Rewilding: definitions, success factors and policy, a European perspective

(1)

1

Rewilding: definitions,

success factors and policy, a

European perspective

Ashleigh Campbell

12910708

Date submitted: 01/12/20

Supervisors:

Kenneth Rijsdijk

and Carina Hoorn

(2)

(3)

3

Abstract

European landscapes are highly urbanised and densely populated, this high level of human pressure has resulted in a fragmented landscape with low habitat heterogeneity. The demand for biodiversity continues to grow as both the quantity and quality of natural ecosystems declines. Rewilding offers an opportunity for degraded landscapes to be restored through natural processes to a state that supports a higher species richness and allows for reintroduction of keystone species. In this review, I look at the varying and disputed definitions of rewilding in literature to determine a common definition. I address and evaluate the ecological success factors of rewilding and assess the relative influence that socio-economic factors and policy can have on rewilding schemes. Through the findings of the review I determine why rewilding is a long-term option for conservation management, in comparison to other strategies. There is no clear consensus on the definition of rewilding in literature, however the continuous theme I found is that, even with initial human intervention through species introductions or ecosystem engineering, the ecosystem should ultimately be left to develop on its own with minimal future human intervention. Reintroduction of megafauna must occur to restore trophic complexity for a rewilding project to be effective. This, alongside increasing habitat connectivity and restoring natural disturbance regimes are essential features to achieve many of the ecological factors that result in rewilding success. Socio-economic aspects of rewilding such as policy, human-wildlife conflict and social conflicts must be considered and mitigated to secure the success of a rewilding project. Rewilding can restore ecosystem processes, provide vital ecosystem services and subsequent economic benefits. Through mitigation of current and future climate change impacts and the sustainable usage of terrestrial ecosystems, rewilding brings us closer to achieving the UN sustainable development goals.

(5)

5

1. Introduction

Urbanisation and population increase are driving a global reduction in biodiversity through the rising demand for both space and natural resources (Seto et al., 2012). Biodiversity is often used as an indicator for the success or health of an ecosystem, the greater the level of biodiversity present, the healthier the system (Spash and Hanley, 1995). Creation and expansions of urban environments for humans and the increased use of land for agriculture to support a growing global population has led to a decrease in the quantity and quality of many natural systems (Bonebrake et al., 2019; Seto et al., 2012). This is either through direct impacts such as habitat fragmentation and destruction or indirect impacts occurring through anthropogenic climate change, sensory pollution (chemical, sound and light), changes in gene flow within populations, or invasive species introduction (Bonebrake et al., 2019). European landscapes are characteristically smaller in size, lower in landscape heterogeneity, more fragmented with a higher human pressure than those generally found in, for example, America (Kuijper et al., 2013). Subsequently, the loss of many ecological processes within an ecosystem can occur, reducing its resilience, complexity and consequently its ability to recover from perturbations (Perino et al., 2019).

With the constant demand for increases in biodiversity, rewilding offers an opportunity for degraded landscapes to be restored through natural processes to a state that can support a higher species richness and allows for the reintroduction of keystone species(Pereira and Navarro, 2015; Torres et al., 2018). Naturally functioning ecosystems are also beneficial for humans in creating income through nature-based tourism, reducing flood impacts and increasing carbon storage, which in turn helps to mitigate the impacts of climate change (Martin and Watson, 2016; Pereira and Navarro, 2015). Implementation and management of new rewilding schemes requires great amounts of research, planning and funding to ensure the project outcomes are a success (Pettorelli et al., 2018).

This review will evaluate the current rewilding schemes and policies, particularly across Europe, and give an insight into the factors that have resulted in rewilding success in these projects and regions. The results of this review can help advise governments on how to improve current rewilding schemes and better implement future rewilding plans. The main research questions addressed will be:

- What is the definition of rewilding?

- What ecological factors are essential for the success of rewilding schemes? o How do socio-economic factors influence the relative success of schemes?

It will also discuss whether rewilding is a viable long-term conservation approach or if a variety of approaches are necessary in order to maximise biodiversity in a fragmented landscape.

This will be a systematic/meta-synthesis review, where I interpret and integrate the findings of multiple studies in order to answer the research questions laid out above. Research for this review was carried out between March and April and then continued from the middle of June until September. I searched for literature using key words such as ‘rewilding’, ‘Europe’, ‘landscape of fear’, ‘biodiversity’, ‘Oostvaardersplassen’, or a combination of these key words with additions such as ‘success’ and ‘progress’, and sought to find the most reliable and up-to-date research. This

Biodiversity: a shortened form of ‘biological diversity’, is used to describe the number, variety and variability of living organisms in

(6)

6 meant selecting papers with high numbers of citations (100+) where possible. As many of the relevant papers I came across were published in the last 3 years and rewilding is a relatively new topic in literature, this was not always feasible. In some instances, grey literature sources were used. In these cases, the most recent sources were selected to provide a more up-to date knowledge and insight or sources from the discussed date for the most accurate context (e.g. newspaper articles). All literature and sources were found through google scholar and the google search engine and stored on free, open-source reference management software, Zotero. I used the referencing style Elsevier – Harvard (with titles) for all sources referred to in this review. In total, I have referenced 50 different sources for this review.

2. Oostvaardersplassen, the Netherlands: Grazer-managed

grasslands in a man-made nature reserve

The Oostvaardersplassen in the Netherlands (Figure 1) is well known for being an extensive man-made wetland, created as a nature reserve that now supports a wealth of breeding and migratory bird species. The management of this reserve, however, has been subject to criticism. Many papers refer to the Oostvaardersplassen as the basis or inspiration behind current rewilding projects (Jepson, 2016)and, as such, I have referenced it as the starting point for this review.

The Oostvaardersplassen is a well-established marshland, managed by Staatsbosbeheer (the Dutch State Forestry Service) since 1996, and is of international significance due to the presence of rare breeding and migratory birds. Since 2010, it has been a part of the Natura 2000 making it one of the top ranked European nature reserves that should be protected, as well as being one of the largest nature reserves in the Netherlands at around 6000 hectares (Vera, 2009).

Figure 1: Map showing the location of the Oostvaardersplassen in the Netherlands (Lorimer and Driessen, 2014, fig.1)

(7)

7 Although often used as a famous example of a rewilding project, the management of Oostvaardersplassen began long before the term ‘rewilding’ was being used in conservation. It is also well known for the great moral controversies surrounding the introduction of large herbivores into the reserve (Keulartz, 2009). The reserve is situated on the South Flevoland polder that was reclaimed from Lake Ijssel in 1968, originally intended for industrial purposes. When this development didn’t occur, the abandoned land became a wetland area. Increased sightings of rare and protected birds in the area led to the management leaning towards conserving the wetland and the many permanent and migratory bird species for which it provides a suitable habitat. Many of these species had not been spotted in the Netherlands for many years and were now being sighted in breeding pairs, highlighting the need for careful management and protection of the wetland reserve (Vera, 2009). Greylag geese colonised the area in large numbers and their grazing of the marshland vegetation changed the marshy landscape to a patchwork of wetland and open water, as well as preventing forest succession. This resulted in the establishment of other species of plants and animals that previously were unable to survive in the area (Keulartz, 2009).

