The Creeping Disaster of Land Degradation in Africa.
Paul L.G. Vlek and Lulseged T. Desta. Center for Development Research, Walter-Flex-Str. 3, Bonn, Germany
Land is defined as the ensemble of soil, its constituent biotic components in and on it, and its landscape and climatic attributes. Land degradation is mainly due to the interaction of the land with its users and should thus be considered a social problem that can be avoided. If recognized too late the process may lead to disasters and human insecurity. In the humid tropics, for example, conditions differ quite markedly from those in the arid subtropics; just as conditions in the rainfed uplands differ from those in the irrigated river valleys. Hence each case of land degradation must be considered and treated individually with consideration of the site-specific factors and processes at play. Our ancestors seem to have continuously affected their environment in ways that tend to destabilize natural ecosystems such as burning, clearing, domestication and cultivation. Once established, agriculture became the chief agent of environmental transformation. Its deleterious effect on land depends on the intensity (mode and duration) of tillage and other forms of mechanical disturbance (including traffic and compaction, irrigation, etc.), as well as the pattern and intensity of cropping, and the consequent net export of nutrients from the field. Cultivation and the subsequent removal of the crop tend to deplete the organic-matter and the nutrient reserves of the soil by speeding up the rate of decomposition; reducing replenishment through plant and animal residues, and causing topsoil erosion. Resulting rates of nutrient depletion in Africa range from a moderate (30 to 60 kg of nitrogen, phosphorus and potassium per hectare, per year in the humid forests and wetlands in southern and Central Africa) to high (more than 60 kg in the East-African Highlands and West African Savannas). Moreover, the moment a farmer arbitrarily separates a tract of land from the adjoining area, for the purpose of cultivation, he is in effect declaring war on the native species. The local flora and fauna are then treated as weeds, or pests to be eradicated by all possible means. As long as agriculture was confined to small localized areas, while the greater continental area remained practically undisturbed, the African environment as a whole was not threatened. Degraded land could be abandoned and thus allowed to recover gradually, while new tracts were cleared, in succession. However, with the population growth, brought about by modern medicine and by the very success of agriculture in improving food security, the cultivated enclaves also grew, until entire extensive regions were subject to continuous grazing or cultivation. To compensate for the loss of natural fertility and to achieve ever-higher yields, farmers have utilized increasing quantities of chemical fertilizers and pesticides. In arid regions, irrigation has been introduced to overcome drought. Erosion, water logging, salinization, pollution, and the eradication of numerous species – such events were the unforeseen, but are now global consequences of humanity's expansive and often injudicious management of soil and water resources. Land degradation has been taking place since the dawn of agriculture. What is new is the intensity of degradation in recent times. The soils of the world are claimed to have lost, on average, 25.3 million tons (M tons) of humus per year since agriculture began some 10,000 years ago. However over the last 300 years the average loss was 300 million tons per year; and in the past 50 years this average has reached 760 million tons. In essence, the last 50 years have been a saga of economic growth and ecological loss. It is argued that the 6 million hectare in annual loss to degradation is practically irreversible and an estimated 1860 M ha, or little more than half of the desertified area worldwide, requires rehabilitation. The cost of rehabilitation over a 20-year period was calculated to be about US$ 213 billions. If not rehabilitated, the income foregone (over a 20-year period) could equal a staggering US $ 564 billions. The cost of replacing nutrients lost from arable land in countries of sub-Saharan Africa is estimated to range from <1% to as high as 25% of the national Agricultural Gross Domestic Product. Even if corrected downward the magnitude of the problem remains evident. Land degradation is a creeping event. The cost of preventing land degradation is not high if action is taken early enough. Once it reaches a point where reclamation becomes economically prohibitive, the land must be abandoned. Late diagnosis adds to the cost of reclamation and can render land practically irrecoverable, causing sustained environmental damage. A much better monitoring and regular reporting on the state of our lands, as is done for our climate by the IPCC, would be a prudent investment.