The Scientific Case for Rewilding

Here’s something a little different; a very chunky 4,000 word article  I wrote on the scientific case for rewilding, taking a broad look at a variety of benefits that rewilding could produce for society and the environment!




Rewilding is a relatively new word, describing a relatively new concept, but one that has already caused huge controversy among the public. This is partly due to differing opinions regarding the aims of rewilding. Some look fondly on Britain’s patchwork landscape and claim that this is what the countryside has looked like for hundreds of years, and is therefore what it ‘should’ look like. Others see it for the ecologically broken, nature-depleted land that it has become, and perhaps would go so far as to say that we should bring back the species that we drove to localised extinction hundreds of years ago. Is there a defensible case for this approach? In this essay, I will attempt to set out the scientific case for the potential benefits of rewilding in its formal definition -– i.e., ‘the restoration of land to its natural uncultivated state’, including arguments for the reintroduction of lost species, which I see as an integral part of the definition and of the process.

Preserving biodiversity

The most obvious benefit of rewilding is preservation of biodiversity. The state of wildlife populations nationally and internationally is critical: the absolute number of animals on Earth has dropped by 40% since 1970 (1), and the extinction rate is 1,000 to 10,000 times the natural level. We lose dozens of species every day.(2)

The single largest factor in this decline is habitat loss and degradation (1), so it logically follows that halting and reversing this trend will be a critical component of population recovery. Restoring natural habitat is, by definition, is what rewilding entails. There is such little ambiguity here that I don’t feel it requires scientific justification.

Perhaps more controversially, I believe that returning lost species to those landscapes is an essential part of the rewilding process, and is not only needed to improve the conservation status of those focal species but is necessary for full biodiversity recovery of the countryside into which they are introduced. Without certain key links in the complex web of interactions that make up an ecosystem, we can never hope to achieve a self-sustaining, optimally biodiverse landscape. Keystone animals – those that have a disproportionately large effect on their ecosystems relative to their abundance – are of particular importance; unfortunately,  many have been lost from Britain, (and most of Europe) over the last thousand years, as man has driven them to local extinction. In their absence, we have established a different state of ecological equilibrium, known as a catastrophic shift. The consequence of this state is that re-establishing the original, thriving, biodiverse ecosystem by simply leaving the land to its own devices would take thousands of years. Counter-intuitively, mankind needs to lend a hand in the process of returning land to a state without human activity, through the returning of our lost species.

Benefits to Biodiversity of Keystone Species Reintroduction

The beaver is a prime example of a keystone species. Hunted to extinction in Britain in the 16th century, they are often described as ‘ecosystem engineers’ –with their capacity to influence landscapes rivalled only by elephants. The largest beaver dam in the world is twice the length of the Hoover dam, and can be seen from space (3).
But even the smaller, ordinary dams and lodges change tame, fast-flowing waterways into a complex network of ponds, meadows and channels, thereby creating a far more varied, natural and ecologically valuable habitat.   And because of the tendency of beaver dams to fail over time, triggering natural succession processes; beaver-modulated habitat is not only geographically but also temporally heterogeneous, creating a dynamic, ever-changing landscape, which only serves to increase the biodiversity and ecological health (4). For example, a Scottish reintroduction of the European Beaver, Castor fiber, was shown to increase the abundance of 88% of species recorded during the study (5), from every class of vertebrate as well as numerous invertebrates and plants. Only a minority of species (lotic habitat specialists mainly) were negatively impacted. The clear value of the beaver is reflected in the Scottish government’s decision to give it protected status after illegal reintroductions across the country.

