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Relative Impacts of Elephant and Fire on Large Trees in a Savanna Ecosystem

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Abstract

Elephant and fire are considered to be among the most important agents that can modify the African savanna ecosystem. Although the synergistic relationship between these two key ecological drivers is well documented, it has proved much more difficult to establish the relative effects they have on savanna vegetation structure at a fine-scale over time. In this study, we explore the comparative impacts of fire and elephant on 2,522 individually identified large trees (≥5 m in height) in the Kruger National Park, South Africa. Data were collected from 21 transects first surveyed in April 2006 and resurveyed in November 2008, to determine the relative importance of past damage by these agents on subsequent impacts and mortality. The occurrence of fire or elephant damage in 2006 affected the amount of tree volume subsequently removed by both these agents; elephant removed more tree volume from previously burned trees and the impact of subsequent fire was higher on previously burned or elephant-utilized trees than on undamaged trees. Mortality was also affected by an interaction between previous and recent damage, as the probability of mortality was highest for trees that suffered from fire or elephant utilization after being pushed over. Subsequent fire damage, but not elephant utilization, on debarked trees also increased the probability of mortality. Mortality was twice (4.6% per annum) that of trees progressing into the ≥5 m height class, suggesting an overall decline in large tree density during the 30-month study period. The responses of large trees were species and landscape-specific in terms of sensitivity to elephant and fire impacts, as well as for levels of mortality and progression into the ≥5 m height class. These results emphasize the need for fine-scale site-specific knowledge for effective landscape level understanding of savanna dynamics.

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Acknowledgments

We are grateful to SANParks for providing access to the study site, while SANParks game scouts are thanked for providing valuable knowledge and ensuring the safety of the research team during the fieldwork. We thank H. Eckhardt for help in designing the 2006 survey, and D. Druce and A. Smith for assistance in collecting the data. This study was funded by Distell (Pty) Ltd through a donation to the Amarula Elephant Research Programme, University of KwaZulu-Natal (UKZN), and the National Research Foundation (Grant to RS: FA2006032300024). UKZN provided Post-Doctoral Fellowships to GS, MT and ATV.

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Authors and Affiliations

  1. Amarula Elephant Research Programme, School of Biological and Conservation Sciences, University of KwaZulu-Natal, Westville Campus, Pvt. Bag 54001, Durban, 4000, South Africa

    Graeme Shannon, Maria Thaker, Abi Tamim Vanak, Bruce R. Page & Rob Slotow

  2. Scientific Services, Kruger National Park, Box 106, Skukuza, 1350, South Africa

    Rina Grant

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  1. Graeme Shannon
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  2. Maria Thaker
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  3. Abi Tamim Vanak
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  4. Bruce R. Page
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  5. Rina Grant
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  6. Rob Slotow
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Correspondence to Graeme Shannon.

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Author Contributions

GS designed the study, performed field data collection, conducted data analysis, and wrote the manuscript; MT and ATV contributed to study design, data analysis, and writing; BRP, RS and RG contributed to study design and writing.

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Shannon, G., Thaker, M., Vanak, A.T. et al. Relative Impacts of Elephant and Fire on Large Trees in a Savanna Ecosystem. Ecosystems 14, 1372–1381 (2011). https://doi.org/10.1007/s10021-011-9485-z

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