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Great Basin Naturalist Memoirs

Volume 2 Intermountain Biogeography: A Symposium Article 7

3-1-1978 Alpine phytogeography across the Great Basin W. D. Billings Department of Botany, Duke University Durham, North Carolina 27706

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Recommended Citation Billings, W. D. (1978) "Alpine phytogeography across the Great Basin," Great Basin Naturalist Memoirs: Vol. 2 , Article 7. Available at: https://scholarsarchive.byu.edu/gbnm/vol2/iss1/7

This Article is brought to you for free and open access by the Western North American Naturalist Publications at BYU ScholarsArchive. It has been accepted for inclusion in Great Basin Naturalist Memoirs by an authorized editor of BYU ScholarsArchive. For more information, please contact [email protected], [email protected]. ALPINE PHYTOGEOGRAPHY ACROSS THE GREAT RASIN

W. D. Billings'

Abstract.—Alpine vegetations and floras are compared in two transects across the Intermountain . The first extends from the in the central to the central Sierra some

1200 km to the southwest. It includes six mountain ranges. The second transect crosses the Mojave from Olancha Peak in the southern to Charleston Peak and thence to Peaks in northern . The largest numbers of -alpine species are in the Beartooth and , indicating migra- tions of these species along the Rocky Mountain cordillera. The lowest numbers of arctic-alpine species are in the central and western Great Basin and in the Sierra Nevada. Sdrensen's Index of Floristic Similarity was calcu- lated for all possible pairs of the nine alpine areas. There is little correlation of floristic similarity with alpine proximity across the Intermountain Region. Rather, any such correlation seems to be in a north-south direction; increase to- this is stronger in the eastern part of the region. Insularity and uniqueness of alpine floras seem to ward the western part of the basin. This is probably due to evolution of alpine endemics from preadapted low- land taxa.

The middle-latitude mountains of North floor has been uplifted in the . America north of , for simplicity and Orogenic activity continues at present. Even convenience, may be grouped into four though the Sierran batholith is rather old, large systems. With few exceptions, the the present Sierra Nevada is primarily a mountains in these systems trend north to product of uplift during the Pliocene and south, a fact of considerable importance in Pleistocene (Axelrod 1962 and pers. comm. the phytogeography of arctic and alpine 1973; Rateman and Wahrhaftig 1966). Fossil plants. The four systems are the Appala- lobed oak leaves at 2850 m in the lower al- chians in the eastern part of the , pine zone on Elephant's Rack, south of Car- the Rocky Mountains, the Cascades-Sierra son Pass, lend additional evidence of recent

Nevada, and last, but not least, the Great Sierran uplift. The high volcanoes of the Rasin ranges. The latter three systems domi- Cascades are also of similarly recent age. nate the western third of the continent. mountain ranges, in their In general, the Alpine Islands in the Great Rasin present forms, are younger the closer they are to the Pacific Coast. The Appalachians There are some 200 individual mountain constitute a very old mountain complex dat- ranges within the Great Rasin. Most of ing from Permian and Triassic times. Much these trend in a general north to south di- of the large Rocky Mountain system origi- rection and are separated by broad desert nated in the Laramide Revolution in late valleys. In the days when mountain ranges Cretaceous and early Paleocene. The oldest were shown on maps by hachures, Dutton basin ranges also rose during the Laramide described the pattern as similar to an "army Orogeny, but most of these ranges, particu- of caterpillars marching to Mexico" (Morri- larly in the west, have been upthrust during son 1965). These basin ranges, with eleva- a period of time from the Oligocene to the tions which vary from about 1800 m to Pleistocene. Additionally, the whole basin over 4300 m, are by no means alike either

Department of Botany, Duke University, Durham, North Carolina 27706.

105 106 GREAT BASIN NATURALIST MEMOIRS No. 2

geologically or botanically. Holmgren (1972) the desert eventually diminishes until it divided the region, on the bases of floristics is blocked by the jumbled mountain masses and geology, into four main divisions made of British Columbia which connect the up of 16 sections. The mountain ranges coastal mountains and the Rockies. within any one section have certain charac- Johnson (1975) used the lower edge of teristics in common but also there are some forest-woodland as the perimeter of his is- rather remarkable ecological differences be- lands. This is a real biological boundary. On tween mountains within the same section. the other hand, Brown (1971), Harper et al.

