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Effects of heuweltjies and utilization on vegetation patterns in the Succulent Karoo, South Africa



Effects of heuweltjies and utilization on vegetation patterns in the Succulent Karoo, South Africa



Journal of Arid Environments 87: 198-205



Heuweltjies are large circular earth mounds created by termites and are important features of the landscape in the Succulent Karoo biome in South Africa. This study demonstrates that heuweltjies and livestock grazing act together to shape vegetation patterns in the region. Using a multifactorial approach, we investigated the combined effects of heuweltjie-induced habitat conditions, grazing pressure and physical disturbance by livestock and native animals as well as the interactions among two distinct plant functional groups, on the composition and cover of vascular plant vegetation. Heuweltjie soils had significantly higher pH-values, finer texture, and higher concentrations of carbon, nitrogen, and phosphorus than those of the surroundings. Neither perennial nor ephemeral cover was different on- and off-mounds. However, species richness, cover of highly palatable plants and livestock grazing pressure were significantly higher between mounds. Grazing pressure generally resulted in a loss of perennial species and a shift to more ephemeral species, probably through the competitive release of annuals and geophytes from perennial plants. We propose that the apparent contradiction between superior nutrient conditions and inferior plant food quality on heuweltjies is caused by a combination of otherwise unfavourable soil properties and historic overgrazing of heuweltjies resulting in local degradation of the vegetation. Heuweltjies are an example of ecosystem engineering. Higher soil nutrient contents in the centre than in the border areas of heuweltjies. Fewer highly palatable plants on heuweltjies lead to less utilization by livestock. Grazing and heuweltjies are key determinants of Succulent Karoo vegetation patterns. Multifactorial approach reveals they cause a homogenization of perennial vegetation.

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Accession: 036572806

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DOI: 10.1016/j.jaridenv.2012.05.007


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