The influence of fire on savanna fauna: implications for conservation management

Abstract

Fire is an important natural disturbance that acts as a major driver of community dynamics and ecosystem function. While fire is increasingly used as a management tool to conserve and manage biodiversity in fire-prone systems, key gaps remain in our understanding of how biological communities respond to fire and the mechanisms driving community assembly. In this thesis, I evaluated the effects of long-term variation in fire regimes on large herbivorous mammals, birds and invertebrates in a South African savanna system. I tested the hypothesis that fire-mediated landscape heterogeneity (pyrodiversity) promotes biodiversity. First, I evaluated this hypothesis for large mammals by examining the relationship between their density and the diversity of fire age-classes on the landscape. Second, I tested this hypothesis for birds by assessing the effects of the diversity and configuration of fire age-classes on species richness and functional diversity at multiple spatial scales. Next, I evaluated how interactions between fire regimes and climate influenced invertebrate communities. Lastly, I assessed whether the indirect effects of fire on avian insectivores were mediated by vegetation structure or food availability. I surveyed for large mammals, birds and invertebrates across a landscape that represented approximately three decades of variation in fire age-classes and fire frequency. I did not find landscape-level pyrodiversity promoted the diversity or density of savanna fauna. Instead, I found that the extent of recently burned (<1-year post-fire) habitat and distance to water were the greatest predictors of large mammal density and that the extent of recently burned and unburned (≥10-years post-fire) habitat were important predictors of avian species richness and functional diversity at two spatial scales (100 ha and 500 ha). I reveal that time-since-fire and fire frequency had opposing and interacting influences on grass-layer and ground-layer invertebrate communities, and these relationships were strongly mediated by seasonal rainfall. Lastly, relationships between fire and avian insectivores were mediated by vegetation structure and invertebrates, and these relationships were regulated by functional traits (i.e., niche breadth and body mass). In this thesis, I have demonstrated the long-term impact that fire regimes have on savanna communities. I suggest that fire management will be enhanced by a mechanistic understanding of fire-fauna relationships and consideration of trophic and climatic interactions. Current fire management practices have led to an insufficient extent of late-seral savanna and efforts should be taken to increase the amount of this habitat to increase faunal diversity, function and ecosystem resilience. Furthermore, management strategies to reduce burning during periods of low rainfall are likely to maximise the diversity and abundance of invertebrates and the species that rely on them.