Although often severe, the problems which arise in most areas experiencing seasonal or contingent drought are seen as transitory, disappearing when the rains return. If the rains do not return, the land becomes progressively more arid until, eventually, desert conditions prevail. This is the process of desertification in its simplest form. When considered in this way, desertification is a natural process which has existed for thousands of years, is reversible, and has caused the world's deserts to expand and contract in the past. This is, however, only one approach to desertification—one which sees the process as the natural expansion of desert or desert-like conditions into an area where they had not previously existed. This process, occurring along the tropical desert margins, was referred to originally as 'desertization' (Le Houerou 1977), but the more common term now is 'desertification', and the concept has been expanded to include a human element.

There is no widely accepted definition of desertification. Most modern approaches, however, recognize the combined impact of adverse climatic conditions and the stress created by human activity (Verstraete 1986). Both have been accepted by the United Nations as the elements that must be considered in any working definition of the process (Glantz 1977). The United Nations Environment Program (UNEP) has tended to emphasize the importance of the human impact over drought, but the relative importance of each of these elements remains very controversial. Some see drought as the primary element, with human intervention aggravating the situation to such an extent that the overall expansion of the desert is increased, and any recovery—following a change in climatic conditions, for example—is lengthier than normal. Others see direct human activities as instigating the process. In reality, there must be many causes (see Figure 3.12) which together bring desert-like conditions to perhaps as much as 60,000 sq km of the earth's surface every year and threaten up to 30 million sq km more. The areas directly threatened are those adjacent to the deserts on all continents. Africa is currently receiving much of the attention, but large sections of the Middle East, the central Asian republics of the former Soviet Union, China adjacent to the Gobi Desert, northwest India and Pakistan, along with parts of Australia, South America and the United States are also susceptible to desertification. Even areas not normally considered as threatened, such as southern Europe from Spain to Greece, are not immune (see Figure 3.2b). At least 50 million people are directly at risk of losing life or livelihood, in these regions. In a more graphic illustration of desertification, the United States Agency for International Development (USAID), at the height of the Sahelian drought in 1972, claimed that the Sahara was advancing southwards at a rate of as much as 30 miles (48 km) (Pearce 1992f). Although these specific numbers are not universally accepted—Nelson (1990), for example, has suggested that all such data be treated with a healthy scepticism—they do give an indication of the magnitude of the problem, and the reason that there has been increasing cause for concern in recent years (van Ypersele and Verstraete 1986).

Desertification initiated by drought

Human nature being what it is, attitudes to drought include a strong element of denial, and when drought strikes there is a natural tendency to hope that it will be short and of limited intensity. According to Heathcote (1987), for example, the traditional Australian approach to drought has been to denigrate it as a hazard and to react to its onset with surprise. The inhabitants of drought-prone areas, therefore, may not react immediately to the increased aridity, particularly if they have progressed beyond the hunting/gathering socio-economic level. They may continue to cultivate the same crops, perhaps even increasing the area under cultivation to compensate for reduced yields, or they may try to retain flocks and herds which have expanded during the times of plenty. If the drought is prolonged in the arable areas, the crops die and the bare earth is exposed to the ravages of soil erosion. The Dustbowl in the Great Plains developed in this way. Once the available moisture had been evaporated, and the plants had died, the wind removed the topsoil—the most fertile part of the soil profile—leaving a barren landscape, which even the most drought-resistant desert plants found difficult to colonize (Borchert 1950). In the absence of topsoil there was nothing to retain the rain which did fall. It rapidly ran off the surface, causing further erosion, or percolated into the ground-water system where it was beyond the reach of most plants.

