Four woodlands - one each in England, Scotland, Wales and Northern Ireland - totalling 1000 acres will be planted as part of the £12 million project to create a lasting memorial to the Great War.
More than three million free trees will also be provided for schools, communities and youth groups to help create hundreds of woods that will stand as a legacy to those who died, fought or lost loved ones in the 1914-1918 conflict.
The Woodland Trust has announced plans to plant the English Centenary Wood on a 640-acre site near Epsom, Surrey. The site, at Langley Vale, will be home to more than 200,000 trees.
Sites have also been identified for the centenary woodlands in Scotland, Wales and Northern Ireland, but will not be revealed until later in the year.
Members of the public will be able to dedicate trees to ancestors at the woods.
The Woodland Trust, which will deliver the project in partnership with Sainsbury's, said it hoped land owners and communities across the country would also get involved in creating hundreds of other woods, containing millions of trees.
Trust project director Karl Mitchell said: "We hope to see many thousands of people getting involved by planting their own tribute or dedicating trees in memory of loved ones."
The first trees will be planted this autumn and the project will run until 2018.