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African Elephants Loxodonta africana Amplify Browse Heterogeneity in African Savanna
Authors:Willem F de Boer  Mike J S Peel  Rob Slotow  Cornelis van der Waal  Ignas M A Heitkönig  Andrew Skidmore  Herbert H T Prins
Institution:1. Resource Ecology Group, Wageningen University, Droevendaalsesteeg 3a, 6708 PB Wageningen, The Netherlands;2. Agricultural Research Council, Animal Production Institute Nelspruit, PO Box 7063, Nelspruit 1200, South Africa;3. Amarula Elephant Research Programme, School of Biological and Conservation Sciences, Westville Campus, University of KwaZulu‐Natal, Private Bag X54001, Durban 4000, South Africa;4. ITC, PO Box 6, 7500 AA Enschede, The Netherlands
Abstract:There is a growing concern that the feeding habits of the African elephant, which include pushing over, uprooting and snapping trees, may have a negative impact on other herbivores. Browsed trees are known to respond by either increasing production (shoots and leaves) or defence (secondary compounds). It is not clear, however, what proportion of the browsed biomass can be made available at lower feeding heights after a tree is pushed over or snapped; thus, it is also unclear how the forage quality is affected. In a field survey in Kruger National Park, South Africa, 708 Mopane trees were measured over four elephant utilization categories: snapped trees, pushed‐over trees, uprooted trees and control trees. The elephants' impact on the leaf biomass distribution was quantified, and the forage quality (Ca, P, K and Mg, N, digestibility and condensed tannin CT] concentrations) were analyzed. Pushed‐over and uprooted trees had the maximum leaf biomass at lower heights (<1 m), snapped trees at medium heights (1–2 m) and control trees at higher heights (>2 m). In all three utilization categories, the minimum leaf biomass was seven times higher than it was for control trees at a height of below 1 m. Leaf nitrogen content increased in all three categories and was significantly higher in snapped trees. CT concentrations increased slightly in all trees that were utilized by elephants, especially on granitic soils in the dry season. The results provide the insight that elephants facilitate the redistribution and availability of browse and improve the quality, which may positively affect small browsing herbivores.
Keywords:browse amplification  browse biomass  condensed tannin  elephants' impact  green leaves  herbivore facilitation  nitrogen  vertical stratification
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