Land Degradation Research Paper

1. Land Degradation: An Old Problem With New Urgency

Land degradation has been advanced as ‘the single most pressing current global problem’ (O’Riordan 2000). Yet, it is an old problem (e.g., Jacks and Whyte 1939), that has undergone a series of often-emotive revivals every decade since the Dust Bowl era in the mid-West USA (e.g., Osborn 1948, Carson 1962, Commoner 1972; Blaikie and Brookfield 1986). The historical stereotype of land degradation is that it is a process ruining the planet, and a destruction caused by ignorant peasants, who will in short time reap the folly of their degrading activities. Hailey’s (1938) African Survey called it the ‘scourge of Africa,’ providing the reader with images of sediment-choked rivers and barren hillsides. Concern about degradation, particularly the processes of soil erosion, has fuelled many campaigns to combat it, and spawned numerous institutions to address it. In colonial Africa, for example, the Federation of the Rhodesias and Nyasaland funded the largest ever soil conservation research program on the continent between 1953 and 1965 to investigate rates of erosion and runoff, as well as the effectiveness of conservation and types of land use. In Southern Rhodesia, research evidence of the potential seriousness of erosion directly led to the formation of the Department of Conservation and Extension (CONEX), which carried out major conservation planning and design works throughout the country. A somewhat different institutional base was set in Malawi in response to perceived land degradation. The Land Husbandry Branch was formed in 1960 to undertake land use planning. This led to the more holistic concept of ‘land husbandry,’ including all farm-level production activities, argued as being a more effective tool for delivering conservation than technical, often structural, measures such as earth bunds (contour embankments to intercept runoff and sediment).

In the US, worries about land degradation supported by pictures of (usually) wind erosion engulfing farmhouses and fields, triggered massive expenditure on research and new institutions. The Soil Conservation Service (now the Natural Resources Conservation Service) was the largest single section of the US Department of Agriculture. Farmers were obliged by law to comply with conservation planning regulations and procedures. Compliance involved using research outputs such as the ‘Universal Soil Loss Equation’ which calculated rates of soil loss for various planned land uses, comparing these with a benchmark known as the ‘tolerable soil loss,’ a rate at which it was said that future production would not be jeopardized. Some of the science underpinning these procedures is now known to be flawed (Stocking 1996a). Yet, there is no doubt that the sustained research and institutional effort in the US, spurred originally by the Dust Bowl era, has not only raised awareness of land degradation but also done much to conserve that nation’s soils today.

At international level, there is now a new urgency in addressing land degradation. While the World Commission on Environment and Development (Brundtland 1987) highlighted sustainable development, land degradation was only then seen as a shadowy adversary in achieving long-term productive agriculture. It was an insidious enemy, often masquerading under other names. The series of Sahel droughts in the mid-1980s illustrates the image problem of land degradation. Headlined ‘drought,’ its main impact came through widespread crop and grazing land failure due to the reduced capability of the degraded soils to support plant growth. The water-holding capacity of a degraded soil is only a fraction of a virgin soil. Land degradation therefore increases the vulnerability of marginal environments and societies.

Nevertheless, in the search for sustainable global futures, land degradation has once again come to the fore. The 1992 United Nations Conference on Environment and Development in Rio de Janeiro revived interest. However, it was not until 1998 that enough signatories drew their pens to ratify the Convention to Combat Desertification, the major components of which are national and international proposals to combat land degradation. Today, the fastest-growing section of the global funding mechanism (the Global Environment Facility, GEF), which supports the incremental cost of developing countries’ efforts to comply with the international environment-development conventions, is for land degradation projects. The driving force for the renewed interest comes from new data from international projects such as the Dutch-based Global Assessment of Soil Degradation (see Table 1). The International Food Policy Research Institute uses such data to show that, while food production may largely be maintained by ever-increasing inputs, there are ‘hotspots’ of serious land degradation in vulnerable places such as north-east Thailand, northern China, and many African drylands (Scherr and Yadav 1996).

2. Land Degradation: Differing Perspectives And Contexts

The strident rhetoric of land degradation continues today. Bolstered by the power of numbers, land degradation is pictured today as getting ever worse: ‘each year, 75 billion metric tons of soil are removed from the land’ (Pimentel, quoted in Reij et al. (1996) who provide a good critique of the selective use of ‘scientific’ findings). This ‘crisis’ perspective is, however, becoming tempered with a new realism (Glanz 1999). One recent study questions estimates such as Pimentel’s: over 20 years in an intensively cultivated drainage basin in Wisconsin, USA, sediment accretion was only about 6 percent of the rate that occurred in the 1930s, despite large stream and valley changes, while sediment yield was relatively constant (Trimble 1999). If predictions of the past had been true, whole continents would now be laid waste. Manifestly, they are not. So what is happening?

