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.

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:

Ten principles were developed by the group:

1. Rewilding utilizes wildlife to restore trophic interactions.
2. Rewilding employs landscape-scale planning that considers core areas, connectivity, and co-existence.
3. Rewilding focuses on the recovery of ecological processes, interactions, and conditions based on reference ecosystems.
4. Rewilding recognizes that ecosystems are dynamic and constantly changing.
5. Rewilding should anticipate the effects of climate change and where possible act as a tool to mitigate impacts.
6. Rewilding requires local engagement and support.
7. Rewilding is informed by science, traditional ecological knowledge, and other local knowledge.
8. Rewilding is adaptive and dependent on monitoring and feedback.
9. Rewilding recognizes the intrinsic value of all species and ecosystems.
10. 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 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.

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