Although the European bison belongs to the same family as the domestic cow, you’d never mistake one for the other. Weighing in at up to a tonne, the bison is one beefy bovine. It has its own mannerisms, too: It scratches against tree trunks, rolls on the ground to take dust baths, and wraps its tongue around almost any vegetation—grass, leaves, branches—to feed.
These traits make the bison a dominating force on its surroundings. It can reshape ecosystems, refurbishing existing habitats and laying foundations for new ones. One rewilding project in Kent hopes to harness the bison’s natural engineering abilities in order to better manage the local woodland and increase its biodiversity, by bringing the herbivorous megafauna to the UK for the first time in thousands of years (and possibly ever).
On July 18, 2022, Kent Wildlife Trust and Wildwood Trust introduced a small herd of bison into West Blean and Thornden Woods, a nature reserve located a short distance from the city of Canterbury. The plan is to leave the bison to chow down on the plants, bulldoze trees, and generally rearrange the ancient woodland as they see fit. The idea is that the bison will achieve naturally what conservationists have struggled with: manipulating the vegetative growth to provide habitats for a greater range of flora and fauna.
“Bison ecology is quite different,” says Kent Wildlife Trust’s Stan Smith, who is leading the project, called Wilder Blean. “Bison are the largest living land mammal in Europe; they can do things more domesticated cattle can’t.”
Walking through the Blean Woods in summer 2021, he points out an area where the sweet chestnut has been coppiced to allow light to reach the forest floor and encourage the trees to regenerate. “This is the sort of thing that we hope those animals will be able to do for us, but not in such a uniform way.”
While the bison may be the main attraction for visitors to the Wilder Blean site, the project is more about what their presence may do for the rest of the woodland. The National Biodiversity Network’s most recent State of Nature report, published in 2019, highlighted woodland management as one of the key factors leading to species loss in the UK. Wilder Blean’s idea is that the bison will be able to take on some of this management, assuming a kind of natural curatorial role in the ecosystem. “We needed a way to get more nature in, but also for it to cost less and be more sustainable,” Smith says. The bison, he hopes, will munch on bark, killing non-native conifers and creating deadwood, a habitat for many invertebrates. They will rub against tree trunks or come crashing through foliage, their hulking bodies creating clearings for the light to shine through. They will roll around like oversize dogs, leaving dusty patches where reptiles can sun themselves.
That’s if all goes to plan. The European bison has never roamed the UK, and it’s debated whether its extinct relative, the steppe bison, ever made it over from the continent. And it’s impossible to predict the full impact of the bison’s presence on Blean Woods in advance. What Smith and his team expect to see is an increase in bioabundance (the total amount of life on the site) and biodiversity (the number of different species), although what exactly this might look like is hard to know. Which is why, ahead of the bison’s arrival, they set up the woods as a living, 560-hectare experiment.
Bison Haydes and Orsk loll on the muddy floor of their enclosures at Wildwood Trust, a wildlife park around 10 kilometers from Blean Woods, their long faces exuding a grouchy, “can’t be bothered” expression. At the gate of their enclosure stands the remains of a tree trunk they have scratched against; it’s thinned to half its width. “It’s almost smooth when you run your hand down it,” Smith says. “We’re hoping they’ll be doing that to a lot of the pine trees.”
Orsk and Haydes will not be part of the rewilding project. At 13 years old, they are too accustomed to paddock life, but will be trialing research gear such as GPS collars. They are kept in separate enclosures to prevent altercations: After the death of a third bison who had acted as a mediator between the pair, the power balance shifted from being in favor of Haydes, previously the dominant figure, to Orsk, who’d had enough of being pushed around. Their keepers say the bison have distinct personalities and changing moods; on a bad day, Haydes has been known to take his bucket of food and fling it around the field (and then appear remorseful when his dinner is soggy).
