| Summary: | Quartz fields contribute significantly to plant diversity in the Succulent Karoo biome. They are distinctly different from surrounding habitats and have high levels of plant endemism. Biological soil crusts are features of quartz field soils and fulfill a vital function in that they stabilize soils. It is important for managers of nature reserves and agricultural rangelands to know what factors influence quartz field soils and vegetation. Both stakeholders could benefit from new information that would allow for informed decision-making regarding land-use on quartz fields. The present study took place in the Namaqua National Park that contains a significant proportion of the Riethuis-Wallekraal quartz fields phytochorion. The first part of the study aimed to understand whether certain land-use activities potentially destabilize quartz field soils, which might have possible ramifications for associated biological soil crusts and vegetation. It was followed by relating variation in soil stability with species richness, cover and species composition of quartz field vegetation. Overall, positions assumed to be impacted by land-use activities had less stable soils compared to positions assumed not be impacted. Soil stability had a significant influence on species richness and cover but to a lesser degree on species composition. Quartz field vegetation was significantly influenced by soil physical and chemical properties as well as location in the quartz fields landscape. The second part of the study aimed at understanding how species richness of isolated quartz outcrops is related to their size compared to that of a mainland body of quartz outcrops. No clear species-area relationships emerged from the study. There were significant differences between isolated outcrops and mainland outcrops in substrate and vegetation composition. Findings are discussed in relation to Island Biogeography Theory.
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