To maintain the grassland areas in the Oostvaardersplassen, an important habitat for the geese, the introduction of wild ungulates was proposed. Heck cattle and Konik ponies were determined to be the best choice and the closest possible to their Aurochs and Tarpan wild ancestors which are now extinct (Vera, 2009). The selected ungulate populations were introduced in 1983-1984 and left to go feral and ‘de-domesticate’ as they were not found in the wild, but taken from zoos (Lorimer and Driessen, 2014). Populations continued to rise annually, and red deer were also introduced to increase the variety in grazing patterns in the reserve. Although successful, the high population numbers began to result in huge food shortages and subsequently many starving animals. There was great concern from the general public and the Dutch animal welfare organisation (Dierenbescherming) about the health of the animals and this sparked protests, court cases and controversy around the management of the Oostvaardersplassen (Lorimer and Driessen, 2014).

The new policy implemented in 2018 sets a maximum for the number of grazers present in the park and that this amount is chosen specifically based on the benefit such a number can have on the landscape and biodiversity in the Oostvaardersplassen. The number will be maintained through movement of individuals to other areas, and if this is not possible then numbers will be controlled through shooting. This manual population regulation ensures that there is enough food supply for the grazers year-round (both ungulate and avian), so additional feeding to prevent starvation is not necessary. It is hoped that these changes will be most beneficial for the rare breeding and migratory bird species present in the reserve, the management for which has shown great success thus far (Staatsbosbeheer, 2018).

Although sharing common features with rewilding such as reintroduction of higher trophic level species and restoration of regulating ecosystem functions like grazing, the management at the Oostvaardersplassen does not fully align with the goals of rewilding (these are discussed in the following chapter) and has never been described by the management as such. It is however a great example of adaptive management, showing the obstacles that may arise when implementing management strategies such as trophic rewilding and how these could be altered or managed within the given ecosystem boundaries (Jepson, 2016).

(8)

8

3. What is rewilding?

Literature on rewilding shows varying definitions, with seemingly no clear consensus on what factors constitute a rewilding scheme or project. The word ‘rewilding’ implies recreation of wilderness, allowing a previously managed ecosystem to become ‘wild’ again. This can create confusion as the question is raised as to what constitutes a ‘wild’ ecosystem. Ecosystems are ever changing, not static and the areas of true wilderness remaining worldwide are few and far between. A common definition laid out in many papers, is that rewilding is ‘promoting self-reorganisation or regeneration of wilderness in an ecologically degraded landscape with minimal ongoing intervention’ (du Toit and Pettorelli, 2019).

The lack of specificity in defining rewilding has been criticised, especially due to the overlap with the definition of restoration of an ecosystem. As famous rewilding projects such as Yellowstone National Park were originally started as an ecological restoration project, it could be argued that rewilding is, in fact, just a form of restoration and should be referred to as such (Hayward et al., 2019). Although seemingly similar in desired outcome, fundamental differences exist in these management strategies. The overall aim of ecological restoration is to return a degraded ecosystem to its prior state (Corlett, 2016). This requires a decision on what the ‘prior state’ of the ecosystem was: is this the state of the ecosystem before anthropogenic land use changes occurred, or further in the past? Once agreed on and restored, continued management efforts are required in order to maintain this state, regardless of changes in environmental conditions (du Toit and Pettorelli, 2019). Many failures in restoration ecology occur from the oversimplification of concepts so that theories can be developed to manage highly complex systems. Examples of this include: working on the basis that nature can be controlled, that there is a single end point, that community assembly can be predicted, and the Sisyphus Complex (when one becomes fixated on treating symptoms rather than the root of the problem, and so becomes susceptible to failure) (Hilderbrand et al., 2005). Rewilding, however, seeks to promote the creation of a new ecosystem to continue the provision of

ecosystem services. Figure 2 (pg. 9) provides an example of how different decisions on the management of an ecologically degraded landscape will dictate which management method is most effective or feasible, based on the desires of investors and stakeholders into the project. Rewilding could

be viewed as a new alternative approach to restoration, that is progressive in considering the ever-changing nature of ecosystems and does not constrain these natural processes to a set ecosystem state, as restoration does.

In their 2019 paper, du Toit and Pettorelli (2019) outlined two approaches to rewilding: active and passive. Active rewilding involves an initial intervention with the degraded ecosystem and may also involve species reintroductions or ecosystem engineering before the ecosystem is left to self-regulate. Passive rewilding uses a ‘wait and see’ approach, where the ecosystem is left completely to develop on its own (du Toit and Pettorelli, 2019). A review by Corlett in 2016 outlined four commonly used terms in conservation research that collectively are beneath the umbrella of rewilding: trophic, passive, Pleistocene and

Ecosystem services: These are the benefits that humans gain from nature. Usually

divided into four different categories: provisioning, regulating, supporting and

cultural (Carpenter et al., 2009).

Ecosystem engineering: Creation, significant modification, maintenance or destruction of a habitat by any organism- in this context, by

(9)

9 ecological rewilding. Corlett (2016) first distinguishes between the most contrasting rewilding approaches: trophic and passive (Corlett, 2016). Trophic rewilding aims to restore previous ecosystem functions through the restoration of top-down trophic interactions, resulting in self-regulating, biodiverse ecosystems (Svenning et al., 2016). With passive rewilding, human interference is minimal from the outset, as in du Toit and Pettorelli’s (2019) definition. Pleistocene rewilding aims at restoring an ecosystem to a pre-human time before large mega-faunal extinctions began (i.e. in the Pleistocene period) (Josh Donlan et al., 2006). The fourth term, ecological rewilding, uses an approach more suitable for European landscapes. In this approach, historical baselines provide ecological knowledge of individual ecosystems so effective conservation strategies can be designed. These strategies aim to provide ecosystem services such as recreation and carbon sequestration, biodiversity is improved, and human control of the ecosystem is reduced (Corlett, 2016). Active management aspects of ecological rewilding (i.e. species reintroductions) may be used on a case-by-case basis, and where the development of beneficial ecological processes (i.e. predation and scavenging) would occur (Pereira and Navarro, 2015).

It seems there can be multiple approaches towards what constitutes a rewilding conservation strategy but regardless of the differences in the approaches, they all follow a continuous theme which differs from that of other conservation strategies. This is that, even with initial human intervention through species introductions or ecosystem engineering, the ecosystem should ultimately be left to develop on its own with minimal future human intervention.

Pleistocene: This is a geological time frame that spanned the world’s most recent period of repeated glaciations, the end of

which corresponds with that of the last glacial period. Occurring between 2,580,000 – 11,700 years ago, the Pleistocene was characterised by the presence of many large

land mammals and birds (Josh Donlan et al., 2006).

