What are the ecological benefits of rewilding?

To be honest, I do not know the answer to my own question. It isn’t as if I haven’t looked for the answer. I have asked the rewilders to provide hard evidence for the support of their claims, and I have received none. I have speculated here, for example, as to what the changes might be to our upland landscapes. My own suggestions, which are founded on basic, known habitat requirements of upland birds, have received no substantive response from the rewilders. It is true that there has been a lot of waffling, hand waving and so forth, but nothing of any substance.

Occasionally, Yellowstone Park is cited as an example of a ‘rewilded’ landscape; of what happens when you re-introduce a keystone species. But Yellowstone Park is not the north of England, the Black Mountains or the Highlands of Scotland. Yellowstone Park is an area of nearly 9,000 Km2, nearly four times the size of our largest national park – the Lake District. Yellowstone receives 3.4 million visitors a year, but the Lake District receives 15.8 million a year (and day visitors number 23.1 million). Yellowstone is 80% forest cover, and most of that is Lodgepole Pine. The Lake District is 12% forest cover – which is high for England. The woodland is both coniferous and broadleaf. The whole park is extremely varied in its biodiversity. But it is not for ecological reasons that the Lake District has been awarded a UNESCO World Heritage status – the award was made for cultural reasons.

The impact of the reintroduction of wolves back into Yellowstone has been heralded as an un-alloyed good and that everything is now balanced and beautiful, where before it was deteriorating without the wolves. Actually, wolves have done so well that they are now raiding cattle ranches outside the park and the ecological impact inside the park is a little more complicated than the rewilders would like to admit. One reason for this is perhaps that when the park was first established, not just the wolves, but another keystone species was removed from the park in order to give the impression that this was a ‘pristine’ landscape. In fact it was humans who are the other keystone species – the Native American tribes who were forcibly removed. Whilst the wolves have been brought back, the Native Americans have not. As a result of this omission, the ecological dynamics have been a little more unpredictable than anticipated.

But still we get the rewilders telling us that everything will be hunky-dory once we get rid of those horrid hill farmers. The photograph (Figure 1) below is typical of the rewilders’ ideas that fencing off an area from human interference (in this case by grazing cattle) brings about an ‘improvement’ in ‘biodiversity’. Professor Alastair Driver has kindly provided the image and his view that this provides an example of what is meant by rewilding. The picture is of a corner of an exclusion area and shows just how quickly trees will take over once grazing is stopped.

On the right-hand side of the exclusion fence, we can see young trees growing cheerfully in an ungrazed environment. The heather is becoming tall and bushy. In a year or two, it will become leggy. As the tree canopy closes, the heather and mosses will gradually die out. It is fair to observe that many of the trees inside the exclosure are non-natives. I am not too good at identifying young trees – the broadleaves look like a mixture of Birch and Rowan, but the conifers are Norway Spruce.

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Figure 1 – Grazed and ungrazed uplands. (Source: Tweet by Alastair Driver)

On the left side of the fence, a broken boulder-strewn hillside is clearly grazed and Prof Driver says it is grazed by cattle. The heather is clearly well nibbled and there are no young trees in the foreground. Although the photograph is unclear, it looks as if some trees in the distance are surviving the cattle.

Using birds as a marker of biodiversity, we can anticipate that exclosure will prompt an increase in numbers of Blue Tits, Great Tits, Long-tailed Tits, Chaffinches, Greenfinches, Robins, Blackbirds along with the possibility of Linnets (or Twites in the north) and Siskins. Black Grouse may benefit initially, but will disappear when the canopy closes and the predators move in. The predators will amount to Buzzards, Red Kite and, when the new forest matures, the possibility of Goshawk. Some owls may arrive, but only when the trees have matured. Then there will be the Magpies and Carrion Crows. Jays will only move in when the trees have matured and then only if there are oaks or beech in the species mix. The populations of these birds will be high within the habitat and so the biodiversity can easily be said to have “improved” because both the absolute numbers of birds have increased, and the number of species has increased.

However, along with the gains achieved by rewilding, we have also to consider the losses. In the open landscape of moors and mountains of northern and western Britain, the typical upland bird species are Golden Plover, Lapwing, Curlew, Common Sandpiper (along the streams), Dunlin, Red Grouse, Hen Harriers and Merlin. In the north of Scotland, Greenshank will also be present. Peregrine Falcons and Ravens will breed on the crags and rocky outcrops. In these circumstances, the numbers of birds per unit area will be low compared to the secondary woodland advocated by the rewilders. The species list will also be shorter than the new wooded area. So here is the justification of rewilding – both species diversity and absolute numbers of individuals are increased when trees are allowed to encroach upon open moorland, because the woodland species are higher in number and greater in density. This is the crux of the rewilders’ argument: that biodiversity has been “improved” and thereby provides the justification for the idea of taking large tracts of land outside human use and handing it over to nature.

