A smorgas board of sophisticated rewilding initiatives are springing up across the UK, capturing the imagination of groups with “nature first”1 values, but also drawing in others and sparking controversy. Meanwhile, it is worth reminding ourselves that in its purest form rewilding is simply ‘letting go’. Unlike most current rewilding projects, passive rewilding can be relatively uncomplicated, inexpensive, scaleable, and potentially a game-changer for nature recovery. Passive rewilding as “de-management” is key to this, a hands-off approach even when trees start to grow unchecked on peatland and species from the past remain absent.
Passive rewilding can contribute significantly to nature recovery, a key aim of the UK government2,3 linked to combating climate change and a “green recovery”4. Passive rewilding shares elements of more active ‘mainstream’ rewilding and has the potential to boost rural economies and generate jobs5,6,7, provide spaces for outdoor recreation in both urban and rural environments8,9,10, improve health11,12,13, improve habitats14,15,16, encourage afforestation17,18,19, support protected species, and genetic, taxonomic, and ecosystemic biodiversity20,21,22, reverse soil carbon losses and increase carbon sequestration23,24,25, reduce flood and drought risks26,27,28, improve air and water quality29,30,31, and address Britain’s reputation as one of the most nature-depleted countries in Europe32,33.
Passive rewilding also has the potential to generate benefits cited in Britain’s 25 Year Environment Plan sooner and more cost-effectively than other UK nature recovery strategies either tested or proposed.
However, passive rewilding opportunities are underminedby science that fails to articulate the ‘big picture’34,35, particularly the importance of ecosystems that assemble and change on their own terms. This leads to rewilding solutions being overcomplicated from a conservation management perspective: too much emphasis on restoration of particular species, habitats and processes, not enough natural autonomy or ‘wild nature’.
Narrow framing of evidence informing conservation action and policy continues to presume primacy of historical species, habitats and processes, often at a cost to more diverse, dynamic and productive novel ecosystems which can emerge through the “do nothing” option. Opportunities and benefits for humans also emerge by allowing nature to develop passively with minimal or no intervention.
In favour of more unguided ecosystems and passive rewilding this paper aims to correct two ‘false assumptions’. These are regularly deployed as ecological arguments against passive rewilding. The first relates to resistance to natural regeneration on peatland: that maintaining a high water table and ‘peatland plant species’ should top all other ecological concerns. The second assumption is that reintroductions are beneficial for rewilding overall. These examples have wider relevance for passive rewilding beyond the UK, particularly where there are extensive modified peatlands or in geographically isolated locations where reintroductions of even relatively mobile mammals and birds are presumed necessary.
An overview of rewilding is provided with a brief discussion of current rewilding definitions, setting out how “passive rewilding” is distinct from those definitions. Two debates relevant to rewilding in the UK are then critically reviewed: Are trees on peatlands a threat to biodiversity, hydrology and climate? Are reintroductions worthwhile in terms of ecological benefits or ecosystem services?
Coined by American activist Dave Foreman around 1990, “rewilding” gained purchase in restoration ecology in the late 1990s36,37. The term has entered into popular usage in the UK and parts of mainland Europe in the past decade. What it means to make areas ‘wild’ is now a topic of animated debate among academics, policymakersand practitioners38,39. Both the North American movement, labeled “Cores [untouched wilderness], Corridors [strips between cores] and Carnivores”40, and contemporary European naturalistic grazing and reintroduction approaches, show through in British rewilding ambitions. For example, rewilding uninhabited upland landscapes, grazing regimes using ponies and cattle simultaneously, and beaver reintroductions. However, more often in the UK traditional conservation aims such as preserving meadows and tree planting are co-opted and rebranded as rewilding. Similarly, conservation actions taken up to 60 years ago in the UK are now said to have been examples of rewilding41.
Accordingly, geographers Steve Carver and Ian Convery remark rewilding is “in danger of becoming all things to all people”42 and therefore meaningless. Definitions of rewilding provided by conservation professionals, academic researchers, advocacy groups, and commentators in the media vary considerably. There are also geographical discrepancies, particularly between approaches in North America and Europe.
Rewilding definitions provided by conservation professionals and academics from the life sciences still lead public debate and tend to present rewilding as an ambitious form of ecological restoration. Rewilding definitions used in the UK context tend to centre on principles of the Lawton Review, “more, bigger, better, and joined” spaces for nature43 with greater focus on animal reintroductions. Proponents claim rewilding is the restoration of 1) natural functions and processes 2) keystone species 3) biodiversity, according to historical baselines aimed at ensuring future self- sustaining ecosystems with reduced future intervention and 4) the return of people and the revitalisation of rural economies. Lastly and fast gaining traction among policymakers, conservationists and academics in the UK, rewilding is 5) the restoration of ‘ecosystem services’ with economic value or ‘natural capital’.
- Geographers Jamie Lorimer and colleagues offer a broad-ranging characterisation suitably covering proposed definitions for active rewilding: Rewilding “has multiple meanings [which] share a long-term aim of maintaining, or increasing, biodiversity, while reducing the impact of present and past human interventions through the restoration of species and ecological processes.”44
- Biologists Nogués-Bravo and colleagues claim: Rewilding is regularly centred on reintroductions of keystone species, those with “disproportionately large and beneficial” effects on restoring natural functions and services.45
- Ecologists du Toit and colleagues attempt to move rewilding definitions away from historical benchmarks, pointing out that rewilding does not necessarily deploy previously extant keystone species but rather calls upon surrogates—such as hardy breeds of cattle. Du Toit and colleagues argue: Rewilding, without demanding taxonomic fidelity, “involves reorganizing and regenerating wildness in an ecologically degraded landscape, with present and future ecosystem function being of higher consideration than historical benchmark conditions.”46 “Correct ecosystem functions” are still measured against past natures, however.
