THE ALPINE FLORA OF THE WHITE MOUNTAINS, CALIFORNIA

2008·9.6 MB·English

by  Philip W Rundel

';
Madrono, Vol. 55, No. 3, pp. 202-215, 2008
THE ALPINE FLORA OF THE WHITE MOUNTAINS, CALIFORNIA
Philip W. Rundel
Department of Ecology and Evolutionary Biology and
Center for Embedded Networked Sensing, University ofCalifornia, Los Angeles, CA 90095
[email protected]
Arthur C. Gibson and M. Rasoul Sharifi
Department of Ecology and Evolutionary Biology,
CA
University of California, Los Angeles, 90095
Abstract
ThealpinezoneoftheWhiteMountainsofCalifornia,definedasnon-forestedareasabove3500 m,
includes 163 native species ofvascular plants in an area of 106 km-. No invasive species have become
well established. Nearly two-thirds of the native species occur in just seven families, led by the
Asteraceae with 30 species. Six genera have five or more species, led by Carex with 14 species. Life
forms ofthe flora are heavily dominated by broad-leaved herbaceous perennials (53%), followed in
importance by graminoid perennials (22%) and mats and cushions (11%). Woody shrubs,
chamaephytes (low subshrubs), and annuals are relatively few in number, and those species present
are generally more characteristic of lower elevation communities. Fellfields form the characteristic
habitat for41% ofthe flora, while moist meadows and open slopes habitats characterize 24 and 22%
oftheflora, respectively. Only31%ofthefloraisrestrictedintheWhiteMountainstothealpinezone,
while nearly a third ofthe alpine flora has a range extending to lower elevations ofthe montane or
cold desert zones below 2900 m. The alpine flora of the White Mountains shares over 70% of its
species with the Sierra Nevada. Only three species are endemic to the alpine zone of the White
Mountains: Draba ca/ifornica, D. monoensis, and Potentilla morefieldii.
Key Words: alpine biogeography, alpine flora, plant life forms. White Mountains.
Generalizations about the patterns of biodi- tions of either sets of ranges. Moreover, warmer
versity and life forms in alpine floras have largely and more xeric climatic conditions during the
come from research conducted in relatively mesic Altithermal period ofthe early Holocene allowed
alpine habitats with summer rainfall regimes, as an upward movement of subalpine conifers,
forexample in the Alps ofcentral Europe and the restricting the area available for growth ofalpine
Rocky Mountains of the western United States communities (Jennings and Elliot-Fisk 1991,
(see reviews by Tranquillini 1979; Chapin and 1993). Thus, the White Mountains present an
Korner 1995; Korner 1999; Bowman and Seast- example where both climate history and geo-
edt 2001). Unhkethemajority ofalpine regions in graphic isolation have played significant roles in
the Northern Hemisphere that share elements of the evolution ofthe alpine flora.
a circumboreal arctic-alpine flora, the high Lying in the rain shadow ofthe Sierra Nevada,
mountain ranges in CaUfornia have developed a theWhite Mountainsreceive onlyabout one-third
unique alpine flora under the influence of ofthe precipitation reaching similar elevations on
mediterranean-climate conditions with relatively the west slope of the Sierra Nevada. These arid
dry summers added to other alpine environmen- conditions, combined with the extremes of low
tal stresses. Although broad ecological studies temperature, wind, low atmospheric pressure and
have been carried out in the alpine elevations of high ultraviolet radiation load that characterize
the Sierra Nevada and White Mountains of most temperatealpineconditions, produce unusu-
Cahfornia (Chabot and Bilhngs 1972; Major ally severe conditions ofenvironmental stress for
and Taylor 1977; Morefield 1992), there is still plant growth. Adding to the habitat conditions oft
a relatively poor knowledge of patterns of the range are high levels of both topographic
floristic diversity and life form distribution of diversity and geologic complexity, with the latter
the alpine flora for these ranges. including granites, dolomites, shales, limestones,
The White Mountains of California and and metavolcanics (Nelson et al. 1991; Ernst et al.
adjacent Nevada (Fig. 1) present a particularly 2003) that have strong influences on florisitic
interesting area for study. This mountain range is composition (Lloyd and Mitchell 1973; Marchand
positioned at the interface between two major 1973; Rundel et al. 2005).
