Pyric herbivory: Understanding fire-herbivore interactions in Gorongosa National Park

Abstract

Fire plays a major role in determining the structure and dynamics of tropical savannas. By removing old biomass and promoting nutritious regrowth, it facilitates the coexistence of grass and trees characteristic of these ecosystems. Though extensive research has been conducted on the immediate and lasting effects of these disturbances on the density and nutritional quality of vegetation, the interactive effects of fire and herbivory on the nutritional landscape are more poorly understood. The frequency with which an area burns may dictate the overall palatability and biomass density of savanna grasses, generating heterogeneity in the vegetation available to grazers and promoting herbivore diversity through niche partitioning. This study examines the interaction of fire, vegetation and herbivores in Gorongosa National Park in Mozambique, in which controlled burns are used as a tool of active management. I found that though the amount of vegetation available to grazers did not vary significantly with fire frequency or herbivory pressure, forage material had significantly higher protein and calcium content in areas with higher grazing intensity and burn frequency. I also found that ungulates tend to avoid recently burned areas, but that small ungulates in general and nonruminants in particular return to burned patches more quickly than large ungulates and ruminants. Accordingly, fires create a heterogeneous landscape of burned and unburned patches that ungulates selectively graze upon based on their body size and digestive strategy.