As agriculture intensifies, soils are certainly changing for the worse. Their intrinsic biological functions to support plant growth (e.g., in the natural processes of making nitrogen available to plants) have diminished. Research shows conclusively that land degradation produces poorer soils and reduced crop yields (Tengberg et al. 1998). Mediterranean environments and the tropics in general are especially vulnerable (Conacher and Sala 1998; Eden and Parry 1996). Typically, the first few tonnes of soil loss show the greatest decline in yields. Depending on actual soil type, up to 75 percent of the starting yield can be lost with 1 cm loss of soil (about 130 tonnes per hectare). Production is only maintained by compensating for the diminished state of the soil resources—through providing nutrients artificially, increasing use of irrigation to supply water that would otherwise have been supplied by a rich soil, new crop breeds that can tolerate degradation-induced toxicities, and so on. So successful are the new technologies that for most farmers they work out cheaper to implement than the equivalent conservation measures to maintain the intrinsic soil quality. Perversely, the economics of commercial farming mean that it is more financially viable to increase production while allowing land degradation than to farm conservatively. Nowhere is this better illustrated than in some intensive farming in Europe, where sandy soils have seen a decline in organic matter to as little as a quarter of 1 percent. By standard guidelines from the FAO, these soils are now severely degraded. Yet, never have they produced greater yields (Pretty 1998). With sophisticated rotary boom irrigators, multiple applications of fertilizer, and relatively cheap soil amendments such as lime, 6–10 tonnes of wheat per hectare is typical. The consequences elsewhere in the environment of substituting technology for combating land degradation can be dire. Nevertheless, society appears to prefer to clear up the consequences than tackle the root causes and processes of land degradation.

Land degradation is best perceived today as the net result of a web of causes and consequences, some of which are easily and cheaply manipulated, while others are fixed. With soil productivity providing the core variables of concern that are affected by land degradation, Fig. 1 demonstrates the complex interactions on biophysical, socioeconomic, political, institutional, and cultural factors. Farming systems, the implementation of soil and water conservation practices, and assistance from external agencies (lower two right hand boxes in Fig. 1) could be manipulated relatively easily for the benefit of soil productivity and the reduction in land degradation. Whether it would be economic so to do, or viable with current institutions, is another matter. On the other hand, geology, climate, the international economy and cultural inheritance are all relatively fixed components, providing a backdrop of largely unchangeable influences that may cause degradation when the land is used. Appreciating the scale of the complex influencing factors and their amenability to external intervention is now seen as essential to developing approaches to environmental problems acceptable both to scientists and society.

3. Land Degradation: Biophysical Processes

Land degradation is usually described by the natural resource that is being depleted (e.g., soil/vegetation/environmental degradation) or the biophysical process by which it operates (e.g., soil erosion by wind or water, sodication, salinization, deforestation). In all these processes of environmental change, the soil is normally seen as the focal resource that diminishes in quality with land degradation. As vegetation degrades in quantity and species composition, for example, the soil changes chemically, physically, and biologically. A vicious cycle is evident in most degradation processes: as the soil degrades, so is its ability to support plant growth or other life-support functions. In soil degradation six processes usually are recognized:

(a) Water erosion. This includes the splashing of soil particles by raindrop impact; sheet erosion whereby a layer of topsoil is removed by flowing water; and gully erosion where a channel is formed. Gullies are often perceived as the most serious form of water erosion because they are obvious features in the landscape. However, sheet erosion by water removes far greater quantities of soil. Worldwide it is by far the most common land degradation process in both amount of soil lost and impacts on production.

(b) Wind erosion. This is the removal and deposition of soil by wind. It is commonest in, but by no means restricted to, arid and semi-arid areas. A principal cause is the removal of vegetation by, for example, overgrazing or preparation for cultivation.

(c) Excess of salts. Salts may accumulate in the water held in the soil (salinization) or sodium cations may increase in proportion to nutrient cations such as calcium attached electrochemically to solid soil particles (sodication or alkalinization). The first is typical of semi-arid areas and of poorly managed irrigation schemes, while the second is largely a natural process accelerated by water runoff and associated concentrations of sodium induced by human land use.

(d) Chemical degradation. This includes a variety of processes. Some are related to the loss of plant nutrients by percolating water (e.g., calcium) or by chemical fixing into a form unavailable to plants (e.g., phosphorus); another is the build-up of toxic levels of chemicals. The pH-related change of aluminum into a free form that can be accessed by plants causes the severest impact on production in certain vulnerable tropical soils.

