Desertification in Sahelian Africa
by L. STROOSNIJDER
The word desertification has gained worldwide recognition since the 1977 United Nations Conference on Desertification in Nairobi, Kenya. However, a comprehensive and generally accepted definition for this complex phenomenon is still lacking. The reader might, there fore, benefit from a kind of visualisation of what is meant by 'desertification'.
On the small spatial scale, the Sahelian zone (in the regional sense) shows a distinct north-south gradient in natural vegetation cover. From being almost devoid of vegetation at the Sahara border in the north, it proceeds, via a Sahel steppe dominated by annual species, into a Sudanian and Guinean savannah with a higher tree density and more perennial grasses. On the large scale, local variation, due to a multitude of factors, is extremely wide, with bare spots next to dense forests.
Due to the semi-arid climate, the natural vegetation is highly dynamic in terms of production as well as in species composition. Again, two scales should be distinguished. Sequences of 3-10 years of drier and wetter (than the average) years occur. This results in north-south shifts (and vice versa) of the various vegetation zones and of certain species (perennial grass is a classic example) of hundreds of kiLométres. In addition, inter-annual variation, often on a large spatial scale, makes vegetation look very different from one year to another.
This dynamism has often misled western scientists visiting the area for a brief period only, and has led to many wrong conclusions with respect to the potential (in wetter years) and desertification (in dryer years) of the area. Shifting dunes at the fringe of the Sahara, spectacular as it may look, should certainly not be regarded only as desertification. Desertification occurs everywhere within the Sahelian zone where humaninduced physical and chemical soil degradation reduces the capacity of the ecosystem to recover from short or long periods of drought and/or overexploitation.
The natural vegetation of the Sahelian zone has been remarkably resilient to climatic changes and for decades, perhaps centuries, there has been a dynamic equilibrium. However, the present fear is that due to a number of interfering causes, such a dynamic equilibrium does not exist any more and that irreversible changes are occuring. Desertification may be taking place right now all across Sahelian Africa!
Significance of the problem
There is overwhelming evidence, though not always expressed in quantitative figures, that the vegetation cover has decreased in recent decades. This can be shown by time series of satellite images, aerial photographs and vegetation surveys. Such surveys also provide information about dramatic changes in vegetation composition, such as the disappearance of perennial grasses, in coverage of shrubs and trees, the replacement of annual species with a long growing cycle by those with a short one and an overall decrease in biodiversity.
It is less clear whether it is the vigour of resilience that has decreased or the effectiveness of that vigour. Restoration of perennial grasses for instance needs a number of years. It is a striking observation that in many cases, on land that has been fenced, perennial grasses germinate in situations where the nearest plants that produce seeds are tens of kiLométres away. However, physical or chemical degradation or lack of protection due to overgrazing may reduce the effectiveness of a still existing vigour. Other land has been physically degraded to the extent that even with protection by fencing, no spontaneous vegetation recovery occurs and germination is observed only after breaking of the soil's crust.
The decrease in vegetation cover leads to a change in reflectance of solar radiation (albedo) and there is a fear that this might damage the climate, i.e. by causing higher temperatures and less precipitation. The fact is that in many locations in the Sahel rainfall has decreased over a period of 20 years. However, since historical rainfall records are scarce, it is still not proven by agroclimatologists whether this decrease is more than a natural long-term persistent dry spell.
The local population experiences the change in daily life. Women suffer from the lack of trees for firewood. Fuelwood is consumed faster than it is produced and cattle dung and crop residues are used more and more as fuel. Soil fertility has declined so that ever more hectares are needed to obtain the same food production. This leads to an expansion of the area used for arable farming which is even faster than population growth, leaving large tracts of land with too little protective vegetation cover and susceptible to wind and water erosion during part of the year.