Holmgren notes that there is greater varia- (this symposium), and I have defined the tion in floristic composition of the alpine lower boundaries of the montane islands zone across the Great Basin from one peak rather arbitrarily. Harper et al. and Brown to another than occurs in any other zone. I have used an elevation of 7500 ft (2286 m) agree. while I have used 9000 ft (2743 m) as an For many years, biogeographers working approximation of the extreme lower eleva- in mountain areas have compared isolated tion of alpine plants (Fig. 1). This latter fig- mountain ranges and summits to islands ure is a somewhat liberal estimate of the (Wallace 1880, Willis 1922). With increased lower limits of alpine islands in the Inter- interest in island biogeography (MacArthur mountain Region, but some alpine sites do and Wilson 1967), several important papers exist this low, particularly in cirques. Tim- have appeared which provide quantitative berline is usually higher than this and is of- information on the geographical relation- ten very ragged at its upper limits. Upper ships among the biota on isolated montane timberline is frequently used as the bound- "islands." Notable among these are those of ary between subalpine and alpine vegeta- Hedberg (1970) on the Afroalpine floras, F. tion in . However, on most Vuilleumier (1970) on paramo avifaunas of mountains of the it is not a particu- the northern , B. S. Vuilleumier (1971) larly good boundary, and it is not a good and Simpson (1974) on paramo floras, boundary on most American mountains ei- Brown (1971) on mountaintop mammals in ther, including those of the Great Basin. the Great Basin, and, recently, Johnson Timberlines almost always exist at much (1975) on bird species on montane islands in higher elevations than the lowest patches of the Great Basin. MacArthur (1972) also car- alpine vegetation. This is often true around ried his theory over to montane islands in glacial valleys, both those with and those the Appalachians in his study of the distri- without glaciers at the present time. For ex- butions of thrush species. It is notable that ample, timberline around the Athabaska two of these papers (Brown's and Johnson's) Glacier in the Canadian Rockies is fully 675 are concerned with the islandlike distribu- m above the terminus of the glacier, where tion of vertebrates in the Great Basin. Nor in the morainal gravels there are a number have plant geographers ignored the island of arctic-alpine plant species but no trees. nature of the Great Basin montane islands The reasons for this ubiquitous phenomenon (P.V. Wells, pers. comm. July 2, 1968, and, are rather simple: those factors which de-

of course, Harper et al. in this symposium). fine the lower limits of alpine species are Both Brown and Johnson have viewed the not necessarily those which limit the up-

Great Basin desert "sea" and its montane is- ward distribution of trees. lands as being bordered on the east and As Figure 1 indicates, even conservative west by large cordilleras, the Rocky Moun- alpine islands in the Great Basin are much tains and Sierra Nevada, which they desig- smaller and more isolated from each other nate as "mainlands" or "." The than the mountain ranges themselves. But

desert sea is open to the south as far as the these alpine islands have been both larger real sea off Mexico. However, to the north, and smaller in the past than they are at 1978 INTERMOUNTAIN BIOGEOGRAPHY: A SYMPOSIUM 107

120°W 46"N-

: j r ° c,?c

ftMi BJ V, , ^ \i

V 18W

represent Fig. I. Map of the Intermountain Region showing, in black, areas above 2750 m in elevation. These areas which are wholly or partially "alpine" at the present time. The dashed line at the 1850 m contour is an approximate estimate of what could have been the lower limit of alpine vegetation at full-glacial. Alpine used in the northern transect are indicated from left to right by letters: P, Piute Pass (Sierra Nevada); W, Pelli- sier Flats (White Mts.); T, Toiyabe Mts.; R, Ruby Mts.; DC, Deep Creek Mts.; B, Beartooth Mts. Those in the southern transect are: O, Olancha Pk and two nearby peaks in the southern Sierra Nevada; C, Spring Mts. (Char- leston Peak); and SF, San Francisco Peaks. 108 GREAT BASIN NATURALIST MEMOIRS No. 2

present. The areas of such islands during tation shadow. There is a trend toward glacial and hypsithermal times have had a more winter snow and summer in a great deal to do with their present floristics. traverse across the basin in an easterly di- For example, Simpson (1974) showed that rection toward the Rocky Mountains. The the larger sizes of Andean paramos as they summer in the east are usually in the

existed at full glacial are more highly and form of freshening thundershowers, which, I significantly correlated with numbers of believe, have much to do with the survival plant species per paramo than are the so far south of populations of certain arctic present sizes of each paramo. Also, the dis- species in the Rocky Mountains and eastern tance between paramos at full glacial is al- basin ranges. most statistically significant in regard to These mountains were much colder and present-day floristic richness—but the effect wetter during glacial times up to at least of present distance between paramos upon 12,000 years BP. Permanent snow was floristic composition is not statistically sig- abundant, and many of the ranges had val- nificant. ley glaciers. These glaciated ranges include Present-day alpine climates on the Great the White Mountains, Toiyabe, Santa Rosa, Basin mountains are quite cold during the Independence, Jarbidge, East Humboldt, winter. In this respect, basin alpine climates and Ruby Mountains. In the latter range, are probably comparable in winter temper- valley glaciers emerged from the mountains ature to alpine areas of the Rocky Moun- onto the now sagebrush-covered plains. tains and the Sierra, although very few al- Even far to the south, there were glaciers pine weather data exist to substantiate this. on the 2 and San Francisco In summer, the basin mountains are far Peaks. Even though these glaciers were cooler than the desert below. Daytime sum- small as compared to glaciers and icefields mer maximum air temperatures are lowest on the Sierra and in the Rocky Mountains, on crests and ridges and nighttime minima they did create cirques which are now the are lowest in cirques and canyons; the same refugia for a number of alpine species. The relative conditions exist in the Rocky Moun- colder, wetter climate also depressed and tains and Sierra Nevada. telescoped vegetational zones and lowered These Great Basin alpine areas are con- timberlines an estimated 600 to 1200 m siderably moister than the desert valleys in (Baker 1970, Loope 1969, Wells and Berger both winter and summer. However, except 1969). Even though timberline in itself is for the Ruby Mountains and nearby ranges, neither the only nor the best indicator of al-

they are drier on an annual basis than al- pine conditions, such a depression would pine regions of the Rocky Mountains or the have greatly increased the size of basin

