11 other tree species
Fig* 13.*- Vector diagrams, illustrating approximate equilibrium (in number of individ¬ uals) at two points on the north slope of the first range: the uppor figure illustrates the conditions halfway up tho slope; the lower figure shows conditions of balance near the top; hemlock has been nearly replaced by maple; CD is represented largely by busBv/ood and iron-
wood
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in fig. 13* The vectors DA, AB, and BC# (upper figure) , illustrate the effective response of the three principal species somewhere up the north slope. Evidently the magnitude of the vectors does not correspond to the number of individuals of each species; in other words, while population may indicate response, it is not a measure of it. The vector CD indicates the effective control of all other species. The lower figure illustrates the conditions of balance near the top of the ridge. If any one species were eliminated from the forest, it would soon come back in approximately the some proportion at any point.
C. Successions leading to the hemlock climax.
1. Primary successions.
The primary successions leading to the hemlock climax may be seen along the shore of Lake Superior, at the foot of the first range. The pioneer stages are present in most cases, but the transition is often rather abrupt. Lack of well marked zonation is probably due to the severe conditions along the shore.
a. Physiographic influences.
The development of the shore line is correlated with the post-glacial history of the Lake Superior region. On account of the gradual withdrawal of the lake.
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Fig* 14* - Kooky shore a few miles west of Union Buy; shows sandstone beds dipping toward the north; the edges of the tilted strata off shore form a rocky terrace, break¬ ing more or less the foroo of tho waves; vegetation roudily establishes itsolf in tho joint und bedding pianos, as shown; white coating on the rock surface is Farneliu luctoa»
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more and more of the north slope of the first range has been uncovered, This has probably been counterbal anoed by erosion, and by the sinking of the ooast in this region, which is believed to be taking place (l).
The rock shore is the predominant type. Where it is gravelly or sandy, a little investigation shows that the rook is not far underneath. The exposed rock is largely red sandstone, dipping everywhere at an angle, as shown in fig. 14. In places conglomerate is exposed and loose boulders along the shore are frequent. The ?/idth of the rock beach varies from 15 to 45 m. Sandy or gravelly beaches in more or less protected places may be narrower than this, so that the forest comes comparatively close to the water, as shown in fig. 15, which shows a narrow gravel beach.
There is such a variation in the slope and character of the rocky shore that it is difficult to divide it into any definite zones in accordance with the ecological faotors influencing plant life. Its lower portion, being always subject to wave action, during both summer and winter, is devoid of plant life, exoept in sheltered corners of the rooks, which escape the direct pounding of the water. The lower limit of plant life is marked, roughly, by the maxi¬ mum height of the waves in summer. The winter waves and
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Fig. 15. - A narrow shingle beaoh, in which the forest comes unusually close to the water’s edge, being protected from the winter storms by the lodge of rod, off shore; note zo no of white birch and arbor vitae lining the shore at this point, bordered by salmon berry and Cornus al torn! foil- ; Bcmisetum arvonse growing in tho shingle.
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ioo usual ly roach much higher than this, and thus mark out the upper limits of u zone in which only tho hardiest per¬ ennials are able to survive.
b* The shoro successions.
Since the surface of tho lake has boon at tho present level for a long period of time, the distribution of the pioneer associations at any point along tho shoro has reached a balance which will remain practically the same so long as the climatic, ecological and historical factors remain unchanged* In other words, it is probably incorrect to say that active invasion or retrogression is taking place at the present time, even admitting the slight changes in coast line, due to subsidence or erosion.
The pioneer associations along the shore are composed of crevice plants, of lichens and of mosses. On account of the frugraontal nature of the rooks, crevice plants appear to be tho moot important pioneers; most of them are per¬ ennials. The seeds lodge in the moist cracks of joint and bedding planes, and germinate even where little or no soil is present. Gradually the seedling intercepts enough soil for tho establishment of a firm root system, and then is able to persist for many years, and spread by means of offshoots. Two of the commonest and hardiest species in tliio connection are Juncus Dudley! W iegand and Dos champ si a
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Fig. 16. - Shows a wall of conglomerate paralleling the shore, and forming a protective barrier to the forest be¬ hind it: oonifers and aspens growing under the xerophytlc conditions at the top; the conifers include a small white pino fin the background j , small specimens of white spruce, balsam, ana arbor vitao, all growing in the crevices of
tiio rod..
Fig. 17. - Shows Deooharapsia oaespltosa and ^stor Faxoni growing in a typioul situation along the shore: note dip of the strata, and fragmental character of the rock*
-32-
oaespitosa (L. ) Beauv. (huirgrass). The former was found growing within 3 dm. of the water; the latter is undoubtedly the commonest grass growing in the crevioes of the shore rooks.
Pig. 14 represents a typical situation for crevice vegetation. Such a habitat enables even woody plants to come in very early. In the foreground is shown a large specimen of ninebark (Physooarpus opulifolius ) and in the background a small speciman of mountain ash ( :pyr us sitchensis j ♦ The former has assumed more or less of the krummholz form of growth, especially on the lake or windward side; its habit of growth thus makes it more efficient as a conserver of soil and moisture.
The rate of succession along the outer shore is evi¬ dently not to be measured by the character of the plant life, the highest forms being found with the lowest. As before indicated, this rate is exceedingly slow, due to the severity of the situation. In spite of this, a large number of species are found. One group may be olassod as typical crevice plants. Among these, besides those mentioned, are Campanula rotund! - folia L. (bluebell), Aster Faxoni Porter, Soneoio Balsamitae Muhl. (groundsel), Fragaria virgin! ana Duchesne (strawberry), Achillea Millefolium L. (yarrow), Bquisetum arvense L. (horse¬
tail ) .
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Fig. 18. - Hocii surface well above the wash of the waves: the cruatose lichen is Parnel ia lactea; the mose (dar£ patches) Grirsnlu qpocarpa; Polypodium vulgar e in crevices near the top
of the boulder
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In the outer portion of the shore line, at least, shrubs often occupy the most exposed situations. The typioal species nre Physooarpus opulifolius (L.) Maxim, (ninebark), Rosa acicularis Lindl. var. Bourgeauiana Crepin (wild rose), Salix petiolaris Sm., and Cornus stolonifera Michx. f. f red -osier dogwood). The seedlings of Populus tremuloides often accompany the willows. Along the inner portion of the shore, tree seed¬ lings are frequent, the commonest being those of Thuja occi¬ dental is L. Here the usual successions occur, with lichens and mosses as pioneers. With a few exceptions, they are well above the wash of the winter wavos. The wash of the higher water can often be very accurately traced on large isolated boulders of conglomerate. This material, on account of its differential weathering, supports a richer flora of lichens and mosses than the sandstone, and the transition from washed to unwashed surface often appears rather abrupt.
Several species of lichen and moss occur in the severest situations. The pioneer crustose lichen appears to be Rhizo- oarpon petraeum (Wulf • ) Koerb. This form persists often under the lash of the winter waves. Other crustose forms common on the rooks further back are Plao odium aurellium (Hoffm. ) Tuck, and Lecanora oineraafL. ) Sommerf. A few species of moss, such as Ceratodon purpureus (L.) Brid., Leptobryum pyri forme (L.) Wils. and Funaria hygrometrioa (1. ) Sibth., occur in
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Pig* ly* - Shows the roots of vihite pine running for several meters along the surface and finally acting as an agent of rock displacement: the roots on the far side of the tree are covered hy a mat of Arctoataphylos Uvu-ursi ; small red pine and aspens bordering the shore in the back¬ ground.
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Pig* 20- - A broad type of ehingle beach, devoid of vegetation on account of the wash of the winter waves*
exposed crevices* In some cases they undoubtedly Jiave the way for higher plants. Further Inshore various foliose and fruticose lichens and mat-forming mosses form a definite stage of the rock succession. Among these may be mentioned Grimmia apocarpa (I.) Hedw., Amblystegium varium (Kedw.) Lindb., Btiota amplissima (Scop.) Mass*, Panne li a conspersa (Ehrh. ) Ach., StereE7caul on paschale (L.) Hoffta. and various, species of Cladonia,
Following the mosses and lichens one often finds the bearberry (arotostaphylos Uva-ursi fL*) Spreng, ) as a pioneer mat former. With the accumulation of more soil, shrubby species become more abundant. Besides those mentioned, the following occur:- Diorvilla Ionic era Mill, (bush honeysuckle), Amelanohier canadensis fL.) Medic, (shad bush), Oornus alter- nifolia L. f. and Rub us parviflorus IJutt. (salmon berry).
