Consultants say Davis Meeker Oak poses moderate risk to nearby hangar and roadway; pruning and support recommended

Consultants hired by the city presented a final, advanced risk assessment of the Davis Meeker Oak at the Tumwater City Council work session on March 11, 2025, concluding that parts of the tree have substantial interior decay while other portions retain structural wood and that targeted mitigation could reduce — but not eliminate — risk to nearby targets including Highway 99 and an airport hangar.

The assessment matters because the oak is a heritage tree near an airport hangar and a public roadway; a large branch failed in May 2023 and landed on the highway beneath the tree, prompting the city to seek a second independent analysis before deciding whether to remove or retain the tree. The consultants presented sonic-tomography readings, an aerial inspection of the crown, root-crown excavation and fungal testing to support their findings.

Todd Prager, principal of Todd Prager and Associates, said the team performed multiple sonic tomography readings through the trunk and stems, plus an air-spade excavation of the root crown and aerial inspections. He and climbing arborist Rick Till described a pattern of relatively thin outer “shell” wood surrounding a large interior cavity at the trunk base, while higher trunk readings and many parts of the stems showed substantial sound wood. Prager summarized the May 2023 failure: “An 18-inch-diameter branch fell from over 40 feet above ground and failed during calm weather,” and that earlier assessments had recommended removal following that event.

Rick Till, who completed aerial inspections and sampling, told the council the second codominant union and the central stems show both historic woundwood and evidence of fungal colonization in places. He said probing and air-spade excavation of the root crown found sound wood around the cavity and “we did not find any significant decay or indication of fungal fruiting bodies” at the root crown. Till emphasized the assessment is qualitative: “This is not an objective system ... it's defined as being qualitative, not quantitative,” and the resulting risk ratings depend on assessor judgment and the risk manager’s tolerance.

The consultants used the International Society of Arboriculture’s (ISA) Tree Risk Assessment framework (five-year time frame) to classify likelihood and consequence for targets beneath and around the tree. For whole-tree failure toward Highway 99 the team judged the likelihood of failure in the next five years to be “possible” and the likelihood of impact to be medium; that combination produced a risk rating of moderate for some targets, and low for others. The stem oriented over the airport hangar produced the highest single-target risk rating (moderate) because the hangar is a fixed target within the fall zone.

The team presented three preservation-tiered options and one removal option. Option A — limited deadwood pruning, root-zone management and monitoring — has the lowest upfront cost but produces the smallest risk reduction. Option B — crown reduction pruning combined with supplemental structural support (cabling), root-zone improvement and monitoring — was identified by the consultants as a “prudent” choice if the city intends to retain the tree: it can significantly reduce risk but requires ongoing inspection and maintenance of supports and periodic reassessment. Option C combines option B with target-management steps (for example, removing parking within the tree’s impact zone) and Option D is full removal, which eliminates public-safety risk but removes the historic tree and its community value.

Prager and Till also ran the tree through two supplemental models (Veil and TreeCalc) to compare outcomes. According to consultants, TreeCalc indicated a robust outer safety factor in the measured locations despite the internal hollow; Veil produced a tolerability analysis used by some municipalities. The consultants cautioned that different assessment tools and reasonable differences in interpreting “possible” versus “probable” likelihood will alter the calculated outcome and that the ISA process contains inherent subjectivity.

City staff provided preliminary, high-level cost estimates and a proposed five-year implementation approach. Staff noted some specific line items from the consultant report (for example, a $2,000 estimate for a limited deadwood pruning in the consultants’ report) and said other costs — particularly for traffic control and the design of a supplemental-support system — will vary by implementation method and contractor. Staff said the city is currently requiring DAHP (Department of Archaeology and Historic Preservation) permits before undertaking preservation work and will need to advertise for and select contractors, decide whether to use city crews or contractors for traffic control, and formalize a work plan if an option to retain the tree is chosen.

Council members asked about the rate of decay, long-term monitoring, ongoing costs and funding options. Rick Till said the consultants cannot calculate a meaningful, reliable annual rate of decay for the tree because decay processes vary, are often compartmentalized by the tree, and Oregon white oak is relatively decay-resistant; he added, “the rate of decay is probably quite slow in relation to the residual strength of the tree.” Several councilors and staff discussed establishing a dedicated donation or special fund (staff and the city attorney indicated it is feasible) and adding monitoring or maintenance responsibilities to the planned urban-forester position. Council members also urged that any long-term preservation plan include formal, written commitments so future councils are clear about ongoing maintenance and funding responsibilities.

No formal decision to remove or retain the tree was made during the work session. Staff said they will continue to refine cost estimates, complete permitting, and return to council with further details and options. The consultants and staff recommended periodic reassessment (for example, scheduled sonic-tomography or aerial inspections) if the city selects a preservation path. Mayor Sullivan and several council members thanked the consultants for the independent analysis and said the report provides a basis for subsequent council deliberation.

Looking ahead, if the council opts to retain the tree staff said the next implementation steps would include finalizing a preservation work plan, selecting contractors, securing any required permits, and establishing a maintenance and monitoring schedule and associated budget. If the council opts for removal, staff noted the city will need to budget for removal and decide what, if any, interpretive or replacement actions (such as signage or replanting) the community wants.