Sierra Nevada because they receive less range alpine islands and decreased the dis- snow. But they do receive enough snow to tances between them. This situation would

form persistent drifts in the lee of cliffs and have increased the chances of establishment

ridges. It is such drifts that shorten the al- of arctic-alpine species by long-distance dis- pine growing season, keep plants well wa- persal and, in certain instances, by direct tered, and allow the growth of alpine plants migration over tundralike terrain. Since tim- of certain species. The ranges toward the berline depression has been variously esti-

southwestern part of the basin are relatively mated and since it did undoubtedly vary

drier than the rest because they lie in the from one part of the Basin to another, I

most extreme part of the Sierran precipi- have compromised by showing in Figure 1

'In botanical literature, the Spring Mountains are frequently, but incorrectly, called the "Charleston Mountains" due mainly to the title of Clokey's (1951) flora of the central portion of the range dominated by Charleston Peak. 1978 INTERMOUNTAIN BIOGEOGRAPHY: A SYMPOSIUM 109 what a 900 m depression would do to the environment, preferably along meso- and sizes and proximity of alpine islands and microtopographic gradients throughout the continents at full glacial. year (Billings 1973). Also, it is necessary to Not only have the alpine islands been know the tolerance ranges of plant popu- larger in the past, they have also been lations in any particular place. This requires smaller. During the hypsithermal, about many field measurements and much labora- 7500 to 4500 years BP, timberlines of Pinus tory experimentation under controlled con- longaeva in the White Mountains and the ditions. We have made only a beginning in Snake Range advanced upward to a level understanding maintenance of some alpine about 100 to 150 m above where they now plant species. Such studies require the inter- stand (LaMarche and Mooney 1967). Such a action of many people; they are not one- long period of warmth and aridity could person jobs. have eradicated some alpine species by for- est shading or by eliminating their snowy Alpine Vegetations refugia on the higher peaks. The hard rock geological history of the In trying to reach at least a partial un-

Basin Ranges is a complex and varied one. I derstanding of alpine phytogeography and shall not go into it here. Suffice to say that in the Great Basin, it is helpful to sedimentary rocks, and thus calcareous sub- start by describing alpine vegetations as strata, are more abundant in the eastern they now exist from the Rocky Mountains ranges while the western rocks tend to be across the basin ranges to the Sierra Ne- igneous or metamorphic, and yet with some vada. A good approach is to look at these dolomites and other calcareous types. To vegetations along a northeast to southwest many alpine plants, the chemical natures of transect from the Beartooth Mountains on these different kinds of substrates are all- the - line to the central important in marginal habitats. Sierra Nevada. Such a transect crosses many of the basin ranges, but of particular inter- est are the Ruby Mountains, the Toiyabe Alpine Vegetations and Floras Range, and the White Mountains. These

In any study of vegetation and flora, it is represent the eastern, central, and western important to distinguish clearly between basin ranges, respectively. "origin" and "maintenance" of each. Origin Quantitative analyses of alpine vegetation

is very difficult to pinpoint, and particularly have been made in the Beartooth Mountains so with alpine floras because they leave al- (Johnson and Billings 1962), the northern most no macrofossils. However, the pres- Ruby Mountains (Loope 1969), the White ence of diploids in widespread polyploid Mountains (Mooney 1973), and the central

arctic-alpine species may play the role of Sierra Nevada (Chabot and Billings 1972). I

"cytological fossils." The origin of a par- do not know of any quantitative alpine veg-

ticular flora on any mountaintop is the re- etational data from the Toiyabe or Toquima sult of the interaction of many factors: past Ranges; perhaps there are some. The floris- geologic events, past climates, migrations of tic information and photographs in Linsdale

each species, polyploidy, evolution, and et al. (1952) are of some help, as are per-

even man's activities. Hypotheses are nu- sonal qualitative observations which I made merous; answers are few. in 1949. While maintenance of an alpine flora and Space does not allow the presentation of

its vegetation is somewhat easier to under- those long tables of vegetational composi-

stand, there is still much work involved. tion which do exist; one simply can refer to One must measure the characteristics of the publications listed above. However, the x>th the physical and biological aspects of alpine vegetation of the Beartooth Moun- 110 GREAT BASIN NATURALIST MEMOIRS No. 2

tains is typically Rocky Mountain alpine etation types which one sees in the Rocky with large expanses of alpine tundra in the Mountains. More vegetational work is true sense: Geum rossii turf in mesic sites, needed in the small and little-known alpine Deschatnpsia caespitosa meadow in moist areas of the central Great Rasin; further sites, and Carex scopulorum in wet bogs. study may change our ideas of these regions The crests and ridges are occupied by of what might be termed alpine desert. rather dense stands of cushion and rosette Another 150 km farther southwest is the plants with Silene acaulis, Carex elynoides, long and high massif of the White Moun- and many other species dominating. Early tains. In contrast to the Toiyabe and To- and late snowbeds are abundant and have quima Ranges, this has been rather in- characteristic species surrounding them. tensively studied environmentally, vege- Alpine vegetation in the Ruby Mountains tationally, and floristically. The alpine lacks the broad expanses of tundra charac- vegetation has been well-described by teristic of the Reartooth. However, south of Mooney et al. (1962), Mitchell et al. (1966),

