Effects of extreme weather events on plant productivity and tissue die-back are modified by community composition

Extreme weather events are expected to increase in frequency and magnitude due to climate change. Their effects on vegetation are widely unknown. Here, experimental grassland and heath communities in Central Europe were exposed either to a simulated single drought or to a prolonged heavy rainfall event. The magnitude of manipulations imitated the local 100-year weather extreme according to extreme value statistics. Overall productivity of both plant communities remained stable in the face of drought and heavy rainfall, despite significant effects on tissue die-back. Grassland communities were more resistant against the extreme weather events than heath communities. Furthermore, effects of extreme weather events on community tissue die-back were modified by functional diversity, even though conclusiveness in this part is limited by the fact that only one species composition was available per diversity level within this case study. More diverse grassland communities exhibited less tissue die-back than less complex grassland communities. On the other side, more diverse heath communities were more vulnerable to extreme weather events compared to less complex heath communities. Furthermore, legumes did not effectively contribute to the buffering against extreme weather events in both vegetation types. Tissue die-back proved a strong stress response in plant communities exposed to 100-year extreme weather events, even though one important ecosystem function, namely productivity, remained surprisingly stable in this experiment. Theories and concepts on biodiversity and ecosystem functioning (insurance hypothesis, redundancy hypothesis) may have to be revisited when extreme weather conditions are considered.