Spatial matters: How spatial processes & patterns affect savanna dynamics (Thomas Groen)
Savanna ecosystems show sudden shifts from one stable state, with both trees and grasses present, to another stable state with only trees, i.e., bush encroachment. A functional understanding of how processes like herbivory and fire can induce or reduce these shifts helps in the formulation of proper management strategies for these ecosystems and to maintain the quality of its services. An emerging issue in ecology that is relevant with respect to the occurrence of ecosystem shifts is the effect that spatial patterns and processes can have on ecosystem dynamics. Spatial processes are hypothesised to mediate the occurrence of ecosystem shifts and increase the stability of ecosystems. In his PhD thesis, my former PhD student Thomas Groen addressed three questions:
1. What is the effect of spatial heterogeneity on spatial processes?
2. How is spatial heterogeneity created by spatial processes?
3. Is the occurrence of sudden ecosystem shifts influenced by these spatial patterns
Van Langevelde, F., C. de Groot, T.A. Groen, I.M.A. Heitkönig and I. Gaigher (2014) Effect of patches of woody vegetation on the role of fire in tropical grasslands and savannas. International Journal of Wildland Fire 23:410-416 (PDF)
Groen, T.A., F. van Langevelde, C.A.D.M. van de Vijver, A.L. de Raad, J. de Leeuw and H.H.T. Prins (2011) A continental analysis of correlations between tree patterns in African savannas and human and environmental variables. Journal of Arid Environments 75:724-733 (PDF)
Groen, T.A., F. van Langevelde, C.A.D.M. van de Vijver, N. Govender and H.H.T. Prins (2008) Soil clay content and fire frequency affect clustering in savanna trees in South African savannas. Journal of Tropical Ecology 24:269-279 (PDF)
De Knegt, H., T.A. Groen, C.A.D.M. van de Vijver, H.H.T. Prins and F. van Langevelde (2008) Herbivores as architects of savannas: inducing and modifying spatial vegetation patterning. Oikos 117:543-554 (PDF)
Surviving and growing amidst others: the effect of environmental factors on germination and establishment of savanna trees (Eduardo Barbosa)
Savanna ecosystems are characterized by a continuous grass layer intermixed with a discontinuous layer of trees and shrubs. A complex set of environmental drivers, such as water, soil nutrients, solar radiance, fire and herbivory, determines vegetation structure and composition in savannas. Such environmental drivers are expected to be strongly affected by future global climatic and land-use changes, potentially modifying savanna vegetation, and consequently savanna fauna. The ability to predict changes in plant community composition is therefore important for management and conservation of savannas. However, the mechanisms controlling plant establishment and growth in savannas are still unclear. Germination and seedling establishment are critical recruitment stages in the life cycle of plants and can influence plant community composition. A better understand of the factors influencing plant species recruitment and their ecology is needed. The thesis of Eduardo Barbosa focuses on seedling recruitment of several savanna tree species.
Barbosa, E.R.M., K.W. Tomlinson, L.G. Carvalheiro, K. Kirkman, S. de Bie, H.H.T. Prins and F. van Langevelde (2014) Short-term effect of nutrient availability and rainfall distribution on biomass production and leaf nutrient content of savanna tree species. Plos ONE 9:e92619 (PDF)
Barbosa, E.R.M., F. van Langevelde, K.W. Tomlinson, L.M.G.R. Carvalheiro, K. Kirkman, S. de Bie and H.H.T. Prins (2014) Tree species from different functional groups respond differently to environmental changes during establishment. Oecologia 174:1345-1357 (PDF)
Tomlinson, K.W., F.J. Sterck, F. Bongers, D.A. da Silva, E.R.M. Barbosa, D. Ward, F.T. Bakker, M. van Kaauwen, H.H.T. Prins, S. de Bie and F. van Langevelde(2012) Biomass partitioning and root morphology of savanna trees across a water gradient. Journal of Ecology 100:1113-1121 (PDF)
Van Langevelde, F., K. Tomlinson, E.R.M. Barbosa, S. de Bie, H.H.T. Prins and SI. Higgins (2011) Understanding tree-grass co-existence and impacts of disturbance and resource variability in savannas. In: M.J. Hill and N.P. Hanan (eds.), Ecosystem function in savannas. Measurement and modeling at landscape to global scales. CRC Press, Boca Raton, FL, USA, pp. 257-271