The biggest-ever ash survey warns that ash trees face several serious problems, including the immediate threat of ash dieback and ‘potentially devasting’ emerald ash borer beetle, which is spreading across Europe.
“It is likely that almost all ash trees in Europe will be wiped out – just as the elm was largely eliminated by Dutch elm disease,” says Dr Peter Thomas, who has written the report.
Ash dieback causes death of leaves, branches and eventually the whole tree.
Caused by the fungus Hymenoscyphus fraxineus, it was first seen in eastern Europe in 1992 and in Britain in 2012.
The disease now covers more than 2 million km2, from Scandinavia to Italy.
In assessments of the likely impact of ash dieback in Britain the worst-case scenario is 95 per cent mortality of ash.
Like ash dieback, the emerald ash borer is native to Asia.
It was accidentally introduced to North America in 2002, where it has killed millions of ash trees.
Recorded in Moscow in 2003, it is spreading west and is believed to have reached Sweden.
The adult beetles feed on ash leaves and do little damage, but the larvae bore under the bark and into the wood, killing the tree.
“Our European ash is very susceptible to the beetle. It is only a matter of time before it spreads across the rest of the Europe – including Britain – and the beetle is set to become the biggest threat faced by ash in Europe – potentially far more serious than ash dieback,” says Thomas.
The loss of ash would change the UK countryside and its biodiversity.
More than 1,000 species are associated with ash or ash woodland, including 12 birds, 55 mammals, 78 vascular plants, 58 bryophytes, 68 fungi, 239 invertebrates and 548 lichen species, many of which are threatened or endangered and likely to decline in number and potentially become locally extinct.
Recent research suggests that some ash clones are resistant to ash dieback, offering hope that breeding programmes could produce trees able to survive the fungus.
But resistance to dieback will not protect trees against the emerald ash borer if it reaches the UK.
4 facts about ash trees in the UK
- Ash trees are native throughout most of the UK.
- The species is an important urban tree in our towns and cities.
- They are the second most abundant tree (after oak) in woodland.
- Outside woods there are 2.2 million ash trees in Britain.
- Ash is our most common hedgerow species and the length of woody linear features (hedgerows and tree lines) composed of ash in the UK is almost 100,000km.
The full review by Dr Peter Thomas has been published in the Journal of Ecology.