Milwaukie urban-forest staff flags emerald ash borer threat, urges assessment rather than wholesale removal
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Summary
New urban-forest staff warned the emerald ash borer could kill nearly all untreated ash trees and urged Milwaukie to inventory and assess trees before choosing between large-scale removal, targeted treatment or replanting to protect canopy goals.
Alfred Mosali, the city's newly introduced urban-forest field staff, told councilors the emerald ash borer presents a serious threat to ash trees and urged the city to assess its inventory before pursuing removal or treatment options. "The beetle will kill 99.9 something percent of ash trees that are left untreated," Mosali said, noting associated fungal issues that can make trees brittle and difficult to remove safely.
Mosali told councilors several cities initially responded to the pest by removing large numbers of ash trees, which avoided immediate risk but also erased significant canopy benefits and required major capital outlays. He recommended an assessment to quantify how many ash trees exist, followed by a cost-benefit judgment: targeted treatment where feasible, selective removal where necessary, and replanting (including understory planting) to sustain canopy goals.
Councilor Adam Fosroboti asked whether the city's 40% tree-canopy goal remains realistic given development pressures and pest impacts. Mosali recommended reevaluating the timeline and doubling down on planting to work toward the goal rather than defaulting to wholesale removal. "A good way to try to strive towards that goal is to start a replant now," Mosali said, calling for funding and maintenance commitments and noting that replacement trees take decades to deliver the same benefits as established canopy.
Councilors and staff discussed maintenance bonds and warranty periods for developer-planted trees, noting many trees planted under short warranty periods are removed after warranty expiration. Mosali cautioned that planting alone will not replicate the benefit of mature trees and stressed the need to integrate policy, funding and maintenance strategies.
Next steps: staff recommended inventory and assessment work be prioritized in upcoming budget discussions so the city can craft a treatment, removal and replanting strategy that aligns with canopy goals and budget realities.