Tree survey timing: leaf cover and winter inspections

Tree survey timing leaf cover affects two things only: how accurately the crown can be described and how confidently defects can be seen. Everything else in a BS 5837:2012 survey, stem diameter, root protection area, position, category, can be recorded on any dry day of the year. That matters because the usual reason a survey gets delayed is a belief that the whole exercise has a season, and it does not.

The parts that do have a season are worth knowing precisely, because getting them wrong produces a survey a council can fairly ask you to redo.

What can be recorded at any time of year

Stem diameter at 1.5 metres above ground, height, position, age class and the preliminary management recommendation are all season-independent. So is the root protection area, calculated in BS 5837:2012 as a radius of 12 times the stem diameter, with the area capped for a single stem tree.

That is most of what the layout designer needs. If the constraint you are trying to resolve is whether a plot can sit clear of the root protection areas, a winter survey gives you a usable constraints plan and the arboriculturist can revisit crown detail later.

Category assignment is where the seasons start to bite. Categories A, B, C and U in BS 5837:2012 rest on quality and estimated remaining contribution, and both depend on condition. A survey that records a category on limited winter evidence should say so in the schedule rather than presenting it as settled. PlanScope's tree survey report drafts the structure and the policy narrative around whatever the arboriculturist records, and it is a starting point for that professional rather than a replacement: councils expect a suitably qualified author for a BS 5837 survey and professional review is strongly advised.

Crown spread and condition in full leaf

Branch spread is measured to the outer edge of the canopy, which is a guess on a bare tree and a measurement on a leafy one. On a broad-crowned oak the difference between a leaf-off estimate and a leaf-on measurement can be a metre or more in each of the four cardinal directions, and that metre lands on a proposed building line.

Crown density is the bigger issue. Assessing a tree's physiological condition means judging leaf size, colour, density and dieback in the outer crown, none of which is available without leaves. For ash in particular, the crown density scoring used to judge ash dieback requires full leaf, usually from July to September, and a winter assessment of an ash cannot tell you whether the tree has two years of useful life or twenty.

So the pattern that works is a winter survey for constraints and a summer revisit for condition on the trees that matter to the design.

Decay indicators visible when the tree is bare

Winter has its own advantages, and they are underrated.

1. Branch architecture, included bark unions and historic failures are visible without foliage.
2. Cavities, woodpecker holes and lifted bark, which are also the bat potential roost features, are easier to find.
3. Deadwood extent within the crown can be mapped rather than estimated.
4. Basal flares, fruiting bodies at the buttress and root plate movement are not obscured by ground vegetation.
5. Ivy coverage can be assessed and, where necessary, severed ahead of a summer inspection.

Ivy is the quiet problem. A heavily ivy-clad stem cannot be inspected at all, and severing ivy at the base only clears the stem after several months of dieback. If ivy is present, deal with it at the winter visit so the summer inspection is worth paying for.

Where a tree carries features that might support bats, the arboriculturist should flag them rather than assess them. Bats and their roosts are protected under the Wildlife and Countryside Act 1981 and the Conservation of Habitats and Species Regulations 2017, and a Protected Species Survey requires a suitably licensed ecologist. Emergence and re-entry surveys have their own window from May to September, which is a separate programme item.

Fungal fruiting bodies and their season

Fruiting bodies are the most useful single piece of evidence on a decayed tree and the least reliably present. Some are perennial and visible year-round. Many of the important decay fungi fruit from late summer into autumn, which makes September and October a good time to walk a site for the second time.

Absence of fruiting bodies in February proves nothing. A survey that concludes a tree is sound because nothing was visible in midwinter is making an argument the evidence does not support, and a competing arboriculturist will say so at appeal.

Validity periods and re-inspection

BS 5837:2012 sets no fixed expiry for a survey. What ages a survey is change: storm damage, a failed limb, ash dieback progression, adjacent works, or simply growth that moves a canopy closer to the proposed building.

Local validation lists vary, so check the council's published requirements rather than assuming. As a working approach, treat a survey as current for about a year, refresh it before submission if it is older than two, and always refresh it after a named storm or where ash is present. Record the survey date prominently on every drawing, not just in the report, because the drawing is what gets attached to the decision notice.

Where a survey is being reused for a resubmission, a short addendum letter from the same arboriculturist confirming no material change is usually enough and costs a fraction of a new survey.

Sequencing the survey against the design programme

The sequence that avoids abortive work is straightforward and rarely followed.

Commission the constraints survey as early as possible, in any season, and get the root protection areas onto the site plan before the layout is fixed. Book the condition revisit for the following summer if the first visit was in winter. Run the bat feature check at the same winter visit so the ecology programme can start. Leave the arboricultural impact assessment and method statement until the layout is stable, because both are written against a specific design.

Illustrative example: a site surveyed in late January gives a constraints plan in February, the layout is tested against it in March, the ash on the northern boundary is re-scored for crown density in August, and the impact assessment is written in September for an October submission. The alternative, waiting for summer to start, loses six months. Dates here are illustrative.

Budget sequencing follows the same logic, and where a survey programme straddles two accounting years our note on planning a survey budget across two financial years covers the practicalities. Ground investigation has a comparable seasonal profile, set out in our piece on winter ground investigation.

What to do with an older survey

If the survey you hold is two or three years old, do not quietly resubmit it. Three options are open.

Commission an update visit and an addendum. Commission a fresh survey where ash or elm is present or where the previous surveyor is unavailable. Or submit the existing survey with a covering note explaining the date, the site's condition since, and an offer to update by condition before work starts.

The third option works less often than applicants hope, and it works at all only when the covering note is specific about what has and has not changed.

Enter your postcode on PlanScope to see which reports a site with trees is likely to need. 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.