What is it?

Tree risk assessment (TRA), as defined by the International Society of Arboriculture, is the systematic process used to identify, analyze, and evaluate tree risk. There are three levels to TRA—limited visual (Level 1), basic (Level 2), and advanced (Level 3).

Basic (Level 2) is the most common form of assessment—entailing a 360° ground-based inspection of canopy, trunk, and surface roots. Mallets and probes may also be used to detect or investigate internal wood decay. Site conditions are examined for their effect on subject tree(s). This information is applied to a risk rating system that considers failure likelihood, the presence of targets, likelihood of failure and impact, and the severity of potential consequences. From here, an overall risk rating is assigned.

When is it important?

Do you own or manage a large tree within striking distance of, or perhaps directly overhanging, frequently-occupied areas? Or perhaps a fixed object of high value—say, your house, or a nice fence, or parked cars*? Were the tree or any large limbs to fail, it also possible for it to impact your neighbor’s property?

If so, and if any of these trees concern you, it may be time for a professional assessment. Whether you are a commercial property manager or a private homeowner, you may be held liable for damages caused by trees located on your property.

What to know?

• As a consulting arborist (not a tree service), sales bias is omitted from my opinions. (In other words: I will not recommend unnecessary tree work!)  My conclusions are based solely on tree biology, observable conditions, and current industry standards.

• Timeframe. Like us, trees are living, ever-changing things; their condition today does not guarantee their condition tomorrow. For that reason, tree risk assessments cover limited timeframes, typically no longer than 18 months, and do not constitute a guarantee.

• As the owner or manager of trees, their management is up to you. Following my assessment, the action taken—whether it be to remove, retain and monitor, prune, etc.—is at your discretion. The role of a tree risk assessor is to empower your decision-making with a well-educated professional assessment.

• Lastly, for higher-risk trees with high monetary or sentimental value, there are sometimes alternatives to removal. (These alternatives—which include cabling, bracing, lightning protection systems, plant health care, restricting access to target zones, and relocating targets—can reduce, but never entirely eliminate, tree risk.) I will consider all practical mitigation options, and present these to you in my report.

• If the decision is made to retain and mitigate risk with your tree(s), periodic re-inspections are essential.