| Abstract |
In many southern African grazing systems wild-ranging wildlife has been replaced by livestock, which often leads to overgrazing. As a result, bush and shrub encroachment is a major problem in southern Africa. It leads to a reduction of grasslands, the invasion of thorn shrubs, a reduced carrying capacity for livestock, desertification and socio-economic problems in arid and semi-arid regions, as previously profitable areas are no longer economically viable. This study aims to determine how standing biomass of grass vegetation and its key chemical characteristics differ between sites with low and high grazing pressure. Furthermore, it determines how much time pasture in heavily grazed areas needs to recover from overgrazing effects to approach the properties of similar sites under low grazing pressure. In heavily grazed areas, grass is of higher quality than in areas with low grazing pressure as the remaining or re-growing grass contains higher percentages of protein and lower concentrations of fiber. However, heavy grazing leads to reduced grass biomass. As a consequence, the absolute amount of protein available per unit area is lower in areas with high than in areas with low grazing pressure, The exclusion of livestock resulted in a rapid increase of grass biomass and therefore higher amounts of fibre, protein and hemicellulose per unit area contents after one wet season, though the chemical concentrations of plant compounds changed remarkably little after exclusion of livestock grazing. Furthermore, at the heavily grazed area we recorded a high abundance of unpalatable plant species. In order to prevent overgrazing and subsequent negative impacts like bush encroachment or desertification in areas where cattle substitutes wild-ranging herbivores, it is necessary to implement rotating grazing systems and lower stocking rates, as well as the use of a combination of different wild and domestic herbivores for sustainable development. |
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