It's been a while since we posted an invasive plant profile. This one is about an invasive tree with some interesting characteristics. We hope you'll help get it under control in Portland.
Sometimes referred to as ‘The Widowmaker’ and other more colorful language, tree-of-heaven (Ailanthus altissima) has made a good living filling in bad habitat like sidewalks and freeway sound walls, as well as yards, parks and other spots around the city. It’s well-known for using invasive roots and huge amounts of winged seed to clear a space for itself.
In addition to these physical strategies, tree-of-heaven uses chemicals in its roots to kill off or limit the growth of neighboring plants. For all of these reasons, tree-of-heaven threatens a wide range of native plants and trees and reduces diversity in our urban forest. This rolls back the investment Portlanders have made in the healthy parks and natural areas that keep our water and air clean.
On top of its environmental impact, tree-of-heaven is hard on our homes and neighborhoods. The leaves of male trees smell terrible, like rancid peanuts or well-used gym socks. Because tree-of-heaven grows so fast, its wood is very brittle, leading to substantial branch drop. It doesn’t even take high winds for large limbs to fall on your car or roof (or head). Fast-growing trees can also become expensive to remove, so acting sooner, rather than later, is often the better choice.
Tree-of-heaven is a Class B invasive species in Portland (see the Portland Plant List). Fully-grown tree-of-heaven can be up to 60-70 feet tall. Trees flower in June or July, and form dense clusters of winged seeds by July or August. Leaves have 11 or more pointed leaflets, which are easily confused with those of black walnut leaves. Other tree-of-heaven look-alikes, such as ash and black locust, have rounded leaflets.
What can you do? Remove tree-of-heaven sprouts as soon as they emerge during the summer, though you may find that the “seedlings” are actually growing from the ends of the tree’s roots! This ability to sprout from roots makes tree-of-heaven hard to manage and difficult to remove, typically requiring an herbicide. But, if you keep at it, frequent repeated cuttings of sprouts and seedlings may exhaust the plant’s reserves and limit the re-growth.
If the trunk is 12” or more across, or growing along the street, removal may require a permit. As a general rule, Portland Parks Urban Forestry regulates all street tree (as well as large tree) activities including permitting for planting, pruning, and removal. To obtain a permit, or for more information, please call 503-823-4489 or visit www.portlandoregon.gov/parks/trees.
Property owners are welcome to contact Mitch Bixby at Environmental Services with non-permit questions.
Invasive species affect us all. They damage our forests, our streams and rivers, and our property. Nationwide, damages associated with invasive species are estimated to be $120 billion each year. In Oregon, the control of invasive weeds and the cost of the damages they create amounts to about $125 million each year. We know that it costs a lot less to control new invasive plants before they become infestations, but we need everyone’s help. Read more here about the problems caused by invasive species and why BES is particularly concerned about their impact on water quality.
Catch up on previous Alien Plant Invader posts: