They may be planted randomly or according to systematic patterns on embankments, terraces, or field boundaries. They provide a variety of products including fruit, forage, fuelwood, fodder, shade, and fence and timber material. Some commonly recommended multipurpose trees are listed in Table 2-2. Once again, local adaptation to and validation for site-specific systems are essential.

Rather than using a random and difficult-to-mechanize system of growing trees with annuals or animals, mixtures can be grown in an improved spatial or temporal arrangement. In an agrisilvicultural system, for example, trees can be grown in alternate rows or strips, as contour hedges to control erosion, or on field boundaries. These orderly arrangements can facilitate the use of animal power and of mechanization of farm operations, save labor, and enhance economic and ecological benefits.

Alley cropping is a common example of a spatial arrangement. Food crops are grown in alleys formed by contour hedgerows of trees or shrubs (Kang et al., 1981). Trees and shrubs can be pruned to prevent shading of the food crops and to provide nitrogen-rich mulch for crops and fodder for livestock. Shrubs and trees also act as windbreaks, facilitate nutrient recycling, suppress weed growth, decrease runoff, and reduce soil erosion (Ehui et al., 1990).