In the wild, European bison have a matriarchal social structure, similar to that of elephants. Adult females lead the herd, and a dominant bull mates with them. Younger bulls will often form a bachelor group somewhat separate from the herd, explains Yvonne Kemp, an ecologist who has worked with bison rewilding projects in the Netherlands and Spain: “The herd itself basically comprises older females, their offspring, and the dominant bull.”
Wilder Blean plans to combine individuals from herds in different countries to produce a more varied gene pool. A double barrier will separate the bison from visitors to Blean Woods: a 1.4-meter high electric fence like those used for livestock will run along the inside, encircled by a 1.9-meter high fence topped with barbed wire, with enough space for a quad bike checking for beaches to zip between the two. The fence is a requirement for keeping bison, which in the UK are considered a dangerous animal under the Dangerous Wild Animals Act 1976, but Smith says he’s more concerned about walkers and dogs misbehaving toward the bison rather than the other way around. “Really, it’s a people fence,” he says.
Bison are not the only animals being introduced. The 560-hectare area is divided into three enclosures. The first hosts the bison along with Iron Age pigs (a hybrid of a wild boar and a domestic pig) and Exmoor ponies. Both popular species for rewilding projects, these animals have different effects on the environment, which Wilder Blean hopes will complement those of the bison: the pigs rootle around in the soil, disturbing seeds and churning the ground with their hooves, while the ponies graze on different plant material. The second enclosure retains the pigs and ponies, but replaces the bison with longhorn cattle. The remaining 100 hectares will be left as a control. The idea is to test whether the animals result in the intended changes to the ecosystem, and whether bison bring different results to other bovines.
The general notion of rewilding is that nature be left to take its course with no human intervention, but this isn’t immediately practical or responsible. “Rewilding is a marathon with a sprint start,” says Alastair Driver, director of charitable organization Rewilding Britain. “You’ve got to be in it for the long term.” On a scale of one to five (where five is totally wild), he says, most rewilding projects in England would be at two. “It will take a long time to get toward that point where nature is taking care of itself,” he says.
Some intervention may always be necessary. “We want to be as hands-off as we can, but that doesn’t mean we won’t intervene if there’s an animal welfare issue,” says Stan Smith.
So it was that in 2021 Wilder Blean advertised for two bison rangers. The roles are filled by Tom Gibbs, previously a conservation officer for Herts and Middlesex Wildlife Trust (he speaks with great enthusiasm, as if he still cannot believe his luck that he gets to work with such an animal in the UK), and Donovan Wright, a former safari ranger who has worked with elephants, rhinos, wild dogs, cheetahs, and Cape buffalo in Southern Africa. Gibbs and Wright have been training with Haydes and Orsk to learn more about bison physique and behavior. “Sometimes they’ll bob their head up and down when you get too close,” says Gibbs, sitting at a picnic bench next to the enclosure. “We know to just sort of back off.”
A day in the life of a bison ranger will involve regularly checking the perimeter fences, tracking the animals’ movements, and monitoring their behavior and health. Gibbs and Wright will also be engaging with the public, including leading walking safaris to find the bison (aided by their GPS collars as well as conventional tracking techniques). “Bison—I was quite surprised—are very placid animals,” says Wright. “You look at them and you think, ‘Wow they’re quite intimidating,’ because of their size, but actually they’re very gentle giants.”
The problem with the woods is the trees. An ancient woodland and designated Site of Special Scientific Interest, Wilder Blean was owned by a bank and planted with conifers for timber production before being taken over by Kent Wildlife Trust. An impenetrable canopy prevents light from reaching farther down and allows for little variation in habitat. Dense forest is not the best for biodiversity.
Throughout 2021, the Wilder Blean team has been collecting data on the flora and fauna of the site, which they will use as a baseline to track future changes against. As we walk through the woods, ecologist Kora Kunzmann points out an antenna spiking up through the foliage. This is a GPS base station, which she uses when monitoring vegetation. Carrying a handheld GPS device, she enters the woodland and heads to one of 145 spatially-referenced points, the base sending signals to correct her path so she ends up in the exact spot. Here, she puts a peg in the ground and measures 9.77 meters in every direction, marking out a 300-square-meter circle with red string.
