Extreme drought reduces climatic disequilibrium in dryland plant communities

Abstract

High rates of climate change are currently exceeding many plant species' capacity to keep up with climate, leading to mismatches between climatic conditions and climatic preferences of the species present in a community. This disequilibrium between climate and community composition could diminish, however, when critical climate thresholds are exceeded, due to population declines or losses among the more mismatched species. Here, we assessed the effect of an extreme drought event on rich semiarid shrubland communities in the south‐eastern Iberian Peninsula. Using a community climate framework, we compared the community climatic disequilibrium before and after the drought episode on three study sites with different levels of precipitation. Disequilibrium was estimated as the difference between observed reference climate and community‐inferred climate, calculated as the mean climatic optimum for the species present, weighted by their abundances. We found that extreme drought embedded within a decadal trend of increasing aridity led to a significant reduction in community climatic disequilibrium, and that this reduction was positively related to water deficit (low P/PET values). In contrast, microhabitat variables such as vegetation cover or slope, did not emerge as significant predictors of changes in community climatic disequilibrium. Our study highlights that extreme drought events pushing communities in the same direction as climate trends may decrease community climatic mismatch, leading to communities more adapted to aridity through loss of drought‐sensitive species. These findings underscore that extreme events will play a crucial role in speeding up climate‐induced community transformations and biodiversity losses.