Isabelle Salomé Helfenstein, Joan T. Sturm, Bernhard Schmid, Alexander Damm, Meredith Christine Schuman , Felix Morsdorf

Biodiversity–ecosystem functioning (BEF) relationships are increasingly recognized as an important aspect of ecosystem research and management thanks to knowledge gained from long-term grassland and, more recently, forest experiments. However, to what extent the behavior of non-experimental systems corresponds to the relationships discovered in BEF experiments remains controversial. We investigated the relationship between trait-based diversity and drought response using data from forests in northern Switzerland, which experienced an extremely hot and dry summer in 2018. We used Sentinel-2 satellite data to assess trait diversity and quantified drought response in terms of resistance, recovery, and resilience from 2017 to 2020. We then analyzed the BEF relationship between trait-based diversity and drought response for different aggregation levels of richness and evenness. Forests with greater richness were more resistant and resilient to the drought event, and the relationship of evenness with resistance or resilience was hump-shaped or negative, respectively. These results suggest that trait-based diversity supported forest drought response via a mixture of complementarity and dominance effects, the first indicated by positive richness effects and the second by negative evenness effects. Our results link ecosystem functioning and biodiversity at large scales and provide new insights into the BEF relationships in real-world forest ecosystems.