In the development of this succession finally come the trees, their roots sometime spreading 3 - 10 m. before finding.a suitable crevice for anchorage (fig. 19). Roots of this kind. form an important barrier for holding back soil washed from above. The fallen trunks also assist in the same manner, as well as finally furnishing additional humus by their decay.
-Types of she re -
The character of the shore vegetation is largely in-
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-35-
fluencQd by variations in physiography. This includes sub¬ merged ledges of rook, shore, cliff 3, coves and the accumula-r tion of shingle barriers. Submerged ledges, breaking the effect of the waves, and coves affording protected areas, are both factors in extending the forested area closer to the water's edge. The effect of these two influences may be seen in fig. 15.
It seemed possible to classify the shore into three general types, as shown in fig. 21. Fig* A shows a type in which the surface immediately back of the shore line is low. It often represents the mouth of a gully, and possibly of a drowned river (see Ruthven (23) p. 25). The area is swampy, usually being occupied by large specimens of Thuja ocoidentalis and Fraxinus nigra. It is sometimes separated from the immediate shore line by a narrow zone of shingle and driftwood. Back of the area, there is often an abrupt rise of from 6 to 10 m. to the typical hemlock forest.
In Bf the hemlock forest extends practically up to th3 shore line, though there is always a fringe of other species on the iimiedi ate outskirts, the commonest being arbor vitae and white biroh. Other species occurring are Abies balsam ea, Acer saooharum and Acer spioatum. Stages inter¬ mediate between A and B occur.
C represents the conditions whene the shore line
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-36-
is bordered by a rocky cliff. In this case the area above is often forested to the very edge of the cliff. On account of the dip of the strata, such areas are so well drained that the vegetation becomes xerophytic in character. This was found to bo true even where the soil was 3 dra. deep as was observed at one point. At this point the ridge had once been covered by a growth of pine, which had been blown dawn, and was being followed by a growth of white birch, aspen and balsam, the two formwr being on the lake side, being better able to adapt themselves to the unusually severe wind con-
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ditions.
2. Secondary successions in the hemlock climax.
In the latter part of the summer of 1919, an extensive fire swept over a portion of the north range, destroying several square miles of virgin hemlock forest.
This fire extended as far east as the range line between town¬ ships 42 and 43. The conffers were killed outright, though many dead trunks were left standing (fig. 22). It was very evident that the deciduous trees, including the sugar maple and especially basswood, were more resi stant to the effects of the fire than the conifers. This was especially trtioeable in the zone between the burned and unburned areas, where the trees were singed. Fig. 22 shows how thoroughly the humus
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. . . ■
37-
w&e burned off, exposing what appears to be ordinary talus material , composed of angular* unwashed fragments of sand¬ stone, mostly 1-3 dm. in diameter.
"Burn" associations had started over the entire area, being further advanced at some points than at others. She commonest herbaceous pioneers consisted of Krigoron canadensis L. (horseweod), JBpiloblum angustlfollun L. fprroat willow-herb ,
Aster raacrophyllus 1., .uraliu hispid a Vent, (bristly sarsa-
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parilla), and Holygonun Pour-la si 1 Greene. Amongst the shrubby species coming in next tho following were noted:- Hub us purvi- florus (s-lmon berry J, hunbueus racemose L. (red-borried eldor), Piervillu henio era Mill* (bush honeysuckle ) , Rhus typhina L. (staghorn sumac), and Kuhns ldaous X,. vur* aouleutlsslmua ( C. a. Mey. ) Hegel & Tiling. Tliese are followed by ? run as p pansy 1- vanica I». f., (wild red cherry), ^ cor spicatun Lam. (mountain maple), seedling aspens and occasional seedlings of sugar rauplo (iicer Bacoharum ) . Hemlock seedlings undoubtedly come in at a later stage, finally displacing the maple. One of the most noticeable elements of this secondary succession is Rubus parviflorus. The plant spreads rapidly over large areas by stems just below the surface, these stems sometimes being several meters long. The foliage forme a "leaf mosaic n which reduces the light to such an extent thut shade-tolerant speci os are able to make on early start, thus probably hastening the
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?i£. 23 • - Quadrat 3. This quadrat represents a stand of trees in a foroat of almost pure maple; it was taicen in sqc»14, about 1U0 m* from the summit of the ridge (see fig* 7)*
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-38-
climax stage.
II. THE MaPLE CLIML.
This is the formation associated with vegetation- al development at the top of tho first range and over the ranges further south. Its mature form may be seen 100 m. south of the summit of the range (fig. 8). Here a 10 m. quadrat was laid out (fig. £3). It represents a stand of almost pure maple. The larger trees averaged about 4 m. apart, the forest canopy being rather dense for maple. The uniformity in the ages of several of the younger trees marked them out as the survivors of a single generation of seedlings. In fact, the presence of several dead saplings varying from 30 to 40 years suggested that these trees had already reached a critical period in their development. Thrifty specimens of Tilia and Ostrya were found just outside the limits of the quadrat. The soil at this point was a rich leaf mold of medium acidity. It was not deep, as indicated by the root systems of fallen trees, exposing the bare rock. Though the forest floor was comparatively open, immature shrubby vegetation was repre¬ sented by specimens of Kubus parviflorus and Sanbuous race- mo sa. The latter species gets to bo vayy large and rampant in maple windfalls, dominating the ground cover. The follow¬ ing are typical herbaceous species:- ^spidium spinulosum
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-39-
(0. F. Mtillar ) Sw. vur. intermedium (Muhl.) D. C. Eaton, Phogopteris Dryopteris (L. ) Pee (oak fern), Afliantum pe datum L. (maidenhair), Botrychium vigfginianum (L.) Sw. (rattle¬ snake fern), Hystrix pa tula Moenoh. (ho ttle -Brush grass).
Hi lium effusum L. (millet grass), Solidago latl folia L. (broad-leaved golderirod ) , Kibes Gynosbatl L. (wild goosfebrryy), Smilaoina raoemosa (L.) Desf. (false spikenard), Actaea alba (I*) Mill, (white baneberry), Viola canadensis, L., Sanguinaria canadensis L. (bloodroot), Aral i a nudicaulis L. (wild sarsa¬ parilla), P olygonatum biflorum (Walt.) Ell* (true Soloman *s seal), and Galium triflorurn Miohx. (bedstraw). The last-named species is one of the commonest of the smaller groxmd covers*
The maple climax, as above described, occupies a comparatively narrow zone on the north side of the first range. As will be shown later its development on the south side is as yet in the early stages, this development being closely related to the physiographic foatures of the range and the adjoining valley of Carp River.
A. General physiographic features.
That the top of the first range still holds out against the mesophytic forest is undoubtedly due to the peculiar topography of this range. As is evident from fig. 3, this topography is associated with the geological formation
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Pig* 24* - Cliff and talus slope, first range: view from a point just east of Carp Lake, looking north; the cliff at this point is about 130 m. abovo the floor of Carp River Valley and 240 m* abovo Lake Superior; the face of the escarpment is approximately 65 m* high at this point; note fringe of forest between talus slope and river valley*
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Pig. 25. - View of cliff in section 15f T. 51 K . R. 43 W. , looicing east: in the foreground are shown tho last stages of the cliff, preceding the formation of a B&&dle; in places the soil has accumulated on the bare roc£; note xerophytic char¬ acter of the vegetation.
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•40
Of Carp Lake, which was once much larger than at present. frha dip oT the strata toward the north has created a great cliff or escarpment, which is continually weathering away, producing a talus slope at its foot (fig. 24). This cliff extends west and west-southwest across T* 51 B. H. 43 V/., a distance of about 10 km. I*c varies from point to point alo r the range as to elevation of summit, height of escarp¬ ment and width of talus slope. At. one point opposite Carp lake the talus descends into the luko; hut at most points there is a fringe of forest between the foot of the talus and flood plain of the river, as shown in fig. 24. In sec.
14, there is a depression in the cliff where the escarpment has entirely disappeared leaving a saddle across the range.
The same thing, though less marked, occurs about a mile west in sec. 15, and in varying degrees at other points along the range, making it possible at such places to descend into the valley without difficulty. Where a saddle i3 sufficiently low, as in sec. 14, the talus is almost entirely covered by soil washed from above, and the fringe of forest, from below may extend clear across the depression. In sec. 15. (fig.
