The ecological benefits of rewilding

Wild Ennerdale Advisory Group

I’ve been following the writings of David Eyles in his blog “Wulfstan’s Ghost” with some interest since he started to analyse and comment on the rise of rewilding; determined as he is to disassemble and discredit the concept. He often raises relevant issues and has (I believe) valid concerns, yet often does so from a rather biased perspective. As with any new idea in whatever field of scientific endeavour you care to choose, it is often good to probe, question and evaluate the facts. In his latest post David looks at the claims and counter-claims about the ecological benefits of rewilding. This follows on from numerous other articles on the subject and provides yet another entertaining romp through the metaphorical backwater of rewilding myth and misunderstanding. It’s often fascinating to see how one’s own area of interest is seen from a different perspective. David raises some interesting topics for discussion that are worth exploring a little further, so here I reply to some of his points in person.

  1. Evidence. The point you make in asking for hard ecological evidence is well made, but needs expanding on. Our knowledge about historic species distributions and numbers is based largely on personal observations and long-term accurate records are limited. We’ve only been collecting coordinated and accurate ecological data for the last 50 years or so and records that go back further are either geographically limited (e.g. Gilbert White’s observations at Selborne) or biased towards particular species (e.g. game bags). Much of this knowledge complicated by the “Shifting Baseline” syndrome. I’ve written about this here. We know a reasonable amount about contemporary species numbers and their distributions, but much less as we go back in time. Even the fossil record is notoriously discontinuous and open to interpretation. The notion that we can say anything definite about future changes to habitats and species under different land management regimes, be that the status quo or some form of rewilding, is somewhat optimistic. We can model the effects of land use and make predictions, but they remain just that… predictions. And as George Box once said; “All models are wrong, but some are useful” (Box, 1976).
  2. Process vs outcomes. Rewilding as a paradigm in conservation practice is more about process than about absolutes. Rewilding aims to give space (and time) to wild nature to allow natural processes to determine ecological outcomes. We cannot necessarily predict anything with the absolute certainty you seem to be hankering for. Ecology isn’t architecture. We cannot be wholy certain about what the outcomes will be in terms of habitats and species per se, but we have a pretty good idea. This is because even though the processes are well-known, exactly how they will play out over time with changing climate, human influences, competition, symbiosis (remember that word?), connectivity, spatial fragmentation, etc. is hard to say. The further you look into the future, the greater the uncertainties are. We all know that. However, the ecosystems we get from rewilding will be more natural and, more likely than not, more biodiverse. This is where Yellowstone comes in, since it teaches us about the importance of process, but to compare it directly to UK national parks is disingenuous and akin to comparing apples and oranges. Yes, they’re both fruits and both spherical, but that’s where the similarities end. We’ve discussed scaling effects before where I describe how all things in nature can scale, including predator-prey relationships. While I used Yellowstone as an example of a trophic cascade (i.e. a process), I didn’t equate it to UK national parks, rather simply use it to demonstrate how “The basic ecology of symbiosis, sympatry and predator-prey relationships, together with the human modification of the landscape for agriculture and game is central to the problem….” of predator-prey imbalances, and then go on to say how species numbers and ecological function are important and co-dependent.
  3. Time. Of course, rewilding being a process, doesn’t happen overnight. It takes time. If you want hard evidence in support of the claimed benefits of rewilding then you must look at existing rewilding sites where land has been abandoned and nature left to her own devices for a period of time. Studies of these sites across a range of different successional stages can be used to extrapolate likely patterns to new projects using an approach known as “time-area substitution”. This can give us a better idea of how a site or landscape may develop once active management has ceased. Fortunately, there are number of good examples around the country and across Europe that can be used to inform the likely outcomes of future rewilding projects. You mention Carrifran and Ennerdale but fail to mention others like the Cuningar Loop in central Glasgow and Scar Close in the Yorkshire Dales. We have limited data for Cuningar, but it has shown how closed canopy woodland can develop on brownfield sites if left alone for 150 years. Scar Close is a limestone pavement from which sheep/cattle grazing has been excluded for the last 40 years. It is better documented than Cuningar and has the benefit of being next to Southerscales; a Yorkshire Wildlife Nature Reserve which is managed under a conservation grazing regime; ostensibly to maintain the site in favourable condition under Favourable Conservation Status (FCS) rules and so attract an agri-environment payment under the Higher Level Scheme (HLS). Here a direct comparison is possible. Scar Close supports nearly 250 different plant species, while Southerscales only supports around 50. Natural England who own Scar Close have forgone the HLS payments in favour of increased biodiversity through rewilding. If you want more information on these and other examples I’ve recently written a book chapter on land abandonment and passive rewilding, but you’ll have to wait until it is published sometime in 2018.
