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Development and Parameterization of a Rain- and Fire-driven Model for Exploring Elephant Effects in African Savannas

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Abstract

We describe the development and parameterization of a grid-based model of African savanna vegetation processes. The model was developed with the objective of exploring elephant effects on the diversity of savanna species and structure, and in this formulation concentrates on the relative cover of grass and woody plants, the vertical structure of the woody plant community, and the distribution of these over space. Grid cells are linked by seed dispersal and fire, and environmental variability is included in the form of stochastic rainfall and fire events. The model was parameterized from an extensive review of the African savanna literature; when available, parameter values varied widely. The most plausible set of parameters produced long-term coexistence between woody plants and grass, with the tree–grass balance being more sensitive to changes in parameters influencing demographic processes and drought incidence and response, while less sensitive to fire regime. There was considerable diversity in the woody structure of savanna systems within the range of uncertainty in tree growth rate parameters. Thus, given the paucity of height growth data regarding woody plant species in southern African savannas, managers of natural areas should be cognizant of different tree species growth and damage response attributes when considering whether to act on perceived elephant threats to vegetation.

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Acknowledgements

We thank P. Cross, K. Duffy, J. du Toit, S. Higgins, J. Lloyd-Smith, D. McCullough, T. O’Connor, N. Owen-Smith, J. Redfern, S. Ryan, R. Scholes, C. Wilmers, and an anonymous reviewer for valuable comments on an earlier draft of this paper. The authors thank South African National Parks and the Scientific Services Division of the KNP for facilitating parts of this study. PWJB also thanks the Mammal Research Institute, University of Pretoria, for use of their facilities. The work was supported by a Foreign Language and Area Studies Fellowship and Andrew and Mary Rocca Travel Scholarship (PWJB) and by NSF grant DEB-0090323 and James S. McDonnell Foundation 21st Century Science Initiative Grant (WMG).

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  1. Peter W. J. Baxter

    Present address: The Ecology Centre, School of Integrative Biology, University of Queensland, St. Lucia, Brisbane, Queensland, 4072, Australia

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  1. Department of Environmental Science, Policy and Management, University of California, 201 Wellman Hall, Berkeley, CA, 94720-3112, USA

    Peter W. J. Baxter & Wayne M. Getz

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

    Wayne M. Getz

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  1. Peter W. J. Baxter
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Correspondence to Peter W. J. Baxter.

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Baxter, P.W.J., Getz, W.M. Development and Parameterization of a Rain- and Fire-driven Model for Exploring Elephant Effects in African Savannas. Environ Model Assess 13, 221–242 (2008). https://doi.org/10.1007/s10666-007-9091-9

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