1. Teshio Experimental Forest, Hokkaido Univ. Horonobe 098‐2943 Hokkaido Japan
2. Dept of Biology, Univ. of Regina Regina SK Canada
3. Forestry Research Inst., HRO Bibai Hokkaido Japan
4. Inst. of Botany and Landscape Ecology, Greifswald Univ. Greifswald Germany
5. Dept of Ecological Science, Faculty of Science, Vrije Univ. Amsterdam The Netherlands