Plants in the American Southwest will experience greater water limitations with climate change due to warming temperatures and altered precipitation patterns. Such changes in hydrological regimes may have large impacts on plants living at or near their water stress thresholds. Differential drought sensitivities among dominant species or plant functional types may alter their distribution and abundance, affecting the structure and function of this sensitive dryland ecosystem. Here we present results from three ongoing precipitation manipulation experiments that examine the impacts of altered hydrological regimes on plant communities in the Colorado Plateau. These experiments focus on plant responses from the leaf to the ecosystem level to three types of precipitation changes: chronic moderate drought, short-term extreme drought and shifts in precipitation seasonality.
Results/Conclusions
Across these various rainfall manipulation studies we focus on three main results. First, grasses were much more sensitive to drought than shrubs; however photosynthetic pathway was as poor predictor of drought tolerance. Second, short-term extreme drought had greater impacts on plants than long-term moderate drought. Third, precipitation regimes dominated by either spring or monsoon precipitation resulted in lower water stress and better plant performance than one with an intermediate precipitation regime. Overall, these results suggest that individual plant responses to drought and altered intraannual precipitation patterns may lead to potentially large ecological effects if such changes in hydrological regimes push species beyond critical physiological and mortality thresholds in this dryland ecosystem.