Rewilding of complex ecosystems | Science

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Facilitate "savagery"

Humans have invaded most of the Earth's land. The current extinction crisis bears witness to the impact of human activity on nature. If there is hope of conserving a biodiversity-rich global system, we must begin to learn to coexist with other species and to give them space. The practice of "rewilding" has emerged as a method of bringing back wild lands and wilderness into landscapes we have changed. Perino et al. review this concept and present a framework to apply it broadly and taking into account the ongoing human interactions.

Science, this number p. eaav5570

Structured abstract

CONTEXT

Rapid global change creates fundamental challenges for the persistence of natural ecosystems and their biodiversity. Conservation efforts aimed at landscape protection have met with mixed success and there is growing recognition that the long-term protection of biodiversity requires the inclusion of flexible restoration alongside protection. Backfilling is one of those approaches that has been both promoted and criticized. Proponents emphasize that backfilling can exploit restoration opportunities while creating benefits for ecosystems and societies. Critics discuss the lack of a coherent definition of reintervention and insufficient knowledge about its potential consequences. Other criticisms stem from the misconception that reclamation actions are planned without regard to acceptability and benefits to society. Here we present a framework for rewilding actions that can serve as a guideline for researchers and managers. The framework is applicable to a variety of rewilding approaches, ranging from passive to trophic rewilding, and aims to promote beneficial interactions between society and nature.

ADVANCES

The concept of rewilding has evolved from its initial commitment to protecting large connected areas for large carnivore conservation to a dynamic, process-driven approach. Based on the concepts of resilience theory and the complexity of socio-ecological systems, we identify trophic complexity, stochastic disturbances, and dispersal as three essential components of the dynamics of natural ecosystems. We propose that restoring these processes, and their interactions, can lead to increased self-reliance of ecosystems and should be at the heart of rewilding actions. Based on these concepts, we develop a framework for designing and evaluating rewilding plans. In parallel with the objectives of ecological restoration, our framework emphasizes the perceptions and experiences of the wilderness and the regulatory and material contributions of the restoration of nature. These societal aspects are important results and can be critical factors for the success of rewilding initiatives (see figure). We also identify current societal constraints on rewilding and suggest actions to mitigate them.

PERSPECTIVE

The concept of rewilding encourages us to rethink our management of nature and broaden our vision of how nature will respond to the changes that society brings about intentionally and unintentionally. The effects of rewilding measures will be specific to each ecosystem. It is therefore essential to have a good understanding of the processes that shape ecosystems to anticipate these effects and take the appropriate management measures. In addition, the decision to adopt a woodlot re-prohibition approach should take into account the needs and expectations of stakeholders. To this end, structured restoration planning – based on participatory processes involving researchers, managers and stakeholders – including monitoring and adaptive management can be used. With the recent designation of 2021-2030 as the "Decade of Restoration of Ecosystems" by the UN General Assembly, policymakers could put regeneration issues at the forefront of discussions on how to reach biodiversity objectives for the post-2020 period.

The actions and results of rewilding are framed by the societal and ecological context.

Rewilding can be assessed by representing the state of ecosystems in a three-dimensional space where each dimension corresponds to an ecological process. The difference in volume between the restored ecosystem (yellow pyramid) and degraded (orange pyramid) is an indirect indicator of the effects of rewilding on the self-sufficiency of the ecosystem. The dashed line in the yellow pyramid represents the boundaries of society that determine the extent to which ecological processes can be restored. Rewilding actions can help push the boundaries of society towards ecological potential (orange arrows) by promoting societal support and opportunities for people to experience the empowerment of ecological processes. in a pleasant way.

Abstract

The practice of rewilding has been both promoted and criticized in recent years. Benefits include the flexibility to respond to environmental change and promote opportunities for society to reconnect with nature. Critics include the lack of a clear conceptualization of rewilding, insufficient knowledge of possible outcomes, and the perception that rewilding excludes people from landscapes. Here we present a rewilding framework that addresses these concerns. We suggest that rewilding efforts should target trophic complexity, natural disturbances and dispersal as an interacting process that can enhance ecosystem resilience and maintain biodiversity. We propose a structured approach to rewilding projects that includes an assessment of the contributions of nature to man and socio-ecological constraints to restoration.

Changing social and environmental conditions, including land use and increasing demand for resources, accelerate biodiversity loss and ecosystem degradation (1–4). The loss associated with many important ecological processes (5, 6) can reduce the complexity and resilience of ecosystems by hindering their ability to recover from disturbances (7–9). Although responses to the biodiversity crisis – particularly the creation of protected areas – have reduced the loss of biodiversity in some cases (ten–12), reports on ineffective protected areas (13) and ongoing declines of threatened species (14) indicate that conservation strategies must go beyond current efforts (15, 16).

A growing body of literature underscores the need for innovative, process-oriented approaches to ecosystem restoration in our rapidly changing world (4, 17–19). Dynamic and process-oriented approaches emphasize the adaptive capacity of ecosystems (4and restoring ecosystem processes that promote biodiversity, rather than aiming at maintaining or restoring particular ecosystem states characterized by predefined species compositions or particular sets of ecosystem services. Such approaches recognize ecosystems as dynamic systems (20) whose future evolution can not always be predicted (21, 22).

