Effects of frequent burning on grass-grazer interactions in a mesic savanna

Master Thesis


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University of Cape Town

Fires are often used as a management tool in both game reserves and rangelands to manipulate food availability for grazing animals. After fires, large areas of the landscape are quickly covered with nutritious new regrowth, which grazers move into and utilise as a food resource. The effect of this change in animal grazing patterns on the grass communities is not yet well understood. Certain grass communities depend on heavy, continuous grazing for their persistence: they are out-competed by taller-growing species in the absence of grazing. Conversely, the taller-growing species die out under heavy grazing. Thus, in many savanna and grassland ecosystems, the grass community present in an area depends on how frequently and how intensively the area is grazed. Every year, fires in these systems are altering the distribution of grazing in space and time, by altering the proportions and distributions of short, palatable grass. In my MSc I present data describing how fire alters grazing patterns, and I show how this can result in the disappearance of intensively grazed patches in the landscape. I also use a model to illustrate how this effect might be mediated by rainfall and grazer density, and by different fire regimes. I investigate long-term consequences of this process on the distributions of alternative grassland states in Hluhluwe Umfolozi Park and show that lawn-grass-dominated areas are associated with a less-frequent fire regime. Thus, although large fires provide high-quality grazing in the short term, in the long term they could be limiting the amount of grazing in an area, because they prevent the initiation and spread of grazing-tolerant lawn-grasslands, which can support high grazer numbers and a high diversity of grazers.

Bibliography: leaves 127-133.