1. Department of Ecology and Environmental Research, Swedish University of Agricultural Sciences (SLU), PO Box 7072, SE‐750 07 Uppsala, Sweden;
2. Southern Swedish Forest Research Centre, SLU, PO Box 49, SE‐230 53 Alnarp, Sweden;
3. Department of Environmental Sciences, Second University of Naples, Via Vivaldi 43, IT‐81100 Caserta, Italy;
4. Department of Natural Sciences, Örebro University, SE‐701 82 Örebro, Sweden;
5. Department of Biology, Universiteit Antwerpen (UA), Universiteitsplein 1, BE‐2610 Wilrijk, Belgium;
6. Duireaskin, Aberfeldy, Perthshire PH15 2ED, UK;
7. Faculty of Forestry, University of Joensuu, FI‐80101 Joensuu, Finland;
8. Department of Physical Geography and Ecosystems Analysis, Lund University, SE‐223 62 Lund, Sweden;
9. INRA, Research Unit EPHYSE, BP81, Villenave d’Ornon Cedex FR‐33883, France;
10. Unit for Field‐based Forest Research, SLU, SE‐922 91 Vindeln, Sweden;
11. Environmental Sciences Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831‐6422, USA;
12. Division of Environmental Science and Policy, Nicholas School of the Environment and Earth Sciences, Duke University, Durham, NC 27708‐0328, USA;
13. Plant Biology and Biogeochemistry Department, Risö National Laboratory, PO Box 49, DK‐4000 Roskilde, Denmark;
14. USDA Forest Service RMRS, 240 West Prospect Road, Fort Collins, CO 80526 USA;
15. Agricultural University of Iceland, IS‐311 Borgarnes, Iceland;
16. Department of Forest Soils, SLU, PO Box 7001, SE‐750 07 Uppsala, Sweden;
17. CEH‐Edinburgh, Bush Estate, Penicuik, EH26 0QB, UK;
18. Department. of Plant and Environmental Sciences, University of Göteborg, PO Box 461, SE‐405 30 Göteborg, Sweden