One of the most famous examples of species reintroduction, however, occurred at Yellowstone National Park in America (6).  In Yellowstone, the main problem – from an ecological perspective – was the high density of elk. The absence of wolves had removed a huge predatory pressure from them and enabled their populations to reach over 19,000 individuals. In consequence, the vegetation was over-grazed, both through the sheer numbers of these large herbivores and due to the fact that they no longer had to remain on the move to avoid wolves, allowing them to graze certain areas more intensively.
Wolf reintroduction had a dramatic effect: the numbers of elk eventually dropped to below 4,000 individuals, and they were forced to be more mobile to evade predation. This in turn allowed over-browsed willow to recover, providing a previously scarce food source for the local beaver populations. Beaver colonies in Yellowstone increased in number from one prior to wolf reintroduction to nine, with the population expected to continue growing. This beaver activity, together with the increase of vegetation around river banks, also drastically changed the hydrology of the landscape.
In addition, increased abundance of willow and aspen following the reduction in elk provided habitat for songbirds, whose populations have recovered significantly. Other apex predators like bears and mountain lions have also increased (8), but it is unclear as to whether this is related to the wolf reintroduction or some other external factors.
The magnitude of the impacts of the wolf reintroduction was unexpected, and many of the subtler outcomes are still only being realised. We can use the Yellowstone reintroduction as a loose indication of what might happen should we reintroduce wolves to Britain – it stands to reason that we might see similarly exciting and unforeseen responses.
That said, the Yellowstone wolves were reintroduced into a habitat that was already almost ecologically natural – an ecosystem virtually complete with the simple exception of the wolf, allowing the reintroduction of that species to cause the impressive trophic cascade that was witnessed (and even then some ecologists argue that the landscape had lacked wolves for so long that the damage of their removal hasn’t completely been reversed [8]). However, in mainland Europe and Britain, unspoilt areas on the scale of Yellowstone are virtually non-existent. The reintroduction of wolves would have to be coupled with the reintroduction of other missing fauna for the process to work – namely, large herbivores.

The Value of Large Herbivores

Until recently, closed-canopy theory was accepted as the original, natural state of our land in Britain and Europe, perceived as vast stretches of unbroken forest from coast to coast (with the exception of the odd mountain and lake). This is understandable: conservationists have been accustomed to seeing naturally regenerating European land turn into just that. However, that completely ignores a vital factor – the presence of large herbivores.
These animals would have grazed the land, maintaining a balance of forest and grassland and creating an overall landscape described as ‘wooded pasture’. This is truly what European wilderness would have looked like – evidence can be found in pollen records in soil (9). And unsurprisingly, being the surroundings that our native European fauna have adapted to, this is the optimum state for maximum biodiversity on a landscape scale.

Rewilding projects run by Frans Vera on mainland Europe and the Knepp project (9) in Britain have demonstrated the ecological importance of these large herbivores.
Both initiatives had to use proxies for some of the wild species that we have driven to extinction: Heck or Longhorn cattle were used as substitutes for the Aurochs that originally roamed the plains of Europe, and Konik ponies replaced the Tarpan. Other ungulates involved in the aforementioned projects include Tamsworth pigs and native deer such as Roe and Fallow. Each was found to have its own ecological niche and specialist functions; whether ‘rooting’ the ground, grazing on grassland, browsing on small shrubs, naturally coppicing trees or spreading seeds on their coats and through faeces, the specific services of each herbivore were essential to generate a balance of vegetation and maintain a varied habitat (which, as noted above, is crucial for biodiversity).
Even the carcasses of these animals are of vast importance to scavengers and insects that feed on carrion – a key feature of our ecosystems which doesn’t seem tolerable any longer under health and safety regulations (9).

Tackling Invasive Species

Another interesting and unexpected benefit to biodiversity of reintroducing species is the elimination of non-native invasive (NNI) species. With increasing globalisation, NNI species have become ever more common, and threaten what biodiversity we have left. Invaders such as Parakeets, Japanese Knotweed and Grey Squirrels have colonised the UK in vast numbers, often displacing other native species in their wake. Their relentless spread has seemed almost impossible to halt – but in some instances, species reintroduction could provide a solution. For example, reintroducing Pine Marten to Wales and England could help Red Squirrels recover their former range (10); Pine Marten predate on both red and grey squirrels, but whilst the former has evolved over millennia to avoid marten predation, the latter has not, so the reds benefit overall.

