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close this bookAgroforestry in the West African Sahel (BOSTID, 1984)
View the document(introduction...)
View the documentAcknowledgements
View the documentPreface
View the documentOverview
View the documentChapter 1: Desertification in the Sahel
View the documentChapter 2: Traditional Land Use Systems
View the documentChapter 3: Uses and Potential of Agroforestry
View the documentChapter 4: Agroforestry Applications
View the documentChapter 5: Sahelian Agroforestry: Institutional Considerations
View the documentReferences
View the documentBibliography
Open this folder and view contentsAppendixes

Chapter 1: Desertification in the Sahel

"Sahel" has become a synonym for environmental degradation and the desperate struggle for survival in a region losing its carrying capacity through a series of severe drought years and the destructive impact of human activity on natural resources, a process commonly termed desertification. In this case, desertification, or desert encroachment, does not refer to the southward extension of the Sahara Desert but to the formation and expansion of desert like patches around cities, villages, wells, and other centers of concentrated activity.* In this report, the term "Sahel" is broadly applied to the semiarid Sudano-Sahelian zone. Areas receiving between 400 and 750 mm of precipitation are emphasized.


While water deficiency can be addressed by instituting a variety of more environmentally sound water use and conservation practices, it remains, nevertheless, the key limiting factor for life in the Sahel.

Rainfall distribution patterns are highly irregular in time and space. The rainy season generally lasts from July to October, with an average of 24 rainfalls, 10-12 of which occur in August. Rainfall intensities range from 5 mm to over 50 mm per event. While 5 mm of rainfall are considered effective for wild and cultivated plants, 20 mm or more are required to produce the surface runoff essential for filling,temporary and permanent water holes and replenishing ground water reserves. Figures 1 and 2 show mean annual precipitation and associated vegetation types in the Sahel.

The climate is further characterized by high diurnal temperature fluctuations and low relative humidity. During the "cool" dry season, from November to February, daytime temperatures often peak above 38°C and fall to 12°C during the nighttime, with relative humidity averaging 15-25 percent during the day and 40-50 percent at night. During the "hot" dry season, from March to mid-July, temperatures commonly exceed 43°C during the day and drop as low as 17°C at night. During the rainy season, from July to October, temperatures range from 35°C during the day to 22°C at night, with relative humidity from 95 to 60 percent. Thus considerable moisture is lost through evaporation. In addition, the harmattan--a dry northeasterly wind--occurs frequently from November through February, causing considerable desiccation and wind erosion.


In addition to the effects of climate on the Sahel's fragile environment, man and livestock also play major roles in desertification. Even where an ecological balance exists among man, animals, and the surrounding natural vegetation--as existed throughout the Sahel a few generations ago--extensive deterioration will generally occur when population pressures exceed a critical level. As a result of a growth rate of 2.6 percent, the population has almost doubled in the last 20 years. By the end of this century, the present population will have doubled again.

With increases in human populations have come increases in herds of cattle and small ruminants and changes in the traditional land use patterns of various ethnic groups. Herders, who once were predominantly nomadic, tend to settle around permanent sources of water in villages and even in towns. They remain with their herds in the northern part of the Sahel throughout the year, whereas formerly they migrated southward to more favorable pastures during the dry season. A network of deep wells, powered by diesel engines, has tapped fossil ground water resources to make water available throughout the year in many areas where it was not previously assured. The net result has been a rapid increase of herds of cattle and small ruminants (Figure 3). As many as 20,000 head of livestock are often concentrated within a few kilometers around wells. The locally available vegetation on which they depend has already been over exploited, degraded, impoverished, and, in fact, has largely disappeared, leaving desert like "islands" around the wells.

FIGURE 1 Mean annual precipitation. (source: Weber 1977)

FIGURE 2 Vegetation zones based on the Yangambi classification of African vegetation types by the Commission for Technical Cooperation in Africa South of the Sahara. (Source: Weber 1977)

The destruction of the herbaceous or grass layer, as a result of overgrazing and trampling by herds, marks the beginning of desertification. Plants die and their roots no longer hold the thin topsoil, which is washed or blown away. Fine clay particles spread over bare patches during the short rainy season, causing surface hardening and sealing. Seeds cannot penetrate these hardened surfaces.

FIGURE 3 Cattle herds have increased rapidly in the Sahel, and in many areas their numbers now exceed the carrying capacity of the pasturelands. IFC/WORLD Bank Photo by K. M. Ibrahim)

Frequently these patches are covered by stagnant water for extended periods during the rainy season. Because of the destruction of the topsoil cover and loss of organic matter, rains are no longer absorbed where they fall but drain toward lower lying areas, causing the slow but certain death of trees and shrubs due to lack of water or, where it accumulates, to waterlogging. In some areas, the process of degradation continues until the ability of the soils to retain water is almost completely lost.

