Arborists and tree health in Washington and Oregon

What an ISA Certified Arborist is, and how to look one up

The International Society of Arboriculture’s Certified Arborist credential requires three years of full-time arboriculture experience, or a two-year degree with two years of experience, or a four-year degree with one year, before a candidate can sit the exam: 200 multiple-choice questions in 3.5 hours, with a 76 percent pass mark. The certification is valid for three years and is kept by earning at least 30 continuing education units in that period or retesting [1][2]. ISA’s own description of what it proves is modest: the holder has the minimum knowledge and skill to work within the scope of the credential, and is bound by a code of ethics [3].

To check someone, use ISA’s public verification directory at certificates.directory.isa-arbor.com (entry page: treesaregood.org/findanarborist) and search by name or certification number. The listing is voluntary, so a certified arborist can be missing from the map view, but a credential number will verify [3]. Ask for the number; “ISA certified” on a truck door is not a number.

Certification is not a contractor license, and the license is what the states check. In Oregon a business that removes or prunes trees must hold a Construction Contractors Board license or a Landscape Contractors Board license (ORS 701.005, ORS 671.525); the LCB also offers an arborist license phase to ISA-certified arborists [6]. In Washington, “performing tree removal services” is inside the statutory definition of a contractor, so the business must be registered with L&I (RCW 18.27.010) [6]. The lookups are in tree service license lookup in Oregon and tree service license lookup in Washington.

TRAQ and the three levels of risk assessment

The Tree Risk Assessment Qualification is ISA’s add-on for people who already hold the Certified Arborist or an equivalent credential or degree. It is a two-day course followed by a half-day of written and performance assessments, and the holder must retrain and retest every seven years. The course covers the limited-visual and basic assessments defined in ISA’s tree risk assessment standards, plus the advanced diagnostic methods used when those are not enough [4].

Those are the three levels you will see named on a report. Level 1 is a limited visual assessment, usually a walk-by of many trees after a storm, looking for obvious defects. Level 2 is the basic assessment: a 360-degree ground inspection of one tree from root flare to crown, with mallet and probe, producing the likelihood-of-failure, likelihood-of-impact and consequence ratings on ISA’s Basic Tree Risk Assessment Form. Level 3 is advanced: resistance drilling, sonic tomography, root excavation or a climbing inspection, ordered when a Level 2 cannot settle the question. What each level can and cannot tell you, and how to read the form, are on tree risk assessment.

Cities have started writing TRAQ into their codes. Seattle’s hazard-tree paperwork is the ISA Basic Tree Risk Assessment Form, which SDCI says must be completed by a qualified TRAQ professional [9]. Lake Oswego may require a report from a “Tree Risk Assessor Qualified Arborist” for a hazard tree permit (LOC 55.02.042(4)) [10], and Shoreline asks for a TRAQ arborist’s determination to remove a non-imminent hazard tree in a critical area (SMC 20.80.075(G)); for its dead or imminent-hazard exemption, the city checklist asks for an ISA tree risk assessment form from an ISA certified arborist [11]. What each city wants before a hazard tree comes down is in hazard tree removal.

Consulting arborists vs tree-care companies

A tree-care company sells the work. A consulting arborist sells the opinion. The American Society of Consulting Arborists, founded in 1967, describes its members as the objective voice property owners, municipalities, attorneys and insurers go to for tree-issue resolution, expert testimony and appraisals [5]. That is who writes the report when the question is whether a 36-inch Douglas fir can stay, or what a neighbor’s cut cost you under ORS 105.810 or RCW 64.12.030 [7].

The practical rule is to separate the diagnosis from the sale when the money is large. If a crew’s estimator says a tree must come out and the removal is a $4,000 job, a second opinion from someone who does not do removals is cheap by comparison. Many Northwest consultants hold both ISA certification and TRAQ; some also hold a contractor license so they can do the pruning they prescribe. Ask which they are. The other arborist roles, from climber to utility forester, are laid out in what does an arborist do.

Choosing an arborist: ISA’s own checklist

ISA’s consumer brochure on hiring lists the checks it wants homeowners to make, and most take one phone call [21]. Pair them with the Oregon CCB/LCB or Washington L&I lookup above, because the brochure describes ISA certification as a nongovernmental, voluntary credential, not a license [21].

• Credential. An ISA Certified Arborist, or the higher ISA Board Certified Master Arborist. Both pass comprehensive exams, and holders must follow ISA’s code of ethics [21].
• Memberships. ISA, the Tree Care Industry Association (TCIA) or the American Society of Consulting Arborists (ASCA) [21].
• Insurance. Ask for proof, then call the insurance company named on it [21].
• Estimates. Get more than one and ask for references. ISA advises against automatically taking the lowest bid; compare the written specifications, the work to be done and the credentials behind each price [21].
• Door-to-door offers. ISA tells owners to be wary of people who go door to door offering bargains [21].
• In writing. ISA notes that most reputable arborists have clients sign a contract; read it and ask questions before you sign [21].