Backfilling is one of these restoration approaches. This strategy aims to restore autonomous and complex ecosystems, with interdependent ecological processes that reinforce and support each other while minimizing or gradually reducing human interventions (23–25). The rewilding also puts the emphasis on the emotional experience and perception of wild nature and wild ecosystems without human intervention (26). Although conventional restoration projects often aim to minimize human intervention, many scientists and practitioners consider that a certain level of management is essential to replace ecosystem processes lost due to human activities or to preserve important aspects of landscapes. cultural27). Such management often focuses on selected processes through precisely defined actions aimed at concrete objectives[ParexemplelagestiondespaysagesdeSatoyamaauJapon([EgmanagementofSatoyamalandscapesinJapan([parexemplelagestiondespaysagesdeSatoyamaauJapon([egmanagementofSatoyamalandscapesinJapan(28)]. Rewilding, on the other hand, recognizes and operates with complexity and autonomy as inherent characteristics of an ecosystem and recognizes their dynamic and unpredictable nature (29).

Despite the potential for rewilding to solve urgent restoration problems, critics have identified several shortcomings that have hitherto prevented the application of rewilding principles. Criticism includes the lack of a consistent definition of rewilding (30) and insufficient knowledge about the possible outcomes of rewilding efforts (31). In addition, concerns have been expressed about the planning of wood regeneration activities to exclude people from the landscape rather than to design them with local support (32).

Here we develop a conceptual framework for rewilding projects that responds to the aforementioned criticisms. We begin with a brief reminder of the history of the rewilding concept, starting with the emphasis on protecting large connected areas for carnivore conservation (33) to the diversity of today's rewilding concepts (25). We provide a framework for designing and evaluating rewilding plans that incorporates the current variety of rewilding approaches. Our framework builds on ecological theory to identify three interacting ecological processes that promote self-organization of ecosystems and, therefore, should be at the center of rewilding actions. For each of these processes, we review ecological knowledge and identify rewilding actions that can help restore resilient and self-sustaining ecosystems (Fig. 1). These actions will vary according to the societal context. Relining may occur spontaneously if humans retreat from landscapes – for example, after abandoning agriculture (34–36) or in areas that have become inhospitable as a result of armed conflict (37–39) or environmental disasters such as the Chernobyl disaster (40, 41). In other cases, rewilding projects are motivated by active choices about how companies want to experience nature (42) and to what extent they can accept autonomy from natural processes. In these cases, the feasibility of rewilding projects also depends on material, non-material and regulatory contributions from nature (Fig. 2). We discuss how rewilding projects should take socio-ecological dynamics into account, taking into account people's preferences and the effects of humans on ecosystems. Finally, we apply our framework to a set of ongoing rewilding projects and illustrate how interactions between key processes can be promoted to increase both ecosystem resilience and societal benefits.

Fig. 1 Promoting interactions between ecosystem processes enhances the resilience of rewilding areas.

(A) Intensively managed areas are often characterized by a decrease in trophic complexity. Dispersal barriers between ecosystems hinder the movement of individuals, particularly at higher trophic levels. The magnitude and frequency of natural disturbances are often suppressed or altered, which can lead to even greater disruption. Impoverished food webs, dispersal barriers and deterministic disturbances can hinder the recovery of depressed populations (open nodes in food webs) after major disturbances. (B) Rewilded areas have restored complex food webs, with functional roles for top predators (red knots), herbivores (yellow knots) and primary producers (blue knots). Improved connectivity between habitats allows species to disperse at all trophic levels. Frequent disturbances occur in the landscape. Dispersal between habitats facilitates the restoration of ecosystems after disturbance by allowing the recolonization and recovery of the affected species population. Large vertebrates in complex ecosystems often play the role of dispersal agents for plants and can introduce stochasticity into a system, for example through predation or grazing.

Fig. 2 Ecological processes restored and their influence on the contributions of nature.

The ecological state of each case study is represented in a three-dimensional space with an axis for each ecological process of our framework (trophic complexity, dispersion and stochastic perturbations). The initial ecological state is represented by the orange pyramids, while the yellow pyramids represent the ecological state after the rewilding actions. Bar graphs show the number of contributions to people (42) that are positively or negatively affected by the rewilding actions. (A) The rewetting of a river branch in the Auwald Leipziger (Germany) has resulted in an increase in the number of flood tolerant species and an overall increase in the species richness of several taxa. Management actions have increased the provision of non-material services (eg, learning and inspiration opportunities) and regulatory services (eg, habitat creation and maintenance). Impacts on physical services are negligible because the project does not affect large agricultural areas or substantially improves nature-based income opportunities. (B) Non-management, the prohibition of hunting and reintroductions have improved trophic complexity and stochastic disturbances in the Swiss National Park. Management actions have promoted economic prosperity (positive material contributions) and the abandonment of agriculture (negative material contributions). The park provides intangible and regulatory contributions (eg opportunities for nature experiences, habitat creation and maintenance). (C) The reintroduction of mammals into Tijuca National Park (Brazil) has improved ecological interactions. The urban location of the park limits the restoration potential of these three processes. Management actions can increase physical contributions (ie revenue generation through ecotourism). Non-material contributions (for example, support identities or option maintenance) may eventually emerge from community projects. (reLand abandonment, protection and reintroduction have restored the community of large mammals in the Chernobyl exclusion zone (Belarus). Positive regulatory, non-material and material contributions include the creation and maintenance of housing, as well as opportunities for learning, inspiration and wildlife tourism.

