An arborist is the person you call when the question is about the tree itself: is it sick, is it safe, can it be saved. On Long Island the credential to look for is ISA Certified Arborist, from the International Society of Arboriculture.
What the ISA credential takes
ISA’s program guide (revised August 2025) sets the bar:
- at least three years of full-time work in arboriculture, or a related two-year degree plus two years of work, or a four-year degree plus one year
- a 200-question multiple-choice exam in three and a half hours, with a passing score of 76 percent
- renewal every three years, with 30 continuing education units or by passing the exam again
Cornell Cooperative Extension describes the exam as one that “verifies that the arborist is knowledgeable of proper and acceptable tree care practices.” ISA also has a higher credential, Board Certified Master Arborist, and its own hiring brochure tells homeowners to look for either one.
What an arborist does besides cutting
ISA’s own brochure, Why Hire an Arborist?, lists work that goes well past pruning and removal:
- plant health care
- cabling and bracing to support weak limbs or split trunks
- soil aeration around stressed roots
- lightning protection for tall trees
- tree risk assessment, for a tree you are worried about
- protecting trees during construction
- consulting and legal work
If the question is “can this tree stay?”, you want the arborist to see it before a crew prices the removal.
How to verify an arborist’s number
ISA’s Find an Arborist directory replaced its old Verify a Credential tool. ISA’s January 2026 FAQ says you can still search by name or by certification ID, and that the name or ID search is the reliable one, because people only appear in a search by area if they added their location. The older tool on TreesAreGood.org stopped updating in July 2025.
Ask for the arborist’s full name and number, then look it up. A company that says it has “an arborist on staff” should be able to give you both.
When Long Island paperwork asks for an arborist
Some towns build the credential into their forms. The Town of Huntington’s tree permit application has a line for the arborist’s ISA number. Long Island Best Tree Service says heritage trees, those 24 inches or more across, usually need an arborist’s report for a permit, and prices that report at $200 to $500 (October 2026).
Licensed arborist, tree surgeon and other names
People search for a “licensed arborist” or a “tree surgeon.” The license tree companies need here is the county home improvement license: Nassau lists tree surgery among the trades that need one, and Suffolk’s code names tree pruners, stump removers and all other tree services. ISA certification is a personal credential on top of that, earned by exam, so a company can hold the license without having a certified arborist, and the other way around.
Questions to ask before the visit
- Is the person coming out an ISA Certified Arborist, and what is the number?
- Will you write down what you found and what you recommend?
- If you recommend removal, could the tree be saved with pruning or cabling instead?
- If treatment is needed, who applies it, and what product?