1. Division Forest, Nature and Landscape, University ofLeuven, Celestijnenlaan 200E, BE‐3001 Leuven, Belgium;
2. Laboratory of Forestry, Ghent University, Geraardsbergse Steenweg 267, BE‐9090 Melle‐Gontrode, Belgium; E‐mail
3. Community and Conservation Ecology Group, University of Groningen, PO Box 14, 9750 AA Haren, The Netherlands; E‐mail