Managing ash dieback

Introduction

This guidance offers practical and sustainable approaches to managing ash trees affected by ash dieback. It is for landowners, woodland managers and anyone who manages ash trees in Wales. It has been written for use in Wales but also signposts to other relevant guidance published by different organisations. If you have any concerns or need specialist advice on managing your ash trees including in relation to health and safety risks, consult a fully insured tree management professional such as a qualified forester or arboriculturist A list of qualified professionals is maintained by the Institute of Chartered Foresters.

Nothing in this guidance document replaces or removes the need to comply with duties under the Occupier’s Liability Act (1957 and 1984) or other legislation. For further information on duties under the law refer to the National Tree Safety Group Common Sense Risk Management of Trees booklet.

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.

Ash dieback presents a significant land management challenge for landowners, land managers and farmers who have ash trees on their land. Whilst the number of ash trees is reducing due to the disease, ash is still an abundant broadleaved species in Wales. It is an important component in our landscape, found both inside and outside of woodlands, along roadsides and railways, in hedgerows or individual trees in fields or parks and gardens.

In this guidance, where we state ‘ash trees’ we refer to Common Ash, or Fraxinus excelsior. Where we state ‘ash dieback’ we refer to the Hymenoscyphus fraxineus fungus, which is sometimes referred to as Chalara or Chalara dieback.

We acknowledge that other, non-native species of ash may be grown ornamentally in Wales and whilst this guidance focusses on the native common ash, it may also be relevant to the management of other ash species.  We also recognise that there are other causes of dieback in ash, such as water stress, which is likely to require a similar approach to management, but they are not specifically covered by this guidance.

This guidance should be read in conjunction with Welsh Government’s Ash dieback policy approach in Wales.

Welsh Government’s Ash dieback policy approach in Wales

Welsh Government has published an Ash dieback policy approach in Wales. It explains that a risk-based approach should be taken by landowners and managers to manage the societal, environmental and economic impacts of the disease, to keep people and our critical infrastructure safe and encourage naturally tolerant strains of ash to emerge and flourish enabling the wider environmental to respond naturally.  

It can take several years following the arrival of ash dieback at a site to identify the more tolerant trees. Tolerant trees can still produce good annual growth increment. Tolerance to the disease is thought to be highly heritable and will be passed onto new generations of trees. This is why it is so important to retain ash trees for as long as possible so that tolerant strains emerge and flourish, enabling the wider environment to respond naturally.

Overall Approach

We recommend a risk-based approach to the management of ash trees, built around four steps, in accordance with the principles and aims of the Strategy.

Step 1: Survey and monitor ash trees

Identify ash trees on your land, whether individual trees or groups of trees and assess their condition, including changes over time.

Step 2: Complete a risk assessment

Consider completing  a risk assessment to inform future management options, with a particular focus on high-risk locations.

Step 3: Plan and deliver remedial works or adaptive management

Plan and deliver remedial works or adaptive management as required, in accordance with the findings of the risk assessment completed in Step 2.  You will need to obtain the necessary licences and ensure health and safety advice is adhered to when carrying out any remedial works or adaptive management. You will also need to consider mitigation measures, such as replacement planting.

Step 4: Review

Review the effectiveness of your approach by going back to Step 1 which requires the monitoring of ash trees on your land to inform future actions. The impact of ash dieback can occur over a range of scales and time frames, so it is important that tree health is regularly monitored to regularly to understand changes over time.

Step 1:  Survey and monitor ash trees     

Identifying the presence of ash trees and determining their condition through survey or assessment is an important first step. A survey should record the number and location of ash trees and any signs or symptoms of ash dieback present at an appropriate scale. For example, along a road or in a public park, you may need to record every tree. Alternatively, if ash trees form the majority of a larger woodland, you may just record them as one entry.

For signs and symptoms, including images, to help carry out a survey, guidance has been produced by Forest Research, Observatree and the Tree Council.

