1. School of Environment; Natural Resources and Geography; Bangor University; Bangor Gwynedd LL57 2UW UK
2. Southern Swedish Forest Research Centre; Swedish University of Agricultural Sciences; PO Box 49 230 53 Alnarp Sweden
3. Statistical Services Centre; University of Reading; Reading RG66FN UK
4. World Agroforestry Centre; PO Box 30677 00100 Nairobi Kenya