- Some academics denote particular forms of rewilding, all characterised as ecosystem restoration. Zoologist Phillip Seddon defines translocation rewilding: “Translocation rewilding may involve the reintroduction or reinforcement of species, or the ecological replacement, assisted colonization, or community construction of ecosystems.”47
- Donlan and colleagues famously proposed the introduction of extinct species to rewild North America, later dubbed “Pleistocene rewilding”48, which the Russian scientist Sergey Zimov has advanced by introducing various surrogate “Pleistocene herbivores” on the Siberian steppe. Pleistocene rewilding aims to return top-down predator and large ungulate controls of Pleistocene-inspired ecosystems.
- Together with less controversial proposals for extant carnivore introductions, Translocation and Pleistocene rewilding can generally be grouped under “trophic rewilding”, defined by Svenning and colleagues from Aarhus University, Denmark: Rewilding that aims to “restore top-down trophic interactions and associated trophic cascades to promote self-regulating biodiverse ecosystems.”49
- This draws inspiration from the seminal characterisation of rewilding in restoration ecology by American ecologists Michael Soulé and Reed Noss in 1998, “…the restoration and protection of big wilderness and wide-ranging, large animals—particularly carnivores.”50
- Blogger Aimee Tweedale captures popular imaginations, playing on lay understandings of wildness: Rewilding is “letting nature run free, restoring itself to a ‘wild’ state”51
- The Woodland Trust argues that ecological restoration is central to rewilding, but that this is important for both people and nature. Rewilding is “about the restoration of natural processes, working with nature to enhance the natural environment and the species it supports but also to provide the goods and services we need as a society.”52
- Rewilding Europe, a network and mouthpiece for more than 60 independent rewilding project teams, navigates between ecological principles and emotive language on their website: Rewilding is “letting nature take care of itself, enabling natural processes to shape land and sea, repair damaged ecosystems and restore degraded landscapes. Through rewilding, wildlife’s natural rhythms create wilder, more biodiverse habitats.”53
What is Passive Rewilding?
Passive rewilding is a distinct subset of rewilding based on “hands-off” management principles, or the “absence of sustained human intervention.”54 Pettorelli and colleagues define passive rewilding as follows:
“Passive rewilding refers to abandoned post-agricultural landscapes that are no longer actively managed [or with] limited active management to facilitate natural processes and allow them to regain dominance.”55
They define active rewilding as:
“. . .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.”56
Building on this distinction, passive rewilding may also extend to any area of previously actively managed land, rural or urban, that is now undergoing extremely limited active management or none at all
This aligns with the definition from author and campaigner Isabella Tree in which rewilding is simply “allowing natural processes to happen, and having no pre-determined targets to meet, no species or numbers to dictate the plan.”57
In a departure from both definitions, this paper does away with the concept of “natural processes”, refigured rather as “mainly unguided” processes acknowledging the very real possibility outcomes may not seem natural at first because they may not compare closely with a historical baseline58. Furthermore, visitors may continue to shape nature albeit in a minor way compared to previous management practices. The following definition of passive rewilding is therefore proposed.
Passive rewilding involves making an educated guess that outcomes will fall within a range of favourable possibilities, and at the same time finding ways to value novel, at times unexpected ecosystems. Passive rewilding does not exclude people but does fully curtail organised extraction and active management, including conservation actions.
Landscape outcomes from passive rewilding, of which some possibilities are discussed below, are inherently more speculative than from traditional conservation, gardening or farming. More is left to chance. However, based on ecological, meteorological, geographical, historical and social site comparisons with existing passive or near-passive rewilding sites in the UK and western/northwestern Europe, evidence does allow for short-medium term prognoses. These may be carried out with satisfactory certainty for many sites ‘left alone’, especially pursuant to more synoptic measures such as biomass, habitat heterogeneity and species biodiversity.
Passive rewilding on peat: Good or bad?
Passive rewilding regularly offers the conditions for natural regeneration of shrubs, scrub and trees in the UK to 650m elevation60 and occasionally higher. On peatlands which dominate at those higher levels, natural regeneration is often prejudicially viewed as a threat to the water table, its associated species, habitats, and soil carbon with climate implications. Passive rewilding on peatlands is regularly viewed negatively due to the potential for vascular plants and trees to establish affecting water tables and soil carbon. Natural woodland or scrub regeneration is often therefore unjustly eschewed for reasons of climate.
Blanket opposition to possible natural regeneration/afforestation through passive rewilding, even on mainly saturated peatlands, is misplaced. A body of evidence reveals 1) no evidence of a climate threat from natural regeneration on peat—only from activities necessary for maintenance of open peatland or mechanical planting and 2) relative paucity of biodiversity and abundance of wildlife on Britain’s peatlands compared to similar soils elsewhere. These harbour more vegetation heterogeneity including trees—and so point to an opportunity for biodiversity gains on UK peatlands.
Opposition arises partly from tradition and aesthetics but also because trees and shrubs can lower the water table, at the expense of communities dominated by peat-forming bryophytes, also increasing soil respiration. A drop in water table and transformation of graminoid plant communities towards vegetation dominated by vascular plants including trees is a possible outcome of natural regeneration on ombrotrophic peatlands61—although trees do not always lower peatland water tables62. Elevated soil respiration in the short term is also a likely outcome due to the presence of oxygen in formerly saturated soils. However, landscape-scale potential for water attenuation, biomass, biodiversity—the diversity of all life—and other benefits across all types of peatland outweigh these considerations.
