Four woodlands are set to be created across the UK as part of a £12m project by the Woodland Trust to mark the centenary of the World War One.
The "centenary woods" - one each in England, Wales, Scotland and Northern Ireland - will be formed by volunteers planting trees.
The woods are expected to span more than 1,000 acres collectively.
Three million free trees will also be available to schools and community groups to plant, the charity said.
The trust said the trees would "transform the landscape into rich, vibrant and flourishing woodland", and prove to be a fitting legacy for those who lost their lives in the 1914-18 war.
Sites in Wales, Scotland and Northern Ireland are yet to be chosen for the woodlands, while for England a 640-acre site near Epsom, Surrey, has already been earmarked.
The site at Langley Vale will be bigger than the Olympic Park and have space to include 200,000 trees, and it will link up pockets of existing woodland.
Woodland Trust project director Karl Mitchell said: "The trees planted during the course of this £12m project will stand for hundreds of years, providing a lasting tribute to all those involved in the First World War.
"We hope to see many thousands of people getting involved by planting their own tribute or dedicating trees in memory of loved ones.
"As well as representing enormous strength and bravery shown by the nation during World War One, the trees that are planted during the course of the project will help strengthen our natural landscape, increasing its resilience to the threats posed by pests and diseases."
The first trees will be planted this autumn, and the project is set to continue until the autumn of 2018.
Schools and community or youth groups will be able to apply for a share of the three million trees, which can be planted anywhere the individual school or group chooses.