Vegetation pattern formation and community assembly under drying climate trends.

Drying trends driven by climate change and the water stress they entail threaten ecosystem functioning and the services they provide to humans. To get a better understanding of an ecosystem response to drying trends, we study a mathematical model of plant communities that compete for water and light. We focus on two major responses to water stress: community shifts to stress-tolerant species and spatial self-organization in periodic vegetation patterns. We calculate community bifurcation diagrams of spatially uniform and spatially periodic communities and find that while a spatially uniform community shifts from fast-growing to stress-tolerant species as precipitation decreases, a shift back to fast-growing species occurs when a Turing bifurcation is traversed and patterns form. We further find that the inherent spatial plasticity of vegetation patterns, in terms of patch thinning along any periodic solution branch and patch dilution in transitions to longer-wavelength patterns, buffers further changes in the community composition, despite the drying trend, and yet increases the resilience to droughts. Response trajectories superimposed on community Busse balloons highlight the roles of the initial pattern wavelength and of the rate of the drying trend in shaping the buffering community dynamics. The significance of these results for dryland pastures and crop production is discussed.