*Department of Natural and Cultural Resources, University of Ferrara, Corso Porta Mare 2, I-44100 Ferrara, Italy, wDepartment of Environmental Sciences, Wageningen University, Bornsesteeg 69, 6708 PD Wageningen, the Netherlands, zLIN’eco, Ecological Engineering, PO Box 51, 2732 Reconvilier, Switzerland, §Department of Botany, Masaryk University, Kotla´rˇska´ 2, CZ-611 37 Brno, Czech Republic, }Faculty of Biological Sciences, University of South Bohemia, Branisˇovska´ 31, CZ 370 05 Cˇ eske´ Bud eˇ jovice,Czech Republic, kDepartment of Ecology, The Royal Veterinary and Agricultural University, Rolighedsvej 21, 1958 Frederiksberg,Denmark, **Department of Earth Sciences, University of Parma, Parco Area delle Scienze 157, I-43100 Parma, Italy, wwSlovenian Forestry Institute, Department of Forest Ecology, Vecˇna pot 2, SI-1000 Ljubljana, Slovenia, zzDepartment of Plant Ecology,Evolutionary Biology Centre, Uppsala University, Villava¨gen 14, SE-75236 Uppsala, Sweden, §§Department of Biology, Universityof Joensuu, PO Box 111, FIN-80101 Joensuu, Finland