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Why are there Approved Street Tree Planting Lists?
Approved Street Tree Planting Lists are part of routine, responsible urban forest management. Trees are selected for each list after careful evaluation to ensure that the tree is appropriate for the space and also with consideration of how selected trees will contribute to the overall health of Portland's urban forest. The primary goals of the Approved Street Tree Planting Lists are to:
- ensure a strong, healthy urban forest- tree diversity provides resilience to pests and pathogens; selection of "climate forward" trees provides adaptability to climate change
- prevent conflicts with sidewalks, streets, buildings, and utilities - "Right Tree, Right Place"
- maximize the important services that trees provide for human health and the environment - where appropriate, larger form trees provide greater benefit over time for people, wildlife and the environment
How do I use the approved street tree planting lists to select the right tree for me?
The new approved street tree planting lists offer a diversity of choices. Tree characteristics such as fall color, showy flowers, fruits/nuts for wildlife, and interesting bark, as well as native and evergreen trees, are distinguished so you can easily select a tree that has the qualities you’re looking for.
After submitting a planting permit application to Urban Forestry, an Urban Forestry Tree Inspector will inspect your site and send you the approved street tree planting list that is appropriate for your site. You can find a searchable table online to help narrow down the choices for your site. Once you’ve selected a tree from the approved list, notify your Tree Inspector, and they will issue your planting permit for that tree.
What characteristics should I look for in a street tree that is adaptable to the changing climate?
Drought tolerant trees are recommended for adaptability to hotter, drier summers and less rainfall, overall, throughout the year. A variety of “climate forward” broadleaf evergreens (such as southern magnolia or live oaks) were included in the updated Approved Street Tree Planting Lists, as they do well in extended droughts but can also manage cooler, wetter winters when they occur.
Look out for specific planting recommendations for trees that are less drought tolerant or may do better in a shady location.
What if I want to plant a tree that is not on the Approved Street Tree Planting List for my site type?
When you get a permit to plant a tree in the City right-of-way, you will be assigned an Urban Forestry Tree Inspector to visit your site and determine where the tree can be planted. The Tree Inspector will also be the one to approve your final species selection. If you want to plant a tree that is not on the approved street tree planting list for your site, talk to your Tree Inspector about alternate options. Tree Inspectors may approve additional species that are appropriate for the space.
How are the Approved Street Tree Planting Lists determined?
Trees are evaluated according to the following criteria:
- tree dimensions and growing habit to ensure that it is the “Right Tree, Right Place”
- site dimensions, soil volume, presence or absence of high voltage power lines
- status on the Portland Plant List (no nuisance trees)
- resistance to pests and disease
- ability to thrive in Portland’s current and future climate
- current canopy diversity to ensure no tree types are overplanted
- good structure for a street tree to avoid conflicts with buildings, sidewalks, roads, cars, bikes, and people
- good strength to survive storms
- potential for wildlife habitat or pollinator attraction
- showy flowers and/or fall color
- minimal fruit or seed drop
- representation of trees native to the Willamette Valley
- local availability at nurseries or growers
Who developed the Approved Street Tree Planting Lists?
This was a collaborative process involving Portland Parks & Recreation, the Urban Forestry Commission, the Bureau of Environmental Services, Friends of Trees, local nurseries, growers, tree care experts, and the public.
When are the Approved Street Tree Planting Lists updated?
The Approved Street Tree Planting Lists are updated approximately every 3-5 years in order to keep up with local availability of trees and new cultivars, emerging pests or pathogens, lessons learned from previously planted trees, and the changing conditions of our city, urban forest and environmental climate.
Why are maples not approved for planting in the City right-of-way?
Maples are currently overrepresented in the City of Portland, making up approximately nearly 27% of Portland’s street tree population, according to Urban Forestry’s 2017 Street Tree Inventory Report. This presents a very risky situation as more than a quarter of our street trees are vulnerable to pests and diseases affecting maples. Decreasing the dependence of Portland’s urban forest on maples and increasing its diversity will help protect the forest from significant future risks.
In order to prevent a catastrophic canopy loss, PP&R Urban Forestry is encouraging planting diverse trees throughout the urban forest, not just in the City rights-of-way. This is an important step toward creating a healthier and more resilient urban forest in the long term.
What are the specific threats to maple trees in Portland?
Of current concern is the threat of Asian longhorned beetle (ALB). Portland is one of three US cities with the highest ALB infestation potential, according to the US Department of Agriculture Animal and Plant Health Inspection Service. ALB has already been found in Oregon but thus far has been contained. ALB attacks all species of maples and several other hardwood genera, killing healthy trees within a short number of years. There is no known cure for ALB, and the only available management remedy is removal of infected and susceptible trees.
Maples are also susceptible to anthracnose, a fungal disease that can cause repeated defoliation and lead to declining tree vitality.
Will maples be allowed for street tree planting in the future?
Maples may be included in the approved street tree planting lists in the future if canopy or inventory studies show that maples are more appropriately represented in the City’s urban forest.
Why are ash trees not currently approved for street tree planting in Portland?
Ash tree populations across the mid-west and eastern US have been devastated by an invasive pest called the Emerald Ash Borer (EAB). EAB is a fast moving pest and can lead to total loss in a short period of time. While EAB has not yet reached the west coast, Portland is taking the proactive measure of protecting our population of urban ash trees, as they make up a significant portion of our urban forest, 4.3% of street trees and 3.1% of park trees.
In order to prevent a catastrophic canopy loss, PP&R Urban Forestry is encouraging planting diverse trees throughout the urban forest, not just in the City rights-of-way. This is an important step toward creating a healthier and more resilient urban forest in the long term. You can do your part to help increase the diversity, interest, and resilience of Portland’s urban forest by picking a less common tree to plant in your planting strip or yard.
Can we expect to see limitations on planting other trees in the future?
The species allowed for planting on City property will change over time due to management needs. The threat of pests may precipitate restrictions on planting certain species in the future. However, the magnitude of the threat also depends on the abundance of the host species. Our urban forest managers will consider the threat of pests and disease and current and future tree species composition when evaluating the need to restrict planting of certain species on City property.