THE ALPINE AND SUBALPINE VEGETATION OF THE LAKE TAHOE REGION

VOLUME LIX NUMBER 4 THE Botanical Gazette APRIL 1915 THE ALPINE AND SUBALPINE VEGETATION OF THE LAKE TAHOE REGION F. J. Smiley (with four figures) Geology The country rock of the region is mainly a coarse granite, which represents the ancient Sierran batholith. The sedimentary rocks which formed the more ancient surface, and under which the intrusives were thrust, have been for the most part completely eroded away; what little remains, as on the summit of Mt. Tallac, has been changed by pressure and heat into schistose rocks, and these have become deeply fissured by jointing. Under the de- grading influence of the alpine climate, with rapid changes of temperature and moisture, these jointed slates and schists have been ever more deeply fractured and loosened from place, giving rise to the immense heaps of angular talus, which skirt the bases of Mt. Tallac, Maggie's Peaks, and Castle Peak. The metamor- phosed sedimentary rocks increase southward, but Reid (i) points out that "The largest areas are little more than a veneer over the granite, so that it is evident that the work of removing the roof of the granite is nearly complete/ ' With the granite the course of events has been in part similar, in part quite different, depending upon the amount of jointing. Where the granite is deeply fissured, the rock is quickly broken to fragments of varying size, and these, falling from place, are soon reduced to coarse sand, often deeply colored with iron. Where the 265 266 BOTANICAL GAZETTE [april joints are horizontal the peaks have a terraced appearance, as on the south flank of Pyramid Peak. The sandy slopes formed from the crumbling granite are very pervious to water, and on their higher reaches only such plants as have especial advantages in obtaining a requisite amount of water can survive. At their bases one finds a distinctly mesophytic association, for the water absorbed above oozes out below and may be of amount sufficient to cause marsh conditions. On the east side of Angora Peak is such a sand slope whereon the plants become progressively more mesophytic as the foot is neared. Since the soil is the same from top to bot- tom, except for the increasing amount of organic material present, such a slope seems to be a direct, though imperfect, gauge for the water factor in plant life. Where the granite is massive the process of rock decay is en- tirely different. While the factors concerned (temperature and moisture) are the same, their action is largely neutralized by the lack of rock Assuring; rock decay becomes almost entirely a matter of exfoliation. Huge slabs become broken from the surface and by their position protect the rock beneath; only as the slabs are slowly broken and slide from place can the process continue. In the granite deserts of Desolation Valley, Rubicon Valley, and Donner Pass, this protecting action of the exfoliated slabs may be particularly well seen. Here the only spots capable of bearing a flora are the small depressions between the glaciated ridges with soil formed in large part of wind blown granite dust. Over the greater surface plant life is impossible save for crustose lichens and a few hardy crevice plants, which have settled in the fissures about the borders of the slabs. Limestone seems to be lacking in the district, though so abun- dant and important a rock base of the Basin ranges. The rocks derived from extrusive lavas are mainly andesites and basalts. The principal vents, from which these flows issued, lie on the crest of the so-called Great Western Divide. From Round Top Peak, some 30 miles south of Lake Tahoe, there is a succession of ancient volcanoes terminating in Castle Peak, northwest of Truckee. The chief center for these flows seems to have been Mt. Mildred (2), 10 miles west of Lake Tahoe. These irruptives 1015] SMILEY— LAKE TAHOE REGION 267 now commonly lie on the top of ridges overlying the schists and granites. On decay they produce a dark red soil, over which are scattered angular or roughly rounded gray or brown andesite boulders. The basalts, which locally may be present in considerable amount, lie above the andesite, which frequently shows a meta- morphosed condition due to the heat and pressure; on the summit of Mt. Tallac is such a contact. These basaltic irruptives are the I :ii&t Fig. 1. — Transition zone: pond vegetation with climax forest; Mount Tallac in the distance. most recent general feature of the geology, and the time inter- vening to the present has not been sufficient to materially modify the flows. The whole district, except the highest summits, has been sub- jected to severe glaciation. This occurred in the later part of the Pleistocene, and the interval since has been too short to obscure the evidences of ice action, particularly at the higher levels where the surface was swept bare. Today these barren areas lie exposed, practically destitute of soil, and constitute some of the most strik- ing evidences of glacial action to be found in the Sierra. At the time of maximum ice the higher levels were all filled with neve 268 BOTANICAL GAZETTE [april fields which fed the glaciers moving down the valleys, transporting the debris that now forms the morainal heaps at 6000-7000 feet. The peaks and ridges, left after the debris was carried away, show many typical features of glaciated mountains: cirques, aretes, dents. A most perfect example of the last is Pyramid Peak, on whose north slope the Rubicon Glacier had its source, thence moving north, scouring out Rubicon Valley and probably debouch- ing into Lake Tahoe through Rubicon Pass (7150 feet) and the valley of McKinney Creek. Ice action varied in its effect upon