Hope from the ashes: This new generation of ash trees is more resistant to dieback

In a rare, real-world example of Charles Darwin’s theory, a new generation of ash trees is evolving genetically, making them more resistant to ash dieback, finds a new study undertaken by scientists at the Royal Botanic Gardens, Kew and Queen Mary University of London. This natural selection is manifesting in thousands of locations within ash tree DNA, says the paper, published in Science, offering a huge amount of hope for the future of the species.

When ash dieback, caused by the fungus Hymenoscyphus fraxineus, first arrived in Britain in 2012, an emergency COBRA meeting was formed and the disease has since spread rampantly across the countryside. It is predicted that up to 85% of our ash trees will perish — a tragedy that now comes with the small silver lining of ‘a revelation for scientists,’ says Richard Nichols, professor of Evolutionary Genetics at Queen Mary University of London. ‘Our detection of so many small genetic effects was possible because of the exceptional combination of circumstances: the sudden arrival of such a severe disease and the hundreds of offspring produced by a mature tree.’

Country Life Gardens Editor Tiffany Daneff explains how, like many of us, she has ‘visited so many gardens where ash have had to be cut down — hundreds went along the stream at Evenley Wood Gardens in Northamptonshire, for example, and many at Glyndebourne in East Sussex — and, even though this has offered opportunities for new plantings of different species, garden owners across the country will be greatly encouraged by this development’.

Richard Buggs, senior research leader at Kew and professor of Evolutionary Genomics at Queen Mary University of London, adds: ‘We are so glad that these findings suggest that ash will not go the way of the elm in Britain. Elm trees have struggled to evolve due to Dutch elm disease, but ash are showing a very different dynamic because they produce an abundance of seedlings upon which natural selection can act when they are still young. Through the death of millions of ash trees, a more resistant population of ash is appearing.’

However, although this is hugely positive news, it may not be enough to save the ash tree altogether and we have a lot of work to do. ‘The existing genetic variation in the ash population may be too low, and as the trees become scarcer, the rate of selection could slow. Human intervention, such as selective breeding and the protection of young trees from deer grazing, may be required to accelerate evolutionary change,’ explains Dr Carey Metheringham, whose PhD research included this study.

Defra has invested more than £9 million in ash dieback-related research since 2012, including the funding of this study, which was carried out at the Woodland Trust’s Marden Park wood in Surrey.