1. Department of Physical Geography and Ecosystem Science; Lund University; Sölvegatan 12; S-223 62 Lund; Sweden
2. Department of Geography; Swansea University; Singleton Park; Swansea; SA2 8PP; UK
3. Finnish Forest Research Institute, METLA; PO Box 16 (Eteläranta 55); FI- 96301; Rovaniemi; Finland
4. Department of Life Sciences; Anglia Ruskin University; East Road; Cambridge; CB1 1PT; UK