Misunderstandings of Sahelian land use ecology
THE Sahelian region of West Africa has played an important role in the history of international environmental conservation. The Sahelian drought and famine during the early 1970s invoked broad international concern about the threat of environmental degradation in rural areas of the developing world (Gorse and Steeds 1987).1 This concern has only deepened over subsequent decades to the point where it dominates international development agendas for resource poor regions such as the Sahel (Turner n.d.). The Sahel is now commonly used as a benchmark of excessive resource poverty and environmental degradation to which other vulnerable areas are compared (Middleton and Thomas 1997) and an example of the destabilization effects of severe environmental degradation on political institutions (Homer-Dixon, Boutwell, and Rathjens 1993; Kaplan 1994).
Academic research has identified institutional failures and social mechanisms that contribute to human-induced environmental degradation in the Sahel (Picardi and Siefert 1976; Franke and Chasin 1980; Bernus 1984; Sinclair and Frywell 1985; Glantz 1987; Bromley and Chavas 1989; Mortimore 1989). Since the mid-1980s, considerable advances have also occurred in the application of remote sensing for environmental monitoring in dryland areas such as the Sahel (Justice and Hiernaux 1986; Franklin 1991; Hutchinson 1991; Tucker, Dregne, and Newcomb 1991; Marsh et al. 1992; Fuller 1998).
Despite three decades of development attention and academic study, there remains considerable confusion about the nature of environmental change in the Sahel. Physical scientists are increasingly able to document changes in vegetative cover over broad areas but have been much less successful in understanding physical processes behind these changes, especially those influenced by human land use. Without more processual knowledge, physical scientists can say little about the persistence of the vegetative cover changes they document and their ‘land use ecology’ simply relies on searching for correlations between such changes and readily available social data (e.g. population density). The stagnation of the desertification literature around arguments for and against climatic or human causes of environmental degradation are symptomatic of this conceptual/methodological deficit.
On the other hand, social scientists’ institutional, behavioural, or structural models are able to explain how various socio-economic factors affect human land use but are unable to establish how changes in land use may lead to persistent environmental change. As a result, physical and social scientific literatures on the social-environment nexus in the Sahel remain isolated and in their isolation, inadequate.
This paper is concerned with the void that lies between existing social and physical analyses – namely, our limited knowledge about the ecological consequences of human land use practices or land use ecology. Grazing ecology in the Sahel will be the primary focus but the general points are relevant to other land uses in the Sahel and other dryland regions. The first section of the paper will briefly characterize conventional views of range management and grazing-induced environmental change in the Sahel. It will be argued that these understandings are have been shaped more by rigid adherence to inappropriate ecological models, developmentalist agendas, and state interests than by good science. This will be followed by a section that discusses how results from more process oriented grazing ecology research leads to different conceptualizations of grazing induced environmental degradation and management interventions.
Despite 30 years of heightened concern about overgrazing in the Sahel, our understanding of its grazing ecology remains limited (Dodd 1994). Our ignorance is in large part a legacy of the reliance by range management experts on succession-climax models of range dynamics, whether they worked within North American range science, systems ecology, or French phytosociological traditions (Braun-Blanquet 1932; Boudet 1975; Stoddart, Smith, and Box 1975; Pratt and Gwynne 1977; Breman and de Ridder 1991). Since the range system was seen as naturally prone to evolve toward an internally regulated equilibrium or ‘climax’ type, the goal of management was simply to identify the deviations from the desired community type (which may differ from the climax) and recommend changes in management that would move the system in the desired ‘direction’.
As described by Westoby et al. (1989), both grazing pressure and poor rainfall were seen as producing changes that move the rangeland away from the more productive state. But since only the stocking rate (i.e., the number of animals per unit area of pasture) can be controlled through management, the proper management response to poor range condition, no matter its cause, was destocking. The beauty of this framework was its seemingly facile application to different socio-ecological situations – management prescriptions could be made without performing controlled studies on grazing impact nor with an understanding of the existing livestock management.
As a result, only a handful of controlled/semi-controlled grazing studies have been performed in the region (Valentin 1985; Grouzis 1988; Hiernaux and Turner 1996) and the relevance of stocking rate prescriptions to mobile livestock production systems (such as the transhumance or seasonal migration practiced by several pastoral communities in the region) have not, until recently, been scrutinized (Bartels, Norton, and Perrier 1993; de Leeuw and Tothill 1993; Turner 1993).