There is already precedent for highly valued forest habitat on peatlands within the UK and worldwide. However, the implied transition from open moorland or fen to a less open, more forested landscape through passive rewilding generates resistance.
Peatland covers around 3 million ha. in the UK63,64 and a significant proportion of the UK’s potential passive rewilding land. Peat exists mainly in areas of low agricultural productivity but with a high propensity to regenerate without planting where seed stock is available65. For instance, at Mar Lodge in the Cairngorms peat regeneration at 700m elevation has been reported 400m from source66.
Around 13% of the UK’s peatlands are “near natural”, >95% waterlogged, relatively stable blanket bogs67. UK “near-natural” peatlands—often incorrectly defined by their vegetation or lack thereof68—are CO2e neutral, replacing carbon dioxide in the atmosphere with methane. However, most are degraded and drained with an already discontinuous or absent peat-forming surface-layer69. Most open peatland in the UK is currently undergoing losses.
Forest habitat types on peat are highly valued, particularly lowland swamps/bog forests of which Germany has protected 317,000 ha.70, an area larger than the Lake District. Scotland too has significant peatland forests, with 21% of shallow peats and 17% of deep peats forested71. 20% of Scotland’s broadleaf woodland is already growing on peatland, much of it protected and prior to Neolithic-Bronze age clearances in Britain a patchwork of forest probably existed on most upland slopes72 with peat accumulation occurring simultaneously. Natural regeneration on peat is the preferred conservation outcome in the tropics73,74 but also embraced in parts of western Europe75,76 where for instance alder woodland has been shown to establish on peatland with a mean water table as high as 20cm subsurface, and where trees including oaks adapt to much wetter conditions, even within a lifecycle, and reproduce successfully.
The potential for further deployment of natural regeneration on peat in commercial forestry is recognised77,78, particularly given the high suitability of moist peat soils with sphagnum moss for seedling germination, although conifer plantations normally thrive with <70% soil water content requiring extensive ground preparation.
Trees on peat: CO2e balance
By lowering the water table, resulting in increased decomposition, trees on peat could cause emissions of carbon dioxide from soil carbon stores, threatening the climate. However, evidence is lacking that passive rewilding would cause this, even if natural regeneration of trees did occur over significant areas of intact peat bogs—the small proportion of peatlands with high enough water tables and the right peat-forming vegetation to sequester carbon. The CO2e balance of existing forest, of naturally regenerating woodland, and of planted woodland on peatland are all important to whether trees on peat really threaten the climate.
Forested peatlands can sequester CO2
Ecosystems comprised of old growth trees such as Canadian black spruce on peat are shown to be carbon sinks, particularly with a partial ground covering of peat-forming species such as sphagnum mosses79. Deciduous forest on peat also acts as a carbon sink, although much forested peatland in the UK is conifer plantation which is thought to be a net carbon emitter80. It is claimed therefore UK plantations should be felled and “restored” to tree-less blanket bog81. Although this claim misses the full carbon cost of active transition and assumes it is possible to fully restore a nationally significant proportion of felled areas, it is also a moot point as most are likely to be felled anyway for wood. The pertinent CO2e question is if and how those forests are replaced, rewetted or not, and if and how new wooded areas establish82.
No evidence natural regeneration drives net CO2e emissions on peatland
The main peatland restoration approach of rewetting mitigates climate warming. However, there are numerous exceptions83. Carbon-intensive methods including helicopter drops and use of excavators are rarely accounted for, and partial restoration can have adverse effects84. There is a particular paucity of evidence around climate impacts of natural regeneration on peat in the mid latitudes including the UK. Where trees are allowed to regenerate naturally on peat in boreal regions there is no evidence to suggest carbon sequestration is reversed. A UK estimate of sequestration potential, among other factors, would need to account for tree biomass accumulation above and below the peat, increase in mass of shrubs and deadwood, mycorrhizal and other soil biota development85, mass of fauna present within the above ground ecosystem, all modelled in the context of a changing climate and possibly changing fire regimes86. The CO2e balance of a blanket bog, versus a possible complex scrub or woodland ecosystem, from a baseline of a degraded peatland in the UK is not proven to be significantly different.
Furthermore, rewetting and natural regeneration are not mutually incompatible as is often presumed. Natural regeneration on peat, a possible localised outcome of passive rewilding, does not require soils to be mechanically disturbed for drainage and planting, so a key mechanism by which afforestation can generate emissions is eliminated87,88. Trees can establish on some peatlands with high water tables and continue to thrive. There is no evidence to suggest natural regeneration ends continuing sequestration to peat layers89 and factors relating to stability may play an increasingly important role. On steep slopes trees can stabilise peat and block gullies potentially increasing overall attenuation and accumulation90.
Even planting trees on peat can sequester CO2
Tree-planting would not fall under the definition of passive rewilding provided but shows the extent to which trees on peat need not threaten climate. In the UK, Scotland’s Centre of Expertise on Climate Change stated in 2018 it is “‘very probable’ that moderate and high productivity forests planted on shallower peat soils with limited disturbance provide a substantial net carbon uptake over the forest cycle”, with the main emissions being associated with ground preparation, not a factor in natural regeneration. Deep peats too, due to the reduced methane output, could in some circumstances become CO2e sinks over relatively few growth cycles when planted using shallow soil disturbance methods91.
