Feodor-Lynen stipend: The interplay of large grazing ungulates, woody, and grassy vegetation in a South African savanna

Savanna vegetation is poor in nutrients but provides food and shelter for high numbers of wild and domestic ungulates. Large single standing trees in savannas are increasingly threatened and reduced by harvesting activities and climate change. On the other hand, the encroachment of woody vegetation, i.e., dense thickets of small bushes and trees on formerly open grasslands, reduces the area of valuable pasture land. These trends are alarming as they can substantially influence the carrying capacity of savanna systems for wild and domestic grazing animals. However, it has not been quantified how these changes in woody cover affect grazing fauna and adjacent flora in the long run and how, in turn, grazing pressure, climatic conditions, and management decisions such as fire frequencies contribute to vegetational shifts in savannas. Here, I plan to quantify the attractive properties woody cover provides for wild and domestic grazer species through empirical, experimental, and modelling approaches. Direct and indirect observation techniques will indicate habitat preferences and food selectivity of grazers. I will further use ^14/15N and ^12/13C isotopic ratios in grass and dung to estimate the amount of grasses growing beneath large trees and ingested by grazing ungulates. Experiments conducted on livestock feeding behaviour will highlight nutritional or structural reasons of possible beneath-canopy feeding preferences. Spatially explicit modelling of nutrient-depositions and uptake will provide estimates on future nutrient fluxes in the savanna systems with respect to tree presence. Last but not least, as savannas might represent a more essential carbon (C) sink as has been acknowledged, yet, I will quantify the C-storage potential of savanna grasses and how it is changed with grazing intensity and climatic conditions. The herewith proposed research will provide insights into tree-grass-grazer relationships and how strongly vegetation structure and diversity can be altered through changing land-use and climatic conditions in African savanna systems.