Elevated temperatures, pronounced drought, and associated reductions in water availability have emerged as predominant characteristics of climate in the western U.S. in the 21st century and are likely to intensify according to IPCC projections. The increased occurrence of drought has triggered widespread decline and mortality of vegetation, but these changes have not been uniform across dryland regions or plant communities, and the temporal scale at which water availability and plant productivity is coupled is not well understood. To effectively manage dryland ecosystems in the future, it is essential to understand how plant communities respond to climate, soil water balance, and periods of water deficit. Our study assessed the vulnerability of different plant communities to shifts in water availability across five dryland regions: the Mojave, Sonoran, Chihuahuan, Colorado Plateau, and Great Basin Deserts. We related changes in water availability at multiple temporal scales to plant productivity detected using remote sensing.
Our results highlight differences in the vulnerability of plant communities to water deficit and demonstrate divergence in the climate and soil water balance windows of time that affect plant productivity across dryland regions. For example, the broadly-distributed shrub Coleogyne ramosissima, was relatively unresponsive to short- and long-term water deficit, whereas grasses and shallow-rooted subshrubs were sensitive to even short-term water deficits. Productivity increased when dry periods were interrupted by wetting events, but the capacity for this increase was reduced under extended dry periods across plant communities. In contrast, the effect of wetting events on productivity saturated during extended wet periods, and the degree of this saturation was dependent on the plant community. Our results help define the temporal scales at which drought effects plant productivity, demonstrates heterogeneity in the vulnerability of vegetation types to water shortages, and can be used to help managers more readily detect changes in vegetation and take appropriate actions.