1. Nature Conservation and Landscape Ecology, University of Freiburg , Tennenbacherstr. 4, 79106 Freiburg , Germany
2. Forest Nature Conservation, Forest Research Institute of Baden-Wuerttemberg FVA , Wonnhaldestr. 4, Freiburg, 79100 , Germany
3. Conservation Biology, Institute of Ecology and Evolution, University of Bern , Baltzerstr. 6, Bern, 3012 , Switzerland