Agroforestry is de®ned as a land-use system in which woody plants [often multipurpose tree species] are grown in association with agricultural crops, pastures or livestock (Breman and Kessler, 1997). Such systems have the potential to increase yields by effectively growing two crops at the same time on a single piece of land (Nair, 1991), and have been promoted as more sustainable agricultural production systems appropriate for developing countries where the use of external inputs is not feasible (Winterbottom and Hazelwood, 1987). Several reasons have been suggested for combining trees and crops on the samepiece of land, as opposed to more traditional systems of crop ®elds and wood lots. These include, among others, reducing soil erosion, limited availability of land, bene®cial shading of some crop species, the distance needed to travel to the nearest source of fuelwood, and a shift in ownership of woodland from communal to private tenure