Lake Peak along the divide there is fairly and Mooney (1973). Over most of the exten- extensive tundra at elevations from 3140 m sive alpine area in the White Mountains, to 3300 m. This alpine vegetation is charac- the vegetation is extremely sparse; Mooney terized by Silene acaulis and Carex pulvi- (1973) reports a plant cover of only 1.5 per- nata. Similar alpine vegetation exists at the cent at 4175 m on the side of White Moun- same elevation on the north slope of Wines tain Peak. Mitchell et al. (1966) say that Peak, with Geum rossii and Silene acaulis vegetational cover on windy, gravelly flats being the dominants. Carex scopulorum on Pellisier Flats, an area of 21 km 2 near grows in dense stands around alpine ponds. the north end of the range, rarely exceeds Some of the best-developed alpine vegeta- 15 percent. However, on seepage banks and tion in the Rubies is in the cirque floors. In meltwater runs, vegetational cover ranges

Island Lake cirque, the vegetation is domi- from 10 to 95 percent. Pellisier Flats at nated mainly by Erigeron peregrinus, Salix 4100 to 4430 m has active frost polygons arctica, Caltha leptosepala, Geum rossii, Sib- and miniature solifluction steps reminiscent baldia procumbens, and Polygonum bistor- of the Reartooth Plateau. The most striking toicles. Oxyria digyna is common on rocky, vegetational feature of the White Moun- moist sites, particularly around snowbanks. tains, however, is the sharp distinction in

One is struck with the remarkable similarity vegetation and flora between the dolomite in species composition and site character- barrens and granite or quartzite fell-fields. istics to the alpine vegetation of the Rear- The dolomite barrens are very desertlike tooth some 700 km to the northeast. Essen- and, although in places they may have veg- tially, the alpine vegetation of the Ruby etational cover up to 12 percent, in other

Mountains is a small, only slightly attenu- places there are almost no plants. Phlox cov- ated, isolated example of Rocky Mountain illei and Eriogonum gracilipes are character- alpine vegetation. istic species on the dolomite. A granite fell- In strong contrast, the alpine vegetation field at 3870 m had a vegetational cover of of the , only 250 km south- 50 percent and was dominated by Trifolium west of the Rubies, apparently bears little monoense and Koeleria cristata; the first is resemblance to that of the northern Rubies essentially endemic to the White Mountains

or to that of the Rocky Mountains. It seems and the second is a cosmopolitan species. to be an open, rocky vegetation with a few The alpine vegetation of the White Moun-

scattered alpine grasses such as Trisctum tains is decidedly unlike that of the Rubies— spicatum and various species of Draba and but both are Basin ranges. Eriogonum, some of which are endemic. There have been several vegetational

There is not the great variety of alpine veg- studies made on alpine vegetation in the 1978 INTERMOUNTAIN BIOGEOGRAPHY: A SYMPOSIUM 111

Sierra Nevada. These vary considerably be- Mountains (McMillan 1948), the Buby tween the northern end of the range and Mountains (Loope 1969), the Toiyabe Bange the southern, where the peaks are higher (Linsdale et al. 1952), the White Mountains and the climate drier. Only 48 km south- (Mitchell et al. 1966), and the central Sierra west of the White Mountain crest and with- Nevada (Chabot and Billings 1972). Addi- in sight of it, is Piute Pass at 3540 m on the tionally, I have included floristic data from Sierran white granite. Here, Chabot and a series of three isolated alpine areas across Billings (1972) found the low alpine vegeta- the southern desert region. From west to tion covering less than 30 percent of the east these are Olancha Peak and its neigh- rocky ground and characterized by Lupinus bors in the Sierra Nevada (Howell 1951), breweri, Antennaria rosea, and Carex helleri. the Spring Mountains (Clokey 1951), and Other common Sierran alpine species in San Francisco Peaks (Little 1941). similar locations on nearby peaks and ridges Many alpine plant species also occur in are Phlox caespitosa, Penstemon davidsonii, the Arctic. As a basis for whether or not Ivesia pygmaea, and Draba lemmonii. At our species do, I have checked each against higher elevations, Oxyria digyna, Polerno- Polunin's (1959) Circumpolar Arctic Flora. nium eximium, and Hulsea algida are con- Species which are not arctic-alpine may be stant members of the alpine vegetation usu- endemic to a continental region of the ally on scree slopes. The most luxuriant middle-latitudes or to the mountain range vegetation near here is along snowbank itself or its near neighbors. While we need meltwater brooks where Dodecatheon jef- much more information on both scores, the freyi, Lewisia pygmaea, and Sedum rosea absolute figures on arctic and endemic spe- occur. On very thin granitic soils which dry cies in each small alpine area can tell us out after snowmelt, only Calyptridium um- something about migrations into an area bellatum, the dwarf Koenigia-like endemic and possibly about the evolution of new Polygonum minimum, and one or two other species after such migrations from afar or species can exist. There is a great difference from the arid regions below. Nor should we in alpine vegetation here, not only from forget that some endemic species may be that of the Beartooth but also from that of relicts or that some widespread arctic-alpine the White Mountains on the near horizon. species may have become extinct during- xerothermic times, or that some may never Alpine Floras have reached certain alpine areas because While there are a few floras for whole of lack of adaptation for long-distance dis- mountain ranges between the Bocky Moun- persal. tains and the Sierra, e.g., Lloyd and Mit- The upper part of Table 1 (the chell (1973) for the White Mountains, the Beartooth-Sierra transect) illustrates immedi- main sources of alpine floras per se appear ately that there are many alpine species in to be journal papers or theses. Beferring the central Bocky Mountains that also occur again to Figure 1, I have assembled at least in the Arctic. In the Beartooth Mountains, tentative figures on the numbers of alpine 91 out of 194, or almost half the alpine

