Ash dieback in the Yorkshire Dales

Ash dieback on a mature tree

There are an estimated 80 million ash trees in the UK, helping to shape some of our best loved landscapes. The National Trust manage 25,000 hectares (61,776 acres) of woodland and 135 landscape sites and deer parks, which include thousands of veteran ash trees and several hundred ancient ash trees over 300 years old. Ash dieback could kill up to 95% of these trees and change the landscape forever.

What is ash die back?

Ash dieback (also known as Chalara dieback of ash) is caused by the fungus Hymenoscyphus fraxineus. The fungus originated in Asia, and since its introduction to Europe 30 years ago it has devastated European ash species as they have not evolved with the fungus, and therefore have no natural defence against it. In Denmark alone, it has wiped out over 90% of their ash trees.

Ash dieback was first recorded in Britain in 2012, but it was probably here before then.  While its progress has been slow it is now present in most areas of England and Wales, and it is on the national risk register.

The fungus affects the vascular system of ash trees and inhibits its ability to draw up nutrients to its branches, which leads to leaf loss and crown dieback.  The fungus may cause the death of a tree, but it can also open a tree up to infection and to other fungi which can kill it.  

As it is a fungal infection it spreads through the air as spores and can travel tens of miles away. The fungus winters in leaf litter on the ground and particularly on the leaf stalks, and the spores are released into the surrounding area between July and October. The fungus lands on the leaves and makes its way into the tree, blocking water transport systems and causing the tree to die.

A healthy tree
A healthy tree
A healthy tree

What does it look like?

Ash dieback can impact trees of all ages, but it is thought that younger trees succumb to the disease more quickly than older ones.

  • Dark patches on leaves

  • Wilt and become black and can shed leaves early

  • Lesions on branches are often dark brown and diamond shaped

  • Epicormic growth is common, it is new growth from previously dormant buds

  • Small branches turn brown and look like dead wood along their length

  • Crown dieback is visible during summer

Ash dieback, Parke, Devon
Ash dieback, Parke, Devon
Ash dieback, Parke, Devon

How will ash dieback impact the Dales?

The ash tree is an iconic part of our woodlands and landscape and we are very concerned about ash dieback. We continually observe and survey our ash for signs of the disease and we are working closely with other organisations, such as the Forestry Commission, Woodland Trust, Defra and the Yorkshire Dales National Park Authority, on the best ways to tackle the disease and manage trees and woodlands infected by it. We are following best practice guidelines and are looking to the most recent research for guidance.

As part of our annual tree safety checks we now look at ash trees very differently as they are much more unpredictable and dangerous. We will conduct further surveys throughout the year to track changes through the seasons which will give us a better idea about the extent of dieback in this area. Although we will not take out ash trees unnecessarily, our surveys may necessitate appropriate action, such as tree felling or crown reduction, in areas where safety issues arise. Ensuring the safety of our visitors, the public and our workers is of paramount importance. However, where appropriate, by allowing diseased ash trees to decline and regrow naturally it is hoped dieback resistant ash trees will regenerate. Furthermore, by allowing nature to take its path the ash trees can continue, for a time, to provide a habitat for the species that depend on them.

We will ensure that any lost ash trees are replaced through planting (using native species) and natural regeneration. In doing this, we will be able to provide a woodland habitat for the thousands of species that rely on it, a varied woodland that is more resilient to change, ensure carbon storage is maintained and a space for people to enjoy nature.

A close up showing the effects of ash dieback
The effects of ash dieback
A close up showing the effects of ash dieback