Dr.

Judith SITTERS

Vrije Universiteit Brussel
Campus Etterbeek, Building F, 7th floor, Room 7F403C
Pleinlaan 2, 1050 Brussels, Belgium

The ratio between trees and grasses is disturbed in many African savannas, with trees becoming increasingly dominant. This shift in the plant component is ascribed to – and will also feedback on – composition of the herbivore community, and the balance (stoichiometry) between the primary elements carbon (C), nitrogen (N) and phosphorus (P). Some interactions and feedbacks between these three major savanna components are well-studied, but others are still poorly understood. The aim of this research project is to examine how changes in the herbivore community and treegrass ratios influence ecosystem C:N:P stoichiometry and how this in turn feedbacks on tree-grass productivity. The research will be performed in a Kenyan savanna and I will use three research approaches: (i) field experiments to examine the effects of different types of herbivores on soil and plant C:N:P stoichiometry, (ii) a meta-analysis of data from studies focusing on the effects of herbivores on soil C:N:P stoichiometry, and (iii) a pot experiment to examine the effects of differences in C:N:P stoichiometry on competition between tree seedlings and grasses. The results of my research will improve our understanding of how changes in the functional composition of the herbivore community will influence savanna nutrient dynamics and consequently tree-grass ratios and will be of importance for savanna management in the face of global climate change and the decline of herbivore populations.

Sitters, J. and H. Olde Venterink. 2015. The need for a novel integrative theory on feedbacks between herbivores, plants and soil nutrient cycling. Plant and Soil 396: 421-426.

Sitters, J., C.L. Atkinson, N. Guelzow, P. Kelly, and L.L. Sullivan. 2015. Woodstoich III. Spatial stoichiometry: cross-ecosystem material flows and their impact on recipient ecosystems and organisms. OIKOS 124: 920-930.

Sitters, J., P.J. Edwards, W. Suter, and H. Olde Venterink. 2015. Acacia tree density strongly affects N and P fluxes in savanna. Biogeochemistry 123: 285-297.

Sitters, J., M. Maechler, P.J. Edwards, W. Suter, and H. Olde Venterink. 2014. Interactions between C:N:P stoichiometry and soil macrofauna control dung decomposition of savanna herbivores. Functional Ecology 28: 776-786.

Blaser, W.J., J. Sitters, S.P. Hart, P.J. Edwards, and H. Olde Venterink. 2013. Facilitative or competitive effects of woody plants on understory vegetation depend on N-fixation, canopy height and rainfall. Journal of Ecology 101: 1598-1603.

Sitters, J., P.J. Edwards, and H. Olde Venterink. 2013. Increases of soil C, N and P pools along Acacia tree density gradients and their feedbacks on trees and grasses. Ecosystems 16: 347-357.