Arborists and arborist reports in Portland, Oregon

When Portland requires an arborist

Most homeowner removals in Portland go through a Tree Removal and Replanting permit, and for an ordinary dead, dying or dangerous tree the city’s pages do not make an arborist report mandatory. The city does recommend hiring a practicing certified arborist for removal work, and several situations under Title 11 do call for one in writing.

The permit thresholds themselves (12 in DBH, Type A and Type B) are on the Portland tree removal page and in the Oregon tree removal permits guide.

Who counts as an arborist under Title 11

PCC 11.80.020 defines an arborist as a professional listed as a certified arborist by the International Society of Arboriculture (ISA), or a consulting arborist registered with the American Society of Consulting Arborists (ASCA). A climber with years of experience but neither credential does not meet the definition, so his or her report will not satisfy a requirement that names an arborist.

ISA certification has to be renewed every three years through ISA’s recertification process. Ask for the certification number, not just a logo on a truck.

What an arborist report has to contain

Portland’s guidelines for development arborist reports list the contents the city reviews. If a report you paid for is missing any of these, expect it to come back:

• The arborist’s name, signature, contact details and ISA or ASCA number
• The date and time of the most recent site assessment
• For each tree: species, DBH, condition, location and the extent of root cover
• How tolerant the tree is to construction impact, given its species and health
• Any earlier damage within the root zone
• How and why the proposed protection measures will keep the tree alive
• A site plan meeting PCC 11.50.070, plus photographs and supporting documents

Dead, dying, dangerous: where a risk assessment helps

Title 11 sets the tests for a Type A removal. A tree is dead when there is not enough live tissue to sustain life; dying when disease, insects or rot have put it in advanced decline that reasonable treatment cannot fix (PCC 11.40.050.A.2). For a dangerous tree, the city first looks at practicable alternatives to removal, and can grant the permit if those would cost significantly more than the tree is worth or would not substantially fix the danger.

That last test is where a written risk assessment earns its fee. An arborist who also holds ISA’s Tree Risk Assessment Qualification (TRAQ) can document the defect, the target and the likelihood of failure, which answers the city’s question directly. See tree risk assessment for what the assessment covers.

How to check a credential

ISA’s Find an Arborist directory lets anyone search credential holders by name or certification ID. Credential holders can hide their profile, so a missing listing is not proof of a fake; ask for the number and search it. ISA’s credential pages describe TRAQ as a separate qualification built on a two-day course and a half-day of written and field assessment.

A credential is not a license. Oregon tree businesses are licensed through the Construction Contractors Board or the Landscape Contractors Board, and our Oregon tree service license lookup shows how to check both. The arborists in Oregon page covers the state picture, and the arborist guide explains what certified arborists do.

What to do next

Check your zoning on the city’s map before you assume a small tree is exempt; overlay zones and plan districts change what you need. If you are subdividing or building, line up the arborist report at the start, because it goes in with the land division or development application. Questions go to Urban Forestry at 503-823-8733 or Trees@PortlandOregon.gov.

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