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The City of Portland, Oregon

Portland Parks & Recreation

Healthy Parks, Healthy Portland

Phone: 503-823-7529

1120 SW Fifth Avenue, Portland, OR 97204

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Invasive Plants

Invasive, non-native plants are one of the biggest threats to our native ecosystems. Because of their aggressive growth and lack of natural enemies in our region, these species can be highly destructive, competitive, or difficult to control. These invaders compete with native plants in many ways: occupying space, changing the structure of the plant community, causing physical and chemical alterations of the soil, and covering and shading native plants. Invasive plants interfere with animal life, too, by altering the structure of their habitat and by eliminating favored food plants through competition. Invasive plants are spread both by human activity and by animals that eat them and carry their seeds.

Here are some of the species that we are battling in the Portland area:

English Ivy (Hedera helix)
This is an aggressive, invasive, introduced species. With nothing to stop its spread, and its ability to grow in almost any situation, this weed covers ground and climbs trees as it transforms natural areas into ivy monocultures, providing no habitat for native wildlife.

Garlic Mustard (Alliaria petiolata)
One of the most invasive forest understory plants in the East and Midwest, this weed is just starting to establish in the area. This non-native biennial can establish in a relatively stable forest understory. It can grow in shade or sun. Plants can produce more than 62,000 seeds per square meter to quickly out-compete local flora.

Giant Hogweed (Heracleum mantegazzianum)
This huge relative of the carrot is not only an invasive weed, but can cause health problems for those unlucky enough to encounter it.

Kudzu (Pueraria lobata)
This vine can grow a foot a day, smothering all other plants in its path.

Purple Loosestrife (Lythrum salicaria)
A pretty flower, but this exotic weed is anything but pretty when it crowds out native aquatic vegetation destroying valuable wildlife habitat. Plant diversity is needed for birds and other animals to thrive, but this weed can take over an entire wetland. Each plant can produce 2.5 million seeds a year.

Old Man's Beard (Clematis vitalba)
A cousin to our garden clematis varieties, but this one is not well behaved. An invasive climber, this plant can grow 30 feet in a season, and is able to smother large trees. Its fluffy seeds spread far and wide.