Figure 2: Decision pathways involved when deciding how best to manage an ecologically degraded landscape. There are three potential outcomes of this decision tree: restoration, active rewilding or passive rewilding (du Toit and Pettorelli, 2019, fig.2)

Rewilding: “the reorganisation of biota and ecosystem processes to set an identified social–ecological system on a preferred trajectory, leading to the self-sustaining provision of ecosystem services with minimal ongoing management.”

(10)

10

4. Why rewild?

Remaining areas of true wilderness are decreasing in size every year, with 77% of land (excluding Antarctica) and 87% of the ocean already modified in some way through the direct impact of human activity (Watson et al., 2018). Wilderness areas persisting without human interference continue to provide vital habitat for many, potentially endemic, species. A large gene pool of important species that has persisted across evolutionary timescales, these species can provide important historical genetic data to be used in many areas of conservation, especially when rewilding degraded landscapes and ecosystems (Godfrey-Smith, 1979). These areas also deliver important ecosystem services which cannot be provided through the many highly modified and degraded landscapes across the world (Watson et al., 2016).

Natural, intact ecosystems are known to sequester large amounts of carbon, regulate hydrological cycles and greatly reduce the risk from climate-related hazards such as flooding, cyclones and sea level rise (Martin and Watson, 2016). The United Nations (UN) assembly has recently designated the time period 2021-2030 as ‘the decade of ecosystem restoration’. The 17 Sustainable Development Goals (SDG) laid out by the UN in 2015 which form a plan of action for ‘people, planet and prosperity’, to be met by 2030 (UN Assembly, 2015). Two of these goals (goal 13 and goal 15) are of interest in the case for rewilding. Goal 13 aims for urgent action to combat climate change and its impacts, while goal 15 focuses on the preservation of life on land through the protection, restoration and promotion of sustainable use of terrestrial ecosystems (UN Assembly, 2015). Although the process of rewilding cannot replicate the complexity of ecosystems in areas of true wilderness that have established themselves over time, it can still aid in the provision of important ecosystem services being lost through urban and agricultural expansion (Pereira and Navarro, 2015). If left to manage themselves, rewilded areas can establish complex, self-regulating systems that in turn will provide a greater range of ecosystem services (mainly regulating and cultural), and increase biodiversity (Torres et al., 2018).

Maintaining biodiversity, particularly genetic diversity, is often crucial to the survival of species. Smaller, isolated populations of species resulting from natural disasters or anthropogenic impacts leads to a bottleneck effect, where the reduction of genetic diversity leaves individuals at higher risk of many issues such as lowered fertility and higher susceptibility to disease. This is caused by inbreeding in the population leading to a further reduction in the gene pool, labelled ‘inbreeding depression’ (Pearce, 2003). Species diversity, often called ‘species richness’, is the most used measurement for biodiversity. Rewilding strategies that aim to restore the natural ecological processes of an ecosystem will simultaneously both maintain and often increase biodiversity, which can result in increased genetic diversity in the degraded system(Torres et al., 2018).

Cultural services provided by natural ecosystems are greatly important for the more spiritual aspect of human well-being through aesthetic, recreational and educational benefits (Carpenter et al., 2009; Leemans and De Groot, 2003). Rewilded areas can therefore create more space for people to escape modern society and urban areas which often lack the ‘green’ spaces necessary for increasing human well-being. As well as the clear social benefits, there are many economic benefits that can come with the rewilding of degraded landscapes. Initial costs and investments into rewilding projects can be high if they involve reintroduction of species and active rewilding of the landscape (Nogués-Bravo et al., 2016). However, as the overall goal of these schemes is to allow the ecosystem to self-regulate without

(11)

11 human interference, it should not require constant injection of funds as with restoration schemes. In fact, the potential economic benefits from rewilding projects are high, in the form of carbon sequestration, water purification, eco-tourism and natural hazard reduction (Pereira and Navarro, 2015; Pettorelli et al., 2018).

Using rewilding as a conservation strategy allows for progression towards meeting the UN’s SDG, mitigating climate impacts and meeting conservations’ biodiversity targets with relatively low long-term costs. Where possible, we should not only conserve current areas of true wilderness but use rewilding as a conservation strategy, as it offers many potential benefits to both wildlife and humans.

5. Policy and socio-economic implications

The lack of clarity in the definition of rewilding has also created confusion at the policy level. Current environmental policy frameworks do not always favour rewilding and are designed towards more traditional in-situ conservation methods aiming to preserve historical environmental conditions (Pettorelli et al., 2018). These frameworks can also prevent certain processes such as ecological succession from occurring (Root-Bernstein et al., 2018).

Policy on biodiversity and agriculture and land use in the EU are the two areas of policy most relevant for rewilding. Intensification and expansion of agricultural practices across Europe are significant drivers of ecosystem service and biodiversity loss in the continent (Pe’er et al., 2020). The Common Agricultural Policy (CAP) provides conditionally incentivised payments to areas of agricultural land that are classed as being in ‘good agricultural condition’ and free from ‘ineligible features’, such as naturally regenerating scrub (Perino et al., 2019). This, as well as often inflated land costs, reduces the potential for future rewilding projects in these areas (Pettorelli et al., 2018). Pe’er et al. in their 2020 study highlight the urgency for adaptations to the CAP that will ensure food security for the long-term, and environmental and societal sustainability. This would be particularly beneficial in the context of conservation and rewilding initiatives, in providing fewer barriers for new projects (Pe’er et al., 2020).

Biodiversity policy is dictated by both the Birds Directive and Habitat Directive Changes, both of which are based on preservation of specific assemblages of species and habitat types (Pettorelli et al., 2018). In many cases, these legislations will align with the targeted results of a rewilding scheme, however the issues arise with the need for acceptance of potentially uncertain outcomes of a project. Currently, rewilding initiatives must be developed with targets aligning with current legislation and commitments which do not undermine present species and habitat protection. Pettorelli et al. (2018) suggest a ‘rethinking’ of relevant legislation responsible for shaping biodiversity and land use in Europe (such as the EU Birds and Habitats Directives), arguing it could provide the opportunity for more support from governments towards well monitored and evaluated rewilding management plans (Pettorelli et al., 2018).The CAP and EU Birds and Habitats Directives, without further change or consideration, may hinder the progression of new and progressive rewilding projects that may be necessary as global environmental changes push ecosystems beyond their limits. Subsequently, restoration of historical ecosystems may not always be a viable option for conservation and maintaining biodiversity.

(12)

12 It is worth mentioning the influence of the general public in implementation of new conservation management strategies - such as rewilding - and in policy changes. Talk of reintroduction of large carnivores into an ecosystem can lead to an outcry from both local agricultural landowners and the general public (Brown et al., 2011). Often this is due to a fear of these large predators and the potential risk they pose to both humans and livestock (Barkham, 2018a). The concept of rewilding can also be misunderstood, as ‘wild’ and ‘wilderness’ are words associated with the absence of humans and could be something unknown and a potential threat. Modern ecosystems are altered from the historical landscape where these predators were once present. Fragmentation and human population density are much higher (Haddad et al., 2015), so these fears are not completely unfounded.