PICTURES: (C) BRIAN GRATWICKE / WIKIMEDIA COMMON; (D) MAX MISCHEK / ADOBE STOCK

A brief history of the rewilding concept

Rewilding, as it was originally designed 20 years ago (33), referred to "the scientific argument for the restoration of large natural areas, based on the regulatory roles of large predators" (33) can play the key role and maintain the resilience and diversity of terrestrial ecosystems through downward control (33, 43). The protection and restoration of "large central reserves, connectivity and essential species" that are strictly protected "(33) were the central features of this first definition of rewilding. Although conservation of large carnivores and their habitats remains an important aspect of woodlot renewal (25, 44), the concept evolved from this original idea to include a range of diverse approaches (25). Trophic rewilding, which is perhaps the closest concept to the original concept, advocates the reintroduction of missing key species, such as large carnivores and large herbivores. Trophic rewilding often promotes the use of functional substitutes, that is, the introduction of non-native species as ecological substitutes for species that have been extinct for centuries or millennia (25, 32, 44). The Pleistocene Rewilding is a special type of trophic rewilding, which aims to restore ecosystems that include and are shaped by late Pleistocene disappeared Megafauna populations, in a long-term evolutionary perspective on biodiversity and ecosystems (44). On the other hand, ecological (or passive) backfilling focuses on the passive management of ecological succession in abandoned landscapes. Passive rewilding actions include the establishment of non-hunting areas, low-intervention forest management, the set-aside of agricultural land, the removal of dispersal barriers and the restoration of natural flood regimes (22, 25, 34).

The ecosystem characteristics that backfilling aims to restore are characteristic of wilderness areas, but are not limited to these areas (45, 46). Instead, we refer to the wilderness, which is the autonomy of natural processes (46, 47) that can occur in a variety of contexts and at different spatial scales. The restoration of wilderness, rather than wilderness, is therefore the main goal of rewilding efforts. The broadening of the original definition of backfilling and the articulation of the restoration of the wilderness rather than that of nature as a main objective make backfilling applicable to all spatial scales and to adapt it to a wide range of societal and landscape contexts, from urban green spaces to abandoned agricultural landscapes (29).

A theoretical framework for rewilding

In many ecosystems, trophic complexity, natural disturbances and dispersal maintain complexity and resilience (48, 49) (Fig. 1). Human activities often result in the degradation of one or more of these ecological processes. Rewilding aims to restore these three ecological processes to foster complex and self-organizing ecosystems that require minimal long-term human management (50). If the missing or degraded ecosystem processes are not expected to recover (on time scales relevant to policies) without assistance, rewetting can include initial interventions, sometimes followed by continuous minimal management. In the following paragraphs, we explain each process in detail, explain how their interactions can promote the resilience of biodiversity and ecosystems, and illustrate how backfilling can be used to restore and promote such interactions.

Trophic complexity

Species at higher trophic levels are often highly linked and functionally important for ecosystems (Fig. 1) (51). Large herbivores exert a strong influence on the diversity and abundance of other taxa such as birds, small mammals and insects (52, 53) and plants (54, 55). These effects occur through direct pathways, such as the supply of excrement and carrion (56) or the facilitation of dispersion (54, 55), but also by the modification of the physical environment, for example by grazing and trampling or the construction of dams by beavers (53, 57). Large carnivores can, through predation, affect the size of the population and the behavior of herbivores and create spatiotemporal heterogeneity in these processes. In the absence of downward control by carnivores, high densities of large herbivores can have adverse effects on the abundance and diversity of other groups of species (52, 53).

Humans modify species composition and modify their interactions by hunting, harvesting or planting selected species in agriculture and forestry (Fig. 1A). Large vertebrates are particularly sensitive to human-made defaunation because of their size, long reproductive cycle and high metabolic needs, hence the need for large areas of research. of food (58–62). Thus, even when large vertebrates are still present in man-dominated landscapes, they may not be able to exert the downward control they exert in wild ecosystems because of their reduced density (63, 64). Selective defaunation of top predators and large herbivores can result in cascading trophic effects and increased susceptibility of ecosystems to collapse (51, 65).

Backfilling can increase trophic complexity through various actions depending on the characteristics of the ecosystem. Passive reconstruction measures may, for example, include the creation of non-hunting areas. Where spontaneous recolonization is unlikely, translocation of species can also restore trophic complexity. The introduction of ecological substitutes may be an option if species have disappeared in the world (44). However, these replacements may involve unforeseeable environmental uncertainties and risks and should be evaluated with caution (25). Relining can also be supported by activities to promote coexistence between humans and wildlife, for example through compensation systems for damage to crops or livestock (66, 67).

