Grassland plant communities have differential response and recovery to an extreme drought across a precipitation gradient

Background/Question/Methods

Extreme drought has the potential to dramatically impact grassland plant communities by shifting plant community structure. While shifts in community structure have been documented during drought, it is unclear whether these changes persist after drought ends. Our study aims to characterize the timing and magnitude of change in grassland plant composition during extreme drought, and to understand how drought responses correspond with recovery dynamics post-drought. We studied four grasslands in the Great Plains that range across a gradient in mean annual precipitation (MAP) from 375 mm to 892 mm and represent the major grassland types of the region. We experimentally imposed extreme drought over four growing seasons and then continued to monitor the sites an additional four years under ambient conditions to assess recovery. Each growing season we estimated the percent cover of every species in the control and drought treatment plots, and used multivariate techniques to assess the impact of the drought treatment on plant composition over time.

Results/Conclusions

We found that the number of years for plant composition to respond to drought conditions varied at the different grassland sites, with the driest site experiencing shifts in composition sooner in the drought than the wettest site. The magnitude of compositional change also varied and was most pronounced at the driest site. Compositional changes at all sites were largely driven by shifts in the abundance of C3-C4 grasses. After four years of ambient conditions, species composition has not fully recovered in each grassland. These findings suggest grasslands may differ in how they respond and recover from extreme drought. This study also shows that there are long-term effects of extreme drought on plant communities in grasslands.