Naïve plant communities and individuals may initially suffer in the face of reintroduced megafauna: an experimental exploration of rewilding from an African savanna rangeland

Truman Young, Department of Plant Sciences, University of California, Davis, Davis, CA; Mpala Research Centre, Nanyuki, Kenya, Duncan M. Kimuyu, Natural Resource Management and Environmental Studies, Karatina University, Karatina, Kenya, Wilfred Odadi, Egerton University, Egerton, Kenya, Harry Wells, Leeds University, Leeds, United Kingdom and Amelia Wolf, Integrative Biology, UT-Austin, Austin, TX

Background/Question/Methods
Excluding large native mammals is an inverse test of rewilding. A 25-year exclosure experiment in an African savanna rangeland offers insight into the potentials and pitfalls of the rewilding endeavor as they relate to the native plant community. A broad theme that has emerged from this research is that entire plant communities, as well as individual plant species, adjust to the absence of herbivores in ways that ill-prepare them for the return of these herbivores.
Results/Conclusions
Three lines of evidence suggest that these “naïve” individuals, populations, and communities are likely to initially suffer from herbivore rewilding. First, plots protected from wild herbivores for the past 25 years have developed rich diversity of woody plants that are absent from unfenced plots, and presumably would disappear upon rewilding. Second, the dominant tree in this system, Acacia drepanolobium, greatly reduces its defences in the absence of browsers, and the sudden arrival of these herbivores (in this case, through a temporary fence break), resulted in far greater elephant damage than for their conspecifics in adjacent plots that had been continually exposed to herbivory. Third, the removal of herbivores favoured the most palatable grass species, and a large number of rarer species, which presumably would be at risk from herbivore re-introduction. In summary, the native communities that we observe in defaunated landscapes may be very different from their pre-defaunation states, and we are likely to see some large changes to these plant communities upon rewilding with large herbivores, including potential reductions in plant diversity. Lastly, our experimental manipulation of cattle represents additional tests of the role of livestock in rewilding. Cattle are in many ways ecologically dissimilar to wildlife (e.g., their greater densities), but in other ways they may serve as ecological surrogates for wildlife, which could buffer ecosystems from some of the ecological costs of rewilding. More fundamentally, African savannah ecosystems represent a challenge to traditional Western definitions of “wilderness” as ecosystems free of human impacts. We suggest that as we “rewild” our biodiversity landscapes, we redefine “wildness” in the 21st Century to be inclusive of (low impact, and sometimes traditional) human practices that are compatible with the sustainability of native (and re-introduced) biodiversity.