Download Climate Change impacts on big sagebrush populations

Draft 10/26/2016
Authors: Adler, Renwick, Curtis, Kleinhesselink, Schlaepfer, Kachergis, Manning, Remington, Thacker,
Aldridge, Bradley, Poulter
Climate Change impacts on big sagebrush populations
Introduction
Sagebrush covers 120 million acres across 14 western states and 3 Canadian provinces, providing habitat for
357 species of conservation concern in the Great Basin alone. Greater and Gunnison sage-grouse, pygmy
rabbits, and sage-thrashers are sagebrush obligates, while many others such as mule deer and pronghorn depend
heavily on sagebrush habitats. Sagebrush rangelands have been used for livestock grazing, oil and gas
development, mineral extraction, and recreation. About _% of the original distribution of sagebrush has been
lost due to conversion to agricultural production or development, or degraded by invasive annuals plants,
altered fire regimes, and other anthropogenic disturbances. Populations of many sagebrush-dependent species
are declining, triggering petitions to list both species of sage-grouse and pygmy rabbits under the Endangered
Species Act, while Gunnison sage-grouse were listed as threatened under the act in 2012. Many sagebrush
obligate species are identified as species of conservation concern in State Wildlife Action Plans. Consequently,
the emphasis of research and management has shifted from sagebrush eradication to restoration and
conservation across the west.
Climate change casts considerable uncertainty over sagebrush conservation and restoration efforts. Given
predicted changes, will sagebrush decline, persist, or even thrive? Where are management efforts likely to
achieve benefits over the long-term? Using “best available science” is a key principle of national efforts to
prepare for the impacts of climate change, including policy specific to land management agencies (e.g.,
Executive Order 13653, DOI Climate Adaptation Plan, USFS National Roadmap for Responding to Climate
Change). Research to predict sagebrush responses to changing climate could resolve some of this uncertainty
by identifying areas where climate change poses the greatest threat to sagebrush and the many species and
ecosystem services that depend on it. This kind of climate change vulnerability analysis can also help decision
makers prioritize areas for restoration, conservation, and mitigation, and ensure efficient budget allocations.
3.
Rationale for model comparison
a.
Lots of models, validation difficult, look for a agreement’
b.
Different models captures different types of responses
c.
Consistency in predictions would build confidence
4.
Research question: How will big sagebrush populations respond to changes in temperature and
precipitation within its current range?
5.
Methods (link to online table)
a.
Scope: Big sagebrush, individual locations across the region, time scales
b.
c.
Characterize GCM projections: warming, little change in precip?
Four models:
i. Spatial, regional correlations (predicts long-term average cover)
ii. Local, temporal correlations (predicts short-term change in cover)
iii. Regeneration processes (predicts probability of establishment)
iv. Biogeographical and biogeochemical processes (cover)
Results
Despite considerable variation in predicted changes among models and climate projections, consistent patterns
in the predictions did emerge. All four models predict that sagebrush will respond positively to climate change
at the coldest locations in the region but will respond negatively at the warmest sites (Fig 1). Furthermore, these
negative responses appear confined to fairly small geographic areas, primarily hot sites near the ecotone with
hot deserts to the south, and sites receiving very little summer precipitation east of the Sierra Nevada. Across
much of the range of sagebrush, our models consistently project weak or positive responses to climate change.
We also found evidence that vulnerability to climate change, as predicted by our models, correlates with the
resistance and resilience classes that represent threats from annual invasive plants and fire. Almost all of our
sites where models consistently predicted negative climate change impacts, and most sites where sagebrush
response was uncertain, are located within the low resistance and resilience class. Our models predict that the
overwhelming majority of sites in the moderate and high resistance and resilience classes will respond
positively to climate change.
Implications
The most important implication of our results is that concerns about climate change impacts should not preclude
investments in sagebrush conservation and restoration. Across much of the current distribution of big
sagebrush, the changes in precipitation and temperature projected by current climate models are likely to have
weak or even positive impacts on sagebrush populations. Within these areas, land management should continue
to focus on other threats to sagebrush habitat, some of which could be exacerbated by warming climates.
In the hotter areas where our models predict negative impacts of climate change on sagebrush, some of which
have low resistance and resilience to invasions and fire, management should focus on protecting sites with
cooler and wetter microclimates where sagebrush is likely to persist. Efforts to promote sagebrush seedling
establishment and stand resiliency to disturbances may become increasingly difficult under climate change.
These recommendations come with important caveats. First, our study only evaluated climate change impacts
on sagebrush within its current range; it cannot address expansion of sagebrush into new areas. Second, our
study focused on a single species and did not consider impacts on composition or abundance (cover) of
sagebrush understory components such as grass and forbs, which are critical components of habitat suitability
for sagebrush dependent species. Given their different life history strategies, grasses and forbs may respond
very differently than sagebrush. Finally, and most importantly, we did not evaluate impacts of climate change
on cheatgrass distribution and abundance or the probability of fire within sagebrush communities. Increases in
either could offset or overwhelm the generally positive effects of climate change on sagebrush cover that our
models predict. While some work has modeled potential future distribution of cheatgrass, an important next step
is to evaluate the influence of climate change on the invasive grass-fire cycle.
For a more complete understanding of this work you are welcome to tune into the webinar, hosted by the Great
Basin LCC:
Predicting climate change impacts on big
sagebrush populations: Diverse models project
similar response to rising temperatures
Friday, November 4
11:00 AM (PST)
To register, click on the link below:
http://us5.campaign-archive2.com/?u=2bd190572e12f69862b0ed30b&id=23c41a72a8&e=d5759766f2