1. Plant and Vegetation Ecology, University of Antwerp, Antwerpen, Belgium.
2. Department of Biological and Environmental Sciences, University of Gothenburg, Göteborg, Sweden.
3. Centre for Environmental Sciences, Hasselt University, Diepenbeek, Belgium.
4. School of Science & Technology, Örebro University, SE-701 82 Örebro, Sweden.
5. Slovenian Forestry Institute, SI-1000 Ljubljana, Slovenia.
6. Institute of Physicochemical and Biological Problems in Soil Science, Russian Academy of Sciences, Puschino, Moscow Region, Russia.