Forestry and streamflow reductions in South Africa: A reference system for assessing extent and distribution

Abstract

Forestry is an important sector of industry in South Africa but the growing of timber places significant demands on the available water resources. Yet, a ready source of information on the extent, and probable hydrological impacts, of afforestation in specific locations in South Africa has not been available. This paper reports on the modelling exercise conducted to produce an easy-touse, handy catalogue to fill this need, and presents some of the notable results of this exercise. Databases of quaternary catchment and magisterial district boundaries, rainfall, streamflow, forestry areas by tree genus, timber rotation lengths (years) and forestry growth potential were combined by means of a geographical information system to delineate uniform blocks of forestry. On these blocks a robust empirical model predicted total and low-flow reductions as a function of rotation length, tree genus, water availability, growth potential and plantation age distribution. The results were summarised by quaternary, tertiary, secondary and primary catchment, and by magisterial district and province.

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