What is rewilding?
Rewilding is a form of environmental conservation and ecological restoration that has significant potential to increase biodiversity, create self-sustainable environments and mitigate climate change. Rewilding aims to do this by reintroducing lost animal species to natural environments. It is an exciting and promising conservation strategy aimed at restoring natural processes and wilderness areas, providing connectivity between such areas (corridors), and reintroducing large herbivores, predators and/or keystone species.
While reintroduction is an approach that many conservationists take to restore and reinforce endangered species populations, rewilding’s focus on animals high up on the food chain like apex predators and large herbivores make it unique. The reason these particular species are targeted by rewilding is that by being high up on the food chain, they influence many species below them by restoring ecological functioning.
Since it was first academically defined in 1998 by American conservation biologists Michael Soulé and Reed Noss, as an approach focusing on “cores, corridors, and carnivores”, the idea of rewilding has evolved in several different directions. The main offshoots of the original idea including Pleistocene rewilding (Donlan et al, 2005), passive wilding (Gillson et al., 2011), and translocation rewilding (Seddon et al., 2014). These variations on rewilding each come with their own set of potential benefits and challenges.
Most rewilding approaches fit the concept of trophic rewilding, defined as: “an ecological restoration strategy that uses species introductions to restore top-down trophic interactions and associated trophic cascades to promote self-regulating biodiverse ecosystems”.
Types of rewilding
Pleistocene rewilding entails reintroducing species or descendants of megafauna species from the Pleistocene era, more commonly known as the Ice Age. Towards the end of the Ice Age, approximately 12,000 years ago, there was massive extinction of megafauna, known as the Quaternary extinction event, which affects almost all megafauna species. Proponents of the idea to reintroduce these species argue that this extinction event left an unbalanced ecosystem. Pleistocene rewilding has a greater potential for uncertain impacts than translocation rewilding. Rather than the reintroduction of a species that recently disappeared from the area, Pleistocene rewilding potentially involves introducing a completely foreign species to an ecosystem.
Passive rewilding takes quite a different approach, aiming to reduce human intervention in ecosystems, giving human cultivated land back to nature and restoring nature, with the goal of letting nature develop and flourish on its own. It entails passive management of ecological succession with the goal of restoring natural ecosystem processes and reducing human influence on landscapes.
Translocation rewilding is a more active approach, also involving the reintroduction of species, but the species it focuses on reintroducing are of more recent origin. It seeks to restore missing or dysfunctional processes and ecosystem functions by reintroducing current descendants of lost species. Two types of translocation are recognised in conservation: (1) reinforcements, involving the release of a species into an existing population to enhance viability and survival, and (2) reintroductions, where the goal is to reestablish a population in an area after local extinction in order to restore ecosystem processes. This is also called trophic rewilding.
Extinction of megafauna and ecosystem degradation
“Since the worldwide expansion of modern humans (Homo sapiens) began, humans have overexploited vertebrates, with a bias to the largest animals being extirpated first, from the Late Pleistocene extinctions of terrestrial megafauna to the ongoing declines of terrestrial, marine and freshwater large-bodied animals. There is increasing evidence that this global wildlife loss, or defaunation, does not only imply the loss of charismatic animals but also the functions they have in ecosystems”.
One of the more well-known, and successful cases of trophic rewilding has been the reintroduction of the wolf to Yellowstone National Park. The wolf reintroduction has had a major effect on the Yellowstone ecosystem. Before the reintroduction, the population of elk was over-grazing the local vegetation. Now the plants, including trees such as cottonwood and aspen have been allowed to recover. Additionally, the wolves have reduced the large coyote numbers, which means that the smaller animals that were being preyed on, or out-hunted by them, such as fawns and smaller predators, have recovered their population.
Another rewilding success story is the reintroduction of an important herbivore species to the United Kingdom and the Netherlands: the beaver. The dams they build are important for regulating the natural water system, preventing flooding and improving soil quality, as well as providing a habitat for a multitude of smaller species. So far, the projects have seen a successful introduction of the beavers to and improvements in their ecosystems.
While rewilding has been a success at Yellowstone and in the UK and other places, there have also been problems, perhaps most famously at Oostvaardersplassen in the Netherlands. An area of marshland had been reclaimed from the sea and repopulated with red deer, Konik horses, and Heck cattle in order to keep the area open and avoid succession to closed forest. While the animals survived several mild winters without large issues, the harsh winter in 2018 caused mass starvation. Over half of the introduced population were culled by the Dutch government before they could starve to death. This translocation failure and the subsequent culling caused public outrage and brought to the forefront many of the issues and decisions that surround rewilding. What happens when rewilding projects fail? Do we really know these complex systems well enough to alter them without serious unintended consequences?
What happened at Oostvaardersplassen is entirely explainable in retrospect. The area that was being rewilded was too small for the herbivore populations, and there were no natural predators to keep the cattle, horse and deer population at a sustainable level, as well as almost no connectivity to other wild areas.
There is much to be learned from what happened there – what happened at Oostvaardersplassen doesn’t represent a failure of rewilding as a concept, but a failure in the execution of it. In order to avoid such issues in the future, scientists argue that more experimentation and data-gathering needs to be done, as well as a careful consideration of the intersectional biological, social, and economic issues which affect rewilding efforts.
Rewilding is the most exciting and promising conservation strategy to slow down or halt the 6th mass extinction of species. It also has tremendous potential for climate change mitigation and has had documented successes in restoring biodiversity and ecosystem processes. It however needs to be applied with a clear vision of the history of an area and what can be restored.