Rewilding – the Radical New Science of Ecological Recovery

Abstract

African Journal of Range & Forage Science is co-published by NISC (Pty) Ltd and Informa UK Limited (trading as Taylor & Francis Group) This publication is promoted by the publisher as part of a series exploring the cutting edge of science and technology – ‘these are books for popular science readers who like to go a little deeper’. Indeed, it is a very accessible, easy read that strikes an upbeat tone despite the parlous state of affairs that rewilding is attempting to address. Already coined in the mid-1990’s, the concept of ‘rewilding’ shot to prominence in 2005–2006. It popularly conjures up an image of charismatic megaherbivores or large carnivores being brought back in an area from which they have been lost. Or, in the words of the authors, ‘the creation of large wilderness complexes and supporting populations of top predators (notably wolves in Yellowstone National Park) and the creation of a Serengeti-like landscape through the re-assembly of a guild of large herbivores in The Netherlands’. These large animals are, however, more often a means to an end. The emphasis of ‘rewilding’ is on restoring lost interactions at the landscape scale (page 5). In the second chapter of the book, the authors go back to the Pleistocene era to understand the potential of rewilding and to make the argument for multiple biodiversity baselines. They describe a past that up until 30 000 to 10 000 years ago was characterised by an abundance of megafauna that co-evolved alongside grasses and shrubs. As megafauna disappeared from much of the Earth towards the end of the Holocene ca. 10 000 years ago, many terrestrial ecosystems transitioned from grassland to more woody habitats. Whereas livestock herding maintained simplified, yet biodiverse ecosystems, these went into decline as a result of intensive livestock farming, land abandonment and rural depopulation. The latter obviously applying more to the north with African savannas and their megafauna in the south remaining more intact. This means that overall, the world’s terrestrial ecosystems have moved to both extremes of the wood-pasture gradient: less productive and abandoned land has become more wooded whereas land with more productive soils has become intensively managed pasture or agricultural fields (page 12). Rewilding is in part about recovering these more open habitats and the ecological richness they produce. Key to the rewilding is getting those animals that disappeared back into the system. In Chapter 4, the practical origins of rewilding are described including the examples of the Oostvaardersplassen in The Netherlands where the emphasis was on the introduction of primitive breeds of horse and cattle, and that of Yellowstone in the United States where the emphasis was on the re-establishment of wolves. At its core, rewilding is ecological restoration. The differences between rewilding and the discipline of restoration ecology in terms of ethos and focus are discussed in Chapter 5. Rather than attempting to turn the clock back to an arbitrary past baseline, rewilding focuses on restoring networks of interactions between communities and organisms and their physical environment. The ‘landscape of fear’ is described in this chapter. Whereas this always goes back to the textbook example of Yellowstone, more recently the concept has been described in Gorongosa National Park in Mozambique that is undergoing restoration after suffering huge declines in its herbivore and carnivore populations during the protracted civil war. Following the extirpation of leopards and African wild dogs from the Park, the forestdwelling bushbuck (Tragelaphus sylvaticus) expanded into treeless floodplains, where they consumed novel diets and suppressed a common food plant (waterwort, Bergia mossambicensis). By experimentally simulating predation risk, it was demonstrated that this behaviour was reversible. Thus, whereas anthropogenic predator extinction disrupted a trophic cascade by enabling rapid differentiation of prey behaviour, carnivore restoration may just as rapidly re-establish that cascade (Atkins et al. 2019). Similarly, the recovering herbivore population on the floodplain of Gorongosa started exerting top–down control of Mimosa pigra, an invasive alien plant species. Mimosa occurrence increased between 1972 and 2015, a period encompassing the near extirpation of large herbivores. From 2015 to 2019, Mimosa abundance declined as ungulate biomass recovered. DNA metabarcoding revealed that ruminant herbivores fed heavily on Mimosa, and experimental exclosures confirmed the causal role of mammalian herbivory in containing shrub encroachment. These results provide mechanistic evidence that trophic rewilding has rapidly revived biotic resistance to a notorious woody invader (Guyton et al. 2020). Rewilding ethics and politics take centre stage in Chapter 7. Indeed the subject of rewilding has led to fierce debates in conservation circles. Nowhere is this more evident than Book Review