Even where there is little wind, terrain is flat, and soils are too sandy to cause runoff, continuous farming of the same fields will eventually deplete the soils to such an extent that the land will have to be abandoned or revegetated unless specific steps are taken to maintain or increase soil fertility. While the revegetation of barren flats is extremely costly, fencing off endangered areas for 3-5 years during the initial phases of degradation can lead to an astonishing recovery of the vegetative cover.

Advanced farming technology can also accelerate degradation. For example, the removal of stumps, indiscriminate and more complete land clearing, and the use of machinery for deep plowing or frequent pillage expose ever larger areas of land to wind and water erosion. The introduction of cash crops such as cotton requires more thorough land clearing and places higher nutrient demands on the soil. Mechanized transport (even bicycles or donkey carts) permits local farmers to reach more land and makes possible the transport of firewood or charcoal over longer distances. Livestock improvement activities require more grazing resources, and irrigated agriculture requires more water.

A final cause of degradation is migration. People of the Sahel and Sudan are mobile by tradition. During the last few decades, however, there has been a steady movement from rural lands toward central settlements, causing rapidly increasing pressure on natural resources in the vicinity. Firewood has been drastically over exploited within a range of about 100 km around many capital cities, resulting in a severe energy crisis. Moreover, many young people are leaving the Sahel to try to make a living in urban centers along the Nest African coast. This exodus is severely draining the area of capable manpower and is reflected in a reduction in the numbers of agricultural workers in the Sahel.


The concept of carrying capacity is useful in looking at development or conservation issues since the limits of the available natural resource base cannot be ignored. It is encouraging that a margin still exists between actual and potential production capacities and that locally appropriate resource management options can be pursued through changes in land allocation and land use. When examining resource conservation measures, the following objectives should be considered:

· Providing people with adequate supplies of basic goods and services
· Conserving those resources that still exist
· Increasing the region's long-term sustained carrying capacity.

Long and often disappointing experience has conclusively shown that any conservation activity, to be applicable, must be understood and accepted by the local population. Without the willingness of villagers to cooperate and eventually integrate whatever technique is introduced into local farm and land use practices, any idea, regardless of how valuable it might be, simply will not take hold. Because it is the rural, local people who ultimately decide the feasibility of any new idea, the following criteria must be taken into account.

First, the intervention must be technically sound and must focus on such factors as the limited amounts and irregularity of rain and the periodic occurrence of drought years. Rainfall, though infrequent and irregular, is often a direct result of violent, local convectional storms of short duration and high intensity. Under such circumstances even small watersheds or catchment areas yield sharp, high peak flows. Spillway capacity of improvement efforts has to be large, as these short, high-volume flows carry unusually large amounts of sediment, which can quickly destroy inadequately designed water control structures. Terraces intended to control water erosion must accommodate such flows, or they will rapidly wash out. Rainfall quantities and distribution patterns, compared with those of temperate zones, are extremely erratic. Mean annual precipitation is little more than a general indicator. Rainy seasons that are above or below average are frequent (Katz and Glantz 1977).

Second, investments in agricultural development activities must be appropriate to local skills, techniques, and tools. Projects relying on heavy equipment, expensive commodities, and outside technical assistance require such a large capital outlay that there is little chance the project can be replicated or continued by the local people once outside help has ceased.

Third, proposed activities will almost certainly require some changes in and adaptation to the existing local socioeconomic framework. Increased production and higher returns are not the only criteria used in calculating whether a new idea or technique is worthwhile to all concerned. In fact, local farmers may be more interested in protection against "downside risks" than in a chance to gain higher returns.

Fourth, to be successful from an institutional point of view, the interventions considered should be compatible with the existing political thought in the region of concern.

Finally, cultural values, including those dealing with traditional patterns of tenure and use of land and natural vegetation, are deep-rooted and reflect generations of experience. Modifying animal herding practices in ways that appear minor to outside project designers may well be the focal point of resistance on which an entire scheme may founder. Cultural attitudes and inflexibility may prove insurmountable in many other ways: restrictive definitions of the role of women, reluctance to abandon seasonal migration, traditional views of land tenure, or open grazing rights can pose serious obstacles to an otherwise well-designed conservation project.

Conservation measures, within these practical limits, are outlined below; agroforestry and related efforts are underlined. (For specific agroforestry techniques, see Chapter 4.)

1. Increased soil fertility
a. Introduction of Acacia albida or other leguminous treesinto farm fields
b. Cover crops, farm management (rotation)
c. Manure, compost, residue
d. Tree crops, combined with agricultural crops (Taungya)

2. Revegetation
a. Access and use control b. Seed bed treatment, direct seeding, planting c. Fire management

3. Erosion control
a. Wind
(1) Shelterbelts/live fencing
(2) Sand stabilization, dune fixation
b. Water
(1) Contour planting/farming to control sheet erosion
(2) Vegetation strips
(3) Infiltration ditches, berms, terraces
(4) Bank and slope protection to reduce channel erosion
(5) Small check structures, gully plugs
(6) Small dams to slow surface runoff.

