1. Department of Biological Sciences University of Toronto Scarborough 1265 Military Trail Toronto OntarioM1C 1A4Canada
2. Hokkaido Research Center Forestry and Forest Products Research Institute Hitsujigaoka 7, Toyohira‐ku Hokkaido062‐0045Japan
3. Department of Ecology Swedish University of Agricultural Sciences Box 7044 Uppsala750 07Sweden
4. School of Forest Sciences University of Eastern Finland PO Box 111, Yliopistokatu 7 JoensuuFI‐80101Finland