مدل سازی سیاست از تجارت کردن بین توسعه کشاورزی و تخریب زمین، مورد سودان

The agricultural policy model of the trade-off between agricultural growth and land degradation that we have developed, with Sudan as an application, shares common features with the computable general equilibrium (CGE) models. The model is used to address two questions. First, what are the future prospects of a green gross domestic product (GDP), are there reasons for alarm or not, and to what extent? Secondly, which among the four policies of price incentives, property rights, poverty reduction, and human capital are more effective than the others? We show that the prospects of natural resource-friendly agricultural development in Sudan—a rising green GDP—are not promising in the medium run, but that, indeed, there is a range of effective policies and choices that could reduce the trade-off between economic growth and land degradation.

Land degradation, deforestation, and desertification can seriously reduce the productivity of land, and thereby jeopardize economic growth. The interdependence between natural resource use and sustainable development is nowhere more obvious than in developing countries where the overwhelming majority of people are engaged in economic activities that are tied to land, such as agriculture, forestry, and animal husbandry. Four adverse relationships are commonly acknowledged. First, lack of well-defined private property rights over natural resources lead to overexploitation and degradation of these resources. Second, farmgate prices in most developing countries are far below their world market levels, this discourages farmers' incentives for soil conservation and encourages soil depletion. Third, inaccessibility of poor farmers in developing countries to modern technical knowledge and information leads to misuse of natural resources. Fourth, pressurised by their poverty, poor people adopt short-term survival strategies, overuse land resources, and, therefore, give environmental protection a low priority. Sudan is a typical country in which the four above-mentioned factors apply and adversely affect the use of land resources (cf. Pearce, Barbier, & Markandya 1990). For example, land tenure insecurity has pushed farmers in mechanised agriculture to “mine” arable land in pursuit of short-run gains. Poverty in subsistence agriculture has compelled farmers to exploit arable land unsustainably. In addition to land tenure insecurity and poverty, the low level of farmers' education and training leads to overexploitation of arable land. In general, farmers' crop and soil husbandry knowledge has far-reaching effects for the sustainable exploitation of arable land. Furthermore, price controls imposed by the government on irrigated agriculture have discouraged farmers from adoption of long-term sustainable cultivation practices. In forestry, open access to woodland is a major cause behind the excessive clearance of forestland. Besides, lack of well-defined property rights over grazing land has left no incentives for livestock owners to invest in improving the prevailing conditions in grazing land. In spite of these negative developments, it has not been established for Sudan, nor for that matter other badly affected developing countries, whether the agricultural growth net of land degradation is positive or negative. In other words, if the notion of green GDP can be quantified, it is important to establish whether this green GDP is on the increase or the decrease. This paper focuses on modelling the trade-off between agricultural growth and land depletion. We take Sudan as a case study, a country very rich and diverse in land potential but equally so with ecological risks. One concern will be to establish quantitatively the future prospects of the green GDP, are there reasons for alarm or not, and to what extent? The other concern is to formulate a framework that can be applied to the appraisal of alternative policies of reducing the trade-off. Which policies are more effective than others? We shall show that the prospects of resource-friendly agricultural development in Sudan—a rising green GDP—are not promising in the medium run, but that, indeed, there is a range of effective policies and choices that could reduce the trade-off between growth and depletion. There are a few policy models that explore the links between economic growth and environment conservation in the context of agriculture and (or) forestry. Those focusing on agriculture include Barbier (1990), who explores incentives for upland farmers in Indonesia for investing in soil conservation as an alternative to existing methods of cultivation that lead to considerable soil erosion. Angelsen and Fjeldstad (1995) developed a microeconomic model of farm decision making for Tanzania, examining the roles of production intensity and investment in soil conservation in determining the magnitude of soil erosion. Bluffstone (1995) examined the deforesting behavior of small holder agriculturists in rural Nepal as off-farm labor market conditions change in the context of an open access regime. There is also the computable general equilibrium (CGE) model for Costa Rica by Persson and Munasinghe (1995), in which the effects of economywide government policies are traced on development of agriculture and forestry. There are also models with a narrower scope that study the environmental effects of stabilisation and structural adjustment programmes supported by the International Monetary Fund and the World Bank, such as Reed (1992) for Thailand, Cruz and Repetto (1992) for the Philippines, and Cromwell and Winpenny (1993) for Malawi. The main conclusions that can be drawn from a review of this literature is that although the policy modelling of the trade-off between growth and conservation in the development context emphasises the need for joint appraisals of economic incentives, property rights, population and poverty pressures, and modern farming knowledge, yet, the available models do not go beyond focussing on one aspect to the exclusion of others. The models also emphasise the need to model the interaction between agriculture and forestry, the importance of relative prices in determining outcome, and, hence, the suitability of general equilibrium models as an analytical tool. This paper is meant to be a step in the directions mentioned above. The policy model that we apply incorporates the joint appraisal of economic incentives, property rights, poverty pressure, and the role of modern farming knowledge in the determination of growth and sustainability of agriculture. The model gives due emphasis to relative prices in influencing the allocation of resources and shares common features with CGE models. Refinements linking agriculture to forestry, livestock, and the rest of the economy are introduced in a later stage. The next section introduces the basic model, other sections will deal with the structure of the model, its estimation, and its use for appraising alternative policies to reduce the trade-off, and discuss the results obtained. There is a final section that treats extensions of the basic model and concludes.