the relief with the several rocks beneath the surface of the glaciers; in the andesite the glacial sapping is especially marked and the cirques of Twin Peak and Mt. Tallac are excellent examples of their kind. On the mas- sive granite the effect seems to have been practically limited to clearing away the loose material overlying the bed rock, which was little, if at all, affected. Topography The region studied is embraced within the area mapped by the United States Geological Survey on the Truckee and Pyramid Peak quadrangles. It is roughly some 50 miles long and 15 wide, and may be considered as a typical section of the Central Sierra. This section of the range does not contain elevations comparable to those further south in the High Sierra of Fresno and Tulare coun- ties, nevertheless several of the peaks rise above 10,000 feet, and one, Freel's Peak, is over 11,000 feet. The area is in shape a trough, with average elevation of the floor about 6500 feet. The rim of the trough is formed on the west of the Great Western Di- vide, which separates those streams flowing westward to the Great Valley of California from those forming a part of the Great Basin drainage system. The eastern margin is the Carson Range, the most eastern of the Sierran ranges. The Great Western Divide is the more deeply dissected of these limiting mountain chains. From Round Top (10,430 feet) in Alpine County this dividing ridge runs north to Echo Lake and then bears west of north, continuing beyond Mt. Lola (9167 feet) into Sierra County. Along this height of land the more promi- 1015] SMILEY— LAKE TAHOE REGION 269 nent peaks are Mt. Tallac (9785 feet), Rubicon Peak (9193 feet), Twin Peak (8924 feet), Tinker Knob (9020 feet), and Castle Peak (9139 feet). The average height of the ridge is above 8000 feet. To the west it falls by a gradual slope to valleys draining into the Yuba, American, and Cosumnes rivers. Its eastern side forms an abrupt scarp closely skirting Lake Tahoe and the valley of the Truckee River. From the lake this scarp appears in places to be almost sheer. From the summit of Mt. Tallac there is a descent \wm Fig. 2. — Canadian zone: the high summit is Pyramid Peak of over 3000 feet in less than two miles. There is some reason to think that fairly uniform elevation of the ridge really represents the remnant of an ancient plateau, traces of which still persist on the south side of Mt. Tallac and Angora Peak. It has been sug- gested (1) that the summits themselves represent a still older erosion surface, but for this there is little direct evidence. This summit accordance is a general feature of the Sierra, particularly marked in the High Sierra (3). On this ancient upland lie the high alpine valleys, of which Faith, Hope, and Charity valleys south of Lake Tahoe are typical. The Carson Range, of which FreePs Peak is the highest sum- mit, is less rugged than the Divide. Its summits are rounded or 270 BOTANICAL GAZETTE [april even flattened cones, though the second highest peak, Mt. Rose (10,800 feet), has a steep ascent to the top. Its much more gentle contours are no doubt due to receiving far less rainfall than the Divide, and to the erosional force being consequently many times less. Between these limiting ranges the drainage all centers in the Truckee River. The Upper Truckee rises north of Round Top, enters Lake Tahoe east of Tallac and, as the Truckee River, emerges from the northwest corner of the lake. Its course is north to the point of union with Donner Creek and then northeast through the Truckee Canon to the floodplains about Reno, Ne- vada. All of its important tributaries enter from the west, having their sources in the Divide's many lakelets. These alpine and subalpine tarns are among the greatest charms of the region. They commonly fill the glacial cirques and often form a series of small basins from whose lowest margin the con- necting brook cascades to the major stream. These pools are being gradually silted up both by sediment washed in from the adjacent slopes and by the vegetation fringing the banks; in time they be- come marshes and finally meadows, which in turn yields to the forest, for, as shown below, the forest is in this region of the Sierra the ultimate phase, since the elevation is not great enough to cause a cold timber line. On the broad ridge between Gilmore Lake and Suzy Lake above Glen Alpine is such a series of nearly filled basins, the largest of which is already converted into a marshy meadow, on whose margin a young growth of lodge pole pine has started. As these lakes are mainly in glacial basins, they are frequently banked on the low side by moraines, which in places become of major importance in the local topography. The glaciers of the region have formed large deposits as lateral and terminal moraines about Independence and Donner Lakes, and on the west shore of Lake Tahoe an ancient extension of the last has been cut off by several terminal moraines of the Fallen Leaf Glacier and now persists as a separate lake, three miles long. The moraines on the sides of this lake are especially large, the eastern one being as long as the lake and 900 feet high. Some of the valleys through which the larger glaciers moved have the U-shaped cross-section characteristic of glaciated moun- 1915] SMILEY— LAKE TAHOE REGION 271 tain valleys, a form very different from the V-shaped canons on the west side of the Divide, and also differing from the lower reaches of Truckee River into which the ice seems not to have entered. A typical example of such a U-shaped valley is the depression once filled by the Fallen Leaf Glacier and now having for its center the channel of Glen Alpine Creek. Climate In attempting a sketch of climatic conditions in the high Sierra, one is confronted with the fact that exact observations are too few w .jflAP*!