A £3 million project will return some of the UK's post-Second World War conifer plantations to original native woodland amounting to the an area almost twice the size of Edinburgh, with some of the most significant sites in Scotland

The ambitious scheme will result in stretches of the Great Glen; round the shores of the Dornoch; Cromarty and Moray firths and the slopes of the Cairngorms being prioritised for restoration.

Conservation charity The Woodland Trust aims over five years to replace the likes of the fast-growing Sitka spruce, which is native to the west coast of North America, with indigenous species such as oak, birch, Scots pine and alder.

The conifers will be removed gradually from a plantation to allow more light to penetrate the canopy, encouraging specialist native species to grow back.

Ancient woodland covers just 2% of the UK's land area. It is classed as land that has been continuously wooded since 1600. Its unique, undisturbed soils and ecosystems are home to 256 rare or threatened species of wildlife.

Backed by £1.9m from the Heritage Lottery Fund, the scheme will begin on the ground next year and aims to restore almost 130,000 acres of woodland from Sutherland to Exmoor, an area one-third the size of London or twice that of Edinburgh. At least 8000 acres will be restored on the Scottish sites.

The trust is to work with more than 1000 landowners, offering information, advice and training to help them restore conifer woods to their natural woodland state.

It has appealed for public donations to make up a £530,000 funding gap.

Tim Hodges, the charity's woodland restoration programme manager, said: "The key to the project is the urgency. Many conifer plantations which have been planted since the Second World War are approaching maturity and due to be felled.

"By working with landowners now to begin restoring these woods, there is a once-in-a-lifetime opportunity to prevent these woods being restocked with a further round of conifers which could compound the damage already done to the wildlife that remains. We have a responsibility to restore our ancient woods and protect them for future generations."

A Woodland Trust Scotland spokesman said: "This is a really exciting project. Some 18% of Scotland's land area in covered by woodland but only 4% is native woodland. So a major restoration project like this will be a major boost to indigenous species."

Meanwhile, Environment and Climate Change Minister Paul Wheelhouse is urging people in Scotland to get involved with a UK-wide initiative that aims to build a comprehensive picture of tree health issues.

The survey of the health of Britain's broad-leaved trees is part of the Open Air Laboratory project, which aims to involve lay people in "citizen science".

The survey has been designed by Imperial College London in partnership with Forestry Commission Scotland, which has also funded 3000 survey packs for distribution around the country as part of its commitment to the Year of Natural Scotland.

Mr Wheelhouse said: "I very much welcome this timely project, which gives people of all ages and at any location in Scotland the opportunity to help us in the ongoing effort to protect our trees and forests. Even with the best will in the world scientists, foresters and woodland managers can't check every single tree or woodland quickly enough to give us a comprehensive picture of the state of health of our trees."