The same brochure lists services beyond pruning and removal that owners often do not think to ask about: cabling and bracing for weak unions, soil aeration, lightning protection systems, tree protection during construction, and consulting or legal work on tree disputes [21].

When a city requires an arborist report

Most Northwest tree codes let a dead or dangerous tree come out faster than a healthy one, and the price of that shortcut is documentation. What a report contains, and who may sign one in nine Washington and Oregon cities, is in arborist report.

Portland. Private trees 12 inches DBH and larger are regulated. Removing a healthy tree 20 inches or larger, or more than four healthy trees 12 inches and up in a year, is a Type B permit with public notice and appeal (PCC 11.40, Table 40-3); dead, dying or dangerous trees go through Type A with no notice [8]. The arborist requirements sit in the development chapter: under PCC 11.50.070 a claim that a tree is exempt for poor health needs supporting documentation from an arborist, and under 11.50.080 an arborist report is required to change which trees are retained once work has started [8]. Urban Forestry also publishes a Supplemental Arborist Form for private trees under 20 inches in a plan district or overlay zone. Removal and replanting applications have been free since July 1, 2025 [8]. The full list of Portland situations, and what the report must contain, is on arborists and arborist reports in Portland.

Seattle. SMC 25.11 limits the number, size and type of trees that can come off a lot, and a hazard-tree removal needs the Basic Tree Risk Assessment Form from a qualified TRAQ professional, photos, and, if applicable, an arborist report [9]. The work must be done by an SDCI-registered tree service provider, which must have an ISA Certified Arborist on staff or retainer and $1 million in liability coverage with the City named [9]. Hazard trees in environmentally critical areas follow Tip 331B [9]. The registry rules, notice periods and provider lookup are on arborists and tree service providers in Seattle.

Elsewhere the pattern repeats. Kirkland says an arborist report may be required with a tree removal permit, which costs $600 plus a 3.5 percent surcharge. Edmonds lets a hazard tree come out without a permit once it has reviewed a Tree Risk Assessment Form from an ISA Certified Arborist/Tree Risk Assessor, with a site plan and photos (handout P46). Bellevue still requires a clearing and grading permit, but a tree that a TRAQ-qualified tree professional rates hazardous (high or extreme risk) falls outside its annual removal limits and replanting rules (BCC 23.76.035; 23.76.060.G), and Bremerton requires a certified arborist’s written determination for a danger tree in a critical area [11]. In Oregon, McMinnville’s simple street-tree removal needs an arborist report showing hazard or disease, and Sherwood requires one for any street tree over 10 inches [12]. All 80 cities are in tree removal permits in Oregon and tree removal permits in Washington.

Tree health problems in the Northwest right now

Five problems account for most of the “is my tree dying” calls west of the Cascades, and each has an official status worth knowing before you pay for a diagnosis.

Emerald ash borer. EAB quarantine The first West Coast detection was Forest Grove on June 30, 2022. Oregon’s permanent quarantine (OAR 603-052-1075) now covers Washington, Yamhill, Marion, Clackamas and Multnomah counties, with 2026 finds from Newberg to Salem to east Portland; ash wood, chips, mulch and the firewood of all hardwoods cannot leave without an ODA compliance agreement, with a civil penalty up to $10,000 [13]. Washington’s first detection came in August 2026: a specimen collected August 3 in Hazel Dell, unincorporated Clark County, confirmed by WSDA and USDA on August 19. DNR’s advice to Washington owners is to inventory ash, stop planting it, remove dead and dying ash, and not move firewood [14]. Details by state: emerald ash borer in Oregon and emerald ash borer in Washington.

Western redcedar dieback. No primary pathogen has been found; the agencies attribute the thinning crowns, topkill and flagging to drought and heat stress, with westside mortality peaking in 2017–2018. ODF, WA DNR and the Forest Service ask people to report pockets of two or more mature trees with symptoms, not single trees, and ODF’s prescription is supplemental summer water and moist, shaded planting sites [15]. Removal is only a question when a dead top becomes a hazard: western redcedar dieback.

Laminated root rot. Endemic across the westside Douglas-fir type, and the reason firs fall over green: infected trees are wind-prone before the crown shows anything, which is why a Level 2 assessment starts at the root flare. WSU’s guidance is to remove infected trees plus a 50-foot buffer and replant only resistant or immune species (cedars and pines tolerate it; maples and alders are immune); ODF uses a 50–75 foot buffer. Roughly 5 percent of highly susceptible host area is out of production because of it [16]: laminated root rot.

