Oregon resilient tree list looks ahead to changing climate

CORVALLIS, Ore. — Trees planted along Oregon streets, in parks and around schools may stand for decades. During that time, they will face hotter temperatures, drought, invasive pests, limited growing space and other pressures of urban landscapes.

Those challenges are driving development of the Oregon Regional Resilient Tree List, a digital resource intended to help communities choose a diverse mix of trees that can persist under changing climate conditions.

The resource, which is in draft form and not yet available to the public, will allow municipal foresters, nursery growers, landscape professionals and others to compare species by climate resilience, drought tolerance, size, form and other characteristics.

An update on the project was presented at Growing the Urban Forests of Tomorrow: A Nursery Symposium, held at Oregon State University on July 15 and hosted by the Oregon State College of Forestry and the Oregon Department of Forestry in partnership with the Oregon Association of Nurseries.

“What we’re choosing now for our canopy is going to impact us decades later,” said Allison O’Sullivan, a community assistance forester with the Oregon Department of Forestry (ODF).

The project team describes climate change as a force that adds to challenges already facing community trees, including pests and diseases, wildfire, development pressure and the difficulty of establishing young trees.

An idea takes shape

The project began in early 2023 with an idea from Scott Altenhoff, manager of ODF’s Urban and Community Forestry Program.

Altenhoff saw a need for an Oregon-focused tree-selection resource that considered not only current growing conditions but also the future of urban forests. The team began developing a framework for the list and held regional focus groups with tree professionals across the state.

The first draft was presented at the Oregon Urban and Community Forestry Conference in May 2025. The team later expanded its outreach and gathered more input through professional conferences, regional focus groups and direct reviews of the list.

Jennifer Killian, an OSU Extension Service statewide urban forestry specialist, and ODF’s O’Sullivan, Alison Herrell and Kat Bethea are the project’s co-leads.

The list draws on OSU’s Landscape Plants Database, tree information and resources available from the Urban Forest Ecosystems Institute at Cal Poly in San Luis Obispo, and Manual of Woody Landscape Plants by Michael A. Dirr. The team has added field observations from municipal foresters, arborists, nursery professionals, researchers, nonprofit organizations and state agencies.

“What sets this list apart from others out there is that we are literally using the real-world experiences of people who see and touch these trees every day,” Killian said. “We get this information from the focus groups and from direct edits to the list that we share.”

A portal for many users

The current draft is organized as a spreadsheet, but the team envisions a web-based portal that users can explore online, print or download.

It includes more than 100 species for Western Oregon, about 90 for Eastern and Central Oregon and more than 100 for southwestern Oregon. The final numbers and design may change as the team incorporates its latest round of feedback.

Information under consideration includes whether a tree is native to Oregon, its expected climate resilience, drought tolerance, plant hardiness zone, form, mature height and width and whether it is deciduous or evergreen.

Different audiences may need different levels of detail. Municipal foresters might focus on climate resilience, mature size and planting-site constraints, while nursery growers might use the portal to anticipate future demand. Landscape professionals and homeowners might need a simpler way to find trees suited to a particular region and site.

The portal isn’t meant to replace local knowledge or guarantee that a species will perform the same way in every location. Soil, water, exposure, maintenance and conditions within the same city can all affect how a tree grows.

Instead, it’s intended as a starting point, especially for communities that do not have an urban forester or the time and resources to develop their own tree list.

Oregon ranks third in the United States in horticultural specialty crop sales, which include nursery and greenhouse products, with $1.29 billion in 2024 sales, according to the U.S. Department of Agriculture.

“At the end of the day, we want to support our nursery growers’ efforts to grow resilient trees so we can get them in our communities for the future,” O’Sullivan said.

Extension brings statewide input

Killian became one of the project’s primary contributors after she joined ODF in March 2024.

While at the agency, she researched and evaluated species information, helped create the framework for the list and facilitated regional focus groups. She also incorporated stakeholder feedback, coordinated collaborators and presented the project to professional audiences.

Killian continued as one of the lead contributors after starting her position in the OSU College of Forestry in March 2025. Her Extension work has focused on refining the list, engaging partners across Oregon and coordinating outreach and feedback.

She also helped organize the recent nursery symposium, which drew nursery growers, urban foresters, arborists, researchers and other professionals. Killian’s presentation with O’Sullivan at the symposium introduced participants to the draft and gave them a chance to help shape what the team hopes will be its final major revision.

The event also opened a conversation between nursery growers and urban forestry professionals about best management practices and the trees Oregon communities may need in the future.

Killian said statewide input matters because the same tree can perform differently among Oregon’s regions and even within one community.

“A tree that thrives in the Willamette Valley might struggle in Eastern Oregon, or vice versa,” she said. “I’ve even seen the exact same tree do really great in one section of Corvallis and just not do great in another part of town.”

Diversity reduces risk

The project team defines a resilient urban forest as one in which trees can be selected, grown and established so they persist and thrive under changing climate conditions and the realities of urban and managed landscapes.

Species diversity is central to that goal because communities that rely too heavily on one or a few species are more vulnerable when a pest or disease arrives. Dutch elm disease transformed streets across North America, and emerald ash borer is now threatening ash trees in Oregon.

“No single species can build a resilient urban forest,” the project presentation states. “Overreliance on a few species increases vulnerability.”

The portal is one part of a larger system that includes seed sourcing, nursery production, planting practices, equitable canopy distribution, care for young trees and long-term replacement planning.

That system matters because the benefits of urban forests depend on decisions made long before a tree is planted. People decide what to grow, how to grow it, where to buy it and where it will be planted.

O’Sullivan said urban forests depend on people throughout that process, from seed collectors and growers to arborists, planners and community members.

“Urban forests do not spontaneously appear,” she said. “A lot of effort goes into establishing an urban forest long before a tree is even planted.”

Killian said the portal’s long-term value will depend on continued work across those groups.

“Resilient trees are important, but resilient urban forests aren’t built one tree at a time,” she said. “They’re built by resilient systems.”