Skip to main content Accessibility help

Soil clay content and fire frequency affect clustering in trees in South African savannas

  • Thomas A. Groen (a1) (a2), Frank van Langevelde (a1), Claudius A.D.M. van de Vijver (a3), Navashni Govender (a4) and Herbert H.T. Prins (a1)...


In this paper, we investigate which factors determine tree clustering in Southern African savannas. This was tested by measuring clustering of trees using the T-squared sampling method in plots of the Kruger National Park experimental burning programme in South Africa. Fire return interval is the main treatment in these plots, but also several auxiliary determining parameters like clay content in the soil, diameter of tree canopies, understorey composition, tree species diversity and average annual rainfall were measured while sampling. In the Kruger National Park 48 plots distributed over four different landscape types and with three different burning treatments (never, once every 3 y and annually) were sampled. First, we related the clustering of trees to these environmental variables. When looking at the most abundant species in each plot, the analysis revealed that clustering is mainly correlated with clay content in the soil. This analysis also showed that fire frequency had a positive effect on the clustering of tree species that are not very abundant. We suggest that less abundant species might be less resistant to fire and therefore adopt a mechanism of clustering to exclude grass fires under their canopy. Finally, we tested the effect of clustering on the impact of fire on trees by analysing the relationship between the distance of a tree to its nearest neighbour and its canopy diameter. We found that clustering reduces the damaging effect of fire on trees. Our study contributes to understanding of savanna functioning by showing which processes are relevant in the distribution of savanna trees.


Corresponding author

1Corresponding author:


Hide All
ARCHIBALD, S., BOND, W. J., STOCK, W. D. & FAIRBANKS, D. H. K. 2004. Shaping the landscape: fire–grazer interactions in an African savanna. Ecological Applications 15:96109.
BAROT, S., GIGNOUX, J. & MENAUT, J. C. 1999. Demography of a savanna palm tree: predictions from comprehensive spatial pattern analyses. Ecology 80:19872005.
BERJAK, S. G. & HEARNE, J. W. 2002. An improved cellular automaton model for simulating fire in a spatially heterogeneous savanna system. Ecological Modelling 148:133151.
BIGGS, R., BIGGS, H. C., DUNNE, T. T., GOVENDER, N. & POTGIETER, A. L. F. 2003. Experimental burn plot trial in the Kruger National Park: history, experimental design and suggestions for data analysis. Koedoe 46:115.
BYRAM, G. M. 1959. Combustion of forest fuels. Pp. 155182 in Davies, K. P. (ed.). Forest fire: control and use. McGraw-Hill, New York.
CAYLOR, K. K., SHUGART, H. H., DOWTY, P. R. & SMITH, T. M. 2003. Tree spacing along the Kalahari transect in Southern Africa. Journal of Arid Environments 54:281296.
CARRICK, P. J. 2003. Competitive and facilitative relationships among tree shrub species and the role of browsing intensity and rooting depth in the succulent Karoo, South Africa. Journal of Vegetation Science 14:761772.
DE RIDDER, N. & VAN KEULEN, H. 1995. Estimating biomass through transfer functions based on simulation model results: a case study for the Sahel. Agricultural Water Management 28:5771.
DE RONDE, C., TROLLOPE, W. S. W., PARR, C. L., BROCKETT, B. H. & GELDENHUYS, C. J. 2004. Fire effects on flora and fauna. Pp. 6087 in Goldhammer, J. G. & De Ronde, C. (eds.). Wildland fire management: handbook for Sub-Sahara Africa. Global Fire Monitoring Centre, Freiburg.
DIGGLE, P. J. 2003. Statistical analysis of spatial point patterns. Oxford University Press, Oxford. 159 pp.
EUROCONSULT 1989. Agricultural compendium for rural development in the tropics and subtropics. Elsevier, Amsterdam. 740 pp.
GERTENBACH, W. P. D. 1983. Landscapes of the Kruger National Park. Koedoe 26:9121.
GIBBS RUSSEL, G. E., WATSON, L., KOEKEMOER, M., SMOOK, L., BARKER, N. P., ANDERSON, H. M. & DALLWITZ, M. J. 1990. Grasses of Southern Africa. National Botanic Gardens/Botanical Research Institute, South Africa. 437 pp.
GIGNOUX, J., NOBLE, I. R. & MENAUT, J. C. 1995. Modelling tree community dynamics in savannas: effects of competition with grasses and impact of disturbance. Pp. 219230 in Bellan-Santini, D., Bonin, G. & Emig, C. (eds.). Functioning and dynamics of natural and perturbed ecosystems. Intercept Ltd, Paris.
GIGNOUX, J., MENAUT, J. C., NOBLE, I. R. & DAVIES, I. D. 1998. A spatial model of savanna function and dynamics: model description and preliminary results. Pp. 361383 in Newbery, D. M., Prins, H. H. T. & Brown, N. (eds.). Dynamics of tropical communities. Blackwell, Oxford. 635 pp.
GOHEEN, J. R., YOUNG, T. P., KEESING, F. & PALMER, T. M. 2007. Consequences of herbivory by native ungulates for the reproduction of a savanna tree. Journal of Ecology 95:129138.
GOVENDER, N., TROLLOPE, W. S. W. & VAN WILGEN, B. W. 2006. The effect of fire season, fire frequency, rainfall and management on fire intensity in savanna vegetation in South Africa. Journal of Applied Ecology 43:748758.
GRICE, T. C. & SLATTER, S. M. 1996. Fire in the management of Northern Australian pastoral lands. Tropical Grassland Society of Australia. Occasional publication No. 8.
HINES, W. G. S. & HINES, R. J. O. 1979. The Eberhardt statistic and the detection of nonrandomness of spatial point distributions. Biometrika 66:7379.
HOWARD, T. 2000. Introduced grasses, poor master, but useful servant. Land Management.
JELTSCH, F., MILTON, S. J., DEAN, W. R. J. & ROOYEN, N. 1996. Tree spacing and coexistence in semiarid savannas. Journal of Ecology 84:583595.
JELTSCH, F., MILTON, S. J., DEAN, W. R. J., VAN ROOYEN, N. & MOLONEY, K. A. 1998. Modelling the impact of small-scale heterogeneities on tree-grass coexistence in semi-arid savannas. Journal of Ecology 86:780793.
JOQUET, P., TAVERNIER, V., ABBADIE, L. & LEPAGE, M. 2005. Nests of subterranean fungus-growing termites (Isoptera, Macrotermitinae) as nutrient patches for grasses in savannah ecosystems. African Journal of Ecology 43:191196.
KENNEDY, A. D. & POTGIETER, A. L. F. 2003. Fire season affects size and architecture of Colophospermum mopane in southern African savannas. Plant Ecology 167:179193.
KONATÉ, S., LE ROUX, X., TESSIER, D. & LEPAGE, M. 1999. Influence of large termitaria on soil characteristics, soil water regime, and tree leaf shedding pattern in a West African savanna. Plant and Soil 206:4760.
MARION, G., SWAIN, D. L. & HUTCHINGS, M. R. 2004. Understanding foraging behaviour in spatially heterogeneous environments. Journal of Theoretical Biology 292:127142.
NDIAYE, D., LENSI, R., LEPAGE, M. & BRAUMAN, A. 2004. The effect of the soil-feeding termite Cubitermes niokoloensis on soil microbial activity in a semi-arid savanna in West Africa. Plant and Soil 259:277286.
PACALA, S. W. & LEVIN, S. A. 1997. Biologically generated spatial pattern and the coexistence of competing species. Pp. 204232 in Tilman, D. & Kareiva, P. (eds.). Spatial ecology: the role of space in population dynamics and interspecific interactions. Princeton University Press, Princeton.
PICARD, N., KOUYATÉ, A. M. & DESSARD, H. 2005. Tree density estimation using a distance method in Mali Savanna. Forest Science 51:718.
PRINS, H. H. T. & VAN DER JEUGD, H. P. 1993. Herbivore population crashes and woodland structure in East Africa. Journal of Ecology 81:305314.
RIETKERK, M., BOERLIJST, M. C., VAN LANGEVELDE, F., HILLERISLAMBERS, R., VAN DE KOPPEL, J., KUMAR, L., PRINS, H. H. T. & DE ROOS, A. M. 2002. Self organisation of vegetation in arid ecosystems. American Naturalist 160:524530.
SCHOLES, R. J. & ARCHER, S. R. 1997. Tree-grass interactions in savannas. Annual Reviews of Ecological Systems 28:517544.
SHEA, R. W., SHEA, B. W., KAUFFMAN, J. B., WARD, D. E., HASKINS, C. I. & SCHOLES, M. C. 1996. Fuel biomass and consumption factors associated with fires in savanna ecosystems of South Africa and Zambia. Journal of Geophysical Research 101:2355123568.
SKARPE, C. 1991. Spatial patterns end dynamics of woody vegetation in an arid savanna. Journal of Vegetation Science 2:565572.
SMITH, T. M. & GOODMAN, P. S. 1986. The effect of competition on the structure and dynamics of Acacia savannas in Southern Africa. Journal of Ecology 74:10311044.
TAINTON, N. M. 1999. Veld management in South Africa. University of Natal Press, Pietermaritzburg. 472 pp.
VAN DE VIJVER, C. A. D. M., FOLEY, C. A. & OLFF, H. 1999. Changes in the woody component of an East African savanna during 25 years. Journal of Tropical Ecology 15:545564.
VAN LANGEVELDE, F., VAN DE VIJVER, C. A. D. M., KUMAR, L., VAN DE KOPPEL, J., DE RIDDER, N., VAN ANDEL, J., SKIDMORE, A. K., HEARNE, J. W., STROOSNIJDER, L., BOND, W. J., PRINS, H. H. T. & RIETKERK, M. 2003. Effects of fire and herbivory on the stability of savanna ecosystems. Ecology 84:337350.
VAN NES, E. H. & SCHEFFER, M. 2005. Implications of spatial heterogeneity for catastrophic regime shifts in ecosystems. Ecology 86:17971807.
WALKER, B. H. & NOY-MEIR, I. 1982. Aspects of the stability and resilience of savanna ecosystems. Pp. 556590 in Huntley, B. J. & Walker, B. H. (eds.). Ecology of tropical savannas. Springer Verlag, Berlin.
WALLMER, M. 1994. Grass fuel build up over time on tropical hillslopes. Pp. 3033 in Van Cuyenberg, S. (ed.). Proceedings of the Fire Ecology Workshop. Parks and Wildlife Commission, Darwin.
ZAR, J. H. 1996. Biostatistical analysis. Prentice-Hall, Upper Saddle River. 931 pp.



Full text views

Total number of HTML views: 0
Total number of PDF views: 0 *
Loading metrics...

Abstract views

Total abstract views: 0 *
Loading metrics...

* Views captured on Cambridge Core between <date>. This data will be updated every 24 hours.

Usage data cannot currently be displayed