Looking at ecosystems from a socio-ecological perspective, you include ecosystem processes and also ecosystem services in a way that humans are viewed as part of the landscape alongside nature, not as a separate entity. Every landscape that is a possible contender for rewilding has either historical use by humans or is influenced by people (Perino et al., 2019). Proposals for new rewilding schemes are often met with resistance, especially from farmers if they feel their livelihoods are not being considered. This is especially the case where the reintroduction of large predatory species such as wolves is involved as part of a rewilding program. It can be hard to persuade farmers of the many benefits of reintroducing top predators into an ecosystem, such as the reduction of overpopulated wild grazing species, if they feel it puts their livestock at risk (Brown et al., 2011). Human-wildlife conflict is a big issue in conservation and not something to be overlooked. The identification of possible social conflicts and implications of a rewilding project therefore need to be thoroughly investigated to mitigate any potential negative consequences (Svenning et al., 2016).

Although ecotourism presents the potential of greater economic security for local or indigenous people, conflicts of interest can arise when management doesn’t consider the historical cultural values of a landscape (Perino et al., 2019). Conflict can also arise when rewilding schemes aim to integrate ecotourism into their project plans in order to generate more money, such is the case with the rewilding project of Swedish Lapland (Koninx, 2019). Although the ‘Rewilding Sweden’ initiative has many ambitious conservation goals centred around ecotourism, many current local ecotourists and wardens had concerns. They worried that the marketing and promotion of the new initiative would result in a ‘different type of nature experience’ that would ultimately undermine the purpose of the rewilding initiative itself (Koninx, 2019). This highlights the importance of inclusivity of local stakeholders and residents in the planning process to ensure conflicts are minimised.

The media can play an indisputable role in the communication of conservation and rewilding projects to the general public and subsequently the depiction the project’s progression and effects. A well-known example of this is the publicising of the management at Oostvaardersplassen, the Netherlands. Though the grazing animals in the Oostvaardersplassen were deemed ‘wild enough’ to no longer be considered livestock and could be left to self-regulate their populations (often through starvation during winter), the subsequent public criticism was huge (Vera, 2009). Protests took place and media outlets reported on the ‘horrors’ occurring on the nature reserve (Barkham, 2018b). This led to a change in policy and management where animals are selectively culled if they are believed to be too weak to survive the winter (Staatsbosbeheer, 2018). This brings to light another influential policy in the reintroduction of species into an area that conflicts with the minimal human influence approach of rewilding. Where previously native

(13)

13 species are now extinct rather than just extirpated, appropriate species substitutes are often used- as was the case for the Oostvaardersplassen (Vera, 2009). These species, selected on their ability to fulfil the ecological niche of their extinct predecessors, may come from captivity (e.g. zoos). These animals are seen as domesticated, so reserve management are still responsible for ensuring they are fed (Lorimer and Driessen, 2014). Consequently, policy may not allow release of animals into an area without management in place to ensure the individuals are provided for.

The United Nations assembly has recently designated the time period 2021-2030 as ‘the decade of ecosystem restoration’ (UN Assembly, 2015). In order to achieve the set goals for biodiversity post-2020, rewilding should be considered as a strong contender for management plans and discussions on achieving these goals by policy setters and major decision makers (Perino et al., 2019). This is especially important as the rate of predicted land abandonment in Europe- particularly agricultural land- is set to increase in the coming years (Ceaușu et al., 2015; Corlett, 2016). Land abandonment can result in huge negative environmental, socio-economic and cultural impacts with decreases in biodiversity, reduction of employment prospects and loss of cultural heritage (Pereira and Navarro, 2015). Abandoned land does however provide new potential rewilding opportunities in the fragmented European landscape where restoration possibilities may no longer be feasible (Lorimer et al., 2015). Organisations such as Rewilding Europe aim to utilise these opportunities and build ‘nature-driven economies that can serve to reverse these damaging trends’ caused by land abandonment (Rewilding Europe, 2020).

Although the potential for socio-economic conflicts from rewilding projects is high if not thoroughly investigated and mitigated for beforehand, the societal and economic benefits brought by rewilding- as mentioned earlier in this review- can be extensive. The non-material contribution of nature areas to humankind has a growing supportive evidence base, reducing stress levels, increasing positive emotions and cognitive function. A successful rewilding scheme, as well as achieving all ecological goals, should also consider the limitation of social conflicts and the impact on residents. Conflict between humans and wildlife or conservation areas can be a limiting factor in the success of a project, and it is therefore imperative that the views and opinions of locals are respected.

6. Ecological success factors and progress in rewilding

Conservation aims and outcomes of rewilding projects may change and adapt over time, so it can be difficult to specify across all ecosystems what the factors of a successful scheme will be. Every ecosystem is unique in its ecological attributes and processes so there is no ‘one size fits all’ strategy. Additionally, the very concept of rewilding is restoration of a degraded landscape through allowing an ecosystem to self-regulate with minimal human interference. This makes the monitoring and measurement of success of a rewilding project an ambiguous area as these ecosystems evolve and adapt in unpredictable ways. There are, however, methods and frameworks that have been produced to effectively measure and monitor success in rewilding.

Extirpation: Synonyms: destruction, eradication, extinction. Often used to refer to locally extinct species, an extirpated species is one that is no longer found in a

(14)

14 Pettorelli et al., in 2018 lay out five research areas in which, if there’s a lack of data, may slow or hinder the success of a rewilding project. These are: (1) Target setting and implementation, (2) Risk assessment, (3) Assessment of potential economic costs and associated benefits, (4) Identifying and characterising likely social impacts, (5) Monitoring and evaluation (Pettorelli et al., 2018). Several studies have presented methods through which specific targets for implementation could be selected and the progress and success of a rewilding project monitored to give quantitative and measurable data (Table 1). This allows ecosystem-specific goals to be set based on the unique ecological processes of the landscape for any individual rewilding project.

A study by Torres et al., in 2018 presented a framework for measuring and monitoring progress of the ecological aspects of rewilding. They also provide a list of potential evidence-based restoration actions which could improve the ecological integrity of a rewilding project. These actions are presented in a table beside the relevant pressure and state variables of the system (e.g. population reinforcement, artificial feeding of wildlife), indicators of whether these variables are present and a points system assigned to rank the potential effectiveness of each restoration action (ranked from 0, no known effectiveness to 4, beneficial). They use three principles for quantifying a measurement of ecological integrity as: E = g(d, c, t); where d represents the naturalness of disturbances and stochastic events, c the connectivity of terrestrial and aquatic systems and t the composition and complexity of the trophic network. In combination with ecological integrity measurements, they use human input and output as a measurement of the pressure of human forcing on an ecosystem. This is defined as: H = f(i, o), where i represents material inputs into a system (e.g. baiting of wildlife) and o material outputs (e.g. timber production, hunting, mining).

