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Elephant (Loxodonta africana) Disturbance to Riparian Woodland: Effects on Tree-Species Richness, Diversity and Functional Redundancy

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Abstract

The substantial increase in elephant populations across many areas in southern Africa over past decades is prompting concerns about the effects on biodiversity. We investigated the outcomes of elephant disturbance on tree-species presence, density, and richness, and on alpha and beta diversity within riparian woodland in Chobe National Park, Botswana. We enumerated all tree species occurring in 32 plots (0.06 ha) along the Chobe riverfront. Plots were stratified by soil type (nutrient-rich alluvium vs. nutrient-poor Kalahari sand covering alluvium) and elephant impact (high vs. low impact on both soil types). We tested four predictions: elephants reduce tree density, richness, and alpha diversity; beta diversity is greater in vegetation subjected to high elephant impact; elephant impact on tree-species composition is greater on nutrient-poor than on nutrient-rich soil; and the loss or decline of abundant tree species on heavily disturbed sites is offset by an increase in abundance of functionally similar species, ones that are minor on lightly disturbed sites. Elephant browsing substantially affected tree-species composition, reducing density, species richness, evenness, and alpha diversity but had no effect on beta diversity. The dominant species on relatively undisturbed areas were partly replaced by functionally similar species on heavily disturbed sites. Soil type influenced species composition on lightly disturbed sites but was less important at higher elephant densities. Our findings are important for areas with extreme dry-season densities of elephants but should not be extrapolated to infer purported effects of elephants on tree diversity at lower densities.

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ACKNOWLEDGMENTS

This study was conducted as part of the Botswana Norway Institutional Capacity Building and Collaboration Program (BONIC), jointly funded by the Department of Wildlife and National Parks (DWNP), Botswana and NORAD. J. T. du Toit, J. E. Swenson, G. Oba, R. Borgstrom and M. Tweheyo, J. Pastor and two anonymous referees improved earlier drafts of this manuscript. We are particularly grateful to Peter Frost for his substantial improvements in language and clarity. W. Marokane and M. Ramotladima helped with the identification of species in the field.

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Authors and Affiliations

  1. Okavango Research Institute, Private Bag 285, Maun, Botswana

    Lucas P. Rutina

  2. Ecosystem Conservation Foundation, P.O. Box 20027, Maun, Botswana

    Lucas P. Rutina

  3. Department of Ecology and Natural Resource Management, Norwegian University of Life Sciences, P.O. Box 5014, 1432, Ås, Norway

    Stein R. Moe

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  1. Lucas P. Rutina
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Correspondence to Lucas P. Rutina.

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LPR and SRM designed the study, carried out the statistical analyses and co-wrote the paper; LPR undertook the field work and initial data analysis.

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Rutina, L.P., Moe, S.R. Elephant (Loxodonta africana) Disturbance to Riparian Woodland: Effects on Tree-Species Richness, Diversity and Functional Redundancy. Ecosystems 17, 1384–1396 (2014). https://doi.org/10.1007/s10021-014-9801-5

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