an arborist who has passed an independent exam administered by the International Society of Arboriculture. and maintains the credential through continuing education.

Certified Arborist (Wikipedia)
James Kinder, an ISA Certified Municipal Arborist examining a Japanese hemlock at Hoyt Arboretum
A Hinoki Cypress receiving some corrective pruning by a Certified Arborist in Oregon

The Certified Arborist credential identifies professional arborists who have a minimum of three years' full-time experience working in the professional tree care industry and who have passed an examination covering facets of arboriculture. The Western Chapter of the International Society of Arboriculture (ISA) started the certification program in the 1980s. As the program proved its worth, it was taken over and expanded by the parent ISA organization. More recently, the ISA added specialty certifications of Utility Specialist, for those maintaining vegetation around electric utility wires, Municipal Specialist, for those with additional experience managing public urban trees, and the Board Certified Master Arborist, for those with extensive knowledge that comes with higher levels of education and experience.

International Society of Arboriculture is a Non-accredited professional organization which has created its own certification program. ISA Certification does not mean the certified individual or organization is bonded insured or licensed by appropriate agencies to operate legally in your area. For a fee candidates can apply for several different types of "certification". After certification there is no review or enforcement of standards applied in the field. ISA certified utility workers regularly damage or remove historic or ecologically important trees with out risk of losing certification. ISA encourages its members to introduce local ordinances that require municipalities to hire only ISA certified Arborist. This practice reduces opportunities and undermines the professional image or Arborists that do not pay fees to ISA. ISA certification does not guarantee best practices or professional performance.

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