Growth,chemical responses and herbivory after simulated leaf browsing in <Emphasis Type="Italic">Combretum apiculatum</Emphasis> |
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Authors: | T Rooke R Bergström |
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Institution: | 1.Department of Animal Ecology,Swedish University of Agricultural Sciences,Ume?,Sweden;2.The Forest Research Institute of Sweden,Uppsala Science Park,Uppsala,Sweden |
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Abstract: | Vegetative and chemical responses to simulated leaf browsing during the growth season, and their subsequent effect on herbivory,
were studied on Combretum apiculatum Sonder (Combretaceae) in Botswana. Treatments (50% and 100% leaf and shoot apex removal) were performed just before the shoot
growth curve levelled out, and responses recorded 3 months later, just before leaf fall. Compared to controls, defoliation
treatments, removing apical dominance, reduced growth in tree height and increased shoot mortality, although the production
of lateral shoots increased. At the end of the trial, there was no difference in total length of annual shoots between treatment
groups. Significant refoliation occurred only after 100% defoliation. Refoliated leaves were smaller and the 100% defoliated
trees had a lower final leaf biomass. Total leaf biomass production was, however, equal for all treatment groups. Refoliated
leaves contained higher levels of N, lower levels of acid-detergent fibre (ADF) and total phenolics, and showed a trend towards
lower levels of condensed tannins, compared to leaves on control trees. Such chemical changes may be due to either carbon
stress or to younger physiological age of new leaves. In spite of the observed potential increase in food quality, we found
no evidence of increased levels of insect or ungulate herbivory on refoliated leaves, which, at least for insect herbivory,
may be explained by the reduction in temporal availability of leaves. We conclude that the single severe defoliation was not
detrimental to C. apiculatum in the short-term, although the resource loss and induced compensatory growth may produce negative effects during subsequent
growth seasons. |
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Keywords: | Defoliation Insect Nitrogen Phenolics Tannins Ungulates |
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