Stochastic disturbances

Natural disturbances often occur stochastically at different locations, magnitudes and frequencies, thus reinforcing the spatial and temporal heterogeneity of ecosystems (48). These disturbances can trigger a reorganization and reconfiguration of ecosystems (68) and can lead to increased complexity of the ecosystem. They promote coexistence, as there is often a trade-off between the competitive capabilities of species and their resilience to events such as fires, floods or pest outbreaks (68). Species capable of surviving disturbance act as a biological heritage that promotes recovery and reorganization (for example, seed banks or small mammals surviving a fire) (48).

In human-dominated landscapes, natural disturbances are often suppressed (such as fire suppression or flood control) or altered in magnitude and frequency (Fig. 1A), which can lead to even greater disruption and potentially devastating (for example, smaller and more frequent fires). Instead, stochastic disturbances are replaced by predictable and constant perturbations.[Parexempleutilisationd'engraisetd'irrigationpourmaintenirdesintrantsconstantsdanslesécosystèmesoumobilisationannuelledessolspouréliminerlesespècesconcurrentes([Eguseoffertilizersandirrigationtomaintainconstantinputstoecosystemsorannualsoilmobilizationtoweedoutcompetingspecies([parexempleutilisationd'engraisetd'irrigationpourmaintenirdesintrantsconstantsdanslesécosystèmesoumobilisationannuelledessolspouréliminerlesespècesconcurrentes([eguseoffertilizersandirrigationtomaintainconstantinputstoecosystemsorannualsoilmobilizationtoweedoutcompetingspecies(48)]. Because these deterministic perturbations often act in the same place for a long time without the affected ecosystem having a chance to recover and reorganize (68), susceptible species may be lost (1). In addition, human efforts to repair the damage caused by natural disturbances can eliminate biological legacies (48, 68) and cause additional disturbances that hinder the processes of natural regeneration and reorganization (69). For example, salvage cutting to remove dead trees after gale or pest invasion often removes resources and habitats important for saproxylic beetles or cavity-nesting species (70).

Rewilding actions aim to release ecosystems from continuous and controlled anthropogenic disturbances to account for natural variability and sources of stochasticity (71) (Fig. 1B). Mowing grasslands can be reduced or replaced by natural grazing. Dams can be removed or their management modified to restore natural flood regimes (72). Logging can be replaced by allowing natural fire regimes and pests.

Dispersion

Populations depend on dispersal between habitats to avoid overpopulation (73), intraspecific competition and loss of genetic diversity (74). Exchange of individuals from different populations can increase gene flow, reduce inbreeding and thus lead to more viable populations (75). Habitat degradation or anthropogenic dispersal barriers reduce connectivity and dispersal of habitat (Figure 1A).

A rewilding approach includes improving connectivity within and between ecosystems to promote their dispersal. While connectivity efforts are often focused solely on corridors, a multi-scale approach should seek to identify and link opportunities ranging from local features, such as hedgerows to bird support or to other areas. insects (76), to large corridors, which allow the re-colonization by large mammals over long distances. Connectivity can also be improved by removing or increasing the permeability of dispersion barriers (Fig. 1B) such as roads, dams or fences. The permeability of inappropriate habitats, especially homogeneous agricultural areas, can be improved by the introduction of natural features of the landscape (77).

Integration in ecological processes

The three ecological processes can influence and promote each other (Fig. 1). Disturbances can, for example, promote habitat heterogeneity and increase resource availability for less competitive species, which can lead to increased species diversity (78). Significant habitat dispersal supports the recovery of ecosystems after (major) disturbance by allowing recolonization and recovery of affected populations (Figure 1B). Large vertebrates in complex ecosystems often act as plant dispersal agents (54, 55) and can introduce stochasticity into a system, for example by predation or grazing (79). Therefore, restoring one of these processes can positively affect the levels of functionality of the other two processes (Figure 1B). Interactions between processes can increase ecosystem resilience by jointly promoting, for example, functional redundancy or recolonization.

Rewilding efforts can be evaluated by representing ecosystems in their degraded and restored states in a three-dimensional pyramid-shaped space where each axis corresponds to an ecological process and where faces represent interaction between processes (Fig. 2). When restoring a process, the respective vertices of the pyramid move away from the origin and the volume of the pyramid increases. The difference in volume between the restored ecosystem and the degraded ecosystem is therefore an indirect indicator of the effect of renewal of the woodland on the resilience of this ecosystem. Since processes interact, restoring all three dimensions simultaneously will restore only one dimension but not consider the other two (for example, the change in the volume of the pyramid is very small when 39, one of the axes is reversed). fully restored but the other two axes remain severely degraded).

