Diversity and composition of herbaceous species in areas with different grazing intensity in Kweneng district, Botswana (Platform)

Abstract

Vegetation surveys were conducted in Kweneng district to make an inventory of herbaceous species in the area. This was done so as to have an inventory of species found in the area and to find out which species are associated with different grazing pressures. Grazing pressure considered were by cattle which are mainly grazers. Assessments were done in 2014 and 2015 mostly during the wet seasons when it was possible to identify grasses and forbs. Vegetation surveys were carried out in 10 m x 10 m temporary set plots in the study areas. The plots were at least 5 km apart to be able to cover a large part of the study area which is relatively big compared to some districts within the country. The area is on the Kalahari sandy soils with annual rainfall around 500 mm. Within the plot, individual grasses and forbs species were identified and counted by species. The grazing intensities were divided into 3 classes being slight, moderate and severe. Grazing intensities were visual assessed. Slight grazing pressure was when the area was estimated to have 5 % and less of the herbaceous layer grazed. Moderate was when grazing on herbaceous layer was estimated to be in the range of 5 % to 25 %. Severe was when more than 25 % of the herbaceous layer was grazed. Relative species abundances, similarity index and Shannon-Weaner diversity index were computed. More than 29 grass species and more than 80 forbs were recorded. Thus the area is still rich in herbaceous species. High species diversity was observed for slightly grazed areas followed by the moderate while severely grazed areas had lower diversities. Perennial grasses dominated in slightly and moderately grazed areas while annual and forbs dominated in severely grazed areas. These results show that grazing need to be moderate to conserve grasses and forbs diversities.