|Agroforestry in the West African Sahel (BOSTID, 1984)|
Traditional systems of agroforestry in the Sahel represent highly sophisticated approaches to food production in regions characterized by extremely variable precipitation, high temperature, often nutrient-poor soils, a variety of crop diseases, and crop predators such as granivorous birds, rodents, and locusts, which can dramatically reduce harvests.
Traditional Sahelian agroforestry systems are structurally arrayed in such a manner that leaf area indices are relatively high, resulting in correspondingly high photosynthetic efficiency and biomass production. Many of the traditionally important grain crops in the region, such as sorghum and millet, are C4-pathway crops, which are capable of converting very high light intensities into growth more efficiently than is possible in exotic C3 crops such as wheat and rice.
These systems of agroforestry are also efficient in locally modifying temperatures and in intercepting rainfall, facilitating infiltration, and maintaining satisfactory soil moisture levels. This, among other benefits, reduces moisture stress in plants and regulates soil temperature fluctuations and soil-water relationships, thereby assuring the survival of critical soil organisms such as nitrogen fixing rhizobial bacteria. Perennials contribute to the enrichment of the agricultural systems through nutrient cycling and help control wind and water erosion. The use of Acacia albida in traditional Sahelian systems is illustrative of the important contributions made by woody perennials to agricultural production in the region.
In the past, Sahelian agricultural systems had greater crop diversity. This diversity resulted in higher levels of assured food availability, because the differing requirements of the various crops and the selectivity of most crop diseases and predators prevented the magnitude of losses that can occur in the less complex mono cropped systems. The range of products, in addition to food, included fodder, fuel, gum, resin, tannin, and medicinal products. Because the annual and perennial crops included in agroforestry systems characteristically are harvested at different times, labor inputs are distributed over longer periods.
In many areas of the Sahel, shifts to mono cropping and open-field cultivation have resulted in lower potential productivity, reduced ground water recharge, disruptions of soil ecology and nutrient cycling, and increased soil erosion. Because these shifts in cultivation practices have been accompanied by widespread environmental degradation in the region and the loss of native plants and animals that have traditionally served as alternative sources of food in the event of crop failure, rural Sahelian populations have become progressively less self-reliant and more vulnerable to natural hazards, such as drought, and to economic adversity.
This report provides an overview of traditional Sahelian production systems and explores approaches by which modern science and technology can complement the knowledge and experience of rural Sahelian populations in developing more dependable, resilient, and socially acceptable agricultural systems.