Background/Question/Methods Drought has immediate and legacy effects on grassland resources like water, and nutrients, which can alter plant community composition. However, past droughts might have lasting legacy effects and we lack a clear understanding of how drought legacy affects changes plant communities responses to subsequent droughts. Here we assessed the drought legacy effect on grassland plant community composition over a three-year experimental drought. We determined plant species composition during a three-year exceptional drought from Jul/Aug 2018-2020 at a long-term ecological research experiment, called the Climate Extreme Experiment (CEE) at Konza Prairie Biological Research Station, Kansas. Drought was simulated since 2010 using rainout shelters such that in the 2018-2020 drought, communities had three drought legacies: (i) zero drought legacy (ii) one drought legacy and (iii) two drought legacy. Using the 2018-2020 datasets we addressed two questions: (1) Does drought legacy affect plant species richness and evenness? (2) Does drought legacy affect changes in composition? Results/Conclusions We hypothesized that plant species richness will decrease with increasing number of drought legacies due to higher plant mortality associated with drought. Similarly, we hypothesized that plant evenness will increase with the number of drought legacies due to a decrease in the abundance of dominant plant species. We found that the one drought legacy treatment had the lowest species richness (mean ± standard deviation = 9.2 ± 5) compared to zero, and two drought legacies (mean ± standard deviation = 12.5 ± 5). Species evenness, however, did not differ for different drought legacies (mean ± standard deviation = 0.35 ± 0.2). Additionally, we had hypothesized that the plant species reordering, and species gains and losses would be the highest for plant communities under zero drought legacy because the plants had never been exposed to drought before. Indeed, we found that plant communities with zero drought legacy had greater species reordering change (p-value = 0.03), and species gains (p-value = 0.04) and losses (p-value = 0.001) from 2018 to 2020 than two drought legacy but not necessarily from one drought legacy. Understanding these changes in plant community composition due to drought legacies over time can inform grassland management, and restoration at present and future climate scenarios.