A survey should also identify the presence of Armillaria (Honey fungus). Secondary infection by Armillaria can occur in lesions caused by ash dieback. This is often the ultimate cause of death of ash trees with ash dieback, especially older ones. If Armillaria is detected, it should feed your risk assessment in Step 2. Other decay fungi may also infect a tree affected by ash dieback.

Step 2: Complete a risk assessment

Based on the results of Step 1 consider completing a risk assessment to inform your decisions about future management options. Useful advice on identifying risks and making balanced decisions can be found in the National Tree Safety Group Common Sense Risk Management of Trees booklet.

 A risk assessment should prioritise trees in high-risk areas, on the basis that these require more immediate attention. High-risk areas include those adjacent to highways, service network infrastructure, buildings or in places or along routes frequently used by the public.

As well as location, consider factors such as the tree’s condition and the likely impact if it were to fall or branches snap.                   

Ash trees that are classed as High Nature Value Woodlands (HNVW) or are ancient or veteran trees require special consideration. The following are classed as HNVW:

• Ancient Woodlands including:
  • Ancient Semi-Natural Woodlands (ASNW).
  • Restored Ancient Woodland Sites (RAWS)
  • Plantation on Ancient Woodlands Sites (PAWS).
• Wood pasture and Parkland; and
• Sites of Special Scientific Importance (SSSI) or other designated sites.

The location of ancient woodlands, wood pasture and parklands and designated sites can be found on DatamapWales

An ancient tree is a tree that has biological, cultural or aesthetic value due to its age, size or condition. Veteran trees may not be very old but has decay features that contribute similar value.

In HNVW and for ancient or veteran trees it’s important to consider the impact of ash removal on biodiversity and the wider environment.  Ash trees support a large number of species, some of which rely on the specific characteristics of ash. In these situations, seek to retain ash trees for as long as possible unless there are overriding health and safety considerations.

If you manage your woodlands to produce timber, you may need to think about economic and financial issues when completing your risk assessment. In accordance with the Strategy, stands containing infected trees should not automatically be classed as high-risk areas and therefore earmarked for premature felling to quickly realise the value of the timber. You should take a measured approach to risk assessment that factors in all issues.

Step 3: Plan and deliver works or adaptive management

If your risk assessment identifies the need for remedial works or longer-term adaptive management practices to deal with high-risk infected ash trees, plan and deliver these.

The type of remedial works or adaptive management practices will depend on why locations have been identified as high-risk areas; the level of infection; the age of the tree or stand; and their setting. Works might include the removal of dead limbs from trees in high-risk areas via tree surgery; the felling of infected trees by thinning or clearfell; work to promote healthy trees to tolerate infection; or work to support the natural regeneration of tolerant strains.

Helpful guidance on planning for the management of ash dieback has been produced by the Tree Council and Forest Research.  

Remember that this Step also involves obtaining the necessary licences and permissions to carry out works and ensuring that health and safety advice is followed when carrying out works, especially if these involve working off the ground. Applying for a Forest management plan may be beneficial when planning and gaining a felling permission for medium and longer term management.

High Nature Value Woodlands

In HNVW that contain ash trees, where preserving wider environmental and biodiversity benefits are the key objectives, a lower level of adaptive management is the preferred option, except where remedial works may be needed in high-risk areas. Retaining ash for as long as possible can provide habitat for those species which depend on ash trees and allow time for tolerant Ash trees to be identified. Your approach could include thinning of younger stands to encourage healthier trees or targeted thinning around healthy trees with large crowns to encourage seed production. Heavy thinning in dense mature stands is not advised. Adopting Low Impact Silvicultural Systems (LISS) where possible can support replacement of the canopy and function of the HNVW as quickly as possible. Clearfell of stands should be considered a last resort to reduce disturbance within these sensitive sites and maintain their characteristics and features.

Other woodlands

In other woodlands, consider selective thinning of younger stands of diseased and supressed trees if disease levels are low. Younger trees are the most vulnerable to the disease, and once infected they usually die quickly. If more than 50 per cent of the ash in the stand is infected, the annual rate of spore production will be very high. Consequently, the condition of the trees will decline rapidly, and it may therefore be appropriate to realise their value sooner and fell them earlier than originally planned.