25} this process has not gone so far. There is still a rock faco varying from 3 to 5 m. high. The relation between the various physiographic features as thoy appear at different points along the range is shown in fig. 26.
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Pig. h6. - Typical cross-sections at various points
through the auranit of tho first range
-41
A represents a stage of the cliff found opposite Carp Lake in sec* 22. Here the escarpment is high and the talus slope dips into the lake. At this point the trap and sandstone portions of the cliff can readily ho di stinguished. The trap is superimposed upon the sandstone, and has under¬ gone a greater disintegration, forming a ledge as shown.
B and 0 typify ordinary conditions whore the escarpment is high and the talus slope from £00 - 300 m. wide, bordered by a more or less mesophytic forest at the foot. At 3) is shown a stage where the top has been rounded off to such an extent that xerophytic tree species, such as red and white pine, are able to gain a footing. The former is usually more abundant under the brow of the cliff, where it is more or less sheltered. The latter is found in the more exposed situations, being the first to creep over the top when the conditions become favorable. Stages B, C, and D may all be seen in section 14. IS and F represent stages at a low point in the range, such as is shown in fig. 25, preced¬ ing the formation of a saddle. Here tho talus slope is much reduced, the forest pushing well up toward the summit,
even though the latter may still remain xerophytic.
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B- Successional relations
I. Xeraroh successions on the first range. m ecological survey of the vegetation
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Pig. £7. - Limit of forotst growth on summit of ridge, looking oast. The prevailing direction of the wind is from the southwest; this is more or less evident from the general direction of the branches in the small pines shown; clump of small red pines in background (to left); basrberry mat on rock in foreground.
-42
involves an examination of the environmental factors and plant successions (1) at the summit (2) along the escarp¬ ment (3) on the talus slope (4) below the talus slope*
(l) Summit of the range.
fa) Ecological factors. In general, the forested area of the north slope may fall short of reaching the crest of the ridge, as shown in fig. 26, E, or may reach slightly over the summit, as at F. From this point to the brink of the precipitous cliff, which averages from 20 - 40 m., there is usually a large amount of bare rock surface. Where the soil has accumulated, it is of very slight depth. There seem to be two principal reasons for this condition, both being due to the presence of the escarpment; fl) the soil due to rock disintegration is washed over the south side of the crest nearly as fast as it is formed, (2) the escarpment itself forms an effectual barrier to the encroachment of the mesophytic forest below. This zone of bare or nearly bare rock surface therefore re¬ mains unprotected. Its exposed situation makes it especially susceptible to the dynamics of weathering, including the frost of winter, the heat of summer, full exposure to rain and to all winds from the south. A portion of the soil wafefced over the crest accumulates in a narrow strip along the top of the talus slope. The rest is gradually washed
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Fig. 28- - A portion of tho summit, looking oust: Carp River in the valley below fat right); small red pines and stunted aspens to tho left, back of which a transition zone occurs as shown in fig- 32, leading to the maple climax of tho north slope; note pines growing from crevices in face of escarpment.
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down through the talus, finally reaching the forested area at its foot. On the other hand, soil found on the north crest is soon cheeked in its descent by the forest. A certain amount of it collects in depressions and irregularities of the rock surface and along the edges of joint planes, affording a foothold for crevice plants and matted vegetation.
(b) The plant associations.
The pioneer stages at the summit consist of lichens and mosses on the bare rock surface, and on the ground. Among the commoner crustose lichens appear such forms as Lecanora cinerea, Rhizocarpon petraeum and PI ac odium aurellium. Following these come foliose species, Parmel ia conspersa (Khrh. ) Ach. being the most conspicuous and covering a large proportion of the rock surface; Physcia obscura ( Schaer. ) Hyl. , Lecanora garovaglii and Gyrophora hyperborea Ach. are less common. Where a slight amount of soil has accumulated on the rock surfaces, fruticose types appear, common species being Cladonia rangiferina (L. ) Web., Claddmia sylvatica (L.) Hoffm. , and Stereocaulon paschale (L.) Hoffm.
Associated with the lichens in the pioneer rock suc¬ cessions are moss species, such as Grimmia apooarpa, Poly- trichum piliferum Schreb. and Tortella tortuosa (L. ) Limpr. ,
the two latter being the commonest. One of the early mat
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Fig. 2^* - Cioae-up of rock eurface, crest of ridgo: in the foreground, Juniperua communis var. deprea8a,Danthonla aplcata. Antennuria noodiolca, Potontillu trldentata. Poly¬ gonum Dougiaeii (lower right) , and Parmelia conapersa, the dominant lichen; Solid ago randii var. nentlcola in the back¬ ground.
formers is Solaginalla rpuestris (L.) Spring., often Cover¬ ing large areas on the rook surface. It is not uncommon to find superposed upon this mat the two common mosses already mentioned. The Selaginella mat becomes nearly 1 dm. thick in plaoes, living plants growing on the dead mat of former generations. This paves the way for her^ baceous plants, such as Danthonia 3picata (L.) Beauv. (wild oat grass), Potenti 11a tridentata Ait. ( three -too tiled cinquefoil), and even for woody species, such as the bear- berry (Arctostaphylos Uva-ursi (L.) Sp r eng. ) and stunted specimens, (2 - 4 dm. high), of staghorn sumac (Khus typhina L.). The roots of the latter creep over the rock surface for several decimeters until finally they may become anchored in a crevice, arctostaphylos is especially well adapted to the severe conditions found on these rock surfaces. Often it occurs in large patches, thus aiding in the retention of more soil and the conservation of soil moisture. Large angular depressions in the rook surface may occasionally be found where enough moisture is retained to support even shrubby growth without being definitely anchored in a crevice. Such a case was illustrated by a low specimen ( 2 - 3 dm. high) of Hew Jersey tea (Oeanothus am eric anus L. ) which had adapted itself completely to the shape of the depression, but could be pulled out bodily as a dense mat.
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-45-
Muoh of the rook at the bare summit is more or less porous in texture; rook fragments are numerous but irregular. Joint and bedding planes are not as distinctly marked as on the face of the escarpment. Whenever a orevice occurs, however, soil readily collects, and a number of plants gain a footing. The summer flora is practically a xerophytic one; the occurrence of certain vernal species, however, indicates that during the spring there is a comparatively large amount of moisture on the ridge, due in part, pro¬ bably, to the melting snow. Of the orevice plants, Danthonia spioata, already mentioned, is one of the most important, on account of it3 abundance and its densely tufted habit of growth. Other noteworthy crevice plants are Soli dago randii Britton var. montioola Porter, Potentilla tridentata. artemisia candata Michx., Woodsia ilvensi s (L.) R. Br., Campanula rotundifolia L. (harebell), Viola arenaria DC.
(sand violet), Aquilegia canadensis L. (wild columbine), Panicum denauperatum Muhl. and Panicum meridionale Ashe.
Where a small amount of dry soil has accumulated, the following occur: Antennaria neodioica Greene (everlasting ) , Lechea striota Leggett (pinweed), Panicum xanthophysum Gray, Satureja vulgaris (L.) Fritsch. (basil), Aralia hispida Vent, (bristly sarsaparilla), Apocynum androesi-
mi folium L. (spreading dog bane ). Bpigaea repeps L. (trailing
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arbutus), Hieraciuri soabrnii Iliohx* (huwkweed), lip il obi pis angnstifoliun L*, ^.ster macro hyllus L., Corydalls semper- vlrons (L • } Pers. , Oerastlun arvonso L«, Fragaria vosc->
L. var. a nor io ana Porter, apd Our ox adust., Boott.
It will be noted that the above are porronnial species* A few annuals occur, such as Silono antlrrhlna L*, (sleepy catchfly), Kr Igor on canadensis L. (horse-weed), and Poly¬ gonum Pouglasll Greene. These annuals lead a precarious existence, as their seeds must, in tho main, bo washed over the cliff each year* The distribution of the above herbaooous species varies considerably from one point of the ridge to another. Their presence results in the accumulation of humus, especially in depressions or in connection with dead mats of Solaginella*
Accompanying the herbaceous vegetation are a few speoies of low shrubs, the commonest being species of blueberry (Yaceiniun p onnsylvani oura Lam. var. angustl- folium (idt«) Gray and Vaooiniuci nigrum Britton). These often form largo patches slightly bach of the summit, where more soil has accumulated. Other spocios found along the summit are:- Juniporus oonmunis L. var. non tana A it., Bosa aclcularis Lindl., Sails humulls Marsh., Dior- villa Lonicora Hill*, Shepherd la canadensis fL.) IJutt., and stunted specimens of Juneborry (iimolanohier oana-
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Fig. 30. - (laaplo oliiaax) t 14, T. 51 ft. ft.
