Tree Hazard Assessment Form: The Level 2 TRAQ Walk, Target First

A tree hazard assessment form records whether a tree, or a part of it, is likely to fail, whether it would hit anything if it did, and how bad that would be. Most practitioners now call it a tree risk assessment, because a defective tree with nothing under it is a hazard but not a risk. In North America the method is set out in ANSI A300 Part 9 and the ISA best management practice Tree Risk Assessment, and the qualification is ISA's Tree Risk Assessment Qualification (TRAQ). The standard walk-around is a Level 2 basic assessment.

This page lists the whole form in the order you'd walk it. The order matters: start at the trunk and you've decided what matters before looking at what's underneath.

The three levels, and which one this is

ISA and ANSI A300 Part 9 describe three levels of assessment. The form changes with the level, so say which one it is at the top.

• Level 1 — limited visual. A walk-by or drive-by to find obvious defects across many trees — a street, a park, a utility line — and pick out the ones that need a closer look.
• Level 2 — basic. A full walk around one tree, looking at the site, the roots, the trunk and the crown, with simple tools: a sounding mallet, a probe, binoculars, a trowel for the root collar, a diameter tape and a clinometer for height. This is the everyday assessment, and it's what this form covers.
• Level 3 — advanced. When a Level 2 finds something it can't answer from the ground: resistance drilling or sonic tomography for decay, an aerial inspection by climbing or lift, root collar excavation. Usually a separate job, often a different specialist.

A good Level 2 form finishes by saying whether a Level 3 is needed. That isn't a failure of the assessment. It's the honest edge of what can be seen from the ground.

1. The assessment details

Before you look at the tree:

• Client, site address, tree ID or location (a tag number, or a note on a site plan)
• Species
• DBH — diameter at breast height
• Height and crown spread
• Level of assessment — 1, 2 or 3
• Time frame — the period the assessment covers. A tree rated today isn't the same tree after five years or a storm.
• Date, time and the assessor's name (and qualification, if the client or the council needs it)
• An overview photo of the whole tree

2. Targets first

A target is anything the tree or its parts could hit: people, buildings, vehicles, a road, a playground, a power line. No target means no risk rating, however bad the tree looks. So targets come first.

For each target:

• What it is — "back deck", "school drop-off lane", "neighbour's garage"
• Photo
• Where it is in the target zone. The target zone is usually taken as the area within the dripline, within 1× tree height, or within 1.5× tree height when the tree or its parts could travel further (a slope, a lean, high winds).
• Occupancy rate — how often it's there. A house is there all the time. A footpath might be used occasionally, a car park often. ISA uses four grades: rare, occasional, frequent, constant.
• Can the target be moved? Can the car park, the bench, the picnic table go somewhere else?
• Is restricting access practical? Can you close the path or fence off the area until the work is done?

Those last two matter later: moving the target is often the cheapest mitigation there is.

3. The site

Look around before you look up.

• History of failures — on this tree, on this species locally, on this site
• Topography — flat or sloped, and roughly how steep
• Site changes — recent construction, grade change (soil added or cut away over the roots), clearing that opened up the tree to wind, cut roots from a trench or a driveway, changes to drainage
• Soil — limited rooting volume, saturated, shallow, compacted, paving over the roots (and roughly what percentage is paved)
• Exposure and prevailing wind — which way the weather comes from, whether the tree has recently lost its shelter, whether buildings funnel the wind
• Common weather — strong winds, ice, snow, heavy rain
• Site photos

4. The tree from a distance

Step back far enough to see the whole tree, then walk around it once.

• Lean — how much, which way, and whether it looks old (the crown has corrected upward) or new (soil heaving on the side away from the lean)
• Crown balance — one-sided, or pushed away from a building or another tree
• Live crown ratio — how much of the height is carrying live crown
• Vigour — low, normal, high
• Foliage — normal, missing for the season, or missing because it's dead; roughly how much is normal, yellowing (chlorotic) or dead (necrotic)
• Dieback — at the top, on one side, throughout
• Pests and disease, and abiotic damage (drought, salt, lightning, mechanical injury) — with photos
• Load factors — wind exposure, crown size and density, how dense the interior branching is, and whether vines, mistletoe or moss add weight or catch wind

5. Roots and root collar

Get down to ground level. Use the trowel.