**^ Fig. 3. — Canadian and Hudsonian zones: Suzy Lake with Dick's Peak at right to justify anything more than provisional statements. The data offered for the several stations have been gathered from the re- ports of the Weather Bureau; since detailed statement for the highest station has only been published since 1906, it has seemed best to make comparisons cover the same years even for stations where data of a kind is obtainable through a longer period. The most constant feature of the alpine climate is the diminish- ing pressure with ascent. While there is little evidence to show that this factor is of itself important in the life of plants and animals, at least within the vertical range of the mountains of western North 272 BOTANICAL GAZETTE [april America, yet it induces change in other climatological factors which are of great importance. "Le fait essentiel d'ou. derivent a peu pres tous les caracteres du climat de montagne est la rarefaction de plus en plus grande de l'air dan les hautes altitudes. De tous les phenomenes meteorologiques des regions elevees, c'est le plus regulier, car c 'est le seul qui ne depende pas des conditions locales du relief" (4). Among these changed factors may be mentioned increased insolation, increased radiation, change of illumination by increase of proportion of violet light, and rapid alteration from saturation to extreme dryness (5). That any considerable ascent is accompanied by a fall of tem- perature is a constant phenomenon all the world over; it is due to the diminished heat capacity of the rarefied air. This fall in tem- perature may be counteracted within narrow limits by the relief; it is frequently noted in the mountains that plants which are indi- cators of a colder habitat are growing at a lower elevation than other plants commonly found much lower down. This is especially true in lately glaciated regions with their usually rugged topog- raphy; the cirques will often have a flora distinctly micro thermic, while the surrounding ridge bears forms suggesting a milder cli- mate. An example of such a contrast is afforded by the cirque on the northeast of Mt. Tallac, in which Tsuga Mertensiana is growing full 500 feet below Pinus Jejfreyi on the bluff overlooking Fallen Leaf Lake. This inversion of temperature, with the colder air sinking to the valleys and the warmer currents sweeping up the ridges, accounts in part for the lingering snow drifts that may lie in the cirques till late in the summer, or even persist throughout the season. It also produces a complexity in zonal maps, the limits of the warmer zones advancing up the slopes and the colder sinking below their average level. In the higher Sierra low temperatures in winter are known comparable to those of the east. The lowest temperature reported from Tamarack, Alpine County (8000 feet), is — 29°F. in January, 1910, or 51 of frost. On the summit of Mt. Rose the lowest record is— io° F. Summer temperatures may become fairly high; Tam- arack reports 86° F. in July, and Summit, Placer County (7017 feet), 90 in October (table B). This last suggests a new feature 1015] SMILEY— LAKE TAHOE REGION 273 of the alpine climate: the displacing of the heat total toward the end of summer and fall. The start of the vegetative period (the local "spring") is delayed till summer is well advanced below, but the brilliant insolation of the alpine day in part compensates for this late beginning, so that "fall" phenomena are nearly contem- poraneous both above and below. "Die Primeln bliihen auf dem Rigi bei 1800 m. ca. 6 Wochen spater als in Zurich, die Herbst- zeitlose dagegen beinahe gleichzeitig" (6). Fig. 4. — Hudsonian and Arctic-alpine zones: Desolation Valley at Lake LeConte and Pyramid Peak. It has been stated that the zone of maximum rainfall in the Sierra is between 5000 and 7000 feet: Colfax (2421 feet), 46.64 in. per year; Cisco (5939 feet), 49.68 in. per year; Summit (7017 feet), 46.58* in. per year (mean of 30 years); but the diminished rainfall at Summit may be due to the influence of the arid east, an influence not barred by high ranges. A comparison of the same period (1909-13) shows at Summit (7017 feet) 40.98 in. mean total precipitation, and at Tamarack (8000 feet) 52.77 in. It will be noted that this would seem to have been a period of less than normal rainfall, the deviation amounting to 12.3 per cent. If such was the case, the precipitation at Tamarack should normally 274 BOTANICAL GAZETTE [april be 59.24 in. On the eastern side of the Great Western Divide the precipitation falls rapidly, Truckee (5218 feet) having but 26.98 in. (table C). Most of the annual precipitation in the high Sierra falls as snow and some astonishing totals are recorded from the Tahoe region. At Summit, in the winter of 1889-90, 776 in. of snow fell, or nearly 65 feet; in a record of 38 years the average was 417 inches (7). In the period limited by the winters of 1908-09 and 1911-12, the average annual snowfall at Tamarack was 515 in., at Emi- grant Gap (5221 feet) 249.3 m -> an d at Glenbrook, Nevada, on the east shore of Lake Tahoe, 208.2 in. This last station, elevation 6282 feet, at the western base of the Carson Range, suggests the aridity of that range as compared to the Divide. At Summit on May 10 there is still a mean depth of snow of 20 inches, nor is the land fully cleared in average years till May 26. At Tamarack the end of June still sees the ground covered every other year. Severe frosts may occur at any time throughout the summer, but the rubric " killing frosts" of the weather reports is inapt when applied to the high mountains, for the simple