1. Swiss Federal Institute for Forest, Snow and Landscape Research (WSL), Zürcherstrasse 111, CH‐8903 Birmensdorf, Switzerland;
2. Institute of Plant Sciences, University of Bern, Altenbergrain 21, CH‐3013 Bern, Switzerland
3. ETH Zurich, Institute of Plant Sciences, Universitätsstrasse 2, CH‐8092 Zurich, Switzerland;