Modelling the impact of climate change on the productivity and water-use efficiency of a central European beech forest

This scenario study is focused on the analysis and causal explanation of the effects of regional climate change on the productivity and water-use efficiency of a pure European beech Fagus sylvatica (L.) forest in western Germany. An ensemble of 9 regional climate model (RCM) simulation results based on the A1B emissions scenario from the ENSEMBLES project was used, along with local observations to drive the physiological forest growth model BALANCE for a 10 yr period. It simulates biomass increments, as well as productivity and efficiency, under different climatic conditions. Despite the RCM ensemble's large bandwidth, the results clearly indicate a decrease in total living biomass under future climate conditions compared to initial conditions and BALANCE control simulations. Net primary productivity was significantly reduced by 30% and water-use efficiency-though more uncertain-by 13% for end-of-the-century climate conditions compared to the control runs. In the A1B scenario, the lowered productivity and efficiency of the beech stand under future climate conditions are caused by higher mortality rates, lower water availability and higher drought stress, though partly counterbalanced by longer growing seasons.