An individual-tree approach is recommended for older stands with infected trees. Where more than 50 per cent of the crown is infected, and where survival of the tree depends on epicormic shoots (growth from buds on the trunk or branches), you may want to consider felling because they have become seriously infected and will be producing large volumes of spores which will infect other trees.

Trees outside woodlands

For individual landscape or urban trees, look to retain these for as long as possible unless public safety is an issue. Veteran and ancient trees in particular can provide many important environmental and social benefits, even when dead.

Sixty percent of hedgerow trees are ash; coppicing or laying ash trees makes them more vulnerable to infection and should therefore be avoided. Retain trees unless safety is an issue and where trees are removed for safety reasons, replacement trees should be identified to grow up and take their place.

If you are in receipt of CAP payment, then you should ensure that you comply with the requirements of cross-compliance.

Options if rare lichens are present

In Britain, 78 threatened lichen species grow on ash, of which 34 have ash as a ‘significant’ host tree.

The majority of these rare lichens grow on mature ash trunks (more than 50cm in circumference), rather than on young trees or on branches or twigs.

Four species of Lobaria lichen have been identified as being of key significance for biodiversity in Wales under section 7 of the Environment (Wales) Act 2016.Lobaria lichens are very large, forming patches the size of a saucer or even a dinner plate. They are vivid green when damp and grey or grey-brown when dry. If you think you have found an ash tree with Lobaria, please seek expert advice.

An alert map for ash lichens is available on DataMapWales and identifies known locations of rare lichens on ash trees.

The presence of a rare lichen on an ash tree in high-risk areas should not prevent management. The following approach is recommended, especially in the case of our rarest lichen species:

• Where possible, retaining the lower 3 metres because most known rare lichen colonies are found on the lower/middle trunk up to this height.
• If the tree needs to be felled, leave the trunk lying in situ, with the rare lichen facing sideways, prolonging the presence of the lichen until the bark falls off and giving a few additional years for colonisation of other trees or translocation to take place.

If an ash tree supporting a rare lichen is not identified as being in a high-risk area, then seek to retain it.

Permissions and licences

Information and guidance about permissions and licences that may be needed when carrying out remedial works or adaptive management practices is provided on our website.

Felling licences

You should first check whether you need a felling licence.

There are certain felling licence exemptions, including for dangerous trees which could apply to trees affected by ash dieback. A dangerous tree is one where there is a real and immediate danger, rather than a perceived danger. If you are challenged you will need to provide evidence that the trees were dangerous, for example through an accredited arboriculturist’s report or photographic evidence. Felling without a licence may result in penalties.

If you are applying for a felling licence for works on HNVW, it is likely you will need to provide more details to ensure the appropriate management of these important sites. This might include addressing the timing of the work to reduce soil compaction and minimise disturbance. You must also be able to explain the rationale for the felling being proposed, particularly if it is clearfell as this should be viewed as a last resort for HNVW.

A felling licence only grants permission for a tree to be felled and doesn’t address timber extraction, stacking, storage, haulage, or biosecurity issues. You should refer to the UK Forestry Standard (UKFS) and associated Practice Guides for legal and good practice requirements and guidelines relevant to wider sustainable forest management.

Protected Trees

Protected trees are those included in a Tree Preservation Order (TPO) or a Conservation Area. Unless the work you are proposing is covered by an exemption you will need a felling licence; and you must consult the Local Planning Authority, guidance is provided here.

Protected species

You will need to consider the impact of remedial works or adaptive management practices on wildlife, including on protected species.

We have published guidance on protecting wildlife during forest operations. If tree works could adversely affect a European Protected Species (EPS) which includes any species of bat, dormouse, great crested newt and otters, you may need a licence under the Conservation of Habitats and Species Regulations (2017). You should follow our guidance on species licensing. If your risk assessment indicates that action is required urgently and is likely to disturb or damage the resting place of EPS, contact the NRW Species Licensing team regarding a species licence application.

