1. School of Forest Sciences, University of Eastern Finland, PO Box 111, 80101, Joensuu, Finland
2. Division for Forestry and Forest Resources, Norwegian Institute for Bioeconomy Research, P.O. Box 115, 1431, Ås, Norway
3. Institute of Biotechnology, University of Helsinki, Research Services, P.O. Box 65, 00014, Helsinki, Finland
4. Department of Crop Production Ecology, Swedish University of Agricultural Sciences (SLU), P.O. Box 7016, S-750 07, Uppsala, Sweden