1. Swiss Federal Institute for Forest, Snow and Landscape Research WSL Birmensdorf 8903 Switzerland
2. Forest Ecology and Management Group Wageningen University Wageningen 6708 PB the Netherlands
3. Institute for Applied Plant Biology Witterswil 4108 Switzerland
4. Department of Environmental Systems Science Institute of Agricultural Sciences ETH Zurich Zurich 8092 Switzerland
5. Laboratory of Plant Ecology Ghent University Ghent 9000 Belgium
6. Department of Plant Ecology and Evolution Uppsala University Uppsala SE‐751 05 Sweden