Effects of simulated browsing on growth and leaf chemical properties in Colophospermum mopane saplings |
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Authors: | Edward M Kohi Willem F de Boer Martijn Slot Sipke E van Wieren Jelle G Ferwerda Rina C Grant Ignas M A Heitkönig Henjo J de Knegt Nicky Knox Frank van Langevelde Mike Peel Rob Slotow Cornelis van der Waal Herbert H T Prins |
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Institution: | Resource Ecology Group, Wageningen University, Droevendaalsesteeg 3a, 6708 PB Wageningen, the Netherlands;, Tanzania Wildlife Research Institute, PO Box 661, Tanzania;, Department of Botany, University of Florida, PO Box 118526, Gainesville, FL 32611, U.S.A.;, ITC, PO Box 6, 7500 AA Enschede, The Netherlands;, Scientific Services, Kruger National Park, PB X402, Skukuza 1350, South Africa;, ARC Range and Forage Institute Nelspruit, PB X05, Lynn East 0039, South Africa;and Amarula Elephant Research Programme, Life and Environmental Sciences, Natal University, Durban 4041, South Africa |
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Abstract: | Browsing intensity influences a plant's response to herbivory. Plants face a trade-off between investment in the production of secondary compounds and investment in growth. To elucidate this trade-off, we simulated four browsing intensities (0%, 50%, 75% and 100%) on mopane saplings, Colophospermum mopane (J.Kirk ex Benth.) J.Léonard, in a greenhouse experiment. This showed that, with increasing defoliation intensity, plants change their investment strategy. At intermediate levels of defoliation (50%), mopane saplings increased the synthesis of condensed tannins, so that tannin concentrations followed a hump-shaped relation with defoliation intensity, with significantly higher tannin concentration at intermediate defoliation levels. When defoliated heavily (75% and 100%), tannin concentrations dropped, and plants were carbon stressed as indicated by a reduced growth rate of the stem diameter, and leaf production and mean individual leaf mass were reduced. This suggests that, at intermediate defoliation intensity, the strategy of the plants is towards induced chemical defences. With increasing defoliation, the relative costs of the secondary metabolite synthesis become too high, and therefore, the plants change their growing strategy. Hence, browsers should be able to benefit from earlier browsing by either adopting a low or a relatively high browsing pressure. |
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Keywords: | condensed tannins induced defence leaf mass leaf production trade-off |
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