4. Conservation of surface water
a. Micro-catchments
b. Water spreading, water harvesting
c. Reservoirs, ponds


Land use planning involving the integration of agriculture, animal husbandry, and useful trees and shrubs can take several courses. Production can be undertaken concurrently and continuously on the same tract of land; systems of alternating or rotating land use can be employed; or production activities can be geographically separated so that use pressures are distributed over a larger area. All of these variations are elements of traditional Sahelian land use strategies (see Chapter 2). Specific future strategies and emphases will naturally vary depending on local needs and preferences. Nevertheless, the key is to balance overall land use so that total economic returns and social benefits are maximized in the short and long runs.

While land use planning is a useful tool, traditional cultural values often govern the way land is used, owned, or transferred by individuals, families, tribes, ethnic groups, or entire nations. In many areas of arid and semiarid Africa, retaining current land use patterns, in the face of increasing demographic pressures and notions of progress, is leading to resource destruction. The "first come, first served" approach to the exploitation of common goods such as rangeland or indigenous trees interferes with conservation efforts, requiring the introduction of access control and use regulations. If land and soil resources are to produce, on a sustained-yield basis, more than they do now, basic readjustments of present use patterns and beliefs must be made.

Changes in land use based purely on resource management logic are unacceptable to most societies, where the first priority has been and still is the survival of the clan or tribe. Seasoned by generations of experience with recurring, devastating droughts, local farmers and herders feel they cannot afford to abandon their current strategies, particularly when they believe no other options are available. Farmers and pastoralists do not destroy their environment out of indifference or carelessness: currently, they have no other options for existing or for surviving periods of drought.

However, more productive land use patterns could be adopted if governments and regional agencies shared the risks. Considering the above constraints, the best that one can expect is that a more "rational," balanced approach to land use can be established gradually, beginning with low-risk, small-scale demonstration projects, which might serve as examples of how things could work. Such demonstrations might include:

. Small watersheds with well-planned conservation measures; controlled, multipurpose use of fuel wood and forage; surface water development

. Agroforestry projects that use land in a balanced manner to serve several local needs (stable farm soils, fuel, fodder)

. Small, well-identified grazing areas with the necessary vegetation and water reserves restored to help small, well-managed herds survive the next drought.

Unfortunately, only a few incomplete (and expensive) demonstrations have actually been carried out in the field so far.

Numerous large-scale land use schemes have been tried, with very mixed results. Group ranching, with or without herder cooperatives, in East Africa is one example. Results, judging by the slow adoption rate by the local herders, are inconclusive.

Large-scale irrigation projects are being constructed in the mayor river basins at current (1982) initial costs of over $10,000 per hectare. Although "poor" herders and farmers are being resettled, the rupture of family ties, abandonment of traditions, and exposure to different life-styles have increased divorce, suicides (practically unheard of before), and mental illness. Social tension, political unrest, and the incidence of diseases such as malaria and schistosomiasis have increased (Bodley 1975).

These experiences suggest that, in spite of knowing what logical and systematic land use measures could stem and possibly reverse resource degradation, there is currently no acceptable answer as to how--at the same time--to meet basic social and cultural needs, which are often closely tied to traditional land use patterns,

Carefully planned, sensitive schemes throughout Africa have attempted to bring about the necessary changes with a minimum of social tension and disruption. While insufficient progress has been made thus far to say that real changes are on the way, encouraging examples do exist.

. In Senegal and in Chad, pastoralists have cooperated in government-sponsored efforts and private initiatives to revegetate open rangeland. Traditional herders have planted trees in open spaces of the grass steppe, strictly on a voluntary basis and without compensation.

. In the Ngong hills of Kenya, local farmers now construct infiltration ditches and gully plugs and plant trees on their farmland to provide additional erosion protection. This initiative was based in part on a recently compiled "District Environmental Profile."

· In Niger, in the vicinity of a project where, with the help of the American private voluntary organization CARE, over 250 km of shelter belts have been planted in the last 6 years, villagers are putting pressure on the local administrators to help them carry out a similar project around their own fields.

Similar projects have been undertaken in other parts of arid and semiarid Africa. Subtle change is possible; some approaches do work. These limited success stories show, however, that new land use techniques must recognize, consider, and work within the basic social, economic, and cultural frameworks of the people involved. Agroforestry would appear to be almost uniquely capable of integrating these diverse environmental, social, and economic variables into coherent, stable systems of production.