Rewilding as a social choice

Ecosystems can not be valued separately from human societies (80). Tous les domaines candidats au réwilding sont influencés par les personnes et / ou ont un historique d'utilisation. En conséquence, tout projet de rewilding peut affecter les moyens de subsistance et le bien-être locaux. Les changements sociétaux peuvent influencer les écosystèmes de manière positive ou négative, et inversement, et les trajectoires des écosystèmes sont souvent définies par des décisions humaines axées sur la fourniture de certaines ressources et services écosystémiques (67, 81). Considérer et gérer les interactions entre les écosystèmes et les populations tout en évaluant et en communiquant les avantages du rewilding pour la société (Fig. 2) peut inciter à des actions bénéfiques à la fois pour les écosystèmes et la société (67), augmentant ainsi l'acceptation et le succès des efforts de rewilding.

La restauration des trois processus écosystémiques peut influer de manière positive sur la vie des gens. Le remblayage joue un rôle important pour les contributions non matérielles de la nature et les valeurs relationnelles de la biodiversité (82). Un nombre croissant de publications concluent que l'exposition à des espaces verts ou naturels peut réduire les niveaux de stress, augmenter les émotions positives et la fonction cognitive, encourager l'activité physique et faciliter la cohésion sociale chez l'homme (83–86). En particulier, les expériences dans la nature offrent à l’écothérapie une occasion de promouvoir la résilience psychologique chez les enfants et les adolescents (87) et transformation personnelle et épanouissement personnel chez les adultes (88). De plus, la satisfaction que les gens peuvent gagner à savoir qu’une espèce ou un écosystème est en plein essor (89, 90) peuvent atteindre des sociétés très éloignées géographiquement d’un site de rewilding réel. La présence d’espèces ou de paysages charismatiques ou symboliques peut inspirer un développement spirituel, artistique et technologique (42). Les espèces éloignées et migratrices empruntant des voies de dispersion peuvent être à l'origine d'activités telles que l'observation des oiseaux (42). L’observation de processus naturels associés aux expériences vécues dans l’enfance, tels que la migration des hirondelles ou des grues, peut favoriser le sentiment d’endroit et l’enracinement et peut être la base des récits, rituels et célébrations qui façonnent l’identité culturelle (42).

Les avantages économiques du rewilding peuvent découler d'opportunités pour les économies basées sur la nature et de sources de revenus alternatives basées sur des contributions non matérielles de la nature[parexempleactivitésdeloisirs([egrecreationalactivities([parexempleactivitésdeloisirs([egrecreationalactivities(42, 91, 92)]. En outre, les perturbations naturelles peuvent déclencher l’innovation et modifier les systèmes socio-écologiques (93). Rewilding encourage d’autres services de régulation et solutions basées sur la nature, tels que la régulation du climat, la qualité de l’air, la pollinisation et la dispersion des semences (42, 94). L’amélioration du potentiel de dispersion et de la complexité trophique peut empêcher l’épuisement des apports matériels de la nature (42), telles que les ressources naturelles importantes sur le plan économique (par exemple, le gibier), non seulement dans les zones en cours de régénération, mais également dans les zones environnantes.

Cependant, le regarnissage peut également avoir des conséquences indésirables pour les personnes. Les perturbations naturelles telles que les incendies ou les inondations peuvent menacer les êtres humains et leurs infrastructures (95). Conflits homme-faune sauvage – par exemple, les cultures endommagées par les grands herbivores ou le bétail tué par les grands prédateurs (96) —Sont de plus en plus fréquentes et graves lorsque ces animaux sont réintroduits ou que leurs populations se reconstituent (97). En outre, les préoccupations concernant la perte de paysages culturels traditionnels, y compris leur patrimoine naturel et culturel unique, se développent en Europe et dans d'autres régions (91, 98, 99). Un malaise particulier a été exprimé concernant les impacts sur la biodiversité des terres agricoles et sur les services écosystémiques culturels, par exemple les valeurs esthétiques (100), sens du lieu (101), ainsi qu’un «effacement» général de l’histoire humaine et de son implication dans la terre, sa flore et sa faune (32).

En résumé, la relation des hommes avec la nature sauvage est et a toujours été caractérisée par des ensembles de paradoxes (102). Celles-ci vont des conceptions contradictoires de la nature sauvage attribuées aux peuples préhistoriques comme «une menace constante pour [human] vie et moyens de subsistance »par rapport à la« source principale de vie et de moyens de subsistance »selon les perceptions contemporaines et contradictoires comme« un lieu potentiellement dangereux, aliénant et stimulant »par opposition à« un refuge potentiellement paisible pour se détendre et profiter à loisir »(102). Cette gamme d’émotions souligne que les projets de rewilding bien planifiés qui atténuent les conflits potentiels ont le potentiel de maximiser les expériences positives et les contributions bénéfiques de la nature.

Appliquer le cadre

Une approche structurée et participative de la reconstitution des forêts est importante pour garantir que toutes les parties prenantes comprennent clairement les objectifs, les options de gestion, les résultats souhaitables et les risques associés (103). La première étape d'un projet de rewilding devrait être une analyse de l'état écologique de la zone ciblée, en identifiant les composants manquants et / ou dégradés. Les données paléoécologiques – par exemple sur les changements de végétation passés, la présence de mégafaune ou la dynamique des feux – ainsi que des informations sur les historiques d'utilisation des terres devraient être prises en compte dans ces analyses (4).

