1. The Norwegian Water Resources and Energy Directorate (NVE), Region South, Anton Jenssens gate 7 Box 2124, 3103 Tønsberg, Norway
2. Norwegian Forest and Landscape Institute, Box 115, 1431 Ås, Norway
3. Corresponding author: Department of Ecology and Natural Resource Management, Norwegian University of Life Sciences, Box 5003, 1432 Ås, Norway mailto:
4. The Norwegian Institute for Nature Research NINA, Box 5685 Sluppen, 7485 Trondheim, Norway
5. Brattlien 38, 5019 Bergen, Norway
6. Midt-Troms Museum, Box 82, 9059 Storsteinnes, Norway