But there are a couple of problems with this argument.

Another glance at the list of birds involved in both rewilded and moorland habitats reveal that the rewilded birds are rather common, mundane species. By contrast, the moorland birds are all very special. Some are critically endangered, either within the UK or internationally. And this provides the reasons why our moorland and mountain areas are of such considerable conservation importance. It is fair to say that these moorland species are declining, but the reasons for this are several and complex. What is clear is that rewilding large tracts of land, replacing open heather and rough grazing with trees, will only serve to make the numbers of these special species decline even faster. Some species will be eradicated altogether – I suggest that the British breeding population of Dunlin would disappear from England and Wales and probably much of Scotland within a few years.

The rewilders claim that they do not want to rewild all of the uplands – which is very generous of them. However, rewilding ‘patches’ of land has an effect far beyond the actual limits of the rewilded areas. For an explanation of the problems of the ‘edge effect’, see here. The fact is that a pair of Buzzards or Carrion Crows do not just hunt in their new secondary woodland home – they range far and wide beyond it, to the continuous detriment of any ground-nesting bird. That means all of the moorland species mentioned above, except for the Ravens and Peregrines. So even if the rewilded areas do not cover the whole of the uplands, their detrimental effect upon many of our most loved species of birds will reach far beyond the limits of the new woodland.

It happens that there are quite large areas within the UK which have been allowed to grow over in the manner suggested by the rewilders. If asked for instances of this, the rewilders will point to Carrifran in the Scottish Borders, which looks absolutely lovely (see Figure 2). Carrifran is a glen which was formerly managed for sheep, but which is now being planted up with native species of trees. However, there are many other instances of rewilding in the UK – both where entirely natural succession has been allowed to take place and follows its natural course, and also where the process has been helped along by deliberate planting of native trees.

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Figure 2 – Carrifran after replanting. (Source: Tweet by Alastair Driver).

During the 19th century, Britain’s railways were built up hills and down dales. As they crossed river valleys and vaulted over flood plains and delved into the hills, they left behind newly constructed bare embankments. Over the years, these have gradually become covered with many millions of trees (Figure 3). Long-suffering commuters to London will be wearily familiar with the announcement that their train has been delayed because of “leaves on the line”. From the 1960s onwards, a similar process of habitat provision occurred when the motorway network was built. Since the 1980s, highways policy has dictated that large embankments were planted with native species of trees. And so we have a situation similar to the railway embankments, but accelerated by artificial planting. These linear habitats, of both types, have brought into London and other large cities a good deal of wildlife such as Foxes, Badgers, Blackbirds, Robins, Blue Tits, Magpies and Carrion Crows. “Rewilding” has therefore been going on in Britain for well over 150 years.

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Figure 3 – Mature trees on a railway line, Swanage Railway. (Source: Dorset Echo)

Having made this comparison, I anticipate shouts of dismay and denial from the rewilding movement. But, whilst I recognise that there are considerable landscape and aesthetic differences between Carrifran and an average motorway embankment, in ecological terms there is very little difference. Both support a similar range of species and at similar densities. Both are intrinsically dynamic and are not held static at any particular point of ecological development, as is the case of grazed upland pasture or grouse moor. Motorway and railway embankments need periodical cutting to maintain free passage of vehicles. Ultimately, Carrifran will need some sort of management – perhaps grazing – to maintain the open areas if that is what is desired. Neither rewilded areas nor the motorway embankments are of any direct use to humans in terms of output of timber or food. Whilst both will support healthy populations of common woodland species, neither will support populations of Golden Plover, Lapwing, Curlew, Red Grouse or Merlin.

When environmentalists talk blithely of ‘biodiversity’ they are often setting a trap for the rest of us. They imply that ‘more’ is always ‘better’ when that is not always the case. Consider a diamond, which is given much greater value than a piece of glass cut to the same size and shape. There are two reasons for this: The first is that diamonds refract the light in a much more satisfactory way than cut glass, and so are judged to have a greater intrinsic beauty. The second reason is that diamonds are scarce; and so the market determines their price to be much higher than glass. It is the same with some species of animals and plants. Conservationists, correctly in my view, ascribe greater importance to those things which are scarce and/or beautiful. This is not to denigrate the common or mundane, merely that the scarce and beautiful deserves especial care when we interact with it. It therefore becomes apparent that in order to assess whether an area has ‘good’ or ‘poor’ biodiversity, we must use a measure of subjective judgement.

