Dealing with ash dieback

In the UK, there are an estimated 185 million adult ash trees, with 60 million of them growing outside of our woodlands. Many of these trees are located near high risk targets, such as roads, railways, public spaces and buildings.

First confirmed in Britain in 2012, ash dieback (Hymenoscyphus fraxineus) is a highly destructive fungal disease that is majorly affecting ash trees in the UK. Once infected there is no cure and the tree quickly becomes brittle and unstable, making them particularly dangerous. Infection also causes them to become vulnerable to other pests and pathogens, especially honey fungus (Armillaria mellea), which accelerates their decline and mortality can occur in as little as two growing seasons.

In the UK, there are an estimated 185 million adult ash trees, with 60 million of them growing outside of our woodlands. Many of these trees are located near high risk targets, such as roads, railways, public spaces and buildings.

Taking Hampshire as an example, there is a substantial sized ash tree within falling distance of the highway roughly every 320 metres (along the major routes), in addition to the thousands that line our rural roads, footpaths, parks, gardens and hedgerows. As the third most common tree in the UK it's a similar picture across the country.

The full impact of ash dieback (ADB) isn't known yet, but it's estimated that anywhere from 70% to 95% of those trees will die within the next 10-15 years. It's clear that ADB poses a serious threat to public safety, and we are already seeing the effects.

 

Safety and habitat: a balancing act

There are over 1,000 species of wildlife that inhabit ash trees, 44 of which have been identified as only ever occurring on living or dead ash. With approximately 5% of trees showing a genetic tolerance to ADB it's crucial that these trees are preserved, not only to retain habitat, but for natural regeneration and for the future of ash trees in the UK. 

The general accepted guidance is that trees should be monitored carefully to ensure they do not become a danger, with felling being seen as a last resort as even standing dead trees provide crucial dead wood habitat for a wide range of nesting birds and roosting bats, as well as a range of invertebrate and fungi. Where ash trees pose a low safety risk, for example trees in remote areas with no public access, leaving trees to die and decay naturally is not an issue. 

However, the largest issue for land owners and councils who manage trees in busy areas with high levels of public access is the threat to public safety due to structural failure, as trees may shed branches and limbs, or even collapse. As a result, any infected trees in such areas require regular inspection and reactive measures, such as crown reduction, pruning/removal of deadwood, and where required, selective felling.

Under both the civil law and criminal law, an owner of land on which a tree stands has responsibilities for the health and safety of those on or near the land and has potential liabilities arising from the falling of a tree or branch. the civil law gives rise to duties and potential liabilities to pay damages in the event of a breach of those duties. the criminal law gives rise to the risk of prosecution in the event of an infringement of the criminal law.
National Tree Safety Group - Common sense risk management of trees

Due to ash dieback, there is the potential for serious damage to property, such as fences, gates, buildings, power lines etc, but more importantly, there is the risk of serious injuries or death. Consequently, it is extremely important for landowners to understand the potential risk to life and the potential insurance claims and litigation arising from landowners failing to address the safety risks associated with ADB.

Identifying ADB

To enable a standard system for describing the condition of a tree using the percentage of its remaining canopy, the Forestry Commission published 'Assessment of Tree Condition' in 1990. Using this methodology, Suffolk County Council developed a system for assessing the overall health of ash trees in 2014 by studying their canopy. 

Using this framework, we can assign a tree to a ‘health class’ which helps guide future action. This helps to establish a point where trees will be removed (likely stage 4, but possibly stage 3, depending on the criteria outlined in an ADB action plan).


The Suffolk County Council Ash Health Assessment System
Class 1 - 100%–76% remaining canopy
Class 2 - 75%–51% remaining canopy
Class 3 - 50%–26% remaining canopy
Class 4 -25%–0% remaining canopy

Spotting the symptoms

Ash trees of all ages can be affected by Ash Dieback. In general, all trees affected by the disease will display these symptoms, although younger trees will succumb more quickly:

  • Leaves develop dark patches in the summer.
  • The leaves then wilt and turn black. Early leaf shedding may occur.
  • In the summer, the leaves and shoots dieback.
  • Lesions develop where the branches meet the trunk. The lesions are often diamond-shaped and dark brown in color.
  • Under lesions, the bark appears brownish-grey.
  • Further down the trunk, buds that were previously dormant are growing. This is called epicormic growth in trees and is a response to stress.

