A tree survey is not an ecology survey
Both documents talk about trees, and councils ask for both. One protects trees from construction, the other protects wildlife from you. Knowing which answers which question stops a scheme stalling at validation.
A council asking for a tree survey and a council asking for an ecological appraisal are asking two different questions, and the tree survey versus ecology survey confusion costs schemes weeks every year. A BS 5837:2012 survey asks which trees are worth keeping and how construction must work around their roots. An ecological appraisal asks what lives on the site and what the law requires you to do about it. The same oak appears in both. It appears for entirely different reasons.
Submit one and you have not covered the other, whatever the tree has growing in it.
What each survey is for
BS 5837:2012, "Trees in relation to design, demolition and construction", sets out a method for recording trees and categorising them by quality and remaining contribution. The surveyor records species, height, stem diameter, crown spread, age class, physiological and structural condition, and any preliminary management need, then assigns each tree to category A, B, C or U. Root protection areas are calculated from stem diameter. The output feeds an Arboricultural Impact Assessment, a tree protection plan and a method statement for any work inside a root protection area.
An ecological appraisal follows the CIEEM approach: a habitat survey of the whole site, a desk study of records within a search radius, and an assessment of the potential for protected species and habitats. The output identifies what further survey is needed, what mitigation the law requires and what the site's baseline is for biodiversity net gain purposes. That is the job of a Preliminary Ecological Appraisal.
One is about the trees as trees. The other is about the trees as habitat, alongside everything else on the site.
Councils rarely spell this out on the validation list. They ask for arboricultural information and ecological information as separate line items and leave the applicant to work out that a single consultant cannot usually supply both.
Where the two overlap on a site
Four points of contact come up on almost every site with trees.
The first is tree removal. An arboriculturist decides whether a tree can be retained given the design. An ecologist decides whether removing it is lawful, when it can be done and what has to happen first.
The second is root protection areas against habitat value. A category C hawthorn with a small root protection area may be the most valuable thing on the site for nesting birds. A category A beech may have no ecological interest beyond its own canopy.
The third is the construction exclusion zone. Tree protection fencing keeps machinery away from roots, and it happens to keep machinery away from the habitat under the canopy. The two documents should show the same fence line, and frequently do not.
The fourth is timing. A tree survey can be done in any month, with foliage helpful for some species identification. Ecological survey windows are fixed by biology, and that is what drives the programme.
Bat roost potential and who assesses it
This is where competence matters most. Bats are European protected species under the Conservation of Habitats and Species Regulations 2017, and they are also protected under the Wildlife and Countryside Act 1981. Damaging or destroying a roost is an offence whether or not bats are present at the time, and the roost is protected even when unoccupied.
Trees are assessed for roost potential against the Bat Conservation Trust's good practice guidelines, which set out categories from negligible through low and moderate to high, based on the features present: rot holes, woodpecker holes, lifting bark, splits, dense ivy, frost cracks. That assessment is ecological work. An arboriculturist recording a cavity as a structural defect has recorded the same feature for a different purpose and has not assessed it for bats.
Where potential is moderate or high, the next step is aerial inspection by a climber with the right endoscopy equipment and the right licence, or emergence and re-entry surveys in season. A Bat Survey of that kind requires a suitably licensed ecologist, and a licence from Natural England is required where a roost will be affected. PlanScope can draft the surrounding documents, but the survey and any licence application are legally the ecologist's work.
A tree report that says "no evidence of bats observed" without that methodology behind it is a sentence written outside its author's competence, and a council ecologist will say so.
How the metric treats individual trees
Biodiversity net gain adds a third reading of the same tree. The statutory metric treats trees as a habitat in their own right, with individual trees outside woodland converted into an area figure by size class, and with condition assessed against published criteria.
That creates a practical tension. A mature tree that an arboriculturist would happily fell as category U because it is structurally unsound may be carrying substantial biodiversity units and substantial roost potential precisely because it is decaying. Veteran and ancient trees sit outside the ordinary trading position altogether and are treated as irreplaceable habitat in national policy.
So the metric run cannot be done from the tree schedule alone, and the Biodiversity Net Gain Assessment has to reflect what the ecologist recorded rather than what the tree survey recorded. Reconcile the two schedules before the metric is run, not after.
Commissioning both without paying twice
Sequence matters more than bundling.
- Commission the desk study and the habitat survey early, because the results set the survey programme and the survey programme sets the planning programme.
- Commission the tree survey once the topographical survey exists, so trees can be plotted accurately rather than by offset.
- Give both consultants the same base drawing, at the same revision, with the same tree numbering.
- Ask each to state explicitly what they have not assessed.
- Reconcile the two schedules into one table before the design freezes.
Shared site visits sound efficient and rarely are, because the two disciplines need different weather, different seasons and different access. Shared base data is where the money is saved.
One more discipline helps on larger sites. Ask for both schedules as spreadsheets rather than as text in a report appendix, so the tree numbers, the habitat parcels and the metric inputs can be cross-checked in one place when the layout changes.
Reports that claim more than their author can
The honest test for both documents is the same. Does the author hold the competence for every statement in the report, and does the report say where the limits are?
A good tree report states the survey date, the method, whether the inspection was from ground level, which trees could not be accessed and what that means. A good ecological report states the survey effort, the constraints, the confidence level and the further work required. Neither should contain a bare conclusion on the other's subject.
Councils increasingly reject validation on exactly this point, and an application held at validation for six weeks while a second consultant is appointed costs more than commissioning them together would have done.
Browse the 66 PlanScope report types to see which surveys your site is likely to need, and get the ecology programme booked before the survey season closes.
This is general guidance, not legal advice. For specialist technical reports, qualified professional input may be required, and protected species surveys require a suitably licensed ecologist. PlanScope provides AI-assisted draft reports for planning applications. Reports should be reviewed before submission. We do not guarantee planning approval.
Frequently asked questions
Does a BS 5837 tree survey cover bats?
No. BS 5837:2012 is a method for recording trees and assessing the effect of construction on them. Bat roost potential is assessed against the Bat Conservation Trust good practice guidelines by an ecologist, using different criteria. An arboriculturist recording a cavity as a structural defect has not assessed it as a potential roost.
Do I need both surveys for a planning application?
Often yes. Councils ask for arboricultural information where trees are on or adjacent to the site, and for ecological information wherever habitats or protected species may be present. Biodiversity net gain adds a further requirement for a metric baseline. Check the council's local validation list, because the triggers differ by authority.
Which survey should I commission first?
The ecology desk study and habitat survey, because the results determine which seasonal surveys are needed and those windows drive the programme. The tree survey can follow once a topographical survey exists, so trees can be plotted accurately rather than positioned by offset from a boundary.
Can one consultant do both?
Some practices offer both disciplines, with an arboriculturist and an ecologist each writing their own section. What matters is that each statement in the report is within its author's competence and that the report says so. A single signature covering both without the underlying qualifications is what council ecologists challenge.
How does the biodiversity metric treat a single tree?
The statutory metric treats individual trees outside woodland as a habitat, converting them into an area figure by size class with condition assessed against published criteria. A structurally unsound tree can therefore carry substantial units. Veteran and ancient trees are treated as irreplaceable habitat and sit outside the ordinary trading position.
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.