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Chalara manual – 2. Managing ash trees and woodland, including logs and firewood

Home tool-and-resource Forestry and tree health resources Pest and disease resources Ash dieback (Hymenoscyphus fraxineus) Chalara manual – 2. Managing ash trees and woodland, including logs and firewood

Ash coppice woodland cropped.jpg

1. Principles

The principles underlying the guidance presented below are:

  • maintaining, where possible, the values and benefits associated with ash woodlands and iconic trees;
  • securing an economic return where timber production is an important objective;
  • maintaining as much genetic diversity in ash trees as possible with the aim of ensuring the presence of ash in the long term; and
  • minimising impacts on associated species and wider biodiversity.

2. Management options

There is currently no cure for chalara ash dieback, and no clear method for stopping its spread. Therefore the aim of management, as outlined in the National Chalara Management Plan, should be to slow the spread, minimise the impact of the disease, and preserve as many chalara-tolerant ash trees as possible.

Before making any changes to existing management regimes, owners and managers should carefully consider their objectives and local circumstances. Any woodland or individual tree can bring a variety of benefits, and be managed for those multiple benefits. The categorisation below is made purely to assist the owner or the manager when thinking about what to do next – in practice a hybrid approach might be appropriate.

3. Managing the safety risk from dead and dying trees

Public safety is likely to be one the biggest management issues for owners of ash trees in woodlands and parks and alongside roads, railways, footpaths and carparks etc as the disease kills or weakens trees.

Trees in areas with high levels of public access therefore need to be monitored carefully for risks to public safety, and some felling or pruning of dead or dying trees is advisable if risk assessments show they are a hazard. When assessing trees’ health, look for signs of lesions (cankers) or honey fungus (Armillaria) near the base of the trunks: these can weaken the trunks and make the trees more prone to falling.

The Tree Council has published detailed guidance on managing diseased ash trees for local authorities and other public authorities which manage trees.

Further information about tree safety is available in the publication Common sense risk management of trees .

4. Reducing the impact on timber crops

For uninfected stands, the best way to slow the impact of any future chalara infection is to promote fast, healthy growth of selected trees. This will not prevent the onset of the disease if spores are present, but will maximise the timber value at the time of felling.

It is therefore essential to ensure high standards of establishment and silviculture. Guidance on this can be found in 'Managing Native Broadleaved Woodland', (available from The Stationery Office), and in 'Growing Broadleaves for Timber'.

This should be carried out in combination with:

  • adhering to biosecurity measures to reduce the spread of chalara; and
  • regular monitoring for signs of chalara ash dieback – see the section on symptoms and identification on our main chalara ash dieback page for help to identify the disease.

If honey fungus is present on a tree being grown for timber, fell within a few seasons of honey fungus being identified, otherwise the fungus will render the timber unusable.

5. Options for chalara-infected timber crops

a) Younger stands (i.e. up to pole stage)

Younger trees are the most vulnerable to the disease, and once infected they usually die quickly. If disease levels are low, selective thinning of diseased and suppressed trees is recommended.

If more than 50 per cent of the mature ash in the stand is infected, the annual rate of spore production will be very high. The economic value and condition of the trees will decline rapidly, and therefore you might wish to realise their value sooner than originally planned. Subject to adherence with UK Forestry Standard, felling all the ash should be considered to allow regeneration, but you might wish to leave some trees which are close to dying to provide deadwood and biodiversity in the stand.

Similarly, you might consider retaining any that still look healthy, e.g. 90 per cent or more of the crown is healthy.

Then:

  • if the stand is a mixture of species, and there are enough trees of other species to form a closed stand within 10 years, it is likely that your management objectives can still be achieved without replanting after felling the ash; and
  • if the stand is a mixture and there are NOT enough trees of other species to form a closed stand within 10 years, it is likely that the stand will have to be regenerated by planting alternative species after felling. (See below for guidance.)

Managing leaf litter during the autumn and winter might help to reduce re-infection levels the following year in very small woodlands, or woodlands with very few ash trees. This disrupts the fungus's lifecycle and reduces spore production and therefore inoculum pressure the following summer. However, this can be very time consuming and expensive on anything other than a small scale, and does not cure the disease, but it might buy some time.

If the stand consists of pure ash you will need to consider what alternative species would do well on the site. (See No. 16 below)

b) Older stands

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, felling should be considered because their economic value is declining, they have become seriously infected, and they will be producing large volumes of spores, which will infect other trees.

Where less than 50 per cent of the crown is infected, trees should be regularly monitored as described above. However, managers should also assess the risk of Armillaria (honey fungus) attack. This is often the ultimate cause of death of ash trees with chalara, especially older ones. Felling should be considered if Armillaria is present on the site and timber production is an important objective.

6. Preserving the environmental benefits of  woodland

A lower level of active management might be your best option where preserving environmental benefits is the key objective. However, you should consider planning to retain ash as a component for as long as possible to provide habitat for those species which depend on ash trees, and allow time for tolerant strains to be identified.

