Ash die-back seems to get little attention in the news media. This disease is going to kill 80% of Britain’s ash trees, cost billions, and threaten native species that are dependent on the tree.
It is caused by a fungus Hymenoscyphus fraxineus, which originated in Asia. It has little effect on Chinese ash species but the European ash evolved without exposure to it and the effects have been devastating over the last 30 years. The disease first emerged in the south east of England. While it may have arrived naturally, we were importing thousands of infected ash saplings from Europe up until 2012.
The fungus invades the nutrient channels in the wood and the tree’s response to this results in the channels becoming blocked. The branches distal to the blockage die. Dormant buds proximal to the affected branch sprout, giving the typical appearance of bare branches with new growth close to the trunk. Dark diamond-shaped patches develop on the dead branches. Young trees are affected most severely. Older trees show some early resistance but eventually die. Once you know the signs, it is obvious the disease is everywhere. Newly-established trees planted at great expense for their amenity value are succumbing.
A small number of our native ashes appear to be resistant but recovery by the spread of these varieties will take at least 50 years. The cost in terms of loss of the beneficial effects of the trees and clearing away the dead ones has been estimated at £15 billion by the Woodland Trust.
The Bohemian Waxwing 