Drought and disturbance in Chihuahuan Desert shrublands: synergistic effects on productivity and diversity

Sam Jordan

Intense droughts and human disturbances occur in many terrestrial ecosystems, but their direct and interactive effects on individuals, communities, and ecosystems remain largely unknown. Research in both disturbance and climate change ecology has a rich history, but there is a paucity of studies that combine both drivers. Using experimental manipulations to isolate the effects of drought, disturbance, and their interaction, we conducted a factorial field experiment in a Chihuahuan Desert shrubland to answer our guiding questions: What are the aboveground ecosystem productivity and diversity responses to drought and disturbance? Do these drivers interact synergistically or antagonistically? Using non-destructive methods, we recorded aboveground net primary productivity and species identity for all species within our experimental manipulations. We utilized both parametric and non-parametric statistical frameworks to fit experimental outcomes within our research question.

Drought and disturbance together reduced aboveground productivity, but these effects varied across plant functional types. Drought caused the largest reduction in species richness, but these effects are tightly coupled with below average precipitation during the 2020 water year. Our experimental disturbance treatment reduced ecosystem productivity in both ambient and experimentally reduced precipitation regimes. There was a negative synergism between disturbance and drought conditions, with the interaction of these drivers most evident in perennial grass productivity. Drought alone consistently reduced productivity of two of the three major plant functional types in these systems: grasses and forbs. In contrast, the third main functional type in our experiment, shrubs, had their productivity increased by disturbance. Our results suggest there is potential for negative synergisms between drought and disturbance in dryland ecosystems, and that these synergisms may be linked to the relative abundance of plant functional types within a site.