1. a Southern Swedish Forest Research Centre , Box 49, SE-230 53, Alnarp, Sweden
2. b Finnish Forest Research Institute, Suonenjoki Research Unit , Juntintie 154, FI-77600, Suonenjoki, Finland
3. c University of Eastern Finland , Mekrijärvi Research Station Yliopistontie 4, FI-82900, Ilomantsi, Finland
4. d Södra Skog , Skogsudden, SE-35189, Växjö, Sweden
5. e Finnish Forest Research Institute , Box 18, FI-01301, Vantaa, Finland