  4. Complexity. Ecology is a complex science and our understanding is limited. I’d be the first to admit that our knowledge is incomplete and, as such, we cannot predict every possible outcome within a landscape, whether managed or not. It was John Muir who said; “When one tugs at a single thing in nature, he finds it attached to the rest of the world.” How right he was. And so, the notion that the land can somehow be simplified into crisp plans and numbers (or is that money?) is puzzling to me. Ecology bears little similarity to architecture.
  5. Conflict. The emphasis on process over absolutes brings rewilding into conflict with traditional conservation practice on various levels. “Conservation” of game for the benefit of “sporting” interests has in itself little to do with conserving natural habitats and non-game species. Rather, these are often quoted as side-benefits from land management for hunting, shooting and fishing. Rewilding has a bad-rep among the game industry because it implies a loss of control. I have written about this recently here and it’s what I say in my pinned tweet. Nature conservation as practiced by government agencies and NGOs is presently beholden to a top-down system of biodiversity targets and action plans. A “bean counting” culture has grown up within the industry aimed at meeting FCS targets, much of which is dependent on traditional agricultural, forestry and game management practices such as hefted flocks, water meadows, muirburn and coppicing. As a result, our network of designated nature reserves are largely held in a state of arrested development, lest God forbid they have the temerity to evolve into something more natural. Rewilding allows successional processes to determine the habitats that develop (and thus, the species that occupy them) as determined by the prevailing edaphic conditions. This flies directly in the face of most modern conservation practice because natural succession invariably means a nature area can be deemed as “unfavourable” under FCS rules because it is moving away from the conditions for which it was originally designated. This results in a black mark against the responsible body. I have also written about this here. Finally, rewilding is generally an unpopular concept among many farmers because the emphasis is on non-productive land “use” and so limits the amount of direct revenue that can be generated from the land. While some farmers may be happy to accept money for agri-environment schemes such as High Nature Value (HNV) farming, the emphasis of rewilding on process over absolutes means uncertainty in the measurable outcomes. I suspect this, and correct me if I’m wrong here, is why you yourself are suspicious of the concept.
  6. The photo. I know exactly where this was taken. I sit on the Wild Ennerdale Advisory Board and have visited the valley many times. You should go take a look yourself. Inside the exclosure is an example of how the vegetation cover might develop in the absence of a domestic grazing pressure. Outside the exclosure, the land is grazed by semi-domesticated Galloway cattle managed by the local farmer, Richard Maxwell. As you point out, in the absence of a grazing pressure, the young trees will mature and start to crowd out light-dependant ground species which will over time be replaced by more shade tolerant species. This is natural succession. However, it worth noting that these exclosures (there’s another one lower down about 300m to the north west) are only 10x10m and the fence which keeps the cattle out also keeps out the local natural grazers (deer) and so inside the exclosure could be said to be as unnatural as outside. However, though the relative levels and style of grazing would be different, and the absence of cattle allows native trees to regenerate. This has been demonstrated further up the valley where cattle were only introduced at a much later successional stage when most trees have reached a size where they are less susceptible to browsing. The species mix is also influenced by “seed rain” from neighbouring non-native conifers that were planted in the valley between the wars. The other factor influencing tree regeneration in the valley is topography. Ennerdale has one of the best altitudinal succession sequences in England from roughly at the point where the photo was taken up to the summits of Scoat Fell, Steeple and Pillar. However, as far as grazing pressure goes it is more about local topography in the form of slope. The trees that you spot outside the exclosure are on a steeper rocky slope. Work by one of my students has shown that biodiversity of ground flora and tree numbers increases in proportion to steepness of slope as this limits cattle mobility. The cattle also browse preferentially on broadleaves meaning that those trees which do manage to get away outside the exclosures are more likely to be conifers which are less palatable, suggesting that the cattle are not helping with regenerating a natural woodland where they concentrate their grazing on the gentler slopes, but so long as numbers are limited, their effect on tree regeneration within the valley as a whole is likely to be slight and/or localised. It’s a different picture with sheep of course as they are more agile and are able to get to all but the most inaccessible rock ledges. Nonetheless, sheep are largely absent from the valley where there are no hefted flocks. What sheep do get in come through gaps in the boundary wall and are largely limited to the higher slopes. That’s probably more information than you need, but I thought it best to cover the detail that underpins what you can see in the photo.
  7. Birds. The concentration on single species groups is not helpful when assessing the overall impact on biodiversity within (and out with) rewilding project areas. Although birds are a useful indicator, focusing on these to the exclusion of other groups (e.g. vascular plants, insects, amphibians and mammals) will limit the scope of inquiry and understanding. Nonetheless, there are plenty of studies that have shown how changing from one land use or habitat type to another, results in changes to avian faunistic composition (e.g. Regos, et al., 2016). There will always be winners and losers associated with landscape change, especially in the face of climate change. See the JNCC report summarising the impacts of climate change on species distribution in the UK here.
