Rewilding is a form of ecological restoration aimed at increasing biodiversity and restoring natural processes. It differs from other forms of ecological restoration in that rewilding aspires to reduce human influence on ecosystems. It is also distinct from other forms of restoration in that, while it places emphasis on recovering geographically specific sets of ecological interactions and functions that would have maintained ecosystems prior to human influence, rewilding is open to novel or emerging ecosystems which encompass new species and new interactions.
A key feature of rewilding is its focus on replacing human interventions with natural processes. Rewilding enables the return of intact, large mammal assemblages, to promote the restoration of trophic networks. This mechanism of rewilding is a process of restoring natural processes by introducing or re-introducing large mammals to promote resilient, self-regulating, and self-sustaining ecosystems. Large mammals can influence ecosystems by altering biogeochemical pathways as they contribute to unique ecological roles, they are landscape engineers that aid in shaping the structure and composition of natural habitats. Rewilding projects are often part of programs for habitat restoration and conservation biology, and should be based on sound socio-ecological theory and evidence.
While rewilding initiatives can be controversial, the United Nations has listed rewilding as one of several methods needed to achieve massive scale restoration of natural ecosystems, which they say must be accomplished by 2030 as part of the 30x30 campaign.
Origin The term rewilding was coined by members of the grassroots network Earth First!, first appearing in print in 1990. It was refined and grounded in a scientific context in a paper published in 1998 by conservation biologists Michael Soulé and Reed Noss. Soulé and Noss envisaged rewilding as a conservation method based on the concept of 'cores, corridors, and carnivores'. The key components of rewilding incorporate large core protected areas, keystone species, and ecological connectivity based on the theory that large predators play regulatory roles in ecosystems. '3Cs' rewilding therefore relied on protecting 'core' areas of wild land, linked together by 'corridors' allowing passage for 'carnivores' to move around the landscape and perform their functional role. Inside these cores, human development, especially the building of roads, is strictly limited. National parks and wilderness reserves are the most common types of 'core' areas. Soulé and fellow biologist John Terbough expanded on the concept of corridors in their book Continental Conservation. They determined that one size does not fit all: narrow, linear corridors might work for some smaller species, but if conservationists wanted to encourage the movement of large carnivores, they needed to make corridors wide enough to allow for daily and seasonal movement of both herds of prey and packs of their predators. The '3Cs' concept was developed further in 1999 and Earth First co-founder, Dave Foreman, subsequently wrote a full-length book on rewilding as a conservation strategy.
History Rewilding was developed as a method to preserve functional ecosystems and reduce biodiversity loss, incorporating research in island biogeography and the ecological role of large carnivores. In 1967, The Theory of Island Biogeography by Robert H. MacArthur and Edward O. Wilson established the importance of considering the size and fragmentation of wildlife conservation areas, stating that protected species and areas remained vulnerable to extinctions if populations were small and isolated. In 1987, William D. Newmark's study of extinctions in national parks in North America added weight to the theory. The publications intensified debates on conservation approaches. With the creation of the Society for Conservation Biology in 1985, conservationists began to focus on reducing habitat loss and fragmentation.
Supporters of rewilding initiatives range from individuals, small land owners, local non-governmental organizations and authorities, to national governments and international non-governmental organizations such as the International Union for Conservation of Nature. While rewilding efforts can be well regarded, the increased popularity of rewilding has generated controversy, especially in relation to large-scale projects. These have sometimes attracted criticism from academics and practicing conservationists, as well as government officials and business people. Nonetheless, a 2021 report for the launch of the UN Decade on Ecosystem Restoration, the United Nations listed rewilding as one of several restoration methods which they state should be used for ecosystem restoration of over 1 billion hectares.
Guiding principles
Since its origin, the term rewilding has been used as a signifier of particular forms of ecological restoration projects that have ranged widely in scope and geographic application. In 2021 the journal Conservation Biology published a paper by 33 coauthors from around the world. Titled 'Guiding Principles for Rewilding', researchers and project leaders from North America (Canada, Mexico and the United States) joined with counterparts in Europe (Denmark, France, Hungary, The Netherlands, Switzerland, and the UK), China, and South America (Chile and Colombia) to produce a unifying description, along with a set of ten guiding principles.
The group wrote, 'Commonalities in the concept of rewilding lie in its aims, whereas differences lie in the methods used, which include land protection, connectivity conservation, removing human infrastructure, and species reintroduction or taxon replacement.' Referring to the span of project types they stated, 'Rewilding now incorporates a variety of concepts, including Pleistocene megafauna replacement, taxon replacement, species reintroductions, retrobreeding, release of captive-bred animals, land abandonment, and spontaneous rewilding.'
