Despite its pervasive poverty, sub-Saharan Africa has substantial natural resources in its rural areas, including forests and grasslands, wetlands, cultivable soils, and other biological resources.8 Although only 40 percent of the total land area is under cultivation or used for pasture, much of it is threatened by one form of damage or another.
Three types of environmental damage are occurring in rural areas of Sub-Saharan Africa: deforestation, degradation, and fragmentation. Deforestation is defined as "the temporary or permanent clearance of forest for agriculture or other uses, resulting in the permanent depletion of the crown cover of trees to less than 10 percent."9 Degradation, on the other hand, refers to the temporary or permanent deterioration in the density or structure of vegetation cover or species composition.10 It results from the removal of plants and trees important in the life cycle of other species, from erosion, and from other adverse changes in the local environment. Fragmentation arises from road construction and similar human intrusions in forest areas; it leaves forest edges vulnerable to increased degradation through changes in micro-climates, loss of native species and the invasion of alien species, and further disturbances by human beings.
While there is no doubt that all three processes are taking an increasingly heavy toll on the forest and woodland areas of sub-Saharan Africa, there is considerable controversy over the exact rate at which this is occurring. Estimates based on the subjective judgment of experts or on data from low-resolution sensors on weather satellites are generally higher than those based on the more accurate data from high-resolution sensors on the Landsat and Spot satellites.11 Until more of the latter data are available, the actual extent of deforestation will remain uncertain.
The United Nations Food and Agriculture Organization (FAO) estimates that forested land was converted to agricultural uses at increasing rates over the period 1981 to 1990 and that such changes accounted for 25 percent of the changes in forest cover during the period.12 These changes were concentrated in the moist and dry forest lowland areas, where the average annual conversion rate was higher than in tropical rain forest areas. Except for the dry forest areas, however, conversion rates in sub-Saharan Africa are lower than those in Latin America and the Asia-Pacific region.
Degradation and fragmentation involve a much larger area than deforestation and pose a greater threat to the diversity of plant and animal life. Selective logging and the failure to pursue a systematic program for forest regeneration (either natural or artificial) are the two major factors promoting rapid degradation of the forest and woodland environment. Owing to the desperate need for foreign exchange, the rate of logging in sub-Saharan Africa rose more than 34 percent between 1979 and 1991, compared with a global average of only 19 percent. Similarly, the lack of foreign exchange to purchase petroleum has led to a rapid rise in the production of fuelwood and charcoal.13
There are no firm estimates of the harm resulting from degradation and fragmentation in the region. Two factors suggest that it is considerable, however: First, the ratio of forest regeneration to deforestation is as low as 1:32 in sub-Saharan Africa, compared with the ratios in 1:2 in Asia and 1:6 in Latin America.14 Second, one out of every six species in the tropical moist forests has some economically valuable, non-timber use.15
Nowhere is this loss of biological resources more marked than in the region's wetlands. These wetlands include river floodplains, freshwater swamps and lakes, and coastal and estuarine environments. They provide a number of valuable resources, including wood; foraging, hunting, and fishing opportunities; and land for crops and pasture. They also contribute significantly to aquifer recharge and flood control, as well as providing habitat for migratory birds and other organisms.
Degradation of these wetlands is due not to population growth or poverty but to modern development, principally the construction of major dams on important rivers. These dams control water flow over much of the rivers' length and impair the agricultural value of wetlands both by lowering water quality and by altering the extent and timing of floods.16 In Nigeria's Benue floodplain, for instance, the reduction in flooding caused by the Lagdo Dam led to a 50 percent reduction in the area used for environmentally friendly flood-recession sorghum farming in the dry years of the mid-1980s.17 Similarly, the Diama Barrage on the Senegal River, built to prevent incursion of salt water during periods of low river flow, is expected to cause the loss of some 7,000 tons of shrimp and fish, while Manantali Dam is expected to greatly reduce the fish catch in that river.
If wetlands are being degraded by inappropriate development, grasslands and other relatively dry areas are being degraded by both rapid population growth and inappropriate technology and land-use practices. Recent studies, however, highlight the resilience of dryland ecosystems and caution against confusing natural changes due to recurring droughts with the long-term degradation caused by human activities.18 They also argue against the simplistic application of the general concepts of overgrazing and carrying capacity in dryland environments.
This is not to say that such factors as overgrazing, overcultivation, and excessive use of wood for fuel have not contributed to the degradation of drylands. Rather, it is to stress that degradation occurs only where these activities lead to detrimental changes to the soil system itself as well as to plant cover. Damage to the soil system results either from erosion or from physical and chemical changes in the soil itself. Erosion by wind or water is a serious problem in dryland areas because the naturally thin soil and its slow rate of formation make recovery difficult. Such erosion accounts for nearly 86 percent of the total degradation of dryland areas in sub-Saharan Africa.19 The remainder is primarily due to the loss of nutrients from excessive cultivation and lack of fertilization.
Estimates based on the GLASOD (Global Assessment of Soil Degradation) approach indicate that by 1992 nearly 320 million hectares of drylands in sub-Saharan Africa had degraded soils, ranging from light and moderate (77 percent) to strong and extreme (23 percent).20 These estimates, however, represent a considerable (almost two-thirds) reduction in the area previously thought to be suffering desertification as a result of human activities. Improved monitoring capabilities are making it increasingly clear that climatic variations are responsible for much of the degradation of soils in the region.
Even so, the loss of biological diversitydue to habitat destruction, the introduction of exotic species, overharvesting, pollution, and other activities that affect natural ecosystemsis a growing problem in sub-Saharan Africa. This is especially significant because biodiversity is greatest in the tropics. According to one estimate, between 40 and 90 percent of all plant and animal species are found in tropical forests.21 Based on current trends in habitat destruction, as many as 11 percent of total species may become extinct during every 10-year period from 1975 to 2015.
Despite international agreements such as the Convention on Endangered Species of Flora and Fauna (CITES), hunting of elephants, rhinoceroses, and alligators is still a major problem in some African countries. The situation is even more serious in the case of birds, because widespread pollution is destroying their habitats, often in imperceptible ways. Tragically, although most endangered species are technically under government protection, as a practical matter they are resources free for the taking.
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