COS 7-4 - CANCELLED - Ghosts from the past: How frequency of past drought affect plant community response to an extreme drought event?

Abstract: Drought, one of the pressing environmental issues predicted with climate change, can cause lasting abiotic and biotic changes in an ecosystem. However, the effect of drought legacies on plant communities remains poorly understood. We assessed how drought legacies affect the aboveground biomass and community composition of tallgrass prairie when subjected to new droughts. The study was conducted from 2018-22 as a part of the Climate Extreme Experiment (CEE) established in 2010 in Konza Prairie Biological Station, Kansas. From 2018-21, intact plant communities were subjected to extreme year-long drought. However, due to their varied in growing season drought legacies, there were four treatments: 1) first drought (C-C-D), 2) second consecutive drought (C-D-D), 3) second drought with a period of recovery (D-C-D), 4) third consecutive drought (D-D-D). The communities were then allowed to recover in 2022. We hypothesized that more frequent drought events would result in a greater change in plant communities. We collected aboveground biomass, analyzed community composition, resistance (ability to withstand drought), resilience (ability to recover from drought), and community change metrics (change in richness, evenness, rank, species gains and losses) for all four extreme drought years and one year post-drought.

Drought legacies had a significant effect on the aboveground biomass (p= < 0.001), such that plant communities with second consecutive drought (C-D-D) had the highest above-ground biomass. Being a grass-dominated system, the effect of drought legacies on aboveground biomass was driven by grasses (p= < 0.001) rather than forbs and woody plants. Additionally, drought legacy treatments had no significant effect on the resistance (calculated as ratio of drought years to pre-drought year) of plant communities to the final drought event. However, there was a year-to-year variation in resistance and it decreased with decreasing annual precipitation (p=0.0011). Similarly, we calculated resilience as the ratio of post-drought to pre-drought aboveground biomass. We found that all plant communities were resilient to drought, and resilience did not differ among drought legacy treatments. We also found that there were no changes in species richness, evenness and species rank but more species were lost (p= < 0.001) from plant communities with three consecutive droughts (D-D-D). Overall, our study suggests that repeated drought events alter some aspects of plant communities, mainly the loss of species, while some aspects (e.g., richness) of the plant communities do not change.