Table 1: Examples of potential targets that could be considered by rewilding initiatives, actions needed to achieve these targets, which ecological processes will be restored or enhanced as a result and measurable outcomes from any implemented actions to achieve these targets (Pettorelli et al., 2018, table.3)

(15)

15 To test their outlined framework, the assessment was applied to three flagship restoration projects with differing characteristics. These were: the highly urbanised landscape of Millingerwaard, close to Nijmegen (the Netherlands); a large, naturalised inland wetland system, the Iberá Project (South America); and an area managed for over a century in an effort to minimise human control over ecological processes, the Swiss National Park (southeast Switzerland). Across all three sites, the framework was shown to be effective in increasing the rewilding score (Figure 3). This was through an increase in ecological integrity (e.g. through maximisation of natural regimes, trophic complexity and connectivity of natural systems) and a decrease or little-to-no increase in the pressure of human forcing on the ecosystem (e.g. minimisation of hunting/mining/fishing). The authors make clear that although positive progress was seen in all of the case studies they cannot be directly compared as the landscapes and starting points differ greatly, and consequently so may the lag times for an increase in ecological integrity (Torres et al., 2018).

Figure 3: The results of applying the rewilding assessment framework to three rewilding projects: Millingerwaard, Swiss National Park and Iberá. Change in rewilding score ‘R’ for each management strategy (b) between the start of the project (light grey) and the current state (dark grey) are calculated based on the scores shown in (a) for different measured variables (Torres et al., 2018, fig.2).

(16)

16 While each rewilding project will have its unique aims and strategies, an adaptive management plan is necessary. Potential ecological outcomes of rewilding can be modelled and predicted within a boundary of error, but as the dynamics of the ecosystem change, ongoing re-evaluation is essential (Varley and Boyce, 2006). If consistent data collection and monitoring occurs before and during a new management strategy, then this becomes a much simpler task as you have a baseline to compare to the progress of different ecosystem functions. Although rewilding aims for minimal human interference, small changes through ecological engineering or species reintroductions could be beneficial to the progress of the rewilding project at a later stage.

Both frameworks presented by Pettorelli et al., (2018) and Torres et al., (2018) display a similar range of measurable ecological factors required to produce success in a rewilding project. Intensively managed systems often have a lack of trophic complexity, suppressed or altered natural disturbance regimes and limited dispersal opportunities which reduces resilience and complexity within an ecosystem (Perino et al., 2019). The restoration of these three factors is what Perino et al., (2019) say is necessary for rewilding initiatives, in order to create “more complex and self-organising ecosystems”, as long-term human management of these systems would be minimal. Increasing trophic complexity through the reintroduction of megafauna to an ecosystem seems to provide the most ecological improvements to a system (Pettorelli et al., 2018). This is due to the multitude of natural processes restored through the reintroduction of large herbivores and carnivores to degraded ecosystems, which will be discussed in greater detail in the following chapter.

7. Trophic rewilding and the landscape of fear

Absence of predators in an ecosystem has repeatedly been shown to allow certain consumers to reproduce high above their ‘usual’ rates, which can result in a trophic cascade. The most common example being where herbivore populations explode due to lack of predators to depress the population (Terborgh et al., 2001). As herbivores need not be as vigilant and cautious in a landscape void of predators, they can spend a greater amount of time foraging (Laundré et al., 2001). This can lead to overgrazing, where plants have insufficient defence against the high abundance of grazers and cannot recover under such pressure. Great changes in the landscape of an ecosystem can occur in these scenarios.

There is still debate and uncertainty as to whether ecosystems regulate through top-down processes, bottom-up processes, or a combination of both, and how these factors influence population dynamics (Smith et al., 2003). It is a common occurrence in certain ecosystems for herbivore populations to be controlled through bottom-up processes such as in the Serengeti and the Ngorongoro crater in Tanzania, Africa. When the population grows too large for the food and nutrients available, weaker members of these populations will starve. The population continues to reduce in this way until it reaches carrying capacity (Schell, 2000). Interestingly, in the Serengeti where lions and hyenas are present as large predators, 75% of wildebeest deaths result from malnutrition and only 25% due to predation (Vera, 2009). This is an example of how self-regulating ecosystems

Carrying capacity: the maximum number of individuals of a population that can be supported by the resources available in

(17)

17 do not necessarily require large predators in order to control the herbivore populations. Having higher trophic levels (both large herbivores and large predators) present in an ecosystem has however been proven to have positive effects on ecosystem function and biodiversity, especially at lower trophic levels and in ecosystems where large predators have been extirpated (Svenning et al., 2016).

Where the top-down pressure of predators is present in a landscape it creates a new dynamic in the ecosystem, formed through a fear response of prey to their predators. This effect is especially apparent where predators are reintroduced to an ecosystem from which they have occurred historically. The re-introduction of wolves into Yellowstone National Park (YNP) in the winter of 1994-1995, after 70 years of absence, has allowed for more than 20 years of monitoring and observations of predator-prey dynamics (Box 1). It was found that seasonal movement and

habitat use of elk (Cervus elaphus), the most abundant ungulate in the park, was altered after wolf re-introduction (Mao et al., 2005). Seasonal movement of such large ungulate populations in these regions is associated with the nutritional quality of the plants on which they feed, as they forage for young, nutrient rich foliage. This seasonal migration is also critical in allowing enough time for grazed areas to recover and increasing nitrogen availability for

Box 1: Yellowstone National Park, USA: Riparian plant recovery

In the early 1900’s, the grey wolves (Canis lupus) were extirpated throughout Yellowstone National Park (YNP) and almost everywhere else in the USA due to hunting, trapping and poisoning. Public opinion of wolves, particularly in rural areas, was negative with many misconceptions. As these large predators were no longer present in YNP or surrounding landscape, large herbivore species such as elk were able to graze freely on vegetation, without the pressure of predators. Over the years, constant high grazing pressures meant that no new recruitment of woody species could occur. Mature, woody plant populations such as willow, which were present along the river and stream, banks deteriorated drastically. This cascading effect on lower trophic levels led to great changes in floodplain function and channel morphology. The riverbanks, void of riparian plant communities, erode at a much faster rate, causing widening of the stream channel. Changes in stream flow and temperature occur due to increased channel widening and incision (Beschta and Ripple, 2006). Channel incision is a natural process where the river becomes deeper due to erosion of the riverbed. The lower riverbed can lead to a disconnection from the rivers’ floodplain (Beschta and Ripple, 2006). By the 1940s, the desire to restore ecosystems towards their naturally balanced state, inclusive of large predators, became more popular. Agricultural landowners had concerns about predation of their livestock and were strongly opposed to wolf reintroductions. Surveys showed however, that the general public opinion favoured the reintroduction of wolves into YNP (Fritts et al., 1997).