The destocking prescriptions made by range managers, while never rooted in a causal analysis, were understandably interpreted by the development community as diagnoses of overgrazing. Such diagnoses made sense to the casual observer for explaining widespread deterioration of grass cover, tree and shrub mortality, declines in the abundance of perennial grasses, and increases in the abundance of short-cycle forbs that occurred during the 1970s. Coincident declines in livestock populations coupled with popular notions of what overgrazing means, seemed to confirm that domestic livestock populations were literally eating all of the vegetation available before starving for lack of cellulose.
Social commentators offered various versions of the ‘tragedy of the commons’ scenario to provide logical explanations for the seemingly illogical behaviour of Sahelian livestock owners (Picardi and Siefert 1976; Sinclair and Frywell 1985). It was only a few anthropologists who raised the point that the same symptoms could be caused by the recurrent droughts in the region since the 1970s (Hjort 1982; Sandford 1982; Horowitz and Little 1987). Their voices were lost within a development community operating in crisis mode.
In short, the narrative of widespread overgrazing in the Sahel served many interests and therefore alternative explanations were not seriously considered (Roe 1991; Ferguson 1994). From the researchers’ point of view, the relevance of socio-economic research on factors shaping resource use would decline if resource uses were not found to be as ecologically damaging as presumed. Developers welcomed an environmental rationale to rationalize rural production systems. More fundamentally, they were and are in the ‘can do’ job of development – accepting the possibility that human tragedy in the Sahel is more a legacy of its geography and less of mismanagement is difficult to accept (Escobar 1995). The overgrazing diagnosis was treated by Sahelian governments as scientific support for political programmes of centralization, villagization, and restrictions on human mobility.
The succession-climax models, which identified the need for de-stocking without on-the-ground ecological research, have come under attack in the 1990s (Ellis and Swift 1988; Westoby, Walker, and Noy-Meir 1989; Laycock 1991; Behnke, Scoones, and Kerven 1993), reflecting the general questioning in ecological sciences of equilibrium based models (DeAngelis and Waterhouse 1987; McIntosh 1987; Botkin 1990; Zimmerer 1994). In an African dryland context, relaxation of equilibrium assumptions has led to a greater appreciation of the strong influence of rainfall variability on rangeland parameters; the multiple and divergent effects of grazing and drought on rangelands; and the resiliency of annual grasslands to both drought and grazing. No longer is the adjustment of stocking rate seen as a necessarily effective response to changes in range condition.
However, the introduction of non-equilibrium ecological perspectives does not, as some popular accounts suggest, lead toward conclusions of a benign influence of grazing or a hands-off approach to range management. Instead, it requires closer study of plant growth factors and how their spatio-temporal distribution are affected by different patterns of livestock actions (defoliation, selective grazing, excretion, trampling etc.) particular to Sahelian management systems.2
An unfortunate legacy of range science as practiced in the Sahel is our continued ignorance of the Sahel’s grazing ecology. We know surprisingly little about the ecological effects of the grazing patterns that are typically produced by different management systems in the Sahel. In this section, I would like to briefly outline major management-relevant features of what we do know about the productive ecology of Sahelian grasslands, the evolution of Sahelian grazing systems, and the ecological effects of different livestock actions. These are not presented in all of their complexity but instead are only sketchily developed in the spirit of providing a framework for research, management, and development action.
The Sahel receives on average 100-600 mm of rainfall a year during a three-four month rainy season. In any one place, rainfall varies tremendously from year to year. The magnitude and timing of rainfall will affect both productivity and species composition of the annual grassland. Therefore, rainfall should be considered as the major factor affecting interannual variation in vegetative parameters. The Sahel is also a region with very infertile soils. As a result, vegetation is multiply constrained by the scarcity of growth factors, most notably soil moisture, nitrogen, and phosphorus (Penning de Vries and Djitèye 1982).