In this section, we report on extending the crop agriculture model to forestry, livestock, and the nonagricultural sectors in an economywide model that shares main features with CGE models. Main features of the CGE economywide model are GDP and intermediate deliveries, taken thus far as exogenous, become endogenous. Sectoral investment requirements supplied by nonagriculture are determined by increase in sectoral future production one period ahead, and sectoral incremental capital-output ratios. The model includes also an equation for the financing of investment purchases by government agencies and private entrepreneurs. Nonagricultural net exports are determined as residual after deducting the net exports of the other sectors from projected foreign capital inflows. While prices of internationally traded goods are exogenous, the price of the nonagricultural product is endogenous. As a result, market clearance occurs in some sectors via quantity adjustment and in other sectors via both quantity and price adjustment. Finally, the distribution of land among the agricultural subsectors, which was exogenous so far, is now relaxed. Actual market clearance in Sudan suggests that a prioritised staging of markets is most representative of what is happening, which we follow here. The market-driven allocation of rain-fed land, forest, and grazing land is done on the basis of changes in relative land values. One important result of the CGE economywide model is that the endogenous growth rate of the GDP turns to be slightly higher, 5.1% per annum, than the exogenously assumed growth rate in the agricultural model of 5.0%; but degradation costs are also higher. Focusing on the results for agriculture, we find that the extended model gives more degradation cost per unit of output, and by equivalence, less value added per unit of degradation than in the agricultural model. These results are explainable in terms of the greater freedom allowed in the extended model for land resources, among other variables, to move towards more productive sectors, that are more costly in terms of environment.5 These results emphasise, first, the presence of the trade-off that becomes greater in the extended model, and second, the increased importance of finding policies to reduce the trade-off. It is necessary to qualify, however, that in absolute terms, the green value added is slightly higher in the extended than in the partial model, 11.60 as compared to 11.56 billion LS, which is a positive signal. The ranking of the policy simulations in terms of their impact on degradation and growth is about the same in both models except that price incentives—Policy I—and human capital—Policy IV—exchange positions in the top in the extended model. This can be expected in view of the greater involvement of improvements in human capital in irrigated, mechanised, and subsistence agriculture in the total circular flow of the economy as compared to price incentives that are limited to the irrigated sector. Our policy modelling of the trade-off between environment and growth has shown that although the problem can be presented more realistically in an economywide model than a compact sectoral model, the latter is simpler and can serve the purpose granted that it is consistently bounded by expected values of macroeconomic variables. The application to Sudan has shown that the trade-off in crop agriculture is present and significant. Economic growth is accompanied by degradation costs that grow at a higher rate. However, there are policies that reverse these tendencies. In particular, investment in human capital and stimulation of price incentives appear to be more effective than security of land tenure and poverty relief. A simultaneous modelling of these policy alternatives and their crossevaluation among more developing countries would contribute to a more solid understanding of ways to reduce the trade-off between environment and growth.