Transition to mosophytic forest top of ridge, at a point in sec. 43 17.; soo description of quadrat
4 and 5
-47-
densis (L.) Medic.
A few dwarfed specimens of white pine (Pinus Strobus ) are scattered along the summit, but the species is much more common over the crest of the ridge (fig. 24), where it receives more shelter and moisture. The gray pine (Pinus Ban Asians Lamb.) was noticed at only one point.
The limit of forest growth is bordered by a very dis¬ tinct transitional zone all along the summit. The general character of this is shown in fig. 28, but it varies a great deal in composition at different points of the ridge, ap¬ proaching more mesophytic conditions at lower elevations. Gnarled and stunted specimens of red oak ( Quercus rubra L.) are mingled with aspen (Populus tremuloides Michx. ) and white birch (Betula alba L. var. papyrif era (Marsh.) Spach. ) , the latter sometimes appearing in almost pure stands.
(c) Quadrat studies.
A detailed study of the transitional zone was made at a point in sec. 14, just west of the saddle (see map).
This is typical of most of the ridgo. Beginning at the area of bare rock surface shown in fig. 29, situated approximately 25 ra. bacA from the face of the cliff, a series of four quadrats was taken in succession, the last being in the mesophytic forest (fig. 50). These quadrats were 10 ra. square, making the total width of the transitional
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Acer sa.ccha.rurn as Qoercua rubra. <^r Bctu I <a_ |utea_ bl Ostry*- virgin I a.n <t ov Populut t. remu lo '• ole*
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Pig. 31.
Quadrat a 4 and 3; see
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zone 40 in. at this point.
QUADRAT 4 (fig. 21) was taken to include a portion oi the rock surface (fig. 29 )f as well as the marginal tree growth. Here the soil was thin and dry, the ground sloping gently toward the south. Several small red pines (Pinus resinosa ) represented the typical tree growth. They stood comparatively close, with small dead ones intermingled, amongst the red pines were a few small white pines and balsams. Aster macrophyllus L. formed a large proportion of the ground cover. Besides this were several other speoies already mentioned as typical of exposed portions of the ridge, such as Salix humulis, Vacoinium spp., Artemisia cauda ta. etc.
QUADRAT 5 typified the zone of scrubby red oaks (fig. 32), a characteristic belt very often following the conifers. The oak growth consisted mostly of sprouts (up to 3 m. high) coming from old root crowns in very shallow soil. This quadrat came Just north of the crest, so that the surface sloped gently towards the north. The conditions, however, were still xerophytic, as indicated by the presence of such plants as Aral ia hispida, Danthonia spioata, and large patches of ffunaria hygrometrica. There were also a few scattered seedlings of aspen, white birch and sugar maple. There were some evidences of burning on this
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Pig. 32* - Zone of transitional tree growth at quadrat 5: note red pines, email red oaks, and aspens; bare rock surface in places; the conspicuous grass is Danthonla spieata.
\
49
quadrat, so that conditions might not have heon entirely typical, Funaria hygr ometri oa was found to be very common in burned areas over various parts of the region. In general the oak sprouts soern to be the ecological equivalent of young rod pine. The ground cover was much the sane as the preceding quadrat, with the exception of Polygonum dume- torum, a very common species along- the edge of the meso- phytic forest,
QUADRAT 6 represents a transitional stage from quadrat number 5, in which the oak constituent has reached a higher 3tage of development, the individuals attaining a height of from 7 - 10 m., with much less sprouting, though still indicating somewhat unfavorable conditions. The pre¬ sence of red maple and numerous sugar maple in the northern half of the quadrat indicated the transition to the meso- phytic maple forest.
QUADRAT 7, The striking feature of this quadrat
I
v/ as the dominance (in numbers) of sugar maple saplings 5-10 cm. in diameter. Intermingled with these were well developed specimens of red oak (up to 15 m. or more high), hop hornbeam (Ostrya virginiana ) and yellow birch (Be tula lutea ) .
Following quadrat 7, the maples gradually in¬ crease in size, of ton accompanied by basswood and a thick
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grcwth of red-berried elder ( Sambucus racemosa ) t the
latter disappearing or becoming less frequent in the denser shade of the mesophytic forest further down the slope. Along the upper limit of the maple forest, it is not uncommon to see the flat, upturned root systems of trees, especially maples, which have adapted themselves to a layer of soil not over 1 dm. thick over the rock surface. This area is more or less subject to windfalls, apparently not because the velocity of the wind is greater here than nearer the summit, but because it forms a critical line between the low types of trees which spread their roots out through the shallow soil, with crevice connections in many oases, and the taller types which owe their increased size to a deeper, richer soil, but which offer a greater leverage to the force of the wind.
The above description of the transition from rocky summit to mesophytic forest applies in general to the higher portions of the range. Variations naturally occur, depdnding op the elevation, exposure, local topo¬ graphy and depth of soil.
(2) The escarpment and its associations.
The height of the rock face or escarp¬ ment varies at different points along the range, as shown in fig. 24. The upper portion may be vertical or nearly
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Pig. 33. - Overhanging ledge of
cliff shown in fig. 25* £z shows dip of the strata (sandstone); various plants gain a foothold in the moist crevices (see text p.5l ) .
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so. The lower portion curves around to meet the talus slope, which is very steep at the top; or there may "be a series of lower escarpments wi th shorter talus slopes be¬ tween as shown at the left (fig. 24). Owing to the dip of the strata, the face of the cliff is alv;ays very uneven, and the seams of the rock, on account of the direction of dip, often retain a sufficient degree of moisture to support the more xerophytic tree types. The unusual sever¬ ity of the situation so far as vegetation is concerned, is due to the continual splitting off of rook fragments from the parent rock.
The cliff is often "broken by ledges, due to different resistances of the various kind of rock to weathering; these may vary in width from a few decimeters to several meters, with corresponding accumulations of soil. On the vertical rook faces, a few species of lichens may be found, such as Locidoa lucida A oh., Gyrophora vellea (L.) ach. and Ainphlloma lanuginosum (Hoffm. ) Uyl. The vortical face of sandstone represented in A, fig. 26, is marked by bands of the yellow lichen, Placodium elegans. Where ledges overhang, as shown in fig. 33, the conditions are more moist on account of the shade. Amphiloma lanupin- osum and the leafy liverwort, Radula complanata, aro usually
abundant; also various foliose and frutiooso lichens, such
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Vig* 34* - Hock ledge on face of escarpment .look¬ ing east: in the foreground, two snail white pines and small specimens of Prurtua pennsylvanlca. Phus typhlna. and Corn us clrcinata; also Arctostuphylos Uva-ural , Artemisia caudata. and Danthonla spicata; in the back- ground, a snail red pine, and loaves of oak (Ouorcus rubra) showing below; Parmelia conspersa on rock sur¬ face above and below; V/ocdsla llvensis and Campanula rotundifolla growing from rock crovices fin foreground)*
such as Physcia obscura (Schaer.) Hyl. , Parmelia caperata 5 Ach. , Puiaullna calicaris (L. ) Fr. , and Qyrophora vallea (L.) Ach* In the crevices of such ledges occur two character¬ istic fern species, namely. Poly podium vulgare L* and Woodsia ilvensls (L.) R. Br.
The flora of the exposed ledges is very variable*
On the smaller, newer lodges, a few lichen epecioa, such as Lecidea lactea (Plot.) Sohaer. and Parmolia conspersa (rlhrh.}
Ach* nay gain a footing* On larger ledges, the higher plants are usually well represented, from small herbaceous species to trees whose roots are anchored in some of the bigger cre¬ vices (fig. 34)* Typical species are shown in the figure*
Among others nay be mentioned Potentilla tridentata. Pan i cue; xanthophyaum. CeanOthus oner ic anus , ??ubus parviflorus. Amel- anchier canadensis. Polystichum Lone hit is , Thuja occidental is . and Juniperus co; munfta L* vur. mentana Ait*
When there is a marked difference in rate of weathering between the sandstone and trap, a bread ledge 10 - 16 m* aoross mey be formed (fig* 26A). On account of the greater deposit of soil and consequent storage of moisture, the con¬ ditions here are much moro stable* Such an area may develop a comparatively thicx stand of pine, thriving under the pro¬ tection of the cliff.
