Morgenroth, Silvia: Sozioökonomische Rahmenbedingungen und Landnutzung als Bestimmungsfaktoren der Bodenerosion in Entwicklungsländern - Eine überregionale empirische Analyse im Kontext der Agrarentwicklung -


Kapitel 10. Summary

By the end of this century, soil erosion has reached an alarming extent in many developing countries. Still, uncertainty prevails regarding the human-induced causes of soil erosion. In consequence, many efforts to design efficient anti-erosion policies and instruments remain erratic.

The actual discussion about human-induced causes of soil erosion focusses on socioeconomic factors that assumably influence the land users´ decisions on agricultural production and soil protection, and, hence, the degree of soil erosion. The most frequently discussed factors are: (i) poverty, (ii) population pressure, (iii) biased agricultural prices, (iv) the introduction of inadequate technical innovations and (iv) insecurity of land tenure. They are basically deduced from and discussed on base of production theory and the theory of induced innovation. Nevertheless, the different views on the importance to be assigned to the single factors are quite controverse. For example, in a rather optimistic scenario, it is argued that poverty and population pressure lead to the development of soil-conserving innovations in the long run. On the other side, poverty and population pressure, in combination with falling agricultural prices, are assumed to lead to a short-termist overuse of the soil. Empirical evidence that supports some of the controverse hypotheses on the causes of soil erosion is restricted to local studies based on local data on soil erosion, their results can hardly be generalized. In this context, the spatial data compiled within the global assessment of human-induced soil degradation (GLASOD; UNEP/ISRIC, 1991) for the first time permits a large-scale empirical analysis of socioeconomic and landuse factors relevant to erosion.

By aggregating the information of the GLASOD data, countries and regions whith marked soil erosion can be identified. While Africa and Asia most contribute to the extent of soil erosion and the loss of nutrients<168> in absolute terms (4,5 mio sqkm each), it is in Southwest Asia (37%), Central America and Southeast Asia (25% each), where the proportion of of the land area - excluding wastelands - that is affected reaches the highest levels. Looked at on a national level, countries with an extreme extent of soil erosion are to be found in Central America and Africa: In El Salvador, Haiti and Costa Rica, 60 to 90 percent of the land area<169> are affected. In Africa, Sahelian Countries as Tunesia, Mauretania, Libya, Niger, Burkina Faso and Mali, as well as the eastafrican highlands of Burundi and Rwanda, and also Cape Verde show the highest proportions of eroded land area2 (40 to 80 %). Water erosion is the most widespread type of erosion, in Central America and Southeast Asia it even contributes with about 70% to the area affected by erosion and the loss of nutrients1.


The methodological approach chosen for the empirical analysis of human-induced causes of soil erosion is an explorative, econometric one, based on national cross-country data<170>. A specific combination of correlation analyses, factor analysis, and regression analysis is designed, that can handle the great number of possible indicators for the assumed causes of erosion, and cope with related problems of multicollinearity and model specification. Those problems result from supposed interrelationships among different human-induced causes of soil erosion. At the same time, many of the causes of erosion have a latent character when considered on a national level<171>, since they are deduced from a microeconomic context. This makes it necessary to define various indicator variables for each of them, which, again, implies additional multicollinearity.

On the basis of the aggregated GLASOD data, a set of operational variables for soil erosion is defined. They basically indicate the proportion of a country´s degradable land area (i.e. land area minus wastelands) that is eroded through wind, water, or degraded by the loss of nutrients and organic matter by the end of the 80´s. In turn, the database for possible determinants of erosion is compiled departing from standard international data sets for the time span 1961-1990. Representative indicators can be defined for many of the causative factors discussed in literature, as well for socioeconomic ones, as for landuse, and also for natural factors. They are adapted in a way that they not only best fit and capture the hypothesized determinants, but also the ecological and timely dimension of the analysis. One important field that is not covered is land tenure. The resulting database comprises about 150 variables for possible causative factors, with a varying number of country-data available.

The results of correlation analyses between the indicator variables for soil erosion and for possible causative factors facilitate a first assesion of relevant relationships. They show, that variables that quantify population pressure and the proportion of forested area are correlated with soil erosion for all countries. Deforestation rates in the 80´s are especially related to water erosion. Considering only countries without extreme climatic conditions<172> correlations are found between soil erosion and variables for the intensity of land use and the degree of expansion of the agricultural frontier. Producer price declines for relevant agricultural products are also found to be correlated with soil erosion in these countries. Corresponding to theoretical assumptions, the importance of different natural factors vary for different types of erosion and climatic zones. Altogether, variables that express structural conditions and can be regarded as the outcome of historical, long-term developments, seem to have stronger correlation with the extent of soil erosion than variables that quantify changes that took place within the time span under consideration, 1961 to 1990.