Inside this plot she records every plant species and their height. Most she can identify by sight, or else with the help of field guides. “Then I have a couple of botanist friends who get random texts here or there,” she says. Some plots are almost all bramble; others have a mix of canopy and ground flora and can take up to an hour and a half to document.
The main expectation of the bison is that they will thin the trees by ringbarking and rubbing against them, resulting in more light reaching through and a greater variety of plant life. In densely wooded areas, Smith says, “at the moment, you’ve probably got some very, very low stuff and some very, very tall stuff, and not very much in between.”
The Wilder Blean project, like many of its ilk, is inspired largely by the work of Dutch ecologist Frans Vera. In his influential book Grazing Ecology and Forest History, published in 2000, Vera questions the prevailing wisdom that vegetation in the lowlands of central and western Europe used to be dominated by closed forest. As a result of this assumption, he writes, farming has been given a lot of credit for increasing biodiversity, as grazing livestock creates different types of vegetation. But Vera argues that this theory ignores the impact of wild animals, and especially large herbivores, which could have played a similar role in creating more diverse landscapes.
To make his argument (which is not without objection), Vera draws on evidence including the effects of wildebeests grazing in the Serengeti and prehistoric pollen samples, and concludes that conservationists today need to update their frame of reference. He calls for large areas to be left free from farming and forestry, and for the reintroduction of once-wild mammals. “Cattle, horses, bison, red deer, elk, roe deer, and wild boar will have to be able to operate as wild animals once again,” he writes. “Without these ungulates the survival of the natural diversity is impossible in the long term.”
Not all herbivores are made equal when it comes to ecosystem-engineering. Bison occupy an intermediate position with regard to feeding habits; they are both grazers, eating grass, and browsers, tackling woody vegetation such as tree branches. And they eat a lot. “Debarking a tree or a shrub over a year or a few years has much more impact than taking some leaves off every now and then,” says Kemp. For this reason, several rewilding projects in mainland Europe have introduced bison, including one in the dunes of Kraansvlak on the Dutch coast, which the Wilder Blean team visited in preparation.
While Kunzmann gathers vegetation data on the ground, Robbie Still takes a macro view. As Kent Wildlife Trust’s GIS and remote sensing officer, he is in charge of the tech at the project—a sort of conservational Q. The team plans to get aerial images of the entire site at a resolution of 20 centimeters by sending up a DJI Matrice drone and methodically flying it above the tree line. “We’re not just on the remote control zooming around; it goes up and follows a very preplanned route,” Still says.
He will process the images with the open source software OpenDroneMap, using different sensors and tools to glean information about the vegetation. In addition to overall coverage, he can tell the width of trees by measuring the diameter of their canopy and their height by measuring the difference between the position of the drone and the objects it senses. Given that the woods was previously home to conifer plantations, much of it consists now of younger, smaller trees arranged in rigid rows—not ideal for biodiversity. “We’d hope that it will even out so it’s much more heterogeneous,” he says.
Using multispectral imaging, which picks up ultraviolet and infrared light as well as the visible spectrum, Still can even tell whether a tree is deciduous or coniferous based on the color signatures of the leaves: The deeper greens of conifers are distinguishable from the lighter palette of deciduous plants. This imaging could even give a sense of the trees’ health: Chlorophyll, the pigment responsible for photosynthesis, absorbs visible light, while plant cells reflect near-infrared light. Algorithms that calculate the difference between the various reflected wavelengths can give a sense of how much a plant is photosynthesizing—an indicator of its general fitness.
Still’s team conducted their first drone survey in the spring of 2022, when the trees were in leaf. They’ll repeat the survey a year later (after the bisons arrive) to see what’s changed. “Monitoring is incredibly important in ecology, but it’s often overlooked,” Still says. “Not because of any one oversight, just because of time.”