geomorphic provinces, the Sierra-Cascade Prov- The White Mountains extend approximate-
ince and the arid Basin and Range Province, yet ly 60 km from their northern end in Nevada
is isolated from direct contact with high eleva- across into California and Westgard Pass in the
2008] RUNDEL ET AL.: ALPINE FLORA OF THE WHITE MOUNTAINS 203
kilometers
Fig. 1. Regional view ofthe White Mountains ofeastern California and adjacent Nevada. The stippled area is
m
that portion ofthe range above 3500 elev.
south, or three times this length if the contigu- floristic diversity and relationships of the full
ous Inyo Range south of this pass is added flora ofthe White Mountains has been described
(Fig. 1). The range is very narrow, however, with in considerable detail (Lloyd and Mitchell 1973;
a width averaging only 20-25 km. As a result, Morefield et al. 1988; Morefield 1992). AUhough
the range rises sharply from elevations of there have been ecological studies of plant-soil
1250 m in the Owens Valley to a high point of relationships in the alpine regions of the range
4343 m at White Mountain Peak over a lateral (Mooney et al. 1962; Mitchell et al. 1966;
distance ofless than 10 km. This peak is tied with Marchand 1973; Ernst et al. 2003), no floristic
Mount Shasta as the third highest summit in research has focused on the alpine region above
m
California. 3500 or analyzed its characteristics specifically.
There has been a long history of floristic and In this paper we present a broad overview ofthe
ecological studies in high elevations ofthe White alpine flora ofthe White Mountains by providing
Mountains where alpine habitats are present. The a detailed analysis of the floristic richness.
MADRONO
204 [Vol. 55
ecological diversity, and biogeographic relation- The classification of species by characteristic
ships ofthe alpine flora present within this zone. elevationalzonewasdesignedto separateobligate
m
alpinespeciesfromthoseextendingabove 3500
Materials and Methods but also occurring at lower elevations. These five
categories listed as the elevational belts oflowest
Floristic Richness and Life Forms occurrence in the White Mountains are cold
desert (1220-1980 m), montane (1980-2900 m),
Thealpine flora oftheWhite Mountains inthis subalpine (2900-3500 m), alpine (3500-4000 m),
study was considered to include all species with a and high alpine elevations (4000^332 m). The
known occurrence above 3500 m, an elevation montanezoneroughlycorrespondstothepinyon-
limit roughly corresponding to upper treeline, juniper zone and the subalpine belt to the upper
although Pinus longaeva reaches elevations ofup pine zone ofvegetation.
to about 3700 m in scattered locations. While The biogeographic range ofeach alpine species
there are certainly alpine-hke communities and was classified into one of five categories. These
species assemblages below this elevational limit, were: widespread speciespresentinmanyhabitats
an occurrenceabovetheupperlimit forgrowth of or regions throughout the world or across North
P. longaeva and P. flexilis indicates a definitive America, cordilleran species widespread in moun-
alpine habitat. Our listing ofthe alpine species to tain regions ofthe western United States, Sierra/
beconsidered was based on a careful examination Cascade species, intermountain species wide-
of published material (Lloyd and Mitchell 1973; spread across the Great Basin, and species
Morefield et al. 1988; Morefield 1992; Hickman endemic to the White Mountains.
1993), herbarium records (Cal Flora, White
Mountain Research Station), and our own field Climate Regimes
observations carried out on numerous visits each
summer from 1999 2006 Scientific names used Climatic data to characterize the alpine envi-
.
here follow those of Hickman (1993), with the ronment ofthe White Mountains was taken from
exception of Poa pattersonii which has been long-term records collected at the Barcroft
m
divided into Poa abbreviata subsp. pattersonii Station at 3801 elev. (37°35'N lat., 18°15'W
and subsp. marshii (Soreng 1991). long.) for the period 1953-1973 (Pace et al. 1974;
Adapting the broad classification scheme set out Powell and Klieforth 1991). The mean monthly
by Morefield (1988, 1992) fortheentire floraofthe maximum temperatures at Barcroft vary from a
White Mountains, we developed a system to high of 11.9°C in July to a low of -5.3°C in
categorizethealpine speciesbylife form, ecological February (Fig. 2). Record maximum tempera-
habitat, elevational zone, and biogeographic distri- tures of 22°C have been reached in July and
bution. Each alpine species was placed into one of August. Mean monthly maximum temperatures
six life forms in a modified Raunkiaer (1934) remain below freezing for six months ofthe year,
classification: phanerophytes (shrubs reaching from November through April. Mean minimum
50 cmormoreinheight),chamaephytes(subshrubs temperatures range from a high of 2.4°C in July
lowerin stature), matorcushionplants(<10 cmin to a low of —14.0°C in March. Mean minimum
height and prostrate in growth, perennial grami- temperatures drop below freezing for every
noids (i.e., Poaceae, Cyperaceae, and Juncaceae), month ofthe year except July and August.