The destiny of the escarpment is the condition seen
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Fig. 36. - View of first range, looking 14: Carp Kiver and valley to the right; shows reduction of escarpment and advance of forest
east, in sec. stage in up the slope*
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-63-
where at present saddles cross the range. Gutting will continue at the top and face, and filling will continue at the bottom until the lines of cut and fill meet. In¬ vasion of mesophytio types will principally be from below, the summit holding out longest against the final meso-
X
phytic forest. Fig. 35 shows a stage approaching such a condition.
(3) Talus slope.
In general the width of the talus slope depends on the height of the escarpment, especially where the latter is not broken by large ledges. When the face of the cliff is low, the band of talus is comparative ly narrow, for here the rock fragments from above do not come in sufficient numbers to prevent invasion of the
forest below. Where the cliff is high, many of the larger
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fsagments may roll 200 or 300 m.,* effectively checking the growth of the forest beyond this point. The resulting area is desolate in appearance ffig.36), very little vegetation gaining a foothold except near the top and bottom.
Where the cliff is principally sandstone, the rock fragments are smaller and more flattened than where trap predominates. In the former case soil apparently collects more quickly and vegetation makes a more rapid invasion.
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Fig- 36. - Bottom of talus immediately west of saddle in seo. 14, looking east: angle of slope here is about 30°; note line of forest as it creeps over the saddle across the low point of the range; the cliff at this point is very high and the talus field 200 m- or more in width; shows character¬ istic clumping habit of white birch when growing in talus-
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-64-
As pointed out bofor \ there are two points on the talus where soil first begins to accumulate, namely, the bottom of the slope along tho margin of tho forest and the very top - at the foot of the asoarprient • Host of that at the top is due to fine material v/hioh is washed over from the summit and hold in place. This finer soil, coupled with the shadier conditions directly under the cliff, gives rise to a narrow strip of vegetation composed of a complex of spool os, some pioneer and some more or less mosophytic in char actor, -among the more important of these are Plnus atrobus . Plnus re si no Sc .Quercus rubra t Prunus pennsylvonica. fop ulus trenuloidos, Coanothus am eri conns, ? sod ora quinque- folia, Rhus Toxicodendron, Oornus circinata. Khus typhina . Oolastrus sc and e ns, Ostrya virgin! ana, Arctostaphylos Uva- ursi, and Symphorioarpos racomosus Miohx. var. pauciflorus Robbins. This plant assemblage, especially as regards the more mesophytic species, is only temporary, for as tho cliff recedes, the vegetation must recode with it. As tho height of the cliff becomes less, tho increased light and lessened degree of moisture make conditions intolerant for the more mesophytic si)ecies. Finally, with the disappearance of the escarpment, only xerophytic species are able to endure , such as occur on the more exposed portions of the smaller talus slopes. The border of tho forest forms a tension
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Pig* 37* - Lichens and moosoa on the talus slope (see fig* 35); the conspicuous foliose lichen is Parmelia conspersa; the throe Cladonius (lower right) are rangif erina. C. eyl - vatica and pyxldatu; Hedwigia ciliata ( extreme left ) •
line at the bottom of the talus. Conditions for growth here are more favorable, not only on account of soil accumulation, but on account of the partial shade, -again, the pioneer species consist of lichens, which become more abundant here than higher up on the more exposed portions of the slope. By far the most conspicuous is Parmelia oonspersa. which covers the top of nearly every fragment of rook (fig. 37). The humus derived from this speoies paves the way for fruticose forms, such as Cladonla rangi- ferina (L. ) Hoffm., Cladonia sylvatioa (L.) Rabenh. and Cladonia pyxidata (L.) Hofffti. Following the lichens or sometimes closely associated with them are three species of moss, namely, Thuidium abietinum (L.) Br. & Sch., Hed- wigia oiliata iShrh. and Ceratodon purpureus (L.) Bride.
The two fern species already mentioned, Po'lypodium vulgare and Woodsia ilvensis, follow the lichens and mosses. They are very common along the bottom of the talus slope, send¬ ing their roots down between the slabs, an early stage of the me sophy tic forest may then follow directly as shown in fig. 36, where the talus is fringed by white birch. The conspicuous ommission of the usual mat stage here is due to the ability of the white birch to invade tho talus be¬ fore almost any other woody form. Clumping specimens with several stems often occur on the bare talus, sending thoir
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Fig. 30. - An advanced stage in the in¬ vasion of the talus slope: note small size of rocK fragments (sandstone); pioneer tree species consist of Populua grandidentata. snail oaks (Quercus rubra) , and small white pines (Plnus -3 1 rob us ) .
- .as .>j'
-56
roots far down between the fragments. In such cases they form nuclei for other pioneer speoies. Populus tremuloides and Populus grand! dontata are the pioneers along 3ome parts of the forest front.
as the cliff wears down and the talus elope becomes proportionately narrower, invasi on from both the bottom and top is accelerated (fig. 38). This is partially due to the fact that less new talus is put down, allowing the forces of weathering to establish a residual soil in which many speoies soon anchor themselves. One of the most efficient of these is Panic urn linear! foil urn Scribn. Evidence seems to show that it starts almost entirely by seeds from above. The warm nature of the talus soil, coupled with its moist condition during the early part of the season, must produce favorable conditions for germination of the many seeds which undoubtedly find lodgment there. Probably a very small percentage of tho seedlings are able to endure the very dry conditions which obtain during the summer. Other species of grass, such as Danthonia spioata, Qryzopsis June ea, and Oryzopsis asperifolia also come in early. Arotostaphylos Uva-ursl and Aster maorophyllus L. form mats over the bare fragments, the latter plant being more prominent as con¬ ditions become shadier. Its large leaves form a very effect-
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ive mosaic 1-2 dm, above the surface, enabling more aesophytio species to start# .associated with these in varying proportions are tho brake (uteris aoqullina h. ), the sulmonberry (Rub us parvifloruo Butt.) and the bush honeyoucklo (Mervilla Lonicora rill#), the latter often being very common on the upper, dryer portions of the slope.
The pioneer tree growth consists of small soattered individuals# If white birch be the pioneer spool os, which seems not always to be the oase, it is soon followed by the poplar spocios alroady mentioned and by scrubby specimens of red oak# Besides many seedlings of the above, several other woody species appear more or less during the early stages of invasion such as hop hornbeam (Ostryi virgin! an a frill# ) k# k och# ) , arrow-wood (Viburnum dent -turn L« ) » choke- cherry (krunus virglnlana L»). buffalo-berry ( Shepherd! a canadensis (L.) Butt.), Rubus procumbens lluhl. , Rosa acicul- aris Lindl#, and seedlings of basswood, white ash and sugar mapla#
Burly herbaceous species, as such, hardly form a definite stage in the succession in the sense of paving the way for woody growth# They may precede or accompany tfco latter, but are lator controlled by reaction# among the oonmoner species may bo mentioned Brigoron canadonsis L.
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(horseweed ) , Silene antirrhina L. (sleepy catolifly), Satur- oj a vulgaris (L.) Fritch. (basil), iiralia hispida Vent*
(bristly sarsaparilla), Convolvulus spithamaeus L. (ereot bindweed), Carey adusta Boott., Antennaria neodioiea Greene (everlasting). Frag aria vasca L. var. amerioana Porter (wild strawberry), Bpilobiuro angustifolium L, (fireweed), Adlumia fungosa (ait.) Greene (climbing fumitory), Apocynum androesimi- folium L. (spreading dogbane) and Campanula rotundifolia L. (harebell ).
The sequence of the invading associations varies greatly at different points along the range. While Be tula alba var. papyri f era is the dominant pioneer tree species at some points, at others it is Populuo tremuloides or Pop ulus grandidentata. The exact ecologioal relationship between these three speoies is an interesting problem, but it was not worked out. Even¬ tually the invading forest merges with the permanent fringe of forest below the talus. The latter is often dominated by sugar maple and red oak, but here again considerable var¬ iation occurs, which will be considered later.
