According to this article an infection is currently threatening Britain's oak trees. The disease which has killed millions of oak trees in California is now a threat in Britain. It is thought to be as deadly as Dutch Elm disease which is responsible for wiping out millions of trees. In an effort to control it thousands of diseased trees are being felled. In 2003 it was present in a handful of oak trees but it has since jumped species and began infecting Japanese and European larch trees. Larch makes up around 5% of the forest cover in Britain so it has the potential to spread rapidly. The main problem is people carrying spores from infected forest areas on their tyres and boots.