Schleicher, J. (corresponding author, firstname.lastname@example.org); Meyer, K.M. (Katrin.Meyer@forst.uni-goettingen.de) & Wiegand, K. (email@example.com): Institute of Ecology, University of Jena, Dornburger Str. 159, D-07743 Jena, Germany Schurr, F.M. (firstname.lastname@example.org): Plant Ecology and Nature Conservation, Institute of Biochemistry and Biology, University of Potsdam, Maulbeerallee 2, D-14469 Potsdam, Germany Ward, D. (email@example.com): School of Biological and Conservation Sciences, University of KwaZulu-Natal, Scottsville 3209, South Africa Schleicher, J.: Current address: Department of Bioinformatics, University of Jena, Ernst-Abbe-Platz 2, D-07743 Jena, Germany Meyer, K.M. & Wiegand, K.: Current address: Ecosystem Modelling, Faculty of Forest Sciences and Forest Ecology, University of Göttingen, Büsgenweg 4, D-37077 Göttingen, Germany.
Disentangling facilitation and seed dispersal from environmental heterogeneity as mechanisms generating associations between savanna plants
Article first published online: 18 JUL 2011
© 2011 International Association for Vegetation Science
Journal of Vegetation Science
Volume 22, Issue 6, pages 1038–1048, December 2011
How to Cite
Schleicher, J., Meyer, K. M., Wiegand, K., Schurr, F. M. and Ward, D. (2011), Disentangling facilitation and seed dispersal from environmental heterogeneity as mechanisms generating associations between savanna plants. Journal of Vegetation Science, 22: 1038–1048. doi: 10.1111/j.1654-1103.2011.01310.x
Co-ordinating Editor: Beverly Collins
- Issue published online: 5 OCT 2011
- Article first published online: 18 JUL 2011
- Received 22 April 2010, Accepted 12 May 2011
- Acacia erioloba;
- Grewia flava;
- Plant interactions;
- Spatial association;
- Wiegand-Moloney O-ring statistics
Question: How can we disentangle facilitation and seed dispersal from environmental heterogeneity as mechanisms causing spatial associations of plant species?
Location: Semi-arid savanna in the Kimberley Thorn Bushveld, South Africa.
Methods: We developed a two-step protocol for the statistical differentiation of association-promoting mechanisms in plants based on the Acacia erioloba–Grewia flava association. Individuals of the savanna shrub G. flava and the tree A. erioloba were mapped on four study plots. Disentangling the mechanism causing the association of G. flava and A. erioloba involved tests of three spatial and one non-spatial null model. The spatial null models include homogeneous and heterogeneous Poisson processes for spatial randomness based on the bivariate spatial point patterns of the four plots. With the non-spatial analysis, we determined the relationship between the canopy diameter of A. erioloba trees and presence or absence of G. flava shrubs in the tree understorey to find whether shrub presence requires a minimum tree canopy diameter.
Results: We first showed a significant positive spatial association of the two species. Thereafter, the non-spatial analysis supported an exclusion of environmental heterogeneity as the sole cause of this positive association. We found a minimum tree size under which no G. flava shrubs occurred.
Conclusions: Our two-step analysis showed that it is unlikely that heterogeneous environmental conditions caused the spatial association of A. erioloba and G. flava. Instead, this association may have been caused by seed dispersal and/or facilitation (e.g. caused by hydraulic lift and/or nitrogen fixation by the host tree).