Ash Dieback on land owned by Exmoor National Park Authority

Ash Dieback (ADB) has been present and spreading in the UK since at least 2012 and in Exmoor National Park since at least 2013.  The disease is caused by a fungus called Hymenoschyphus fraxineus (previously known as Chalara), which is native to northern China and parasitizes the species of ash native to that area.  Because our native European ash species didn’t evolve with the fungus it can’t defend itself and usually succumbs, leading to decline and the likely death of the tree.  It appears from studies so far that only 5-10% of ash trees infected with the fungus survive.  There are an estimated 800,000 ash trees in Exmoor National Park.

Exmoor National Park Authority (ENPA) owns around 7% of land in the National Park, and one of our responsibilities as a landowner under the Occupiers’ Liability Act is to be aware of and respond to risks posed by trees on the ENPA estate.  This is part of our legal duty of care to anyone entering our property.  For these reasons, we carry out annual surveys on our tree stock to monitor health and deal with any hazardous trees as they are identified. This survey work is targeted in areas which are frequently used by the public or which are adjacent to buildings or roads.  We base our assessment on objective measures and make safety judgements based on common sense and experience.

With the extent and speed of decline posed by ADB, we have had to take a robust, responsible and proactive approach.  When ash is affected by ADB, the wood structure becomes very brittle and more dangerous to work on as trees can no longer support the weight of arborists and can be less predictable to fell.  This means that we have to act rapidly to deal with the issue in order to minimise the risks to workers as well as to the public.

We have identified approximately 2000 ash trees in our high priority areas which will almost certainly die of the disease and pose a potential risk to life and property.  These trees make up around 5% of the estimated 40,000 ash trees on the ENPA estate. They are situated in prominent and highly visible locations as by their nature they are in areas commonly frequented by the public.  The remaining 38,000 ash trees will be left for the disease to progress.  These trees are largely situated in woodlands and will decay slowly and harmlessly, providing a temporary ecological niche via an increase in deadwood.  Some of these trees may display natural resistance and, we hope, give rise to future generations of ash which have resistance to the disease.

ADB is only one of many pests, diseases and climate stresses affecting Exmoor’s trees. This situation is extremely unfortunate and comes at a time when the country is gearing up to plant millions of new trees.  We will re-plant felled areas as appropriate with a mixture of native trees designed to replace the ecosystem functions of ash.  In this way, we can begin to recover from the loss of biodiversity and improve the resilience of our woodlands to pests, diseases and climatic extremes.

If you are an Exmoor resident and fear you may have ADB on your land, you are welcome to contact us at if you need help on how to proceed, though there is no requirement to notify us.  ENPA does not offer arboricultural advice and we always recommend getting advice from a competent and insured arborist (preferably a member of the Arboricultural Association).  The usual laws and regulations apply to felling trees with ADB; the owner of the tree is responsible for obtaining a Felling Licence (if applicable) and for applying to the Local Authority (ENPA) for permission to work on protected trees.

Please see our page on getting permission for tree work for more information.

For further information and advice on ADB, please visit Forest Research or The Tree Council, where a Toolkit is available to help landowners assess the risk of ADB on their land and explain the risk assessment processes used by many Local Authorities.