• Root collar — visible, or buried under soil, mulch or paving? A buried collar hides exactly the defects you're looking for.
• Girdling roots — roots wrapping around the stem
• Dead roots, root decay, cut or damaged roots
• Fungal fruiting bodies — conks or mushrooms at the base or in the root zone, with a close-up photo (identification later often depends on it)
• Ooze, cavities, cracks
• Root plate lifting — soil heave or cracks on the side away from the lean
• Soil weakness
• Response growth — swelling or extra wood the tree has put on around a weakness

6. Trunk

Walk round it slowly, low to high. Sound it with the mallet as you go.

• Dead or missing bark, and bark with an abnormal texture or colour
• Cracks and seams — where, how long, whether they're open
• Cavities and nest holes — the size of the opening, and how far the probe goes in
• Cankers, galls, burls
• Sap ooze
• Sapwood damage, heartwood decay — what the sounding tells you (a hollow note is a finding; it's also a reason to consider Level 3)
• Conks or mushrooms on the stem
• Codominant stems and included bark — two stems of similar size with bark trapped in the union are a classic failure point
• Poor taper
• Lean
• Lightning damage
• Response growth

7. Scaffold limbs, branch unions and crown

Binoculars now.

• Deadwood — how much, and the diameter of the largest dead branch
• Hangers — broken branches lodged in the crown, waiting to come down
• Broken branches — how many, and the largest diameter
• Over-extended limbs — long, heavy ends with little support
• Weak branch unions — codominant stems and included bark again, higher up
• Cracks, cavities, cankers, conks, decay on the limbs
• Previous branch failures — old stubs and tear-outs show how this tree tends to fail
• Pruning history — crown cleaned, thinned, raised, reduced, topped, lion-tailed, flush cuts. Topping and lion-tailing leave weakly attached regrowth and badly loaded limbs, so they're findings too.

For each of the three zones — roots, trunk, crown — end with the main concern, the load on that defect, and a first view of its likelihood of failure.

8. Rating each part, not the tree

This is the core of the form, and it's done once for each part or condition of concern against each target. A tree with a dead limb over a lawn and a cracked union over a house has two risk entries, and they'll probably rate differently.

For each entry:

• Tree part — "south scaffold limb", "codominant union at 4 m"
• Condition of concern — "included bark with a 40 cm crack below the union"
• Part size and fall distance
• Target — from your target list — and any protection it has (a roof, a car's own body, a shelter)
• Likelihood of failure — improbable, possible, probable or imminent, within the time frame you set
• Likelihood of impact — very low, low, medium or high: if it fails, how likely is it to hit that target?
• Combined likelihood — ISA's first matrix combines those two into unlikely, somewhat likely, likely or very likely
• Consequences — negligible, minor, significant or severe
• Risk rating — the second matrix combines the combined likelihood with consequences into low, moderate, high or extreme

The matrices are lookups. The judgement is in the three inputs, and those are what the assessor puts their name to.

9. Mitigation, residual risk and the close

For each risk entry:

• Mitigation options — prune the part, reduce the crown, cable or brace, move the target, restrict access, remove the tree
• Residual risk — the rating that's left once that mitigation is done. Mitigation should bring it down. If the client declines the work or puts it off, the residual risk stays where it was, and the form should say so.

Then close the assessment:

• Overall tree risk rating — the highest of the entries
• Recommended reinspection interval
• Is further inspection needed? If yes, what kind (Level 3, aerial, resistance drilling, tomography, root collar excavation, lab analysis, re-inspection after the work), why, and who to refer it to
• Limitations — what you couldn't see or reach: a buried collar, ivy over the trunk, the top of the crown hidden by a neighbour's tree, no access to the back of the property, the weather on the day
• Tools used
• Signature and date

Hazard, risk, and the UK methods

In the UK and parts of Europe, two other systems are widely used. QTRA (Quantified Tree Risk Assessment) estimates the probability of harm as a number and compares it with thresholds for tolerable risk. VALID uses a validated risk model to reach a tolerable-or-not decision. Underneath, each asks the same questions — what could fail, what could it hit, how bad would it be — so the field list above still covers what you need to see on site. Use whichever method your clients, insurer or council expect.

