The impact of heavy grazing on an ephemeral river system in the succulent karoo, South Africa
Journal of Arid Environments
ARC-LBD: Range and Forage Unit, Private Bag X17 Bellville, 7535, South Africa; Biodiversity and Conservation Biology Department, University of the Western Cape, Private Bag X17, Bellville, 7535, South Africa; Lesley Hill Institute of Plant Conservation, Botany Department, University of Cape Town, Private Bag, Rondebosch 7700, South Africa
The impact of long-term high grazing pressure on geomorphological features, plant community composition and cover and soil characteristics of an ephemeral river system in Namaqualand, South Africa, was compared to that of lighter grazing pressure across fencelines which crossed the river system. Under heavy grazing the river system was less braided and a higher proportion of the river width was unvegetated runoff channels. The river system was generally dominated by very sandy soil. However, more silt and organic matter, and less sand were found in soil under plants growing in the river bed. Since vegetation cover was much higher under light grazing, river soil was more fertile when grazing was light. A plant species compositional shift when grazing pressure was high resulted in riparian vegetation which more closely resembled the surrounding rangelands. Graminoid growth forms were encountered more frequently in the lightly grazed river. A rest from grazing of 33 months resulted in increased plant cover in another section of the river system. Heavy grazing alters the physical and soil features of this river system by reducing plant cover. Riparian vegetation, by slowing flow rates and catching light soil particles increases landscape heterogeneity and creates productive sites in the landscape. © 2007 Elsevier Ltd. All rights reserved.
community composition; ephemeral pool; grazing pressure; Karoo Supergroup; landscape; livestock; plant community; plant-herbivore interaction; riparian vegetation; river system; sedge; vegetation cover; Africa; Namaqualand; Southern Africa; Sub-Saharan Africa; Animalia