broad-leaved herbaceous perennials (tussocks, ro- Meanannual precipitationat Barcroft Stationis
mm
sette perennials, biennials, and geophytes), and 478 (Fig. 2). There are elements ofa mediter-
annuals (therophytes). With very few exceptions, ranean-type pattern of winter precipitation but
plant species in the alpine zone have very narrow with a strong influence of summer convective
leaves or leaflets with blades <10 mm wide, and storms from the east that bring scattered precip-
would be classified as leptophylls with leafsurface itation events throughout the growing season.
areas <25 mm- (Raunkiaer 1934). Mean mmomnthly precipitation ranges frommamhigh
Designations ofecological habitatswere adapt- of 56 in December to a low of 18 in
ed from characterizations of Morefield (1988, September, but year-to-year variation is high. The
1992) and our experience to provide seven extremes in annual precipitation over the record
categories. Along a rough gradient of mesic to period have ranged from242 to 852 mm. With the
xeric these ecological habitats are aquatic sites, exception of the summer months ofJuly through
wet sites (areas with saturated soils and riparian September, all ofthis precipitation falls as snow.
habitats), moist sites (e.g., wet meadows and
areas with snow melt accumulation), fellfields Results
with seasonal moisture availability, talus slopes,
open slopes, and dry rocky slopes. Where a Native Flora
species occurred broadly across more than one of
these habitat categories, it was placed in what we Defining the alpine zone as non-forested areas
considered its most typical habitat. occurring at or above 3500 m, the alpine flora of
2008] RUNDEL ET AL.: ALPINE FLORA OF THE WHITE MOUNTAINS 205
-20
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
Time (date)
Fig. 2. Meanmonthlyclimaticconditionsat the Barcroft Station at 3801 min theWhite Mountains, 1953-1973.
Data from Pace et al. (1974).
the White Mountains includes 163 native species that shares the characteristic of a prostrate
occurring in an area of 106 km^. Rather than growth form with either a central taproot or
representingtheproportionalfamily relationships multiple points of rooting through layering.
ofthe Cahfornia flora overall, the alpineflora has These form an ecologically significant component
just seven families that account for nearly two- ofplant cover on fellfield slopes and the margins
thirds of its total species. Leading this group is ofdrainage swales. A different group ofspecies is
the Asteraceae with 30 species, followed in order present, however, dominates on granitic versus
by the Brassicaceae (18 species), Poaceae (17 dolomitic substrates. Common mats and cush-
species), Cyperaceae (15 species), Rosaceae (9 ions on the widespread granitic substrates include
species), Caryophyllaceae (9 species), and Poly- Draba oligosperma (Brassicaceae), Trifolium an-
gonaceae (7 species). Genera with large numbers dersonii var. beatleyae (Fabaceae), Eriogonum
of alpine species in this flora include Carex ovalifolium var. nivale (Polygonaceae), and Pen-
(Cyperaceae, 14 species), Arabis (Brassicaceae, 7 stemon heterodoxusvar. heterodoxus (Scrophular-
species), Draba (Brassicaceae, 7 species), Poa iaceae). On dolomitic substrates, there is a shift in
(Poaceae, 6 species), Potentilla (Rosaceae, 5 dominance to species such as Erigeronpygmaeus
species), and Eriogonum (Polygonaceae, 5 spe- and Stenotus acaulis (Asteraceae), Astragalus
cies). Several species just miss our lower eleva- kentrophyta and Oxytropis parryi (Fabaceae),
tional limit of3500 m, and thus are not included Linum lewisii (Linaceae), Eriogonum gracilipes
in our figures here, although they occur in alpine (Polygonaceae), and Castilleja nana (Scrophular-
fellfield and open slope habitats. These include iaceae). These dolomite species however, may
,
Antennaria dimorpha (Asteraceae), Tonestuspeir- occur on other soil parent materials over their
sonii (Asteraceae), and Eriogonum urnbeIlaturn ranges.