Back on the ground, Kunzmann directs us off the path and through the scrub, weaving through grasses, brambles, and birch to reach an insect trap hanging from an oak branch and flapping in the wind like a kite. It consists of four panes of fine mesh in a cross formation, with collection bottles at the top and bottom. Any insects that happen to fly in its path hit the mesh and end up in one of the bottles. “Flies and wasps and bees tend, when they hit something, to go upward, whereas beetles will go down,” she says.
There are 15 such traps across the site, five in each zone. Kunzmann will take down the bottles once a month and examine their contents to see how insect populations change in the different areas, including the section with the bison. First she will weigh the combined insect mass—a measure of bioabundance. The collected insects will then be stored and volunteers will help to identify the different species and track biodiversity.
As we make our way back to the path, brambles scratching at our ankles, she points out the yellow flowers of common cowwheat and the lance-shaped leaves of ribwort plantain, two food sources for the heath fritillary butterfly. This small, orange-and-brown-speckled butterfly is one of the UK’s rarest, but thrives in the Blean Woods. Sometimes known as “woodman’s follower,” it favors freshly coppiced woodland as a habitat.
Surveying invertebrate life is freelance ecologist and entomologist Graeme Lyons. With experience working on baselines for other rewilding projects, Lyons says he’s always been drawn to the bottom of the trophic pyramid: “As soon as things get a spine, I’m a lot less interested in them.”
Each month from April to September, he visits 24 different plots across the Blean Woods site, spending 30 minutes in each one. Here he employs the bug hunter’s toolkit to pluck his many-legged prey from their hidey-holes: There’s a sweep net to brush them out of shrubs, a beating stick to knock them out of trees, and a suction sampler to slurp them from grass and moss. At Blean, he says, the leaf litter is “absolutely amazing”; in spring he passes samples through a sieve and picks out rare specimens. He tries to identify as many of his finds as possible in field notes, but anything that can only be reliably identified under a microscope is popped into a labeled tube of 70 percent industrial methylated spirits for preservation, to be identified at home over winter when the fieldwork dies down. “I go from being outside every day for six months and walking five or ten miles a day, to sitting at a microscope and writing up reports for six months,” he says.
Open plots host more treasures than dense canopy. On a good day in May or June, the busiest bug months, Lyons says he can identify 50 to 70 different species on the spot. When we speak in September he still has that month’s rounds to do, but has so far identified a total of 578 species of invertebrate just from field notes, before any microscope work. “And the best thing is that there’s a really high proportion of those that are rare or scarce,” he adds. An arachnophile on a personal mission to record 400 different spider species this year, he takes particular delight in his sightings of Pistius truncatus, a critically rare shrub-dwelling crab spider last recorded in the UK in 2001 but which he has spotted twice in Blean Woods, and Walckenaeria mitrata, a money spider with an unusual bobble-shaped head which has never been spotted elsewhere in the UK.
Other species are much more common. Walk around and you will inevitably spot huge nests of the red wood ant, Formica rufa, even if you don’t particularly want to. “Formica rufa is a real driving force in terms of the ecology of the Blean Woods site,” Lyons says. Sometimes his sweep net is so full of them, he has to race to make his notes before they’ve eaten everything. Lyons is cautious of the ants, having once accidentally knelt on a nest while photographing a rare longhorn beetle, but has greater appreciation for some of the rarer invertebrates that occur in their wake, such as Coccinella magnifica, the scarce seven-spot ladybird (not to be confused with Coccinella septempunctata, the seven-spot ladybird most common in Europe).
There's no doubt that Blean Woods is already humming with invertebrate life. As well as seeing changes in individual species, Lyons’ data should be able to reveal trends that give broader insight into the site dynamics. Are species that prefer one kind of habitat increasing or declining? Are there more or fewer species that rely on flowers as a food source? Invertebrates, he says, are particularly good for tracking changes precisely because there are so many of them. “With greater diversity comes greater sensitivity to change,” he explains. “When you’ve got lots of different things jostling for pole position, you only have to change things slightly before that results in a big change in species composition.”