reason that the plants may be frozen but are not killed. I saw on a morning in August plants of Gentiana calycosa stiff and brittle with frost on the shoulder of Mt. Tallac, yet in the afternoon the same colony was apparently none the worse for the freeze (table D). This great burden of snow acts upon the plants of the district in at least three ways: it furthers tree growth, but impedes the growth of the forest; it favors the meadow, and particularly the wet meadow; it favors summer ephemerals. In the Tahoe region at present there is no glacial ice, and but few snow banks persist for longer than one season. Where these occur, they are always on the east or northeast of the ridges and peaks, for the prevailing wind from the southwest piles up the snow on these exposures. No true snow line exists. Alpine winds are keen and drying, and, in spite of their actually moving smaller masses of air, exert a marked influence upon the forms of plants. "Wind cripples" are a constant feature of the arboreal vegetation on the higher summits. On Mt. Rose veloci- ties of 50 miles an hour have been recorded. In the spring a 1915] SMILEY— LAKE TAHOE REGION 2 75 " chinook" wind quite commonly melts the snow very rapidly. Beside these general winds, mention should be made of the so-called " mountain and valley" winds which reverse their move- ment twice daily, flowing down the valleys at nightfall and attain- ing considerable force when the valley narrows suddenly below, and flowing toward the summits when these have been heated by the morning sun. These winds are of moment in alpine plant dis- tribution as being probably among the most effective agents for extending the vertical limits of species. TABLE A Mean monthly and annual temperature (F.) 2 ■8 ■s 3 < 3 C/3 < u t/3 u ■s 1 25-3 28.3 32.9 40.0 48.4 57-4 65.4 63-4 55-9 45-i 36.5 28.7 26.8 27.7 32.0 35-9 44.6 5i-2 57-6 5«-0 53-8 46.5 34-8 28.0 21.5 21. 7 26.8 32.5 36.5 45-8 55-2 56.3 48.1 39-i 29.8 19.8 Truckee58i8 ft... Summit 7017 ft.. . Tamarack 8000 ft.. 43-9 41.4 36.1 TABLE B Monthly extreme temperatures* January February March April May June Summit . . Tamarack 55 49 - 4 -29 35 64 52 53 - 8 -25 46 64 53 64 6 -17 31 54 71 69 — 2 -14 30 58 85 8l 12 6 39 46 82] 28 8oj 18 43 50 Summit. . Tamarack July August 27 30 September 80 October November December -26 28 52 * Under each month the first column gives the highest temperature ever recorded at the station; the second, the lowest temperature; and the third, greatest daily range ever recorded in the month. TABLE C Total precipitation in inches 1909-1913 Jan. Feb. Mar. Apr. May June July Aug. Sept. Oct. Nov. Dec. Annual Summit Tamarack 13-58 16.85 3.22 5 08 6. 22 4-74 2.69 3-39 1. 17 I.78 0.07 2.40 0.97 i-5 0.03 0.31 1 .0 1. 12 0.85 i-75 4.94 6.69 6.24 7.16 40.98 52.77 276 BOTANICAL GAZETTE [APRIL TABLE D Seasonable snowfall in inches Sept. Oct. Nov. Dec. Jan. Feb. March April May Year Summit T 1 .0 6.2 16.6 38.7 55- 1 52.2 60.5 166. 2 198.7 47.2 76.2 62.0 Si-5 23 -5 36.5 12 18 408.0 496.I Tamarack Life zones Transition zone. — The problem of attempting to discover the zonal limits of the various species collected in the Tahoe region is complicated by the very irregular topography; the line between adjacent zones is nowhere clearly defined, and, where the relief is especially rugged, often becomes very tortuous. Mapping can only express the general distribution, at least on maps of such a scale as are available. In addition to the complication caused by the relief and consequent frequent change of exposure, the soil characters cause a variableness in the zone boundaries; on the dark chocolate colored trap lives a flora whose members are dis- tinctly more xerophytic than those of granite soils. A very evi- dent change of plant life, for which this edaphic factor seems the only one assignable, is that found on the ridge connecting Suzy Lake with the mountain group culminating in Dick's Peak. The ridge runs northwest to southeast and the south slope is fairly even, but where the trail runs out of the granite into the trap a break in the general aspect of the flora occurs: typical Upper Transition on the granite with Abies concolor and Pinus Jejjreyi as the chief trees, and Canadian on the trap with Juniperus occidentalis giving the tone to the forest. Another more difficult factor in the problem of assigning plants to definite zones is the fact that the plants often refuse to be so assigned; the stragglers from the general rank are too numerous. Yet in spite of this it seems desirable and feasible to group the vegetation within certain altitudinal categories and, while many individuals of a given species will be often found outside the zone of their greatest frequency, as a whole the assemblage of plants denominated the " Transition flora of the Sierra" has a general coherence, and the expression conveys a definite meaning to those who have considered the whole Sierran flora. ipisl SMILEY— LAKE TAHOE REGION 277 In the Tahoe region this Transition flora covers approximately 25 per cent of the total area, which is equivalent to saying that by far the larger part of that flora lies below the region considered in the present report, and we are here dealing with that fraction of the total which has been called Upper Transition, a flora showing more relationship to the life zones above than to those below. It is this fact of alliance with strictly alpine and subalpine floras that requires us to consider it here. The Upper Transition forest, as of all the higher zones, is ex- clusively a coniferous forest; what few arboreal or arborescent angiosperms are present are only found close to streams or lake shores and hence are to be regarded as members of the stream