1. Biotechnical Faculty, Department of Wood Science and Technology, University of Ljubljana, p.p. 95, Rozna dolina, Cesta VIII/34, 1111 Ljubljana, Slovenia
2. North‐eastern Research Station, U.S. Department of Agriculture, Forest Service, PO Box 640, Durham, New Hampshire 03824, USA (for correspondence)
3. Slovenian Forestry Institute, Vecna Pot 2, 1000 Ljubljana, Slovenia