In general, ash woodlands of high environmental benefit also include a mixture of other tree species which will secure many of the same environmental benefits, albeit with a loss of diversity if ash cannot be retained. However, upland ashwoods could decline in environmental benefits if appropriate interventions are not made.

Taking no action will:

  • eventually reduce the proportion of ash in the woodland;
  • increase the amount of deadwood (standing and on the ground);
  • allow chalara-tolerant trees to be identified; and
  • lead to increased spore production from the woodland.

A more proactive management approach will:

  • help to reduce spore levels and the rate of onward infection;
  • open up the woodland to allow natural regeneration to take place;
  • let more light into the stand; and
  • encourage regeneration and structural diversity.

See also the comments in No 5 (a) above about managing leaf litter.

7. Priority or protected species on site

If there are rare, threatened or protected species which have a particular need for ash, specific advice might be needed for that site to maintain them. Current advice recommends a presumption against felling living mature ash trees, with which some European Protected Species are associated. However, impact on protected species should be considered in all forest operations.

8. Protecting valuable veteran ash trees, pollarded ash, or ash trees in towns

Currently the only effective option to reduce spread of the disease in these circumstances is to remove all ash leaf litter from around the trees in the autumn and winter. This will disrupt the fungus's life cycle and thereby reduce spore production the following summer.

There is some evidence from continental Europe that leaf removal, possibly coupled with the lower humidity levels in parkland and urban tree environments, can reduce and slow the impact of chalara, and in some circumstances i.e. for high value trees (biodiversity/economic etc.) this may be a suitable course of action.

Urban and veteran ash trees should be surveyed to establish the level of infection present, and the disease status of the tree should, ideally, be assessed by a professional before agreeing any work programme.

Where no infection is present or suspected, any routine, planned work on ash trees should continue. The timber and brushwood can be removed, chipped and processed as usual. Arisings can be left on site, and if required, processed there through composting or burning where possible. However, if removing from site, best practice would include transporting material in a covered vehicle to a site where it can be safely burnt or composted.

The ecological benefits of leaving deadwood on site should be noted. (UK Forestry Standard, Forests and Biodiversity Guidelines)

For pollarded trees the current recommendations from the Swedish authorities, where there is a long history of pollarding, is to avoid all restoration cutting of old pollarded ash trees for the time being if there is not an acute risk that they will fall apart.

However, pollarding of both healthy and infected ash trees which have been pollarded regularly should continue until such time as we know more. Avoid pollarding all trees in the same year if possible, but spread the pollarding over several years. It is very important to revisit these trees regularly to assess the impact of chalara ash dieback.

9. Infected urban or veteran trees

There should be a presumption to leave these trees standing if at all possible, unless public safety is an issue. Veteran trees in particular can provide many important environmental and social benefits, even when dead.

Any work on a tree should be undertaken after a risk assessment, which should consider age, condition, the number and species of other trees in the locality, the potential risk of further infection, and the danger to the public. The cost of taking or not taking action is also likely to be a factor in any final decision.

Chalara management in mainland Europe often includes crown reduction of infected urban trees, and felling then takes place only when a tree has been unable to maintain its crown for three years.

Arisings can be left on site, and if required, processed there through composting or burning where possible. However, if removing from site, best practice, would include transporting material in a covered vehicle to a site where it can be safely burnt or composted. 

Local councils and other public authorities which manage trees can find further detailed guidance in the Tree Council's Ash Dieback Action Plan Toolkit.

10. Infected trees in hedgerows and rural situations

Hedgerow and rural trees often make significant visual contributions to the landscape, and many also provide environmental benefits. Public safety and cost are likely to be key considerations in managing these trees, and expert advice is advisable.

Management options will depend on the trees’ situations and locations, and the environmental and social benefits they provide. Managers are therefore advised to consider the points above on preserving environmental benefits and managing veteran, urban and garden trees for guidance.

Planting replacement trees of an alternative species will ensure that the benefits of ash standard trees in hedgerows will be continued. See 'Alternative species for planting' below.

11. Trimming ash hedges

There is no specific advice about this. However, the guidance for ash trees in parks and gardens above is relevant. Arisings can be left on site, and if required, processed there through composting or burning where possible. However, if removing from site, best practice, would include transporting material in a covered vehicle to a site where it can be safely burnt or composted. 

However, we recognise that this is unlikely to be an option for hedges in the countryside, particularly where hedges are cut using a tractor with a mechanical flail. At present there is no practical control strategy in these circumstances. If a hedge requires cutting, it is probably better to do so rather than neglect it.

It is best to avoid cutting during the summer months and during the bird-breeding season, when the spore production from dead leaves on the ground is highest, and disturbance might increase dispersal.

