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Differential effects of defoliation by mopane caterpillars and pruning by African elephants on the regrowth of Colophospermum mopane foliage

Published online by Cambridge University Press:  01 May 2009

Halszka Hrabar*
Affiliation:
Mammal Research Institute, Department of Zoology and Entomology, University of Pretoria, Pretoria, South Africa
Dawood Hattas
Affiliation:
Department of Botany, University of Cape Town, Private Bag X3, Rondebosch, 7701, Cape Town, South Africa
Johan T. du Toit
Affiliation:
Mammal Research Institute, Department of Zoology and Entomology, University of Pretoria, Pretoria, South Africa Department of Wildland Resources, Utah State University, Logan, UT 84322-5230, USA
*
1Corresponding author. Email: [email protected]

Abstract:

Plant responses to herbivory vary depending on herbivory type, yet the comparative effects of defoliation (e.g. by insects) and pruning (e.g. by large mammals) on a single tree species are poorly documented. We investigated this in the Northern Province of South Africa by comparing the regrowth of Colophospermum mopane trees previously defoliated by caterpillars or pruned by elephants, the two main browsers of C. mopane foliage. Shoots were up to 160% and 125% longer after natural (elephant) and simulated pruning and leaves ~25% longer in regrowth after natural pruning (n = 13–15 trees per treatment). Shoot density and chemical defences in leaves (tannin:protein ratio and total polyphenolic concentration) were, however, no different from control trees. Simulated defoliation resulted in statistically insignificant changes to regrowth in terms of leaf and shoot size (both slightly decreased) and shoot density (slightly increased). Natural (caterpillar) defoliation, however, resulted in regrowth with significantly decreased shoot and leaf size (about 50% and 20% of control lengths, respectively), as well as decreased leaf chemical defence. Shoot and leaf length were longer on trees flushing for the first time after pruning and late-season defoliation had a greater negative impact than mid-season defoliation. Despite the differences in regrowth characteristics after pruning and defoliation, mopane plants showed no apparent trade-off in investment between tolerance and resistance after either herbivory type, as neither regrowth nor chemical defence occurred at the expense of the other.

Type
Research Article
Copyright
Copyright © Cambridge University Press 2009

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