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Accueil du site → Doctorat → Royaume-Uni → 1990 → Soils, vegetation and herbivores in the Sabi-Sand Wildtuin, Transvaal, S.A.

University of Oxford (1990)

Soils, vegetation and herbivores in the Sabi-Sand Wildtuin, Transvaal, S.A.

Ben-Shahar, Raphael

Titre : Soils, vegetation and herbivores in the Sabi-Sand Wildtuin, Transvaal, S.A.

Auteur : Ben-Shahar, Raphael.

Université de soutenance : University of Oxford

Grade : Doctor of Philosophy (PhD) 1990

Résumé
Soils, vegetation and large herbivores were studied in the Sabi-Sand Wildtuin, a semi-arid nature reserve bordering the south western perimeter of the Kruger National Park, South Africa. Classification and ordination of soil samples that included physical factors and chemical composition showed continuous gradients which corresponded to the variations of the geological formations and the relative position of samples along the gently undulating terrain which characterizes the region. Ordination of vegetation plots showed that the variations in plant species composition and abundance had a strong affinity to their relative position along the local catenary landscape. Soil moisture dynamics on crests and slopes of catenary landscape were measured during two successive annual rainfall periods. The general pattern showed a rapid saturation of soil which was followed by a slow dry out. There was some segregation between soil depths, although the duration of saturation in the rainy season and subsequent dry out of soils levels differed more between rainy seasons that between soil levels at a particular season. Patterns of woody plants dispersal in bush encroached areas confirmed that the relationships between tree species could be explained in terms of intra and inter-specific competition. It appeared that within defined plant communities, a transition of relative abundance was occurring between dominating tree species namely, A. senegal became dominant in areas previously dominated by A. tortilis while E. divinorum was replacing previous A. nilotica dominance. The local movement patterns of zebra (Equus burchelli), wildebeest (Connochaetes taurinus) and impala (Aepyceros melampus) were recorded between four habitat types that were defined in relation to the geo-morphological features of the area. Zebra were common in the dolerite areas. Wildebeest and impala in contrast, were aggregated in bottomland areas during the mid and late summer months. A time series analysis confirmed that the latter trends were seasonal. Analysis of monthly diet composition showed that considerable overlap in grass species composition existed between the diets of wildebeest and zebra. Seasonal patterns were apparent in the diet composition of wildebeest in contrast to zebra. Grass nutrient contents were analyzed in Panicum maximum, Dactyloctenium aegypteum and Themeda triandra that were principal foods of wildebeest and zebra and dominated habitats along the granitic catena and dolerite formation. Results of moisture, nitrogen and phosphorus levels were not indicative of their respective measures in the soils where the species were abundant. Correlations between the seasonal fluctuations of nutrient levels in grasses and habitat preferences and grazing patterns of wildebeest and zebra indicated that ungulates were responding to variations in nutritional contents of grasses. Grazing patterns of ungulates suggested that wildebeest were more sensitive to variations in the nutritional contents of grasses while zebra had affinities to particular grass species. Overall, both ungulates appeared to satisfy their food

Mots clés : Transvaal ecosystems Zoology Ecology Botany Zoology Ecology Botany

Présentation : EThOS)

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