December 2012 Number 1 - Utah Native Plant Society

Utah Native Plant Society
Shehbaz and Windham 2007; Tiehm and Holmgren
1991), Boechera ophira (Morefield 2003) and Potentilla
cottamii (Holmgren 1987). Penstemon rhizomatosus is
reported only from carbonate substrates (Holmgren
1998) while Cymopterus goodrichii is known from slate
and limestone sedimentary rocks (Welsh and Neese
1980). Ipomopsis congesta var. nevadensis may also
occur on carbonate substrates but no systematic surveys
have been completed (Morefield 2001). Eriogonum
holmgrenii is reported from quartzitic, carbonate, and
granitic substrates (Goodrich 1979; Reveal 1965), while
Polemonium chartaceum occurs on rhyolite in the
Sweetwater Range of California (Hunter and Johnson
1983), on open slopes of metavolcanics and nonbasic
rocks at the summit of White Mountain Peak in the
White Mountains of California (Crowder and Sheridan
1972; Morefield 1992; Rundel et al. 2008; Van de Ven
et al. 2007), and on granitic rocks in the Boundary Peak
area of the White Mountains in California and Nevada
(Kartesz 1987; Pritchett and Paterson 1998). Similar to
their montane counterparts, these taxa are typically
found on poorly developed soils derived directly from
weathered bedrock or in association with scree, talus, or
bedrock ledges, cliffs, and crevices. These substrates
and habitats are common regionally and locally and the
presumed rarity of these taxa is most likely determined
by other ecological or historical factors. The sole exception
to this among the high elevation species is Primula
capillaris, which occurs on moist meadow soils derived
from glacial till (Holland 1995; Holmgren and Holmgren
1974).
Vulnerability to Climate Change
The vulnerability of any plant species or population
to climate change is influenced by many factors in addition
to climate and substrate, including physiological
tolerances, life-history strategies, phenological plasticity,
relative probabilities of extinctions and colonizations,
dispersal abilities, and disruptions in plantpollinator
or herbivorous insect-host plant interactions
(Parmesan 2006). Unfortunately, few data exist on most
of these factors for any plants, including the 33 plants
examined herein. This analysis, therefore, provides preliminary
predictions that will be tested as climate
change progresses over the coming decades.
Previous studies have concluded that with progressive
climate change we can expect ongoing upward
shifts in both forest and alpine plant species and subsequent
declines in arctic-alpine plants at the southern
margin of their range (Lenoir et al. 2008; Lesica and
McCune 2004; Walther et al. 2005). The results reported
here suggest that losses of endemic plants in the
Great Basin may be highest within the lower elevation
sagebrush and salt desert zones. This is consistent with
similar results reported from Utah where the highest
levels of plant endemism were found between 1000 m
and 2000 m (Ramsey and Shultz 2004). Meyer (1978)
also found that the percentage of edaphically restricted
species in the Mojave-Intermountain transition zone
dropped sharply with an increase in altitude. This may
be because xeric environments tend to be more heterogeneous
than mesic habitats in response to variables
other than moisture and heterogeneous environments
tend to restrict the migration of specialized plant species,
thus reinforcing endemism.
Previously published studies of climate change in the
Great Basin have largely focused on the montane biogeography
of birds and mammals (e.g., Beever 2003;
Brown 1971, 1978; Lawlor 1998), phytogeography
(Billings 1978; Harper et al. 1978) or dominant tree and
shrub distributions (Wells 1983; West et al. 1978). Most
often these studies have applied colonization-extinction
models (sensu MacArthur and Wilson 1967) to mountain
ranges as “sky islands” within an homogenous
“sagebrush sea” rather than actual landscape patterns of
local plant endemism. While such imagery has popular
appeal, it can mask the reality that low elevation ”sea”
contains many distinctive ecological islands supporting
edaphic plant endemics, contributing significantly to the
overall biodiversity of the Great Basin.
This is not simply a matter of scale because ecological
islands in the valleys are more-or-less equivalent
counterparts in both area and isolation to subalpine and
alpine habitats on ridges and peaks. The principal difference
with respect to vulnerability to climate change is
that montane and higher elevation habitats possess a
nearly continuous array of microclimates produced by
variations in slope and aspect across a wide range of
elevation. In contrast, valley habitats have much less
variation in either slope or aspect within a much narrower
elevation range. Thus, lower elevation plant endemics
are likely to have fewer ecological options as
their bioclimatic envelope shifts. This greater vulnerability
to climate change is compounded by the fact that
valley habitats are also more susceptible to invasion by
non-native plants and habitat modification or destruction
by human activities (e.g. transportation or energy
corridors and off-road recreation).
Conceptual Model
Based on the foregoing analysis, I am proposing a
conceptual model for assessing the potential effects of
climate change on rare plants in the Great Basin of Nevada;
this model also may have general application
throughout areas of the west with similar “basin-andrange”
topography (Figure 3a). The model begins with a
generic Great Basin landscape of playas, sand dunes,
and terraces comprised of older lake sediments on valley
fill. At the base of the bounding range, the valley fill
is overlain by alluvial fan deposits. The bounding range
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