Diplom thesis  Open Access 

Diplom thesis in Biology at University of Hamburg

VII + 56 + XV pp.

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Keywords: biodiversity, compositional shift, endozoochory, herbivory, intermediate disturbance hypothesis, Namaqualand, nature conservation

English abstract: The vegetation of the Knersvlakte, which is part of the southern African Succulent Karoo Biome and known for its high diversity and endemism, has been subjected to domestic livestock grazing for centuries. In the course of establishing a conservation area there, it became relevant to assess the suitability of alternative future landuse practices from a conservation point of view. In this study, I investigated the effects of grazing on the vegetation of the Knersvlakte in terms of diversity and species composition of plant communities as well as plant size and reproduction of selected species and endozoochorous dispersal. Data were sampled on four largely adjacent farms, one of which was ungrazed, one moderately and two intensively grazed. Plant community and population data were collected on 27 quartz and 24 non-quartz plots, representing the two major habitat types of the region. Within each of the 1000 m² plots, 100 subplots of 400 cm² size were sampled and analysed for diversity and compositional changes. Endozoochorous dispersal was assessed by the seedling-emergence method from domestic and wild herbivore dung, sampled on the plots. ANOVAs revealed that the species richness and abundance of endemic species on quartz fields was only slightly reduced through grazing. An association of plant strategy type and grazing intensity could not be detected, as abundance of annuals seemed to be mainly driven by rainfall which seemed to have varied spatially in the year of investigation. Ordination and fidelity analyses indicated that the species composition differed between grazing intensities and that the ungrazed and moderately grazed plots both contained unique locally endemic habitat specialists. Reproduction of Drosanthemum schoenlandianum and Argyroderma fissum was increased through moderate grazing, which in the case of D. schoenlandianum was ascribed to overcompensation for experienced biomass losses. The low number of seedlings on the moderately grazed plots was attributed to lower rainfall on the respective farm. The germination experiment revealed that dispersal of Aizoaceae was facilitated by endozoochory through domestic livestock, whereas Fabaceae mainly germinated from wild herbivore dung. From the nature conservation point of view, either the ungrazed or the moderately grazed plots showed the most favourable status in most of the parameters. In the Knersvlakte, both ungrazed areas and moderately grazed areas therefore seem to be important for the conservation of the existing plant diversity, vegetation pattern and their underlying processes.

Suggested citation:
Haarmeyer, D.H. (2009): Effects of domestic livestock on the vegetation of the Knersvlakte, South Africa - 3 in Biology at the University of Hamburg: VII + 56 + XV pp. DOI: 10.7809/thesis.diplom.002.