1. Laboratory of Forest Sciences, Department of Biological Environment, Akita Prefectural University, Akita 010-0195, Japan
2. Tohoku Research Center, Forestry and Forest Products Research Institute, 92–25, Morioka Iwate 020-0123, Japan
3. Laboratory of Forest Plant Ecology, Graduate School of Bioagricultural Sciences, Nagoya University, Chikusa, Nagoya 464-8601, Japan
4. Environmental Sciences Laboratory, Faculty of Social and Information Studies, Gunma University, 4–2 Aramaki, Maebashi Gunma 371-8510, Japan