  8. Alpha, Beta, Gamma. There are different types of biodiversity, and different ways to measure it. While there is diversity within species (genetic diversity) and between species (species diversity), we are mainly concerned here in the diversity between ecosystems (ecosystem diversity). This is essentially the variety of the species diversity (i.e. number of different species) found within a specified area (e.g. landscape, habitat or site). The total species diversity in a landscape (gamma diversity) is determined by both the mean species diversity within individual habitats at the local scale (alpha diversity) and the differences in biodiversity between the habitats making up an ecosystem (beta diversity). Your arguments about biodiversity seem to favour alpha diversity over beta and gamma diversity while focusing on some of the country’s most heavily managed (and therefore unnatural) ecosystems, such as grouse moors. I have written about this peculiarity of the UK landscape and the obsession with ground nesting birds here and here and here, describing the linked fortunes of moorland species and their dependence on intensive management for large game bags as an “inconvenient inconvenient truth”. Your previous writings on the impacts of upland farming, touch on beta and gamma diversity but in a seemingly negative light, blaming woodland on the moorland edge for all manner of ills. There’s scope for another discussion here on the implications of habitat fragmentation/homogeneity and the effect on edge to area ratio, distance from edge, predation and landscapes of fear, but perhaps this is for another time. It is sufficient to say here that habitat mosaics need to be expressed in terms of both beta and gamma diversity when considering biodiversity at the landscape scale. Alpha diversity may be important on a site by site basis, but thinking back to John Muir’s observation, they cannot be managed in isolation.
  9. Ecosystem dynamics. Ecosystems consist of dynamic mosaics of changing habitat patterns and associated species diversity. The idea of the “balance of nature” isn’t necessarily apposite because nature is dynamic, and ecosystems respond to both internal and external drivers. Here the only constant is change itself. We’ve largely swapped this dynamism in the UK for a highly managed landscape that responds mainly (at least in the short term) to economic and/or policy drivers and the whims land ownership. We are fortunate enough to live in a country that is tectonically stable and not subject to great extremes of weather and climate, thus the vast majority of us have no first-hand experience of natural disasters, poverty and hunger. Our country is, in the main, tame. We have made it so. Even conservation practice is focused on maintaining everything in stasis, underwritten as it is by FCS rules and the desire to garden and control. I’m reminded of a quote from Aldo Leopold’s A Sand County Almanac at this point; “We all strive for safety, prosperity, comfort, long life, and dullness. The deer strives with his supple legs, the cowman with trap and poison, the statesman with pen, the most of us with machines, votes, and dollars, but it all comes to the same thing: peace in our time. A measure of success in this is all well enough, and perhaps is a requisite to objective thinking, but too much safety seems to yield only danger in the long run. Perhaps this is behind Thoreau’s dictum: In wildness is the salvation of the world. Perhaps this is the hidden meaning in the howl of the wolf, long known among mountains, but seldom perceived among men.” While I’m grateful for the peace in our time, I am always embarrassed by our country’s lack of any real wild(er)ness.
  10. Linearity. The best idea you have in the whole post is about the “rewilding” of railway and motorway cuttings and embankments, though I don’t know why you think we’re somehow in denial about it. However, you are most certainly wrong about the lack of ecological differences between landscape scale rewilding like Carrifran and linear features such as railway embankments. Here we need to refer to our discussion of process and spatial scale, pattern and form. Railway and motorway embankments are linear in nature and so have extremely low area:perimeter ratios compared to most landscape scale rewilding projects (In the case of a railway embankment A << P where A = patch area and P = patch perimeter). Similarly, there are huge differences in patch depth or “thickness” with railway and motorway embankments being very shallow or narrow patch features whereas landscape scale rewilding projects having greater depth. Don’t get me wrong, these linear patches of unfarmed land that run alongside our railway and motorway network are ecologically valuable. They provide habitats for species associated with woodland and natural grasslands (e.g. kestrels and voles) but perhaps more critically they provide connectivity between larger patches of natural habitat so allowing for greater mobility of wildlife through another otherwise highly modified landscape.