The next methodological step consists in different factor analyses for 62 of the variables that express possible causative factors and for 73 countries with approximatively complete data sets. The principal objectives are to detect structural interrelationships among the multitude of variables and to reduce their number on the basis of these interrelations, in a way to obtain a set of variables that are largely independent of each other. It turns out that the structure of the 62 variables under consideration can clearly be reproduced by about 10 factors, with about 75% of their total variance being explained. These factors prove to be robust with respect to changes in the set of included variables, and in the methods of extraction and rotation.

It is noteworthy, that many of the identified factors refer to cause-effect relationships that are discussed in literature. For instance, the factor that explains the greatest part of total variance, combines variables that quantify the long-run intensification of land use with others that stand for structural population pressure and a limited buffer for the expansion of the agricultural area. Other important factors relate to structural poverty, in combination with high rates of rural population growth; to the long-term and recent deforestation and to total population pressure; to development paths that aim at sopisticated animal procuction and permanent culture rather than at a mere expansion of the agricultural area. Other factors stand for the prevailing natural conditions. Based on a factor analysis for a reduced number of countries, it can be shown that declinig aggregate agricultural producer prices<173> are associated with the factor ´recent deforestation rates´.

To quantify the relative importance of the identified factors, stepwise regression analyses are then carried out, with soil erosion as the dependent variable and selected representative variables for each of the factors as presumed independent variables<174>. Three human-induced factors, or developments, show to have particular relevance for the extent of soil erosion, that they can explain to up to 75%: (1) the long-run historical expansion of the agricultural frontier at the expense of the forested area, in combination with a population pressure well above the corresponding supporting capacities in the 80´s; (2) recent deforestation rates in conjunction with total population growth. This effect can rather be associated with a growth of demand for agricultural and forestral products and declining agricultural prices than with pressures directly resulting from agricultural population and expansion; (3) the long-run intensification of land use, mainly throug the conversion of permanent pastures to arable land, the shortening of fallow periods, and the increase of animal densities. This type of intensification is associated with and possibly induced by high structural population pressure in agricultural areas. Another important result is that poverty seems to have minor impact on the extent of soil erosion at the aggregate, national level. None of the included variables that represent the factor ´poverty´ shows a si-


gnificant relative impact, neither in the models for the sum of erosion nor for specific types of erosion or climatic zones. This fact supports the low correlation coefficients for altogether 15 different poverty indicators that were calculated in the context of simple correlation analysis.

Specific models for specific types of erosion and climatic zones show that there exist characteristic patterns of explanation for each type and zone. Recent deforestation rates and the associated features (factor (2))are particularily important in the explanation of water erosion, especially in countries with predominant humid climate. The impact of production-intensity in terms of factor (3) is specific for water erosion, and for countries without extreme climatic conditions, together with the factors (1) and (2). This is also where the negative effect of declinig agricultural prices appears to be strongest. At the same time, the development of sopisticated animal procuction and the growth of the area under permanent culture in contrast to a mere expansion of the agricultural area seem to be favourable to the soil in this context. In the explanation of wind erosion and loss of nutrients, natural factors are in the foreground.

The identified, human-induced pressures related to long-term population growth, intesification, agricultural price decline and recent deforestation are consistent with important theoretical hypotheses. Those pressures are clearly not of the type that can be overcome over night through political intervention. Nevertheless, they lead to the following areas of intervention that should be given priority in the design of policy measures for the reduction of soil erosion:

  1. A reduction of population pressure through an increase in site-specific production potentials, based upon innovations that match the prevailing agro-ecological and economic conditions. Special attention should be given to low potential areas.
  2. A stronger focus on forest policy and the regulation of commercial forest use especially in the humid zone.
  3. A selective, long-term improvement of economic incentives for the production of soil-conserving crops with soil-conserving methods, by means of economic policy as well as through improved institutional conditions.

Policies that aim at the reduction of poverty can not be expected to play a decisive role in the reduction of soil erosion. In spite of that, it is most necessary that policy makers keep in mind that the poor certainly are most affected by and vulnerable to erosion damages.

At a global scale, the quality of future research on the topic will largely be determined by data availability and quality: concerning soil erosion, information at different points in time is necessary; for anthropogenic factors, spatial datasets will bring a new dimension into scientific research. Parallel with global analyses, further in depth local studies are necessary for a comprehensive and detailed insight into why and which land users degrade the resource they depend on in a specific socioeconomic context.



The loss of nutrients and organic matter, independent of soil erosion, is also considered and is abbreviated with the term ´loss of nutrients´ in this text.


Again, it is the land area excluding wasteland that is being referred to.


Spatial data sets are not avaiable yet for socioeconomic factors related to soil erosion.


I.e. it is not known a priori, how these causes can be measured and quantified.


I.e. countries without predominant arid, hyper-arid or humid agroclimatioc conditions.


The availability of data for the variable in cause is limited to 56 coutries.


Reciprocal effects that soil erosion might have on anthropogenic factors are not very likely to occurr within the considered time span, except a possible increase of poverty due to erosion.

[Titelseite] [Widmung] [Abkürzungsverzeichnis] [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [Bibliographie] [Danksagung] [Selbständigkeitserklärung] [Lebenslauf] [Anhang]

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