Recording a tree as category U and what follows

A category U tree under BS 5837:2012 is one in such a condition that it cannot realistically be retained as a living tree in the context of the current land use for longer than ten years. That is the whole definition, and every argument about a category U classification comes back to it. The category is about the tree's condition and remaining safe useful life, not about whether it is in the way of the proposed building.

Officers know this, which is why a category U tree standing exactly where the new access needs to go attracts more scrutiny than any other entry on the survey schedule.

What category U means in the survey

The British Standard sorts trees into four groups. Category U for trees that should be removed for reasons of sound arboricultural management. Category A for trees of high quality with an estimated remaining contribution of at least forty years. Category B for moderate quality with at least twenty years. Category C for low quality with at least ten years, or young trees with a stem diameter below 150mm.

Categories A, B and C carry subcategories for the reason the tree is valued: arboricultural, landscape, or cultural including conservation. Category U has no subcategories, because a tree that cannot be retained has no value to subdivide.

The standard gives examples of what belongs in category U. Trees with a serious irremediable structural defect. Trees that are dead or showing signs of imminent collapse. Trees infected with pathogens of significance to the health of other trees nearby, or very low quality trees suppressing adjacent trees of better quality. The common thread is that removal is the right arboricultural answer whether or not anyone is developing the site.

One consequence often missed. Category U trees are excluded from the design stage as a matter of course, but their root protection areas still matter during the period before they are removed, and their removal still needs authorisation if they are protected.

The evidence needed to justify the classification

A category U entry in a schedule with no supporting observation is worth nothing. The tree officer will assume the classification is convenient rather than arboricultural.

Record what you saw. The defect, its location on the tree, its extent, and why it cannot be remedied by pruning or by reducing the target. Fungal fruiting bodies identified to species where possible, with the position on the stem or buttress noted, because a bracket at the base carries a different meaning from one on a lateral branch. Decay indications, cavity extent and any decay detection work carried out. The structural condition of the union where a co-dominant stem is the concern.

Photographs help more than prose on this one. A dated photograph of the defect attached to the schedule entry ends most disputes before they start.

Say what you did not do. If the assessment was a ground level visual inspection without aerial inspection or decay detection, record that limitation, because an officer reading a category U classification for a mature protected oak will ask whether anyone climbed it.

Where the defect relates to structural roots or to a subsidence claim, the evidential position is different again and is covered in trees and subsidence claims on neighbouring property.

Why officers scrutinise category U trees

The suspicion is straightforward and largely earned. A category U classification removes a tree from the constraints plan, takes its root protection area off the layout, and means the scheme no longer has to design around it.

Three patterns attract attention.

A single category U tree in an otherwise healthy population, positioned precisely where the development requires clear ground. Category U applied to a tree that the council's own records show as healthy at a recent inspection. And a survey where several category U classifications rest on the same generic phrase, such as extensive decay, without any tree-specific observation.

If your assessment is correct, none of this is a problem. Set the evidence out and invite the council's arboriculturist to inspect. Councils frequently do inspect, and an officer who has stood under the tree and agrees with you is worth more than three pages of justification.

Protected trees recorded as category U

A Tree Preservation Order does not fall away because the tree is category U. Neither does conservation area protection.

The order includes an exemption for trees that are dead, and for the removal of dead branches from a living tree. That exemption is narrower than people assume. A dying tree is not a dead tree, and a tree in poor condition with live foliage is not covered. Where the exemption is relied on, five days written notice to the authority is generally required before the work, except in a case of urgent necessity to remove an immediate risk of serious harm, where notice is given as soon as practicable afterwards.

The safer route on a protected tree is an application for consent to fell, supported by the arboricultural evidence. It takes eight weeks and it produces a decision you can rely on. Felling a protected tree on the strength of your own category U assessment, and being wrong, is an offence carrying an unlimited fine on conviction in the higher court.

In a conservation area, works to trees over 75mm in diameter need six weeks written notice, and the authority can respond by making an order over the tree you were about to remove.

Where the works involve more than a small volume of timber, a felling licence from the Forestry Commission may also be needed, and the interaction is set out in woodland felling licences and when planning is not enough.

Removal sequencing and safety

Removal timing matters for reasons beyond arboriculture.

Nesting birds are protected while nesting, and the main breeding season runs March to August, so felling outside that window or preceding it with a check by a competent person is the standard approach. Bats roost in mature trees with cavities, loose bark and rot holes, and a tree with roosting features needs assessment by a licensed ecologist before it comes down, whatever its category. A category U classification is an arboricultural judgement and has no bearing on the ecological one.

On site, a category U tree that has been left standing while construction proceeds around it is a live risk. Either remove it early or fence it at a distance that reflects its failure potential rather than its root protection area.

Replacement expectations

Where a protected tree is felled under consent, the authority can impose a condition requiring replacement, and in some circumstances a statutory duty to replace arises. Expect to replace, and expect the replacement to be specified by size, species and position.

The practical argument to have early is about species and position. A replacement of the same ultimate size may be impossible on a constrained plot, and it is better to propose two smaller trees in viable positions, or an off-site contribution, than to accept a condition requiring a specimen that the site cannot support. On larger schemes the replacement belongs in the landscape strategy rather than sitting as an orphaned condition.

Challenging a category assigned by another surveyor

Reviewers are regularly asked to comment on somebody else's schedule. Keep the challenge narrow.

Go to the tree, inspect it, and record your own observations against the same criteria the standard uses. Disagree about the evidence rather than about the conclusion. If the original surveyor recorded a basal fruiting body and you found none, say what you found, when, and how you looked. If the disagreement is about remaining contribution rather than about a defect, say which category you would assign and why, because the gap between category U and category C is often the real argument.

Avoid re-surveying the whole population to make a point about one tree. And put the disagreement in writing to the local planning authority rather than to the other surveyor, because the authority is the decision maker.

A tree survey and arboricultural impact assessment that records category U honestly, with dated evidence, is far easier to defend than one that arrives at a convenient answer.

This is general guidance rather than legal advice. Check the position with your local planning authority or a qualified professional before relying on it.