An aristocratic couple struggling to run a large farm may not elicit much sympathy. And the tale of how they turned around a loss-making business may seem a niche interest. But Wilding, Isabella Tree’s story of how the Knepp estate in West Sussex was rewilded, has not only sold a quarter of a million copies worldwide and been translated into eight languages, it has inspired thousands of landowners, large and small, to rewild fields and gardens in an attempt to halt catastrophic biodiversity losses. The Knepp effect is about to get bigger with the publication of The Book of Wilding by Tree and her husband, Charlie Burrell. This 560-page behemoth is a practical manual for aspiring rewilders, from businesses and landowners to urban community groups and individuals with window boxes. The book gives guidance on everything from keeping water buffalo to reducing light pollution in gardens; from preventing flooding in cities to rewilding schools. The Book of Wilding came about because Tree, who was giving nearly 100 public talks a year before the pandemic, and Burrell, who has offered countless behind-the-scenes tours and guidance to policymakers and politicians, were besieged with practical questions about how to follow Knepp’s example. “We’re getting questions all the time, not just from people with land but who have a back garden or a window box,” said Tree. “Some people are very territorial about rewilding – they say, oh, it’s not real rewilding unless you’ve got 100 acres or free-roaming herbivores or apex predators. We wanted to get across this idea that rewilding is on a spectrum and everybody is on it, no matter how tiny the amount of soil under your jurisdiction is. It can even be a planter on your doorstep.” Knepp’s 3,500 acres were a conventional dairy and intensive arable farm until the turn of the century, when financial losses and the visit of an ancient tree expert convinced Burrell to stop farming. Fields scrubbed up, free-roaming longhorn cattle, pigs and ponies were introduced, and wildlife flocked back. Last summer more than 50 singing male nightingales – one of Britain’s rarest birds – were recorded at Knepp alongside near-extinct turtle doves. The rewilding project is considered the best site in Britain for the elusive purple emperor butterfly, and reintroduced beavers and storks are thriving. For years, the farm’s transformation was greeted by indifference from other landowners and drew hostility from neighbours who complained that the farm spread “weeds” such as ragwort. But the publication of Wilding in 2018 was a turning point, and suddenly landowners large and small started following Knepp’s example. “Until it was explained in a book, in a story, nothing was happening,” said Burrell. “Then the book came out and it was a constant, constant flow of visitors.” Forms of rewilding – or “wilding” (the r-word is particularly controversial in upland Britain) – have been embraced by high-profile farmers, from sheep farmer and writer James Rebanks in Cumbria to Jeremy Clarkson in the Cotswolds. Large landowners have turned to rewilding in the hope of matching the profits at the formerly loss-making Knepp. The farm’s finances are boosted by lucrative business rentals in its old buildings and its glamping and wildlife safaris are now worth £1m each year. The conventional farm employed 23 people before it shut down but the rewilded enterprise employs more than 50, with another 50 jobs to be created when Knepp’s restaurant and farm shop, run by the couple’s son, Ned, opens. Knepp sold £350,000 of free-range meat produced on its land direct to consumers last year. Burrell has also launched a company, Nattergal, which is buying farms to restore nature as a commercial enterprise, with new revenues not from producing food but from payments for biodiversity credits, as well as carbon credits and government support for ecosystem services such as reducing flooding or improving water quality. The company is rewilding a 1,525-acre farm in Lincolnshire it bought for £13.75m and has begun rewilding its second acquisition, a fenland farm in Norfolk. Knepp has also had a profound impact on conservation charities and community groups, many of whom have embraced its rewilding model. Charities including Suffolk Wildlife Trust, Hampshire & Isle of Wight Wildlife Trust and Radnorshire Wildlife Trust have bought farms on which they are restoring nature by stopping intensive farming and introducing “extensive” free-roaming livestock, (which may produce some food via free-range meat). Kent Wildlife Trust has introduced bison as well as free-roaming pigs and ponies into the ancient Blean Woods near Canterbury as part of an ambitious rewilding scheme inspired by Knepp. Evan Bowen-Jones, chief executive of KWT, said: “Knepp is an iconic project in UK conservation terms now. All these serendipitous benefits have proved the case around things like nightingales not being dependent upon coppicing.” He also noted that letting pigs roam freely had churned up the ground and allowed for goat willow, the favoured food of purple emperor caterpillars, to regrow. He said Knepp showed that “the open-ended restoration of native habitat in a dynamic way has huge biodiversity and bioabundance benefits that have not been replicated anywhere else on sites of special scientific interest (SSSIs) or national nature reserves or all these other alleged jewels in the crown that we’ve been trying to preserve against the tide of climate change. “We need to be trying different things and the fact that Knepp tried something so different and it has proven so successful is fantastic.” Knepp has attracted criticism too. Purist rewilders say its use of livestock to mimic the grazing of extinct herbivores is not meaningful rewilding because there are no apex predators and it is not at a landscape scale. Many conservation scientists oppose rewilding nature reserves, predicting that Britain’s rarest species will become extinct without targeted management, while other conservationists wonder if Knepp’s successes will be sustained. Ben McFarland, director of wildlife conservation and recovery at Suffolk Wildlife Trust, which recently bought an organic farm to return to nature as Martlesham Wilds, said: “Knepp is brilliant and they’ve done something really special. But scrub is transitional habitat. Will their grazing regime retain scrub levels where they are at the moment? The jury is out. If scrub becomes mature woodland, will they put their hands up and say, ‘We’ve lost our turtle doves but we’re wilders, we’re going to keep going’ or are they going to say, ‘We love our turtle dove, we’re going to do a bit more intervention’? I’d do more intervention and keep the turtle dove.”