1. Institute of Biology, Komi Science Centre, Russian Academy of Sciences , Kommunisticheskaya 28 , Syktyvkar 167982 , Russia
2. The Forestry Research Institute of Sweden (Skogforsk) , Ekebo 2250, SI-26890 Svalöv , Sweden
3. Natural Resources Institute Finland (Luke) , Latokartanonkaari 9, FI-00790 Helsinki , Finland