Die Auswirkungen des globalen Wandels auf Schweizer Wälder aus ökophysiologischer Sicht | Effects of global change on Swiss forests from an ecophysiological point of view

As a consequence of global change, our forests experience abruptly changing environmental conditions. Atmospheric CO₂, temperature, water availability and nutrient (particularly nitrogen) deposition are the key drivers of environmental change. The present contribution summarizes the current state of knowledge from an ecophysiological point of view and provides some guidelines for research and forest management. Rising mean temperatures hardly affect photosynthesis and carbon stocks, but rather cause changes in species composition. In summer, they lead to increased evapotranspiration, which exacerbates the danger of summer droughts likely to become more frequent until the middle of this century. Increasing nitrogen deposition has probably contributed to increased tree growth during the past century. However, deposition rates often occur at such high levels that negative effects (immobilization and leaching of other essential nutrients, soil acidification) dominate. Increased atmospheric CO₂ concentration may promote tree growth in Switzerland in young individuals, but overall, its effect on tree water relations is probably more important. Species-specific water savings and consequences for soil moisture and runoff could affect catchment hydrology. Interactions between factors such as the one between water availability and CO₂ concentration are of prime interest. However, there are only few long-term ecophysiological experiments testing interactive effects on forest trees. Many open questions could be answered by such experiments, which are an important basis for model parametrization and eventually decision-making in forest management.