Europe could be about to lose all of its ash trees, as the plants are being hit by disease on two separate fronts. While the fungus that causes the deadly ash dieback has already made its way across much of the continent, including crossing into the U.K. in 2012, a new threat has arrived in the form of the emerald ash borer, an invasive beetle that has spread from Asia. In the largest ever survey of the ash tree, researchers have come to the bleak conclusion that its odds of survival are not great.
The species is incredibly widespread, being found across much of Europe from Spain in the west to Russia in the east, and is a common feature not just in deciduous forests, but also in many cities. Yet since 1992, the European trees have been suffering from ash dieback, also known as Chalara, which is caused by the Hymenoscyphus fraxineus fungus. Starting at the tips of the leaves, the fungus causes them to go brown and die, spreads to the branches, the trunk, and eventually kills the entire tree. The fungus is already thought to affect over 2 million square kilometers (770,000 square miles) of forest.
The fungus has caused widespread declines of ash throughout Europe, although not all trees succumb, and while some suggest that between 15 and 20 percent do not die, others predict that it could kill almost 95 percent of all ash trees in the U.K. alone. But those trees that do pull through are now at risk of being hit again by the emergence of the borer beetles, and the researchers simply don’t think that the species can survive a second round. The beetles themselves don’t harm the tree, but their larvae bore under the bark and into the wood, eventually killing it.
Ash dieback has been sweeping across Europe, killing many trees and even entire forests, as seen here. debs-eye/Flickr CC BY-NC-ND 2.0
“Between the fungal disease ash dieback and a bright green beetle called the emerald ash borer, 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,” explains Dr. Peter Thomas, who co-authored the paper published in the Journal of Ecology. While France lost over 90 percent of its elms from Dutch elm disease, which also came over from Asia like the borer beetle, it is estimated that in the U.K. over 25 million elm trees died.
The elimination of ash trees would be catastrophic not just for the species itself, but also the hundreds of creatures that rely on them. More than 1,000 have so far been associated with ash, including 12 species of birds, 55 mammals, and 239 insects. “Of these, over a hundred species of lichens, fungi, and insects are dependent upon the ash tree and are likely to decline or become extinct if the ash was gone,” says Dr, Thomas. “If the ash went, the British countryside would never look the same again.”
Main image: AJ Cann/Flickr CC BY-SA 2.0