Investigating the vulnerability of an African savanna tree (Sclerocarya birrea subsp. caffra) to fire and herbivory

Chantal Helm, Gwyneth Wilson, Jeremy Midgley, Edward Witkowski, Laurence Kruger

Research output: Contribution to journalArticlepeer-review

15 Citations (Scopus)


Sclerocarya birrea ssp. caffra (marula), a typical savanna tree, is vulnerable to the effects of fire, herbivory and their combination. This paper investigated the relative importance of these agents of disturbance, at the level
of the individual stem, by specifically focusing on the following questions: (i)What is the greatest cause of mortality in adult marula stems in conservation areas with both elephants and fire? (ii) Does fire interact with bark stripping
to cause adult stem mortality and if so what is the dominant mechanism? (iii) At what stem diameter are marulas resistant to fire? Field surveys quantified the extent of damage in marula individuals in the Kruger National Park,
South Africa, highlighting the high levels of extreme herbivory such as toppling (7%) and pollarding (8%), relative to bark stripping (only 6% with more than 50% of the circumference stripped). In addition to extreme herbivory,
the progression from bark stripping through to invasion of the soft, exposed heartwood by wood borers, often facilitated by fire, through to toppling of the weakened stem after successive fires, appears to be the dominant
mechanism by which fire interacts with herbivory to cause adult stem death. Bark stripping and fire manipulation experiments indicated that bark stripping failed to increase the vulnerability of stems to fire directly through
transport tissue damage. However, the combination of bark stripping and fire reduced the ability of the stem to regrow bark, increasing the vulnerability of the exposed stem to boring insects and future fires. Fire manipulation
experiments were used to identify the minimum stem diameter of resistance to fire. Marula resisted stem death when greater than 3.4 cm in basal diameter.This paper emphasizes the importance of both fire and herbivory in the
development of woody plant population structure and by extension, the relative proportion of trees and grasses in savanna landscapes
Original languageEnglish
Pages (from-to)964-973
JournalAustral Ecology
Issue number8
Publication statusPublished - 2011


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