bank association. This Transition coniferous forest is formed by Abies concolor, Pinus Jeffreyi, Finns ponder 'osa, Libocedrus decurrens, and Pinus Lanibertiana, in frequency in approximately the order named. The forest growth is dense in but a few favored localities, as on the floor of the ancient Fallen Leaf Glacier at the south end of Fallen Leaf Lake. Generally the trees are scattering and indi- vidual trees relatively small compared to the average size of the same species on the western slope of the Sierras. The white fir alone maintains its average form. The sugar pine is scarce, since in the district the moderately moist rich flats frequented by this tree commonly lie above its range. The yellow pine is a common tree about Tahoe and northward to Truckee, but is dwarfed in size, and appears excessively parasitized by Arceuthobium occiden- tal. At the south end of the lake the nearly allied species Pinus Jejfreyi makes with Abies concolor two-thirds of the forest cover. As a rule, the woods away from the streams are free from under- brush, the surface vegetation consisting of low perennials mainly, such as Corallorhiza Bigelovii, Pyrola asarifolia incarnata, Ptero- spora Andromeda, Pedicularis semibarbata, Antennaria argentea, Antennaria Geyeri, and in sunny glades Balsamorhiza sagittata, Erigeron diver gens, and Madia exigua. Next to the forest in importance in the general aspect of the Transition flora comes the stream bank association, which advances up all the water courses, cutting the coniferous forest into isolated fragments. In this stream bank vegetation Populus trichocarpa, Populus tremuloides (there is a charming aspen grove on the low 278 BOTANICAL GAZETTE [april shelf just east of Fallen Leaf Lake), and Salix lasiandra form the superior stratum, and beneath them grow Alnus tenuifolia, Rubus parviflorus, and Cornus pubescens as undershrubs, while the herbs most frequently found are Car ex rostrata, Allium validum, Habe- naria leucostachys, Thalictrum sparsiflorum, Cicuta vagans, and Heracleum lanatum. The lowest stratum, made up of delicate herbs for the most part, shows Listera convallarioides , Polygonum Douglasii, Kelloggia galioides (which is also found in the forest), Galium bifolium, and Anaphalis margaritacea. Scrub (chaparral) becomes of considerable importance on dry sunny slopes in the Tahoe Upper Transition; the principal species are Amelanchier alnifolia, Cercocarpus ledifolius, and on sandy benches Artemisia tridentata, the last being present as a consider- able factor in all the zones below the true alpine. Among these shrubs one finds Lilium Washingtonianum, Eriogonum nudum, Collomia tincloria, Mimulus Breweri, Mimulus leptaleus, and Mimulus Torreyi. When the relief becomes too sharp and the soil covering too scanty for chaparral shrubs, there is found a flora of rocky outcrops and benches, composed of small perennials and annuals. Here grow Eriogonum Douglasii, Oxytheca spergulina, Heuchera rubes- cens lithophila, Apocynum androsaemifolium, Gilia pungens, Cry plant he a finis, a form of Monar delta odoratissima {Madronella pallida Heller), Adenostegia tenuis, Chrysopsis hispida, and Serico- carpus rigidus. The meadow formation is well developed along Truckee River, about Donner Lake, and where the Upper Truckee enters Lake Tahoe both east and west of Tallac. Almost exclusively it is a wet meadow, since the dry meadow is speedily invaded by trees and grows into the climax forest. Such an invasion and young forest growth is now taking place just back of Tallac, Pinus Jeffreyi seedlings being the chief entrants. On the wet meadow are Spar- ganium simplex, many carices {Carex lanuginosa here below its average level, Carex nebraskensis) , J uncus nevadensis, Veratrum calif or nicum, Urtica gracilis, Delphinium decorum patens, Tri- folium cyathiferum, with Trifolium pratense and Trifolium re pens as immigrants into the meadows about Donner Lake, Hypericum 1915] SMILEY— LAKE TAHOE REGION 279 Scouleri, Agastache urticifolia, and Solidago elongata, the two last being especially common about meadow borders within the ring of Salix macrocarpa argentea that commonly hedges the wet meadow. The dry meadow formation, as stated above, is less evident, but still exists and shows a considerable list of species: Sporobolus depauperatus, Zygadenus venenosus, Myosurus apetalus, Hosackia americana, H. crassifolia, Gomphocarpus cordifolius, Allocarya hispidula, Cryptanthe geminata, and Aster canescens being the more numerous. Canadian zone. — Of the several life zones discoverable in the Tahoe flora, the Canadian is at once the most extensive and most difficult to define. Its lower limit conforms generally to the 7000 feet contour line, while the upper boundary may be placed at about 8500 feet as a maximum; within this range of 1500 feet lies the greater part of the district. This zone includes most of the ridges connecting the peaks rising into the alpine region; it covers the lower flank of the Divide, and encircles Mt. Rose below 9000 feet, for in the Carson Range the greater aridity and higher mean tem- perature of the growing season causes all the life zones to rise higher than they do in the mountains west of Lake Tahoe. This rise of the zonal limits reaches a maximum on FreePs Peak, which has small groves of Pinus Murrayana, perhaps the one best "Leit- pflanze " of the Canadian flora, even at the 10,000 feet level. These slopes are frequently composed of loose granite sand, and, as mentioned in the case of the slope east of Angora Peak, support a characteristic flora of shrubs rarely found outside the Canadian life zone. The edaphic factor must be constantly kept in mind in locating zonal limits, and in our district this