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Ash dieback An ash sapling showing typical foliage die back as a result of infection

Ash dieback

First recorded in 2012, Ash Dieback (caused by the non-native invasive fungus hymenoscyphus fraxineus) is now widespread across the whole of the UK – presenting a threat to the UK’s treescape on a scale not seen since the Dutch Elm disease epidemic of the 1970s.

It has been estimated that ash dieback will kill up to 95% of ash trees in the UK and cost British society £15 Billion, as well as changing the appearance of the landscape and threatening many species which rely on ash.

The landscape of the Yorkshire Dales in particular is characterised by important ancient semi-natural ash woodlands, and hedges and individual ash trees that are important for providing connections between habitats. Many of our ash trees are veteran or ancient trees and are irreplaceable. As the disease becomes more obvious within this landscape we are inevitably receiving more enquiries about the disease, particularly from concerned landowners wanting advice on how to manage their trees that are infected.

Dealing with ash dieback in the National Park

Trees that need managing

Trees showing no symptoms, or only mild symptoms, should be left but monitored closely.

Trees with targets which are showing some or all of the following may need to be felled or reduced to manage any hazards:

  • Trees where extensive dead and brittle wood is evident, particularly where disease has spread to large diameter branches;
  • trees which have cracks on the underside of large branches;
  • trees with signs of fibre buckling, cracks in the main stem or basal lesions;
  • trees showing signs of secondary infection which could render the tree dangerous – such as basal or root decay fungus like honey fungus;
  • trees which have around 40% or less normal leaf cover in summer particularly where the remaining leaf cover is patchy/ clumpy and concentrated in the central part of the tree canopy; and,
  • trees where most of the remaining leaf coverage is stress growth.

Protected trees with Ash Dieback

Dealing with trees infected with ash dieback is no different to how we treat any other diseased or dangerous tree. A diseased or dead tree becomes dangerous when it is a threat to public safety, when it is overhanging a building or public right of way for example. When this is the case it needs to be dealt with as soon as possible.

The duty of care lies with the landowner to ensure that any trees within their ownership are not posing a threat to the safety of the public, and it is their responsibility to remove the tree or carry out works in order to make it safe. Please ensure to check to see if your tree is protected by a Tree Preservation Order or a Conservation Area before carrying out any works as you will need to obtain the necessary permissions from the Trees and Woodlands Team if this is the case. For infected trees which are not protected, be aware that felling licence restrictions may apply and you should contact your local Forestry Commission for more advice.

Trees should be felled by a qualified arborist who understands the risks to felling ash trees. Restrictions also exist concerning the timing of works and the impact on wildlife – bird nesting season is generally March to August. Bats use the canopy of some trees in summer for maternity sites and use tree cavities for hibernation in winter so these times of year should be avoided for trees with bat potential.

Looking to the future

We are helping to build the resilience of our woodlands to current and future diseases and climate change by using a wide mix of native species when planting new woodlands, and managing the spread of other diseases and pests by carrying out biosecurity measures. You can do your bit by planting trees that are considered a good replacement for ash (based on the species they support , such as alder, small leaved lime, sessile oak, rowan), by cleaning your shoes and bike wheels before and after visiting a woodland, and avoiding taking plant material or cuttings from the countryside.

More information on how we are responding to ash dieback can be found within the Dales Woodland Strategy and our Position on Ash Dieback.

Further Information

The Woodland Trust, Forestry Commission, and Arboricultural Association have some excellent information and resources on their websites, providing first hand information about the disease, how to recognise it, the current distribution and what the current status is

If you have any questions or concerns, or require guidance about how to deal with an infected ash tree, please contact the Trees and Woodlands Team