Intensification of weather extremes is currently emerging as one of the most important facets of climate change. First evidence suggests, that extreme drought and heavy rain can accelerate shifts in species compositions and biogeochmical cycles, thereby facilitate changes in ecosystem functioning and services. Here, we present results of the EVENT-experiment (Bayreuth, Germany, temperate zone), in which planted grassland and shrubland communities were exposed to annually recurring drought and heavy rainfall events in early summer or to recurrent freeze-thaw cycles in winter for a period of five years. The magnitude of manipulations imitated the local 100/1000-year weather extreme according to extreme value statistics.

Results/Conclusions

Surprisingly, above ground productivity (ANPP) of grassland and shrubland remained stable in the face of recurrent extreme drought and heavy rain, despite significant effects on tissue die-back, competitive interactions among species and nutrient cycling in leaves and soil. Drought and heavy rain events caused phenological shifts in plants of the same magnitude as one decade of gradual warming. The phenological response of individual species was modified by community composition, functional diversity, and intra-annual variability. Several measures of soil biotic processes, namely fine root length, cellulose decomposition, and soil enzyme activities, remained remarkably stable during and after the application of the extreme weather events Nevertheless, drought events were found to alter carbon uptake into the system and carbon allocation within the plants. We conclude, that extreme weather events excite ecosystem regulating functions for maintaining stability in productivity.