1. a Institute of Terrestrial Ecology, ETH Zürich, Grabenstrasse 3, 8952 Schlieren, b Swiss Federal Institute for Forest, Snow and Landscape Research, 8903 Birmensdorf, Switzerland, and c Institute for Crystallography and Applied Mineralogy, Ludwig‐Maximilians‐Universität München, Theresienstrasse 41, 80033 München, Germany