Prolonged drought in pastoral areas is equally damaging. It reduces the forage supply, and, if no attempt is made to reduce the animal population, the land may fall victim to overgrazing. The retention of larger herds during the early years of the Sahelian drought, for example, allowed the vegetation to be overgrazed to such an extent that even the plant roots died. In their desperation for food, the animals also grazed on shrubs and even trees, and effectively removed vegetation which had helped to protect the land. The flocks and herds had been depleted by starvation and death by the time this stage was reached, but the damage had been done. The wind, its speed unhampered by shrubs and trees, lifted the exposed, loose soil particles and carried them away, taking with them the ability of the land to support plant and animal life. In combination these human and physical activities seemed to be pushing the boundaries of the Sahara Desert inexorably southwards, to lay claim to territory which only recently supported a population living as comfortably as it could within the constraints of the environment. Out of this grew the image of the 'shifting sands', which came to represent desertification in the popular imagination. As an image, it was evocative, but the reality of such a representation has been increasingly questioned in the 1990s (Nelson 1990; Pearce 1992f).

Desertification caused by human activity

Climatic variability clearly made a major contribution to desertification, in both the Sahel and the Great Plains—perhaps even initiating the process—and in concert with human activities created serious environmental problems. An alternative view sees human activity in itself capable of initiating desertification in the absence of increased aridity (Verstraete 1986). For example, human interference, in areas where the environmental balance is a delicate one, might be sufficient to set in motion a train of events leading eventually to desertification. The introduction of arable agriculture into areas more suited to grazing, or the removal of forest cover, to open up agricultural land or to provide fuelwood, may disturb the ecological balance to such an extent that the quality of the environment begins to decline. The soil takes a physical beating during cultivation: its crumb structure is broken down and its individual constituents are separated from each other. In addition, cultivation destroys the natural humus in the soil and the growing crops remove the nutrients, both of which normally help to bind the soil particles together into aggregates. If nothing is done to replace the organic material or the nutrients, the soil then becomes highly susceptible to erosion. Modern agricultural techniques, which allow the soil to lie exposed and unprotected by vegetation, for a large part of the growing season, also contribute to the problem. When wind and water erode the topsoil it becomes impossible to cultivate the land, and even natural vegetation has difficulty re-establishing itself in the shifting mineral soil that remains.

The removal of trees and shrubs to be used as fuel has had similar effects in many Third World nations, where the main source of energy is wood. In Sudan, for example, the growing demand for fuelwood was a major factor in the reduction of the total wood resource by 3.6 per cent annually in the 1970s and early 1980s (Callaghan et al. 1985). Le Houerou (1977) has estimated that, in the areas along the desert margins in Africa and the Middle East, a family of five will consume, every year, all of the fuel available on one hectare of woody steppe. With a population close to 100 million dependent upon this form of fuel in the area concerned, as much as 20 million hectares per year are being destroyed, and all of that area is potentially open to desertification.

No change in the land-use is required to initiate such a progression, in some regions. The introduction of too many animals into an area may lead to overgrazing and cause such environmental deterioration that after only a few years the land may no longer be able to support the new activity. Forage species are gradually replaced by weeds of little use to the animals, and the soil becomes barren and unable to recover even when grazing ceases. In all of these cases, the land has been laid waste with little active contribution from climate. Human activities have disturbed the environmental balance to such an extent that they have effectively created a desert.

Although human activities have been widely accepted as causing desertification, and the processes involved have been observed, there is increasing concern that the human contribution has been overestimated. Current academic and popular attitudes to desertification owe a lot to the findings of a United Nations Conference on Desertification (UNCOD) held in Nairobi, Kenya in 1977. At that conference, the role of human activities in land degradation was considered to be firmly established, and the contribution of drought was seen as secondary at best. Since human action had caused the problem, it seemed to follow that human action could solve it. In keeping with this philosophy, UNEP was given the responsibility for taking global initiatives to introduce preventive measures which would alleviate the problem of desertification (Grove 1986). Fifteen years and $6 billion later, few effective counter measures have been taken, and the plan of action is widely seen as a failure (Pearce 1992a).

