1. Graduate School of Environmental Science, Hokkaido University, Nayoro, Japan
2. Uryu Experimental Forest, Field Science Center for Northern Biosphere, Hokkaido University, Moshiri, Horokanai, Hokkaido 074-0741, Japan
3. Shikoku Research Center, Forestry and Forest Products Research Institute, Kochi, Japan
4. Graduate School of Agriculture, Hokkaido University, Sapporo, Japan
5. Northern Forestry and Development Office, Field Science Center for Northern Biosphere, Hokkaido University, Nayoro, Japan