Protected sites

You will need to consult us if you intend to carry out, or cause or permit to be carried out operations likely to damage the special interest of a SSSI. As part of the notification of a SSSI, owners and occupiers are provided with a list of operations likely to damage the special interest that is specific to the individual SSSI.

We have guidance on the SSSI responsibilities of owners and occupiers, and the SSSI responsibilities of public bodies and statutory undertakers should be referred to.

Where European Protected Sites (SACs and S may be affected, a Habitats Regulation Assessment (HRA) may be required under the Conservation of Habitats and Species Regulations 2017 (as amended). The organisation responsibility for carrying out a HRA depends on the type of permission required under the WCA.

Roadside Trees

If a formal notice is issued by a Local Authority under the Highways Act 1980 which  identifies dangerous tree(s), this notice would provide an exemption from the need for a Felling Licence for those specific trees, but not other trees in the general vicinity, for example nearby trees along the length of a hedgerow that borders a road or footpath.  If you receive a Local Authority notice, you may need to clarify with the Authority which specific trees the notice refers to. The notice will only provide evidence of an exemption for the specific trees identified. In all other circumstances, the onus is on the landowner to demonstrate that tree(s) pose a real and immediate danger and are exempt from the need for a Felling Licence.

A Local Authority may send you a letter informing you that there are potentially diseased ash trees on your land and that you may be served by a notice. We do not consider that this letter is sufficient evidence that the trees are exempt from requiring a Felling Licence.

Operations – health and safety

If ash dieback is present, the structural integrity and inherent strength of an ash tree may be severely affected by the disease and by associated secondary pests or pathogens. These may create high-risk felling conditions for any operators working on or adjacent to that tree.

Only trained and experienced tree surgeons or forestry workers should undertake work on ash trees showing obvious ash dieback symptoms or advanced signs of ash dieback.

Given the difficulty of assessing the structural integrity and inherent strength of an affected ash tree, we recommend taking a precautionary approach to managing potential health and safety implications. Mechanised felling, harvester or tree shears provide greater protection to operators than chainsaw felling/pruning. Access to infected trees may determine the method of the operation and therefore influence your decisions about management.

Further health and safety guidance on felling dead ash is published by the forestry sector through the UK Forest Industry Safety Accord (UKFISA) and also the Aboricultural Association.  

Mitigation measures

Under Step 3, you will need to consider plans for replacement planting. A felling licence will usually be conditional which means restocking by either replanting or regeneration will need to take place to maintain tree cover in the local landscape. Failure to comply with the restocking conditions of a felling licence is an offence under the Forestry Act (1967).

Your restocking decisions around suitable alternative species to ash should be guided by:

• your management objectives
• site conditions including soil type
• the designation status of the site
• the ecosystem services that ash previously provided; and
• future resilience to pests and diseases.

Guidance on selecting species to replace removed ash trees is available from Forest Research. If the site is designated for conservation purposes (e.g. SSSI, SAC or SPA), you may need specialist advice or consent from NRW to help inform your restocking decisions.

Forest Research’s Ecological Site Classification (ESC) tool can be used to investigate the suitability of species to a site, and will help you consider the options with regard to longer-term climate change. Non-native species can also be considered for sites with few constraints, using Forest Research’s tree species database.

Appropriate selection of provenance is also critical to successful establishment of many, if not all, tree species, but is often overlooked. Our guidance on improving the genetic diversity of Welsh woodlands contains helpful information. Alternatively, promoting natural regeneration from local ash (in the right place) may support the development of tolerant strains. Where ash has been the dominant component of a woodland, we will build in flexibility to the restocking conditions to support some ash regeneration. However, use of coppice shoots from felled, infected trees is not recommended as the disease persists in the roots, so regeneration is also likely to be infected.

Step 4: Review

Changes in the condition of trees affected by ash dieback can occur rapidly. Review your approach in a continuous feedback loop, going back to Step 1 which requires the monitoring of ash trees and subsequent action if required.

Useful links

NE_FC_Ash_dieback_SSSI_management_advice_V2_April_19.pdf (publishing.service.gov.uk)