Climate variability and change acting at broad scales can lead to divergent changes in ecosystem condition at more local scales. To improve our understanding of heterogeneity in ecosystem response to climate, we compared how vegetation greenness (a proxy for net primary production) responded to changes in water availability across deserts and plant communities in the southwestern U.S. We developed a novel “climate pivot point” approach to identify plant community responses and drought resistances using Landsat satellite imagery (30-m resolution) across the entire Southwest.
Cool-season water availability drove production in the Great Basin (r2=0.56), Sonoran (r2=0.71), and Mojave Deserts (r2=0.53), warm-season water availability in the Chihuahuan Desert (r2=0.65), and a mix of cool- (r2=0.35) and warm-season (r2=0.41) water availability in the Colorado Plateau. Communities dominated by grasses and deciduous trees had large responses to increases in water availability and low resistances to water deficit, while shrublands and evergreen woodlands had variable responses and high drought resistances. Plant communities that spanned multiple deserts had different responses and resistances to seasonal water availability in each desert. For example, creosote bush shrublands were more responsive to warm-season water availability and less drought resistant in the Chihauahuan compared to the Sonoran and Mojave Deserts. Response of a community within a desert also showed variation, as grasslands were increasingly responsive to warm-season water availability in southern reaches of the Colorado Plateau. Our results reveal that production was suppressed by low temperatures in the cold Great Basin and Colorado Plateau but not in warm deserts. These divergent sensitivities to seasonal water availability among deserts and communities have large implications for carbon storage, wildlife habitat, and the future vulnerability of ecosystems in the southwestern U.S.