December 2012 Number 1 - Utah Native Plant Society

Calochortiana December 2012 Number 1
Assessing Vulnerability to Climate Change Among the
Rarest Plants of Nevada’s Great Basin
Steve Caicco,
Conservation Planner, Planning Branch, National Wildlife Refuge System,
Portland, OR
,
Abstract. The Great Basin of Nevada provides habitat for many narrowly distributed endemic plant species. To assess
the vulnerability of 33 of the rarest of these plants to climate change, I used the elevation range of all reported
locations as a surrogate measure of their bioclimatic envelopes. The results show that 14 of these taxa occur on or
near the valley floors, nine taxa occur in montane habitats, and 10 taxa occur at high elevations. While the majority of
the 33 taxa are restricted to highly specialized edaphic habitats, valley endemics are distributed through a smaller elevation
span than montane or high elevation endemics. In addition, valley habitats have less variability in slope and
aspect and their highly specialized habitats do not occur above the valley floor. These habitat restrictions are likely to
constrain migration in response to climate change. Montane and high elevation habitats are more diverse topographically
and, although often specialized, are more common both locally and regionally. This imposes fewer constraints
on natural migration and offers more conservation options in the face of climate change. Our inability to accurately
predict the actual parameters of climate change and its effects at a scale relevant to rare species will require a comprehensive
inventory and monitoring effort to identify those species affected by climate change. An integrated long-term
seed storage program will ensure adequate representation for genetic conservation.
Pollen, woodrat midden, tree-ring, and lake level
data spanning the past 50,000 years has demonstrated
that the Great Basin is highly sensitive to climatic
change (Wharton et al. 1990). During the 20 th Century,
an average annual warming of 0.3 to 0.6 °C occurred
and projections for the next century are for an additional
rise of 2 to 5 °C (Cubashi et al. 2001; Wagner 2003).
Alterations to the precipitation regimes are harder to
predict, but seem likely to include a greater proportion
falling as rain, decreasing winter snowpack, and earlier
arrival of spring conditions, thereby affecting runoff and
plant phenology (Mote et al. 2005; Snyder and Sloan
2005).
The basin-and-range topography that characterizes
the Great Basin of Nevada has generated much interest
among biogeographers and numerous seminal works
have been published focused on the distribution and relationship
of its vascular flora or specific aspects of
plant endemism in this region (Billings 1978; Charlet
1996; Harper and Reveal 1978; Holmgren 1972a; Pavlik
1989; Reveal 1979; Shreve 1942; Wells 1983). A published
proceedings of a symposium on intermountain
geography includes numerous papers on many aspects
of biogeography in the Great Basin (Harper and Reveal
1978). Several sources of information are available on
the rare plants of Nevada (Morefield 2001; Mozingo
and Williams 1980) or parts of Nevada (Anderson et al.
1991; Spahr et al. 1991; Weixelman and Atwood undated).
A conservation blueprint for the Great Basin has
been prepared that includes general discussions of the
ecological systems represented and their associated species
conservation targets and identifies a portfolio of 20
priority landscape scale conservation sites; climate
change and adaptation options are also discussed but no
explicit assessment of species vulnerability was conducted
(Nachlinger et al. 2001).
Narrowly endemic plants are expected to be at far
greater risk of extinction from climate change than are
more widespread plants because of their limited range,
small populations, and genetic isolation (Committee on
Environment and Natural Resources 2008; Peters and
Darling 1985). Alpine plants are often identified as at
particular risk due to isolation and lack of an “escape
route” (Grabherr et al. 1995; Halloy and Mark 2003).
Among the observed and predicted effects of climate
change on plant species are phenological changes, trophic
level disruptions, range shifts and contractions, and
extinctions (Parmesan 2006). Documented effects include
an accelerated trend in upward shift of alpine
plants in the Swiss Alps over the last few decades
(Walther et al. 2005), a significant upward shift in optimum
elevation of forest plants in Europe in the 20 th century
(Lenoir et al. 2008), a decline of arctic-alpine plants
from 1989-2002 in Glacier National Park (Lesica and
McCune 2004), and an advance in the mean flowering
dates of lilac and honeysuckle in the western United
States of 2 and 3.8 days per decade, respectively (Cayan
et al. 2001).
Extinction is predicted for 3–21 percent of the flora
in Europe, 38–45 percent in the Cerrado of Brazil, 32–
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