1. Department of Geosciences and Geography; University of Helsinki; P.O. Box 64 00014 Helsinki Finland
2. Department of Environmental Sciences; Environmental Change Research Unit (ECRU); University of Helsinki; P.O. Box 65 00014 Helsinki Finland
3. Department of Landscape Ecology; Institute of Ecology at Tallinn University; Uus-Sadama 5 10120 Tallinn Estonia
4. School of Forest Sciences; University of Eastern Finland; PL 111 80101 Joensuu Finland