Wales' Celtic rainforests in £6.5m restoration project
They have flourished for at least the last 400 years, but Wales' ancient oak rainforests are under threat.
Invasive species and poor management have all put unsustainable strain on the Welsh woodlands.
On Thursday, experts are gathering to officially launch a £6.5m bid to reverse the decline.
Celtic Rainforests Wales aims to eradicate rhododendron plants and thin out conifer plantations so native trees and wildlife can thrive.
The project is being funded with £2m from the Welsh Government and access to a further £4.5m from the European Commission's Life nature and biodiversity programme.
The rainforest scheme is a partnership of environmental organisations, including RSPB Cymru, the Woodland Trust, Natural Resources Wales, and Welsh Water.
It is being led by the Snowdonia National Park Authority, which is one of five areas of Wales covered by the project.
Other woodlands include the Meirionnydd oak wood and bat sites in Gwynedd, Artists Valley in Ceredigion, the Elan Valley in Powys, and Cwm Doethie-Mynydd Mallaen spanning Carmarthenshire and Ceredigion.
Environment minister Lesley Griffiths said Celtic rainforests were "critical to Wales' wellbeing".
"This project is strengthening the resilience of some of our most precious ecosystems and making a vital contribution to Wales' response to the current climate and ecological crises," she said.
Wales' ancient oak woodlands
95,000hectares of ancient woodland in Wales
Over 3,000mmof rain can fall in some parts of the Welsh woodland
Halfthe world's Western Atlantic sessile oak is in Wales
As well as targeting non-native rhododendron and non-native conifer trees, the scheme will look at how introducing grazing by cattle, sheep and ponies in some woodlands could improve land management.
Project leaders said there would also be a focus on community involvement.
"It's not just important to restore these sites - it's important to get people involved in them, to get them to share the excitement, the magic that they can invoke," said Natalie Buttriss, director of the Woodland Trust in Wales.
"If people really value something, they'll help to protect it."