var. covillei (Polygonaceae). Shrubs (phanerophytes) and subshrubs (cham-
The life form distribution of the native alpine aephytes) are few in the alpine flora ofthe White
flora of the White Mountains is strongly domi- Mountains. Just three shrub species reaching
nated by herbaceous perennials, as is typical of heights of50 cm have a range that extends above
temperate alpine habitats elsewhere. Within 3500 m: Ribes cereum (Grossulariaceae), Poten-
herbaceous perennials, the assemblage of peren- tilla fruticosa (Rosaceae), and Salix orestera
nial graminoids (mostnotablygrasses and sedges) (Salicaceae). All of these shrub species are more
form 22% of the total flora, mats and cushions typical of lower elevations. Only Ribes cereum is
form 11%, and other herbaceous perennials such common in the alpine zone, and its distribution is
as broad-leaved tussocks, rosettes, and biennials highly correlated with large granite outcrops
form 53% (Fig. 3). Combined, herbaceous peren- where thermal and hydrologic characteristics
nials thus comprise 86% ofthe flora. may be significant in providing favorable micro-
There are 18 native species of mats and sites for this species.
cushions, all low in stature and mostly relatively Seven species of low woody subshrubs are
smallin size, thatmakeup a heterogeneousgroup present, representingjust two families. These are
MADRONO
206 [Vol. 55
100
shrub subshrub mat/ herb. graminoid annual
cushion perennial perennial
Fig. 3. Life form distribution ofthe native vascular plant species in the alpine zone above 3500 m in the White
Mountains.
Artemisia rothrockii, Chrysothamnus viscidiflorus many categories, however, is too small for
subsp. viscidiflorus, Ericameria discoidea, and E. relevant statistical tests of association. Broad-
suffruticosa (Asteraceae), and Leptodactylonpun- leaved herbaceous perennials, the most common
gens, Linanthus nuttallii subsp. pubescens, and life form, have virtually the same proportional
Phlox pulvinata (Polemoniaceae). These three distribution among habitats as does the entire
Polemoniaceae are quite low in stature in their flora (Table 1). Perennial graminoids, likewise,
alpine habitats and approach becoming mats in generally match the overall pattern but with an
life form. The highest elevation reached by any of over-representation of species in moist and wet
these woody species occurred with Chrysotham- habitats and an under-representation in drier
nus viscidiflorus, which extends to near 4000 m at open habitats. Among the lesscommon lifeforms
the top of Barcroft Peak. there is a much stronger association with specific
Thirteen annual species are present, makingup habitats. Annual plant species are strongly
8% of the flora. The majority of the annual associated with fellfield habitats (77% ofspecies).
species that extend their range into the alpine Cushion plants and mats are over represented in
zone are more typical of open habitats at lower open spaces and rocky habitats, rare in moist
montane or subalpine elevations. Most of the habitats, and absent from wet habitats. Both
annuals are relatively uncommon. chamaephytes and shrubs favor open slopes and
The greatest numbers of alpine species in the moist sites.
White Mountain occur in habitats intermediate Separating species into categories of eleva-
along a moisture gradient between wet sites with tional ranges overwhich they occurdemonstrates
saturated soils and dry slopes (Fig. 4). Drainage that 51 species (31% of the flora) are alpine
courses and associated fellfield habitats with specialists in the White Mountains that are
m
seasonal moisture availability are the typical largely restricted to sites above 3500 (Fig. 5).
habitat for 67 species (41% of the flora). Open However, a few of these alpine-restricted species
slopes that become relatively dry in summer are in the White Mountains, as for example the
second in significance as thecharacteristic habitat aquatic Callitriche verna and the wet site Juncus
for 34 species (21% ofthe flora). Moist meadows hryoides, occur at lower elevations in wetter
are home to 39 species (24% ofthe flora), mostly mountain ranges. Among the alpine species are
graminoids. Only a small number of species seven high-elevation alpine specialists that occur
m
typically occur on wet sites with saturated soils only above 3960 (Morefield et al. 1988). These
(11 species), aquatic habitats (1 species), or dry species are Erigeron vagus (Asteraceae) Anelsonia
slopes (4 species). eurycarpa (Brassicaceae), Cerastium beeringianum
Plant life forms showed mixed patterns of (Caryophyllaceae), Polemonium chartaceum (Po-
correlation with alpine habitats across a moisture lemoniaceae), and three grasses; Elymusscribneri,
gradient. The number of species represented in Poa lettermanii, and P. suksdorfii.
