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Stem mortality of Acacia nigrescens induced by the synergistic effects of elephants and fire in Kruger National Park, South Africa

Published online by Cambridge University Press:  01 November 2008

Glenn R. Moncrieff ,
Laurence M. Kruger  and
Jeremy J. Midgley
Glenn R. Moncrieff
Affiliation:
Department of Botany, University of Cape Town, Private Bag Rondebosch 7701, South Africa
Laurence M. Kruger
Affiliation:
Department of Botany, University of Cape Town, Private Bag Rondebosch 7701, South Africa Organization for Tropical Studies, Skukuza, South Africa
Jeremy J. Midgley*
Affiliation:
Department of Botany, University of Cape Town, Private Bag Rondebosch 7701, South Africa
*
1Corresponding author. Email: Jeremy.Midgley@uct.ac.za
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Abstract:

One manner in which elephants utilize trees is by removing their bark. This type of utilization is concentrated on the largest trees in the landscape. The role of bark removal in increasing the vulnerability of large trees to fire and the mechanism through which fire damage is mediated were investigated in Kruger National Park, South Africa, by experimentally removing bark and burning Acacia nigrescens stems with diameters ranging between 30 and 68 mm. Also, field surveys were conducted subsequent to natural fires in order to investigate mortality patterns of large trees with dbh greater than 15 cm with bark removed by elephants. An increasing probability of mortality was associated with increasing amounts of bark removal but only if trees were burned. When trees had bark removed but were not burnt, simulating damage only to cambium and phloem, none of the 12 treated stems died in the 4-mo period over which the experiment ran. Moreover, low levels of cambium damage were detected in large burned stems. This suggests that bark removal increases fire-induced xylem damage and that this damage contributes towards stem mortality. In a survey of 437 large trees, bark removal by elephants was frequent on large stems (44%) and larger trees have greater amounts of bark removed. Post-fire mortality of large trees was significantly associated with increasing bark removal and stem diameter. These results indicate that bark removal by elephants increases the vulnerability of stems to fire, resulting in mortality of large stems otherwise protected from fire.

Keywords

Acacia nigrescensbark removalelephant–fire interactionsfireLoxodonta africanasavannastem mortalityxylem
Type
Research Article
Information
Journal of Tropical Ecology , Volume 24 , Issue 6 , November 2008 , pp. 655 - 662
Copyright
Copyright © Cambridge University Press 2008

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