1. Lammi Biological Station; University of Helsinki; Pääjärventie 320 Lammi FI-16900 Finland
2. Department of Biological and Environmental Science; University of Jyväskylä; P.O. Box 35 Jyväskylä FI-40014 Finland
3. Finnish Environment Institute; P.O. Box 140 Helsinki FI-00251 Finland