Trees reduce peat runoff and peak flows downstream
Trees on peat intercept a sizeable proportion of precipitation reducing runoff and peak flow and increase evaporation through transpiration with the same effect92. Furthermore, where runoff from peatlands with flowing drains contributes to flooding, afforestation through passive rewilding in peat gullies may be a faster and more cost- effective method of mitigating this risk, for instance compared with mechanically blocking peat drains/burns. The high elevation ‘birch belt’ of southern Norway offers an interesting comparison to Scotland where deciduous woodland up to 1200m, regularly on peat or peaty podzols, provides an “effective ‘sponge’ for rainfall, reducing flood and erosion risk”93,94.
Trees on peat: Biodiversity
Passive rewilding on peat can increase habitat and within-habitat heterogeneity, particularly through increased variety in vegetation height and type including trees95, which in turn improves biodiversity outcomes, species abundances and productivity. More species are likely to benefit than experience declines in range and population through passive rewilding, particularly in the long term. Avian studies offer perhaps the best evidence to date. On Deeside in Scotland, avian species richness in mature birch forests was four times that of moorland, and higher diversity of species in areas of natural regeneration98. In the Cairngorms, only 3% of internationally important taxa present prefer moorland as their primary habitat, the rest benefit more from different vegetation assemblages99.
Although positive overall, the potential impact of passive rewilding on biodiversity is uneven96. Change will not impact all species equally and may disadvantage some—although habitat stasis through preservation has the same effect. Species such as juniper, dwarf or downy birch, capercaillie, black grouse, golden eagle97, red squirrel, hedgehog, wildcat, and roe deer are likely to benefit from passive rewilding on peatland. Clearly locations will differ markedly and in some, introduced species such as muntjac, feral cats, nonnative conifers or rhododendron may also thrive. Greater tolerance for introduced species, which may anyway exhibit only temporary or highly localised proliferations, is a prerequisite for large-scale passive rewilding. Also necessary is an acknowledgement they may contribute to an overall increase in the diversity of life in a landscape context.
Passive Rewilding not reintroductions
Reintroductions regularly fail
A literature review published in 2000 found only a quarter of wildlife reintroductions worldwide were successful at creating viable, self-sustaining populations, supplementing populations, or reducing human-wildlife conflict. Another quarter were considered failures, and half the outcomes were unknown100. In 2008, reintroduction success remained poor across multiple species and locations101,102 and again in 2011, in a global study, unsatisfactory reintroduction outcomes across many taxa were reported, including plants103,104. In 2018, research showed improvement in global reintroduction outcomes although with the incorporation of ‘partial successes’ in that assessment and significantly higher average funding105. Definitions of success are loose with particular questions remaining around what should constitute a viable population106, but it is clear reintroduction outcomes are at best a mixed bag. Reintroductions into the wild are high risk to those translocated individuals and demand expensive preparation and monitoring107. Furthermore, successes may not be lasting with fast-changing conditions. The UK’s first conservation reintroduction, the Capercaillie in the 1830s, might have been considered successful but the bird is now in danger of going extinct for a second time108,109.
Reintroductions in the UK fail less but overall benefits are limited
Although recent reintroductions into the UK have seen above average success in terms of population growth and distribution, costs and ongoing support have been high. For example, the Great Bustard reintroduction cost at least €2.2million/£1.9 million110 between 2010 and 2015. Direct costs associated with the latest of multiple Sea Eagle reintroductions reached £235,000111 in just one year and the ongoing Scottish Sea Eagle Management Scheme cost £874,000112 between 2015 and 2019. The Scottish Beaver Trial was estimated in 2015 to cost £2.1 million113 and The River Otter Beaver Trial has so far cost lead partner Devon Wildlife Trust £500,000114. The initial three-year Kent bison project “Wilder Blean” will cost at least £1.125 million with ongoing costs to be met through partnerships and donations115. The Scottish Wildcat project will cost at least £3.6 million116. Although economic returns such as through increased tourism are possible, benefits of reintroduced species to nature remain difficult to establish and species individuals can experience suffering.
Red Kites (Milvus milvus)
Red kites were reintroduced into the UK in the Chilterns in 1990 and the programme continued to bolster numbers through translocation of chicks in subsequent years. As with all raptors, the environmental/ecological impacts of red kite reintroduction are difficult to measure given their ability to fly long distances from release sites and the dispersed nature of their feeding and breeding activities during a potentially decadal lifetime. Significant other contemporaneous environmental changes have taken place over thirty years which make the effects of the species even more difficult to isolate.
Although their environmental impacts are little known, the welfare of the reintroduced birds and their offspring is better understood. Red kite individuals are at risk from lead poisoning. Although practices have now changed, in the past this resulted from lead in their food in captivity. Lead poisoning continues from lead in carrion and in live prey117, mainly arising from organised shoots. Elevated, dangerous and even deadly levels of lead have been found in red kites, especially post-mortem118. Deliberate and accidental poisoning by rodenticides has also been reported119 and raptor persecution on estates including shooting persists120 as well as traffic collisions and electrocution121.
The success of the reintroduction programme is easily evidenced in terms of population growth, increased distribution, and breeding success, particularly since the mid-2000s122,123,124. However, the suffering of individuals mutes this success and there is a lack of evidence for wider environmental benefits.
White Tailed Sea Eagle (Haliaeetus albicilla)
Sea eagles are another raptor, making their environmental effects following reintroduction difficult to assess. They were introduced to western Scotland in 1983 and currently number around 123 pairs nationwide125, numbers low enough that they are red listed “needing urgent action”126 nearly forty years on.
