Ash dieback: policy approach 2024 to 2029

Ash trees which may be dead or dying can be highly dangerous, pose a risk to people, property and critical infrastructure.  The risks may not be obvious or visible, so managing and working with affected trees should only be undertaken by trained professionals. 

This document sets out the high level Welsh Government approach and provides links to sources of advice. You are strongly advised to consult and engage the services of a fully insured tree management professional such as a qualified forester or arboriculturist when undertaking any work.

The purpose of this document is to explain Welsh Government’s policy approach to the management of ash dieback across Wales. It confirms a risk-based approach should be taken by landowners and managers to manage the societal, environmental and economic impacts of the disease.

Ash dieback is a very visible reminder across the landscapes of Wales of the damage which tree pests and diseases can do, and of the importance of resilient ecosystems.

This document sits under the GB Plant Biosecurity Strategy, which Welsh Ministers have agreed alongside their counterparts with responsibility for plant health in England and Scotland.  It also reflects the context of the climate and nature emergencies declared by Welsh Ministers in the last five years. 

We know pests, pathogens and invasive non-native species have the potential to impact on the health and resilience of the natural environment in Wales and that these risks will only increase with climate change. We must all act in a responsible way, in line with the principles set out in the Wellbeing and Future Generations (Wales) Act 2015, working to maintaining resilient, biodiverse ecosystems across Wales.

This document has been created for anyone involved with the management of ash trees across Wales.   

In this policy approach we have adopted terms which are in common usage for ease of understanding. For example, where we state ‘ash trees’ we refer to common ash, or Fraxinus excelsior. Where we state ‘tolerant’ we refer to tolerant and resistant trees.

This policy approach refers to ash dieback caused by the Hymenoscyphus fraxineus fungus, which is sometimes referred to as Chalara or Chalara dieback of ash based on its initial scientific description. We recognise that there are other causes of dieback in ash, such as water stress, which is likely to require a similar management strategy, particularly if it is unclear as to the cause of the dieback.

The following principles are the foundation of our approach to living with ash dieback:

• to encourage naturally tolerant strains of ash to emerge and flourish enabling the wider environment to respond naturally. As far as possible, within the constraints of safety and economy, ash trees which are affected by dieback should not be felled prematurely but be allowed to respond naturally to the progression of the disease, so that any tolerant trees can be identified, can produce seed, and be allowed to give rise to more tolerant offspring to gradually replace lost ash trees in our countryside. While it may seem strange, dead, and dying trees will often have significant conservation and environmental benefits and allowing the environmental impacts of ash dieback to progress naturally over a number of years, and even decades, will provide scope for natural processes to adapt. Dead and dying ash trees have an important role to play in supporting biodiversity, providing habitats for insects, birds, lichens and fungi, amongst others
• to promote a risk-based approach for decision making relating to the management of ash dieback. Taking a risk-based approach to prioritising ash management recognises the significant challenge and potential economic impact of ash dieback for landowners and managers, while balancing this with social and environmental factors. This approach recognises there is a need to balance multiple risks as we seek to deal with ash dieback, including risks to people and infrastructure but also to the environment such as habitat loss
• to keep people and our critical infrastructure safe. Landowners and land managers should act to safeguard the public, those working with trees and our critical infrastructure from the risk posed by weakened or dangerous ash trees. Where ash trees are growing adjacent to critical infrastructure such as telephone, electrical or broadband wiring, public roads, railways and rights of way or other land to which the public have access, the presence of diseased trees poses an increased risk which landowners and managers have a responsibility to manage. Links to relevant health and safety guidance are included under 'Related strategies and advice' within this document

Our long term aims for ash dieback are to:

• minimise the social, economic, environmental and cultural impacts of ash dieback
• raise awareness of the disease and the need for good biosecurity measures and safe removal where needed following health and safety guidelines
• encourage landowners and managers to manage their ash trees through the provision of appropriate guidance
• take an approach to ecosystem and habitat management which allows disease-tolerant ash to continue to form part of our natural environment 
• prioritise management of ash which poses the highest health and safety risk
• encourage long-term planning across all land uses affected by ash dieback, recognising woodland owners need to proactively manage their land for environmental and economic purposes, whilst seeking to retain ash trees where possible

While there is already advice available, we recognise the need for more specific guidance in a Wales context which identifies different management approaches depending on the level of risk and the location of the ash trees. This has been developed by Natural Resources Wales (NRW) and provides practical, operational advice required by those dealing with ash dieback. 

The guidance includes information on managing ash trees in high-risk areas, managing ash trees in areas of high conservation value, and ash trees in the wider countryside and urban areas. 

