Trees on allocated sites: getting the plan stage right

Most site allocations are drawn to a red line and a unit number, and neither of them knows where the trees are. The capacity figure in a local plan is usually derived from a gross site area and a density assumption, so a site with a mature oak group along its only sensible access will still be allocated for the number of houses the arithmetic produced. Fixing that at reserved matters is expensive. Fixing it during plan-making costs a survey fee and a well-drafted representation.

If you are promoting land, the tree work belongs at Regulation 18 and Regulation 19 stage, not after allocation. A survey to BS 5837:2012 done before the draft plan is published gives you something no other party has: an evidenced net developable area.

Why capacity assumptions ignore trees

Site assessment at plan stage is a desk exercise across dozens of sites. Officers work from aerial imagery, constraint layers and a density multiplier. Tree cover shows up as green, and green is often read as either developable or as incidental landscaping.

What the desk exercise cannot see is the root protection area. Under BS 5837:2012 the root protection area for a single-stem tree is calculated as a radius of twelve times the stem diameter, capped at 707m² in area. On a mature tree with a 900mm stem that is a circle nearly 11m in radius before you have drawn a single house. Add the shade footprint, the future pressure for crown reduction from occupiers, and the manoeuvring space a refuse vehicle needs clear of the canopy, and a group of three category A trees can remove a quarter of a small site from development.

The result is a plan that allocates 45 units on a site that will accommodate 32 without felling. Nobody benefits from that. The authority loses trust in its own supply figures, the promoter is held to a number it cannot deliver, and the trees become the reason the scheme is refused rather than the reason it is well designed.

Surveying before you promote

Commission the tree survey before the site is submitted through a call for sites, not after. What you want from it at this stage is narrower than a full impact assessment:

1. Categorisation of every tree and group as A, B, C or U under BS 5837:2012, with the retention span.
2. Root protection areas plotted to scale, with any offsets justified by soil conditions or existing hard surfacing.
3. Existing statutory protection identified, meaning Tree Preservation Orders, conservation area status and any hedgerow that may be important under the Hedgerows Regulations 1997.
4. Ancient woodland and veteran trees flagged separately, because they are irreplaceable habitat and the standing advice expects a buffer of at least 15m.
5. A plain statement of the developable area that remains.

That last item is the one that does the work at examination. The constraints drawing is what turns a survey into a planning argument, and the way it shapes layout is set out in the tree constraints plan and the layout it forces.

Representations on allocation policy wording

Two things are worth asking for in a Regulation 19 representation, and they pull in opposite directions, so be clear which one you want.

The first is a corrected capacity figure. If the survey shows 32 rather than 45, say so with the drawing attached and ask for the policy figure to be amended. Authorities resist this because supply totals are finely balanced, but a figure that survives examination unchallenged becomes a stick used against you at application stage.

The second is flexibility in the wording. Ask for "approximately" rather than a hard minimum, and for the policy to refer to a concept layout rather than a unit count. Where an authority insists on a minimum, ask that the supporting text acknowledges the tree constraint and the resulting indicative capacity. Supporting text is not policy, but an inspector reads it when interpreting the policy, and an officer quotes it in a report.

Avoid asking for the trees to be removed from the constraint list. It reads as special pleading, it invites a tree officer objection on the public file, and it will be quoted back at you for the next ten years.

Concept masterplans that hold the constraint

A concept plan submitted with a representation does more than illustrate. It fixes the case that the allocation is deliverable.

Keep it honest and keep it simple. Show the retained tree groups with their root protection areas, the access taken clear of them, the developable parcels, and the green infrastructure that the retained trees sit within. Avoid showing a road threading between two category A trees with 300mm to spare, because the highway authority will need a construction width you have not drawn and the whole plan then loses credibility.

Where trees are being retained inside public open space rather than private gardens, say so. Trees in front gardens generate pressure for works within five years; trees in a managed landscape parcel with a maintenance commitment do not. That distinction is worth spelling out in the accompanying landscape strategy, because it is the difference between retention on paper and retention in fact.

Testing deliverability at examination

At examination the question is whether the allocation is justified and effective, which in practice means whether the site can deliver what the plan says it will. Tree constraints come up in three ways.

An objector, often a local group, argues the site cannot take the numbers because of the trees. If your survey supports a lower figure, you are aligned with them on the arithmetic and opposed on the principle, and the useful position is to accept the constraint and defend the reduced capacity.

The authority's own evidence base is challenged for having missed a constraint. This is the strongest reason to have submitted your survey early. An inspector who has a BS 5837 survey in front of him or her will prefer it to an aerial photograph interpretation.

The promoter argues for a higher figure than the constraint allows. This rarely ends well, and it makes the later application harder.

Carrying the constraint into reserved matters

An outline permission with an indicative layout does not protect trees. What protects them is the combination of a parameter plan that fixes the tree groups and the green infrastructure, and a condition requiring an arboricultural method statement and tree protection plan before any work begins.

Write the parameter plan so the retained groups are a fixed parameter rather than an illustrative one. At reserved matters stage the detailed layout is then tested against a boundary that cannot be quietly eroded by 2m per parcel across four phases. And where loss is unavoidable, deal with replacement planting properly at the outset rather than leaving it to a condition nobody drafts carefully, which is covered in replacement planting conditions after tree loss.

Biodiversity net gain adds a reason to get this right at plan stage. Trees and woodland carry habitat units, and losing a mature tree group changes the baseline the statutory metric is run against. A layout that retains the group may need no off-site units at all, while one that clears it may need a purchase that was never in the appraisal.

Where a tree makes an allocation undeliverable

Sometimes the answer is that the site does not work. A single veteran oak in the centre of a 0.4 hectare infill plot, with a root protection area and a buffer that between them cover most of the land, is not a site for six houses.

Say so early. A promoter who withdraws a site at Regulation 18 with a clear arboricultural reason keeps credibility for the next one. A promoter who carries it to allocation, then applies for permission to fell, spends three years and a lot of fees discovering the same thing in public.

The harder case is the site that works at a lower density and a different typology. Two large houses with generous gardens around a retained group will often be acceptable where eight terraced units are not. That is a viability conversation rather than an arboricultural one, and it is better had before the land is optioned.

Enter your postcode on PlanScope to see which tree and landscape reports a site is likely to need before you promote it.

This is general guidance rather than legal advice. Check the position with your local planning authority or a qualified arboriculturist 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.