But even before we exercise our judgement on a change of land use (e.g. from managed grouse moor to rewilded moor) we must first of all conduct a survey to determine what is there at the moment; and what would be there if we change our management – a kind of ecological cost-benefit analysis or impact assessment. We need the rewilders to submit their plans for what is proposed, so that we can assess whether their new development is an acceptable replacement for what is there at the moment. Sadly, I can find no evidence that the rewilders have actually done any assessment of this kind. They are like an architect going to a meeting to get planning permission, without any drawings or impact assessment of their proposed development. His assurances that ‘it will all be perfectly wonderful’ is unlikely to cut much ice with the planning committee, who will think that he is wasting their time and will reject his application in short measure.

As things stand, the rewilders resemble our metaphorical architect with no drawings. They are evading any discussion of the potential losses if their plans were put into action. Neither have they acknowledged that their intended replacements amount to little more than the mundane and commonplace. They wish to replace Merlin, Golden Plover, Lapwing, Curlew, Dunlin, Greenshank, Common Sandpiper, Meadow Pipit and Red Grouse with Blackbirds, Robins and Blue Tits.

Their assurances that this is somehow an ecological benefit just does not cut any ice – and should be rejected accordingly.



  1. Hi there. First let me say that this is a well put together article, and I appreciate a healthy debate and critique of things like rewilding, that have the potential to cause such significant positive or negative changes to the environment, depending on how they are executed.

    However, I feel that you have in some ways misinterpreted the notion of rewilding and made some false equivalences.

    Primarily is that rewinding is not mindless forestry, as the Forestry Commision did in the late 20th century in Scotland and Northumbria – the common phrase used is a ‘patchwork’ or ‘mosaic’ of many different ecosystems, not just blanket forest. Furthermore, the claims made are not just of a biodiversity increase, but moreover of a more balanced working ecosystem with proper predation and grazing – ultimately this restores a natural order that maintains all the species involved in a cycle.

    This will of course take time to re-establish and ‘get right’ because the process is over decades rather than millennia and from a very different starting point, but proper monitoring will undoubtedly ensure the longevity of all species: I appreciate your concerns about Curlews (beautiful birds that fly over my home nightly) and other grassland birds, but reintroducing predators will not decimate them: I would note that predation is natural of course, but also that expanding and naturalising their habitat will boost their numbers.

    That brings me on to my final point – predators and rewilders. Just as predators are not villains, neither are rewilders – we of course have no interest in killing off birds in favour of trees, but ensuring the longevity of all species. Indeed, Monbiot (who I feel you are inevitably alluding to) has shared and supported the propositions made for the avian rewilding of the Peak District by naturalising the moorland there. There’s no need for us to be antagonistic – if you get involved with the rewinding movement, you can make clear to those mistaken of the importance of these threatened birds.

    I might also add that comparing motorway embankments to forests is beyond false equivalence, and a pretty ludicrous comparison. Motorway embankments have indeed served as wildlife corridors to an extent, but they are not equivalent to forests – they are little more than grass with young trees, whilst just one old oak can support hundreds of species on itself and around it.

    And one more thing to finish the ramble (sorry I can’t actually scroll up and edit this comment): I agree that biodiversity isn’t everything, just a good marker of the health of the ecosystem. Indeed, rewilding is less about biodiversity and more about balance and a self-supporting natural world. But if we look at the COAST rewilding project off Arran, we see that when we stop interfering the system starts to hold itself up again – the only difference being that on land, some hands on guidance is required. You’re correct though, that can go well and even provide economic returns – eg the Knepp Estate – or it can be catastrophic, but it’s anything but an architect without plans: the pilot projects are already in motion across Europe. I encourage you to help protect threatened species by working with people who are advocating rewilding to ensure that wetlands etc are properly considered, to steer change from within, rather than rubbishing what has the potential to be the greatest rejuvenation of our crippled living world in a millennium. Thank you.

    1. Thank you for your detailed comments. They are worthy of response, but I shall be able to tackle this until well after the weekend, so forgive me if I seem a little tardy.

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