The importance of nutrient availability as limiting vegetative production is strongly affected by rainfall. In good rainfall years (400 mm), there is greater potential for nutrient availability in soils to limit rangeland production (Penning de Vries and Djitèye 1982). Annual grasses and forbs have historically dominated Sahelian rangelands. The growth cycles of these plants range from three weeks to three months. A large fraction of a plant’s nutrients are translocated to seeds, seed drop is rapid, and seeds are wind or animal dispersed. Once seeds are dispersed, grazing of vegetative material by ungulates or termites will only affect litter cover and soil exposure at the beginning of the following rainy season (if rangeland is not burned).
Historically, a large fraction of Sahelian livestock were managed in transhumance systems that involved the movement and dispersal of livestock over the vast northern pastures (100-300 mm/yr) during the rainy season followed by a return to pastures and cropland to the south after the drying of northern pans at the beginning of the dry season. This general pattern of regional mobility resulted in any one site during the rainy season experiencing short periods of severe defoliation pressures followed by periods of relatively limited grazing. Along transhumance corridors, grazing pressure generally declined with distance from encampments located in proximity to water points. Shifts in the livestock ownership, agricultural encroachment on transhumance paths, military conflict and banditry in the north, and despecialization of livestock husbandry as an occupation has led to a decline in the prevalence of transhumance and a growing fraction of livestock grazed year-round near permanent villages in the southern Sahel.
One major conceptual problem blocking the development of a more dynamic understanding of Sahelian rangeland ecology is the common treatment of grazing pressure as a singular, aggregated stress on particular vegetative parameters. For example, popular perceptions view grazing as influencing vegetation simply through direct consumption (e.g. defoliation). Grazing in fact involves a range of livestock actions that can influence any vegetative parameter (vegetative cover, species composition, etc.) through multiple pathways (Vale 1982).
Once one distinguishes these pathways and determines their relative importance in different situations, one can gain a better understanding of the dynamic and spatially differentiated nature of grazing on rangeland vegetation (Turner 1999a). Three major proximate factors affecting the productivity of Sahelian rangelands on sandy substrate are photosynthetic surface area, species composition, and soil nutrient availability. These proximate factors are affected by grazing at different spatial scales through pathways working at different time scales.
Grazing-induced defoliation affects vegetation in small patches (around 10 m2) and within the same season. Clipping studies have found that the defoliation has to be severe and throughout the rainy season to significantly affect grassland production (Hiernaux and Turner 1996; Turner 1999c). Such defoliation pressures are likely to be generated by village based sedentary management when animals graze highly circumscribed pastures throughout the rainy season. Livestock affect nutrient availability primarily by consuming vegetation and then depositing dung and urine (which contain a significant amount of nitrogen and phosphorous) across the landscape. This leads to a spatial redistribution and, in the case of nitrogen, a net loss of these nutrients.
In contrast to the defoliation effects of grazing, grazing patterns in the Sahel affect nutrient availability at larger spatial scales (around 50 km2) over many decades (Turner 1998a; Turner 1998b). Still, such gradients in soil parameters have been found to affect species composition to a greater extent than recent defoliation pressure (Turner 1999c).
As mentioned above, significant advancements have been made in the monitoring of dryland vegetative cover over the past three decades. Monitoring studies have generally found vegetative cover in the Sahel to fluctuate tremendously from one year to the next, with fluctuations largely driven by rainfall (Tucker, Dregne, and Newcomb 1991). Areas of persistently lower vegetative cover are located around larger villages and towns. The findings of these studies are consistent with the results of field studies that find Sahelian grassland production to be resilient to drought and grazing (Hiernaux, Diarra, and Maiga 1988; Hiernaux 1995; Turner 1999c). It is in areas where livestock are grazed year-round within highly circumscribed pastures that reduction in vegetative cover and shifts in species composition become most evident.3
This pattern of vegetative change, as interpreted by the findings of the latest grazing ecological work in the Sahel, argues for changes in the resource management strategy that dominates rural development in the Sahel. Conventional rural development has focused on reducing regional livestock populations. Concern about overgrazing has been translated into development actions to encourage herd offtake (culling), reduce human population growth, and privatize common rangelands. But the latest grazing ecological work shows the annual grasslands are in fact highly resilient to drought and grazing and that grazing induced degradation is highly localized where livestock movements are restricted.