The data upon which the UNEP responses were based are now considered by many researchers to be unrepresentative of the real situation. Nelson (1990), for example, has suggested that the extent of irreversible desertification has been over-estimated, although he does not deny that it remains a serious concern in many parts of the world. The main problems with the data arose from the timing and method of collection, and were aggravated by the UNEP premise that human activity was the main cause of the land degradation that produced desertification. The basic data, apparently indicating the rapid creation of desert-like conditions, were collected in the early 1970s at a time of severe drought in sub-Saharan Africa. They therefore failed to give sufficient weight to the marked rainfall variability characteristic of the area, and in consequence over-represented the effects of the drought. A great deal of the information was obtained using remote sensing. The changing location of vegetation boundaries were identified from satellite photography, for example. This seemed to confirm the steady encroachment of the desert in areas such as the Sudan, and the results were incorporated in the UNCOD report of 1977. Since then, however, they have been widely disputed, and subsequent studies have found no evidence that the large scale desertification described in the 1970s continued into the 1980s. (For summaries of current thinking on desertification see Nelson (1990), Pearce (1992f) and Hulme and Kelly (1993).)

Failure to appreciate the the extent of annual fluctuations in vegetation boundaries— differences of as much as 200 km were reported on the Sudan/Chad border between 1984 and 1985—combined with inadequate ground control may have contributed to the problem (Nelson 1990). A general consensus seems to be forming among those investigating the issue that the approach to defining desertification in terms of vegetation needs to be re-examined. In parts of East Africa, for example, drought and possibly overgrazing have combined to allow the normal grass cover to be replaced by thorn scrub. On satellite photography this appears as an improvement in vegetative cover, yet from a human and ecological viewpoint it is a retrograde step (Warren and Agnew 1988). A more accurate approach to land degradation might be to study the soil. Vegetation responds rapidly to short-term changes in moisture, but damage to soil takes much longer to reverse. Thus, the measurement of soil conditions—nutrient levels, for example—might give a more accurate indication of the extent of land degradation (Pearce 1992f).

UNEP's insistence on explaining most desertification as the result of human activities may also have contributed to the misrepresentation of the extent of the problem. Natural causes such as short-term drought and longer-term climatic change were ignored or given less attention than they deserved, yet both can produce desert-like conditions without input from society. With short-term drought, the vegetation recovers once the drought is over; with changes induced by lengthier fluctuations, little improvement is likely even if the human use of the land is altered. The inclusion of areas suffering from short-term drought may well have inflated the final results in the UNEP accounting of land degradation. Failure to appreciate the various potential causes of desertification would also limit the response to the problem. Different causes would normally elicit different responses, and UNEP's application of the societal response to all areas, without distinguishing the cause, may in part explain the lack of success in dealing with the problem (Pearce 1992f).

The prevention and reversal of desertification

The debunking of some of the myths associated with desertification, and the realization that even after more than 15 years of study its nature and extent are inadequately understood, does not mean that desertification should be ignored. There are undoubtedly major problems of land degradation in many of the earth's arid lands.

Table 3.3 Action required for the prevention and reversal of desertification

1 Prevention a Good land-use planning and management e.g. cultivation only where and when precipitation is adequate animal population based on carrying capacity of land in driest years maintenance of woodland where possible b Irrigation appropriately managed to minimize sedimentation, salinization and waterlogging c Plant breeding for increased drought resistance d Improved long-range drought forecasting e Weather modification e.g. rainmaking snowpack augmentation f Social, cultural and economic controls e.g. population planning planned regional economic development education

2 Reversal a Prevention of further soil erosion e.g. by contour ploughing by gully infilling by planting or constructing windbreaks b Reforestation c Improved water use e.g. storage of run-off well-managed irrigation d Stabilization of moving sand e.g. using matting by re-establishment of plant cover using oil waste mulches and polymer coating e Social, cultural and economic controls e.g. reduction of grazing animal herd size population resettlement

Perhaps sensing an increased vulnerability as a result of the current controversy, and certainly fearful of being left behind in the rush to deal with the problems of the developed world, the nations occupying the land affected appeared at the Rio Earth Summit in 1992, and proposed a Desertification Convention to address their problems. Despite its lack of success following UNDOC, the provisions of the Convention are likely to be managed by UNEP, which has proposed a budget of $450 billion over 20 years (Pearce 1992f).

