Human impacts on the functioning of African savannas

Abstract

Human impacts increasingly threaten savanna ecosystems on the African continent. Because of strong population growth in sub-Saharan Africa, even large, protected areas, such as the Serengeti-Mara Ecosystem in East Africa, are now under great pressure due to increased migration towards the borders of these areas (so-called ‘edge areas’). This development leads to a new set of ecological challenges, which includes a better understanding of the impact of human activities in and around protected areas on the functioning of savanna ecosystems. The shift in the form and the intensity of herbivory is one of the major human-induced changes in savannas. In this thesis I investigate the consequences of this shift for 1) the resilience of the landscape to drought, 2) vegetation structure, and 3) the attractiveness of edge areas for native herbivores. I also explore the usability of camera traps in the estimation of aboveground productivity, a key ecosystem function in savannas. The results show that human impacts on savannas are predictable based on abiotic environmental variables. The recent and alarming increase in woody plants in areas grazed by livestock is, for example, progressing faster in areas with lower soil fertility and finer soil texture. A second result is that edge areas still provide habitat for native animals. This is mainly so at night and predominantly to smaller species, which can be linked to a form of safety from predators in human-modified landscapes. The insights of this thesis can contribute to new strategies for the coexistence of man and nature in savannas.