The Wildome

To date, we have only looked at rewilding as a macro-level concept, but a novel thought on consequences of rewilding can be offered in the fast-growing field of epigenetics. If we modify the environment, returning it to a natural state, will that trigger previously dormant, inactive genes in current wildlife populations (or indeed ourselves) to be expressed? What effects might this have?
Epigenetics explains the existence of phenotypic plasticity – the ability of one genotype to produce multiple phenotypes. A system of chemical markers are overlaid on our histones, which determine which genes are expressed by compressing or decompressing the chromatin, and thus either allowing or disallowing the code to be read.
Many variables can change these epigenetic markers: diet, chemical exposure, and even social experiences (11). Studies have shown that even relatively subtle environmental changes can influence the epigenome enough to produce a noticeable variation in phenotype. For example, butterflies of the species Vanessa urtica and Vanessa io were found to grow larger when raised in dark conditions, and develop more intensely coloured wings upon exposure to red light during development (12).
Surely then, the relatively extreme environmental changes that would occur in a rewilding context will be significant enough to alter the phenotypes of organisms.

We may, for example, hypothesize that deer experiencing heightened levels of stress due to wolf presence may inhibit the expression of a gene that affects the amount of a digestive protein that they produce, and thereby lead to an increase in undigested material in the animal’s faeces and increase chances of seed dispersal for various plants. There is no evidence to support this example – it is purely imagined – but hopefully illustrates the wide variety of potential consequences, which may at first seem inconsequential but could alter ecology significantly. The activation of the ‘wildome’ is an area that could provide some fascinating potential for research in future years.


 In reality, rewilding for nature’s sake will not meet current politicians’ motivations. Luckily for rewilding proponents, the restoration of natural landscapes has proven to have a huge variety of economic and social benefits.
Our agriculture is in a dire state, with dependence on intensive farming and food imports to sustain our ever-increasing population. However, rewilding has shown potential solutions to the myriad of problems that we face. Knepp Estate (9), a farm in Sussex, exemplifies these benefits, and therefore is used frequently in this subtopic as a case study.

We have a soil crisis in Britain. Intensive farming has removed soil organisms and degraded soil structure, causing water and nutrients to leach away, and topsoil to erode. As a result of this, we have only 100 harvests left in most of Britain (13). This problem is fast-growing on the rest of the world too: estimates suggest that 80% of global farmland is moderately or severely eroded (9). Until recently, it was widely believed that this soil layer would take years to reform. Now, however, data from Knepp suggests that soil can regenerate much faster than expected – when subjected to rewilding. 13 years since the rewilding project began at Knepp, 18 species of worm have returned to the soil. Microrrhizae have spread rapidly through the soil, showing their presence in the form of fruiting bodies of fungus, and anthills, some over half a metre high, have become abundant. All of these are indicators both of good soil health and of diminishing concentrations of pollutants. But they are also key actors in the restoration of soil themselves. Worms, for example, concentrate the organic constituents of the matter that they consume in their casts, providing patches of soil that are high in nutrients. They also aerate the earth, improving drainage and oxygen availability for the roots of plants. Finally, they have a fantastic ability to expand the topsoil – one study found that under favourable conditions, worms add up to 5mm per year simply by leaving their casts on the soil surface. Another trial found that they may regenerate 18cm of soil within 30 years (14). And this is just one aspect of rewilding’s agro-economic benefits. It can also increase numbers of pollinators, introduce natural, biological pest control and return nutrients to the soil.

Consequently, it has been suggested that we need to take a more holistic approach to Britain’s land use. A field rotation system (on a larger scale than traditional farming practice used to employ) could be implemented. A ‘pop-up Knepp’ would be left to rewild for 20-40 years; during this time, it would provide alternative forms of economic income (together with subsidies), while neighbouring fields are managed for food. This ensures that there is always a balance of land for arable farming and habitat for wildlife, while allowing each field to regenerate its soil quality.  Looking further ahead, wildlife corridors could then be set up between these larger patches of wild land to connect the populations of animals, maintaining genetic variety and allowing populations to move depending on resource availability.