Although obscured by the current controversy and lost in the complexity of the attempts to define the issue of desertification more accurately, two questions remain of supreme importance to the areas suffering land degradation. Can desertification be prevented? Can the desertification which has already happened be reversed? In the past, the answer to both has always been a qualified yes (see Table 3.3) and seems likely to remain so, although some researchers take a more pessimistic view (e.g. Nelson 1990). In theory, society could work with the environment by developing a good understanding of environmental relationships in the threatened areas or by assessing the capability of the land to support certain activities, and by working within the constraints that these would provide. In practice, non-environmental elements—such as politics and economics—may prevent the most ecologically appropriate use of the land. A typical response to the variable precipitation, in areas prone to desertification, is to consider the good years as normal and to extend production into marginal areas at that time (Riefler 1978). The stage is then set for progressive desertification when the bad years return. Experience in the United States has shown that this can be prevented by good land-use planning, which includes not only consideration of the best use of the land, but also the carrying capacity of that land under a particular use (Sanders 1986). To be effective in an area such as Africa, this would involve restrictions on grazing and cultivation in many regions, but not only that. Estimates of the carrying capacity of the land would have to be based on conditions in the worst years rather than in the good or even normal years (Kellogg and Schneider 1977; Mackenzie 1987b). Such actions would undoubtedly bring some improvement to the situation, but the transition between the old and new systems might well be highly traumatic for the inhabitants of the area. Stewart and Tiessen (1990), for example, point out that in the Sahel cattle are a form of crop insurance. When the crops fail, farmers plan to survive by selling some of their cattle. Any attempt to limit herds, and prevent overgrazing, must therefore be accompanied by a suitable replacement for this traditional safety net. Without it the pastoralists would lose the advantages of larger flocks and herds in the good years. Some of the cultivators might have to allow arable land to revert to pasture—or reduce cash-cropping and return to subsistence agriculture—and members of both groups might have to give up their rural life-style and become urbanized.

As with the other elements associated with land degradation, the widely accepted relationship that linked growing numbers of livestock to overgrazing and the eventual onset of desertification, has been questioned (Nelson 1990). This in turn has led to a reassessment of the methods by which desertification in pastoral areas can be prevented. Traditional herding techniques involving nomadism and the acceptance of fluctuating herd sizes seem particularly suited to the unpredictable environment of an area such as the Sahel. The nomadic herdsmen of that region may in fact be better managers of the land than the farmers in the wetter areas to the south (Warren and Agnew 1988; Pearce 1992f). They may also know more about dealing with pastoral land-use problems than they are given credit for by scientists from the developed nations. Pearce (1992f) has concluded that there is no evidence that nomadic herdsmen in places like the Sahel actually destroy their pastures. They represent the best way to use land in an area where there is no natural ecological equilibrium, only constant flux. That situation may apply only as long as the flux remains within certain established limits. Too much change in one direction, as occurs during major drought episodes, without concomitant change in herding methods could still encourage desertification. Although the links between herd size, overgrazing and land degradation are considered less firm than was once thought, they have not yet been disproved, and it does not follow that they are entirely absent. In attempts to deal with desertification in pastoral areas, such links cannot be ignored. They clearly need additional investigation.

The problem of the destruction of woodland will also have to be addressed if desertification is to be prevented. Trees and shrubs protect the land against erosion, yet they are being cleared at an alarming rate. One hundred years ago in Ethiopia, 40 per cent of the land could be classified as wooded; today only 3 per cent can be designated in that way (Mackenzie 1987b). Good land-use planning would recognize that certain areas are best left as woodland, and would prevent the clearing of that land for the expansion of cultivation or the provision of fuel wood. The latter problem is particularly serious in most of sub-Saharan Africa where wood is the only source of energy for most of the inhabitants. It also has ramifications which reach beyond fuel supply. Experience has shown that where wood is not available animal dung is burned as a fuel, and although that may supply the energy required, it also represents a loss of nutrients which would normally have been returned to the soil. Any planning involving the conservation of fuelwood must consider these factors, and make provision for an alternative supply of energy or another source of fertilizer.