species for the same NE-SW transect along flora, also occurs in the Arctic. This is in which the trend in alpine vegetation has contrast to the 24 arctic-alpine species in been described. These figures will certainly the Deep Creeks and 47 in the Bubies; but be changed with additional collecting and these are somewhat smaller ranges. The publication, particularly of more volumes of composition of the alpine floras of both of

Cronquist et al. Intermountain Flora and the latter ranges, however, is very much a Howell's proposed Sierran Flora. The Bocky Mountain-type flora. In contrast,

sources are the Beartooth Mountains (John- west of the Buby Mountains there is a dra- son and Billings 1962), the Deep Creek matic drop in not only the total numbers of 112 GREAT BASIN NATURALIST MEMOIRS No. 2 alpine species in the Toiyabe, the White gration across the Great Basin appears to

Mountains, and the Sierra Nevada, but also have been a chancy thing even at full- in the number of arctic-alpine taxa present. glacial. Only species with propagules easily The arctic-alpine element consists, in these dispersed by wind or birds appear to have ranges, mostly of such easily dispersed, made it to the central Great Basin moun- ubiquitous species as Oxyria digyna, Trise- tains. Even after possible establishment, tum spicatum, Cystopteris fragilis, and An- some alpine species may have become ex- drosace septentrionalis. Even common spe- tinct on the Great Basin peaks in dryer, cies such as Silene acaulis are missing, not postglacial times. Axelrod (1976) also sug- to mention relatively rare taxa such as Koe- gests extinctions of moist environment sub- nigia islandica, Saxifraga flagellaris, or alpine conifers and alpine species in the Phippsia algida. Widespread arctic-alpine Great Basin during these xerothermic epi- species such as Silene acaulis, Polygonum sodes. I believe that extended post-glacial viviparum, and Salix arctica reach their dry periods also could have eliminated such western limits in the Great Basin in the dry-site arctic-alpine species as Silene Ruby Mountains and do not reappear in the acaulis and Saxifraga cespitosa in the Sierra Sierra Nevada (Loope 1969). Since these Nevada where they do not occur today. species are not that particular in their envi- This suggestion, of course, must assume that ronmental requirements (there are apparent these species migrated into the Sierra Ne- places in the Sierra Nevada where they vada, probably from the north, during fa- could grow), they either must be poorly vorable Pleistocene times. adapted to long-distance dispersal or there Looking at the southern transect in Table is or has been an advantage to migrating 1, the same dearth of arctic species is ap- north or south along the old tried and true parent in the Olancha Peak group at the Rocky Mountain pathway. Those arctic- southern end of the Sierra and particularly alpine species in the Sierra Nevada most so on Charleston Peak in the isolated Spring likely came down from the north in glacial Mountains where only 9 arctic species or cooler times during the Pleistocene. Mi- are known to occur. In contrast, only

Table 1. Total numbers of true alpine species and those which also occur in the Arctic (arctic-alpine) in two transects across the Intermountain Region. Data from several sources.

Total No. No. of Percent of of Alpine Arctic-Alpine Arctic-Alpine Location Species Species Species

Northern Transect Beartooth Mts. 194 91

Deep Creek Mts. 80

Ruby Mts.

Toiyabe Range

White Mts.

(Pellisier Flats)

Piute Pass (Sierra)

Southern Transect Olancha Pk., etc. (Sierra) 102

Spring Mts.