Dealing with dead and dangerous ash

To reduce the risk when felling infected ash, it is crucial to thoroughly assess the situation and to plan the work. This might involve road closures and traffic management planning, or fencing to restrict certain areas to the public. Also, whenever possible, trees must be felled mechanically, with operators protected from falling branches and tops in a cab, and chainsaw operations should be kept to an absolute minimum.

Because infected trees are structurally unstable, climbing into the crown and dismantling them manually can be extremely dangerous. The increase in crown deadwood also greatly affects the chances of operators being struck by falling branches and tops whilst operating on the ground. We have already seen instances in the past few years where highly trained operatives, wearing full PPE, have been seriously injured, even by relatively small branches (Safety guidance published by FISA can be found here).

Furthermore, it is difficult to determine where the weakened timber is exactly, particularly if the tree is also infected with honey fungus, meaning the risk of a tree breaking and falling in an uncontrollable manner increases dramatically, putting nearby infrastructure and operators at risk.

It’s for these reasons that we decided to invest in the equipment and machinery to enable mechanised dismantling and felling. Utilising our fleet of forestry machinery, civil excavators and RRVs, combined with specialist attachments such as our saw grappling heads, not only allows for safer working, but also greatly increases productivity.

We also possess whole tree chippers, which are ideal for producing biomass grade wood chips from the arisings, leaving the ground free of excess material.

 

Work on a plan and stay compliant

If you’re lucky enough to not yet see signs of ADB, then then now would be a good time to start work on an Ash Dieback Action Plan (ADAP). In short, an ADAP is designed to assess and address the possible likely impact and risks posed by the impact of ash dieback, outlines plans to conserve the site biodiversity and ecosystems ash trees are found in, and prepare for an extended regeneration period.

The Tree Council has developed an ADAP toolkit which contains resources and materials provided by Local Authorities and other agencies as they prepared to manage the impacts of ADB.

Without following the correct procedures, it is illegal to prune, cut down, or damage a protected tree. When dealing with ADB the usual legislation around trees applies, unless the trees are dead, dying or dangerous, and pose an immediate threat.

Felling licences - Felling trees without a licence, where one would have been required, is an offence. Although there are certain exemptions here, including the location, type of work being carried out, and the diameter and volume of timber being removed. 

Tree Preservation Orders (TPO) - It is necessary to obtain the express consent of the local planning authority, which normally takes 8 weeks to resolve. The potential for ADB to spread further won't be a significant factor, since it is considered unnecessary to fell infected ash trees. 

It is not necessary to submit an application for dead or dangerous trees, however, the planning authority must be notified five days in advance.

If a tree has been felled that is protected by a TPO then the landowner is legally required to replace the tree. This also applies if the tree is dead, dying, or has become dangerous.

Conservation Areas - The local planning authority must be notified six weeks in advance of the intended works. Like TPOs, dead and dangerous trees are exempt from application, but notice must be given to the planning authority five days in advance, and the tree(s) must be replaced.

European Protected Species - Ash trees can support bats, nesting birds and possibly dormice, which are all protected under The Habitats Directive

If it’s discovered through a survey that works could adversely impact a protected species, you’ll need the appropriate wildlife licence from Natural England in order to proceed. The specific licence needed will be influenced by the species in question and the anticipated impact of the tree works.

What to do with felled timber?

Despite the doom and gloom, there are still viable markets for ash.

Ash timber has been a sought after product for many years due to its attractive grain and versatility. If felled early enough, and the timber hasn't suffered from staining caused by ADB, then ash can be sold as large diameter timber for flooring, joinery and furniture. More likely uses for infected ash in its later stages is the firewood market, where prices continue to increase. Trees that aren't suitable for timber or firewood, and all brushwood can be chipped and sold into the biomass market, which is stronger than ever thanks to a focus on renewable energy targets.

As one of the largest timber harvesting contractors in the UK, we have long-standing relationships with a wide network of sawmills and processing plants. We're also 100% independent, and will work hard to secure the best possible prices for your product, giving you a financial return to help pay for the management of diseased ash.

We have delivered a range of solutions for our clients. From woodlands to roadside ash, and onto nature reserves, and are confident we we can help you find a suitable way to deal with your trees that have been affected by ADB.

Further reading

Ash Dieback an Action Plan Toolkit - The Tree Council

Chalara in Non-woodland Situations - defra

The potential ecological impact of ash dieback in the UK - JNCC


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