1. a Institute of Forest Ecology and Forest Inventory, Johann Heinrich v. Thünen-Institut (vTI), Federal Research Institute for Rural Areas, Forestry and Fisheries , A.-Möller-Straße 1, D-16225, Eberswalde, Germany
2. b Department of Silviculture and Forest Ecology of the Temperate Zones, Faculty of Forestry and Forest Ecology , Georg-August-University Göttingen , Büsgenweg 1, D-37077, Göttingen, Germany
3. c Southern Swedish Forest Research Centre , Swedish Agricultural University (SLU) , P.O. Box 49, SE-230 53, Alnarp, Sweden
4. d Department of Applied Ecology, Forest & Landscape Denmark , Vedelsgade 6, DK-7100, Vejle, Denmark
5. e European Forest Institute (EFI) , Torikatu 34, FI-80100, Joensuu, Finland
6. f Department of Forest and Environment , University of Applied Sciences Eberswalde , A.-Möller-Straße 1, D-16225, Eberswalde, Germany