Arboricultural Impact Assessment outline to BS 5837
BS 5837 keeps the survey, the constraints, the impact and the protection method apart. A report that merges them cannot be checked against the drawings.
An arboricultural impact assessment outline that follows BS 5837:2012 keeps four things apart that weaker reports merge: the survey, the constraints, the impact of the proposal, and the method by which trees are protected during construction. The standard is structured that way for a reason. A case officer and a tree officer read the constraints before the design, and the design before the method, and a report that answers all three at once cannot be checked against the drawings.
What follows is the section sequence, written for the person producing or reviewing the report rather than for the applicant.
Survey data and the tree schedule
The survey comes first and it is a factual record. For each tree, group or hedge within the site and within influencing distance outside it, the schedule records a reference number, species, height, stem diameter measured at the standard height, branch spread by quadrant, height of crown clearance above ground, age class, physiological condition, structural condition, preliminary management recommendations, and an estimated remaining contribution in years.
Two details separate a usable schedule from a decorative one. Trees on adjoining land have to be surveyed where their root protection areas or crowns reach the site, and they are surveyed from within the site if access is refused, with that limitation stated. And the survey date and the leaf condition at the time of survey belong on the schedule, because a winter survey of a deciduous canopy carries a caveat a summer one does not.
Where a tree is subject to a tree preservation order or stands in a conservation area, note it against the tree rather than in a separate paragraph. That is the field the tree officer looks for first.
Categorisation and the constraints plan
Categorisation is the judgement the rest of the report rests on. The standard separates trees that cannot realistically be retained for longer than a decade in the current context from those that can, and then grades the retainable trees as high, moderate or low quality, with subcategories reflecting whether the value is mainly arboricultural, mainly landscape or mainly cultural including conservation value.
Two things to watch when reviewing a categorisation.
A tree graded low quality solely because of poor form may still carry landscape value as part of a group, and the subcategories exist to capture that. And a category assigned to remove an obstacle to the layout is the commonest form of bias in these reports. If the categorisation was made before the layout existed, say so, because it is worth saying.
The tree constraints plan then presents the survey spatially: the stem positions, the crown spreads, the root protection areas and the shade patterns cast by retained trees. The root protection area for a single-stem tree is calculated as the area of a circle with a radius of twelve times the stem diameter, subject to the cap the standard sets, with the shape modified where site conditions justify it and the modification explained.
That plan is a design tool. It should be issued to the design team before the layout is drawn, not after.
The proposal against root protection areas
Now the assessment proper. Overlay the proposal on the constraints plan and quantify the incursions.
For each retained tree affected, state the area of the root protection area lost, expressed as a proportion of the total, and the location of the loss relative to the stem. A ten per cent incursion on one side of a mature tree is a different proposition from the same area taken from two sides.
Then deal with everything that is not the building footprint, because that is where assessments go thin: driveways and parking, service trenches and their routes, drainage runs and soakaways, level changes and retaining structures, scaffolding, site compounds and material storage, crane positions and delivery routes, and the boundary treatments.
Where the incursion is unavoidable, say what engineering solution makes it acceptable, whether that is a no-dig cellular confinement construction, a trenchless service crossing, a cantilevered or pile-and-beam foundation, or a change of level achieved above existing grade.
Direct and indirect impacts
Separate the two, because they have different remedies.
Direct impacts are removals, crown reduction and pruning required by the proposal, and root severance. State the number and category of trees to be removed and the reason for each, and distinguish removals required by the proposal from removals recommended on condition grounds, since only the first are a planning consequence.
Indirect impacts are the ones argued at appeal. Soil compaction and changes to soil moisture from new hard surfaces, shading of retained trees by new built form, changes to wind exposure after adjacent removals, pressure for future pruning from new windows and gardens, and post-occupation pressure on trees whose shade falls on a new terrace.
That last effect deserves a sentence in every report. A retained category A oak overhanging a new patio will generate a pruning application within five years, and an assessment that does not acknowledge it is not describing the development that will exist.
