1. Hokkaido Research Center, Forestry and Forest Products Research Institute , Hitsujigaoka 7, Sapporo 062-8516 , Japan
2. Department of Plant Ecology, Forestry and Forest Products Research Institute , Matsunosato 1, Tsukuba 305-8687 , Japan
3. Department of Ecology, School of Ecology and Applied Meteorology, Nanjing University of Information Science & Technology (NUIST) , Nanjing 210044 , China
4. Institute of Low Temperature Science, Hokkaido University , Kita-19, Nishi-8, Kita-Ku, Sapporo 060-0819 , Japan