Implications of changing land use and introducing extralimital giraffe on vegetation in the subtropical thicket, South Africa

Abstract

Land use change has increased in southern Africa as many livestock farms convert to game reserves, to restore degraded and overgrazed lands. This leads to a change in herbivore communities with potential positive and negative consequences for vegetation and landscape productivity. This study aimed to look at the effect of land use change and subsequent herbivore community changes, on thicket vegetation structure, composition, and landscape productivity. To attain the study objectives, data were collected from four game reserves and their adjacent livestock farms within the Eastern Cape province in South Africa. These sites were selected because they are within the Subtropical Thicket biome (similar vegetation) and were once used for livestock farming. At each study site, vegetation composition and structure were assessed using a unique bush clump sampling technique along fence line contrasts. Six plots were sampled at each site, three plots on the game reserve lands and three plots on the adjacent livestock farmlands during the dry (July/August 2020) and wet (January/February 2021) seasons. The Normalized Difference Vegetation Index (NDVI), in-situ leaf area index (LAI) and the fraction of intercepted photosynthetically active radiation (FIPAR), were used to assess vegetation productivity between the two land use types. Additionally, diet of an extralimital herbivore, giraffe (Giraffa camelopardalis), was assessed during contrasting seasons (dry and wet) to infer the role this species might have on these landscapes. The diet of giraffes was assessed through field observations, recording plant species that giraffes were feeding on. Floristic results showed that there were no differences in vegetation structure, species composition and richness between the two land types. There was no difference in the overall diversity of plant species on the game reserves than in the adjacent livestock farms. The primary productivity was greater on the game reserves compared to the livestock farms. Field observations of giraffe feeding showed that they fed predominantly on Vachellia karroo followed by Searsia longispina. Their diets did not differ between the two seasons. My study provides an insight into the effects of changing land use and this information can be used to infer the extent to which these changes might have on restoration of degraded landscape and how land use changes may be effective in restoring the degraded thicket vegetation caused by overgrazing and overstocking of domestic livestock.