Dans un deuxième temps, les gestionnaires devraient évaluer la viabilité écologique de différentes options de gestion et les synergies potentielles entre celles-ci. En collaboration avec les principales parties prenantes (défenseurs de l'environnement, agriculteurs, chasseurs et grand public), les responsables doivent identifier les contraintes socio-écologiques (telles que la dispersion des infrastructures, les conflits émergents entre l'homme et la faune sauvage ou les risques associés à la restauration des perturbations naturelles) et évaluer les avantages et inconvénients associés à l'intervention de rewilding.

La troisième étape est la mise en œuvre d'actions de rewilding via une approche de gestion adaptative. Cela inclut le suivi des différentes interventions, idéalement avec une approche BACI (avant-après-contrôle-impact) (104) qui prend en compte à la fois les résultats écologiques et sociétaux. Les résultats de cette surveillance peuvent conduire à des ajustements dans les interventions de rewilding en cours ou à la nécessité de prendre d'autres mesures et décisions de gestion. La phase de mise en œuvre devrait s’accompagner d’une stratégie de communication faisant participer les communautés touchées aux décisions, ainsi que d’activités de sensibilisation qui informeraient le grand public des résultats du remaniement. Ceux-ci devraient idéalement être offerts via un éventail d'opportunités d'expériences dans la nature (visites guidées dans la zone de régénération, outils d'éducation à la nature et possibilités d'activités de loisirs). Additionally, managers may seek to develop opportunities for sustainable business opportunities to increase the acceptance of rewilding among stakeholders.

Our stepwise approach can also be applied for passive rewilding projects. In such cases, there is no deliberate decision to initiate a project, but instead managers can take advantage of ongoing social-ecological dynamics (e.g., farmland abandonment). If such an opportunity is identified, the first step will involve an assessment of the ongoing passive rewilding dynamics, associated risks and benefits, and potential impediments to those dynamics. The second step will focus on identifying options to support those dynamics and mitigate threats. This step will often involve the consolidation of ongoing nonintervention (e.g., establishment of no-hunting arrangements or protected areas) or the mitigation of emerging conflicts. As in active rewilding projects, the third step involves adaptive management, monitoring, and outreach activities.

We now describe the stepwise application of our framework with four rewilding case studies, spanning a range of scales, ecosystem types, and degrees of intervention (Fig. 2). As will become apparent, the development of a rewilding project is rarely a linear process. Owing to the adaptive nature of our approach, some of the steps will be carried out repeatedly and/or in parallel.

Restoration of the natural flood regime in the Leipziger Auwald city forest, Germany

The Leipziger Auwald is an alluvial forest surrounding and crossing the city of Leipzig in Germany. Since the middle of the 19th century, flood suppression and changes in forest management have led to a well-documented shift in tree community composition with increasing dominance of sycamore (Acer pseudoplatanus), Norway maple (Acer platanoides), and common ash (Fraxinus excelsior), mainly at the expense of hornbeam (Carpinus betulus) and oak (Quercus robur) (105). In this state, connectivity between the Auwald’s waterbodies is severely diminished, so active management is necessary to restore the flood regime (Fig. 2A).

After identifying flood disturbance as a major missing component of this ecosystem, city managers initiated yearly experimental flooding of a pilot area in the early 1990s (106). Results of concomitant monitoring confirmed the effectiveness and suitability of this management action. Flooding led to an increase of flood-tolerant species, such as oak and hornbeam, and a decrease or local extinction of some plant species that are intolerant to flooding but had become dominant after flooding had been suppressed (e.g., sycamore and Norway maple) (106). At the same time, (re)colonization by moisture-tolerant slug species and several ground beetle species associated with alluvial forest systems was observed (106). The findings of this long-term experiment thus inform the project’s implementation phase, in which the natural flood regime is restored in several drained branches of the Luppe River (Lebendige Luppe project) (72) (Fig. 2A).

The implementation phase is accompanied by an extensive outreach strategy that offers several opportunities for the public to engage with the ecosystem in the Auwald. Examples include multimedia teaching material to support environmental education and tools (e.g., magnifying glasses, landing nets, and maps) for interactive experiments that allow children to learn about the ecology and topography of the alluvial forest and explore its flora and fauna. A local conservation nongovernmental organization (NGO) organizes excursions to inform residents about ongoing management activities, and regular public discussion forums offer the opportunity to engage actively in the project. Two concomitant research programs assess the ecological outcomes of the project and monitor and evaluate the acceptance and perception of natural processes in the Auwald, respectively (107).

Nonintervention policy in the Swiss National Park

Established in 1914, the Swiss National Park is the oldest national park in Europe and the largest protected area in Switzerland (108). In 1909, the park’s founders—botanists and naturalists concerned with the widespread development of tourism infrastructure threatening the area’s unique flora and fauna—identified the region around the Pass dal Fuorn as a suitable target area, owing to its remoteness and species richness (108).

