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Foreign Invaders infiltrate Britain's ancient woodlands

Foreign Invaders infiltrate Britain's ancient woodlands

In July 2013, a large, strangely shaped beetle emerged from the fabric of a wooden chair that had just been bought in the UK. The inch-long creature had developed inside the chair’s wooden frame before it ate its way to the surface and burst through the seat’s plastic covering – much to the alarm of its purchaser. Crucially, the furniture had been made in, and imported from, China.

Analysis by us, it showed the beetle was a Japanese pine sawyer. Worse, the beetle was found to be infested with a second serious pest: the pinewood nematode worm. In combination, the beetle (Monochamus alternatus) and worm (Bursaphelenchus xylophilus) have been linked to widespread damage to pine forests in China and Japan. Now it is spreading through parts of Europe.

But the warning was clear. Britain and its trees are coming under increasing pressure from a range of foreign pathogens, a point underlined last week when scientists revealed that the horse chestnut tree was now being threatened by a different invader – the leaf miner moth, which has spread through England and Wales, and was recently discovered in Scotland.

The leaf miner (Cameraria ohridella) does not kill conkers directly but leaves trees weakened, while their seeds are small and shrivelled. Younger trees are killed off, and mature trees are left susceptible to deadly diseases such as bleeding canker.

The threat to the British landscape is one of the worst since Dutch elm disease wiped out millions of trees in the 1970s. It includes ash dieback (Hymenoscyphus fraxineus), which is caused by a fungus that quickly kills young ash trees, and older trees more slowly. Our scientists have warned that the fungal spores spread so easily that the disease could eventually wipe out the UK’s estimated 80 million ashes, one of our commonest trees.

The British tree is being ravaged as never before, it would seem. “There is no doubt that the threat from foreign pathogens to our trees is growing,” said Professor Rick Mumford. “You can see a clear trend. More and more are appearing, and dealing with them is getting harder and harder.”

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