A tree health check

What you can see from the ground

The International Society of Arboriculture publishes a checklist any owner can use. Among its questions:

• Are there large dead branches?
• Are there detached, hanging branches?
• Is there loose bark on the trunk?
• Are there cracks or splits in the trunk or where branches are attached?
• Are there cavities or rotten wood along the trunk or in major branches?
• Are mushrooms present at the base of or under the tree?
• Have the leaves developed an unusual yellow color or do they seem smaller in size?
• Has the tree been topped or heavily pruned?

“If you answered ‘yes’ to any of the questions,” the brochure says, the tree “should be examined by an ISA Certified Arborist.”

What the arborist looks at

For health, the ISA describes four signs of vitality: “new leaf or bud formation, leaf size, twig growth, and absence of crown dieback.” A drop in twig growth from one year to the next is, in its words, “a fairly reliable cue that the tree’s health has recently changed.” For stability, the arborist looks for the defects on the checklist and for what would be hit if part of the tree failed. The ISA advises that mature trees be inspected at least once a year.

Risk assessment and written reports

A tree risk assessment weighs how likely a tree or a part of it is to fail against what it would hit. It matters most when there is a decision to make: keep, prune, support or remove. In some places a written assessment also has legal weight. In Florida, section 163.045 bars local governments from requiring a permit to prune or remove a tree on a single-family lot if an ISA-certified arborist or a Florida-licensed landscape architect documents that it poses an unacceptable risk. Ask in advance whether you need the findings in writing. Permits

Checking the credential

ISA certification is, in the society’s own words, “a nongovernmental, voluntary process.” Certified arborists have passed an exam and must keep up continuing education. The ISA’s Verify a Credential tool at TreesAreGood.org confirms whether a person holds the credential. Some states also license tree work separately; the state pages say where we found such a rule. Hiring a tree service

Updated 2026-10-11.