Britain's ancient forests are in danger as climate change threatens native trees such as oak, beech and ash, new research has claimed.
Traditional woodlands are facing their biggest upheaval since the last Ice Age as global warming and disease threaten indigenous species that have flourished in Britain for thousands of years.
Experts have predicted that native trees are likely to retreat from the warmer regions in the south of the country leaving forests dominated by imported species that are better adapted to dealing with dry conditions.
Trees such as the Corsican pine and Spanish oak, which were introduced to Britain by the creators of ornamental gardens, are likely to replace traditional species.
The strong survival instincts of foreign invaders has been demonstrated by the success of the American giant redwood, which is thriving in the wild.
Disease is proving to be another major threat to forests in the south, south west and East Anglia, according to the research which is to be presented to the British Ecological Society next month.
Studies have shown that half of Britain's two million horse chestnut trees are suffering from bleeding canker, which disfigures the trunk and branches.
Oak and beech trees are being hit by sudden oak death, a fungus carried by rhododendron plants which has devastated oaks on America's west coast.
Beech is also particularly vulnerable to summer drought, because of its shallow root system.
At the National Trust's Kingston Lacy estate in Dorset an avenue of beech trees planted over 170 years ago is dying as a result of recent dry summers and wet winters. A total of 150 have had to be felled.
While studies of British beech trees by Surrey Wildlife Trust over the last two decades has seen a decline in their growth and health.
"Climate change will have a (big) impact over the next five decades," Dr Keith Kirby, a woodland scientist with Natural England, said.
"Our woods will change. Many species will cope with some warming but there is uncertainty about what happens with extreme events such as droughts and storms, which we expect to become more frequent."
Forestry Commission researchers have predicted that numbers of oak and beech will decline sharply across the south east by 2050. Such changes would alter the environmental landscape across the Chilterns, Cotswolds, North Downs and South Downs.
James Morison of the Commission's environmental group suggested that the changes could be subtle with native species being replaced by similar European species.
It is difficult to make accurate forecasts about changes to the environment due to climate change as scientists are generally unsure how the global temperature rise of 2-3 degrees Centigrade predicted for 2050 will affect Britain.
Some experts believe that the planting of trees that are better adapted for dry conditions ought to be encouraged as the most sensible method of preserving wooded habitats.
Tony Kirkham, head of the world renowned arboretum at Kew Gardens in London, said: "We need to look further afield for new species. The right way to go is to plant different strains of our native trees, perhaps using seeds from France or Germany."