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Browsing-induced Effects on Leaf Litter Quality and Decomposition in a Southern African Savanna

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Abstract

We investigated the linkages between leaf litter quality and decomposability in a savanna plant community dominated by palatable-spinescent tree species. We measured: (1) leaf litter decomposability across five woody species that differ in leaf chemistry; (2) mass decomposition, nitrogen (N); and carbon (C) dynamics in leaf litter of a staple browse species (Acacia nigrescens) as well as (3) variation in litter composition across six sites that experienced very different histories of attack from large herbivores. All decomposition trials included litter bags filled with chopped straw to control for variation in site effects. We found a positive relationship between litter quality and decomposability, but we also found that Acacia and straw litter mass remaining did not significantly vary between heavily and lightly browsed sites. This is despite the fact that both the quality and composition of litter returned to the soil were significantly different across sites. We observed greater N resorption from senescing Acacia leaves at heavily browsed sites, which in turn contributed to increase the C:N ratio of leaf litter and caused greater litter N immobilization over time. This, together with the significantly lower tree- and herb-leaf litter mass beneath heavily browsed trees, should negatively affect decomposition rates. However, estimated dung and urine N deposition from both browsers and grazers was significantly greater at high- than at low-herbivory sites. We hypothesize that N inputs from dung and urine boost litter N mineralization and decomposition (especially following seasonal rainfall events), and thereby offset the effects of poor leaf litter quality at chronically browsed sites.

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Acknowledgments

We thank A. Hester, R. Bardgett, C. Skarpe and S. Hobbie for comments and discussion. Two very knowledgeable reviewers greatly contributed to improve the manuscript. This research was funded through a grant from the National Research Foundation to Johan du Toit (GUN 2053601). The Kruger National Park provided data on rainfall and fire regimes, as well as logistic support during the entire duration of the project.

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Authors and Affiliations

  1. Department of Ecology, Evolution and Behavior, University of Minnesota, St. Paul, Minnesota, 55108, USA

    D. A. Fornara

  2. Mammal Research Institute, Department of Zoology and Entomology, University of Pretoria, 0002, Pretoria, South Africa

    D. A. Fornara & J. T. Du Toit

  3. Department of Wildland Resources, Utah State University, Logan, Utah, 84322-5230, USA

    J. T. Du Toit

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  1. D. A. Fornara
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  2. J. T. Du Toit
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Correspondence to D. A. Fornara.

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Fornara, D.A., Du Toit, J.T. Browsing-induced Effects on Leaf Litter Quality and Decomposition in a Southern African Savanna. Ecosystems 11, 238–249 (2008). https://doi.org/10.1007/s10021-007-9119-7

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