Ash Dieback Surveying & Risk Management
Ash dieback — caused by the fungal pathogen Hymenoscyphus fraxineus, formerly known as Chalara — is the most significant tree disease affecting the United Kingdom's ash population. It is estimated that the disease will eventually kill the majority of the country's 150 million ash trees, and landowners with ash trees on their property have a legal duty of care to survey for the disease, assess the risk posed by affected trees, and respond proportionately to protect public safety.
Urban Tree Management provides ash dieback surveys, risk assessments, and management plans for landowners, local authorities, highways departments, housing associations, and estate managers across Greater Manchester, Lancashire, Cheshire, Merseyside, and nationwide.
Not Every Infected Ash Needs Felling
Worth saying at the outset, because it is the single most expensive misunderstanding on this subject.
Ash dieback is assessed on a four-class scale of decline. A tree in the earlier classes may stand and function for years, and a proportion of ash show genuine tolerance worth preserving. Wholesale removal of every infected ash on a site is rarely necessary, frequently unaffordable, and removes trees that would have contributed for another decade.
Equally, an infected ash close to a road, footpath, playground or building becomes brittle and unpredictable long before it looks obviously dead — and those trees need addressing on a timescale that reflects the risk rather than the budget cycle.
The work is in telling the difference. A proportionate survey identifies which trees genuinely need action now, which can be monitored, and which can be left — and produces a phased schedule that spreads cost across budget years instead of triggering a single unaffordable clearance.
As independent consultants carrying out no tree works, we have no interest in the quantity of felling recommended.
What is ash dieback?
Ash dieback is a highly contagious fungal disease that infiltrates the vascular system of ash trees — the network of vessels responsible for transporting water, nutrients, and gases through the tree. Once established, the fungus causes vessel obstruction, branch girdling, crown dieback, and ultimately the death of affected parts. Most infected trees will eventually die either from the disease itself or from secondary infections such as honey fungus, which exploit the tree's weakened defences.
A small proportion of ash appear to show some degree of genetic resistance, and research into identifying and propagating these individuals is ongoing. However, the overwhelming majority of infected trees will continue to decline and will eventually need to be managed for safety as their structural integrity deteriorates. The rate of decline varies significantly between individual trees, sites, and growing conditions, making regular monitoring an essential part of any management strategy.
Surveys should ideally take place between July and September when trees are in full leaf, as the characteristic symptoms — wilting and blackening of leaves, diamond-shaped lesions on stems, and dieback of shoots from the tips — are most clearly visible.
Ash Dieback Surveys — Phase 1 and Phase 2
Urban Tree Management carries out ash dieback surveys using a two-phase process that allows the extent and severity of infection across a site to be assessed efficiently before detailed individual tree assessments are commissioned.
Phase 1
Identifies the areas of significance across the site, establishes overall levels of infection, assesses the potential clearance impact of removing affected trees, and classifies the percentage dieback recorded in each tree or group.
The clearance impact assessment is a critical element. Removing a single tree in dense woodland has a very different landscape and ecological consequence to removing a lone ash in an open field, and that distinction must inform the management response.
Phase 2
Builds on the Phase 1 findings to identify the specific stems requiring removal, produce a phased management plan for the affected trees, and establish the restocking levels required to replace what will be lost.
Depending on the size of the site and the level of infection found at Phase 1, Phase 2 data can sometimes be captured during the same visit. Following each phase we provide a full written report of findings, risk ratings, and management recommendations.
Specialist Ash Dieback Inspections
Some assessments require a higher level of inspection than a ground-level walkover. Where trees are of significant size or amenity value, or located in high-target areas such as roads, footpaths, or play areas, more detailed investigation may be required before a management decision is made.
We carry out aerial climbing inspections where detailed examination of the upper crown is needed. Where structural decay is suspected — a common secondary consequence of ash dieback as the tree's defences weaken — Rinntech Resistograph R650 and Arbotom sonic tomography testing establishes internal condition and informs the most proportionate recommendation.
All inspectors carrying out ash dieback surveys are qualified to Level 6 in Arboriculture — significantly above the Level 3 or Level 4 minimum accepted by many organisations — and are experienced in working with large ash populations across a wide range of site types.
A Note on Felling Ash Safely
Ash affected by dieback becomes brittle in a way that other declining species do not, and standard climbing methods can become unsafe well before the tree looks dangerous from the ground.
Where felling is recommended our specification records the condition of the tree and flags where a ground-based approach or mechanical assistance is likely to be required, so the contractor can price and plan the work properly rather than discovering the problem on site.
We specify the works; we do not carry them out.
Your Legal Responsibilities as a Landowner
As a landowner, if you have ash trees on your property you have a duty of care under the Occupiers' Liability Acts and Health and Safety legislation to ensure they do not pose an unacceptable risk to people or property. Where ash dieback is present this obligation intensifies as the disease progresses, because structurally compromised trees are significantly more likely to shed branches or fail than healthy trees of the same species and size.
Regular surveys that are documented, acted upon, and reviewed provide the most robust evidence that you are meeting your duty of care proportionately. We produce reports in a format that supports this audit trail, and advise on the most cost-effective and proportionate approach for ash populations of all sizes.
Because ash dieback is progressive, monitoring matters as much as the initial survey. This work is available on a retained basis — tracked reinspection dates across the whole site so decline is measured against a baseline rather than reassessed from scratch each time.
Frequently Asked Questions
Do I have to fell ash trees with ash dieback?
Not necessarily. Ash dieback is assessed on a four-class scale, and trees in the earlier classes can often be retained and monitored, particularly away from targets. Some ash show genuine tolerance worth preserving. Trees within falling distance of a road, footpath or occupied area are assessed differently because the consequences of failure are greater.
When is the best time to survey for ash dieback?
July to September, when trees are in full leaf and the symptoms — wilting and blackening foliage, diamond lesions, and shoot dieback — are most visible. Surveys outside this window are possible but the assessment of crown decline is less reliable.
How often should ash be reinspected?
More frequently than most trees, because the disease is progressive. A tree assessed as low risk this year may not be next. Intervals of twelve months are common where ash sits near targets, extending where the population is remote from people and property.
Do I need a felling licence to remove ash?
Possibly. Felling licence thresholds apply by volume within a calendar quarter, and exemptions vary. Where trees are also protected by a Tree Preservation Order or sit in a conservation area, separate consent is required — a TPO does not fall away simply because a tree is diseased. We set out the statutory position in every report.
What happens to the ecology when ash is removed?
Ash supports a wide range of associated species, and clearance has ecological as well as landscape consequences. Standing deadwood retained away from targets has real habitat value, and our recommendations distinguish between trees that must come down entirely and those that can be reduced to safe monoliths.
Ash Dieback Surveys & Management — Greater Manchester, Lancashire & Cheshire
Ash dieback needs a proportionate response, not a precautionary one. We identify the trees that genuinely require action, those that can be monitored, and those that can be left — with a phased schedule that spreads cost across budget years and a monitoring programme that tracks decline against a recorded baseline.
Get in contact with our highly experienced and personable team of arboricultural consultants today, to discuss your requirements and to obtain your zero obligation quotation.
