Agroforestry: principles and practice : proceedings of an International Conference 23-28 July 1989 at the University of Edinburgh, Edinburgh, UK held under the auspices of the International Forest Science Consultancy a part of Land and Timber Services, Edinburgh, UK and the Department of Forestry & Natural Resources now a part of Institute of Ecology and Resource Management, University of Edinburgh, Edinburgh, UK / ed. by P.G. Jarvis