Regulating Afforestation for Water Conservation in South Africa

Abstract

It is necessary to regulate afforestation in South Africa because of the high demand exotic forest plantations make on the scarce water resources of the country. The present procedure and information base for the regulation of afforestation with exotic plantations in South Africa are useful, but rely on a large degree of subjectivity and exclude recent research information from the procedure. The problem of regulating afforestation can also be dealt with as a simple linear programming model. Solution of the linear programming model requires quantitative and qualitative information obtained by using different methods. The use of the Analytic Hierarchy Procedure (Saaty, 1983) as a qualitative method to determine a preference rating for the water demand of five user categories, i.e. terrestrial ecosystems, river ecosystems, industry, irrigation and dam storage, is demonstrated. Quantitative relationships between afforestation and annual water yield are updated. We suggest the use of this new procedure in preference to the present one. Suggestions are made for incorporating hydrological aspects such as spatial variation of evapotranspiration in catchments, critical low flow constraints and the influence of rotation age on water use. The need for accurate determination of evapotranspiration, not only of exotic plantation, but also of natural vegetation being replaced by the plantations, is emphasised.