A charity committed to restoring Scotland's equivalent of the rainforest will plant its one millionth tree at the weekend.

Despite planting trees for more than two decades, Trees for Life still has more than 200 years of work to achieve its goal of covering more than 600,000 acres of land west of Loch Ness with a new Caledonian Forest of native species.

The landmark planting this weekend will be held at the charity's 10,000- acre Dundreggan Estate in Glen Moriston, which it bought in 2008.

Its vision is not to create a commercial forestry operation, but to restore a wild forest for its own sake, as a home for wildlife and to fulfil the ecological functions necessary for the wellbeing of the land itself.

Trees for Life's story began at an environmental conference in Findhorn in October 1986 when Alan Watson Featherstone – who at that time had no experience of conservation work, no funding and no access to land – made a commitment to delegates to launch a project to restore the Caledonian Forest.

He said the forest had once covered much of the Highlands, with native pinewood over 1.5 million hectares. But by the 1980s only 35 isolated remnants remained. Deforestation, largely through human activity such as land clearance, wood use and farming have taken a toll.

According to the charity: "Gone with the trees are all the large mammals, with the exception of the deer. Species such as the brown bear and the wild boar had become extinct by the 10th and 17th centuries respectively, while the last to disappear was the wolf, when the final individual was shot in 1743."

Trees for Life's practical conservation work began in June 1989, when volunteers placed tree guards around Scots pine seedlings in Glen Cannich.

Mr Featherstone, now Trees for Life's executive director, said: "Our Millionth Tree planting day will be a major milestone in our history, as well as a celebration of our work, and of Scotland's outstanding biodiversity and world class wild landscapes. It will be an inspiring reminder that despite the serious environmental challenges facing our world, we can make a positive difference and improve our quality of life at the same time."