Many of the techniques which could be employed to prevent desertification are also considered capable of reversing the process. Certainly there are areas where the destruction of the land is probably irreversible, but there have also been some successes. In parts of North America, land apparently destroyed in the 1930s has been successfully rehabilitated through land-use planning and direct soil conservation techniques such as contour ploughing, strip cropping and the provision of windbreaks. Irrigation has also become common, and methods of weather modification, mainly rain making, have been attempted, although with inconclusive results (Rosenberg 1978). Many of these methods could be applied with little modification in areas, such as Africa, where desertification is rampant. Dry-farming techniques have been introduced into the Sudan (CIDA 1985); in Ethiopia, new forms of cultivation similar to contour ploughing have been developed to conserve water and prevent erosion (Cross 1985b); in Mali and other parts of West Africa, reforestation is being attempted to try to stem the southward creep of the desert (CIDA 1985). Most observers consider the success rate of such ventures to be limited (Pearce 1992f). Problems arise from the introduction of inappropriate technology, from the unwillingness of farmers or pastoralists to adopt the new methods and from a variety of economic factors, including, for example, fertilizer costs and the availability of labour (Nelson 1990). There is clearly no universal panacea for desertification. Solutions will have to continue to be specific to the issue and the location, but even then there can be no guarantee that solutions which appear ideal in the short-term will not ultimately exacerbate the problem. The lack of moisture has been tackled directly in many areas, for example, by the drilling of boreholes to provide access to groundwater. Logical as this may seem, without strict control, it may not be the best approach. Extra water encourages larger flocks and herds which overgraze the area around the borehole. Le Houerou (1977) has pointed out that around some of the boreholes drilled at the time of the Sahelian drought, the pasture was completely destroyed within a radius of 15-30 km around the bore. Subsequent investigation, however, has suggested that this was primarily a local problem at only a few wells, and its impact was therefore much less than originally estimated (Pearce 1992f).

All of these developments deal directly with the physical symptoms of desertification, but it has been argued that many studies have overlooked economic and social constraints (Hekstra and Liveman 1986). Ware (1977) has suggested, for example, that insufficient development of markets, transportation and welfare systems made a major contribution to the problems in the Sahel, and future planning must give these factors due consideration. The profit motive is also an important factor in some areas. In Kenya, experience in agroforestry schemes indicates that the best results are achieved when the farmers can see clear and immediate rewards in addition to the less obvious longer-term environmental benefits (Pegorie 1990). On the human side, population growth rates and densities must be examined with a view to assessing human pressure on the land. Over-population has traditionally been regarded as an integral part of the drought/famine/ desertification relationship, but that too has been re-examined. Mortimore (1989), for example, has suggested that high population densities may not be out of place in areas where proposed soil and water conservation schemes are labour intensive. Ironically, some areas suffer from rural depopulation. In the early 1980s, urban populations across Africa increased at about 6 per cent per year, due in large part to the exodus from rural areas (Grove 1986). Where relief from population pressure is needed, it may come in the form of family planning or through relocation. Despite potentially serious social and political concerns, these may be the only ways to tackle the population problem (Mackenzie 1987b).

The fight against desertification has been marked by a distinct lack of success. Recent reassessments of the problem, beginning in the late 1980s, suggest that this may be the result of the misinterpretation of the evidence and a poor understanding of the mechanisms that cause and sustain the degradation of the land. The additional research required to resolve that situation will further slow direct action against desertification, but it may be the price that has to be paid to ensure future success.

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  • bianca
    What environmental problem is caused by desertification in africa?
    4 years ago

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