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A Summary of Perino et al 2019

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A Summary of Perino et al 2019

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The three principles of rewilding are brilliantly explained in Rewilding Complex Ecosystems – a 2019 paper by Perino et al. 

We’ve rewritten this for a wider audience, to help scientists, farmers and conservationists understand how to run a successful rewilding project. 

Who This Article is For

This is a great article for conservationists, as it lays out a framework for how to understand rewilding, then applies it to explain how to design and manage a project that will appeal to the general public. It’s also a good introduction to some basic rewilding concepts.

Rewilding Complex Ecosystems

Journal: Science

Published: 2019

Authors: Andrea Perino, Henrique M. Pereira, Laetitia M. Navarro, Néstor Fernández, James M. Bullock, Silvia Ceaușu, Ainara Cortés-Avizanda, Roel van Klink, Tobias Kuemmerle, Angela Lomba, Guy Pe’er, Tobias Plieninger, José M. Rey Benayas, Christopher Sandom, Jens-Christian Svenning, Helen Wheeler.

Introduction

Biodiversity is dropping and the typical conservation approaches, while they have worked in some instances, often fail to reverse or even stop this decline. New ways of restoring ecosystems have been tested, which bring back natural unpredictability rather than keeping landscapes as a fixed habitat with a set list of species. 

Rewilding is one of these approaches, which focuses on cutting back human activity and restoring nature by increasing complexity. In rewilding, the end goal is for nature to take back control. Rewilding has been criticised as lacking a proper scientific definition, failing to predict outcomes and excluding humans from landscapes. 

This article will briefly explain the history of the field, then suggest a new framework for understanding and practising rewilding. This framework is built upon three key pillars [Ed. note: ‘processes’ in the original paper], each of which are linked to human activity. Rewilding can happen spontaneously or deliberately, but society’s opinion plays a crucial role in deciding whether it is ultimately successful.

History

20 years ago, when the term ‘rewilding’ was first coined, it was used to describe a ‘top-down’ process of carnivore reintroduction. The thinking was that the introduction of ‘keystone’ species such as wolves could restore an ecosystem without any other actions. 

Nowadays, there are several different styles of rewilding, and this is just one, which is described as ‘Trophic rewilding‘. Typically, this involves reintroducing large herbivores or carnivores, however, this may include replacement species e.g. replacing bison with longhorn cattle when bison are too dangerous for the setting. These replacements may be called ‘ecological proxies‘, or ‘functional replacements’. 

Pleistocene rewilding involves reintroducing species which were present in the ancient past (or proxies for these species). 

Passive rewilding is a lower-effort approach where land is left to nature, with hunting bans, removal of barriers like fences or restoring rivers e.g removing levees to rewet floodplains.

The authors define ‘wildness‘ as returning land to processes run by nature, as opposed to ‘wilderness‘, which is land in its original pre-human state. Wildness can be achieved even in smaller plots or urban areas.

Framework

The three pillars of this framework (defined below) are trophic complexity, natural disturbances and dispersal. They work together to make a self-sustaining ecosystem. Rewilding aims to restore all three, and let nature take over, though human support might be required if one or more of these pillars is blocked or weakened by our activity.

Pillar 1: Trophic Complexity

This refers to how complicated the food web is and how many different interactions there are between animals and plants in the ecosystem. Animals at the top of the web (or ‘food chain’ as you might have heard it called) have an oversized influence on the species below them by changing the habitat around them through grazing and trampling, helping move seeds around and acting as a source of dung and meat. 

The threat of predators affects where herbivores move through the landscape, as they avoid potential hiding places – this means predators can affect grazing patterns. When predators are wiped out, the resulting increase in the number of herbivores can impact the quality of a habitat, which reduces species diversity.

Humans have wiped out or reduced numbers of large herbivores and carnivores through hunting, habitat destruction and breaking up wilderness into smaller chunks that can’t support large animals. This has led to some food webs breaking down or becoming very weak, as the links at the top have fallen apart – a ‘trophic cascade‘. Rewilding can reverse this trend by reintroducing the missing links, whether with the original species or ‘proxies’. However, the impact of reintroductions isn’t always predictable and they might damage ecosystems or human activities. It is important to compensate people if this happens.

Pillar 2: Natural Disturbances

Natural or ‘stochastic disturbances‘ are events like wildfires, trampling of vegetation and flooding that occasionally cause changes to ecosystems. They vary in impact and how often they occur, leading to mosaic-like landscapes with complex patterns of different habitats that change over time. 

Disturbances are good for diversity, as species which thrive in disturbed environments, like newly-burned forest, will live alongside those that thrive in more settled habitats. However, humans tend to stop disturbances from happening, or minimise them. This means that species diversity is reduced, especially if humans ‘repair’ a landscape after disturbance, rather than letting nature recolonise it. Disturbance repair can also occur on a lower level e.g. dead trees, which humans remove from woodland, taking away the habitat of deadwood-eating insects. Rewilding lets natural disturbance return and removes or reduces barriers to disturbance like dams.