San Francisco Pks. 1978 INTERMOUNTAIN BIOGEOGRAPHY: A SYMPOSIUM 113

350 km to the southeast, the San Francisco environments and systematic description of Peaks have at least 19 arctic species in spite the taxa. of their isolation. Also, there is a distinct One way of comparing alpine floras is to Rocky Mountain cast to their alpine flora. use Srirensen's (1948) Index of Floristic Sim-

A possible pathway for migration into this ilarity. This is expressed as: Pleistocene volcanic mountain may have been at full-glacial through the Arizona IS. X 100 1/2 (A + B) White Mountains to the southeast, or the where, IS = Sdrensen's Index of source may have been through the Wasatch S Similarity Plateau to the north. Again, we come to the c = number of species origin versus maintenance problem: these held in common arctic species would not remain in the vol- by two alpine areas canic cinders or the glacial cirques of this A = total number of isolated mountain, no matter how they got alpine species there, except for the summer thunder- in Region showers reinforcing the winter snows as a A B = total number of source of water. Much more poorly known are the endem- alpine species in Region B ics of all of the above mountain ranges. Al- pine endemics are much less common in the Taking the available alpine floristic data central Rocky Mountains than in the Sierra from each of the nine alpine areas on both

Nevada. This may be due to lack of isola- transects, I calculated SeSrensen's Indices for tion along the Rocky Mountain system. The each possible comparison. These indices are Sierra Nevada as a whole has many endem- presented as percentage values in Table 2. ic alpine species but I do not know how Also, in the same table, direct distances in many of these may be narrow endemics re- km between the alpine areas are shown. stricted to the two small regions listed in When the Indices of Similarity are plotted

Table 1. The White Mountains have several against distance for each pair of alpine alpine endemics, and since they cover so areas, the result is a great deal of scatter in much less area than the Sierra Nevada, the the points. There is little evidence of in- chances of these being narrow endemics are verse correlation of floristic similarity be- better than in the latter range. The same tween these alpine regions with distance. fact holds true for the isolated ranges of the Out of 36 possible combinations, only 4 central Great Basin. Some of these latter show indices above 30 percent combined endemics may also prove not to be so nar- with distances below 200 km. These are the row, except edaphically, upon further ex- Deep Creek—Ruby Mountains in the east- ploration. For example, consider Primula central Great Basin and Pellisier Flats- nevadensis (Holmgren 1967). The isolated Olancha Peak, Pellisier Flats-Piute Pass, and Spring Mountains, with an alpine flora of Piute Pass-Olancha Peak, all in the Sierra only 39 species at most (some of these are Nevada-White Mountain complex at the ex- probably subalpine), has at least 4 endemic treme southwestern edge of the Great Basin. alpine species. It seems that alpine endem- Two others had indices almost equally as ism tends to be more common in relation to high but at distances between 500 and 700 total alpine floras on isolated, nonvolcanic km; these are the - peaks and ranges in the southwestern part San Francisco Mountains and Beartooth- of the Intermountain Region; this includes Ruby Mountains combinations. The most the southern part of the Sierra Nevada. The distant range, the Beartooth, has higher in- real answer to the question of distribution dices of similarity with the Ruby Mountains, of endemics lies in more collecting in alpine Deep Creek Mountains, and San Francisco 114 GREAT BASIN NATURALIST MEMOIRS No. 2

Mountains alpine floras at distances of 650 are equally distant from the Deep Creek to 1100 km than any of these latter ranges Mountains.

have with the Spring Mountains at distances The rather low indices of similarity in- less than 500 km. The distant Rocky Moun- dicate at least one fact rather clearly: these tains alpine flora as exemplified by that of Intermountain Region alpine areas are very

the Beartooth has as great or greater an in- much like newly isolated islands. This is fluence on those of most of the Great Basin well illustrated along the southern transect mountain ranges than does that of the much from Olancha Peak to Charleston Peak to

closer Sierra Nevada. There is even a great- San Francisco Peaks. With the two gaps er (two to three times) similarity between being only 225 and 378 km across, respec- the alpine floras of San Francisco Moun- tively, the indices of similarity are only 13

tains and the Deep Creek Mountains at a and 14 percent. The Olancha Peak group is

distance of 531 km than there is between clearly Sierran, Charleston Peak is unique, the Deep Creek flora and those of the and San Francisco Peaks show strong rela- Sierra Nevada and White Mountains, which tionships to the Rocky Mountains and

Table 2. Sdrensen's indices of floristic similarity (in percent) between alpine floras for all combinations of al- pine areas in both transects. Numbers in parentheses are distances (in km) between the alpine regions. Also, see map in Fig. 1. 1978 INTERMOUNTAIN BIOGEOGRAPHY: A SYMPOSIUM 115 mountain ranges far to the north. These af- arctic-alpine species appear to be able to finities of the San Francisco Peaks alpine migrate far: Oxijria digyna, Saxifraga flora have also been noted by Moore (1965). cespitosa, Trisetum spicatum, and Cys-

