Browsing by Author "Coetsee, Corli"

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    Herbivores shape woody plant communities in theKruger National Park: lessons from three long-termexclosures
    (2014) WigleyI, Benjamin J; Fritz, Herve; Coetsee, Corli; Bond, William J
    The role of grazers in determining vegetation community compositions and structuring plant communities is well recognised in grassy systems. The role of browsers in affecting savanna woody plant communities is less clear. We used three long-term exclosures in the Kruger National Park to determine the effect of browsers on species compositions and population structures of woody communities. Species assemblages, plant traits relating to browsing and soil nutrients were compared inside and outside of the exclosures. Our results showed that browsers directly impact plant species distributions, densities and population structures by actively selecting for species with traits which make them desirable to browsers. Species with high leaf nitrogen, low total phenolic content and low acid detergent lignin appeared to be favoured by herbivores and therefore tend to be rare outside of the exclosures. This study also suggested that browsers have important indirect effects on savanna functioning, as the reduction of woody cover can result in less litter of lower quality, which in turn can result in lower soil fertility. However, the magnitude of browser effects appeared to depend on inherent soil fertility and climate. CONSERVATION IMPLICATIONS: Browsers were shown to have significant impacts on plant communities. They have noticeable effects on local species diversity and population structure, as well as soil nutrients. These impacts are shown to be related to the underlying geology and climate. The effects of browsers on woody communities were shown to be greater in low rainfall, fertile areas compared to high rainfall, infertile soils.
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    Long-term effects of fire on nitrogen cycling in a broad-leaf savanna, Kruger National Park, South Africa
    (2007) Coetsee, Corli; February, Edmund C; Bond, William J
    Fire with herbivory, climate, and soil properties including nutrients are said to be important in regulating the structure and function of savanna ecosystems. Frequent fire is often held responsible for a decrease in nitrogen pools and availability and the maintenance of low fertility conditions. However, previous research in the Kruger National Park (KNP) and elsewhere found conflicting results for the effects of fire on nitrogen pools and transformation rates. The main aim of this study was to gain a better understanding ofthe long-term effects of fire on nitrogen cycling in the KNP. The KNP provided an ideal opportunity for this study because of the initiation of a fire experiment in 1954. The Experimental Bum Plot (EBP) experiment was initiated in four representative landscapes of the KNP to determine the effects of fire on vegetation structure. I tested the effect of burning on nitrogen cycling and productivity in four fire treatments situated in Pretoriuskop Sour Bushveld (broad-leaf savanna). The fire treatments included a late winter, annual bum (August), late winter and summer triennial bums (August and February) and a fire exclusion treatment. Total soil nitrogen, available nitrogen, woody biomass and herbaceous production were measured. 1 hypothesized that vegetation adapted to low N conditions with low N foliage would be expected to dominate in frequently burnt areas if fire was to decrease N pools and fluxes.