The autumn tree colours are appearing, but all is not quite what it seems. Horse chestnut leaves started falling weeks ago like crispy brown pieces of paper, a sign of leaf miners infesting the trees.
These are the caterpillars of a tiny moth, and a big tree can be infested with about 2m of these pests, which weakens the tree. Even more pernicious is a disease of horse chestnuts called bleeding canker, which can kill the tree.
These are just two of many new pests and diseases attacking British trees in recent years.
Native oak trees are being hit by acute oak decline, a disease causing black weeping fluid to seep from splits in the bark on the trunks of mature trees, and a severe infection can lead to the death of the tree within a few years. The disease is mostly found across East Anglia, the Midlands and south-east England, but it appears to be spreading.
In the 1970s, Dutch elm disease killed off Britain’s elm trees, since when there’s been a steady increase in new pests and diseases of our trees, often caused by importing infected trees without proper checks.
Climate change aggravates the problem, because these alien pests and diseases can become more established in a warmer climate, and existing ones can thrive.
Our woodlands are more vulnerable to serious tree pests and diseases because 77% of England’s broadleaf woodlands are made up of just five tree species - oak, ash, beech, sycamore and birch. It shows the urgent need to plant a wider range of native tree species.