Mitigation and replacement planting
Mitigation covers more than planting. It includes design changes already made, which should be recorded so the authority can see the iteration, plus engineering solutions, protective measures and management commitments.
Replacement planting should be specified rather than described: species, stock size, root condition, position, soil volume available and the establishment maintenance period. Planting to the recognised standard for trees from nursery to independence is what makes a replacement scheme deliverable, and the soil volume figure is the one that decides whether a street tree survives.
Where the local plan sets a replacement ratio or a canopy cover target, address it explicitly with numbers. Where it does not, propose a ratio and justify it against what is being lost.
Method statement and tree protection plan
The arboricultural method statement is the construction document. It sets out the sequence of operations in relation to the trees, the specification of protective barriers and ground protection, the position and extent of the construction exclusion zone, the special engineering details, the arrangements for services, the facilities excluded from the zone such as welfare and washout areas, and the pre-commencement site meeting.
The tree protection plan is the drawing that goes with it. Barrier positions and type, ground protection extents, exclusion zones hatched, and the trees to be removed marked distinctly from those retained.
Both are usually secured by condition, and both are usually conditioned pre-commencement, so they belong in the application rather than being left for later. Further detail on the drafting is in the arboricultural method statement section by section and in the method statement and protection plan pairing.
Monitoring and supervision
The final section is the one that gets cut and then gets conditioned anyway.
Set out who supervises, at what stages, and what is recorded. The stages that matter are barrier installation before any other work, excavation within or adjacent to a root protection area, service installation, surfacing within a root protection area, and barrier removal at the end. Specify a written record of each inspection sent to the authority, and name the arboriculturist's role rather than an individual.
An Arboricultural Impact Assessment prepared to this standard is normally expected to be the work of a suitably qualified arboriculturist, and councils will look for that. A draft gives the structure and flags the missing site data, and the qualified author supplies the judgement. Arrange review through the professional directory.
Where new planting forms part of a wider scheme, coordinate with the Landscape Strategy so the two documents do not specify different trees in the same position. PlanScope provides AI-assisted draft reports for planning applications. Reports should be reviewed before submission. We do not guarantee planning approval. This is general guidance rather than legal advice, so check the position with your local planning authority or a qualified professional before relying on it.
Frequently asked questions
What has to be recorded for each tree in the survey schedule?
A reference number, species, height, stem diameter at the standard measuring height, branch spread by quadrant, crown clearance above ground, age class, physiological and structural condition, preliminary management recommendations and an estimated remaining contribution in years. Add the survey date, the leaf condition at the time, and any tree preservation order or conservation area status against the individual tree.
How is a root protection area calculated?
For a single-stem tree it is the area of a circle with a radius of twelve times the stem diameter, subject to the cap the standard sets. The shape can be modified where site conditions justify it, for example around an existing structure, provided the equivalent area is retained and the reasoning is explained in the report rather than simply drawn.
Do trees on neighbouring land have to be surveyed?
Yes, where their root protection areas or crowns extend into the site or would be affected by the proposal. If access to the adjoining land is refused, survey from within the site and state that limitation clearly. Omitting an off-site tree whose roots run under the proposed footprint is one of the commonest grounds for a tree officer objection.
What indirect impacts should the assessment cover?
Soil compaction and moisture changes from new hard surfaces, shading of retained trees by new built form, altered wind exposure after adjacent removals, and post-occupation pressure for pruning where new windows, gardens or terraces sit under a retained canopy. That last one should be acknowledged, because it will generate an application within a few years.
Are the method statement and protection plan needed at application stage?
Usually yes in outline, because both are commonly secured by pre-commencement condition and the special engineering details affect the layout. Submitting them with the application lets the authority condition approved documents rather than requiring a fresh submission, which removes a discharge round from the programme before work can start.
Sources and further reading
This article is general guidance about the planning system in England and, where stated, the rest of the UK. It is not legal or professional advice. Check your local planning authority’s validation requirements and take professional advice for your specific site.