(e) Physical degradation. Adverse changes in properties such as porosity, permeability, bulk density and structural stability may arise through farming practices. The commonest physical degradation is the formation of a surface crust by raindrop impact, causing decreased water infiltration and greater runoff. (f) Biological degradation. Organic matter is a transient component of soils. Where it is lost through natural processes such as mineralization at a rate significantly faster than it is resupplied by vegetation, the soil deteriorates in its overall biological functions. This happens on most intensively farmed agricultural soils.

These processes of degradation in soils all threaten the sustainability of agriculture. Usually, several processes occur simultaneously. Water erosion, for example, results in loss of soil structure, surface crusting, waterlogging, reduction in organic matter, and breakdown of stable aggregates. In the face of such an onslaught, soil resources very quickly deteriorate. Farming becomes more difficult and more costly.

4. Land Degradation: Economic And Social Impact

Explanations of land degradation have been made at a number of spatial and temporal scales. They express the influence of, and the impact on: (a) the resource endowments of land users; (b) the nature of agrarian society and of the state; and (c) even the imperfections in the international world economy (see Blaikie 1989 for his original presentation of a political economic analysis of land degradation; also O’Riordan 2000 for an updated version). Such an analysis gives a useful entry to socioeconomic understanding of the impacts of land degradation, helping to identify where interventions are possible and by whom. They help to counterbalance the excessively technical and place-based focus of most attempts at combating land degradation. They also explain why many soil and land conservation projects have failed because of inadequate attention to the root social and economic causes of degradation.

A partial listing of social impacts would have to include examples of major disruptions that accompany land degradation. War and conflict, as in the Horn of Africa, and around Liberia and Sierra Leone, have caused massive migrations and concentrations of people in adjacent areas. Pastoralists, in particular, live in sensitive semi-arid environments, where overgrazing of vegetation and trampling by animals is a constant danger. In normal times, society has its local institutions that manage access to the pool of common property resources of rangeland; in times of conflict, these institutions are often first to disappear. Political decisions can also have unintended side effects of promoting land degradation. Ujamaa (or villagization), forcibly promoted by Julius Nyerere’s Tanzanian Government in 1972–73 on the grounds of better provision of education, health, and communication services, had the effect of concentrating formerly dispersed settlements into villages up to several thousand people. In vulnerable but fertile areas such as Mwanza and Shinyanga, this had disastrous consequences for the soil and land resources close to villages.

The economic impact of land degradation has received attention only recently. Valuation of the quality of land is fraught with uncertainty, and depends upon the perspective of the analyst. There are two principal choices for valuation: the production or the resource value approaches. The first assesses the impact of land degradation in the value of production lost, usually in market prices of the staple crop. This is a useful device for commercial farming situations, where production foregone is a real loss to the land user. The greater cost of farming the land/or the increased investments in fertilizers or irrigation to compensate for land degradation have also been added to the value for lost production. The resource value approach, which has been the commonest because the data have been collected from experimental plots in the past, values land degradation in terms of the quantity of nutrients lost in the sediment. The means for placing a monetary value is through fertilizer prices. This second approach tends to give much larger and often unrealistic costs to land degradation than the first. Environmentalists would, however, argue that the resource value approach calculates a cost for society and future generations, and not just the immediate impact on land users.

5. Combating Land Degradation: Future Directions

Land degradation is, therefore, a complex biophysical, social, and economic issue, which affects many lands and peoples, particularly in the tropical developing world. The processes involved have immediate on-site impacts, rendering land diminished in quality and ability to support plant growth. Off-site impacts are also significant in, for example, reservoir sedimentation, eutrophication, and other downstream damages. Combating land degradation needs a commensurately broad armory of approaches and techniques, targeted not just at root biophysical causes, but also at social and economic controls, which may persuade farmers that it is in their interests to farm more conservatively.

Seeking the right intervention for the appropriate target is the major challenge for land managers. There are no shortages of techniques to combat land degradation. However, the heterogeneity of local society, the varying wealth status and resource endowments of local people, and property rights that affect security of tenure, all determine whether a technique is rational and viable for any one household. Future research will have to concentrate on matching solutions to specific environmental situations, societies, and economic demands. A better appreciation of indigenous technologies has already led to rehabilitation projects that combine elements of local knowledge with formal science. Low cost technologies which use primarily biological means will be the main focus of interest for the most seriously degraded lands.

The term land husbandry has been coined recently to emphasize that control of land degradation must be seen as part of the agricultural production enterprise and environmental management practice. For too long, conservation has been an additional activity. It may have attracted subsidies and incentives, but these in the longer term have simply reinforced the burdensome and uneconomic nature of many of the techniques being promoted. Land husbandry fosters the notion that integrated, grassroots approaches to the land involve the total production cycle, land users’ constraints and opportunities, access to land, labor, and capital, and the technical appropriateness of solutions.

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