i
1
2008] RUNDEL ET AL.: ALPINE FLORA OF THE WHITE MOUNTAINS 207
Another large group of 59 species (36% ofthe viscidiflorus subsp. viscidiflorus that occurs com-
flora) has a range extending into the alpine zone monly from 1550^000 elevation.
from subalpine forests and shrublands at eleva- It is instructive to combine the data on life
tions above 2900 m. Forty-two species (26% of form and elevational range of occurrence to
the flora) present in the alpine zone ofthe White assess if certain life forms are more likely than
Mountainscan also be found inmontane habitats others to have broad elevational ranges. Among
as low as 1980 m. Finally, there are six species in the alpine flora described here, broad-leaved
the alpine that reach to cold desert elevations as herbaceous perennials, graminoids, and cushions
low as 1220 m, as exemplified by Chrysothamnus and mats have 75%, 72% and 81%, respectively.
Table RelationshipBetween Plant Lieeformand HabitatoeCharacteristicOccurrenceeorthe
1.
Alpine Plant Speciesoethe White Mountains, California.
Cushion/ Broad-leaved Perennial Total
Shrub Chamaephyte mat herbaceous perennial graminoid Annual flora
Number ofspecies
Aquatic 0 0 0 0 0 1 1
Wet 0 0 0 7 4 0 1
Moist 2 2 2 20 11 2 39
Tallus slope 0 0 4 2 0 7
Fellfield 0 1 4 36 16 10 67
Open slope 1 3 9 18 3 0 37
Rocky site 0 0 3 1 0 0 4
Total 3 7 18 86 36 13 163
Relative values (%)
Aquatic 8 0.6
i^ Wet 8 11 7
Moist 50 29 11 23 31 15 24
Tallus slope 14 5 6 4
,
Fellfield 14 22 42 44 77 41
Open slope 50 43 50 21 8 21
Rocky site 17 1 2
Total 100 100 100 100 100 100 99.6
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70
cold desert montane subalpine alpine high alpine
(>1220 m) (>1980 m) (>2895 m) (>3500 m) (>3960 m)
m
Fig. 5. Typical habitat occurrence ofthe native vascular plant species in the alpine zone above 3500 in the
White Mountains.
oftheir species restricted to subalpine and alpine the Intermountain Ranges arecharacteristic of41
habitats (i.e., elevations above 2900 m). This is a species (25% ofthe flora).
far greater proportion than that present in Just three species are endemic to the alpine
phanerophytes, chamaephytes and annuals where zone of the White Mountains, while three other
only 50%, 38%, and 54% of species respectively species come close to being endemic. The
are limited to these higher elevations. Obligately endemics are Draba californica, D. monoensis,
alpine species in the White Mountains fall almost and PotentUla morefieldii. The high alpine Pole-
entirely into just three life forms - broad-leaved monium chartaceum occurs principally in the
herbaceous perennials (33 species), graminoid White-Inyo Range with a disjunct occurrence in
perennials (17 species), and cushions/mats (3 the Klamath Region of northern California.
species). Only one chamaephyte. Phlox conden- Recent studies have shown that thesepopulations
sata, hasthiselevational restriction, anditisquite are morphologically distinct and deserve more
mat-like in its growth habit. The two other alpine careful study (Pritchett and Patterson 1998).
specialists are the wetland annuals Callitriche Draba siibumbellata and Arabispinzlae reachjust
verna and Juncus bryoides that would be expected beyond the White Mountains into the eastern
to occur at lower elevations in the White slope ofthe Sierra Nevada in northwestern Inyo
Mountains if suitable habitats were present. County, and D. sierrae extends only slightly
These data are consistent with the generalization further into the Sierra Nevada (Price and Rollins
that upright woody plants and annuals have 1988; Rollins and Price 1988; Constance-Shull
relatively low abundance and diversity in alpine and Sawyer 2000).
habitats.
The biogeographic affinities ofthe alpine flora Introduced Flora
show strong links throughout the mountains of
the western United States. Only 26 species in the Alpine habitats are generally inhospitable for
alpine flora are widespread or transcontinental alien plant species, and the White Mountains are
species. The largest group, 55 species (34% ofthe no exception. Seven species of introduced plants
flora), has broad linkages to western cordilleran have been reported from the alpine zone: Senecio
regions including the Rocky Mountains and/or vulgaris (Asteraceae), Capsella bursa-pastoris.