A much larger predator than the red kite, it is suggested that they may control numbers of hooded crows, ravens, and foxes which are thought to be overrepresented within species assemblages, for instance in parts of Ireland127. It is also suggested that they reduce carrion in livestock farming areas which is beneficial to farmers. Research has pointed to the disturbance of seabird nesting sites by sea eagles as potentially devastating for seabird colonies128, but other factors are strongly implicated in the apparent disappearance of seabirds in locations where they cohabit129. There is no consensus, within the scientific community or otherwise, whether sea eagles’ environmental/ecological effects are widely observable.
On the basis of wider ecological impacts, there are few conclusions to be drawn regarding the success of White Tailed Sea Eagle reintroduction, although the birds themselves seem to tolerate conditions in the UK and are breeding in the wild. Given their ability to fly great distances and the costs of reintroduction, it may have been sensible to await their arrival from Europe, and simply focus on reducing pressures on inshore marine habitats, fish stocks and potential nesting sites, with benefits to multiple species.
Great Bustard (Otis tarda)
After a failed attempt in the 1970s, the Great Bustard was reintroduced to Salisbury Plain in Wiltshire in 2004, using eggs collected in Russia. For the first 10 years of the trial, breeding success remained anaemic, the birds also unexpectedly migrated to locations in the south of England and even France, then disappeared130. Numbers have risen to 100 individuals, but they have not established breeding sites in other locations131. Their possible impacts on the environment are limited to a single site and they are not considered “landscape changers” by conservationists132. This project has had such limited geographical and ecological impact that cost and time factors outweigh localised species-population benefits.
Passive rewilding achieves comparable beneficial outcomes for free
The opportunity cost of reintroductions with high capital investment and resource-allocation133,134 makes reintroductions difficult to justify from an ecological standpoint. The three UK reintroduction case studies presented highlight ecological benefits are largely unknown. A final UK case study shows even when wider ecological benefits and ecosystem services are apparent, other passive options may still be preferable.
Simpler alternatives Eurasian Beaver (Castor fiber)
Beaver reintroductions have had measurable ecological success in the UK, although they have also drawn more financial and expert resources than any other reintroduction.
Beavers went extinct in the UK in the 16th century (earlier in England)135 and are shown to have an “overwhelmingly positive” effect on biodiversity based on a meta- analysis of studies from across their range in Europe, Asia and North America136. Beavers are predicted to benefit species of conservation concern in the UK such as otters, and great crested newts, as well as boosting species biodiversity overall in river and stream corridors. The risks to habitats and species in the UK are considered minor, associated with felling of trees in the absence of rapid regeneration.
The mechanisms by which beavers are said to engineer ecosystems and support biodiversity are cited in the first proposed definition of an “ecosystem engineer”: a species active in the “creation, modification and maintenance of habitats”137, and therefore central to natural processes favoured in rewilding. Clive Jones and colleagues state, by “cutting trees and using them to construct dams [beavers] alter hydrology, creating wetlands that may persist for centuries.”. Naiman and colleagues explain: “These activities retain sediments and organic matter in the channel [. . .] modify nutrient cycling and decomposition dynamics, modify the structure and dynamics of the riparian zone, influence the character of water and materials transported downstream, and ultimately influence plant and animal community composition and diversity”138. The basic processes of beaver habitat management are well understood, with habitat heterogeneity/within-habitat heterogeneity also said to benefit greatly due to the uneven intensity of impacts, from largely untouched stands of vegetation to permanently flooded areas139,140,141.
Studies are relatively recent in the UK. The first beavers were introduced illegally onto the River Otter in Devon around 2007142/2008143. Later formalised as The River Otter Beaver Trial they were eventually permitted to remain by the government in 2020144. A devolved matter, the first beavers were released legally in Scotland at Knapdale in 2009 but had appeared through illegal release in the Tayside catchment by 2006145. The Knapdale release became The Scottish Beaver Trial. These studies offer the longest running monitoring providing for tentative conclusions about early environmental impacts in the UK. Beaver impacts are highly context-specific with variable intensity, type and location, layered onto different existing land or water uses in that area146.
Results in both cases are in line with research outside the UK, with benefits to sediment load and flows147,148 potentially reducing river erosion, flooding and benefitting riverine aquatic organisms149. Fish abundance increased, probably due to the introduction of woody debris, flow refuge and increased invertebrates150,151,152.
Beaver reintroductions are one of multiple strategies for improving river catchment attenuation/hydrology and riverine biodiversity including ecosystem diversity. Another low cost strategy is to reduce or cease mowing, cutting or grazing of river banks, gullies and flood plains to allow natural regeneration of scrub and trees, particularly willow.
This slows and reduces runoff into watercourses153,154,155, and on the lower banks allows for material capture creating living dams, or for the death and collapse/felling of trees into the flow with similar effect156,157,158. Although resulting pools and dams/logjams may be less substantial than larger beaver dams, potentially limiting ecological and species biodiversity benefits at those sites, cost savings against existing management regimes and against future costly beaver reintroductions would be considerable. This would allow for investment in further schemes with greater overall ecological benefit.
Based on the costs of beaver trials to date, and potential future reintroductions, simply reducing bank and floodplain clearances allowing natural regeneration would offer more cost-effective solutions, with slightly different benefits, of equal value to hydrology, and wild flora and fauna. This would also provide habitat for beavers to spread naturally over the coming decades and multiply those benefits.
