1. Department of Ecology and Natural Resource Management, Norwegian University of Life Sciences, PO Box 5003, NO‐1432 Ås, Norway
2. Microbial Evolution Research Group (MERG), Department of Biology, University of Oslo, PO Box 1066 Blindern, NO‐0316 Oslo, Norway
3. Norwegian Forest and Landscape Institute, Fanaflaten 4, NO‐5244 Fana, Norway
4. Department of Botany, Natural History Museum, University of Oslo, PO Box 1172 Blindern, NO‐0318 Oslo, Norway