After examining the existing floristic data topteris fragilis, for example. Therefore, it is on alpine species across the Great Basin, it advantageous for ancestral species to be is tempting to delineate some alpine phyto- nearby when mountains arise or new alpine geographic boundaries. Certainly, there is a areas come into existence by climatic sharp boundary just west of the Ruby causes. It also seems to be advantageous to Mountains separating Rocky Mountain types be on a north-south migration route such as of vegetation and flora from that of the the old Rocky Mountains, or even the much Great Basin. Where this boundary goes to younger Cascade-Sierran system. The ability the south, I am not prepared to say. Cer- to evolve rapidly by adaptive radiation is tainly, it would appear to be west of the also advantageous, as for example, in the Snake Range and perhaps west of the Grant genus Espeletia in the Andean paramos. Range; but this is tentative and probably Such plasticity, plus pure luck in being premature. It obviously lies between San near refugia, either edaphic or micro- Francisco Peaks and the Spring Mountains. climatic, also helps. Interglacial refugia are Another alpine phytogeographic boundary fully as important as glacial refugia. Such lies between the White Mountains and the interglacial refugia can be mountaintops Sierra Nevada and winds north in sinuous such as Mount , New Hamp- curves until it divides the Carson Range on shire, altered volcanic rocks as in the Vir- the west from the Range on the ginia Range of (Billings east; but several species pay no attention to 1950), alpine snowbanks, and the moist, such an imaginary line and go their way cool floors of impervious cirques (Loope from the Sierra Nevada into the altered an- 1969). Loope ascribes the presence of many desites of the Virginia Range (Billings 1950) arctic species in the Ruby Mountains today and the neve cirques of the Pine Nut and to its nonporous (moist) cirque floors as

Wassuk Ranges (Billings 1954). Again, if compared to the porous, dry cirque floors edaphic or moisture conditions are of the Jarbidge Mountains to the north and right,some species can get to seemingly in- those of the Snake and Schell Creek ranges hospitable mountain ranges and stay there to the south. perhaps by infraspecific physiological adap- There are other sources of alpine floras in tations (i.e., ecotypes). the Intermountain Region. These are the surrounding desert floras as suggested long Possible Origins of ago by Went (1948) and experimentally in- Intermountain Alpine FlorAs vestigated by Klikoff (1966) and by Chabot and Billings (1972) for the Sierra Nevada. Alpine floras originate in all mountains The principal findings reported in the latter by migration and/or evolution; the moun- paper would apply almost as well to the tains of the Intermountain Region are no mountain ranges of the Great Basin, provid- exception. Refugia, both glacial and inter- ed there are suitable sites for such migra- glacial, are also important. As Figure 1 tion and evolution, and providing there are shows, and as Simpson (1974) has demon- species and genera of sufficient genetic strated for the paramos, successful long- plasticity near at hand. The derivation of a distance dispersal is greatly influenced by new alpine flora from a desert or semidesert the sizes and proximity of alpine islands. flora is aided by the following:

Such islands were obviously larger and a. preadaptation of winter annuals and closer during glacial and cooler times. From perennials in regard to physiology and distributional evidence, only a relatively few morphology, No. 2 116 GREAT BASIN NATURALIST MEMOIRS

b. the ability to migrate upward during Baker, R. G. 1970. Pollen sequence from Late Qua- sediments in Yellowstone Park. Science favorable climatic periods into new ternary 168: 1449-1450. but not altogether dissimilar environ- Bateman, P. C, and C. Wahrhaftig. 1966. Geology ments, of the Sierra Nevada, pp. 105-172. In: E. H. c. selection for metabolism at low sum- Bailey (ed.), Geology of northern . Ca- mer temperatures, lif. Div. Mines and Geol. Bull. 190: 1-508. Billings, W. D. 1950. Vegetation and plant growth d. selection for low temperature starch as affected by chemically altered rocks in the degradation and sugar translocation at western Great Basin. Ecology 31: 62-74. night, 1954. Nevada Trees, 2d ed. Univ. Nevada

e. selection of populations and ecotypes Agric. Extens. Serv. Bull. 94: 1-125. which acclimate metabolic-ally rapidly 1973. Arctic and alpine vegetations: sim- ilarities, differences, and susceptibility to dis- and ideally, and turbance. BioScience 23: 697-704. f. selection for flowering and seed-set in 1974. Adaptations and origins of alpine seasons. short, dry cool growing plants. Arctic and Alpine Res. 6: 129-142. elaborated in detail by Bil- 1971. Mammals on mountaintops: These have been Brown, J. H. lings (1974). nonequilibrium insular biogeography. Amer. Naturalist 105: 467-478. There is every reason to believe that such Chabot, B. F., and W. D. Billings. 1972. Origins upward evolution of new "alpine-desert" and ecology of the Sierran alpine flora and veg- Basin. But taxa is taking place in the Great etation. Ecol. Monogr. 42: 163-199.

