Grazing lawns affect vegetation composition and diversity of the endangered silcrete fynbos in the Bontebok National Park

Abstract

Grazing animals affect their environment. The Bontebok National Park hosts a number of hooved animals, which causes alterations to the habitat, resulting in the establishment of grazing lawns. The proliferation of these lawns may pose a threat to the intact natural vegetation occurring in the park. The aim of this study was to determine how the existence of these lawns impact the endangered Swellendam Silcrete Fynbos vegetation in the park. Sites were identified in three categories in the park, namely lawns, ecotones, and natural vegetation areas. Vegetation was sampled to assess the species diversity and composition in the three zones, and soils were collected to investigate physio-chemical parameters. Species diversity indices were calculated for the vegetation that were sampled. Soil physico-chemical parameters were used to generate a PCA and box plots for comparison between the different zones sampled in the BNP. Dendrograms were created to show similarities in plant species across the various sites that were sampled. The BNP is dominated by shrubs and grasses, with compositional shifts taking place from the natural vegetation transitioning to lawns. Plant assemblages showed a noticeable decrease in diversity in larger lawns, and the greatest diversity was seen in the ecotones. Soils found in the lawns had higher amounts of macro- and micronutrients, as well as heavy metals. Medium and large lawns also had higher pH levels causing soils to become more basic. These factors all play a role in contributing to the composition shift of vegetation in the intact vegetation from being dominated by shrubs to lower growing vegetation such as grasses and forbs in the lawns. Grazing can have dire impacts on vegetation diversity and can pose a major threat to the endangered vegetation and soil physiochemical parameters in the park. Park management should monitor grazing animal densities adaptively to reduce the spread of lawns and loss of biodiversity in the adjacent vegetation assemblages.