Therefore, while standard development actions may improve the situation on a North American ranch, they are clearly insufficient and even damaging in a Sahelian context. Reduction in the size of livestock herds may actually lead to greater concentrations of livestock around market towns, exacerbating ecological problems (Ensminger 1992; McPeak 1999). The relevance of social models, such as ‘tragedy of the commons’, that have been built to explain the ‘overstocking’ of rangelands is suspect once one considers Sahelian grazing ecology. The parameters of greater relevance are those that affect the distribution of livestock on available rangeland such as the availability of herding labour (Turner 1999b) and social and physical barriers to herd movements.
Given the present situation where the social organization of grazing is increasingly in the form of an impoverished group of professional herders herding the livestock of the rich on agriculturally encroached pastures, strong measures by national governments, non-governmental organizations, and local communities are required to reinvigorate livestock mobility/dispersion. Embracement of indigenous knowledge by recognizing the rationale behind transhumance systems is insufficient given present structural constraints.
The development of a land use ecology requires an understanding of not only the productive ecology of the resource in question but of local resource management and how it affects spatial and temporal patterns of land use. Improved understanding of anthropogenic environmental change on Sahelian rangelands is hindered by our ignorance of their land use (grazing) ecology. This ignorance does not result simply from the complexity of Sahelian ecology but has been produced by a mutually reinforcing set of conditions including: rigid inherence to inappropriate ecological models by range experts, developers’ interest to transform indigenous production systems; and the political interest of national governments to limit the movements of people and animals within and across state boundaries.
Compared to other rural regions of the South, the Sahel has received long term sustained conservation attention. The intellectual, moral, and political failures which underlie the limited success of resource management approaches in the Sahel are undoubtedly common throughout the Third World. Conventional approaches in the applied ecological sciences of North America and Europe (range management, forestry, wildlife management) mislead as much as they guide the development of proper resource management strategies in the tropical Third World situation.4
The confusion caused by the rigid adherence to such management templates provides a greater opportunity for those with power to use environmental analysis for political ends and for developers to argue for production systems that mimic those of the temperate West. Much more work is needed to develop land use ecologies that are relevant to Third World land use practices and the tropical ecologies on which they depend.
1. The Sahel is defined here as the strip of land lying south of the Sahara desert that receives 100-600 mm of rainfall on average per year. Concerns about environmental change in the Sahel and other dryland areas in Africa are not new and have long dominated European perceptions of the region (Swift 1996; Ribot 1999). Colonialist concerns about the environmental consequences of indigenous land use practices led to coercive soil conservation, forestry, and destocking programmes (Baker 1984; Beinart 1984; Anderson and Grove 1987; Grove 1994). Still, the globalization of environmental concern and conservation practice since the 1970s is a new phenomena (Buttel and Taylor 1994).
2. An understanding of any region’s grazing ecology requires research in at least three areas: (a) The production ecology of the forage resource (grassland, shrubs etc.), with particular attention to the proximate biophysical factors (e.g. seed stock, nutrient availability, defoliation pressure, moisture availability) affecting its species composition and productivity. (b) Variations in grazing management in the region and how these variations affect the pattern of livestock actions (grazing, trampling, excretion) that can affect the ecologically important proximate factors above. (c) The long term and short term effects of variations in the timing and magnitude of livestock actions (relevant to the management system) on forage growth factors. This understanding will develop best through experimental work (grazing trials, exclosures, gradient analyses, clipping studies etc.).
These areas of research remain only partially developed (especially b and c) and poorly integrated.
3. Still, there remains considerable confusion about the importance of grazing in leading to more persistent changes in grassland soils and vegetation. With very little work focused on the interaction of rainfall and grazing initiated changes in soils and vegetation, scientific discourse has stagnated around the dichotomy of drought versus grazing as the major factor behind changes. What becomes clear from more process-oriented range ecological research is that grazing effects are highly contingent on rainfall (Turner 1998a; 1998b) since rainfall determines the relative importance of different growth factors in limiting production. The same livestock action will have remarkably different effects on the vegetation depending on rainfall and recent rainfall history.
4. For example, the simple adoption of North American forestry principles to a tropical forest situation may be highly misleading, not only because of the different production ecologies of temperate and tropical forests, but also because people in tropical forests may harvest parts of trees rather than whole trees. Conventional forestry science provides few tools for understanding ecological effects of such land uses (Lélé 1994).
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