What is the City doing?

Ash trees are widespread across Lake Oswego – in parks, natural areas, rights-of-way, and private property – making this a citywide risk, not an isolated one.

As part of its 2026 goals, the City Council prioritized adopting a strategy to address the impacts of EAB on trees in City-owned properties and public rights-of-way.

About 20% of the City’s total tree canopy is located on publicly-owned or managed property – including parks, natural areas, and public rights-of-way – while the remaining 80% is on private property.

The City is actively working to minimize the impacts of the loss of ash trees across the city and protect the public and City staff from ash trees as they become hazardous. 

Fall/Winter 2026

In October, with new City Tree Code updates going into effect and with adult EAB entering their dormant season, the City will begin preemptively removing approximately 150 trees from City-owned properties including parks, open spaces and facilities. Trees scheduled for removal will be marked with a red X.

As outlined in the multi-year EAB Readiness & Response Plan adopted by City Council on August 4, 2026, this management strategy, along with chemical treatment and leaving trees in place, will help minimize the impacts of the loss of ash trees across the city and protect the public and City staff from ash trees as they become hazardous. 

Tentative locations where ash trees will be removed this fall and winter include:

* Work will occur from October – May. Exact timing will be dependent on contactor availability, how long removals actually take, and field conditions. The actual number of trees will be dependent on budget allocations. Some locations may be deferred until next year. 

Click the blue dot on the map to find out more about that location. Zoom in to see number of ash trees at location - ash trees may be removed, chemically treated or left as a snag/habitat poles.

Tree markings.png

May/June 2027

In ash-heavy neighborhoods, tree removals will be staggered and timed with chemical treatment (injections) to limit large-scale canopy loss and prevent a surge of hazardous trees. Chemical treatment is most effective in May or June (before EAB eggs hatch) and must begin before 30% of the canopy is lost. Notable, culturally significant ash trees may also be treated. 

Mitigation tree plantings will occur in advance of and in tandem with removal of ash trees. 

Fall/Winter 2027

Depending on budget allocations, the City will begin removal and replacement of ash trees in public rights-of-way.

Other Key Actions and Background

The City has been preparing for the arrival of emerald ash borer (EAB) since 2023. Working closely with state and local agencies, the City is taking proactive steps to protect the urban forest and reduce the long-term costs associated with infested trees.

• Development of an EAB Readiness & Response Plan to guide the management of ash trees across City-owned or managed parks, natural areas, and rights-of-way. This plan was adopted in August 2026. The EAB Readiness & Response Plan is intended to proactively guide the City in advance of and during an EAB infestation. This plan:
  • Outlines the threat that is posed by the invasive beetle. 
  • Acknowledges, manages, and minimizes the ecological, economic, and aesthetic effects that EAB will have on public property owned or managed by the City of Lake Oswego. 
• Proactively removing ash trees identified as hazardous by an ISA Certified Arborist to improve safety and reduce future costs. 
  • Following the EAB Readiness & Response Plan, the City, using its contracted tree care companies, will begin a strategic ash tree management program. This program includes, removal of ash trees throughout the city. Chemical treatment will also be used for specifically identified trees. 
• Conducting comprehensive ash tree inventories. These inventories are a critical component of the City’s EAB Readiness & Response Plan and will provide the data needed to guide the long-term management of Lake Oswego’s urban forest.  
  • In 2025, the City conducted a comprehensive ash tree inventory City-owned or managed park property. Trees inventoried were within 100 feet of property borders with significant adjacent targets (homes, utilities, roads, sidewalks, etc.), and ash within 60 feet of trails. Ash trees at City-owned facilities were also inventoried.
  • In July 2026, the City began a comprehensive inventory of ash trees located within public rights-of-way throughout Lake Oswego to develop a comprehensive understanding of the distribution of ash trees in publicly-managed areas outside of parks and natural areas. This inventory should be complete in fall 2026.
  • A citywide all-tree inventory, a goal of the Urban & Community Forestry Plan (UCFP), is expected to take place in 2027.
• Updating the City’s Tree Code to support effective EAB response and long-term urban forest management. In August 2026, City Council finalized updates to Lake Oswego’s Tree Code. Effective in October 2026, the updated Tree Code will allow private and public property owners to remove irreversibly diseased trees with more flexibility and provides a free and streamlined tree removal permitting process to remove ash trees as part of a community-wide effort to respond to EAB infestation. 
• Replanting with a diverse mix of tree species to strengthen long-term resilience of our tree canopy. 
• Chemically treating select ash trees, including 28 trees in Foothills Park in 2023, as a preventative measure. 
• Monitoring for EAB in coordination with the Oregon Department of Forestry, including trap inspections and specialized staff training. 
• Educating the community through workshops, events, videos, and informational materials to help residents identify ash trees and signs of infestation. 

Through early planning and proactive management, the City is working to slow the spread of EAB, reduce future costs, and protect the health and resilience of the urban forest.