(4) Forest below talus slope.
This extends in general from the flood plain of the valley below to the bottom of the talus slope above, pushing up tov?ard the summit or even reaching it at low points in the range. It may vary in width from a mere
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Pig* 39* - View of escarpment, looking north: vertical rock face about 70 m. high at tliia point; below this £00 - 300 m* of talus material, being invadod by pines and aspens; below the talua elope iu the front of the advancing forest, which slopes to the valley of Carp River bolow*
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-59
fringe of trees us ut A, fig. £6, to several hundred meters at P. While the trees species are mainly deciduous, espe¬ cially above, oonifers often occur near the bottom. These include white and red pine, balsam, arbor vitae, white spruce and hemlock. In fact, tlie last named speoies sometimes forms groves of large treos, similar to the climax forest of the north slope.
A transect of the forested area was made at a point just east of the saddle in sec. 14. Hear the top, the talus slope was being rapidly invaded by small oaks and
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aspens, as shown in fig. 33, Populus grandidentata being the dominant species, intermingled with scattering white birch and maple saplings. A little further down, the open spaces became fewer, the trees taller (up to 15 m. ), gradually form¬ ing a canopy above, giving perceptibly shadier conditions.
The soil contained more humus, derived largoly from the leaves of the aspens. Here patches of Aster maorophyllus and Aralia nudi caul is formed a large proportion of the ground cover. Occasional small specimens of white ash, balsam, hop hornbeam, and basswood were noted as invaders at this stage. The unfavorable conditions for anchorage produce remarkable clumping of the stems in certain speoies, espec¬ ially in the sapling stage of the hop hornbeam, sugar maple and red oak. Wine stems were counted in one specimen of
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Pig* 60* - Lower odge of foreot, border ing flood plain: the large tree in foreground io blade aeh; in the bacicground, Botula alba var* papyrifora. Bopulua tremuloidoa, Ac or rub rum. Cornua atolonif era. .hi! lx rootrata ana oalix petiolarie*
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hop hornbeam. Basswood overcomes the difficulty by ex¬ cessive sprouting. Approximately half way down the slope, a bench occurred, 15 - 20 m. wide, and nearly level. A striking feature hero was the appearance of rather large conifers, including specimens of white pine (up to 5 dm. dia. } balsam, white spruce, and arbor vitae. Poplar as the dominant species was replaced by red oak and white birch, ilore mesophytic oondi tions were indioatod by the presence of such species as Smilacina racomosa (L.) Desf. (false spikenard), Galium triflorum Iliohx. (sweet-scented bed straw ) , Hepatioa triloba Chair (liver-leaf), liaianthamum oanadense Pesf. (false lily-of-the-valley ) , Strootopus roseus Michx. ( tv/is ted -stalk ) and Mitohella re pens L. (part¬ ridge-berry). Gradually the oaks were replaced by the sugar maple, which became the dominant species to the edge of the flood plain, with white pine still frequent as a subdominant. At the edgo of the forest bordering the flood plain, the increased light and moisture conditions produce a marked change in tho ground cover, with a great diversity of species coming in. Seedlings of aspen (Pop ulus tremuloides ) and hazel ( Oorylus rostra ta ) seem to be responses to tho in¬ creased light. Tho frequent occurrence of wild black cherry (Prunus aorotina ) along the margin of the forest is undoubted ly a response to tho same conditions. Groves of aspon
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Fig. 41. - Gullying on south aide of first rung©, about halfway down the slope: white birch and aspen in the background; in the foreground, snail specimens of sugar maple and yellow birch; shoviu clumping specimens of hop hornbeam (upper right); ground cover mainly com¬ posed of Aral la nudicaulls.
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saplings mixed with white hi rah aro not uncommon (fig .40).
The appearance of many other woody species is due more to the itncreased moisture along the margin of the flood plain. Among these may he mentioned ffraxinus nigra Marsh. (black ash), Sal lx di pooler Kuhl • (glaucous willow). Viburnum Opulus L. ( cranberry- tree ) , nlmus inoana (L.) Moench.
(speokled alder), .acer rub rum L. (red maple), Spiraea salici - folia L. (meadow-sweet) and Cornus stolon! for a Llichx. (red- osier dogwood).
l'he complex of ibrost and flood plain species is very variable in its composition. This may be explained partly by the very unstable conditions in the valley and partly by ohanges in the edaphio conditions produced by gullying down the side of the rungo, with the consequent deposition of new soil near the bottom of the slope. A noteworthy instance of the latter occurs opposite the saddle in sec.
14 (fig. 41). Gullying in this case is due to the in¬ creased drainage over the saddle, resulting mainly from the melting snow in the spring. In the summer, its upper portion at least may be dry.
II. Hydraroh successions in the valley of Carp River.
As before indicated, the mesophytic forest be¬ low the talus slope is bordorod by Carp River or its flood plain. This flood plain is comparatively broad in the
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Fig* 42* - "Cedar swamp" # north edge of Carp Kivor valley: the lurge trees near the center are arbor vitae (Thuja occidentalia) ; the shrubs in the background are Alnus Inc ana, arid Cornua etolonifera*
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vicinity of the lake, due to the flat nature of the valley.
At this point the river is a sluggish, meandering stream 20 - 40 m. wide, doing very little vertical cutting, but shifting its course from time to time. Carp Lake is merely a broadened part of the river. According to Wright (28 ) the valley resulted not from the erosive action of a former river but to the pounding action of the waves on the shores of a vanished lake which covered the area. The present floor of the valley is subject to periodical flooding, in which a certain amount of sediment and debris from higher levels is laid down. There is thus a lack of stabilization in the edaphic conditions which prevents the encroachment of the mesophytic forest. The lino of demarcation between forest and flood plain is usually very abrupt, as shown in fig. 40. Flooding has the effect of producing irregularities and telescoping in the hydraroh successions paralleling the river, so that these successions are evidently not playing a prominent part in the formation of the forest. There are a few points along the range, however, where transitional bog forests may be found. One occurs between secs. 13 and 18, T. 51 H. (fig. 42). This is near the mouth of a drainage system coming directly from the ridge. This forest is quite limited in extent. Its interest lies in the suggestion it gives as to the character of the bog
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forest which will eventually procode the meso phytic forest as the latter claims the entire valley. The typical tree species are arbor vitae, white spruce, balsam, tamar- aoli and black ash. The forest floor is rough and often covered with a mass of shrubs, fallen logs and herbaceous grow tli. The soil is typical muck, having a fine texture.
In July the water table was approximately 3 dm. below the surface. Characteristic herbaceous plants are Aral! a nud i oaul i n . as tor naorophyllus . Galium asprollum Ilichx. , Aspiflium crista tun (L.) Sw., Clintonia borealis fiJLt. ) Raf • , Clrcaou alpinu L., Carox loptaloa .ahlerib. , and Habenaria hyperboreu fL.) Rydb.
The hydraroh successions of the river a nX flood plain contain many of the eloments of typical peat bog areas suoh us described by Davis flOa) for the Upper Peninsula.
On the other hand, there is a lack of definitoness in the sequenoo of the associations; and the sphagnum element, with its accompanying vegetation, is not at all common.
The latter condition is duo to the influx of fresh water during at least a portion of the year. A year of unusually high flood may destroy the continuity of vegetational development along cortain linos. This is well attested near the intake of Carp Lake by the dead und dying trunks of small black ash treos. Periods of exoessivo flooding
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Pig* 43* - Carp Kivor from the summit of the first range, looking i»* 3* i£*: the river flows west, emptying into Carp Lake; flood plain in the distance covered by an alder swamp*
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may approximately be measured by the oldest of these.
After such periods of high water, pioneer species again come in, initiating a new course of succession. A patch- work results, which is especially evident in the shrubby vegetation. This patchwork is further modified by the varying ability of the different species to withstand the presence of excessive water about their roots. The shorter -lived herbaceous forms often show more definite zonation, especially along such restricted areas as mud flats or sandy beaches bordering the river or lake. They are able to adapt themselves more readily to changing con¬ ditions.
In order to illustrate the tendency of the hydraroh successions in the valley, the associations found in the river, lake and flood plain, will be briefly described.
a. Carp River (fig. 42;.