Less is More: Less managed peatlands and fewer reintroductions
Passive rewilding as de-management can benefit ecosystems in the UK. Positive outcomes for species biodiversity and wildlife abundance are more likely through passive rewilding compared with employing active rewilding or restoration strategies. Positive outcomes also become more likely for hydrology and species individuals. Passive rewilding’s potential is greater still in relation to broader notions of life’s complexity in which we must find novel aspects of biodiversity value, for instance new kinds of human-wildlife interactions and aesthetics. Crucially passive rewilding can be much less complex and expensive than active approaches, so resources stretch further.
Likely outcomes from passive rewilding include natural regeneration on some UK peatlands. This should be tolerated and even encouraged from an ecological perspective. On peatlands, passive rewilding could simultaneously reduce management costs, improve species and habitats diversity, and benefit flood management. Greater acknowledgement of the scientific unknowns regarding climate-oriented land use strategies, which currently seem to go against passive rewilding on peatlands, would contribute to better nature recovery policies. The CO2e balance of passively rewilded peatland in the UK, either modified or “near-natural”, twenty or a hundred years into the future is indeterminable. Yet in the absence of evidence afforestation is framed as a potential climate disaster159. Meanwhile, working with what we do know, on peatland passive rewilding is more likely than preservation, and even active rewilding or restoration, to provide increased genetic, taxonomic, and ecosystemic biodiversity at scale, and flood management benefits.
Reintroductions, a central tenet of current UK rewilding schemes, provide few additional ecological benefits compared to passive rewilding strategies and require high capital input. This is particularly the case with introduced large mammals which must be fenced and closely managed. Notwithstanding the lure of exotic—if technically “native”—beasts, resources should instead be allocated towards higher impact passive rewilding in more locations; for instance, incentivising land managers to undertake much less active management, an approach that has long been utilised through agri-environment schemes but must be far more ambitious. Passive rewilding, by reducing direct management, frees up resources and leads to ecological outcomes which benefit both wild nature and ourselves. Although sometimes less certain, ecological outcomes fall within a beneficial range of possibilities to achieve this. With nature recovery ‘Less is more’.
1 Sweikert, L. A., & Gigliotti, L. M. (2019). A values-based private landowner typology to improve grassland conservation initiatives. Society & Natural Resources, 32(2), 167-183.
2 For example a speech by Environment Secretary May 2021: https://www.gov.uk/government/news/environment-secretary-to-set-out-plans-to-restore-nature-and-build-back-greener-from-the-pandemic
3 For example Local Nature Recovery Strategies in the new Environment Bill (2021): https://publications.parliament.uk/pa/bills/cbill/58-01/0009/20009.pdf
4 George Eustice Blog, Thursday, 29 July 2021 “Green Recovery Challenge Fund”: http://georgeeustice.blogspot.com/
5 Rewilding Europe (2019) “Nature based economies”: https://rewildingeurope.com/rewilding-in-%20action/nature-based-economies/
6 Rewilding Britain (2021) “Rewilding and the Rural Economy: How Nature-Based Economies can help boost and sustain local communities”: https://s3.eu-west-2.amazonaws.com/assets.rewildingbritain.org.uk/documents/nature-based-economies-rewilding-britain.pdf
7 Luttik J, de Boer T, Goossen M, Groot Bruinderink G. (2006) Nature development and the regional economy in the Gelderse Poort. Wageningen, The Netherlands: Alterra. [In Dutch, translated using DeepL https://www.deepl.com/en/translator]
8 Colding, J., and Barthel, S. (2013). The potential of ‘Urban Green Commons’ in the resilience building of cities. Ecological Economics, 86, 156–166.
9 Cerqueira, Y., Navarro, L., Maes J., Marta-Pedroso C., Honrado J., & Pereira H. (2015) “Ecosystem Services: The Opportunities of Rewilding in Europe” In Pereira, H. & Navarro L. [eds.] Rewilding European Landscapes. 1st Ed. Ch. 3.
10 Laar Svd, Lycklama T. (2012) [Opening up pays off! The effect of nature and opening up on the leisure economy along large rivers]. The Netherlands: Office for Space and Leisure. [In Dutch, translated using DeepL https://www.deepl.com/en/translator]
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13 Mills, J. G., Weinstein, P., Gellie, N. J., Weyrich, L. S., Lowe, A. J., & Breed, M. F. (2017). Urban habitat restoration provides a human health benefit through microbiome rewilding: the Microbiome Rewilding Hypothesis. Restoration ecology, 25(6), 866-872.
14 Carver, S. (2019). Rewilding through land abandonment. In N. Pettorelli, S. Durant, & J. Du Toit (Eds.), Rewilding (Ecological Reviews, pp. 99-122). Cambridge: Cambridge University Press. doi:10.1017/9781108560962.006
15 Morel, L., Barbe, L., Jung, V., Clément, B., Schnitzler, A., & Ysnel, F. (2020). Passive rewilding may (also) restore phylogenetically rich and functionally resilient forest plant communities. Ecological Applications, 30(1), e02007.
16 Thers, H., Bøcher, P. K., & Svenning, J. C. (2019). Using lidar to assess the development of structural diversity in forests undergoing passive rewilding in temperate Northern Europe. PeerJ, 6, e6219.
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18 Citizen Zoo (2021) “Why we must embrace nature in the fight against climate break down” 12th November: https://www.citizenzoo.org/2021/11/cop26-nature-based-solutions-and-the-role-of-rewilding/
19 Broughton, Richard K., James M. Bullock, Charles George, Ross A. Hill, Shelley A. Hinsley, Marta Maziarz, Markus Melin, J. Owen Mountford, Tim H. Sparks, and Richard F. Pywell (2021) “Long-term woodland restoration on lowland farmland through passive rewilding.” Plos one 16 (6): e0252466.
