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Inter- and intra-plant variations in nitrogen, tannins and shoot growth of Sclerocarya birrea browsed by elephants

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Abstract

Impacts of elephants (Loxodonta africana africana) on woody vegetation has attracted substantial attention for decades, but plant-level responses remain a gap in the understanding of savanna ecology. Marula (Sclerocarya birrea caffra) forms an important part of elephant diets. We investigated the relationships between browsing intensity and shoot/leaf size, nitrogen (N) and condensed tannin (CT) concentrations in upper and lower canopies of male and female marula individuals in Hluhluwe-iMfolozi Park, South Africa. Browsing intensity (54%) did not differ between sexes, suggesting no preference by elephants for either sex. Females had higher [CT] than males and tannin decreased with increasing browsing intensity in both sexes. In lightly or moderately browsed trees, [CT] was controlled by unmeasured factors such that within-tree impacts of browsing were more variable in lightly/moderately browsed than heavily browsed trees. There was little change in [N] up to ~60% browsing intensity, but [N] increased dramatically at higher intensity. Shoots and leaves on broken branches in the lower canopy were larger (2.5 and 1.2 times, respectively) than those on unbroken branches in either upper or lower canopies. Chemical responses were systemic and potentially influence browsing among trees, while growth responses were strongly localised and potentially influence browsing within trees. Although marula trees are able to compensate vigorously for browsing at the scale of individual organs, trees may become progressively carbon-deficient and have their lives shortened if total plant growth is negatively affected by chronic browsing, e.g. near permanent water.

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Acknowledgments

The National Research Foundation, University of Zululand and University of KwaZulu-Natal provided financial support. Bruce Page contributed to designing the methods. Dave Druce provided logistical support. Douglas Makin, Megan Welsford, Tiffany Pillay, Vanessa Stuart and Desale Okubamichael helped in the field and lab. The comments from three anonymous reviewers improved the manuscript.

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Authors and Affiliations

  1. Department of Agriculture, University of Zululand, Private Bag X1001, KwaDlangezwa, 3886, South Africa

    Peter F. Scogings

  2. School of Biological and Conservation Sciences, University of KwaZulu-Natal, Scottsville, 3209, South Africa

    Robert W. Taylor & David Ward

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  1. Peter F. Scogings
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  2. Robert W. Taylor
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  3. David Ward
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Correspondence to Peter F. Scogings.

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Scogings, P.F., Taylor, R.W. & Ward, D. Inter- and intra-plant variations in nitrogen, tannins and shoot growth of Sclerocarya birrea browsed by elephants. Plant Ecol 213, 483–491 (2012). https://doi.org/10.1007/s11258-011-9996-x

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  • DOI: https://doi.org/10.1007/s11258-011-9996-x

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