Lord Randal Plunkett strides through the hip-high grass of Dunsany, a 650-hectare (1,600-acre) estate in the middle of Ireland, trailed by an invisible swarm of midges and his four jack russell terriers: Tiny, Lumpy, Chow and Beavis & Butt-Head.

The cattle and sheep are long gone, so too are the lawns and many of the crops. In their place is a riot of shrubs, flowers and trees, along with insects and creatures that call this fledgling wilderness their home.

It is probably Ireland‘s most ambitious attempt at rewilding on private land, an attempt to recreate a vanished landscape in a swath of County Meath, 20 miles north-west of Dublin.

According to the UN, the world needs to rewild and restore an area the size of China to meet commitments on nature and the climate – but not everyone applauds Ireland’s pioneering effort. “You’d be surprised when you live in a castle how many times people think you’re an idiot,” says Plunkett, the 21^st baron of Dunsany.

The 38-year-old, who was once a steak-eating bodybuilding death metal fan with no interest in land, is now vegan and on an environmental mission.

He still loves death metal, and sports a ponytail and (fake) leather jacket, but he decided seven years ago to turn over 300 hectares of his estate to nature – no livestock, planting, sowing or weeding.

Some people considered it disgraceful neglect of an estate associated with agricultural innovation, he said. “They just thought I was a complete waster. Decadent, a fool. One farmer said I should be ashamed of myself for destroying the farm.”

Plunkett says vindication has come in multiple forms. Before, the estate had just three types of grass, now it has 23. “I didn’t do it, the birds did.” Trees regenerated and multiplied – oak, ash, beech, Scots pine and black poplar. “I see a lot of saplings growing that I haven’t planted.”

Lush, diverse vegetation attracted butterflies and other insects – “it’s like a buffet for them” – which drew more birds, including rarely seen woodpeckers, barn owls, red kites and sparrowhawks.

“I heard the call of a corncrake. I had to Google it to know what it was.” There have also been sightings of snipe and stoats and an unconfirmed report of red squirrels.

Botanists from Trinity College Dublin have started visiting to study the transformation. Last year Dunsany became the first Irish member of the European Rewilding Network, an advocacy group for wildernesses across Europe. In one striking success, wildcats have returned to Dutch forests after centuries of absence.

Ireland has a poor environmental record, despite its green image. In the 1980s it had more than 500 rivers and lakes with pristine water, now there are just 20, according to the Environmental Protection Agency. About 250,000 hectares of wetlands have been lost in the past two decades. Pollution from farming is widely blamed.

The state has an ambitious tree-planting scheme but critics say too many of the new forests are sitka spruce, which carpet soil with acidic needles and smother wildlife.

“We’re a fantastic country for remembering our history and culture but absolutely terrible at looking after our environment,” says Plunkett.

The Plunketts are one of Ireland’s most storied families. Installed at Dunsany since 1402, their fortunes rose and fell over the centuries.

Oliver Plunkett, a Catholic archbishop, was executed in England in 1681 on suspicion of a “popish plot”; he was canonised in 1975. Horace Plunkett championed rural development and farming innovations in the early 20^th century. Other Plunketts were leading figures in politics and the arts.

Randal became the 21^st baron after his father, Edward, died in 2011. Educated in the US, England and the Netherlands, he wanted to make films, not manage a farm and high-maintenance castle. “I’ve never been a country bumpkin. I saw it as a burden, a life of servitude.”

Uneasy about the climate crisis, at first Plunkett tried converting the estate to organic farming. When concern about the planet turned to alarm, he became vegan and decided to let a chunk of the estate revert to nature.

He also resolved to block poachers and horse-mounted hunters: “I decided to go to war.”

Plunkett patrolled the estate’s forests and meadows, confronted interlopers, filmed them, summoned police and threatened legal action. “I’ve been threatened to my face and on social media with being beaten up, having my tyres slashed, you name it.”

He is bracing for the resumption of hunting season: “Come September, all hell breaks loose.”

Plunkett runs Dunsany on income from the remaining farm land, which is mostly tillage, and from film-making.

His first full-length indie feature, The Green Sea, which he wrote and directed, was released last month. A dark mystery filmed at Dunsany, it tells the story of an American writer who moves to a remote Irish setting and is haunted by characters from her novel. The title came from the landscape around the castle. “It’s a sea of green.”

Plunkett, who recently had a baby daughter with his fiancee, allows small groups to visit the estate but does not want big crowds. “Paths, signs, a cafe? No.”

He intends to continue making films – the next is a horror film – and to look after the estate in hope his daughter will eventually take over.

In keeping with family tradition, the vegan baron will not purge inherited furniture – not even the tiger-skin rug with head – but adds his own touches. “I might be the first generation here to bring in Ikea,” he says.