Under natural conditions, i.e. without external inputs by man, annual biomass production is in equilibrium with the amounts of available water and plant nutrients. Geologically, the African Sahel is an old weathered landscape with chemically poor soils so that the majority of plant nutrients are stored in the organic matter of the soil. Each year, about 2 % of the available amount of organic matter mineralises so that nitrogen (N) and phosphorus (P), which are the main plant nutrients, become available. In order to maintain the stock of soil organic matter at an equilibrium level, fresh organic material must be added to the soil each year and converted into soil organic matter by soil (micro)biological activity.
Decades ago, with fewer people to feed, farmers were able to maintain the fragile natural resource base by utilising pastoral animal husbandry systems and shifting agriculture for crop production. In a situation of dynamic equilibrium, the formation of biomass was equal to the losses, leading to a constant level of soil organic matter. Losses were due to biological breakdown of dried or dead biomass, occasional burning as the result of lightning and the limited use of biomass by man and animals. The presence of perennial grasses and trees with their considerable stock of above- and below-ground biomass (root systems) had a stabilising influence on year-to-year variations.
In recent decades, biomass losses have increased rapidly. Man started burning the savannah as a management practice and this resulted in a significant loss of carbon and nitrogen. The livestock population increased as a result of the drilling of water holes and improved services, hence consumption of biomass increased. In the opening-up of land for arable farming, huge amounts of biomass were burned and the organic matter in the top soil was carried away by water and wind erosion. Gradually, under the influence of long persistent droughts, the occurrence of perennial grasses and trees, with their slow and long growing cycles, has decreased, thus reducing the buffering capacity of the biomass-soil organic matter turnover system.
The resulting decrease in the organic matter content of the soil means that fewer plant nutrients become available each year, triggering a downward spiral in biomass production. In addition, a lower soil organic matter content also has a physical influence on the soil. Soil structure decreases and surface crusting becomes the rule rather than the exception. The proportion of the annual rainfall that does not infiltrate into the soil but runs off into depressions or rivers can increase by up to 60%. This further aggravates the downward spiral in biomass production.
Much has been theorised in the literature about who to blame for desertification. In our view it is certainly not the ignorance, obstinacy or lack of interest of the local population or the 'tragedy of the common man' or colonial imperialism. The central issue is overpopulation: not in absolute terms since Sahelian population density is among the lowest in the world, but in relative terms with respect to the 'natural' carrying capacity as determined by poor natural resources and the harsh climate. In this respect lessons can be learned from agricultural development which occurred, relatively recently, in the developed world. There, economic development in other sectors of the economy provided the means to supply inputs to the agricultural sector, thus boosting the carrying capacity of the environment.
Experiences: what does not work
If we understand and accept that, in order to stop further desertification or reverse the present trend, we must increase biomass production, we can also understand why so many concepts intended to fight desertification have failed. To mention a few:
(1) Attempts based on the idea that the low biomass production is due to water shortage have failed. Plants need both water and nutrients and both are in low supply. By improving one of the two, the other quickly becomes the growth-limiting factor.
Hints towards a direction that might work
(1) Without external inputs, climatic change in the positive sense or drastic changes in land use, desertification will continue and probably at an increasing rate.
What is going on?
Our understanding of the complexity of 'the Sahelian problem', of which desertification is part, has increased. We have accepted that the washed-out state of an area may be linked to an area with excess manure elsewhere in the world. In other words, we are aware of the global nature of environmental problems which can only be solved if international terms of trade are taken into account. There is a world-wide interest in environmental studies in a global context. More and more comparative studies are being started and is education changing from being site and country specific to dealing with underlying concepts and understanding.
Since 1976, regional research in the Sahel has been coordinated by the Sahel Institute (INSAH) in Bamako, Mali. This is the result of coordination between Sahelian countries and donors (CILSS and Club du Sahel). INSAH's 1990-1994 anti-desertification programme comprises the following three aspects: (1) improvement of soil and water conservation measures with an emphasis on nutrient conservation, (2) reafforestation with an emphasis on local multi-purpose species and (3) monitoring the dynamics of desertification by building a data base. This all looks very promising but there is a fear, based on experience, that too much bureaucratic coordination kills initiatives and actions.