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23 Rewilding Britain (2021) Rewilding and Climate Breakdown: https://www.rewildingbritain.org.uk/news-and-views/research-and-reports/rewilding-and-climate-breakdown
24 Increased soil biota could mean increased carbon storage: Artz, R. R., Anderson, I. C., Chapman, S. J., Hagn, A., Schloter, M., Potts, J. M., & Campbell, C. D. (2007). Changes in fungal community composition in response to vegetational succession during the natural regeneration of cutover peatlands. Microbial Ecology, 54(3), 508-522.
25 Natural regeneration stabilises peat: Bain, C. G., Bonn, A., Stoneman, R., Chapman, S., Coupar, A., Evans, M. & Worrall, F. (2011). IUCN UK commission of inquiry on peatlands. IUCN UK Peatland Programme.
26 Dixon, S. J., Sear, D. A., Odoni, N. A., Sykes, T., & Lane, S. N. (2016). The effects of river restoration on catchment scale flood risk and flood hydrology. Earth Surface Processes and Landforms, 41(7), 997-1008.
27 Rewilding Britain (2016) “How Rewilding Reduced Flood Risk”: https://www.rewildingbritain.org.uk/news-and-views/research-and-reports/how-rewilding-reduces-flood-risk-2
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30 Brazier R. (no date) “The Restoration Game. How landscape restoration reduces flooding, improves water quality and combats climate change”, Policy Briefs, Exeter University: https://www.exeter.ac.uk/media/universityofexeter/research/gateway/feature/research/pdfs/Exeter__policy_briefing.pdf
31 Cerqueira, Y., Navarro, L., Maes J., Marta-Pedroso C., Honrado J., & Pereira H. (2015) “Ecosystem Services: The Opportunities of Rewilding in Europe” In Pereira, H. & Navarro L. [eds.] Rewilding European Landscapes. 1st Ed. Ch. 3.
32 Wingate, S. (2021) “UK is one of world’s most nature-depleted countries, new data shows”: https://www.standard.co.uk/news/uk/natural-history-museum-none-earth-china-japan-b959693.html
33 Davis J. (2020) “UK has ‘led the world’ in destroying the natural environment”, Natural History Museum: https://www.nhm.ac.uk/discover/news/2020/september/uk-has-led-the-world-in-destroying-the-natural-environment.html
34 Lacks discussion of natural regeneration or woodland on peat: Anderson, R., Vasander, H., Geddes, N., Laine, A., Tolvanen, A., O’sullivan, A., & Aapala, K. (2016). Afforested and forestry-drained peatland restoration. In A. Bonn, T. Allott, M. Evans, H. Joosten, & R. Stoneman (Eds.), Peatland Restoration and Ecosystem Services: Science, Policy and Practice (Ecological Reviews, pp. 213-233). Cambridge: Cambridge University Press. doi:10.1017/CBO9781139177788.013
35 Fails to mention opportunity cost of Lynx reintroduction to other conservation activities: White, Chris, Ian Convery, Adam Eagle, Paul O’Donoghue, Steve Piper, Petrina Rowcroft, Darrell Smith, and Erwin van Maanen. “Cost-benefit analysis for the reintroduction of lynx to the UK: Main report.” (2015): 1-47.
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37 Soulé, Michael & Reed Noss (1998) “Rewilding and biodiversity: complementary goals for continental conservation.”, Wild Earth, 7:3, pp. 19–28.
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40 Foreman, Dave. 2004. Rewilding North America: A Vision For Conservation In The 21st Century. Washington D.C., Island Press, 129
41 Marley J. (2021) “Monks Wood Wilderness: 60 years ago, scientists let a farm field rewild – here’s what happened”, Blog: The Conversation, 22nd July 2021: https://theconversation.com/monks-wood-wilderness-60-years-ago-scientists-let-a-farm-field-rewild- heres-what-happened-163406
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49 Svenning, Jens-Christian, Michael Munk, and Schweiger, A. (2019) “Trophic rewilding: ecological restoration of top-down trophic interactions to promote self-regulating biodiverse ecosystems.” Rewilding 73.
50 Soulé, M., & Noss, R. (1998). Rewilding and biodiversity: complementary goals for continental conservation. Wild Earth 8, 19.
51 Tweedale, Aimee. (2021) “How rewilding can fight climate change by restoring the UK’s natural beauty”. Blog post for Ovo Energy. 7th Jan 2021: https://www.ovoenergy.com/blog/green/what-is-rewilding-and-how-does-it-work
52 The Woodland Trust (2017) Position Statement on Rewilding: https://www.woodlandtrust.org.uk/media/1718/rewilding-position-statement.pdf
53 Rewilding Europe Website (2021) “What is Rewilding?”: https://rewildingeurope.com/what-is-rewilding-2/.
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60 Scottish Natural Heritage (2000) Montane Scrub: https://www.nature.scot/sites/default/files/2017-06/Publication%202002%20-%20Montane%20Scrub.pdf
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65 Sunström, E., & Hånell, B. (1999). Afforestation of low-productivity peatlands in Sweden—the potential of natural seeding. New forests, 18(2), 113-129.
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125 British Trust for Ornithology (no date) Bird Facts: White-tailed Eagle Haliaeetus albicilla”: https://app.bto.org/birdfacts/results/bob2430.html
126 RSPB (no date) “UK conservation status explained”: https://www.rspb.org.uk/birds-and-wildlife/wildlife-guides/uk-conservation-status-explained/
127 O’Rourke, E. (2014). The reintroduction of the white-tailed sea eagle to Ireland: People and wildlife. Land Use Policy, 38, 129-137.