Where this stream flov^s through the flood plain it is comparatively shallow with a muddy bottom. The slow-moving current makes the ecological conditions very similar to those found along the margins of many of the smaller lakes in the Upper Peninsula. Among the immersed aquatics may be mentioned, Potamogeton pusillus L., Potamogeton heterophyllus Schreb., Potamogeton zosteri- folius Schumacher, Potamogeton amplifolius Tuckerm.,
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Fig* 44* - Carp Kiver near north edge of flood plain: the a3i rub lining the bank at this point is principally Ainu a inoana: the aquatics are Spar gan iron euryoarpua and Mynphaoa advena; top of first range just visible in tho background (upper right)*
65-
Potamogeton natans L., Myriophyllum Farwellii Morong. ,
Ranunc ulus aquatilis L • var. oapillaoeue PC • , Hippuris vulgaris L.
The commonest large aquatic is Nymphaea advena Ait. (yellow pond lily); it sometimes forms patches extending half way across the stream. Castalia tuberosa (Paine) Creene (white pond lily) is much less common, though it occasionally occurs in large patches; the same may he said of the water-shield (Brasenia Schg&beri Gmel.).
In many places the stream is fringed with overhanging shrubs as shown in fig. 44. Mud banks often occur at the bends, supporting various aquatic or amphibious species, such as Potentilla palustris (L.) Scop, (marsh cinque-foil), Sparganium eyryoarpum Engelm. (bur-reed)., Bleocharis aoicularis (L.) R. & S.t Carex filiformis Good, (bog sedge) and Car ex striota Lam. The last two species form clumps at various points along the bank, thus enabling other species to obtain a footing.
The shrubby growth along the banks consists principally of the following:- ALmus incana (L.) Moench. (hoary alder). Hex verticillata (L.) A. Gray (win¬ ter-berry), Cornus stolonifera Miohx. (red-osior dogwood), Chamaedaphne calyculata (L.) Moench. (leather-leaf).
Spiraea salioifolia Roi (meadow-sweet), Salix petiolaris
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66-
Sol lx pedicellarls ?ursh (bog willow) and lucida iiuhi. (shining willow)* Two fern species, namely Osmund a regalia L. and Aopidium Tholypterls (L. )
Sw* » often occur at the margin of the water, more or lees shaded by the shrubs. Ciianaodaphno calvculata. though not the commonest shrub lining the river bank, is pro¬ bably the moat important in the formation of floating mats, these often starting from sedge hummocks. One effect of the mats is to cut off quieter bodies of water where various aquatic and amphibious specios are more success ful in establishing themselves.
One thing seems clear in connection with the successions along the margin of the river, namely their instability. Kven when Carp Lake as such, is gone, the river will still continue, though not in its present bed, as the bottom of the valley will have been raised through sedimentation.
b. Carp Lake (fig. 1) •
The lake lies parallel to the main ridges, covering the floor of the valley for a distance of about 2 km. Its broadest portion is near the east end, where it has u width of approximately 0.5 km. Excepting at this end, the nesophytic foest oxtends nearly to the water* s edge. At the east end a broad delta has been
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Pig. 45. - Delta, east end of Carp Luke, looking east: in the foreground, aclrpus occidentulis t aquisetura fluviatlle, and flypphaoa ad vena; narrow channel of tho river shown in the background; first range in the distance, showing saddle in
section 14
-67-
forraed, where Carp River enters the lake (fig# 45). The submerged part of the delta extends well out into the lake, being several hundred meters broad at its widest portion (fig. 46). Hero the water is shallow, varying from 3-10 dm. in depth. The west end of the lake is also shallow, and ohoked with aquatic growth and debris, especially near the outlet. In general the beaches are very narrow. Most of those on the north side are of the shingle type. In places they are entirely lacking, the shore line being directly bordered by a fringe of shrubs similar to those along the bank of the river. Sandy beaches occur on the south side and near the west end on the north side. They are broader than the gravel beaches and show more clearly the zonal development of vegetation. The edaphic con¬ ditions are naturally more stable around the margin of the lake than along the river. Especially is this true on the south side where deposition is occurring more rapidly than on the north.
The free-floating aquatic vegetation of the lake, being very similar to that of the river, need not be mentioned. The best evidences of plant succession are seen on the flat sandy beaches and on muddy flats near the delta. At the delta there is a zone of rushes extending from 50 - 100 m. out into the lake. Its outer part consists
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Fig* 46* - iSast end of lake, looking south toward second range: the zone of rushes ( Sclrpua cceidentulis) marks the shallow water over the submerged portion of the delta; the group of balsams along the opposite shore indicates the pres¬ ence of a small stream flowing into the lake*
-u8-
of the bulrush (Scirpu3 occldentalis (Wats.) Chase; then comes a zone of Equisetum fluviatlle L. (pipes) covering a large area. The inner portion of the zone consists of a mixture of Glyoeria borealis (Nash ) Batohelder (northern manna grass), Leersia oryzoides (L.) Sw. (rice cutgrass), and along the muddy shore El eo char is palustris (L.) R. &
S., Ac or us Calamus L. (sweet flag), Dulichium arundinaceum (L.) Britton, Polygonum amphibium L. (water smartweed), Glyoeria canadensis (Miohx. ) Trin. (rattlesnake grass), Solypus atrovirens Muhl., Eleooharis obtusa (Willd.) Schultes (blunt spike -rush) and Saglttaria latifolia L. form& Gracilis (Pursh) Robinson, apparently the common form in northern Michigan. The immediate shore is fringed with clumps of Salix lucida, interspersed with open areas covered with Oalamagrostis canadensis (Miclix.) Beauv. (blue joint). Logs lying almost concealed tell the story of flooding at this point; this is also shown by standing specimens of Alnus inoana and Salix petiolaris, dead above, but making vigor¬ ous gew growths at the base.
In the shallow water bordering the sandy
beaches, the rushes are often accompanied by areas of pipe- wort (Eriocaulon artioulaturn (Huds.) Morong. This may produce unusually long stems when growing with Soirpus occidentalism Among the commoner species occurring on the
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sandy beaches are the following:- Juncus brevicaudatus (iSnglem*) Pernold, Hypericum elliptlcum Hook* (pale St* John's wort), Cladiun nariscoidos Terr* (twig-rush) , Ranunculus Plemcmla L. (smaller spearwort) , Him ulus r ingens L* (nonkey flower), Slum clout aef ollnm Schrank (water parsnip), Agr ostia hy emails (Walt.) BSP* (hair grass). Car ex erinita Lam*, Car ex rostrata Stokes, and Carex Ooderi Betz. Both the sandy and gravelly beaches are very often backed by a shrubby association composed of 6hamaedaphne cal you - lata. Ilex verticlllata. and nlnua Inc ana* With these often occur Spiraea salicifolia and Praxinus nigra, fringing tho me so phytic forest.
It is evident from tho above description that tho transition from lake to me so phytic forest is rather abrupt; this is especially true on the north side of tho lake, where the angle of slope is greatest* The few asso¬ ciations notod along the narrow beaches consist of plants which are able to endure submergence for brief periods. The shrubby growth backing the beaches, though only a little above the mean level of the lake, is high enough to escape mostly the destructive influences of high water.
c. Blood plain.
On account of tho varying influence to which the flood-plain is subjected, the successions are not
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-70-
in general , well marked. In the broader portions of the valley, as in ooo. 24. ?. 61 H. R. 43 W. . there is a dense growth of Alnua Inc ana . intermingled with occasional in¬ dividuals of tamarack. In the northwest corner of the above section there is a small "tamaracK swamp", forming a typical stage in the filling up of a peat bog. The ecological stages of such a bog have been well described by Transeau (25), Cooper (5), and others and will not be treated here. In sections 23 and 14, immediately east of the lake, the flood- plain is covered by a grassy marsh (fig. 40), with a shrubby zone lining the river, as already described. The flora of this area is very composite in character. Portions of it are dominated by a dense growth of blue joint (Calamagrostls canadensis ) . The list of specios observed here includes the following: - Ascloplas incarnata L. , Verbena hast at a L. , Aster punlc eus L. , iSupatorlum purpureum L. , Sclrpus Cyperlnus (L. ) Aunth. , Osmund a regal is L. , Onoclea aenslbillfe L. , Solidago aerctlna Ait • , Anemone canadensis L . , Chelono glabra L. , Aapldium Thelyptorlo (L. ) Sw. , Pteris aquillna L. ,
Glyceria canadonsi s (Hichx. ) Trin. , Lysimachla torrestria
N
(L. ) BSP. , Iris versicolor L. 9 Cicuta bulbif era I. , Suutel- laria lateriflora L. , Thai ict rum dasycarpum Fisch. & Lall.,
Galium asprollum Hichx. , Conn strictum Ait. , Impatlens bi¬ flora Valt. , Hum ex vertic Hiatus L. , Hypericum vlrglnloum I. ,
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-71
Campanula ullginosa Rydb • f Phalarls arundi nacea L . , Clematis virgin! ana L . , Leersla oryeoldes ( L • ) Sw • , Kumulus Lnpulus I<« , Ranunculus Pennsylvania us L. f., Gal ium Clayton! Miohx., Radioula palustris (L.) Moench., Garex filiformis L., and Oarex tribuloides Wahl*
The grassy marsh described above un¬ doubtedly oocupies the position of a former delta. It thus represents a stage in the gradual filling up of the valley with sediment and organic remains.