is largely conditioned by the degree of glaciation and subsequent erosion. Where the country rock was swept bare, a typical Hudsonian assemblage of plants is apt to be found, even though well below the 8500 feet limit, as in Desolation Valley at 7800-8000 feet. Where depo- sition has given a sufficient soil cover, conditions are decidedly ameliorated, and the Canadian flora develops typically even above its general level, as in the high alpine valleys south of Lake Tahoe. The Canadian forest is, for the most part, a thin forest; as a rule the trees stand well apart, only exceptionally preventing 280 BOTANICAL GAZETTE [april sunlight reaching the ground in quantity insufficient for a varied herbaceous ground flora. This in effect brings the meadow into the forest, or rather the forest into the meadow, since the last is antecedent to the climax vegetation of the district, the conif- erous forest. There is then difficulty in describing these associa- tions apart, though they are distinct enough below. The one tree of this forest which usually forms dense stands is the red fir (Abies magnified). It favors low benches and bottoms of valleys and is not often found upon the slopes save as a fringing forest along water courses. It does form a considerable element in the forest on the great moraines, however, the loosely aggregated soil of which permits deep root penetration. On the great moraine east of Fallen Leaf Lake the red fir is the principal tree. This dark fir forest has few shrubs, but does support a characteristic flora of ericaceous perennials, such as Pyrola pallida, P. picta, Chimaphila Menziesii, C. umbellata, and Sarcodes sanguinea. The fir forest is an exclusive association, few of the other Canadian species en- tering into it, doubtless excluded by the insufficient light for seed- lings. The Canadian pine forest has a very different aspect, being open or even parklike in the spacing of the trees. Neither of the two pines which compose it {Pinus Murrayana and Pinus monticola) attain large size, but are widely branching, especially at their upper levels. Pinus monticola continues into the Hudsonian and at times becomes a tree line form, but Pinus Murrayana is relatively constant about Lake Tahoe as a Canadian exemplar. The lodge pole pine is a vigorous seeder, and all about the meadows in the Canadian, where drainage has permitted, the young seedlings form a dense border. By subsequent drying out of the weaker individuals the open character of the mature forest is attained. Pinus Murrayana is often attacked by Arceuthobium americanum. Within this open forest grow several shrubs : Salix Scouleriana along the damp ravines, and with it Vaccinium occidental, Ribes cereum, R. neroadense, Purshia tridentata (this forming rounded clumps which in the Hudsonian become dense polsters) , and above all as a typical undershrub, Ceanothus cordulatus. The herba- ceous flora embraces Melica aristata, Spraguea umbellata, Stellaria Jamesiana, Lupinus calcaratus, L. apertus, Viola Nuttallii, Ortho- igisl SMILEY— LAKE TAHOE REGION 281 carpus cryptanthus, Aster integrifolius, A. yosemitanus, Erigeron inornatus, and Senecio lugens. The other tree found commonly in the Canadian is the Sierra juniper (/. occidentalis Hook), which in the Tahoe region is con- fined exclusively, so far as I could determine, to the slate outcrops, never appearing on granite in this lowest of the boreal zones. It often attains large girth at base (one measured on the Dick's Peak- Suzy Lake trail was 16 feet in circumference), but branches low and reaches a height of 20-25 feet. At Camp Agassiz, at the lower limit of the Canadian, it is parasitized by Phoradendronjuniperinum. The Canadian scrub (chaparral) is a constant feature of the vegetation on the dry rocky hillsides: Amelanchier alnifolia and Cercocarpus ledifolius continue up from the Transition and are associated with Amelanchier glabra, Holodiscus microphyllus, Ceanothus velutinus, Arctostaphylos patula, A. nevadensis, and Grossularia Roezli. On these dry slopes among the shrubs are found Silene Douglasii, Gay ophy turn ramosissimum,Zauschneria calif ornica, Chaenactis Douglasii, and Eupatorium occidentale. On the slopes where the weathering has reduced the rock debris to finer particles we find at the top sedums deeply rooted in the loose sand (Sedum obtusatum and its close ally Gormania Burnhami), and below, where the influence of the water content of the slope becomes appreciable, bordering thickets of Acer glabrum (Acer Torreyi Greene), Sorbus calif ornica, and below these, Prunus emarginata. Spiraea arbuscula occurs at the base of such slopes where the water supply is abundant. The true rock plants include Quercus vaccinifolia, the only oak of the boreal region, which forms dense espaliers over rounded rock surfaces, but is more evident as a cover for the roches moutonnees in the glaciated Hudsonian valleys. This shrub seems to be re- stricted to the granite at Lake Tahoe. Nama Lobbii is a plant of similar habit and covers many granite boulders about Cisco. Other rock-plants are Eriogonum Lobii, E. umbellatum, Sedum stenopetalum (the last forming extensive patches), Lupinus Breweri (a typical dry lithophyte), Apocynum androsaemifolium pumilum, Pentstemon J affray anus, P. deustus, and Hieracium horridum. The xerophytic ferns Pellaea Breweri and P. Bridgesii are common on the trap outcrops, while another rock fern of similar habit, Woodsia scopulina, was seen but once. 282 BOTANICAL GAZETTE [april The series of hydrophytic associations begins with plants of lakes and pools. Of these in the Tahoe Canadian are present about the edge of the basins Nymphaea polysepalum, Callitriche verna, Hippuris vulgaris (very abundant