Pacific Northwest (Fig. 6). Another 36 species Sisymbrium irio, S. orientale, and Descurainia
(22% ofthe flora) are linked directly to the Sierra Sophia (Brassicaceae), Stellaria media (Caryo-
Nevada/Cascade Ranges. Together then, more phyllaceae), and Chenopodium rubrum (Cheno-
than 70% of the alpine flora of the White podiaceae). The first six of these are ahen to
Mountains is shared with the Sierra Nevada. CaHfornia, while the last in this list is now
Strong biogeographic connections to the flora of questionably considered to be native. All seven
2008] RUNDEL ET AL.: ALPINE FLORA OF THE WHITE MOUNTAINS 209
70
species, however, owe their presence in the alpine in carbohydrate storage over the winter months
zone of the White Mountains to unintentional (Mooney and Billings 1960; Billings 1974).
human introduction. None ofthese species is well The herbaceous perennials include species with
established, with only Capsella bursa-pastoris a variety of ecological forms and life history
reported in multiple small colonies along the strategies of carbon allocation to belowground,
roadside. Six of these species are annuals aboveground vegetative, and reproductive tissues
attempting to survive near theirupper elevational (Rundel et al. 2005). Within this broadly defined
limits. The one exception is Chenopodium rubrum, category are perennial graminoids, broad-leaved
which although an annual at lower elevations, tussocks, mats and cushions, rosettes, and
takes on a biennial growth form in the alpine biennials (Raunkiaer 1934). Many of these are
zone ofthe White Mountains (Spira and Wagner relatively long-lived plants surviving for decades
1988). (Billings 1974; Pollak 1991), while others are
biennials living for only two years. Perennial
Discussion graminoids commonly dominate plant communi-
ties ofwet meadows that dry earlier than fellfield
Floristic Richness and Life Forms communities. Incontrast, fellfield habitatsexhibit
a mixed dominance ofmats and cushions, broad-
The total flora of the White Mountains leaved tussocks, perennial graminoids, and ro-
includes 988 species (Morefield 1992), and thus sette plants (Rundel et al. 2005).
the alpine flora as defined here thus includes 16% The perennial graminoids themselves include a
ofthis flora. diverse set ofecological strategies. Whereas these
Although conditions of the total and seasonal species comprise a large portion of the species
distribution ofrains differ in alpine habitats from and heavily dominate the cover ofwet areas with
the Sierra Nevada eastward across the Great saturated soils and moist meadows, they also
Basin to the Rocky Mountains, the relative include a number of more drought-adapted
dominance of a few life forms does not change fellfield species as well. The fellfield grass
dramatically across this gradient (Billings 1978, Muhlenbergia richardsonis, a species with C4
2000). Herbaceous perennials represent the dom- metabolism, reaches a remarkable elevation of
inant life form in all ofthese alpine regions. This nearly 4000 m at the summit of Mount Barcroft
Hfeformin alpine regionshas thecharacteristic of (Sage and Sage 2002). This is likely the highest
maintaining large proportions of total biomass elevation reached by any C4 species in the United
belowground where they play an important role States or Canada.
MADRONO
210 [Vol. 55
Longer-lived species commonly allocate less to vascular plant species (Scott 1995). Although a
reproductive tissues than shorter-lived species. specific enumeration of the alpine flora of the
This can be illustrated by the alpine gentians of Sierra Nevada has not been made, it has been
the White Mountains, forexample, where relative estimated to be about 600 species (Chabot and
allocation to reproduction in the broad-leaved Billings 1972).
