Visual tree assessment: what the guidance describes

This page reports what the official source says. It is not legal advice: ask the office named here.

This page describes what five published sources say about looking at trees for defects. It does not assess any tree and does not say what a reader should do. Only the National Tree Safety Group, a UK body, uses the exact term visual tree assessment. The four US publications describe a ground-level look in their own words, so the table sets each source's wording beside the next.

The levels the National Tree Safety Group describes

The group's 2024 guidance defines visual tree assessment as an inspection method that uses observation of visual signs to help diagnose a tree's health and structure within its setting. It separates several levels of checking, from quick to detailed.

Drive-by: a driver and an observer check trees beside a road from a slow vehicle. The guidance says only defects visible from the vehicle can be noted, and that relying only on drive-bys along busy routes and in urban areas is unlikely to be sufficient.
Walk-over: an on-foot check of many trees from accessible viewpoints. The guidance says it takes minutes or even seconds per tree and may lead to tapping and probing of features reachable from the ground.
Formal visual check: a brief look that takes account of health and structure. The guidance says it is not reasonably practicable to view every part of every tree, and that the level of detail depends on the site and the parts that can be reached.
Detailed inspection: a closer visual assessment by a competent tree specialist, which may extend to soil and roots, aerial inspection or specialist tools. The guidance calls it time-consuming and relatively expensive and says it is generally reserved for individual trees of concern.

The same guidance says that in the great majority of cases a management decision can be made from a simple visual check. It also says the duty holder is not expected to guarantee that any particular tree is safe, and describes seeking specialist advice when concerned and uncertain.

The sources side by side

Source	What it says is examined	The closer step it names
National Tree Safety Group	Overall condition and setting first; then base, trunk and crown if the first look raises an issue	Detailed inspection by a competent tree specialist, in special cases with specialist diagnostic tools
USDA Forest Service	Roots, root or trunk flare, main stem, branches and branch unions, on all sides, with binoculars for high branches; also condition, species, age and size	Consult an arborist when in doubt; it recommends that corrective actions be carried out by professional arborists
University of Florida	Crown, main structural branches, trunk and roots	A qualified arborist, who can state the likelihood of failure and the consequence if targets are struck
ISA Trees Are Good	A checklist of eleven questions, from large dead branches and cracks to cavities, mushrooms, changes to the site and topping	A professional arborist, for judging how serious a defect is
University of Kentucky	Trees near structures and places where people gather first; rotten wood, loose bark, dead branches, large cracks and poor form	A professional forester or arborist for specific recommendations

Timing and context

The Forest Service brochure says inspections can be done in any season, leaf-on or leaf-off, and names the periods after leaf drop in fall, after leaf-out in spring and after severe storms. It also says green foliage in the crown does not ensure the trunk and branches are sound. The Kentucky sheet says trees far from where people go are less likely to cause damage, and the National Tree Safety Group says a large tree in a rarely used area may present a low risk whatever its defects. The Florida publication says one of the most difficult parts of tree risk assessment is rating the likelihood of failure, and that no definitive rules separate sound and unsound trees.

Where the sources differ

The UK guidance builds its levels around how many trees there are and how much a place is used, so it scales from roadside populations down to single trees. The US publications are written for owners of single trees or small woodlots, so they list defects and signs instead of levels. None of the five sources gives a single procedure that covers both. For the methods that rate likelihood and consequence see how a tree risk assessment works and tree risk assessment methods. For the defects named above see structural defects in trees.