Reintroduction of wolves into YNP has resulted in visible recovery of the riparian and woody plant communities. Reduced ungulate browsing occurring directly and indirectly as a result of wolf presence (predation and increased vigilance) meant a higher recruitment of these plant species could occur (Ripple and Beschta, 2012). In some cases recruitment was occurring for the first time in decades (Beschta and Ripple, 2010). Originally, YNP management was a restoration strategy, long before ‘rewilding’ was a term used by the scientific community. It is now referenced in many papers as one of the greatest successes in rewilding, particularly regarding wolf reintroduction.

(18)

18 plants (Frank, 1998). A study by Ripple and Beschta in 2012 found that wolf reintroduction in YNP had restored a trophic cascade involving the wolves, elk and plants, increasing woody plant species such as aspen, cottonwood and willow in certain areas. These plants, prior to wolf reintroduction, were unable to grow above grazing height due to overgrazing by the large elk populations. The subsequent ‘landscape of fear’ created by the wolves meant elk populations decreased and the threat of predation limited the distribution and movement of elks around the park, allowing for the regrowth of woody species. Additionally, both beaver (Caster canadensis) and bison (Bison bison) numbers increased in the park, likely due to a reduction in competition for food resources with elk (Ripple and Beschta, 2012).

Foraging theory predicts that prey animals will reduce the effort they put into feeding in order to reduce the risk of predation, this is achieved through a reduction in the amount of time spent foraging and increasing the time spent being vigilant when in a high risk area (Brown, 1999). Kuijper et al., (2013) published a study that looked at both the direct and indirect effects of predators on ungulates in a European landscape. They found that the cascading effects in the distribution and performance of trees in the Białowieża Primeval Forest in Poland, result from not only lethal (direct) impacts of predators on the ungulate species, but also as a result of non-lethal (indirect) effects (Kuijper et al., 2013). In areas where predator threat was highest, tree regeneration increased. This study demonstrated that in densely forested areas - in European systems where the scale of national parks is smaller than in America – predator ranges may overlap substantially more, making it harder to assess the impacts of a landscape influenced by fear.

There is the potential for huge benefits from the reintroduction of large predators, such as wolves, to countries where large populations of grazers are more destructive than beneficial to the ecosystem. Large herbivores can have many detrimental effects on ecosystems through impacting primary production, nutrient cycling, disturbance regimes, habitat heterogeneity and seed dispersal (Svenning et al., 2016). In Scotland, the wolf is thought to have gone extinct at around 1700 AD and discussions about the potential reintroduction of wolves to Scotland has been ongoing since the 1990’s (Arts et al., 2016). The populations of red deer in Scotland are high and their grazing and browsing results in harmful effects on upland ecosystems, especially through the prevention of semi-natural woodland regeneration (Brown et al., 2011). In landscapes such as this, it is likely that wolf reintroduction could help regulate deer populations, and consequently their patterns and intensity of grazing. As Scotland has a highly fragmented and agricultural landscape, there are often more obstacles and considerations than in vast landscapes such as that of YNP.

It is possible to artificially create a landscape of fear where large predator reintroduction into an area overpopulated by grazing herbivores is not feasible. Having hunters present to periodically cull herbivores can simulate a fear response like that provided by the presence of a large predator (Arts et al., 2016). This strategy is used in many nature reserves such as the Oostvaardersplassen to regulate populations of herbivores and prevent overgrazing (Staatsbosbeheer, 2018). The behavioural responses of prey animals associated with the constant presence of a large predator are, however, impossible to replicate exactly. Selective culling will never have the same regulating effect as that of a wolf pack (Arts et al., 2016). This complex landscape of fear concept can be a useful tool for conservation management and rewilding projects involving reintroductions of large predatory species. It facilitates the quantification and prediction of potential outcomes of predator-prey interactions and how it can substantially alter ecosystem dynamics and processes resulting from cascading effects (Laundré et al., 2010).

(19)

19 The importance of reintroducing large herbivores into an ecosystem must also not be overlooked. Megafauna once present in many ecosystems are often extinct and so cannot be reintroduced. In certain instances, such as the Oostvaardersplassen, it is possible to find species which can fill a similar ecological niche to that of their extinct predecessors (Svenning et al., 2016). There is also ongoing research into the possibility of using synthetic biology to create organisms resembling extinct species, this would be carried out either through back-breeding, cloning or genetical engineering (Shapiro, 2017).

Trophic rewilding is no simple feat. There may be policies in place or resistance from other parties that prevent or slow species introductions where there are disagreements about the suitability and feasibility of the reintroduction. Much consideration must also be taken into the potential effects of a large species being reintroduced into an ecosystem as well as the predicted costs. That said, increasing the trophic complexity of a degraded landscape through megafaunal reintroductions is crucial in order to achieve many of the desirable ecological success factors of a rewilding project.

8. What factors are essential for success in a rewilding project?

In this review I discussed how humans are not separate from nature and should not be viewed as such. Rewilding strategies give an opportunity for the recovery of degraded ecosystems to occur alongside the modern urbanised landscape. The benefits drawn from rewilding through the provision of essential ecosystem services show it is in humankind’s best interest to use rewilding as a conservation strategy in areas where restoration is not feasible. These projects, if successful, have the potential to be greatly beneficial to both the targeted ecosystem as well as the local economy and ecosystem services.

In order to achieve the self-regulating system with minimal human management that is the ultimate goal of all rewilding schemes (Pettorelli et al., 2018), both trophic complexity and connectivity in a system must be increased and natural disturbance regimes restored (Perino et al., 2019). Although connectivity can be more difficult to achieve in a fragmented European landscape, increasing trophic complexity and restoring natural disturbance regimes can be very simple and requires little ongoing management. For a self-sustaining and biodiverse ecosystem to be established, restoration of top-down processes through reintroduction of large-bodied herbivores and carnivores must occur (Perino et al., 2019). This may be through active reintroductions by management of extirpated species or fauna that fill comparable niches to those of their extinct ancestors, or spontaneous re-colonisation by a species that was previously extirpated. This increases trophic complexity in the ecosystem, often resulting in a trophic cascade and a complete restructuring of the predator prey dynamics. Subsequently, drastic changes can occur in landscape that will restore lost or disrupted ecosystem processes (Laundré et al., 2010). Many ecological success factors that can be both measured and monitored during a rewilding project occur either directly or indirectly as a result of the reintroduction of megafauna (Table 2).

(20)

20 Many non-ecological factors can be influential in the initial implementation of a rewilding project, and the potential successes. These include ecological limitations, policy, funding, socio-economic implications and the influence of both the media and general public. While current policies may restrict the progress or execution of rewilding initiatives, many have been successful within the current European laws and restrictions. However, in order to meet the current targets for biodiversity and climate change, evidence presented in this review suggests that rewilding should be a part of discussions and planning by both stakeholders and policymakers (Perino et al., 2019). Changes in policy could also lead to an increase in state funding possibilities for rewilding schemes so that reliance on private funding is not so restricting in planning and implementation projects (Pettorelli et al., 2018). Careful consideration of potential socio-economic impacts and conflicts is essential in the planning phase of a rewilding project to ensure that potential mitigation strategies can be discussed and applied. This will reduce any negative impacts that a rewilding scheme may bring. In many cases the socio-economic benefits will greatly outweigh any negatives, all relevant social groups (farmers, local businesses and residents) must be considered to maximise potential benefits (Svenning et al., 2016).