What most tree hazard assessment forms get wrong

No target. A form that describes the tree beautifully and never says what's underneath it can't produce a risk rating. It's a condition survey.

No time frame. "Likelihood of failure: probable" means nothing without a period. Probable in the next year, or in the next ten?

Rating the tree, not the part. "Tree risk: high" with no part named leaves the client unable to act. Which limb, over what, and what would fix it? A tree often has one high-risk part and nothing else wrong.

No residual risk. If the form recommends a crown reduction but doesn't say what the risk will be after it, nobody can tell whether the work is worth doing, or whether removal is the only real answer.

No photo of the defect. An overview of the whole tree isn't evidence of a crack at 6 m. Each defect that drives a rating needs its own photo, taken where the reader can find it on the tree.

No limitations. "Root collar not visible — buried under 30 cm of mulch" protects the client and the assessor. A form without limitations implies you saw everything, and after a failure somebody will ask whether you did.

Doing it with a mallet in one hand

A Level 2 is done on foot, looking up, with a mallet, a probe or binoculars in your hands. A clipboard competes with all of that, so notes get shortened in the field and written up later from memory and a camera roll full of bark photos.

Speak while you walk, and the document the law or the client wants writes itself. At the trunk you say: "Codominant union at about four metres, included bark on the east side, crack running down about forty centimetres, photo. Load moderate, likelihood of failure probable. Target is the back deck, frequent use." The defect, the photo and the likelihood are recorded together, at the tree, at the time, and the rating is built from what you actually said.

ReportWalk is an iPhone and iPad app that works this way: you speak and photograph as you walk, and the report writes itself. Its Tree Risk Assessment (Level 2) template, shaped with a practising TRAQ-qualified arborist, follows the walk above: targets, site and load factors, then crown, trunk and roots, each flagged defect with its own photo and note. In each risk entry you pick the part from your flagged defects and the target from your list, choose the likelihoods and consequences, and the template looks up the two ISA matrices from your choices. It warns, without blocking, if residual risk comes out higher than the rating before mitigation, and closes by asking whether a Level 3 is needed. It follows the familiar structure; it isn't endorsed by ISA.

Related

• Arborist reports — what arborists write up, and why the report is the product
• Tree risk assessment report — the finished document this walk produces
• Take 5 examples — the task check before climbing, cutting or rigging
• Site visit report template — the general structure for any site visit write-up

Frequently asked questions

What should a tree hazard assessment form include? Assessment details (species, DBH, height, level, time frame), targets and occupancy, site conditions, overall condition and load factors, defects in the roots, trunk and crown, then a risk entry for each part of concern: likelihood of failure, likelihood of impact, consequences and risk rating. It ends with mitigation, residual risk, a reinspection interval, whether further inspection is needed, and the limitations.

Is a tree hazard assessment the same as a tree risk assessment? In practice, yes. "Hazard" is the older term. The current ISA and ANSI A300 approach talks about risk, because risk depends on a target as well as a defect. A decayed tree in an empty field is a hazard, but the risk is low.

What is a Level 2 tree risk assessment? A basic assessment: a detailed walk around one tree — site, roots, trunk and crown — with simple tools such as a sounding mallet, probe, binoculars and trowel. It's the most common level. Level 1 is a limited visual check of many trees; Level 3 adds specialist equipment.

How is the risk rating worked out? With two ISA matrices. The first combines likelihood of failure (improbable to imminent) with likelihood of impact (very low to high) to get a combined likelihood. The second combines that with the consequences (negligible to severe) to give a rating of low, moderate, high or extreme. It's done for each part of the tree and each target, and the tree's overall rating is the highest of them.

How big is the target zone? Commonly the area within 1 to 1.5 times the tree's height, depending on how far the tree or its parts could travel if they failed. Slope, lean and wind can push it towards the larger figure.

How often should a tree be reassessed? There's no fixed interval; the assessor sets one from the tree's condition, the rating and the targets. Look again after a major storm, after construction nearby, or when the site's use changes.