Fire and life in Tarangire : effects of burning and herbivory on an East African Savanna system

This thesis investigates the effects of fire on quality and quantity of forage for grazers in the savannas of East Africa where fire has been used as a tool in pasture management for centuries. Hereby the mechanisms that cause the effects, as well as the manner in which the effects are influenced by abiotic conditions, are also discussed. Generally fire enhances the quality of forage with higher concentrations of mineral nutrients, higher digestibility and improved structural vegetation characteristics that determine forage intake. Increased nutrient concentrations in post-fire regrowth can be ascribed to higher leaf:stem ratios, rejuvenation and reduced dilution of nutrients due to lower levels of standing biomass as compared to unburned vegetation. Forage available for grazing is not enhanced through fire. Rather, especially in growth seasons of below average rainfall, the availability of forage is reduced in the post-fire growth season.With water being the prime determinant of plant growth in these systems, reduced vegetation production after burning can be explained by the reduction of soil water content as result of vegetation litter removal, which increases loss of water through evaporation. This negative effect of fire on forage availability can have dire consequences for both domestic and wild herbivore populations when no areas are available with additional resources.Results suggest that, with increased human activity in the East African savanna biome, causing a decline in natural/pastoral areas as well as an increase in grazing intensities and fire frequency, the practice of burning should be reduced rather than advocated, especially because grazing itself improves forage quality. This thesis also shows that the concentration of wildlife in protected areas, particularly elephants, and high fire frequencies, also due to increased human activities, affect the tree structure but not the density. Restriction of wildlife habitat to protected areas which lie in the dry season range will however have large consequences for migratory herbivore population numbers due to insufficient quality and quantity of forage.