Ash dieback's impact on millions of trees in hedgerows and field edges could have serious consequences for the landscape and wildlife, experts have warned.
The Woodland Trust is using data which maps 280 million trees across England and Wales to assess the potential impact of tree diseases such as chalara ash dieback, which threatens to wipe out many ash trees, on the wider countryside.
The mapping, which allows experts to see the full extent of the tree canopy across the countryside, in hedgerows, field margins and roadsides as well as in woods and forests, reveals the importance of trees outside woodland.
In some areas there are up to half as many trees again outside woodlands as there are in wooded areas, including mature trees which form part of hedgerows or copses at the corners of fields.
The loss of such trees could significantly affect how the landscape looks, break up the connections they provide through the countryside for nature and reduce habitat, the Woodland Trust warned.
By analysing the data alongside estimates of ash trees in the countryside, with around 12 million ash trees outside woodlands, the trust is beginning to get an idea of the scale of the problem if they disappeared due to disease.
Initial indications suggest even minimal tree loss from outside woodlands would have a huge impact.
And with no requirements for such trees to be replaced, the trust is concerned that diseases such as ash dieback could spell a "one-way ticket" for trees being lost from the wider countryside.
Woodland Trust director of conservation Austin Brady said: "What's interesting about these trees in the wider countryside is that the majority will be native broadleaf trees, typically things like oak, ash, field maple and hawthorn, which are important not just for how the countryside looks but for wildlife too.
"A lot of these trees are quite old, so they are important habitat for everything from hole nesting birds such as owls and woodpeckers, roosting sites for bats, hosting all kinds of butterflies and insects and fungi that require mature trees."
He warned: "The difficulty with these trees in the wider landscape is there is no obligation on people to replace them if they die, so it's a one-way ticket for many of these trees.
"In lots of hedgerows, field corners and roadsides, it's difficult to imagine how these trees will get replaced."
And he said: "By the time people really notice the problem, we've almost left it too late to do something about it."
The organisation has launched a pilot planting scheme, with 1,000 subsidised "disease recovery packs", each with 45 native trees, which they are urging landowners and managers to plant in hedgerows, verges, field edges and watersides in the countryside.
The pilot is being targeted at five English counties badly affected by ash dieback: Norfolk, Suffolk, Kent, East Sussex and Northumberland.
All the trees the Woodland Trust provides are now grown in the UK from fully traceable seeds gathered in the UK and Ireland to prevent the importation of diseased trees.
A Defra spokesman said: "Our aim is to ensure that the graceful ash tree continues to have a place in our forests.
"British trees and woodlands are among our greatest natural assets, we have a duty to protect them for the next generation to enjoy. That is why we invest heavily into tree health research, including £4.2m since 2012 to specifically combat ash dieback."