Making space for natural processes and conducting research on their development are central missions of the park’s management (108). The establishment of the park and management decisions were advised by cartographers and naturalists with extensive knowledge of the area and its ecosystems (109). The protection status of the area was secured by a lease agreement negotiated with the local municipalities and financed through the foundation of the Swiss Federation of Nature Conservation.

Since its establishment, the National Park has been subject to a strict nonmanagement approach and has been fully protected from human activities such as hunting, agriculture, and forestry. Trophic complexity was promoted through targeted reintroductions of ibex (Capra ibex) in 1920, 1923, and 1926 and bearded vultures (Gypaetus barbatus) from 1991 to 2007 (110). Natural disturbances are not managed, and dispersal potential is high for most species (Fig. 2B). Ecosystem development has been monitored continuously, and many of the monitoring schemes have been in place for decades (109). Conflicts with local communities were mitigated via selected active management measures. For example, public discontent over sapling damage caused by red deer (Cervus elaphus) was alleviated by organizing hunting events outside the borders of the park (109). The nonmanagement approach has resulted in the recovery of large populations of red deer, chamois (Rupicapra rupicapra), ibex, and roe deer (Capreolus capreolus), species that were nearly extinct or very rare in Switzerland when the park was established (111). The increased red deer population density has resulted in higher plant species richness in subalpine grassland (112). Additionally, wolves (Canis lupus) and brown bears (Ursus arctos) have recently been sighted, suggesting the imminent recolonization of the area by large predators. Socioeconomic studies show that the park attracts ~150,000 visitors per year, contributing substantially to the economic prosperity of the region (109, 113, 114).

Restoring ecological interactions in the Tijuca National Park, Rio de Janeiro city, Brazil

The Atlantic Forest of Brazil is a globally important biodiversity hotspot. However, most of the protected areas containing Atlantic Forest remnants have been defaunated (115). One of these remnants is the Tijuca National Park in Rio de Janeiro. During the 17th and 18th centuries, deforestation for agricultural purposes and hunting pressure led to severe losses of native fauna. Because the forest is completely surrounded by urban infrastructure, the affected animal species could not fully recover after the area was reforested in the 19th century (116), and dispersal of mammal species to other ecosystems is still inhibited.

The REFAUNA Project was established in 2012 to restore the mammal community via gradual reintroductions of species that have disappeared from the Atlantic Forest (116). Tijuca was considered suitable for first reintroductions because its relatively small size and urban location would allow for easy monitoring and control of the released animals (116). Researchers identified two native, locally extinct candidate species, the red-rumped agouti (Dasyprocta leporina) and the howler monkey (Alouatta guariba), both of which were expected to promote ecological interactions. Agoutis are important dispersers of large seeded plants (117) and increase seed survival by transporting them to locations with lower densities of conspecific tree species. Howler monkeys influence dung beetle abundance, and the decomposition of howler dung by the beetles can enhance nutrient cycling and soil fertilization (118).

Concomitant monitoring revealed that the presence of agoutis and howler monkeys enhanced ecological interactions in the park. Agoutis broadened their diet and improved the dispersal and germination success of several large-seeded plants. By interacting with the dung beetle community, howler monkeys promoted the dispersal of large seeds, with likely positive effects on forest regeneration (116) (Fig. 2C). Although Tijuca is Brazil’s most popular national park (119), there is little emotional connection between the park and people living in adjacent communities (120). To improve the linkage between the park and local communities, the park administration has installed a park council through which representatives of governmental institutions, NGOs, and the private sector aim to reach satisfactory management decisions for all stakeholders (121). A community-based, cooperative project has trained locals as tourist guides and offers tours through the park and a neighboring favela. Additionally, the cooperative runs a restaurant that offers local cuisine prepared with products growing in the forest and community gardens (122, 123).

Ecosystem and wildlife recovery in the Chernobyl exclusion zone, Belarus

The meltdown of the nuclear reactor in Chernobyl on 26 April 1986 resulted in massive contamination, especially in the immediate surrounding area (124–126). The evacuation of the entire local population within a 30-km exclusion zone around the reactor and the most strongly contaminated areas outside this zone resulted in the abandonment of ~1400 km2 of agricultural land (40, 41). The breakdown of the Soviet Union, with widespread outmigration and an additional 36% of all farmland abandoned in Belarus and Ukraine, further lowered human pressure in the region surrounding the Chernobyl site (41).

Two years after the meltdown, the Belarusian part of the exclusion zone and adjacent areas were turned into the strictly protected 1300 km2 Polesie State Radioecological Reserve. In 1993, the reserve was extended by 850 km2, making it the largest nature reserve in Belarus (127). Management of the exclusion zone on both sides of the border has since followed a paradigm of minimal to no intervention. Targeted reintroductions of European bison (Bison bonasus) in the Polesie State Radioecological Reserve and of Przewalski’s horses (Equus ferus przewalskii) in the Ukrainian exclusion zone to restore trophic interactions in the Chernobyl area were exceptions to this passive approach. Recognizing the growing ecological and conservation value of the Chernobyl area, the Ukrainian government established the 2300-km2 Chornobyl Radiation and Ecological Biosphere Reserve—an almost 5000 km2 contiguous rewilding area in the heart of Eastern Europe—in 2016 (128). Management activities in the biosphere reserve aim to recover biodiversity and ecosystem resilience and include monitoring of the ecological, medical, and radiation status of the area, as well as educational activities (128).

