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A Meta-Analysis of the Impact of African Elephants on Savanna Vegetation

A Meta-Analysis of the Impact of African Elephants on Savanna Vegetation,10.2193/2007‐072,Journal of Wildlife Management,Robert Guldemond,Rudi Van Aar

A Meta-Analysis of the Impact of African Elephants on Savanna Vegetation   (Citations: 19)
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ABSTRACT Large herbivores such as elephants (Loxodonta africana) apparently have a negative impact on woody,vegetation at moderate,to high population densities. The confounding effects that fire, drought, and management history have may complicate assignment of such impacts,to herbivory. We reviewed,238 studies published,over 45 years and conducted,a meta-analysis based on 21 studies that provided sufficient information on response of woody vegetation to elephants. We considered size and duration of studies, elephant densities, rainfall, fences, and study outcomes in our analysis. We detected a disproportionate citation of 20 published studies in our database, 15 of which concluded,that woody,vegetation responded,negatively to elephants. Our analysis showed,that high elephant densities had a negative effect on woody vegetation but that rainfall and presence of fences influenced these effects. In arid savannas, woody vegetation always responded negatively to elephants. In transitional savannas, an increase in elephant densities did not influence woody vegetation response. In mesic savannas, negative responses of woody vegetation increased when elephants occurred at higher densities, whereas elephants confined by fences also had more negative effects on woody,plants than elephants that were not confined. Our analysis suggested that rainfall and fences influenced elephant density related impact,and that research results were often site-specific. Local environmental,conditions and site-specific objectives should,be considered,when,developing,management,actions to curb elephant,impacts,on woody,vegetation. (JOURNAL OF WILDLIFE MANAGEMENT 72(4):892–899; 2008) DOI: 10.2193/2007-072 KEY WORDS African savannas, citation bias, elephant impact, evidence-based conservation, vegetation response, wildlife
Journal: Journal of Wildlife Management - J WILDLIFE MANAGE , vol. 72, no. 4, pp. 892-899, 2008
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    • ...The concern is that these populations have become sufficiently abundant to diminish natural woodlands and associated biodiversity (Cumming et al. 1997; de Beer et al. 2006; Kerley and Landman 2006; Kerley et al. 2008; O’Connor et al. 2007; Guldemond and van Aarde 2007, 2008)...

    Adrian M. Shraderet al. Elephant survival, rainfall and the confounding effects of water provi...

    • ...Yet debate has raged about the importance of elephants as drivers of this ecological change, with scientists tending to have polarised views depending upon elephant impacts on their study site (see review by Guldemond and Van Aarde 2008)...
    • ...Such studies provide contradictory results and are poorly replicated, lack suitable controls and incorrectly assign response variables to elephants (Guldemond and Van Aarde 2008)...

    Matt W. Haywardet al. Increasing elephant Loxodonta africana density is a more important dri...

    • ...2004; Owen-Smith 2006; Guldemond and van Aarde 2008; Cowling et al...

    James O. Farlowet al. Giants on the landscape: modelling the abundance of megaherbivorous di...

    • ...African elephants Loxodonta africana alter savannas by reducing the abundance of trees (Barnes, 1983), which may transform woodlands to shrublands (Smallie & O’Connor, 2000; Guldemond & van Aarde, 2008)...
    • ...These repeated visits to the same places within seasons, between seasons and across years may accentuate the impact of elephants on vegetation (see Owen-Smith et al., 2006; O’Connor et al., 2007), particularly on woody vegetation (see Guldemond & van Aarde, 2008 and references therein)...
    • ...Thus, differences in spatial use patterns between wet and dry savannas may partially explain differences in elephant impacts on woody vegetation at different places (see Guldemond & van Aarde, 2008 and references therein)...
    • ...All of these findings may explain the different impacts that elephants have on woody vegetation among sites (see Guldemond & van Aarde, 2008)...
    • ...Because differences in vegetation structure between wet and dry savanna sites seemed to alter the seasonal influence of vegetation productivity on elephant spatial use during the dry season and between seasons, the intensity of impacts on woody vegetation noted for dry savannas may not be readily extrapolated to wet savannas (see Guldemond & van Aarde, 2008)...

    K. D. Younget al. Elephant spatial use in wet and dry savannas of southern Africa

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