In some Sahelian countries there has, since colonial times, been an export commodity oriented infrastructure. Examples are the networks for cotton and irrigated rice in Mali and groundnuts in Senegal. The gradual transformation from colonial to national management of these networks has paved the way to use this infrastructure more and more for combating degradation.
The World Conservation Union (IUCN) has a special Sahel Programme which focuses on nature conservation by improving subsistence security and lengthening the time horizon of the local population. Nevertheless many projects wrongly take 'ignorance' of the local population as their starting point.
The European Community supports a research network (R3S) that studies, among many other topics, agricultural intensification by improving irrigation in inland valleys. Indirectly this reduces the pressure for the expansion of rainfed agriculture on marginal soils. The Organisation for Economic Cooperation and Development (OECD) undertakes studies looking at alternative development scenarios for the Sahel. All this helps to mobilise national and international opinion for political change.
Studies are undertaken to understand feedback mechanisms in global climate changes. Is it true that changes in reflection due to the decreased vegetation cover cause rising surface temperature and affects the local climate? And does increased runoff lead to a reduction in precipitation ?
A large number of forestry oriented projects attempt to solve the shortage of wood. Communal systems have a bad record of success, private approaches seem better. The majority of these projects still assume that there is a significant potential for natural resilience. Quantitative estimates of cycles of and the need for water and nutrients to achieve certain production goals are often lacking.
So-called integrated projects help the local population with a variety of short duration improvements but leave longterm prospects hidden.
Though the message seems old-fashioned, outdated and not popular, the slow progress in reducing population growth is a major constraint in fighting desertification. It is too easy to state, and presented as a law of nature, that family planning in sub-Saharan Africa will be successful only if poverty is eradicated. Family planning has been successful in countries like Indonesia and Thailand and seems more related to education and communication levels than to poverty The local population, at least the women, seems to be aware of the circular nature of such reasoning; poverty is the result of population growth and population growth cannot be stopped because of poverty. The large migration out of marginalised areas and the subsequent social sufferings form the basis of knowledge of and willingness for family planning, provided the means are made available.
At present, a great deal of project organised development aid is spent in the Sahel. Most is of short duration, embraces only a small area and is, in spite of much research during recent decades,; based on the wrong assumptions.
Local institutions, including governments, are not able to cope with the complex problem and the massive assistance that is needed to halt desertification.
The limited education and health status of the local population as well as the vacuum of social structure between old and new institutions hampers the bottom-up approaches which are needed for a real breakthrough in cooperation.
The economic conditions of the local population, their governments and terms of trade in the world market do not allow a competitive development of the agricultural sector. Development of other economic sectors which should provide the means for agricultural inputs is not likely.
Finally, too much emphasis and public support is still being given to cosmetic actions eradicating symptoms instead of attacking basic problems and constraints. For the large part, this is due to the stereotype image of African poverty and ignorance that is presented by the western press. This is justified as the only way to maintain public support for donor aid but it has, in reality, more to do with the I sensationalist nature of the popular press.
The above discussion of desertification in Sahelian Africa is very general. It should be realised that there are large local differences and that combating desertification is only possible if the local conditions are carefully taken into account and measures are tailored to these local conditions.
The cause of desertification seems to be known and the technical means to stop the process of desertification are known. However, Africa is not at present able to make the necessary investments. The developed countries need to make a serious long-term commitment to stopping the desertification of Sahelian Africa. Failure to recognise and solve this problem could have serious negative effects for developed countries as well.
Research should be site-specific, focus on optimum returns on investments in agriculture and take the social repercussions of a change in land use and farming system into account. The problem cannot be solved with the traditional disciplinary approach. Multi- and interdisciplinary attacks have become popular, but their superiority in identifying viable development paths is still to be proven.
So-called integrated projects too often put up a smoke screen for unclear or unrealistic targets based on the wrong assumptions and resulting from a lack of understanding of the underlying processes. More research, slow as it is and expensive as it might seem, is still needed. L.S.
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