Ash dieback and protected ash trees on a site

A declining ash tree is still a protected tree. Ash dieback does not switch off a Tree Preservation Order, it does not bring the tree within the dead tree exemption until the tree is actually dead, and it does not entitle anyone to fell without either consent or a properly evidenced exemption. That catches developers out on sites where a whole boundary line of ash is visibly failing, because the obvious commercial answer is to clear the lot and the lawful answer is more careful than that.

Work through the assessment, the consent route and the replanting duty in that order. All three are manageable if you start before the machines arrive.

How decline is assessed and recorded

Assessment uses crown condition. The widely applied approach places each tree into one of four classes by the proportion of crown lost, running from little or no loss through to almost total loss, and removal is usually considered only once a tree reaches the upper classes. Check the current published classification, because the class descriptions and the recommended responses have been refined.

Record each tree individually rather than describing the group. A BS 5837 survey schedule with species, dimensions, condition, category and a dieback class per tree is the document that supports everything that follows. Photograph the crowns from a consistent position so a re-inspection in twelve months can be compared.

Two features matter beyond crown loss. Basal lesions, which are the sign that a secondary decay organism has entered the stem base, because that is what turns a standing declining tree into a collapse risk. And target occupancy, meaning what sits within falling distance: a footpath, a road, a play area, a boundary with neighbours, or nothing at all.

A tree in an advanced class with no targets beneath it can often be retained. The same tree over a public footway cannot.

Whether a declining ash is still protected

Yes, and the exemptions are narrower than site teams assume.

Under a Tree Preservation Order, the dead tree exemption applies to a tree that is dead, and the burden of showing it was dead sits with whoever removed it. A tree with 80 per cent crown loss and live epicormic growth is not dead. The dangerous tree route requires the work to be limited to what removes the immediate danger, with written notice to the authority as soon as practicable, and where the danger is not immediate a period of written notice is required before the work.

In a conservation area without an Order, six weeks written notice under section 211 is required, and the authority may respond by making an Order.

The consequences of getting this wrong are real. Offences under section 210 of the Town and Country Planning Act 1990 carry unlimited fines and the court is directed to consider any financial benefit gained, and contractors are prosecuted as well as clients. Brief the clearance contractor on the Order before anything starts, and discharge the tree protection condition before plant reaches the site.

There is also a biodiversity net gain trap. Clearing declining trees before the baseline survey does not reduce the gain you have to deliver, because the pre-development biodiversity value can be assessed at an earlier date where habitat has been degraded without permission. Removing the ash early makes the scheme harder, not easier.

Consent routes for removal

Pick the route that matches the reason and the timing.

1. Where development is proposed, deal with the trees through the planning application, with the arboricultural information submitted and removals shown on the tree protection plan. A permission that shows the removals authorises them, and no separate Order application is needed for works necessary to implement it.
2. Where no development is proposed, apply under the Order for consent to fell or to carry out the works, and expect the authority to ask why crown reduction or monolithing will not do instead.
3. Where the tree is dead, rely on the exemption and document the evidence before touching it.
4. Where danger is immediate, act to remove the danger only, notify in writing at once, and photograph the tree before and after.
5. Where the trees are in woodland, a felling licence may be needed as well, and woodland orders and felling licences do not overlap tidily with the Order regime.

Apply for more than the worst trees. A phased consent covering a defined programme over two or three seasons is far more useful than repeated single applications, and authorities grant them where the method statement is clear.

Safety and the timing of works

Advanced dieback changes how the work has to be done, which changes the price and the programme.

Brittle failure is the issue. Once decay is established, limbs shed without warning and climbing becomes unsafe, so work moves from climbing to mechanised access or felling from the ground. That means access for a platform or a crane, which means ground protection, which means the works have to be programmed before the site is built out rather than squeezed in afterwards.

Season matters for wildlife rather than for the fungus. Nesting birds are protected from March to August under the Wildlife and Countryside Act 1981, so felling in that window needs a nesting check by a competent person immediately beforehand. Ash frequently carries cavities and loose bark used by bats, and bats and their roosts are protected under the Conservation of Habitats and Species Regulations 2017. Where features are present, a licensed ecologist has to assess them, and a licence may be required. That is a legal requirement rather than a recommendation, and it is the constraint most likely to delay a clearance.

Replacement planting and species choice

Removal under an Order brings the section 206 duty to replace, with a tree of appropriate size and species at the same place, as soon as reasonably practicable. The duty arises automatically and runs with the land.

On a development site the replacement is usually negotiated into a landscape scheme instead. Aim for a mix rather than a single substitute species, because replacing a monoculture of ash with a monoculture of anything repeats the mistake. Consider what the ash was doing: hedgerow standard, woodland edge, parkland specimen or street tree, and match the function rather than the appearance.

Retain apparently healthy ash where you can. A small proportion of the population shows tolerance, and those individuals have value for future natural regeneration, so blanket clearance of every ash on a site is the wrong instinct. Say that in the arboricultural method statement, because it reads as a considered position rather than a cost saving.

Specification and aftercare decide whether the replacements survive, and the standards for planting specification and establishment apply here as to any planting condition.

Habitat value of standing deadwood

Standing dead and declining wood is scarce habitat, and ash dieback has created a lot of it at once.

Where targets allow, the better arboricultural answer is often to retain the stem as a monolith: reduce the crown to a safe height, leave the trunk standing, and let it decay in place. That keeps the deadwood resource, keeps the feature for invertebrates and fungi, and keeps something of the tree's presence in the landscape.

Monolithing works where the tree is away from paths, boundaries and buildings, and where the landowner accepts a feature that will progressively collapse. Set a re-inspection interval and record it. On a development site, a monolith within a retained landscape buffer is straightforward and is usually welcomed by the ecologist.

Felled material has value too. Log piles, standing stacks and retained root plates are low cost habitat features that count in a landscape scheme.

Wording a phased removal into a method statement

The method statement is what the authority conditions and what the site team follows, so write it for both readers.

• A tree schedule with dieback class, target occupancy and the proposed action for each tree.
• The programme by season, with the trigger for moving a tree into the removal phase.
• The re-inspection interval and who carries it out.
• The access method for each removal, including ground protection where plant is used.
• The wildlife protocol: nesting check, bat feature assessment, and the position where a licence is needed.
• Monolithing locations and reduction heights.
• Replacement planting by species, stock size, position and aftercare period.
• Reporting back to the authority after each phase.

An illustrative example: a 3 hectare site with 22 ash in a boundary hedgerow, ranging across the classes. Twelve are retained, four monolithed within a landscape buffer, and six removed because they overhang a public footpath. Consent is granted for a phased programme over three seasons with annual re-inspection, a bat feature assessment identifies two trees needing a licensed ecologist, and replacement is 30 mixed native standards along the same boundary with a five year maintenance period.

Arboricultural and ecological evidence sits across several documents. PlanScope drafts the tree survey narrative and a Biodiversity Net Gain Assessment from your site details, structured to UK planning policy. The statutory biodiversity metric must be completed by a competent person under the Environment Act 2021 regime, and protected species work requires a suitably licensed ecologist, so the drafts are starting points for those professionals rather than substitutes.

This is general guidance, not legal advice; check the current classification guidance and the position with your local planning authority 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.