1. a Department of Silviculture , Swedish University of Agricultural Sciences (SUAS) , Umeå, S‐901 83, Sweden
2. b Department of Biometry and Forest Management , SUAS , Umeå, S‐901 83, Sweden
3. c The Forest Research Institute of Sweden , Box 3, Sävar, S‐910 36, Sweden
4. d Department of Forest Yield Research , SUAS , Garpenberg, S‐776 98, Sweden