A risk assessment assesses a target, not just a tree.

The three questions

Formal tree risk assessment reduces to three judgements, made separately and then combined.

1. How likely is this part to fail? Not the tree in general — the specific part. A codominant union with included bark, a limb over the drive, a root plate, a decayed section of trunk. Each gets its own answer.
2. If it fails, how likely is it to hit the target? This is where the target comes in. A limb over a garden shed nobody enters and a limb over a bedroom are the same limb with wildly different answers. Occupancy matters: a driveway used twice a day is not a patio in constant use.
3. If it hits, how bad is that? A four-inch branch onto a car and a twelve-inch limb onto a screened porch with people in it are not the same consequence.

The three combine into a rating — low, moderate, high, extreme — which is a communication tool, not a physical measurement. It exists so an owner can compare one tree against another and decide where the money goes.

What is actually looked at

The inspection runs bottom to top, because the failures that kill people are usually at the bottom.

• The site. Recent construction, trenching, grade changes, a new driveway over the root zone, irrigation habits, drainage, and which way the prevailing wind loads the tree.
• The root collar. Does the trunk flare into the ground or go in like a post? A missing flare often means the tree was planted too deep or buried by grading, and it can mean girdling roots. Fungal fruiting bodies at the base are read carefully — the decay is always older than the mushroom.
• The trunk. Cavities, seams, old wounds, bulges and depressions, sounding with a mallet where it is warranted, and whether there is enough sound wood shell left around whatever is hollow.
• The unions. Included bark, cracks, previous partial failures, and the presence or absence of a branch bark ridge.
• The crown. Dead wood, hangers, previous topping and the weak regrowth it produced, end weight on long limbs, and whether the foliage this year matches the foliage the tree ought to have.

Levels of assessment

There are three, and they cost different amounts because they are different work.

• Limited visual. A pass over many trees, often from a vehicle or on foot at a distance, looking for obvious defects. Appropriate for screening a large property, not for answering a question about one tree.
• Basic. A walk-around, ground-based, three-hundred-and-sixty degrees, looking at the site, roots, trunk, unions and crown, with binoculars and a mallet. This is what almost every homeowner needs and what “a tree risk assessment” normally means.
• Advanced. Tools and climbing: resistance drilling or tomography to map decay, an aerial inspection of a union that cannot be seen from the ground, load testing. Commissioned when the basic assessment leaves a specific question unanswered and the answer is worth paying for.

What you get

A written report. Each tree identified by species and location, each defect described, each part rated, and a set of options with what each one buys you. Options normally include doing nothing, monitoring on a stated interval, reducing end weight, installing hardware, moving the target, and removal — and they are presented as options rather than as a quote with a foregone conclusion.

The report says what conditions it was made under and how long it is good for. A tree assessed in April is not certified for the following January, and any assessment made before a hurricane describes the tree that existed before the hurricane.

Why it is a separate service

Because an assessment written by the person hoping to sell the removal is worth less, and everyone knows it. It is quoted and paid for as its own piece of work, and the report stands whether or not any work follows. If it recommends nothing, that is the finding.