G., mechanised agriculture is responsible for major vegetation clearance in Sudan, and mechanised agriculture is

heavily subsidised. See D.W. Pearce, Natural Resource Management in West Sudan, Government of Sudan, Khartoum, and World Bank (Washington, DC, July 1987).

While the focus here is on natural resources, especially renewable resources, in rural areas, the quality of the urban environment affects the lives of some 32 per cent of Africa's population on average. In some countries (such as Rwanda and Lesotho) urban population is as low as five per cent of the total population, while in others (such as Algeria) it is as high as 66 per cent. Systematic and reliable data on the quality of urban environments are scarce. Thus the proportion of the urban population with access to sanitation services is not known in many cases. However, where these data are available, access rates range from 13 per cent (Lesotho) to 100 per cent (Zambia and Libya). Air quality is poorly measured so that reasonable comparisons are very difficult to make. The most casual observation indicates the scale of traffic congestion and inadequate waste disposal facilities.

2.3 The Environment-Economy Interaction

For some time now, it has been recognised that a relationship exists between environmental quality and economic performance. Traditionally, the relationship has been seen as a trade-off. Environmental quality could be maintained or improved, but only at the expense of economic growth; a country could grow economically, but only by degrading its environment. Faced with this trade-off, the policy problem became how much growth to sacrifice in order to protect the environment. Since the environment appeared to be dispensable, and economic growth urgent,

in poor countries, an illusion was created that natural environments could be exploited at limited cost.

Recently it has been recognised that environment-economy interactions are more complex than was originally thought, and that developing countries are unique even apart from their low incomes per capita. In developing countries, growth depends to a large extent on the maintenance of environmental quality, and environmental quality depends on incomes in these countries;

environment-economy interactions are more complementary than in developed nations. The question is not how much environmental

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m quality to sacrifice in order to raise GNP per capita, but how much to invest in environmental protection so that a healthy rate of economic growth can be sustained in the future. This idea of the complementary relationship between environment and economy, at least m at low levels of income, is one of the fundamental features of the theory of sustainable development discussed in the Introduction.

The sustainable development philosophy stresses the importance of natural environments to economic development and the need, in broad

» terms, to maintain the stock of natural assets so that emerging and future generations can have equal or improved access to the quality and quantity of environmental services - soil fertility, clean and abundant water, fuelwood and rangeland.

The traditional theory of growth in economies based on natural resources suggests that depletion, or equivalently a deterioration in the productive capacity of the resource base, is m not necessarily a bad thing. Economic growth can still occur provided there is a sufficiently large stock of alternative capital (such as machinery) and an ability to substitute alternative inputs (labour as well as capital) for natural resources in production.

* The limiting effects of resource depletion can also be offset if there is a sufficiently large rate of technical progress such that more output can be produced using less of the resource input. If the economy's performance indicator is income per capita, an

» additional requirement is that population growth should not be too high.

In the context of Africa, environmental degradation is a m macroeconomic problem precisely because these conditions are not met. Alternatives to natural resources simply do not exist on the scale that is needed. The share of agriculture in GDP exceeds 50 per cent in some countries, even by official statistics. In rural m areas, agriculture (including forestry and livestock) is virtually the only source; of income, and very often provides a subsistence living. Other inputs can substitute for environmental services -chemical fertilisers, for example, can offset natural reductions in J soil fertility. But such substitutes are often not economic given

the prices received for the output and the prices paid for alternative inputs. Furthermore, such substitutes are often not technically appropriate. The use of large tractors on thin topsoils, for example, can cause more harm than good. Because of

problems such as these, substitution of alternative inputs has not _ led to the rates of technical progress needed to offset the deterioration in environmental services. In some cases, high technology inputs have made matters worse.

Despite these problems, agricultural and food production have increased. Whether these increases (small by world standards) can be sustained is perhaps an open question (although some of these gains are due to extensive development, and there is reason to believe that because of environmental degradation current gains may lead to future losses) . But there can be no doubt about the drag on economic performance caused by ever larger numbers of people. If population growth were accompanied by high rates of technical progress which more than compensated for the increases in resource demand, the natural resource problem would be less important. But high population growth combined with low technical progress is devastating to both the economy and environment.

3. THE ECONOMIC IMPORTANCE OF ENVIRONMENTAL DEGRADATION

3.1 Environmental Linkages

The importance of natural environments arises from their pervasive influence on the workings of the national economy. Figure 3.1 illustrates some of the environmental linkages that have economic impacts. As land is cleared for sedentary or unsustainable fallow agriculture, for example, so aeolian and sheet soil erosion occurs. Man-made erosion adds to natural erosion rates to cause sedimentation of irrigation channels, waterways and reservoirs, and pollution of estuaries and coastal regions. Flood plains are raised and water supply is affected. The removal of trees adds to fuelwood problems and increased burning of animal waste may occur to compensate. Use of natural fertilisers as fuels deprives the soil of nutrients from the application of dung and crop residues to

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# soils, exacerbating the erosion by reducing nutrient content, giving