The work will take three days, says the national park
More than 100 tonnes of heather are being airlifted onto a hill to repair a common damaged by wild fires more than 30 years ago.
The 120 heather bales are being lowered onto the 700m (2,296ft) peak of Hay Bluff, in the Brecon Beacons, as part of project to reduce carbon emissions.
The eroding peat bogs and moorland are the "largest known area of eroded upland" in the Beacons national park.
A lack of money has prevented work from starting on the site in previous years.
Hay Bluff in the Black Mountains straddles the border between Wales and England, but falls within the confines of the Brecon Beacons National Park.
It is also home to the largest remaining population of red grouse.
The park's wardens, the Black Mountains' graziers and the ancient Michaelchurch Estate are spending three days co-ordinating the airlift, which started on Monday.
Wintry conditions, the remote location and the altitude mean a helicopter is the safest and most convenient way carrying out the work on the common, which is a Site of Special Scientific Interest (SSSI).
The national park's senior ecologist, Paul Sinnadurai, said: "This site is the largest known area of eroded upland in the Brecon Beacons National Park which also makes it the largest area of restoration being undertaken by us at the moment.
"Back in 2003, we undertook a massive assessment of the conservation status of the hillside with our partner organisations and found that most of the hill was in an unfavourable condition including massive areas of upland erosion.
"We are very aware that areas of eroding peat bogs and moorland are contributing to greenhouse gas emissions, so rejuvenation work of this kind will not only help reverse that trend but will also recover conditions on the hillside.
"This will also improve grazing conditions for livestock."
The heather has been cut from Hatterrall Hill, a peak in the Black Mountains, and the work is being funded by Natural England.
Richard Ball, the national park's access officer, said: "The wildfires caused a lot of damage to this area and it will be a lengthy process to restore the SSSI back to its former glory.
"All our partners have taken great care to ensure that the methods we are using take into account the environmental sensitivity of the SSSI and the people who get enjoyment from accessing the site."