  11. Biodiversity. While biodiversity is a useful concept, it is not the be all and end all of rewilding, nor even of conservation in the wider sense. Biodiversity is a numbers game that is complicated by spatial scale and pattern (see our discussion on alpha, beta and gamma diversity). The bigger the area, the more habitat types there are likely to be and so the greater the number of species present. This is the “species-area relationship”. We can map biodiversity hotspots by passing a spatial filter of a fixed size over a geographical area and adding up the total number species present within each group (see for example, Myers et al. 2000 and You correctly identify that rewilding may have both winners and losers in terms of biodiversity. Just as with your birds example, we might expect to see some species decline while others increase in rewilded landscapes. The critical thing from a rewilding point of view is what are the species and their relative numbers we might think of as natural within a rewilded landscape? Many of the species you appear to favour are perhaps only abundant in the landscapes you mention (i.e. uplands and grouse moors in particular) because of patterns of human land use and management. Again, I have already written about this here and here. You set up a false dichotomy when you agree with those of us that might ascribe greater importance to those species which are rare and/or beautiful. This is the “good nature, bad nature” dichotomy, and is a distinction that only humans make. Nature makes no such judgment. Whether we apportion special measures to protecting a particular species and/or habitat ought to depend on both careful consideration of its rarity and the threats it faces within the wider landscape setting. It is a moot point as to whether a species that is locally rare yet globally common deserves special protection when its habitat where locally rare, if left to rewild, might yield far more valuable and interesting habitats and species. After all, the UK has roughly one third the tree cover of our European neighbours, so the idea that we protect and promote treeless open landscapes over native woodland is again puzzling to me. However, at the end of the day, we need to be careful not to confuse biodiversity with wildness and naturalness. They are not the same things. I write about this in the Six Rules of Re(al)wilding here but to correct you, rewilding does not assume that more is always better, rather it assumes wilder equals better. These relationships between biodiversity and wildness do exist but they only kick in at certain (i.e. regional) scales. A multiscale analysis of biodiversity versus wilderness quality reveals that biodiversity is driven by potential evapotranspiration (PET) at the global scale (i.e. warm and wet climates promote high biodiversity, while cold/hot and dry climates tend to the opposite). At regional scales it is human landscape modification (i.e. agriculture, forestry, urbanisation, etc.) that limit biodiversity and so this is where a positive relationship with wilderness quality can best be seen. However, the relationship changes again when moving to local scales where microclimates and soil moisture seem to be the main drivers. You can read more about this here.
  12. Ecosystem service value. Much of the emphasis of your attack on rewilding seems, in the main, to focus on the lack of direct economic benefit… “Neither rewilded areas nor the motorway embankments are of any direct use to humans in terms of output of timber or food” (my emphasis). Here you assume that the function of land is to produce profit for owners and food and timber for the rest of us. Nothing wrong with that, but when we pursue such a world view to the exclusion of other benefits then we are missing out. There is a much greater value to land than that which can be sold solely for profit. Aldo Leopold recognised this in developing his “Land Ethic” and governments across the world are at last coming around to his way of thinking. The concept of ecosystem services classifies the “services” that the environment provides in four categories: provisioning, supporting, regulating and cultural (De Groot et al., 2002). Your view of land as a unit of production falls largely into the category of provisioning services, but tends to ignore the other three. Even in the UK, where much of our landscape is heavily modified by centuries of human management, the services a unit of land provides are not just about space and produce, but include providing drinking water, flood protection, erosion control, carbon storage and sequestration, nutrient cycling, recreational environments, wildlife habitats, etc. Even if you must think about land only in terms of human benefits, rewilding can still provide better value than agriculture in some circumstances or areas, especially where agriculture is marginal and highly dependent on economic subsidies. In these areas, the wider benefits to the wider population from other ecosystem services are perhaps better met from rewilding. This need not, as you seem to be suggesting, exclude all forms of productive and profit generating land use. While Knepp may not be rewilding-max, it is on the spectrum and provides a range of ecosystem services through rewilding-lite that are not solely based on producing food, though it is still a farmed landscape. I have written about this here. Similarly, in upland landscapes, some farmers are finding that less is more in terms of increasing profit margins through reducing fixed costs by reducing stocking densities. The benefits to the environment in terms of biodiversity, reduced runoff, landscape, etc. are obvious, yet there is still a farming presence in the landscape. See Nethergill Farm in Upper Wharfedale for example. I am very much of the opinion that we need to reverse the oft quoted 3 P’s mantra of “Profit, People, Planet” to be “Planet, People, Profit” since without a healthy functioning ecosystem (i.e. planet), there will be no people and certainly no profit! Yet the simple pursuit of profit tends to only benefit a few people and causes harm to many via environmental degradation. Rewilding offers the opportunity to reverse some of that decline in those places where the ecological balance sheet indicates that a return to nature is the most profitable and prudent policy.

I’m sorry if that was a rather long reply, but you raise a great many important issues and I felt that these needed a considered and detailed reply. I would never presume to think that this is a definitive and final answer however, nor is rewilding the answer to all of the country’s environmental problems (see previous post on #rewilding) but it does need the kind of careful and informed debate that we’re having here.

Happy New Year!

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