Pillar 3: Dispersal

Animals and plants need to move between habitats to avoid overcrowding and find a suitable mate. When humans put up barriers between wild areas or reduce their size, inbreeding becomes a problem. Barriers to movement include roads, dams, fences and even large blocks of vegetation like conifer plantations or fields.

Rewilding can encourage movement on small and large scales, for example with hedgerows or ‘stepping stone’ habitats in the wider landscape. 

3 Pillar Interactions

Each of the three pillars can interact with each other:

  • Creating wildlife corridors (dispersal) allows new animals to flow in after a wildfire (natural disturbance). 
  • Introduced bison (trophic complexity) can carry seeds across their large range (dispersal) and their trampling may create a suitable place for it to germinate (natural disturbance). 


Thus, restoring one of the pillars may help to begin building back the other two.

We can imagine the interactions between the pillars as if each pillar were one side of an upside-down pyramid. This pyramid is a graph that allows us to visualise ecosystem health and provides a way for other scientists to understand the health of rewilded habitats. 

The volume of the pyramid represents the health and resilience of the ecosystem – when all pillars are fully restored (the chart shows a high mark on each pillar), the pyramid is full. When the ecosystem is weak, all pillars are degraded (the chart shows a low mark on each pillar), so the pyramid is empty. One pillar can be restored, which can begin to refill the volume, but more than one is needed to have a big impact on the volume (ecosystem health).

Rewilding & Society

All ecosystems are intrinsically linked to human society, so it is crucial to maximise the benefits for both humans and nature when designing rewilding schemes. There are social benefits, such as green spaces improving wellbeing, health, self-fulfilment and promoting bonding, but also wildness and the creatures that live there inspire us and help us to form a cultural identity. 

The economic benefits of rewilding come in the form of recreational activities, reversing climate change and air pollution. The rewilded land also acts as a breeding ground for game animals and fish stocks, helping to replenish areas where hunting and fishing are allowed.

However, rewilding can also have negative impacts on humans, such as crop damage, livestock killed by predators, or more frequent (less severe) fires and floods. Loss of traditional farming landscapes is a growing concern among many cultures, in Europe and elsewhere. 

‘The wild’ is a complicated idea in human cultures that is equally associated with dangerous animals and scary places, as well as peace, tranquility and a refuge from society. Rewilding projects must embrace the second idea if they want to avoid the stigma of the first.

Applying the Framework

Active Rewilding Projects

How to apply the framework for an active rewilding project which involves making significant changes to the landscape and/or natural processes:

Step 1

Ensure all stakeholders have a clear idea of the goals, expected outcomes, risks and management options. Study the plot to determine its ecology, including missing or weakened aspects. Identifying the history of the land, including its  largest species, wildfire frequency and severity, and land use, is a useful starting point.

Step 2

Determine which management strategy (e.g. trophic rewilding) is most likely to be effective. Consider combinations of strategies where appropriate. Identify problems with strategies in collaboration with stakeholders (farmers, hunters, public etc), e.g. crop damage, fences obstructing movement. Try to work out the pros and cons of the final management strategy, to avoid nasty surprises.

Step 3

Take action and roll out the management plan, in a scientific way, by measuring the impact before and after, and using a control (a ‘BACI’ approach). Measure the effects on both wildlife and society, and use these results to inform changes to the plan – involve affected communities in this decision-making. Be sure to do outreach like tours, creating nature education tools and leisure activities to improve people’s understanding of the rewilding project. Help to develop sustainable associated businesses, as this will also benefit public perception.

Passive Rewilding Projects

How to apply the framework for a passive rewilding project, e.g. if people are moving out of a region, leaving towns and villages abandoned:

Step 1

Do a study of the region’s current ecology, including potential pros and cons of continuing to passively rewild the landscape.

Step 2

Find ways to remove any obstacles to rewilding, e.g. physical barriers, hunting. Look for ways to support the passive rewilding e.g. securing land, creating related jobs, compensating farmers for crop damage.

Step 3

As with active rewilding, the project should be continually monitored, for both wildlife and societal impacts. Any findings should feed back into its planning – affected communities should be involved in this decision-making. 

Source

Open Access Link

NB. The source also contains 4 interesting case studies, which are not included in this article, as we wanted to keep the content to a readable length.

Summary

At How to Rewild, we’ve taken this work by Perino et al (2019) and put our own spin on it, interpreting it for landowners. This new version is described as the ‘3 D’s of rewilding’. There are 3 dimensions – dispersal, diversity and disturbance. As each dimension increases in strength, the ecosystem health improves, although disturbance becomes damaging beyond a certain threshold level.

Here’s an infographic to explain this concept – feel free to use this in your own work – this image is shared with a CC BY-ND license (i.e. you can use it commercially, but you must not crop/edit out the image credit).

The 3 D's of Rewilding

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