Twenty teenagers from across the UK are taking control of the management of more than 300 acres in the Brecon Beacons National Park.
The nature conservation project is thought to be the biggest in the world to be led by children.
Aged 12-17, the "youth leaders" will restore wildlife habitats and develop sustainable farming and forestry.
Local farmers and wildlife experts will be brought on board to help them with their ideas.
The teenagers will be involved in all aspects of managing the Penpont Estate in Powys, including planting trees, rearing livestock, dealing with finance and publicising the project.
The team will be expected to plan work with local school pupils and others to help them learn more about nature conservation.
"I feel very lucky - it's a really exciting opportunity," said Hannah from Sheffield, one of the participants selected by charity Action for Conservation.
"It's difficult to find people who are as passionate as I am about nature so it's nice to be with so many of them in one place."
"I can't wait to get started," added Deep from London, while Lily from Cambridge said it would be "absolutely incredible in terms of youth involvement in helping out the environment".
The young people will visit Penpont four times a year, and also keep up with progress via regular meetings held over video link.
The project's timeline is open ended and the idea is that as the participants grow up and move on to the world of work or university, others will take their place.
Gavin Hogg, owner of the Penpont Estate said one of the biggest lessons he hoped to learn from the project was "letting go of control, allowing the young people to have freedom of choice and management".
He wants to see greater biodiversity across the 2,000 acre estate and hopes neighbouring farms will come on board too.
But he insisted there will also be a big focus on continuing to farm the land to produce food, as well as conserve nature.
"We're very keen that we don't just become one of these glorified rewilding projects - we have to have food security and we have to have biodiversity security - the two need to run side by side."
"I hope the project will be a success and others will come here, learn from it and then take the experience away and create their own little bubbles for wildlife."
Action for Conservation's chief executive Hendrikus van Hensbergen said it wanted to tap into the momentum of the recent climate change strikes by school pupils.
"We hope [it] will inspire others and cause a ripple effect," he said.
Youth leader Helen from Derbyshire added: "What we really want is for this to be a pioneering project, that others take on our sustainable aims and hopefully our passion for nature spreads across the country."