1. Department of Environmental and Biological Sciences, University of Eastern Finland, P.O. Box 1627, Kuopio FI-70211, Finland.
2. Department of Environmental and Biological Sciences, University of Eastern Finland, Joensuu, Finland.
3. School of Forest Sciences, University of Eastern Finland, Joensuu, Finland.
4. Natural Resources Institute Finland, Rovaniemi, Finland.
5. Natural Resources Institute Finland, Kuopio, Finland.