12. Increasing woodland's resilience to chalara

The single best strategy is to increase the genetic and age diversity of your woodland. Developing stands of mixed species should make your woodland less vulnerable to disease, and adopting a continuous-cover approach, where practicable, can promote higher levels of species and age diversity.

13.  Encouraging ash regeneration

Unless you have a source of seed on site, planting ash is currently not possible because of the prohibitions (see 'Official action' on main page) on moving ash planting material, but it would not be recommended even if these restrictions were lifted.

Natural regeneration is the preferred method of replacing ash stands. Tolerance of chalara dieback of ash is likely to be highly heritable, so natural regeneration from tolerant trees is the preferred option for replacing the species in areas which retain sexually mature trees, that is, trees more than 30 or 40 years old.

Guidance on the successful use of natural regeneration can be found in 'Managing Native Broadleaved Woodland', (available from The Stationery Office) and in 'Growing Broadleaves for Timber'.

14. Regeneration from coppice

Regenerating a stand using coppice shoots from felled, infected trees is not recommended. Chalara can be isolated from roots, and it is thought to be highly systemic, so coppice regrowth from the infected trees is also likely to be infected.

Recently coppiced non-tolerant ash will become infected with chalara and rapidly die. There should therefore be no need to chemically treat any stumps when restocking the site with other species or encouraging ash natural regeneration to grow.

Conversely, the presence of any chalara-tolerant ash trees should become apparent soon after coppicing, and these valuable trees are worth protecting for the future. Browsing animals such as deer will target healthy ash trees in preference to diseased ones, so we particularly advise efforts to protect them from browsing damage.

In ancient woodlands or woodlands where coppice is an important cultural factor:

  • avoid carrying out a traditional coppice operation where ash forms more than 30% of the canopy: the loss of a proportion of these stools might be expected if licensed coppicing of ash is agreed as the correct management prescription;
  • continue planned work, or consider cutting areas containing species other than ash first;
  • retain as many ash trees in the canopy as practicable to encourage seed production; and
  • where creation of temporary open space is not critical, leave about 50–70% cover by maintaining some canopy of ash and other species, and retaining standards and maidens.

15. Options if there are no tolerant mature ash trees on site

If, after several years of chalara ash dieback on the site, there are no apparently tolerant mature ash trees left on a mixed-species site, and regeneration has failed, and if there are enough trees of other species to form a closed stand within 10 years, it is likely that your management objectives can still be achieved without carrying out further regeneration.

In other cases the stand should be regenerated by planting alternative species, until chalara-tolerant strains of ash can be made available.

16. Alternative species for planting

The choice of species must always be guided by management objectives, site conditions and designation status of the site. For example:

  • on brown earth soils the range of alternative broadleaved species is wide and includes aspen, beech, birch, cherry, field maple, hornbeam, oak, lime, rowan, sweet chestnut and sycamore.

On other sites the choice is much more restricted. For example:

  • on ground-water gleys – alder, aspen, willow and oak are possible alternatives;
  • on rendzinas – beech, birch, field maple, whitebeam, hawthorn, holly and the wayfaring tree could be considered; and
  • if the site is designated for conservation purposes (for example, as an SSSI, SAC or SPA), or is an ancient woodland, advice should be sought from conservation agency advisers.

Detailed guidance on species choice in native broadleaved woodland can be found in 'Managing Native Broadleaved Woodland'.

Ecological Site Classification (ESC) can also be used to investigate the suitability of species to a site, and will help managers consider the options with regard to longer-term climate change. See our online Decision Support Service.

Non-native species can also be considered for sites with few constraints, using our guidance.

It is important to note that some alternative species, such as beech, sycamore and Norway maple, are very susceptible to bark stripping by grey squirrels.

17. Re-using tree shelters if they had diseased ash plants

Even if H. fraxineus spores are present in them, used shelters will not pose a risk to any non-ash saplings being grown in them, so re-using them on the same site will pose no problems.

There is a small risk of transferring the disease to another site by moving leaves or spores with the shelters or stakes. If you must use shelters or stakes on another site, you should ensure that any leaf litter is fully removed.

18. Deer control

Deer should always be controlled where establishment by planting or natural regeneration is an aim. This is particularly important when regenerating ash stands with chalara ash dieback, because it is likely that deer will tend to target healthier, tolerant ash seedlings, rather than susceptible, diseased and dying plants.

19. Logs and firewood

Ash logs 1018750 FC cropped.jpg

Spread of chalara ash dieback in wood is considered to be a low risk, so ash wood from infected as well as uninfected sites may continue to be moved without restriction within Great Britain (England, Scotland and Wales).

However, we strongly recommend the simple precaution of brushing leaf and shoot material from logs, firewood and vehicles before they leave the site. This is a precaution against the possibility that the disease might be present, but not obviously apparent, and could be spread unintentionally with logs and firewood.

See also the government guidance on the regulations applying to imports and exports of wood and wood products into and out of Great Britain.

 

 

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