Pruning specifications and writing them properly

A pruning specification has to survive three readings: the tree officer deciding whether to consent to it, the contractor pricing and executing it, and whoever inspects afterwards to see whether what was consented is what was done. A specification that says "crown reduce by 30 per cent and tidy up" fails all three, and yet it still arrives on tree officers' desks every week.

The standard is BS 3998:2010, and the discipline it asks for is straightforward: name the tree, name the operation, express the result as a measurement, and state where the cuts go. Everything else in a good specification follows from those four.

The terms, and what each one means

Precision starts with using the right word for the operation.

Crown lifting is the removal of the lowest branches, and of branches on the lower part of the main stem, to give a specified clearance above ground level. It is expressed as a height, and the height should be stated separately over a highway, over a footway and over a garden, because they differ.

Crown reduction is a reduction in the height or spread of the crown, or both, achieved by shortening branches back to suitable growth points. Crown thinning is the removal of a proportion of the secondary branch growth throughout the crown, to reduce density while keeping the shape and size. Those two are constantly confused, and they produce very different trees.

Crown cleaning is the removal of deadwood, broken branches, stubs and climbing plants without altering the shape or size of the crown. Pollarding is a management regime, not a single operation, and should only be specified for a tree that has been pollarded before or is being started on that regime deliberately. Formative pruning applies to young trees and is about structure rather than size.

Use the term that matches the intended outcome, then define the outcome. A specification that says "crown thin" when the client wants more light through a window will disappoint everyone, because thinning changes density and not spread.

Specify by measurement, not by percentage

This is the point where BS 3998 departs from older practice, and the reason many specifications get queried.

A reduction expressed as a percentage is ambiguous. Thirty per cent of what: height, spread, volume, leaf area? Two contractors will interpret it differently and both will be defensible. The standard's approach is to express the intended result as the final dimension of the crown, or as the length of branch to be removed.

So: "reduce the crown of T4 to leave a final height of approximately 9m and a radial spread of approximately 4m from the stem, by shortening branches by no more than 1.5m back to suitable growth points" is a specification. "Reduce by 30 per cent" is an aspiration. Where a photograph or a marked-up elevation helps, include it.

Thinning is the one operation still commonly expressed as a proportion, because it does concern the amount of secondary growth removed, and the standard cautions against removing too much. State the proportion and cap it.

Why topping is not a specification

Topping means cutting the crown back to stubs, without regard to growth points. It produces large wounds that the tree cannot compartmentalise, a flush of weakly attached epicormic shoots, and a tree that is more hazardous in ten years than it was before the work.

It should not be specified, consented to or carried out, and a specification that in effect asks for it, by requiring a reduction far beyond what the crown can support, will and should be refused. Where the demand behind the request is unreasonable, such as a request to halve the height of a mature beech because it blocks afternoon light, the honest answer is that the operation would damage the tree and that the options are a smaller reduction, thinning, or removal and replacement.

Saying that clearly at the specification stage is easier than defending it at appeal.

Cut position and the growth point rule

Where the cut goes matters as much as how much comes off. Branches should be shortened back to a lateral branch of adequate size, large enough to take over as the leader of that limb, which BS 3998 expresses as a proportion of the diameter of the part removed. Cuts elsewhere leave a stub that dies back.

Specify that cuts are made just outside the branch bark ridge and branch collar, without leaving a stub and without cutting flush into the stem. Do not specify wound dressings: the standard does not support them and they can trap moisture.

For larger limbs, specify a three-cut technique to avoid tearing bark, and require the target pruning of any torn tissue. These are contractor competence matters, but writing them into the specification gives a basis for rejecting work that was done badly.

Timing, species and wildlife

Timing constraints come from three directions, and all three belong in the specification.

Species physiology first. Birch, maple, walnut and hornbeam bleed heavily if pruned in late winter and early spring, so defer to summer. Prunus species, including cherry and plum, should be pruned in the growing season to reduce the risk of silver leaf and bacterial canker. Many broadleaves are best pruned in late summer when compartmentalisation is most effective.

Wildlife law second. It is an offence under the Wildlife and Countryside Act 1981 to damage or destroy the nest of a wild bird while it is in use or being built, which puts the main breeding season from March to August out of bounds unless the tree is checked immediately beforehand by someone competent to check it. Bats roost in cavities, splits and behind loose bark, and works to a tree with those features need an inspection first. Where evidence is found, stop: a bat roost is protected whether or not it is occupied.

Local constraints third. Some areas have controls relating to particular pests, and the position should be checked before specifying works on susceptible species.

Deadwood, and what to leave

Blanket deadwood removal is a habit rather than a specification. Standing deadwood is habitat, and the standard supports retaining it where it does not present an unacceptable risk.

Write the specification to target: remove deadwood over 50mm in diameter above the footpath and the parking area, retain deadwood elsewhere, and retain any monolith or habitat feature identified in the survey. That gives the contractor a rule they can apply and gives the tree officer a reason to consent. Where a limb must be removed for safety but has habitat value, consider specifying a reduction to a monolith rather than removal to the stem.

Wording that can be conditioned and enforced

A condition can only be enforced if a reasonable person can tell whether it has been complied with. Build the specification so it can be lifted into a condition or a schedule to an agreement.

Each entry should carry the tree number matching the tree survey, the species, the location, the operation named in BS 3998 terms, the measured outcome, the timing window, and the standard the work is to be carried out to. Add who supervises and what record is to be provided afterwards.

Avoid "as necessary", "as required", "to be agreed on site" and "tidy". Each of those transfers the decision to the contractor on the day, which is exactly what the specification exists to prevent. The related approach to specifying crown works councils will accept covers the consent side of the same problem.

Checking the work afterwards

Inspect against the specification, not against an impression. Measure the final crown height and spread where a reduction was specified, check the cut positions on a sample of branches, and look for stubs, torn bark and flush cuts. Photograph from the same positions as the before shots.

Where the work exceeds what was consented on a tree protected by a Tree Preservation Order or standing in a conservation area, that is an offence rather than a contractual dispute, as the note on penalties for damaging a protected tree sets out. Record what you find and report it. Where the work forms part of a longer regime, the cycle and the next intervention date should be captured in the tree management plan rather than left to memory.

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.