Ash dieback in the Chilterns

Date: 09th September 2024

First identified in England in 2012, ash dieback is now thought to have been in the country since 2006. The impact of this disease has become more noticeable in recent years.

After beech, ash is the second most common woodland tree in the Chilterns National Landscape. It is probably the most common tree found outside woods and often grows in hedges and gardens. Sadly, many ash trees are affected by a fungal disease known as ash dieback. Caused by Hymenoscyphus fraxineus, fungal spores are spread through the air.

Originating in Asia and gradually spreading west through Europe, ash dieback has infected millions of trees. Symptoms include leaf loss, wilted and shrivelled leaves which turn black in mid- to late summer, and distinctive diamond-shaped lesions on the trunk. Symptoms are easier to spot during the summer months when healthy ash trees should be in full leaf.

Safety is the key concern with this disease, as dead branches in the canopy can become brittle and fall, the trees can lose strength and split, and if trees are also infected by other fungi, such as honey fungus, the roots and base can decay and collapse.

Infected trees growing close to buildings, roads, overhead cables, and other infrastructures are sometimes felled as a safety precaution; a felling licence from the Forestry Commission may be required if the tree is still alive. As the disease progresses, it can be dangerous to fell an infected tree so harvesting machines and cherry pickers are often used to avoid the need for tree surgeons to climb on the brittle tree limbs.

Uprooted ash due to dieback (John Morris).

Ash is fast growing, useful for firewood and timber, and rarely damaged by bark stripping by grey squirrels, unlike most other native broadleaved trees. Unfortunately, there is no cure, and many young ash trees will die once infected. The disease takes longer to affect mature trees and not all of them will necessarily die. A worst case is that we might lose 90% of our ash over the next 10 years.

But it is hoped that some of the surviving ash trees will be resistant or tolerant to the disease, and that ash populations may recover over time. So, it is important to retain healthy ash as a seed source to aid their recovery in the future.

Learn more about ash dieback

This article was adapted from “Ash dieback in the Chilterns” by John Morris, originally featured in Outstanding Chilterns Magazine 2020/21. You can read the current and previous issues of Outstanding Chilterns online.

Featured image above shows ash dieback next to healthy young ash (John Morris).