128 Hipfner, M. J., Blight, L. K., Lowe, R. W., Wilhelm, S. I., Robertson, G. J., Barrett, R. T. & Good, T. P. (2012). Unintended consequences: how the recovery of sea eagle Haliaeetus spp. populations in the northern hemisphere is affecting seabirds. Marine Ornithology 40: 39–52.
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130 Alonso, J. C. (2015). The Great Bustard: past, present and future of a globally threatened species. Ornis Hungarica 22(2):1-13
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133 Hilbers, J. P., Huijbregts, M. A., & Schipper, A. M. (2020). Predicting reintroduction costs for wildlife populations under anthropogenic stress. Journal of Applied Ecology, 57(1), 192-201.
134 Nogués-Bravo, D., Simberloff, D., Rahbek, C., & Sanders, N. J. (2016). Rewilding is the new Pandora’s box in conservation. Current Biology, 26(3), R87-R91.
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136 Stringer, A. P., & Gaywood, M. J. (2016). The impacts of beavers Castor spp. on biodiversity and the ecological basis for their reintroduction to Scotland, UK. Mammal review, 46(4), 270-283.
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140 Smith, J. M., & Mather, M. E. (2013). Beaver dams maintain fish biodiversity by increasing habitat heterogeneity throughout a low‐gradient stream network. Freshwater Biology, 58(7), 1523-1538.
141 Willby, N. J., Law, A., Levanoni, O., Foster, G., & Ecke, F. (2018). Rewilding wetlands: beaver as agents of within-habitat heterogeneity and the responses of contrasting biota. Philosophical Transactions of the Royal Society B: Biological Sciences, 373(1761), 20170444.
142 Auster, R. E., Puttock, A., & Brazier, R. (2020). Unravelling perceptions of Eurasian beaver reintroduction in Great Britain. Area, 52(2), 364-375.
143 Devon Wildlife Trust (no date) “Government landmark decision means Devon’s beavers can stay!”: https://www.devonwildlifetrust.org/what-we-do/our-projects/river-otter-beaver-trial#:~:text=Government%20landmark%20decision%20means%20Devon’s%20beavers%20can%20stay!&text=It%20was%20the%20first%20legally,now%20has%20a%20secure%20future.
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145 Ward, K. J., & Prior, J. (2020). The Reintroduction of Beavers to Scotland. Conservation & Society, 18(2), 103-113.
146 Brazier, R.E., Elliott, M., Andison, E., Auster, R.E., Bridgewater, S., Burgess, P., Chant, J., Graham, H.A., Knott, E., Puttock, A.K. and Sansum, P. (2020). River otter beaver trial: Science and evidence report. University of Exeter: https://www.exeter.ac.uk/creww/research/beavertrial.17.
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148 Brazier, R.E., Elliott, M., Andison, E., Auster, R.E., Bridgewater, S., Burgess, P., Chant, J., Graham, H.A., Knott, E., Puttock, A.K. and Sansum, P. (2020) River otter beaver trial: Science and evidence report. University of Exeter. https://www.exeter.ac.uk/creww/research/beavertrial.70.
149 Brazier, R.E., Elliott, M., Andison, E., Auster, R.E., Bridgewater, S., Burgess, P., Chant, J., Graham, H.A., Knott, E., Puttock, A.K. and Sansum, P. (2020) River otter beaver trial. 77: Science and evidence report. University of Exeter. https://www.exeter.ac.uk/creww/research/beavertrial
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153 Scottish Environment Protection Agency (2015) Flood Management Handbook: https://www.sepa.org.uk/media/163560/sepa-natural-flood-management-handbook1.pdf
154 Stratford, C., Miller, J., House, A., Old, G., Acreman, M., DuenasLopez, M. A., Nisbet, T., Newman, J., Burgess-Gamble, L., Chappell, N., Clarke, S., Leeson, L., Monbiot, G., Paterson, J., Robinson, M., Rogers, M. & Tickner, D. (2017). Do trees in UK relevant river catchments influence fluvial flood peaks? A systematic review. In: NERC/Centre for Ecology & Hydrology (ed.). Wallingford, UK
155 Metcalfe, P., Beven, K., Hankin, B., & Lamb, R. (2017). A modelling framework for evaluation of the hydrological impacts of nature‐based approaches to flood risk management, with application to in‐channel interventions across a 29‐km2 scale catchment in the United Kingdom. Hydrological Processes, 31(9), 1734-1748.
156 Sear, D. A., Millington, C. E., Kitts, D. R., & Jeffries, R. (2010). Logjam controls on channel: floodplain interactions in wooded catchments and their role in the formation of multi-channel patterns. Geomorphology, 116(3-4), 305-319.
157 Dixon, S. J., Sear, D. A., Odoni, N. A., Sykes, T., & Lane, S. N. (2016). The effects of river restoration on catchment scale flood risk and flood hydrology. Earth Surface Processes and Landforms, 41(7), 997-1008.
158 Thomas, H. and Nisbet, T.R. (2012) Modelling the hydraulic impact of reintroducing large woody debris into watercourses. Journal of Flood Risk Management 5(2):164-174.
159 Prof. Gideon Henderson, Chief Scientific Adviser to DEFRA, presentation at Magdalene College, Cambridge, Thursday 16th Jan 2020 with follow-up email exchange.