1. Institute of Botany; University of Basel; 4056 Basel Switzerland
2. Potsdam Institute for Climate Impact Research; P.O. Box 601203 14412 Potsdam Germany
3. Swiss Federal Research Institute WSL; CH-8903 Birmensdorf Switzerland
4. Institute of Geography; University of Neuchatel; Espace Louis-Agassiz 1 2000 Neuchâtel Switzerland