It is not enough to only focus on the present state of ecosystems as large changes in management strategies may require many years before the benefits of these changes are made apparent in the form of increased ecological integrity. Depending on the complexity of the ecosystem and changes to be made, lag times can vary hugely. An example would be reintroducing species that historically have great ecological importance but were extirpated, it may take hundreds or even thousands of years before the ecosystem has fully recovered (Torres et al., 2018). Case and ecosystem specific goals and time frames must be set to ensure that the assessed necessary changes and improvements to the degraded ecosystem are fulfilled and that the amount of time required is not underestimated.

Table 2: Ecological success factors of rewilding and the rewilding management strategies required to achieve them (created using data from Pettorelli et al., 2018; Torres et al., 2018; Perino et al., 2019).

Ecological success factors of rewilding

Rewilding management strategies required

Increased trophic complexity Reintroduction of large herbivores and carnivores

Increased biodiversity Removal of non-native ‘invasive’ species, reintroduction

of extirpated species (large herbivores and carnivores)

Regeneration of native plant species

Megaherbivore reintroduction and/or herbivore exclusion/eradication. Removal of non-native ‘invasive’ species. Allowing natural regeneration to occur.

Higher genetic diversity within populations Creating habitat corridors to enable movement between habitats, reintroduction of extirpated species

Increase in carbon storage

(or reduction in the amount of carbon lost)

Megaherbivore reintroduction (trampling, seed dispersal)

Increased habitat connectivity Creating habitat corridors to enable movement between

habitats Restoration of natural fire regimes

(changes in fire occurrence/severity)

Megaherbivore reintroduction (grazing, carbon sequestration)

Restoration of natural hydrological regimes (changes in flood occurrence/severity)

Reintroduction of keystone species, removal of dykes/channels/dams

(21)

21

6. Conclusion

Rewilding is a conservation strategy defined by the aim of allowing an ecosystem to develop independently into a self-regulating system, with minimal future human intervention. This makes it unique to other conservation strategies, such as restoration, which tend to use a more ‘hands-on’ approach to their management strategies. Rewilding can be regarded as an optimal long-term conservation approach, restoring ecosystem processes, providing vital ecosystem services (aesthetic, cultural, regulating) and subsequent economic benefits. Through mitigation of current and future climate change impacts and the sustainable usage of terrestrial ecosystems, rewilding can bring us closer to achieving the UN sustainable development goals. However, the reintroduction of megafauna, must occur to restore trophic complexity for a rewilding project to be effective. This, alongside increasing habitat connectivity and restoring natural disturbance regimes are essential features to achieve many of the ecological factors that result in rewilding success. Socio-economic aspects of rewilding such as policy, human-wildlife conflict and social conflicts must be considered and mitigated to secure the success of a rewilding project.

Further research and reports on individual rewilding projects in varying ecosystems in Europe are needed to gain more knowledge on the success factors for individual projects and which management approaches were responsible for these successes. A greater data pool will encourage policymakers and governments to consider rewilding as an environmental management strategy that provides essential ecosystem services and moves us towards reaching the global biodiversity and sustainable development goals.

(22)

22

References

Arts, K., Fischer, A., van der Wal, R., 2016. Boundaries of the wolf and the wild: a conceptual examination of the relationship between rewilding and animal reintroduction. Restoration Ecology 24, 27–34.

Barkham, P., 2018a. Harmless or vicious hunter? The uneasy return of Europe’s wolves. The Guardian.

Barkham, P., 2018b. Dutch rewilding experiment sparks backlash as thousands of animals starve. The Guardian. Bonebrake, T.C., Guo, F., Dingle, C., Baker, D.M., Kitching, R.L., Ashton, L.A., 2019. Integrating Proximal and Horizon

Threats to Biodiversity for Conservation. Trends in Ecology & Evolution 34, 781–788.

Brown, C., McMorran, R., Price, M.F., 2011. Rewilding–a new paradigm for nature conservation in Scotland? Scottish Geographical Journal 127, 288–314.

Brown, J.S., 1999. Vigilance, patch use and habitat selection: foraging under predation risk. Evolutionary ecology research 1, 49–71.

Carpenter, S.R., Mooney, H.A., Agard, J., Capistrano, D., DeFries, R.S., Díaz, S., Dietz, T., Duraiappah, A.K., Oteng-Yeboah, A., Pereira, H.M., 2009. Science for managing ecosystem services: Beyond the Millennium Ecosystem Assessment. Proceedings of the National Academy of Sciences 106, 1305–1312.

Ceaușu, S., Hofmann, M., Navarro, L.M., Carver, S., Verburg, P.H., Pereira, H.M., 2015. Mapping opportunities and challenges for rewilding in Europe. Conservation Biology 29, 1017–1027.

Corlett, R.T., 2016. Restoration, reintroduction, and rewilding in a changing world. Trends in ecology & evolution 31, 453–462.

du Toit, J.T., Pettorelli, N., 2019. The differences between rewilding and restoring an ecologically degraded landscape. Journal of Applied Ecology 56, 2467–2471.

Frank, D.A., 1998. Ungulate regulation of ecosystem processes in Yellowstone National Park: direct and feedback effects. Wildlife Society Bulletin 26, 410–418.

Godfrey-Smith, W., 1979. The value of wilderness. Environmental Ethics 1, 309–319.

Haddad, N.M., Brudvig, L.A., Clobert, J., Davies, K.F., Gonzalez, A., Holt, R.D., Lovejoy, T.E., Sexton, J.O., Austin, M.P., Collins, C.D., 2015. Habitat fragmentation and its lasting impact on Earth’s ecosystems. Science advances 1, e1500052.

Hayward, M.W., Scanlon, R.J., Callen, A., Howell, L.G., Klop-Toker, K.L., Di Blanco, Y., Balkenhol, N., Bugir, C.K., Campbell, L., Caravaggi, A., 2019. Reintroducing rewilding to restoration–rejecting the search for novelty. Biological conservation 233, 255–259.

Hilderbrand, R.H., Watts, A.C., Randle, A.M., 2005. The myths of restoration ecology. Ecology and society 10. Jepson, P., 2016. A rewilding agenda for Europe: creating a network of experimental reserves. Ecography 39. Josh Donlan, C., Berger, J., Bock, C.E., Bock, J.H., Burney, D.A., Estes, J.A., Foreman, D., Martin, P.S., Roemer, G.W.,

Smith, F.A., 2006. Pleistocene rewilding: an optimistic agenda for twenty-first century conservation. The American Naturalist 168, 660–681.

