Ash dieback and what it changes in a tree survey

Ash dieback does not turn every ash on a site into a category U tree, and a survey that records it that way will be challenged. The British Standard on trees in relation to design, demolition and construction puts a tree in category U when it cannot realistically be retained as a living tree in the context of the current land use for longer than about ten years. Plenty of infected ash fails that test. Plenty does not, and the difference has to be recorded tree by tree with the evidence written down.

For a landowner with a few hundred ash across a holding, the practical consequence is that a survey is now a two part document: a condition assessment that records the stage of decline on each tree, and a programme that says what happens to it and when.

Recording the disease rather than labelling the tree

Ash dieback is caused by the fungus Hymenoscyphus fraxineus, known for years as Chalara. What an arboricultural survey should record is what is visible, in terms someone else can check:

• The proportion of the crown showing dieback, expressed on the four class crown decline scale used in ash dieback management, from light through to severe.
• Epicormic growth on the stem and main branches, which is the tree's response to crown loss and a sign of how far the process has run.
• Whether basal lesions are present, where on the stem, and how far round the circumference they extend.
• Signs of secondary pathogens, honey fungus in particular, which is what usually kills a weakened ash.
• The structural consequence: brittle deadwood in the crown, loss of the upper canopy, included unions now carrying more load.
• The target. A declining ash over a byway is a different proposition from the same tree in the middle of a paddock.

Record the date of inspection and whether the tree was in leaf. Ash dieback is far easier to assess in full leaf between June and September, and a winter survey of ash will usually need revisiting. Say so in the report rather than letting a case officer assume otherwise.

Categorising declining ash honestly

Here is where surveys go wrong in both directions. A developer's survey that puts every ash in category U delivers a free clearance and a lower biodiversity baseline, and tree officers have seen it often enough to read it at a glance. A survey that retains severely declining ash next to a road exposes the owner to a different problem entirely.

The defensible approach is to let the dieback class and the basal condition drive the category:

That last row carries the operational point. A basal lesion compromises the stem at ground level, so the tree can fail without the crown giving warning, and it cannot be safely climbed. The work becomes a mechanised or platform operation, which changes the cost, the access requirement and the ground protection needed. Budget for it at survey stage rather than discovering it when a contractor declines the job.

Monolithing, which means reducing a tree to a standing stem for habitat, is worth considering where there is no target. Dead and dying ash is good habitat, bats use the loose bark and cavities, and retaining standing deadwood in a field corner keeps value that felling removes. It also keeps the tree in the Tree Survey schedule as a constraint rather than deleting it, which matters if the land is later developed.

Safety management where there are targets

Owners owe duties to visitors and to trespassers under the occupiers' liability legislation, and separate duties where land is a workplace. Those duties are discharged through a reasonable, documented inspection regime rather than through perfection.

A zoned approach is what most holdings end up with:

1. Zone the holding by target: public highway and footpath frontages, farm tracks and yards, buildings and parking, then open land with no regular access.
2. Set inspection intervals by zone, with the highest target zones inspected most often and in leaf.
3. Record each inspection, including the ones that find nothing, because the record is the defence.
4. Act on the findings within a stated period, and note where work has been deferred and why.
5. Re-inspect after major storms along the high target zones.

Where ash overhangs an adopted highway, the highway authority has powers to require work, and a notice is a worse outcome than a programme you set yourself. Where ash overhangs a neighbour's land, the position on self help and on notice is a civil matter, and it is better settled in a letter than after a branch has landed.

Protected ash and the narrower exemption

This is the part that catches rural owners most often. The Town and Country Planning (Tree Preservation) (England) Regulations 2012 narrowed the old exemption. The pre-2012 wording covered trees that were dead, dying or dangerous. The 2012 Regulations provide an exemption for works to remove a dead tree, and a separate exemption for works urgently necessary to remove an immediate risk of serious harm.

So a dying ash with 60 per cent crown dieback is not exempt. It is a protected tree that needs an application for consent, and consent may be granted with a replacement condition. The exemptions that do apply come with procedure:

• For a dead tree, five working days' written notice to the authority before the work, except where the work is urgently necessary.
• For urgent works, notice in writing to the authority as soon as practicable after the work is carried out, with evidence of the risk.
• The duty to plant a replacement tree in the same place, as soon as reasonably practicable, applies when a tree is removed under the dead tree exemption. The extent and duration of that duty is covered in tree replacement conditions and how long they bind.

The same narrower test applies to trees in conservation areas, where the section 211 notice procedure otherwise requires six weeks' notice. Photograph the tree before the work, from several positions, with the basal area visible. The commonest dispute is about whether the tree was dead or merely declining, and the only evidence that settles it is a photograph taken beforehand. What to do when an allegation has already been made is set out in responding to an unauthorised tree felling allegation.

Phasing removals across a holding

Felling every declining ash in one winter is expensive, bad for the landscape and usually unnecessary. A phased programme does better on all three counts, and councils respond well to one.

Sequence by risk rather than by convenience. High target zones first, then trees with basal lesions, then severely declining trees in medium target areas, leaving low target trees to be monitored or monolithed. Spread the work across several seasons and keep outside the bird nesting season where you can, since nests in use are protected and most ash removal happens in the months when birds are active.

Two further points. Where a tree may support bats, a bat assessment is needed before work, since roosts are protected whether or not bats are present at the time, and that assessment requires a suitably experienced ecologist. And where the holding is in a woodland grant or management agreement, check what the agreement requires before felling, because some schemes have their own notification steps.

Replacement planting and biosecurity

Do not replant ash. Beyond that, the choice is about resilience rather than matching what was lost.

Spread the risk across species, genera and families. The widely used planting rule of thumb limits any one species to about a tenth of a population, any one genus to a fifth and any one family to under a third, and after a generation of elm and then ash losses the logic needs no explanation. Match the species to the soil, the exposure and the eventual size available, and where the planting is replacing a hedgerow tree, pick something that will tolerate the management the hedge receives.

Biosecurity matters as much as species choice. Buy from nurseries that can evidence plant health standards and, where possible, UK provenance and UK growing, and inspect stock on delivery. Follow the establishment guidance in the relevant British Standard covering trees between nursery and independence, because a replacement tree that dies in year two satisfies nobody and may leave a planting condition unmet. Larger schemes should set the planting out in a Landscape Strategy with a maintenance specification and a replacement clause.

Evidence the authority expects

For a planning application, a tree survey to the British Standard with the dieback class and basal condition recorded per tree, a tree constraints plan, an arboricultural impact assessment, and a method statement with tree protection details.

For works to protected or conservation area ash, the application or notice, photographs showing the condition including the stem base, the inspection record, and where urgency is claimed, a dated note of the risk and who assessed it.

For a holding wide programme, the zoned inspection regime, the phased removal schedule and the replacement planting plan, which together answer the question an authority or an insurer will ask, which is not whether trees are declining but whether anyone is managing them.

This is general guidance, not legal advice; check the position with your local planning authority or a qualified professional before relying on it. PlanScope provides AI-assisted draft reports for planning applications. Reports should be reviewed before submission. We do not guarantee planning approval. To see which tree documents a site is likely to need, enter your postcode on PlanScope.