in Lily Lake near Glen Alpine), and the buckbean (Menyanthes trifoliata). These plants of the open waters in decaying advance the margin of the land into the water; in their wake appears Carex spectabilis. The drying margin supports a growth of willows {Salix californica, S. Lem- monii, and at the higher levels S. sitchensis), while beneath them grow Ranunculus flammula reptans, Cheiranthes asper, and in such an evironment in one locality was found Botrychium calif or nicum. The ultimate end of such an invasion is the filling of the lake and beginning of the wet meadow association, which about Lake Tahoe in the subalpine includes Sparganium simplex, Sagittaria latifolia, Carex aurea, Juncus bufonius, Veratrum calif ornicum, Spiranthes Romanzoffiana, Ranunculus alismaefolius alismellus (continues into Hudsonian and alpine), Hosackia Torreyi, Hyperi- cum anagalloides, Veronica humifusa, Helenium Bigelovii, and allied forms. On the drier edge of such swampy meadows are found Agropyron diver gens, Phleum alpinum, Stipa occidentalis, Tofieldia intermedia, Polygonum aviculare, Saxifraga integrifolia sierrae, Frasera speciosa, Pedicularis attolens, Arnica mollis, and Erigeron salsuginosus, the last being more abundant in similar localities in the Hudsonian. About the edge of such meadows and along their drainage channels will be found Salix macrocarpa argentea, Cornus pubescens, and Alnus tenuifolia, the last a characteristic Canadian shrub of stream banks. When the drainage has progressed beyond the wet meadow stage, such plants as Melica fugax, Phleum pratense, Stipa viridula, Allium campanulatum, Calochortus Leichtlinii, Polygonum imbrica- tum, P. Kelloggii, Lupinus sellulus, Epilobium brevistylum, Gilia Harknessi, G. ciliata, Erigeron Breweri, and Gnaphalium palustre appear to be followed by seedlings of the lodge pole pine and the ultimate forest phase. The third distinctive association, that of the fringing vegetation of stream channels, includes such plants as Habenaria sparsiflora, Aconitum columbianum, Aquilegia truncata, Delphinium glaucum, ipisl SMILEY— LAKE TAIIOE REGION 283 Sphenosciadium capitellatum, besides the willows and the alder above named. Hudsonian zone. — This zone in the generally accepted scheme of zonal arrangement ends at tree line; it ought then by hypothesis to be a simple matter to distinguish the upper limit. Unfortu- nately, tree line is conditioned by so many factors, any one of which may be decisive at any particular place, that in the field it is often nearly impossible to define the line that separates the last of the forest zones from the true alps above. In the Tahoe dis- trict this is all the more true since, as stated above, a cold tree line seems not to exist. The factors that impede and ultimately pre- vent tree growth are in our district wind currents, edaphic con- ditions, and the mechanical effect of deep snow. The formative influence of wind upon tree growth is apparent enough at low levels; trees near a beach are commonly strongly modified in shape, but in this case the mechanical effect of the wind seems to account for much of what is observed. At high latitudes and on high mountains the wind appears to exert the same stress plus a drying out power which the tree cannot with- stand. In the Tahoe region it is this desiccating wind that most often determines the limit to the forest; on one side of an arete tree growth will dwindle out scores, even hundreds of feet below the summit, while on the other side trees of normal shape rise to the top. As the wind is prevailingly from the southwest, trees on a north slope ought to rise higher, other conditions being equal. This they do in a few cases, as on the north side of the arete above Gilmore Lake, connecting Mt. Tallac and Jack's Peak. More often the sheltering effect of the ridge is discounted by the deep snow drifts which the southwest wind drops on the north and east sides of the peaks and ridges. In the glacial cirques on the east side of the Divide one commonly finds trees growing up to the chord of the arc, rarely within the cirque itself, and the inference seems warranted that this tree line is a deep snow line. Quite as often the tree line is a product of the soil conditions; trees cannot grow on the unfractured rock, and where this is massive and ex- posed a tree line exists; this is the explanation of the treeless Rubi- con Valley. A limit to the growth of trees is also set by an excess of ground water; many of the peaks and ridges about Lake Tahoe 284 BOTANICAL GAZETTE [april are unwooded at their summits because of wind conditions; their sides are compassed by heaps of talus more or less fragmented, but not affording a footing for the seedling pine or fir, while below these rubble heaps marsh conditions prevail due to the seepage of water from the slopes, and the trees are kept at a distance. All of these factors, either singly or combined, operate to make the line a very sinuous one that divides the true alpine region from the Hudsonian forest. In that forest the principal trees are the white bark pine (P. albicaulis), the silver pine (P. monticola), the Sierra juniper, and the alpine hemlock {Tsuga mertensiana) . The first is the tree line tree of the Sierras par excellence, being found along the whole Sierran crest. In the Tahoe region the largest forest of this pine is on the southwest flank of Mt. Tallac; here it forms a nearly pure stand and decreases from a tree 40-50 feet in height to prostrate wind cripples at the base of the actual peak. The finest examples of single trees noted grew on the plateau between Angora Peak and Ralston's Peak. Pinus monticola is not common in the south end of the Tahoe district, but increases northward