In accordance with the principles and aims set out in this document, the Welsh Government in conjunction with NRW and the Wales Strategic Ash Dieback group have identified the following actions over the next five years: 

• produce guidance to support landowners and managers in Wales dealing with ash dieback 
• proactively communicate this guidance to stakeholders to raise awareness and ensure legal requirements and good practice are followed
• maintain a stakeholder forum (the Wales Strategic Ash Dieback group) to discuss issues relevant to the delivery of this approach, including the development of guidance and resolving practical issues
• maintain links to GB and UK wide strategies, forums and groups relevant to the management of ash dieback, and global research into tree health more generally
• maintain links to the Science and Innovation Strategy for Forestry in Great Britain which includes collaborative work on research priorities around ash dieback and tree health more generally 
• periodically evaluate and review our approach and guidance to ensure they remain up to date reflecting the latest scientific knowledge, understanding and research on ash dieback

• working with dead and decaying trees is always a highly hazardous task and links have been provided to advice already available for those working with ash trees affected by ash dieback
• the danger may not be easy to detect and the severity of the disease present may not always be obvious, so it is vital that the work is carried out by trained professionals who have the necessary equipment and skill to carry it out safely. It will often be these tree professionals who are exposed to the greatest risk but other people nearby such as road or footpath users may be at risk, as may property or critical infrastructure
• the impact of safety should always be a priority for decision makers and be considered fully when considering retaining ash trees, in line with the approach set out in this document. This includes where protected species of animals or birds are involved, and further guidance is available from Natural Resources Wales (NRW) on the processes to follow in these situations

Since its first identification in Great Britain in 2012, ash dieback has spread rapidly, and the disease is now endemic in Wales. 

Ash dieback presents a significant land management challenge for landowners, land managers and farmers who have ash trees on their land. While numbers are being reduced due to the disease, ash is still an abundant broadleaved species in Wales, found both inside and outside of woodlands, along roadsides and railways, in hedgerows or individual trees in fields or parks and gardens.

Ash is a major canopy species, occupying more than 20% of the canopy in 48% of Welsh Lowland Broadleaved woodlands and also in 18% of Upland Welsh Broadleaved Woodland (Broome and Mitchell 2017). The strength and flexibility of its timber makes it ideal for uses as diverse as boat frames, tool handles and baseball bats and hurley sticks. 

According to the National Forest Inventory (NFI) (on forestresearch.gov.uk), there is approximately 17,500 ha of woodland in Wales where ash is the dominant canopy component. Approximately 600ha of this ash woodland is located within the Welsh Government Woodland Estate managed by NRW. Many ash trees are present outside woodlands, however the NFI cannot produce accurate estimates for the number of ash trees which are individual ash trees, make up linear features such as hedgerows and street trees, road verges and railway embankments or are within woodland stands smaller than <0.5ha on private land.

Ash woodland has important biodiversity benefits and is the host to many organisms, including some for which it is “obligate”, meaning it is the only ecosystem which supports them. For example, ash is of particular importance to epiphyte communities of mosses, liverworts and lichens and has become increasingly important following the widespread loss of elm trees. This significant importance is associated with the high bark pH of ash trees (Joint Nature Conservation Committee, 2014). 

Ash trees are also culturally significant and are valued for a wide variety of reasons including heritage, spiritual and recreation, as well as for their contribution to the landscape (Hall et al, 2021). 

Since the first finding of ash dieback in Britain in 2012 there has been a concerted effort from scientists across GB to fund and lead research into ash dieback. A large amount of the research is contained in Defra’s Ash Dieback Research Strategy (on gov.uk) and the Science and Innovation strategy for Forestry in Great Britain (SIS). Within the SIS further research is being carried out to better understand the potential relationship between Armillaria spp. (honey fungus) and ash dieback.

In their research on ash dieback so far, scientists have found:

• the spores are unlikely to survive for more than a few days
• trees need a high dose of spores to become infected
• there is a low probability of dispersal on clothing or by animals and birds
• the disease becomes obvious within months rather than years
• wood products would not spread the disease if treated properly
• once infected, trees cannot be cured, and
• not all trees die of the infection - some are likely to have genetic factors which give them tolerance of the disease

This policy approach will initially be in place for 5 years and will be periodically reviewed to ensure it keeps pace with the latest scientific knowledge about ash dieback. Two current research programmes are covered below: 

The Living Ash Project (on livingashproject.org.uk) is in its second phase, and aims to identify a large and diverse number of ash trees with good tolerance to ash dieback, to secure this material for further breeding work, and to quickly make this material available to industry. Trees that are selected will be further screened for tolerance in two different ways, via chemical fingerprinting and directly through controlled inoculations. You can contribute to their work by reporting tolerant ash specimens to the project.

Since 2012, when ash dieback was first identified in the UK, Forest Research has been actively involved in work to understand the characteristics and behaviour of the ash dieback pathogen Hymenoscyphus fraxineus and the effects of the disease on ash populations in this country (on forestresearch.gov.uk). This important work has included tolerance and resistance trials, investigations of pathogen sporulation and infection strategies, and of the ecology and pathology of ash dieback disease. All of the knowledge gained is essential for more accurate disease modelling and improved disease management accurate disease modelling and management.

Despite the current challenges, it is believed that genetic diversity of common ash trees growing in the UK will include a proportion of individual trees which are tolerant to ash dieback which can form the basis for the species to continue to form part of our natural environment as mature trees in future. 

