Modelling streamflow reductions resulting from commercial afforestation in South Africa: From research to application

Abstract

Numerous local and international studies have indicated conclusively that forest plantations consume more water than natural forests, grasslands or shrublands, and hence reduce water yield (streamflow) from afforested catchments. These water use concerns led to the initiation of South African forest hydrological research in 1935, and resulted in the establishment of long-term paired catchment research stations. The findings and recommendations emanating from this research led to the introduction, in 1972, of legislation that required timber growers to apply for permits to establish commercial plantations. Applications to establish forestry plantations became mandatory, and were rejected if it was deemed that the afforestation would use an unacceptably high proportion of water. The legislation has undergone a series of refinements since then, as research results and simulation models have improved. The current licensing and regulation system required an updated means of accurately assessing the impacts of industrial afforestation on water resources in South Africa. The terms of reference were for a scientifically defendable yet pragmatic tool that would aid water use authorisation and forestry license allocation processes by the Government Department of Water Affairs and Forestry. Simulation modelling on a national scale was identified as the most practical solution.