About the Arboretum
The Ainsworth Linear Arboretum is in Portland, Oregon.
How did a dying monoculture become the Ainsworth Linear Arboretum, a showplace for tree diversity?
When the Ainsworth Linear Arboretum started in 2005, there were only six species of trees represented in the Ainsworth medians in just four genera: maples, ash, oak, and beech. Today, that near monoculture has been greatly diversified. As we catalogued in the Tree Library, there are now 46 species in 32 genera in 21 families in the median alone! Where there were once only broadleaf deciduous trees, there are now evergreen broadleaf and conifer trees, and even conifers that drop their needles each autumn.
Read below to learn about the history of the Arboretum, the many contributors to its health and vibrancy, and how members of a neighborhood Tree Team steward this community resource today.
The Portland Urban Forestry Commission dedicated this space as an official arboretum.
History of the Ainsworth Linear Arboretum
Early in the 20th century, the famed Olmstead landscape firm developed a parks plan for Portland. The plan envisioned people arriving from the east would be ushed into the city via a great tree-lined boulevard reaching to the Willamette River. Only one portion of this was ever realized - a wide median in the middle of NE Ainsworth from Martin Luther King, Jr. Boulevard (then Union Avenue) to NE 37th.
Some time after World War II the median was planted with Norway maples, a species now on the City’s do-not-plant list because of its invasiveness. In the 1980s, several blocks east of NE 33rd where trees had died were planted by the City of Portland with red oak, European beech and Raywood ash. By the early 21st century, 80% of the thin-barked European beech had died, mostly from sun scald. Many of the shallow-rooted Raywood ash had toppled over, leaving several unplanted gaps.
Hearing concerns about the deterioration in the median from neighbors up and down Ainsworth, Concordia resident and neighborhood tree steward Jim Gersbach, with the support of James Rishky of Vernon and Paul Cone of Woodlawn, set out to rejuvenate the median with a bold idea. He reimagined its purpose as a place where Portlanders could become familiar with less well-known approved street trees. Here, too, promising new species could be planted and observed to test their suitability as street trees.
In 2005 he successfully petitioned the City of Portland’s Urban Forestry Commission to designate the Ainsworth median and planting strips between street and sidewalk as a city arboretum. In granting the designation, the Commission accepted Gersbach’s proposal that the new arboretum be a place for uncommon and investigational plantings.
Since then, the median - now called the Ainsworth Linear Arboretum - is being transformed from a near monoculture to a place where the diversity of trees that can be grown in Portland is celebrated.
There are about 180 trees in the median, more than a third of which are Norway maples. The most common tree in Portland, these maples are reaching the end of their lifespan all about the same time. A few maples in the median die each year.
The City’s Bureau of Maintenance is the median’s owner but doesn’t have funds for replanting. So replacement trees have been privately donated by individuals or Friends of Trees, which hosted the original website for the arboretum (thank you!). More recently, City of Portland Parks and Recreation’s Urban Forestry division has used mitigation funds (paid by developers) to purchase and establish new trees, watering them for two years and providing mulch.
New trees are selected for diversity and interest. For example, the median facing Alberta Park showcases many unusual evergreen species being trialed, from drought-tolerant cypress native to southern Oregon and California to rarely seen evergreens from Asia, Australia and South America.
Some trees in the arboretum planted before 2005 are a valuable piece of the show. For example, a bambooleaf evergreen oak (Q. myrsinifolia) planted in 2003 by Friends of Trees but still rare in Portland. The arboretum now boasts about a dozen different oaks, including three other kinds that are evergreen.
Many of the exceptional trees planted between 2005 and 2015 are marked with a black horticultural plaque. Look for these as you stroll along Ainsworth - they are on a concrete block set level with the sidewalk.
Many of Portland’s other arboretums are in park settings (see the Hoyt Arboretum or Columbia Children’s Arboretum). The Linear Arboretum is unusual in extending for over a mile along a residential street. A boon for visitors is that featured trees can be located by house address.
Ainsworth is easily reached by public buses, bike or automobile. It can also be navigated by wheelchair, being mostly flat. Trees in the median can be viewed from wheelchair-accessible sidewalks on Ainsworth’s north and south sides.
“This amazing collection of trees from around the world is truly a people’s arboretum. Located in neighborhoods that were once redlined, diverse tree choices for our urban forest are viewable by anyone for free.”
— Jim Gersbach, founder of the Ainsworth Linear Arboretum
Tree Teams for the Ainsworth Linear Arboretum
Portland Parks and Recreation Urban Forestry believes in the power of Portlanders to help shape and care for their urban forest. That belief propelled them to create a neighborhood tree steward course. Most of the people who later formed the Concordia Tree Team are graduates of the thorough education on all things related to Portland’s trees. One of the Team’s members, Jim Gersbach, persuaded tree lovers from the Vernon and Woodlawn neighborhoods to join Concordia in seeking a brighter future for the Ainsworth corridor as the Ainsworth Linear Arboretum.
Concordia Tree Team members help plant ,water and mulch trees in the Ainsworth Linear Arboretum. But it’s far from all they do.
In 2011 they partnered with the Cully neighborhood, NE 42nd Business Association and the City of Portland’s Bureau of Environmental Services to create the Cully-Concordia International Grove at NE 42nd and Lombard. They continue to care for trees there.
The Team also created and continues to care for the Learning Landscape Arboretum at Meek School . They turned a sun-baked grassy field into an outdoor classroom showcasing the diversity of oaks from around the world as well as relict tree genera, which are down to only one or two species.
The team welcomes all interested people in or near Concordia who love trees and want to lend a hand to participate. Upcoming projects include summer watering at Meek, neighborhood pruning of street trees and reprising the 2010 inventory of Concordia street trees.
Credit and Grateful Acknowledgements
Concordia Tree Team:
Mallory Pratt (convener)
Jim Gersbach (technical lead)
Rebecca O’Neil (website)
And many others!
Organizational Support:
City of Portland, Urban Forestry
Portland Public Schools
Columbia Slough Watershed Council
Friends of Trees
Generous Donations of Time and Skill:
Tree Library, Map and Data Management: Steve Heard and Kim Freeman
Logo Design and Project Advisor: Mette Hornung Rankin at Bureau of Betterment
Website Photography: Julian Wixson and Dhruv Bhatnagar