BayCEER Workshop 2008

Effects of extreme weather events on productivity and phenology of experimental grassland and heath communities

Intensification of weather extremes is currently emerging as one of the most important facets of climate change. Research on extreme events has increased in recent years and now amounts to a fifth of the experimental climate change studies published. Numerous examples ranging from microbiology and soil science to biogeography demonstrate how extreme weather events can accelerate shifts of species compositions and distributions, thereby facilitating changes in ecosystem functioning and services. Here, we present first results of the EVENT-experiment (Bayreuth), in which planted grassland and heath communities were annually exposed to a single drought event, a heavy rainfall event, or recurrent freeze-thaw cycles. The magnitude of manipulations imitated the local 100-year weather extreme according to extreme value statistics. Our results reveal that, for example, overall productivity (ANPP) of both plant communities remained stable in face of drought, despite significant effects on tissue die-back and species-specific responses. Further, we report how drought and heavy rain events caused phenological shifts in plants of the same magnitude as one decade of gradual warming.