As well as benefits to agriculture, rewilding provides other ways of making a profit: Knepp generates a proportion of its huge income through ‘glamping’. They now turn over £50,000 of profit from a single 10-acre field – a third of their annual income for the whole 3,500 acres before the project started. And bear in mind that this is in Sussex –an area little known for ecotourism.
Rewilding areas all over the country have the potential to generate immense economic income from ecotourism. In Scotland, over 1 million trips are made annually primarily to see wildlife, worth £1.4 billion to Scotland’s economy (15). And considering that around one-fifth of Scotland is grouse moor, where wildlife persecution is rife and the land bare and ecologically dead, consider how much that value could increase with rewilding.
People would come simply to see wilder landscapes, but I think profit would be maximised through the reintroduction of iconic species. For example, a case study in the Harz Mountains, in Germany, showed that the presence of Lynx in those mountains was a major factor in the decision of more than half of all tourists to visit the area, despite the improbability of seeing such an elusive predator. This is estimated to bring £8-13 million to the Harz Mountains each year (16). Similarly around a quarter of all visitors to Mull in Scotland consider the presence of White-Tailed Eagles to be an important factor in their decision to visit the area. In Cors Dyfi Reserve in Wales, a single pair of ospreys brings in £350,000 every year, and a single dolphin on the Moray Firth in Scotland, by calculation of the proportion of annual income it generates every year, could be worth £4.5 million over a lifetime (17). These examples demonstrate the significant financial potential of species reintroduction.


Public health

Rewilding could make an important contribution to public health. The true development of a tamed, urbanised environment has only occurred in the last couple of hundred years – definitely not on an evolutionary timescale. We are still primarily adapted to a natural environment, and the consequences of being increasingly removed from it are manifold. Here in Britain especially, where over 40% of children never play outside at all and ¾ spend less time outside than prisoners (18), the effects of an urban lifestyle are profound. Poor air quality causes 29,000 premature deaths in the UK every year (19). Furthermore, the noise and air pollution from busy roads has been linked to Alzheimer’s disease, heightened blood pressure and increased risk of stroke. People who live in urban environments are also less inclined to exercise, and therefore suffer higher rates of obesity and obesity-related diseases. Children, less inclined to play outside, spend more time on screens, leading to insomnia and, in many cases, myopia (20).
Local, small-scale urban and suburban rewilding would increase the health of city residents. Indirect benefits would be numerous (21): vegetation reduces noise, increases the amount of physical exercise that people perform, school children’s concentration improves, helping them attain higher grades; it cleanses the air of pollutants and reintroduces air-borne antigens which benefit the immune system. The NHS have even found that hospital patients need fewer painkillers after surgery and recover faster if they have views of nature from their beds (9).

As well as these physiological benefits, interaction with nature has been showed to play a crucial role in mental health. 1 in 6 in the UK suffer from depression, anxiety, stress, phobias, suicidal impulses, obsessive compulsive disorders, or panic attacks. This costs the NHS £12.5 billion, the economy £23.1 billion in lost output, and thousands of people their lives. Spending time outdoors in a natural environment has been shown to reduce severity of all these mental illnesses (9).

Why should nature be so good for our mental health? EO Wilson’s biophilia hypothesis suggests that we have an innate desire to connect with the natural world as a product of evolution, and that denying ourselves that causes us stress and mental discomfort. Ulrich elaborates on this in his psycho-evolutionary hypothesis (22): being in an unthreatening natural environment, he says, activates a positive affective response, leading to a subconscious inclination to seek or remain in such environments. In any case, although the precise mechanism of nature’s benefit to mental health remains unclear, the evidence for it is building. The advantages of such interactions with a natural environment are so widely recognised now that they are being prescribed by some branches of the NHS (23)

Climate Breakdown

Perhaps the single most important benefit of rewilding, and the one which presents the greatest case for its absolute necessity, is to combat global warming. As George Monbiot said in a talk at the national Rewilding Conference in Cambridge this January, it is no longer enough to simply cut out carbon emissions – we have to start actively sequestering it in order to meet targets and avoid the worst impacts of climate breakdown. Already, even if we limit global average temperature rise to 1.5 degrees, a rise in the Arctic of 3-5 degrees Celsius is ‘locked-in’, due to thawing permafrost releasing huge quantities of stored greenhouse gases (24). Arctic summers will be iceless by the 2030s. The urgency of this crisis is hard to overestimate, and rewilding is (as George would argue) our only hope of avoiding the worst impacts. For example, the world’s farmlands, if properly managed, could capture up to 10 billion tonnes of carbon dioxide a year– more than the annual carbon dioxide accumulation in the atmosphere. Similarly the Carbon Farmers of America estimate that increasing the amount of organic matter in the world’s farmed soils by only 1.6% could ‘solve global warming’ (9).