Swiss needle cast. A Douglas-fir-only foliage disease worst on the low western flanks of the Oregon Coast Range; the 2024 aerial survey mapped about 900,000 acres and found roughly 500,000 acres of affected Douglas-fir [17]. In a yard it is a thin, yellowing fir holding only a year or two of needles. ODF’s advice is not to grow Douglas-fir in the severe zones [17].

Sudden oak death. Confined to Curry County since 2001, but 2024 brought 15 new infestations outside the 2015 quarantine line, and the 515-square-mile quarantine gained about 148 square miles of emergency expansion [17][18]. Tanoak is the tree that dies; rhododendron and Douglas-fir carry it on foliage. Host material cannot leave the quarantine [18]: sudden oak death in Oregon.

Two more with calendar rules: Portland bars pruning elms from April 15 to October 15 and requires pruned elm wood to be disposed of within 24 hours (PCC 11.60.060), because the beetles that carry Dutch elm disease fly in that window; and OSU says not to prune birches in summer when bronze birch borer adults fly [19]. The full list is at tree pests and diseases in Washington and Oregon.

What a tree health assessment looks at

A health assessment and a risk assessment overlap but answer different questions: is the tree declining, and is it likely to hurt something. For a single yard tree, a certified arborist’s visit runs roughly in this order:

• Site and history. Grade changes, trenching, new patios or driveways within the dripline, irrigation, and recent drought summers. Most redcedar and birch decline starts here [15][19].
• Root flare and lower trunk. Buried flares, girdling roots, conks at the base, bark bleeding, and a mallet sounding for hollow wood. Root rots show here before the crown [16].
• Trunk and unions. Cracks, cavities, included bark in co-dominant stems, and old topping cuts with weakly attached regrowth, the common failure point in ice.
• Crown. Dieback pattern (top-down suggests roots or water; scattered suggests disease or pests), needle retention on conifers, epicormic sprouts, and D-shaped exit holes on ash.
• Targets. What is under the tree and how often: a bedroom, a driveway, a busy sidewalk, or nothing. This is the half of the risk rating people forget.

How often to look: ISA’s mature-tree guidance is an inspection at least once a year, checking four signs of vitality: new leaf or bud formation, leaf size, twig growth, and the absence of crown dieback. Shorter twig growth than in past years is one of the more reliable cues that the tree’s health has changed recently, and an arborist can read it from the last few seasons of growth on a branch [23].

If the arborist cannot name the problem, the next step is a sample to a diagnostic lab (WSU Puyallup takes suspected sudden oak death samples in Washington [18]) or a Level 3 instrument test. A tree that is merely stressed gets water, mulch and time; a tree with a structural defect over a target gets a crown reduction, cabling, or a removal recommendation with the reasoning written down.

What an arborist costs

Assessments are usually a flat fee quoted up front for the visit, and the fee differs by whether it is a Level 2 look at one tree or a survey of a lot, and whether a written report follows. An arborist report that a city requires for a permit is a separate written deliverable with its own fee: it has to follow the city’s form, carry the assessor’s credential number, and survive an appeal if a neighbor files one. This site publishes no fee figures for assessments or reports because there is no public source for them; ask what the written report costs separately from the site visit.

Ongoing plant health care (PHC), where an arborist monitors your trees and treats problems before they get serious, is billed one of two ways according to ISA: a monitoring fee with each treatment billed separately, or an annual fee that covers the season’s monitoring visits and many of the treatments. ISA says there is no standard PHC program, so the price follows a site visit; ask which model you are being quoted [22].

The public numbers are on the city side. Seattle charges half its land-use hourly rate for a hazard, emergency or pest permit and nothing for a dead-tree removal [9]. Portland’s Urban Forestry hourly rate is $160 for FY2025–26, though its removal and replanting applications are free [8]. Kirkland’s tree removal permit is $600 plus 3.5 percent [11]. The labor index behind every quote is public too: the BLS May 2025 mean wage for tree trimmers and pruners is $35.40 an hour in Oregon and $32.20 in Washington [20]. If the assessment ends in a removal, the modeled crew-hour ranges are on tree removal cost; if it ends in pruning, on tree trimming cost. Modeled estimate, not quotes (method).

Arborist services by area

Statewide rules, costs and storm seasons: Arborist services in Washington · Arborist services in Oregon. City pages where the code names an arborist: Portland arborist reports · Seattle arborists and tree service providers.

Related guides

• What does an arborist do? Roles, credentials and when you need one
• Arborist report: what is in it, and when WA and OR cities require one
• Tree cabling and bracing: when it saves a tree and how long it lasts
• How to become an arborist in WA or OR
• Arborist salary in Washington and Oregon
• Mushrooms on trees: which fungi mean decay
• How to tell if a tree is dead: seven checks