Agroforestry can build up soil fertility and prevent soil erosion; particular planting systems can use soil water more efficiently. It can provide extra benefits, including cash in hand, for the farm family through various tree products -- fodder, fuelwood, food, building materials and more. It can also alleviate tropical deforestation by providing alternatives to slash-and-burn techniques carried out by landless farmers, many of them migrants to the tropical forests. Preliminary research indicates that for every hectare put into agroforestry alternatives, five to ten hectares of rainforest can be saved. For example: (a) grevillea is demonstrating considerable potential as an upper story tree for timber in banana/bean systems. At Gitega, Burundi, it is achieving a height of 5.3 metres after 30 months of growth, without any negative effect on either banana or bean yields; (b) the prunings of leucaena contour hedges in western Kenya, when fed to dairy cattle as a protein supplement, are 3.5 to 7 times more profitable than using them as mulch to fertilize maize; (c) crops of maize grown under the canopy of [Faidherbia albida] (acacia) trees have produced higher yields than from open fields. The tree improves nitrogen mineralization of the soil and competes little for light and water.
A study in south India showed that agroforestry systems can reduce the risk of crop production and enable farmers to invest in more risky cash crops. However, the beneficial impacts of agroforestry on crop allocation, input use and income differs due to the differences in resource availability of farmers. The influence of agroforestry on nutrient availability of the farm households also differs based on the components of agroforestry, orientation of farming and the nature of farming systems. Design of agroforestry systems should consider differences in resource constraints in farming systems and risk attitudes of farmers towards their allocation decisions and that such considerations would largely enhance the successful adoption of agroforestry in developing countries.
A World Bank field study reported seven case studies conducted by an interdisciplinary team, covering indigenous and innovative systems found in the highlands of East Africa, the semi-arid zone, and the humid lowlands of West Africa. This review identified a number of issues that need to be considered in the design and implementation of agroforestry projects for Africa in order for them to be successful. Key findings include the importance of understanding the economics of agroforestry systems from the farmer's point of view as well as from the broader perspective of the benefits to society. Project evaluation should therefore take into account local markets and opportunities for off-farm employment offered by tree products, as well as the opportunity costs perceived by farmers in making adoption decisions. Farm households are not homogeneous, and project design should be adapted to the socioeconomic level, age and gender of the people who are expected to adopt the proposed technology. In Africa, trees are integral parts of agro-sylvo-pastoral farming systems and should be considered in this sociocultural context, with particular attention to the constraints imposed by customary and legal rules regarding land and tree tenure. The institutional framework for implementation should be selected and developed with a view to long-term sustainability.