Degradation of natural habitats has contributed to the global warming crisis. When we destroy salt marshes, for example, we create a significant greenhouse gas source (20). Conversely, restoring these wetlands to their natural state – rewilding them – would not only negate that huge source of emissions, but actually remove equivalent quantities of gas. We would be creating an extremely effective carbon sink. And, while coastal wetlands offer some of the greatest potential for carbon sequestration, rewilding offers other carbon-capture opportunities. Converting the 5 billion hectares of degraded grassland worldwide to functioning ecosystems could terrestrially sink 10 gigatonnes of carbon and return the atmosphere’s carbon dioxide levels to pre-industrial concentrations in only decades, according to Alan Savory, a Zimbabwean ecologist (25).
Similarly, given that over 70% of land in the UK is farmland, improving its management through rotational rewilding – the ‘pop-up Knepp’ system — could help the UK to meet the Paris climate targets. Why invest in expensive artificial carbon-capture technologies when we can sequester carbon in a natural way, that will at the same time increase biodiversity, improve air and water quality, benefit public health, and boost the economy?

What does the future hold?

Although from a purely ecological point of view the reintroduction of locally extinct species would be beneficial, from a social point of view, the situation is far more controversial. Wolves and bears pose obvious risks to humans, Lynx have the potential to predate on small livestock, and there are even fears over the safety of dogwalkers walking through fields of Longhorn cattle. Many of these risks can be controlled and minimised; nevertheless, rewilding is as much of a social issue as an ecological one, and the confidence and consent of affected communities should be obtained before any species reintroductions can occur. I maintain that in order to return areas of Britain to fully functional, self-maintaining ecosystems, these animals need to be introduced. I do however acknowledge that if not socially acceptable, it is possible to provide many of the benefits of rewilding without some of these creatures. It will simply require further human intervention – environmental management – to compensate for their absence.



In conclusion, rewilding has numerous and diverse benefits, a full exploration of which is beyond the scope of one essay. Briefly, they include:

  • Preservation of biodiversity. Most would accept that this is worthwhile in itself; those who need additional arguments should consider the benefits of maintaining a source of evolutionary end-points that could form the basis of new drugs or other beneficial products.
  • Knock-on ecological effects of keystone species reintroduction, include reversing invasion by non-native species, and broad-reaching effects on the biotic and abiotic environment. Future research may well see these benefits reflected at the molecular level, as environmentally-induced epigenetic modifications spread through populations.
  • Benefits not only for wildlife, but also for people. The public are more likely to accept rewilding if they understand the associated benefits for mental and physical health, the economy (ecotourism), food supply, and – perhaps above all – its necessity for tackling climate change.

For many conservationists, rewilding is a topic of overwhelming optimism. It is a reminder that whatever destruction we see unfolding around us, it need not be permanent. All is not lost. There is hope for the future.



(1) WWF

(2) Guardian

(3) Telegraph

(4) B.GOLDFARB Eager. Chelsea Green, 2018


(6) G.Monbiot Feral. Puffin, 2014

(8) USAToday

(9) I.TREE Wilding. Picador, 2018

(10) Guardian

(11) WhatIsEpigenetics

(12) Nature

(13) Guardian

(14) New South Wales Government Report

(15) Rewilding Britain

(16) Lynx Trust

(17) Rewilding Britain

(18) Guardian

(19) DEFRA

(20) WIRED


(22) Ulrich, R.S., R.F. Simons, B.D. Losito, E. Fiorito, M.A. Miles, and M. Zelson. 1991. Stress Recovery During Exposure to Natural and Urban Environments. Journal of Environmental Psychology 11, 3:201-230.


(24) UN Environment

(25) Knepp Estate

(26) Clarifying the role of coastal and marine systems in climate mitigation. Frontiers in Ecology and the Environment, 2017; 15 (1)



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