Guide to Invasive Trees in the City of Vancouver
Some species of trees may thrive in locations which conflict with city infrastructure or private property. Learn how to identify common invasive trees and effective strategies for management. This page will highlight some common invasive trees, control and removal methods, and replanting options.
Common Invasive Trees
Tree of Heaven
Tree of Heaven is a fast-growing tree reaching over 80 feet tall, and is a prolific seeder that can quickly take over sites. Its root system is extensive and new sprouts have been known to cause damage to sewers and foundations. Because it is weak-wooded, it frequently suffers storm damage. Tree of Heaven has a tropical appearance. The large leaves are 1-4 feet in length, and when crushed may smell like “burnt peanut butter”. The tree’s bark is smooth and gray. Seeds appear in large clusters.
Black locust is a fast growing tree reaching 100 feet in height. It is quickly re-sprouts through vigorous root suckers. Black locust leaves are pinnately compound, often identified by the multiple leaflets sharing a single stalk, with an odd number of leaflets, highlighted by one leaflet at the tip. A pair of short, sharp spines occur where the leaf is attached to a zig-zag stem. The white flowers each have a yellow blotch on the uppermost petal, and occur in clusters that appear in May or June and develop into seed pods up to 4 inches long.
Treatment and Control
Cutting, Digging, and Chemicals
Elimination of invasive trees requires hard work, due to their abundant seed production, extensive root systems, or prolific vegetative reproduction. Removed trees should be monitored and any new suckers or seedlings treated as soon as possible. In addition to removal, establishing new quality replacement trees will help shade out and discourage establishment of invasive trees.
Cutting alone is usually counter-productive because these trees respond by producing large numbers of sprouts and root suckers.
Digging up young seedlings may be effective. Take care to remove the entire plant including all roots and fragments, as these will likely be able to re-grow.
Chemicals and herbicides are the most effective method to eliminate invasive trees. Chemicals can be applied to the leaves, although it’s not as effective as applying directly to the stump. For direct stump application, apply immediately after cutting with a brush, sponge, or dropper. Alternate stump application includes drilling several holes in the stump and applying chemical into the holes. Timing is important; Fall is usually the best time of year to apply chemicals. While it is easier to destroy the above ground portion of Tree of Heaven the root system must be killed to to prevent the stump from sprouting and root suckering. Always use caution when applying chemicals, and follow product directions.
Management and Permits
It is important to consider that not all invasive trees cause problems. There is a right place for every tree, and they may not cause problems if they are properly maintained and cared for.
If you do wish to remove a tree, it is important to determine if a permit is required. Permits are always required for street tree work, and may be required for private properties as well. Not sure if you need a permit? Email Urban Forestry with your property address and photos or call 360-487-8308. Many tree removal permits require a tree replacement plan.
Think of your trees as a lifetime investment. How well your tree, and investment, grows depends on the type of tree you select, the location you plant your tree in, the care you provide when the tree is planted, and follow-up care the tree receives into the future.
There are many options for purchasing a new, quality tree:
Friends of Trees: Non-profit tree planting program Friends of Trees aims to build community through volunteer tree planting events. Work with staff to choose a high quality tree for your location. Tree costs range from $35 to $50, depending on your neighborhood and grant funds, and is planted by volunteers during a community event. Visit the Friends of Trees website for more information.
TreeFund: Vancouver’s tree refund program is an easy way to plant a new tree and get a refund on the tree costs. For details, visit the TreeFund page.
In the Pacific Northwest, the ideal time to plant is during the fall and winter, when the trees are dormant. The Arbor Day Foundation has tips and resources on proper tree planting.
Right Tree, Right Place
Vancouver Urban Forestry develops guidelines for planting quality trees in appropriate locations to maximize the benefits of our trees and to protect public and private infrastructure. Unfortunately, nuisance trees such as Tree of Heaven or Black locust seed themselves and thrive without care. These fast-growing invasive trees can grow and thrive in tight locations and may quickly damage existing structures.
Information provided here is starting point, and is not intended as instructional material for invasive tree removal.