about Cisco. The Sierra juniper (/. occidentalis) appears to have an interesting dis- tribution about Tahoe; in the Canadian it is always found on the slate outcrops, but in the Hudsonian seems to be the chief krumm- holz tree of granite basins. It was not noted on the higher lying volcanics (andesites). The chief groves of the alpine hemlocks in the region are on the Lucile Ridge and in Desolation Valley, where along the east side of the valley it forms a pretty continuous forest for several miles. Unlike the forest of white bark and silver pines, the hemlock forest is dark and the ground flora sparse. In the more open pine forest the ground cover is made up in part of Poly- gonum Davisiae, Fragaria virginiana platypetala forma sibbaldifolia Hall, Lupinus Lobbii, L. meionanthus, L. montigenus, Epilobium obcordatum (the last on the higher ridges), Hieracium gracile de- tonsum, and Whitney a dealbata. About the edges of the hemlock forest were growing Aster Andersoni and Artemisia norvegica. Above the forest, rising toward the peaks and aretes, are exten- sive talus slopes, and higher still the country rock offers on ledges and in crevices lodgement to many plants of peculiar habit and ex- traordinary adaptation to their inhospitable surroundings. It is igisl SMILEY— LAKE TAHOE REGION 285 on this rocky surface that one finds many of the growth forms associated with extreme life conditions: polsters, mat plants, es- paliers. It is this region of the high mountains that offers the closest analogies to the forms of desert plants, and it is here that some of the peculiarly desert genera (such as Eriogonum and Arte- misia among flowering plants, Cheilanthes for desert ferns) have made their deepest mark upon the alpine flora. Conditions on the broken talus are quite different from those of ledges, and a different group of plants grows on it: a high altitude dwarf chapar- ral formed of Ribes montigenum, R. viscossissimum Hallii, Grossu- laria lasiantha, Purshia tridentata, Aplopappus macronema, and Artemisia arbuscula. These may all grow intricately together, or separately, when all assume the same growth form, hemi- spherical polsters. On the more solid rock the mat form is the more common (Spraguea umbellatata, Phlox Douglasii diffusa, Chaenactis nevadensis) . In crevices will be found Eriogonum marifolium, E. Wrightii, Gilia congesta palmifrons, Polemonium pulcherrimum, Eriophyllum integrifolium, and Senecio canus. Over the glaciated granite surfaces exposed in Desolation Valley Quercus vaccinifolia forms dense espaliers. On the granite also was found the only specimen seen of the arctic-alpine shrubby cinquefoil, Potentilla fruticosa. On wet granite ledges grow Scirpus criniger, Sedum integrifolium, Parnassia calif ornica, and Erigeron Coulteri. Where a soil cover has accumulated on moist ridges are to be found Cas- siope Mertensiana, Lappula Cusickii, and Pentstemon procerus geni- culars. As in the Canadian, so in the Hudsonian pine forest the mea- dow spreads under the trees and among the grasses (Agrostis Rossae, Festuca scabrella, Melica stricta) will be growing Brodiaea gracilis, Calochortus Leichtlinii, Gay ophy turn caesium, and Aplo- pappus apargioides. A characteristic feature of high mountain meadows is the large percentage of carices and junci present; in the Hudsonian meadows of Lake Tahoe have been identified Carex capitata, C. Helleri, C. luzulaefolia, Scirpus pauciflorus, Juncus Parryi, J. nevadensis, and /. subtriflorus . Common herbs of these wet meadows are Stellaria longipes, Saxifraga bryophora, Trifolium monanthum, Gentiana Newberryi, Mimulus pilosellus, Antennaria media, and Erigeron salsuginosus. 286 BOTANICAL GAZETTE [april Hudsonian lakes are generally fringed by Salix glaucops, Ledum glandulosum, and Phyllodoce Breweri; while along the marshy margins of the outlet will be found Carex straminiformis, Viola Macloskeyi, Dodecatheon alpinum nanum, and Kalmia glauca micro phylla. Arctic- alpine. — A feature of the flora of the boreal region as compared to the Transition is the gradual merging of the forest and meadow due to the thinning out of the former. At tree line the forest becomes zero and the meadow becomes the dominant formation, for in a sense the rocky fields about the summits them- selves are inchoate meadows; between the boulders meadow conditions prevail. These diminutive meadows do not differ essen- tially from the larger expanses below the rock fields. The only formations to dispute the territory are that of rock crevices and the true lithophytes. As stated above, it is questionable if a true climatic tree line exists about Lake Tahoe; nevertheless certain plants (Oxyria digyna, Ranunculus oxynotus, Draba glacialis, Juniperus communis sibirica, Primula suffrutescens , Hulsea algida, Ivesia Schockleyi may be cited) are present, which are constantly found only above tree line in regions where such a line unquestionably exists. In the absence of a better understanding of this vestigial arctic- alpine flora, a discussion at present would be premature. Stanford University LITERATURE CITED i. Reid, J. A., The geomorphogeny of the Sierra Nevada northeast of Lake Tahoe. Univ. Cal. Pub. Geol. 6:89-161. 191 i. 2. Lindgren, W., Truckee Folio. U.S. Geol. Atlas, folio 39. 1897. 3. Lawson, A. C, The geomorphogeny of the Upper Kern River. Univ. Cal. Pub. Geol. 3:291-576. 1904. 4. De Martonne, E., Traite de geographic physique. Paris. 1909. 5. H ann, J., Handbook of climatology. Pt. 1. General climatology. Ward's transl. New York. 1903. 6. Schroeter, C, Das Pflanzenleben der Alpen. Eine Schilderung der Hochgebirgsflora. Zurich. 1908. 7. LeConte, J. N., Snowfall in the Sierra Nevada. Sierra Club Bull. 6:310- 314. 1908.