Keulartz, J., 2009. Boundary work in ecological restoration. Environmental Philosophy 6, 35–55.

(23)

23 Kuijper, D.P.J., De Kleine, C., Churski, M. v, Van Hooft, P., Bubnicki, J., Jędrzejewska, B., 2013. Landscape of fear in

Europe: wolves affect spatial patterns of ungulate browsing in Białowieża Primeval Forest, Poland. Ecography 36, 1263–1275.

Laundré, J.W., Hernández, L., Altendorf, K.B., 2001. Wolves, elk, and bison: reestablishing the" landscape of fear" in Yellowstone National Park, USA. Canadian Journal of Zoology 79, 1401–1409.

Laundré, J.W., Hernández, L., Ripple, W.J., 2010. The landscape of fear: ecological implications of being afraid. The Open Ecology Journal 3.

Leemans, R., De Groot, R.S., 2003. Millennium Ecosystem Assessment: Ecosystems and human well-being: a framework for assessment. Island press.

Lorimer, J., Driessen, C., 2014. Wild experiments at the Oostvaardersplassen: Rethinking environmentalism in the Anthropocene. Transactions of the Institute of British Geographers 39, 169–181.

Lorimer, J., Sandom, C., Jepson, P., Doughty, C., Barua, M., Kirby, K.J., 2015. Rewilding: Science, practice, and politics. Annual Review of Environment and Resources 40, 39–62.

Mao, J.S., Boyce, M.S., Smith, D.W., Singer, F.J., Vales, D.J., Vore, J.M., Merrill, E.H., 2005. Habitat selection by elk before and after wolf reintroduction in Yellowstone National Park. The Journal of Wildlife Management 69, 1691–1707.

Martin, T.G., Watson, J.E.M., 2016. Intact ecosystems provide best defence against climate change. Nature Climate Change 6, 122–124. https://doi.org/10.1038/nclimate2918

Nogués-Bravo, D., Simberloff, D., Rahbek, C., Sanders, N.J., 2016. Rewilding is the new Pandora’s box in conservation. Current Biology 26, R87–R91.

Pearce, D.W., 2003. The value of biodiversity. Microbial Diversity and Bioprospecting 469–475.

Pe’er, G., Bonn, A., Bruelheide, H., Dieker, P., Eisenhauer, N., Feindt, P.H., Hagedorn, G., Hansjürgens, B., Herzon, I., Lomba, Â., 2020. Action needed for the EU Common Agricultural Policy to address sustainability challenges. People and Nature 2, 305–316.

Pereira, H.M., Navarro, L.M., 2015. Rewilding european landscapes. Springer Nature.

Perino, A., Pereira, H.M., Navarro, L.M., Fernández, N., Bullock, J.M., Ceaușu, S., Cortés-Avizanda, A., van Klink, R., Kuemmerle, T., Lomba, A., 2019. Rewilding complex ecosystems. Science 364.

Pettorelli, N., Barlow, J., Stephens, P.A., Durant, S.M., Connor, B., Schulte to Bühne, H., Sandom, C.J., Wentworth, J., du Toit, J.T., 2018. Making rewilding fit for policy. Journal of Applied Ecology 55, 1114–1125.

Rewilding Europe, 2020. Nature-based economies | Rewilding Europe [WWW Document]. URL

https://rewildingeurope.com/rewilding-in-action/nature-based-economies/ (accessed 11.29.20). Ripple, W.J., Beschta, R.L., 2012. Trophic cascades in Yellowstone: the first 15 years after wolf reintroduction.

Biological Conservation 145, 205–213.

Root-Bernstein, M., Gooden, J., Boyes, A., 2018. Rewilding in practice: Projects and policy. Geoforum 97, 292–304. Schell, D.M., 2000. Declining carrying capacity in the Bering Sea: Isotopic evidence from whale baleen. Limnology and

Oceanography 45, 459–462. https://doi.org/10.4319/lo.2000.45.2.0459

Seto, K.C., Güneralp, B., Hutyra, L.R., 2012. Global forecasts of urban expansion to 2030 and direct impacts on biodiversity and carbon pools. Proceedings of the National Academy of Sciences 109, 16083–16088.

(24)

24 Shapiro, B., 2017. Pathways to de‐extinction: how close can we get to resurrection of an extinct species? Functional

Ecology 31, 996–1002.

Smith, D.W., Peterson, R.O., Houston, D.B., 2003. Yellowstone after wolves. BioScience 53, 330–340.

Spash, C.L., Hanley, N., 1995. Preferences, information and biodiversity preservation. Ecological economics 12, 191– 208.

Staatsbosbeheer, 2018. Large grazers [WWW Document]. URL https://www.staatsbosbeheer.nl/over-staatsbosbeheer/dossiers/oostvaardersplassen-beheer/grote-grazers (accessed 8.21.20).

Svenning, J.-C., Pedersen, P.B., Donlan, C.J., Ejrnæs, R., Faurby, S., Galetti, M., Hansen, D.M., Sandel, B., Sandom, C.J., Terborgh, J.W., 2016. Science for a wilder Anthropocene: Synthesis and future directions for trophic

rewilding research. Proceedings of the National Academy of Sciences 113, 898–906.

Terborgh, J., Lopez, L., Nuñez, P., Rao, M., Shahabuddin, G., Orihuela, G., Riveros, M., Ascanio, R., Adler, G.H., Lambert, T.D., 2001. Ecological meltdown in predator-free forest fragments. Science 294, 1923–1926. Torres, A., Fernández, N., zu Ermgassen, S., Helmer, W., Revilla, E., Saavedra, D., Perino, A., Mimet, A., Rey-Benayas,

J.M., Selva, N., Schepers, F., Svenning, J.-C., Pereira, H.M., 2018. Measuring rewilding progress. Phil. Trans. R. Soc. B 373, 20170433. https://doi.org/10.1098/rstb.2017.0433

UN Assembly, G., 2015. Resolution adopted by the General Assembly on 19 September 2016. A/RES/71/1, 3 October 2016 (The New York Declaration).

Varley, N., Boyce, M.S., 2006. Adaptive management for reintroductions: updating a wolf recovery model for Yellowstone National Park. Ecological Modelling 193, 315–339.

Vera, F.W., 2009. Large-scale nature development--The Oostvaardersplassen. British Wildlife 20, 28.

Watson, J.E., Shanahan, D.F., Di Marco, M., Allan, J., Laurance, W.F., Sanderson, E.W., Mackey, B., Venter, O., 2016. Catastrophic declines in wilderness areas undermine global environment targets. Current Biology 26, 2929– 2934.

Watson, J.E., Venter, O., Lee, J., Jones, K.R., Robinson, J.G., Possingham, H.P., Allan, J.R., 2018. Protect the last of the wild. Nature Publishing Group.

Rewilding: definitions, success factors and policy, a European perspective