Divergent climate change effects on widespread dryland plant communities driven by climatic and ecohydrological gradients

Plant community response to climate change will be influenced by
individual plant responses that emerge from competition for limiting
resources that fluctuate through time and vary across space. Projecting
these responses requires an approach that integrates environmental
conditions and species interactions that result from future climatic
variability. Dryland plant communities are being substantially affected by
climate change because their structure and function are closely tied to
precipitation and temperature, yet impacts vary substantially due to
environmental heterogeneity, especially in topographically complex
regions. Here, we quantified the effects of climate change on big
sagebrush (Artemisia tridentata Nutt.) plant communities that span 76
million ha in the western United States. We used an individual-based plant
simulation model that represents intra- and inter-specific competition for
water availability, which is represented by a process-based soil water
balance model. For dominant plant functional types, we quantified changes
in biomass and characterized agreement among 52 future climate scenarios.
We then used a multivariate matching algorithm to generate fine-scale
interpolated surfaces of functional type biomass for our study area.
Results suggest geographically divergent responses of big sagebrush to
climate change (changes in biomass of -20% to +27%), declines in perennial
C3 grass and perennial forb biomass in most sites, and widespread,
consistent, and sometimes large increases in perennial C4 grasses. The
largest declines in big sagebrush, perennial C3 grass and perennial forb
biomass were simulated in warm, dry sites. In contrast, we simulated no
change or increases in functional type biomass in cold, moist sites. There
was high agreement among climate scenarios on climate change impacts to
functional type biomass, except for big sagebrush. Collectively, these
results suggest divergent responses to warming in moisture-limited vs.
temperature-limited sites and potential shifts in the relative importance
of some of the dominant functional types that result from competition for
limiting resources.