When he’s worked on other rewilding project baselines, he’s heard people say they don’t want him to find too much because they want to show the best possible change. But starting with a high baseline, he says, should only lead to greater improvement: “If you start with one and you times by ten you get ten, but if you start with 100 and you times by ten, you get 1,000.”
Lyons says that while he’d love the bison project to work, he’s “always cautiously skeptical about everything” and emphasizes the importance of an open feedback loop between monitoring and management. “I think if it doesn’t work in the way that is expected, then the most important thing is that there’s some self-reflection and rapid changing of the model,” he says. “I think that’s an area where rewilding can sometimes fail.”
One issue could be if the grazing pressure becomes too high. If the animals are too efficient at their task, they may keep the scrub down but also annihilate nectar sources that many invertebrates rely on. An open-minded approach is required, says Lyons; there are more ways for such a project to go wrong than right. “I often think of the natural world as like an infinitely large jigsaw puzzle,” he says. “And just as you think you’ve cracked it, you pan out and you’ve just done one tiny little corner.”
There's a limit to how “wild” rewilded woods can be. After all, the animals are being introduced and will be artificially controlled. Isabella Tree, co-owner of Knepp Estate in West Sussex, a 3,500-acre rewilding project that has become something of a flagship for the movement in England, says that it’s hard to define the term “rewilding,” which is largely contingent on the scale of a site. The smaller the space, the more intervention is required; your animals might be free-roaming, but only within permitted confines.
One concern is what’s known as carrying capacity. If animals are left to breed naturally, their numbers can increase exponentially, especially where there are no natural predators. Where too few grazing animals can result in closed forest, too many can have the opposite effect. “They’ll be taking out vegetation that could actually be creating wonderful habitats,” Tree says.
An overabundance of large herbivores can also pose animal welfare concerns. A rewilding project at the Oostvaardersplassen nature reserve in the Netherlands drew outrage when the numbers of animals grew to a point where they could no longer be sustained by the available grazing in winter, causing the suffering and death of thousands of red deer, Konik horses, and Heck cattle. As the site is fenced, the animals could not migrate in search of more food. Numbers are now controlled.
Not all agree that the die-offs were worse than can be expected in the wild; after all, nature can be brutal. A harsh winter or drought can take out whole herds, and a boom-and-bust cycle can occur when an initial overabundance of food causes populations to grow, only for them to then require more food and the population to decline. Rewilding projects often inhabit an awkward space where there are ambitions to mimic nature as closely as possible, yet without some of the gnarliest bits; and introducing animals to a site—even if you believe they should have been there all along—brings with it a greater responsibility for their well-being. Knepp, which has introduced longhorn cattle, Exmoor ponies, Tamworth pigs, and various species of deer, culls animals annually to keep populations at low levels.
For now, Wilder Blean has a license for ten bison—much less than the project’s ecologists believe the site can hold. As more bison are born, the site will likely import and export animals to and from other rewilding projects to control numbers and increase herd genetic diversity.
There will also be winners and losers among other species in the woods. While the team expects overall bioabundance and biodiversity to increase—that is the point of the project—there may be some species that fare less well in the new ecosystem. It’s also highly likely, Smith says, that something unusual will turn up at some point. At Knepp, the Purple Emperor butterfly appeared and established a colony. “If that happens, we’re not going to suddenly change everything that we’re doing and do everything to protect that one species, because in a truly functioning ecosystem, species will naturally increase and decrease over time and move from place to place,” Smith says.
For him, a personal marker of success will be when the first bison is born on site. He also wants to see the bison embraced by the local community, perhaps even adopted as a mascot; he recalls seeing a bison-themed bowling alley in a town local to Kraansvlak. For all the careful monitoring being done, he adds, he thinks the success of the project should be obvious. “I feel like you will just know,” he says. “I think you’ll just walk into the woodland, it’ll be thrumming with insects in the middle of summer, there’ll be so much diversity in terms of vegetation, people will be having a good time coming to watch the bison. You’ll just know.”
This article was originally published in the January/February 2022 issue of WIRED UK magazine.
