Contrasting responses of Swiss grasslands to simulated summer drought

Climate models predict that future summers in Switzerland will be up to 20% drier by mid of the century while temperatures will rise by almost 3 °C. Therefore, we studied the effects of drought on three Swiss grasslands at different altitudes. Using transparent rain-out shelters, we simulated pronounced summer droughts (excluding between 200 and 300 mm, about 45% of summer precipitation), and assessed the effects on the ecophysiological performance of selected species as well as on productivity and plant functional type composition of the communities. Plant ecophysiology was negatively affected at all three sites, but the effects of drought at the community level were strongly dependent on grassland type. While reducing precipitation created water stress for the alpine grassland site, the effects were less clear in montane and lowland grasslands. Here, total green biomass production did not change significantly, despite strong negative effects of drought on ecophysiological performance of selected plant species. At the lowland site, grasses were more affected than forbs, leading to a change in competitive interactions between plant functional types, favouring weed species. At the montane site, we found strong interactions with specific cutting dates. Thus, our results indicate relevant consequences of climate change for grassland management, particularly in terms of productivity and weed pressure.