Empowered by a directive from the International Union for the Conservation of Nature to produce a document on rewilding that reflected a global scale inventory of underlying goals as well as practices, the group sought a 'unifying definition', producing the following:'Rewilding is the process of rebuilding, following major human disturbance, a natural ecosystem by restoring natural processes and the complete or near complete food web at all trophic levels as a self-sustaining and resilient ecosystem with biota that would have been present had the disturbance not occurred. This will involve a paradigm shift in the relationship between humans and nature. The ultimate goal of rewilding is the restoration of functioning native ecosystems containing the full range of species at all trophic levels while reducing human control and pressures. Rewilded ecosystems should—where possible—be self-sustaining. That is, they require no or minimal management (i.e., natura naturans [nature doing what nature does]), and it is recognized that ecosystems are dynamic.'
Ten principles were developed by the group:
Rewilding utilizes wildlife to restore trophic interactions. Rewilding employs landscape-scale planning that considers core areas, connectivity, and co-existence. Rewilding focuses on the recovery of ecological processes, interactions, and conditions based on reference ecosystems. Rewilding recognizes that ecosystems are dynamic and constantly changing. Rewilding should anticipate the effects of climate change and where possible act as a tool to mitigate impacts. Rewilding requires local engagement and support. Rewilding is informed by science, traditional ecological knowledge, and other local knowledge. Rewilding is adaptive and dependent on monitoring and feedback. Rewilding recognizes the intrinsic value of all species and ecosystems. Rewilding requires a paradigm shift in the coexistence of humans and nature.
A paper was published in 2024 that offered a "broad study of rewilding guidelines and interventions."
Rewilding and climate change Rewilding can respond to both the causes and effects of climate change and has been posited as a 'natural climate solution'. Rewilding's creation of new ecosystems and restoration of existing ones can contribute to climate change mitigation and adaptation through, inter alia, carbon capture and storage, altering the Earth's albedo, natural flood management, reduction of wildfire risk, new habitat creation, and enabling or facilitating the movement of species to new, climate safe habitats, thus protecting biodiversity and maintaining functioning, climate resilient ecosystems.
The functional roles animals perform in ecosystems, such as grazing, nutrient cycling and seed distribution, can influence the amount of carbon that soils and (marine and terrestrial) plants capture. The carbon cycle is altered through herbivores consuming vegetation, assimilating carbon within their own biomass, and releasing carbon by respiration and defecation after digestion. The most beneficial effects on biogeochemical cycling and ecosystem structure are reported through rewilding large herbivore species. A study in a tropical forest in Guyana found that an increase in mammal species from 5 to 35 increased tree and soil carbon storage by four to five times, compared to an increase of 3.5 to four times with an increase of tree species from 10 to 70. A separate study suggested that the loss of megafauna that eat fruits may be responsible for an up to 10% reduction in carbon storage in tropical forests. Furthermore, acceleration of nutrient cycling through browsing and grazing may increase local plant productivity and thereby maintain ecosystem productivity in grassy biomes.
It is also posited that grazing and browsing reduces the risk of wildfires (which are significant contributors of GHG emissions and whose smoke can alter the planet's albedo - the Earth's ability to reflect heat from sunlight). For example, the loss of wildebeest from the Serengeti led to an increase in un-grazed grass, leading to more frequent and intense fires, causing the grassland to turn from a carbon sink to a carbon source. When disease management practices restored the wildebeest population, the Serengeti returned to a carbon sink state.
Rewilding's effect on albedo is not only through potential reduction of smoke from wildfires but also through the effects of grazing itself. By reducing woody cover through browsing and trampling, large herbivores expose more ground surface and thus increase the albedo effect, reducing local surface temperatures and creating a net surface cooling effect during spring and autumn.
Other forms of ecological restoration as part of rewilding can also assist with mitigating climate change. For example, reforestation, afforestation and peat re-wetting can all contribute to carbon sequestration. While carbon sequestration could allow carbon offsetting and carbon trading as a way to monetize rewilding there has been concern that the highly speculative nature of carbon markets encourages 'land grabbing' (i.e., buying large areas of land) and 'greenwashing' from natural capital investors and multi-national companies.
Types of rewilding
Passive rewilding Passive rewilding (also referred to as ecological rewilding) aims to restore natural ecosystem processes via minimal or the total withdrawal of direct human management of the landscape.Gillson L, Ladle RJ, Araújo MB. 2011. Baselines, patterns and process. In: Ladle RJ, Whittaker RJ, Eds. Conservation biogeography. Oxford: Wiley-Blackwell. p 31–44. https://doi.org/10.1002/9781444390001.ch3 An abandoned area later reclaimed by nature is an example where direct human management is completely absent. In such cases, wildlife will rebound and recolonize when given the chance.
Active rewilding