December 2012 Number 1 - Utah Native Plant Society

Calochortiana December 2012 Number 1
in this model is comprised of bedded carbonates overlain
by more erosion-resistant quartzite, a typical landscape
throughout much of eastern Nevada. In other parts
of the Great Basin, the ranges may be comprised of volcanic
rocks or, locally, intrusive granitic rocks.
The valley currently provides suitable habitat for
endemic plants that are typically restricted to specialized
edaphic conditions, such as playa edges, the periphery
of sand dunes, or specific microhabitats within older
lake sediments. Montane endemics are restricted to carbonate
or siliceous rock types or, in some cases, are
more restricted to habitats characterized by coarse materials
weathered from various substrates, such as gravels,
angular slates, talus, or scree. At the highest elevations
are the mountaintop endemics in subalpine-alpine habitats
or, in the lower mountain ranges, on ridge tops
within lower vegetation zones (Figure 3b).
As climate changes, populations of those endemic
plants with the most restrictive and least common habitat
constraints are likely to shrink in areal extent and
become more isolated from one another. This is most
likely to happen in the valleys, where many of the rarest
endemics occur. But all plants restricted to highly specialized
habitats, such as mountain tops or carbonate
substrates, are vulnerable when physiological limits are
exceeded as their bioclimatic envelope shifts to unsuitable
habitats. Less specialized endemics may be less
susceptible to habitat shifts but are still likely to decrease
in extent since less area is available at higher elevation
(Figure 3c). The eventual outcome of this scenario
is likely to be extirpation of populations and eventual
species extinctions throughout the landscape, with
the highest rates likely in the valleys where the greatest
edaphic specializations occur (Figure 3d). As noted
3a.
3b.
3c. 3d.
Figure 3. Conceptual model of the effects of climate change on endemic plants in the Great Basin. a) Generalized
landscape typical of the Great Basin in eastern Nevada showing a playa lake, sand dunes, and Pliocene-Pleistocene
lake sediments on the valley floor, overlain by alluvial, and a fault-block mountain range comprised of a band of
carbonate sediments overlain by erosion resistant quartzite that forms the ridge; b) the current landscape occupied
by endemic plant populations restricted to playa edges, sand dunes, carbonate rocks, montane plants that occur on
both carbonates and quartzite, and higher elevation plants; c) as climate change progresses, populations of plants
restricted to specialized habitats contract in place, while those less specialized migrate upward or onto more suitable
aspects as their bioclimatic envelope shifts; d) eventually, populations of plants on highly specialized habitats
are extirpated and the taxa go extinct while other species continue to migrate upward where less habitat area is
available.
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