1. Department of Forest Vegetation Ecology, Faculty of Forestry, Swedish University of Agricultural Sciences, SE901 83 Umeå, Sweden.
2. Landcare Research, Post Office Box 69, Lincoln, New Zealand.
3. Museum of Forestry, Box 176, SE921 23 Lycksele, Sweden.
4. Department of Plant Sciences, University of Cambridge, Downing Street, Cambridge CB23EA, UK.