Short-term grazing exclusion impacts using brush packs on soil and grass layers in degraded communal rangelands of semi-arid South Africa and implications for restoration and pasture utilization

Abstract

Brush packs from very thorny tree branches were used to simulate grazing exclosures to measure differences in herbaceous vegetation and soil characteristics over 2 years on small ungrazed plots and large continuously grazed communal rangelands on 3 semi-arid soil types [shallow, red stony ground (SRSG); shallow, dark sandy loam (SDSL); and deep, dark clay-loam (DCL)]. Pasture presentation yields within exclosures exceeded those on continuously grazed areas for all soil types by: 98% (SRSG), 128% (SDSL) and 152% (DCL). Herbage samples harvested from the exclosures contained higher acid detergent fiber (P≤0.001) and acid detergent lignin (P<0.05) concentrations than those from the grazed areas. In SRSG and SDSL soils, herbage samples harvested from the exclosures were deficient in phosphorus (P) for all livestock species. Depending on soil type(s), soil magnesium, organic carbon, nitrogen, P and manganese concentrations were significantly higher within exclosures than in continuously grazed areas (P≤0.05). Any response from nutrients supplied by leaf drop from the brush packs could not be separated from response due to absence of grazing, and this deserves further investigation. Our results indicate that grazing exclusion for short periods (2 years) on these semi-arid rangelands allowed pastures to produce significant growth, demonstrating that pastures were still productive. Our experiences highlighted the difficulties in erecting and retaining conventional fences to exclude livestock from given areas because of theft. Grazing immediately after vegetation recovery may necessitate judicious nutritional intervention with protein, energy and mineral supplementation to get effective utilization of the available forage.