Ash dieback

Ash dieback is a disease that affects ash trees, caused by a fungus called Hymenoscyphus fraxineus. The fungus blocks water transport in the tree, leading to lesions in the bark, leaf loss and the dieback of the crown.

Ash dieback fungus is believed to have originated in Asia. It was first discovered in Europe in Poland in 1992, and is now found widely across the continent. The first confirmed case in the UK came in 2012, since when it has spread across England and to Scotland, Wales, Northern Ireland, and the Isle of Man.

The main symptoms of ash dieback are:

• Dead branches
• Blackening of leaves which often hang on the tree
• Discoloured stems often with a diamond-shape lesion where a leaf was attached

Trees may eventually drop limbs, collapse or fall. The symptoms are often easier to spot in mid-late summer, when a healthy ash should be in full leaf. It becomes much harder in autumn, when leaves are naturally changing colour and falling.

Once a tree is infected the disease is usually fatal, either directly, or indirectly by weakening the tree to the point where it succumbs more readily to attacks by other pests or pathogens, such as honey fungus. These secondary pathogens can cause butt or root rot, leading to the tree falling.

The disease can spread locally (over tens of miles) by wind dispersal. The reproductive stage of the fungus grows on the previous year's fallen leaves, producing fruiting bodies that release spores between June and September. These spores are dispersed by the wind and settle on the leaves of healthy trees. If a healthy tree receives a high enough dose of spores, it too will become infected.

Over longer distances, the disease may be spread by the movement of infected ash plants.

Visitors to sites where ash dieback is present can help to reduce the spread by brushing soil, mud, twigs, leaves and other plant debris off their footwear and wheels - including the wheels of cars, bicycles, mountain bikes, baby buggies and wheelchairs - before leaving the site. They should then wash these items at home before visiting another similar site.

Diseased ash trees can become extremely unstable and are at an increased risk of dropping limbs or complete collapse. The Trust has a duty of care to ensure that visitors, staff, volunteers and our neighbours are safe on or adjacent to land which the Trust is responsible for.  As such it is inevitable that as trees become unsafe a significant number will need to be felled. This will be necessary on an annual basis until the disease has run its course.

Yes. We will only remove trees which are at risk of causing injury to the public, our volunteers, staff or our neighbours.  All other infected trees will be retained.  It is possible that some trees will survive the fungus and recover to good health. These trees could produce new generations of tolerant ash trees for the future.

In any ash removal, we will consider the needs of protected species, such as bats, along with other woodland wildlife.  This will include actions such as:

• Only felling in areas deemed ‘high risk’ - such as adjacent property boundaries, roadsides and around carparks and benches.  Across the majority of reserves ash will be left to die naturally.
• The closure of permissive paths will be considered in order to increase areas where felling is not required.
• Phasing works over a number of years, rather than in a single operation, when safety requirements allow.
• ‘Soft-felling’ of trees with high bat roost value, where tree limbs are cut and left grounded over night to allow any bats to make their way out.
• Ensuring felling takes place in the winter so that it has limited negative impact on species.

In some woodlands the loss of ash may provide an opportunity to improve woodland structure, create open space, diversify tree species and increase dead wood, an important habitat for groups such as fungi and invertebrates.  

The most sustainable way to replace felled trees is to allow the trees and shrubs to regenerate naturally. A small percentage of ash trees will be resistant to the disease and healthy trees will be retained to allow the seed from these trees to naturally regenerate.  The loss of ash from woods may allow other native tree species to benefit, colonising newly created open areas.

We will retain as many potentially tolerant ash trees as possible. Newly created open areas will allow natural regeneration by seed from healthy ash trees, as well as other native species.