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

Published online by Cambridge University Press:  01 May 2008

Thomas A. Groen ,
Frank van Langevelde ,
Claudius A.D.M. van de Vijver ,
Navashni Govender  and
Herbert H.T. Prins
Thomas A. Groen*
Affiliation:
Resource Ecology Group, Wageningen University, PO Box 47, 6700 AA, Wageningen, The Netherlands International Institute for Geo-Information Science and Earth Observation, PO Box 6, 7500 AA, Enschede, the Netherlands
Frank van Langevelde
Affiliation:
Resource Ecology Group, Wageningen University, PO Box 47, 6700 AA, Wageningen, The Netherlands
Claudius A.D.M. van de Vijver
Affiliation:
Plant Production Systems, Wageningen University, Haarweg 333, 6709 RZ Wageningen, The Netherlands
Navashni Govender
Affiliation:
South African National Parks, Scientific Services, Private Bag X402, Skukuza, 1350, Republic of South Africa
Herbert H.T. Prins
Affiliation:
Resource Ecology Group, Wageningen University, PO Box 47, 6700 AA, Wageningen, The Netherlands
*
1Corresponding author: Groen@itc.nl
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Abstract:

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.

Keywords

Africafire frequencyregressionsavanna ecologyspatial patterntree clustering
Type
Research Article
Information
Journal of Tropical Ecology , Volume 24 , Issue 3 , May 2008 , pp. 269 - 279
Copyright
Copyright © Cambridge University Press 2008

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