Institution: | 1. Department of Forest Ecology, University of Helsinki, P.O. Box 27, FI‐00014 Helsinki, Finland;2. E‐mail: jinrong.lu@helsinki.fi (for correspondence);3. Finnish Forest Research Institute (Metla) Punkaharju Research Unit, Finlandiantie 18, 58450 Punkaharju, Finland;4. University of Joensuu, Faculty of Forest Sciences, P.O. Box 111, FI‐80101 Joensuu, Finland;5. N‐K University of Applied Sciences, L?nsikatu 15, 80110 Joensuu, Finland |