Long-term effects of fire on nitrogen cycling in a broad-leaf savanna, Kruger National Park, South Africa

Doctoral Thesis


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University of Cape Town

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.

Includes bibliographical references (p. 118-139).