Globally, dryland plant communities are projected to be especially affected by climate change because their structure and function are closely tied to precipitation and temperature. However, the outcome of changing climate will not be uniform and will depend on spatially-structured environmental conditions. Rising temperatures are projected to increase the fraction of precipitation lost to evaporation, resulting in reduced soil water availability with especially detrimental effects in locations that are already dry. In contrast, at higher elevations and latitudes that are cooler and wetter, warmer temperatures may extend the growing season without decreasing the suitability of conditions, as long as soil moisture is adequate. To explore the context-dependent effects of climate change on dryland plant communities, we utilized an individual-based plant simulation model to quantify changes in 91 big sagebrush (Artemisia tridentata) plant communities throughout the western US. Our modeling approach incorporates a process-based representation of soil water availability and simulates intra- and inter-specific competition for shifting limiting resources. We ran simulations for current conditions and 52 future climate scenarios to quantify uncertainty. We characterized changes in functional type biomass and composition for big sagebrush, perennial grasses, and perennial forbs along existing climatic gradients and for different geographic regions.
Results/Conclusions
On average, our simulations suggest declines in big sagebrush biomass (mid-century: -7%, end-of-century: -34%) and small increases in perennial grass and forb biomass by end-of-century (+16%, +10%). The largest declines in big sagebrush biomass were in low elevation, warm, dry sites that currently support the highest big sagebrush biomass. These sites were mostly located in the Great Basin. In contrast, we simulated small declines to moderate increases in big sagebrush biomass in cool, wet sites found at the highest elevations. The largest increases in perennial forb biomass were also simulated on currently cool and wet sites. Simulated perennial C3 and C4 grass biomass increased most on sites that are currently warm and dry and characterized by low perennial C3 and higher C4 grass biomass. For most sites, there was strong agreement among climate scenarios on declines in big sagebrush biomass. Agreement was slightly weaker for perennial grasses and for forbs in particular. Despite slight to moderate declines in big sagebrush, simulations suggest that few sites will experience dramatic shifts in plant functional type composition. Collectively, these results suggest divergent responses to climate change depending on underlying environmental conditions, but relative stability for big sagebrush plant communities in the future.