DYK? Trees are also stormwater filters!

street trees are proven stormwater filters
Street trees are proven stormwater filters


Why all the fuss about managing stormwater? Simply put, stormwater pollutes waterways.

Stormwater runoff carries dirt, oil and other pollutants to rivers and streams. It can also cause erosion and flooding that harm properties and wildlife habitat.1

“Portland’s trees are also playing an underappreciated role every time it rains: They’re helping us prevent major flooding and avoid erosion; they are literally holding Multnomah County together.” 4

Traditionally, and still common throughout the country, stormwater is primarily managed through “grey” solutions such as massive construction and excavation projects that install giant pipes to divert the wastewater. Thinking green, Portland conducted a study and found there could be significant savings in the cost of the Big Pipe project by including green infrastructure along with wider sewer pipes.2 Other cities are catching on; Friends of Trees regularly receives inquiries from other cities (a recent call came from Louisville, KY) looking for more information about this partnership and its benefits.

Per an agreement between Portland Parks and Recreation and BES, “Portland’s Bureau of Environmental Services recognizes that, among the numerous environmental, economic, and social benefits trees provide, they can work for clean rivers by helping to manage stormwater where it falls. Planting trees can expand and enhance the urban forest canopy and help the city meet key goals of several plans,” including the City’s Climate Action Plan and Watershed Management Plan.3

In other words, BES recognizes the multiple bottom line trees deliver, and how essential trees are to a healthy, equitable and livable city. For more information about trees and stormwater management (and to check out a very cool interactive model that demonstrates trees’ impact), visit our friends at the Arbor Day Foundation. And when you can safely swim in a river or eat fish from a lake this summer be sure to thank the trees.

Read more about trees + stormwater.

  1. BES
  2. City of PortlandECONorthwest, et al reportNRDC report
  3. Portland Parks and BES agreement
  4. Multnomah County Trees Are Doing Much More Than We Think, OPB, 2019

Trees: Fighting climate change, growing community AND managing stormwater


In 2008, Friends of Trees and the City of Portland Bureau of Environmental Services embarked together on a transformative journey to boost green infrastructure in Portland. This initiative built on the Big Pipe project and used green infrastructure to reduce environmental impacts of urban stormwater. Along with creating bioswales, installing green roofs and adding new natural areas, this project mandated the planting of tens of thousands of trees in Portland.

This partnership resulted in 38,000+ street trees planted in Portland from 2008 – 2021, and these street trees intercept 9.6 million gallons of rain each year.1 The trees planted through this partnership represent just a portion of all street and yard trees planted by Friends of Trees since 1989, which is more than 50,000 across the region.

Why all the fuss about stormwater? Learn more here.

This project didn’t just plant small trees and hope for the best. Then-Mayor Sam Adams prioritized planting and caring for large stock trees. Planting larger trees means, of course, that all of the benefits are realized much sooner than if smaller trees were planted.

Caring for the trees is equally important: Friends of Trees’ program includes post-planting support and care, which helps ensure that the trees we plant survive and thrive. Our monitoring program builds on that, telling us how many of the trees we plant survive—and our trees have an excellent survival rate: The survival rate for urban trees planted by Friends of Trees is 97% (based on Portland street trees planted during our last two seasons).

It’s not just stormwater. These trees deliver a triple bottom line, beyond stormwater management:

1. Most of the trees planted through this partnership are planted in historically under-served, low-canopy neighborhoods, bringing the countless benefits of trees to the neighborhoods that need them most.

2. The trees planted are now on the front lines of fighting climate change; each tree we plant will offset 13-48 lbs. of carbon annually.2

3. When planted the Friends of Trees way, with thousands of volunteers, trees grow community. And now more than ever, we need ways to come together as a community, and we need trees.

We’re not done! About 100,000 street tree planting locations remain available in Portland, not to mention throughout our service area that runs from Southwest Washington down to Lane County. We plant a lot of trees every year: Just last season we planted 3,500 street & yard trees and 46,000 seedlings and native shrubs. We know our region and our planet needs more trees and more community-building, and we look forward to enhancing and expanding the wide variety of partnerships we enjoy toward planting a greener and healthier future.

  1. Data provided by City of Portland Bureau of Environmental Services
  2. Depending on the age of the tree.

Some of this content is from a video about the project, check it out here.