the rate may be slower than in the Sierra Clokey, I. W. 1951. Flora of the Charleston Moun- Nevada due to a smaller preadapted flora tains, Clark County, Nevada. Univ. Calif. Publ. Bot. 24: 1-274. and also due to the drier and less snow-pro- Hedberg, O. 1970. Evolution of the Afroalpine tected environments on the peaks. In such a flora. Biotropica 2: 16-23. edaphic case, there could be a trend toward Holmgren, N. H. 1967. A new species of primrose endemism because other kinds of habitat di- from Nevada. Madrono 19: 27-29. versity are in relatively short supply. Such 1972. Plant geography of the Intermountain Region, 77-161. In: A. Cronquist, A. H. upward mobility and long-distance dispersal pp. Holmgren, N. H. Holmgren, and J. L. Reveal over great distances in a north-south direc- (eds.), Intermountain flora. Vol. 1. Hafner Publ. of the tion seem to be the principal sources Co., New York. these isolated montane is- T. 1951. The arctic-alpine flora of three alpine floras of Howell, J. Leafl. W. Bot. 6: lands in the central Great Basin. peaks in the Sierra Nevada. 141-156. Acknowledgments Johnson, N. K. 1975. Controls of number of bird species on montane islands in the Great Basin. This work has been aided by National Evolution 29: 545-567. The al- Science Foundation Grant BMS72-02356 Johnson, P. L., and W. D. Billings. 1962. pine vegetation of the Beartooth Plateau in re- A01 (General Ecology) for which I express lation to crvopedogenic processes and patterns. my appreciation. Many people have helped Ecol. Monogr. 32: 105-135. discussion; I thank particu- with data and Klikoff, L. G. 1966. Temperature dependence of larly Lloyd Loope, Brian Chabot, Juliana the oxidative rates of mitochondria in Dan- and Si- Mulroy, Gaius B. Shaver, and Shirley Bil- thonia intermedia, Penstemon davidsonii, tanion hystrix. Nature 212: 529-530. lings. LaMahche, V. C, and H. A. Mooney. 1967. Literature Cited Altithermal timberline advance in western . Nature 213: 980-982.

\\mh(»1). 1). I. 1962. Post-Pliocene uplift of the A., T. Howell, and M. Lins- Linsdale, M. J. J. Sierra Nevada, California. Bull. Geol. Soc. dale. 1952. Plants of the Toiyabe Mountains Amer. 73: 183-198. Biol. 10: 129-200. area, Nevada. Wasmann J. 1976. Historv of the coniferous forests, Cali- San Fran- Little, E. L., Jr. 1941. Alpine flora of fornia and Nevada. Univ. Calif. Pub. Bot. 70: Arizona. Madrono 6: 65-96. 1-62. cisco Mountain, 1978 INTERMOUNTAIN BIOGEOGRAPHY: A SYMPOSIUM 117

Lloyd, R. M., and R. S. Mitchell. 1973. A flora of Morrison, R. B. 1965. Quaternary geology of the the White Mountains, California and Nevada. Great Basin, pp. 265-285. In: H. E. Wright, Jr. University of California Press, Berkeley. and D. G. Frey (eds.), The Quaternary of the Loope, L. L. 1969. Subalpine and alpine vegetation United States. Princeton University Press, of northeastern Nevada. Unpublished doctoral Princeton, New Jersey. dissertation, Duke University, Durham, North Polunin, N. 1959. Circumpolar Arctic Flora. Cla- Carolina. rendon Press, Oxford.

MacArthur, R. H. 1972. Geographical ecology: Simpson, B. B. 1974. Glacial migrations of plants: patterns in the distribution of species. Harper island biogeographical evidence. Science 185: and Row, Publications, New York. 698-700. MacArthur, R. H., and E. O. Wilson. 1967. The Sorensen, T. 1948. A method of establishing groups theory of island biogeography. Princeton Uni- of equal amplitude in plant sociology based on versity Press, Princeton, New Jersey. similarity of species content. Kongel. Danske McMillan, C. 1948. A taxonomic and ecological Vidensk. Selsk. Skr. (Copenhagen) 5(4): 1-34. study of the flora of the Deep Creek Mountains Vuilleumier, B. S. 1971. Pleistocene changes in the of central western . Unpublished master's fauna and flora of . Science 173: thesis, University of Utah, . 771-780. Mitchell, R. S., V. C. LaMarche, Jr., and R. M. Vuilleumier, F. 1970. Insular biogeography in con- Lloyd. 1966. Alpine vegetation and active tinental regions. I. The northern Andes of South frost features of Pellisier Flats, White Moun- America. Amer. Naturalist 104: 373-388. tains, California. Amer. Midi. Naturalist 75: 516-525. Wallace, A. R. 1880. Island life. MacMillan and Mooney, H. A. 1973. Plant communities and vege- Co., London. tation, pp. 7-17. In: R. M. Lloyd and R. S. Mit- Wells, P. V., and R. Bercer. 1967. Late Pleisto- chell (eds.), A flora of the White Mountains, cene history of coniferous woodland in the Mo- California and Nevada. University of California jave Desert. Science 155: 1640-1647. Press, Berkeley. Went, F. W. 1948. Some parallels between desert Mooney, H. A., G. St. Andre, and R. D. Wright. and alpine flora in California. Madrono 9: 1962. Alpine and subalpine vegetation patterns 241-249. in the White Mountains of California. Amer. Willis, C. 1922. Age and area: a study in geo- Midi. Naturalist 68: 257-273. J. graphical distribution and origin of species. Moore, T. C. 1965. Origin and disjunction of the Cambridge University Press, Cambridge. alpine tundra flora on San Francisco Mountain, Arizona, Ecology 46: 860-864.