作者单位:Dept of Biological and Environmental Science and Konnevesi Research Station, Univ. of Jyvaskyla, PO Box 35, FI–40014 Univ. of Jyvaskyla, Finland[1]Dept of Biology, Univ. of Turku, FI–20014 Turku, Finland. OH also at: Finnish Forest Research Institute, Suonenjoki Unit, Juntintie 154, FI–77600 Suonenjoki, Finland[2]