tussock Gentiana newberryi is significantly lower Alpine floras of smaller ranges across the
than in the biennial Gentianella tenella and Great Basin vary in size depending on not only
Gentianaprostrata (Spira and Pollak 1986). Such the area ofhabitat present, but also the degree of
biennial growth forms, however, are relatively isolation ofthe mountain range. In general, these
uncommon in the alpine flora White Moun- small ranges with relatively low rainfall have
tains where harsh growing conditions select smaller alpine floras than comparable areas of
against plants with short life spans. Beyond alpine habitat in either ofthe larger and less xeric
these two gentians, the other six species of Sierra Nevada or Rocky Mountains. Ranges
biennials are all members of the Brassicaceae. lying closer to the Rocky Mountains generally
These are Arabis divaricarpa, A. holboelii var. show strong florisitic linkages to this range, while
peduncuocarpa, A. inyoensis, Descurainia incana, those lying on the western margins of the
Draba albertina, and Halimolobus virgata (More- Intermountain Region have floras more strongly
field et al. 1988). linked to the Sierra Nevada. Loope (1969)
Annual plants, for the same reasons of short reported 189 alpine species from the Ruby
and severe growing conditions, are generally rare Mountains in northeastern Nevada, with this
in the typical circumboreal arctic-alpine floras of flora showing a strong affinity to alpine floras of
the Northern Hemisphere, comprising only 1-2% the Rocky Mountains. The isolated San Fran-
of the flora (Billings 2000). Although not cisco Mountain in Arizona with only 5.2 km^ of
abundant, annuals, nevertheless, are relatively alpine habitat has 80 species and likewise shows
more common in the summer dry alpine of the strong floristic relationships to the Rocky Moun-
Sierra Nevada and White Mountains where they tains despite its separation (Schaak 1983). In
comprise about 8% of the floras (Jackson and contrast, the Sweetwater Mountains lying 33 km
Bliss 1982; Jackson 1985; Spira 1987; Spira and west ofthe Sierra Nevada supports a flora of 173
Wagner 1988). Annual plants are largely restrict- species in 16 km^ of alpine habitat, with 94% of
ed to specific habitats in the alpine zone of the this flora common to the Sierra Nevada (Bell
White Mountains. Sandy drainage channels are Hunter and Johnson 1983). The small alpinezone
the habitat for such annuals as Cryptantha on Mt. Grant to the north of the Sweetwater
glomeriflora (Boraginaceae), Gayophytum race- Mountains in western Nevada is just 2.6 km^ in
mosum (Onagraceae), Gymnosteris parvula (Po- area supports a flora of70 species dominated by
lemoniaceae), and Mimulus suksdorfii (Scrophu- Sierra Nevadan elements (Bell and Johnson
lariaceae) (Morefield 1988; Spira 1991). Such 1980).
microsites provide relatively high growing tem- Comparing checklists at the species level (i.e.,
peratures and available water early in the ignoring subspecific taxa), the alpine flora ofthe
growing season, a time critical for annual plants White Mountains exhibits a much stronger
to complete their life cycle. biogeographic relationship to the Sierra Nevada
Subshrubs and shrubs are less rich in species in than to the central Rocky Mountains. Thus, 87%
the White Mountains alpine than typical circum- of the species in the alpine flora of the White
boreal arctic-alpine floras. Their unusually low Mountains are also found in the Sierra Nevada
diversity in the alpine flora of the White (Hickman 1993) compared with only 58% that
Mountains reflects perhaps the relatively dry occur in the ranges of the central Rocky
conditions and low nutrient availability in this Mountains (Scott 1995). These values are signif-
area. There has been little study to date of these icantly higher for both ranges than earlier
species in the White Mountains. estimates made on incomplete data (Lloyd and
Mitchell 1973). The alpine flora of the White
Biogeographic Patterns ofSpecies Richness Mountains, like the Sierra Nevada, lacks many of
the typical circumboreal alpine species commonly
A number ofchecklists ofregional alpinefloras present in other alpine regions ofNorth America
exist for the western United States, and these can (Billings 2000).
aid in examining patterns of biogeographic
relationships. It is interestingto compare patterns Acknowledgments
of species richness among these alpine areas, We greatly acknowledge the financial and logistical
adilftfheoruignhg smoamnencearustioinnishnoecwessaalrpyinbeecazuosneesofatrhee sRuepspeoarrtchoffSetrateidont.o tIhins ppraorjteicctulbary twhee WthhiatnekMCoautnhteariinnse
defined. Alpine regions of the central Rocky Kleier, Frank Powell, Dave Trydahl, and Mike
Mountains that extend over an extensive area of Morrison for the assistance with various parts of this
hundreds of square kilometers include 609 research. Two anonymous reviewers provided invalu-
2008] RUNDEL ET AL.: ALPINE FLORA OF THE WHITE MOUNTAINS 211
able data in their comments on an earlier draft ofthis Lloyd, R. M. and R. S. Mitchell. 1973. A flora of
manuscript. the White Mountains of California. University of
California Press, Berkeley, CA.
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