The basis of Welsh Government’s approach is on doing all we can to collectively foster the survival of disease-tolerant ash trees in Wales.

Welsh Government will continue to work with plant health authorities across the UK to prevent the introduction of other threats to ash trees, especially the emerald ash borer (Agrilius planipennis). This includes legislation to prevent the importation of ash trees from non-EU third countries which continues to be prohibited by plant health regulations, under a provision which prohibits the import of certain ‘high-risk’ species. This mitigates the main risk of introducing new strains of ash dieback present in Asian countries but not Europe, as well as pests such as the emerald ash borer. 

There is no plant health regulation which requires the removal of ash trees in the UK, indeed there is a presumption in favour of leaving these trees standing in order to aid survival and growth of populations of tolerant trees and enable long term survival of the common ash as a widespread species in our countryside.

There is no legal restriction on the movement of ash trees within the UK and no restriction on the movement of the timber of ash trees. There are, however, currently no guaranteed disease-tolerant ash trees on the market in the UK.  

The planting of ash trees and the movement of ash plants for planting is not advisable given the risk that they will already be infected or will soon become infected. However, this advice is not intended to prevent collection or propagation of potentially tolerant ash seedlings.

The disease is found throughout Wales and while many trees will have been affected for several years, the progression of the disease, and the impact it has on the trees is variable. This map shows ash dieback in the wider environment (on chalaramap.fera.co.uk).

Neighbouring trees can show widely differing apparent impacts which in part may be due to differences in the genetic potential of individual ash trees to tolerate the fungus. However, there are many factors at play, including the prevalence of secondary infecting organisms, the morphological complexity of the tree and the general health status of the individual ash tree. 

H. fraxineus is an ascomycete fungus which infects leaves and petioles through airborne spores. Symptoms range from leaf spots to branch dieback and death of ash trees and other Fraxinus species (Stokes. J. and Jones, 2019). Symptoms of the disease can be found on the Forest Research website.

In Asian ash species, the trees response to infection is for the leaves and petioles to fall off the tree preventing further infection into the branches and main stem. This defence mechanism is not present in European ash. Once the fungus spreads to the woody parts of the tree, lesions and dieback can occur, firstly in the shoots and twigs and ultimately in the branches and main stem.

The disease is unlike other pathogens affecting trees in Wales such as Phytophthora ramorum, which once they have entered their host will continue to grow year on year. With H. fraxineus, infection is isolated rather than continuous, and after the growing season re-infection with fresh spores is needed for the disease to progress further. After successive years of infection, the crown will start to thin and branches will desiccate (Enderle, 2019). The speed of decline varies but mortality can occur within two growing seasons with the tree becoming weak in timber strength and prone to structural failure. Severely affected trees create high risk felling conditions for operators working on or nearby the tree (Forestry Commission, 2018).

Another important feature of ash dieback is the impact it can have on the base and root system of the tree as any decay in that area can significantly impact the structural integrity of the tree. 

The fungus spreads through airborne spores, these are released by fruiting bodies which emerge on previously infected leaves, often found in the litter layer around the infected ash tree.

Fruiting bodies can be seen from June to September which is when spores are released. Researchers have found the released spores can travel up to tens of kilometres via wind dispersal. 

Ash trees and ash woodland are an important component in our landscape. Even when affected by the disease, they provide important habitats for other plant and animal species. Dead and dying trees provide resting places for bird and animal species like bats and woodpeckers. 

Where possible and safe to do so, ash trees should be left to decay naturally instead of being felled. When felling ash trees, great care should be taken to avoid damage to important habitats and advice should be obtained from NRW where protected species could be affected.

Other related strategies and advice which should be read in conjunction with this policy approach include: 

Strategies

• in the GB Plant Biosecurity Strategy (2023 to 2028), we are working in partnership to approach the challenges arising from the climate and nature emergencies. This strategy sets out ways in which we will work together to prevent other pests and diseases from entering and spreading across Wales as well as a clear focus on research
• the Woodlands for Wales (2018) strategy makes a commitment to bring more woodlands into management, expand woodland cover in Wales and increase the resilience of woodlands and trees to deliver more benefits for the public
• the Common Sense Risk Management of Trees (on ntsgroup.org.uk) published by the National Tree Safety Group sets out a pragmatic, proportionate approach to risk and dealing with infected trees and the danger they may pose, aimed at land owners and managers

Advice and guidance 

• Natural Resources Wales (NRW) has produced practical guidance for those dealing with ash dieback
• the felling of ash trees may require a felling licence but there are exemptions for dangerous trees, as outlined in existing guidance (link above) published by Natural Resources Wales
• clear guidance on all aspects of tree work has been published by the Health and Safety Executive
• the Forest Industry Safety Accord (FISA) (on ukfisa.com) has provided further information notes focused on ash dieback detailing best practice and suggestions regarding manual felling when dealing with ash trees that are either dead or infected
• the Tree Council (on treecouncil.org.uk) has also published detailed guidance on managing diseased ash trees which is aimed at local authorities and other public authorities