The region now harbors the entire portfolio of extant European large carnivores[wolflynx([wolflynx([wolflynx([wolflynx(Lynx lynx), and brown bear], large herbivores[Europeanbisonwildhorsemoose([Europeanbisonwildhorsemoose([Europeanbisonwildhorsemoose([Europeanbisonwildhorsemoose(Alces alces), red deer, roe deer, and wild boar (Sus scrofa)], a rich mesopredator community[egEuropeanbadger([egEuropeanbadger([egEuropeanbadger([egEuropeanbadger(Meles meles), raccoon dog (Nyctereutes procyonoides), and red fox (Vulpes vulpes)], and key ecosystem engineers, such as the Eurasian beaver (Castor fiber). The Chernobyl exclusion zone is the only area where these species interact in sizable numbers in a large wilderness complex and can thus be considered one of the most iconic natural experiments on rewilding in recent history.

The way forward

Rewilding directly aims to restore ecological functions instead of particular biodiversity compositional states. Therefore, the effects of rewilding may be indirect and unexpected. Consequently, the development of sound rewilding plans requires a deep understanding of the interacting ecosystem processes that lead to resilience and the socioeconomic context in which rewilding occurs. Interdisciplinary training of scientists and practitioners is necessary to develop such understanding. Moreover, objective, evidence-based assessments of rewilding initiatives are needed to make rewilding projects fully accountable to funders, the public, and the research community. A recently proposed method to assess the progress of rewilding projects through a combination of expert opinion and monitoring data (129) is a step toward this goal.

Unfortunately, current landscape management and conservation policies do not provide sufficient opportunities for rewilding to be implemented on a broader scale. For instance, the European Union’s common agricultural policy incentivizes agricultural activities in low-production areas, impeding opportunities for rewilding (130). Restoration policies often focus on the safeguarding of current or historical conditions (130) and the protection of certain species and habitats (24, 130, 131). Therefore, the successful contribution of rewilding to national and international biodiversity goals depends on policy changes that shift the conservation focus toward restoring the ecological processes identified in our framework (131).

Discussions on post-2020 biodiversity strategies by the signatory countries of the Convention on Biological Diversity are currently being initiated, and the United Nations General Assembly has recently declared 2021–2030 the “decade of ecosystem restoration” (132). We believe that rewilding provides one of the possible pathways toward the vision in which “By 2050 biodiversity is valued, conserved, restored and wisely used, maintaining ecosystem services, sustaining a healthy planet and delivering benefits essential for all people” (133). Perhaps innovative policy changes that favor rewilding can add to the current momentum for novel approaches to restoration (19, 134). For instance, Aichi Biodiversity Target 15, which aims to restore 15% of degraded ecosystems by 2020, could be revised to recognize rewilding as a major approach to ecological restoration. An ambitious positive target of increasing wildness across the globe by 2030 could be a truly inspiring goal, infusing energy and public support into global biodiversity policies.

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Acknowledgments: A.P. thanks M. Marselle, I. Rosa, A. Torres, C. Meyer, and J. Hines for valuable comments on earlier drafts of this manuscript and three anonymous reviewers whose comments helped to substantially improve this article. Funding: A.P., H.M.P., L.M.N., G.P., R.v.K., and N.F. are supported by the German Centre for Integrative Biodiversity Research (iDiv) Halle-Jena-Leipzig, funded by the German Research Foundation (FZT 118). J.-C.S. and S.C. thank the Carlsberg Foundation (Semper Ardens project MegaPast2Future, grant CF16-0005 to J.-C.S.) and the VILLUM FONDEN (VILLUM Investigator project, grant 16549 to J.-C.S.) for economic support. A.L. was supported by the Portuguese Science and Technology Foundation (FCT) through grant SFRH/BPD/80747/2011 and the FARSYD project (PTDC/AAG-REC/5007/2014-POCI-01-01-0145-FEDER-016664). A.C.A. was supported by a Viçent Munt postdoctoral contract from the Juan de la Cierva Incorporación (IJCI-2014-20744) of the Spanish Ministry of Economy and Competitiveness and by a postdoctoral contract of the Vicepresidencia y Consejería de Innovación, Investigación y Turismo of the Govern de les Illes Balears (PD/039/2017). J.M.B. acknowledges funding from CEH NC project NEC06895. J.M.R.B. was supported by the Spanish Ministry of Economy and Competitiveness (grant CGL2014-53308-P) and the Madrid government (project S2013/MAE-2719 REMEDINAL-3). H.C.W. was supported by the Belmont Forum. Competing interests: H.M.P. is a former supervisory board member of the Rewilding Europe Foundation. C.J.S. is the director of Wild Business Ltd. J.-C.S. is a past or present advisory board member of two rewilding projects in Denmark.

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