Tree retention categories under BS 5837

BS 5837:2012 sorts trees into four categories. U for trees that should go anyway, and A, B and C for retention categories of high, moderate and low quality. The dividing line between them is an estimate of how long the tree will keep making a contribution: at least 40 years for category A, at least 20 for B and at least 10 for C.

Those figures are not a life expectancy. They are an estimated remaining contribution in the context of the site, which is a different and more useful judgement, and it is the part most often misread by designers reading a survey for the first time.

What the categories record

A tree survey to the standard records, for every tree, its species, height, stem diameter at 1.5 metres, crown spread in four directions, crown clearance, an age class, a physiological and structural condition note, any preliminary management recommendations, and the category.

The category is an assessment of quality and value as an existing feature, made before any design exists. That order matters. The survey happens first, the constraints plan follows, and only then is the layout drawn. A survey produced after a layout has been fixed tends to find exactly the trees the layout needs removed.

Categories are colour-coded on the tree constraints plan so a reviewer can read the site at a glance: dark red for U, light green for A, mid blue for B and grey for C.

The subcategories, and what they are for

Each retention category carries a subcategory describing why the tree matters.

Subcategory 1 covers mainly arboricultural qualities: form, vigour, rarity, an especially good specimen of its species. Subcategory 2 covers mainly landscape qualities, meaning the tree's contribution to the character of the place, screening, or its role in a group or avenue. Subcategory 3 covers mainly cultural values, including conservation, heritage, commemorative or veteran interest.

So a tree can be B2 because it is an ordinary field maple doing important screening work, and another can be A3 because it is an ancient pollard with a bat roost and a name on the tithe map. The subcategory tells a designer what would be lost, which the letter alone does not.

Trees are assessed collectively where they read as a group. A hedgerow or a shelterbelt gets one entry and one category, because removing a third of it destroys the thing the category was recording.

Category U, and what it does not mean

Category U covers trees in such a condition that they cannot realistically be retained as living trees in the context of current land use for more than about ten years. Severe irreversible decline, a major structural defect that cannot be managed, or a serious stability problem.

Two cautions attach to it.

A U tree should be removed for sound arboricultural management reasons whether or not development goes ahead, so it is not a credit in the ecological or landscape balance. Applicants who present the removal of U trees as mitigation are missing the point.

And ecological value survives condition. A hollow, decaying veteran with a bat roost or saproxylic invertebrate interest is not simply a U tree to be cleared. The standard recognises trees of special value, and a veteran should be considered for the cultural subcategory rather than dismissed on physiological grounds. Where a bat roost is suspected, a survey by a licensed ecologist is needed and the licensing regime applies regardless of the tree's category.

Category is not amenity value

This is the distinction that causes most confusion at application stage.

BS 5837 categories describe quality and value for the purposes of design. Tree Preservation Orders are made on the basis of amenity, assessed by the council under its own approach. The two are related but they are not the same test, and they are made by different people for different purposes.

A category C tree on a prominent street corner can be protected by an Order. A category A specimen in the middle of a private garden with no public visibility may have no protection at all. Neither outcome is an inconsistency.

So run both checks. Categorise the trees for design purposes, and separately establish which trees are protected by Order, stand in a conservation area, or form part of a hedgerow with its own protection.

Where categorisation gets disputed

Tree officers read categories sceptically, and with reason. The commonest dispute is a tree downgraded from B to C, or from C to U, in a survey commissioned by the applicant after the layout was drawn.

What settles it is the condition note. A category has to be justified by observations, so a survey schedule that records "fair condition, minor deadwood, good vigour" and then assigns category C invites a challenge. One that records specific defects, their extent and their management implications is far harder to argue with.

Where the council disagrees, it can commission its own survey, require a revised assessment by condition, or refuse on the basis that the arboricultural evidence is inadequate. Expect the second survey to be less generous than the first.

Two practical defences. Survey in leaf where the assessment turns on crown condition, and note the date and conditions. And record the reasoning for any tree close to a category boundary, because those are the ones that get looked at.

Using the categories to drive the layout

Work in the order the standard sets out.

1. Commission the survey before the design starts.
2. Produce the tree constraints plan, with root protection areas and crown spreads drawn accurately rather than as symbols.
3. Design the layout so that category A trees are a fixed constraint, treated like a watercourse or a level change.
4. Accept that category B trees are a strong constraint that can be traded against real design benefits, with reasons given.
5. Treat category C trees as a weak constraint, and say so, because arguing to retain every C tree weakens the case for the ones that matter.
6. Produce the Arboricultural Impact Assessment, then the tree protection plan and the method statement.

Councils expect a suitably qualified author for this work and professional review is strongly advised before submission. Loss of a category A tree is a refusal reason in its own right on many schemes, and no amount of replacement planting answers it, because a 40 year contribution cannot be replaced by a whip in a tube.

Illustrative example. A survey of a 0.6 hectare site records one A1 oak, a B2 group of five limes along the frontage, and eleven C category trees including self-set sycamore. The first layout loses the oak. The revised layout keeps it in public open space, loses six C trees and two of the limes, and the council accepts the balance. The detail is illustrative.

Getting it into the submission

Set out the category schedule as a table in the assessment, with the constraints plan alongside the proposed layout at the same scale so the reader can overlay them. Explain in the Design and Access Statement what the retained trees do for the scheme, and cover the replacement planting and long-term management in a Landscape Strategy rather than as a note on a drawing.

Anyone scoping a site can check which reports apply before commissioning the survey, which avoids paying for arboricultural work that misses the season.

This is general guidance, not legal advice. Check the position with your local planning authority or a qualified professional before relying on it.

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