An assessment of water use by Acacia longifolia trees occurring within the hillslopes and riparian zone of the Heuningnes Catchment, Western Cape

Abstract

The increasing expansion of Acacia longifolia trees along the riparian zones in South Africa demands an urgent intervention as the species is listed in the National Environmental Management: Biodiversity Act (2004). This list includes species that are prohibited from growing, or being imported into South Africa. The detrimental effects of alien vegetation have been observed on the hydrology of the ecosystems invaded. However, the actual water use by Acacia longifolia has never been quantified. Therefore, there is inadequate knowledge of the actual rates and the differences in water use rates by A. longifolia occurring in the riparian zones and hillslopes. This study addresses this gap in knowledge by quantifying the diurnal and seasonal transpiration dynamics of hillslope and riparian A. longifolia. The variations of climate and soil water content on the hillslope and riparian zones were also examined in this study. The study was conducted on the Spanjaardskloof hills and along the Nuwejaars River (Moddervlei) in the Heuningnes Catchment, Cape Agulhas.