Ash trees are our second most common tree in the UK and most common hedgerow tree throughout the country, making them an integral component of the south west landscape across each county. As one of the toughest hardwoods, ash trees have been an important commercial species, used for everything from tool handles and oars to furniture and fire wood. The Viking’s referred to it as the ‘tree of life’ for good reason. It’s open canopy structure, late bud burst and early leaf fall allow light down to the woodland floor throughout the year, providing excellent conditions for shrub species such as hazel and woodland ground flora. As a long-lived species, ash trees provide continuity for deadwood specialists and nesting opportunities for birds and small mammals. However, these trees are now facing a grave threat, which has the potential to cause changes in our countryside not seen since Dutch Elm Disease devastated the UK’s elm population in the 1970s.

Ash dieback is caused by the fungus hymenoscyphus fraxineus. Originally from East Asia, the disease has now spread across Europe. Since its discovery in the UK in 2012, the disease has now been identified in all the English counties and in recent years, become much more apparent in our countryside.

Ash dieback can cause leaf loss, lesions and dieback within the tree’s crown by blocking the tree’s water transport systems often resulting in tree death. Young ash trees are particularly vulnerable to the disease and often die quickly once infected. The majority of mature trees will decline and die over a 10-15 year period. All common ash are susceptible to the disease, however a small percentage (1-5%) have shown a tolerance to the disease which can be passed on to their progeny.

It is our duty as woodland managers to ensure ash trees are given the best chance to persist in our woodlands and prepare for the potential impact of this disease on our woods and landscape.

The Forestry Commission has produced new guidance on managing ash in woodland in light of ash dieback (Operations Note 046).

The guidance outlines the current situation and how best to reduce the impacts of ash dieback while still achieving other management objectives. Emphasis is given to accessing woodlands individually and making management decisions based on what proportion of the woodland is ash, visible signs of the disease as well as the age of the stand. Retention of tolerant trees, showing few symptoms of the disease, is encouraged, with the intention that these trees will go on to provide a potentially tolerant seed source within the woodland. As such, tolerant trees should be given room to grow during thinning operations.

Coppicing ash is discouraged as recent studies in East Anglia have shown that 80% of coppiced ash dies within four years due to increased susceptibility to the disease.

Supplementary planting and restocking with alternative species may be necessary on some sites. Unfortunately, there is no species that perfectly mimics ash trees in terms of their environmental requirements or ecology. Alternative species should be guided by management objectives, site conditions, current stand composition and the site’s history and designations.

Trees affected by ash dieback also become more susceptible to secondary pathogens including honey fungus (Armillaria spp) which can cause butt or root rot and can vastly speed up the trees becoming hazardous. Trees showing signs of basal lesions or identified as being infected by honey fungus should be felled as soon as possible.

The Forestry Commission Guidance mentioned above gives excellent information on how to plan the management of your woods in light of ash dieback. For further advice please contact your local FWAG SW adviser.

New cases of the disease should be reported to the Forestry Commission through Tree Alert service. Dead and dying ash trees can be dangerous to the public and woodland workers. Forestry Industry Safety Accord (FISA) safety advice on felling diseased ash should be followed when felling diseased or dead ash.

Biosecurity is also very important in slowing the spread of ash dieback from woodland to woodland. Equipment, boots and clothing should be cleaned and disinfected where appropriate in accordance with the ‘Keep it Clean’ campaign.