Even Bergseng1, Jon Andreas Ask1, Erik Framstad2, Terje Gobakken1, Birger Solberg1, Hans Fredrik Hoen1
1Department of Ecology and Natural Resource Management, Norwegian University of Life Sciences, P.O. Box 5003, N-1432 Ås, Norway
2Norwegian Institute for Nature Research, P.O. Box 736 Sentrum, N-0105 Oslo, Norway