1. Graduate School of Environmental Science, Hokkaido University, Sapporo, Hokkaido, Japan
2. Nakagawa Experimental Forest, Field Science Center for Northern Biosphere, Hokkaido University, Otoineppu, Hokkaido, Japan
3. Teshio Experimental Forest, Field Science Center for Northern Biosphere, Hokkaido University, Horonobe, Hokkaido, Japan
4. Field Science Center for Northern Biosphere, Hokkaido University, Sapporo, Hokkaido, Japan