Local benefits of retaining natural vegetation for soil retention and hydrological services

Abstract

Renosterveld is a grassy shrubland with a diverse understory of geophytes. Exceptional plant diversity and endemism, combined with considerable fragmentation due to transformation to cropland, make this vegetation type a conservation priority. The provision of formal reserves is difficult in highly fragmented landscapes. One possible way of motivating for conservation is to demonstrate the ecosystem services derived from the retention of remaining natural fragments, as a motivation for their conservation on private land. This study explored the benefits of retaining renosterveld fragments at the farm-scale based on the hydrological and soil retention services they provide. Rainfall simulations were carried out at paired sites of renosterveld and transformed renosterveld, and renosterveld and managed transformed renosterveld (requiring physical inputs). Infiltration rates, runoff volumes, sediment loads and plant species cover were recorded. This study found that infiltration was linked primarily to vegetation cover, with the highest infiltration rates experienced in renosterveld and managed transformed renosterveld dominated by alien grasses. Similarly aeolian loads and wind speeds among these three vegetation states were explored using suspension traps and hand-held anemometers. Renosterveld remnants were demonstrated to significantly reduce wind speed and aeolian load. Renosterveld provides an important service in reducing runoff, facilitating infiltration and retaining topsoil without expensive management interventions.