STOIMAHI
The ranges of the Porcupine Mountains are entirely surrounded by a low plain, so that the mountains were islands for some time after the final retreat of the ice sheet. As the water subsided, the higher ranges to the south were first uncovered. Pioneer invasion probably took place where the wash of the waves was not too severe, following stages analagous to those found in the present shore line. At the present time, these southern ranges or hills, including Government Peak, the highest point, are clothed with a mesophytio forest to the very top (fig. !)• This mesophytio forest was possibly preceded by a zero- phytic coniferous forest dominated by pine species, as
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suggested by Ruthven fl,p. 27). In this ease the pines began their invasion near the water's edge, following the heath mat stags# They made their last stand at the top of the mountains, being followed up and replaced by a mesophytio fbrest, the successions being correlated with the greater accumulation of soil near the base of the slope.
The top of the first range is unique in still holding out against the mesophytio forest. This is un¬ doubtedly due to the peculiar topography of this range.
As is evident from fig. 3, this topography is associated with the presenoe of Carp Lake, which once covered a much greater area than at present. The ddp of the strata to¬ ward the north, coupled with the subsidence of Carp Lake, has created a great cliff or escarpment, which is con¬ tinually wearing away, producing a talus slope at its foot.
The development of vegetation over the region has led to two climax formations, namely the hemlock climax and the maple climax.
The presence of the hemlock climax on the north elope of the first range seems to be conditioned by the physical factors of temperature, moisture and light. Great¬ er humidity and more uniformity in temperature noar the shore is due to the presenoe of a largo body of water. The
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average temperature of points along the coast is several degrees warmer than inland points a few miles bach, and the average precipitation during the winter months is 30/ii more than at Bergland, 26 km* hack from the shore* Keduced light intensity at the lower, more humid elevations on the north slope is probably more favorable to hemlock as compared with maple.
The maple climax occurs on the higher portions of the first range (excepting the summit) and on the ranges further south. As compared with hemlock, maple seems to be more tolerant of extremes of temperature and light.
The principal succession leading to the hemlock climax is along the shore. The pioneers in the more exposed situations are erevioe plants. In the severer situations tliese can initiate only very short or incomplete lines of succession. Where conditions are less severe, which may be only a few meters further inshore, the pioneers consist of lichens, mosses and crevice plants, which lead to more definite lines of advance; but the irregularities of the shore line produce such varied conditions that there is often a lack of any gradual transition from lower to higher ecological forms. At practically all points along the shore, the climax forest has pushed do wn to the limit of its possible extension undor present conditions; and this has
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74-
resulted in a telescoping of the ordinary transitional stages •
Lines of succession leading to the maple climax may be seen at the summit of the first range and in the valley of Carp River. In the first case the climax is reached through xerarch series, beginning with crustose lichens and xerophytic mosses on the exposed rock surface of the summit. One of the principal pioneers is Selaginella rupestris « which often forma a layer of humus 1-2 dm. thick. This together with various low-growing species, in¬ cluding crevice plants such as Danthonia spicata and Panic urn depauperatum. paves the way for the heath mat, which is composed largely of two species of Vaccinium (see text). A zone of scrubby conifers and oaks then leads gradually to the maple climax on the north side of the summit.
On the south side the presence of the cliff forms a direct barrier to invasion from below, except where the escarpment has been worn down so as to produce a saddle aoross the range. Below the escarpment there is a talus slope of varying width, fringed by a mesophytic forest ex¬ tending below to the flood plain of Carp Hiver. In general this mesophytic forest is young and heterogeneous in char¬ acter, but it is approaching the maple climax. Its upper border is irregular, but forms a more or less sinuous
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-75-
curve representing a line of invasion on the talus. Since the width of the talus depends on the height of the escarp¬ ment, the line of invasion extends high at low points in the range.
Suocessional continuity on the talus is more or less broken, at least in the earlier stages. Lichens and certain moss species are undoubtedly important, but Betula alba var. papyrifera is one of the noteworthy pioneers adapting itself to unuaually severe conditions. This is followed sooner or later by aspens, after which there is a gradual transition toward the mesophytic climax.
As the cliff wears down the summit of the range will eventually be claimed by the mesophytic forest. At present the xerarch series forms a connecting link between the maple climax in the valley and on the north side of the summit.
The lower edge~ of the mesophytic forest below the talus forms an abrupt border to the flood plain of Carp River. This is due to periodical flooding, which produces irregularities and telescoping throughout the hydrarch series on the comparatively flat floor of the valley. Any marked building up of the mesophytic climax from this source must therefore await a change in physio¬ graphic conditions along the river valley. This will
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mesophytic forest (m^-ple cl/md.X )
Fig# 47. - Diagram shewing linos of vogatational development leading to the maple climax on the first
range.
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-76-
oome with the gradual filling up of the valley through sedimentation, thus changing* the conditions under which flooding now ocours. The present successions along the valley of Carp River and Carp Lake aro of comparatively little moment; however they indicate the character of a portion of the hydruroh series which will eventually lead to a mesophytic climax covering the entire floor of the valley*
The principal * ones of vegetation in connect¬ ion with the development of the maple climax on tho first range are shown in the diagram (fig* 47). The letters a, b, £, d, indicate the lines of succession. The line £ begins with lichens, mosses, and crevice plants at the bare summit, and culminates in the maple forest on the north elope; b originates largely from seeds washing over the N summit; £ represents a line of invasion on the talus slope from Ihe forest below; d is a broken line representing the discontinuous nature of the hydrarch succession from the valley of Carp River. Part of this succession leads to the mesophytic forest on the second range.
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77-
-RKFERENCE8-
1. ADAMS, C. C. , An ecological survey in northern Michigan.
A report from the University Museum, University of Michigan, published, by the State Board of Geo¬ logical Survey as a part of the report for 1905. Lansing, Mich. 1906. Part I, pp. 17 - 47, written by Dr. A. 0. Ruthven, deals with the general ecological relations of the Porcupine Mountains, and pp. 75 - 92 contain notes on the flora of these mountains. 1905.
2. BEAL, W. J., Observations on successions of forests in
northern Michigan. Rep. Mich. Forestry Comm.
1:25 - 29. 1888.
3. BURT, W. A., Catalogue of the plants collected in the
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4. CLEMENTS, F. E. , Plant Succession, An Analysis of the
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'• _ _ » The influence of underlying rooks on
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10a. DAVIS, C. A., The formation, character and distribution
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12. _ , Report on the geology of the Lake Superior
land district. Part II, the iron region. Sen. Doc., Spec. Sess., 32d Cong. Vol. 3, 1851. Contains a list of plants from the Upper Peninsula, including some from the Porcupine Mountains.
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-79-
13* FROTHIHGHAM, E. H. , The northern hardwood forest; its composition, growth and management* Bull. 285, Contrib. For. Serv. , U. S. D. A* 1915.
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forests. Forestry Quart. 1:50 - 55. 1903.
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of Indiana and Michigan and the History of the Great Lakes. U. S. Geol. Survey. Monograph 53. 1915.
21. MOORE, B. , Reproduction in coniferous forests of
northern New England. B0T« GAZ. 64:149 - 158.
1917
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22. ROBINSON, B. L. , and FERNALD, M. L. , Gray* s Manual
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23. RUTHVEN , A. G. , Notes on the plants of tho Porcupine
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26. WHITFORD, H. N. , The genetic development of the forests
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29. ZON, Raphael, Principles involved in determining
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1908.
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