Invasive Species

Invasive plants may be the greatest threat to native plant and animal communities. According to Sandy Diedrich of the No Ivy League, we lose 4,600 acres of habitat a day to invasive species. Since they evolved in a different locale, invasive species have limited natural population control mechanisms. They are also well adapted to disturbed environments, which allows them to quickly spread and prevent the successful reproduction of native plant species by competing for water, sunlight, space and nutrients. Since native insects, birds and mammals have evolved to be dependent on native plant food sources, invasive plants also harm wildlife populations. Once established, invasive plant species can be extremely difficult and expensive to control.

You can help by not planting invasive species in your yard and by volunteering with local environmental groups at invasive species removal work parties. Our Natural Area Restoration program offers volunteer opportunities during the summer and fall to remove invasive species and to mulch and water newly planted trees and shrubs.

Below is a partial list of invasive species. You can visit our invasives search page to learn about other invasives.

Reed canary grass

Phalaris arundinacea

Family: Poaceae

This is the most invasive grass species in wetlands of the Pacific Northwest. It is a rhizomatous, mat-forming perennial, which takes over wetland habitats. It is especially fond of wet, disturbed areas. Reed canary grass is a native of Eurasia. It was widely planted in this area between the 1930s and 1980s for erosion control.

Characteristics:

• robust, bamboo-like stems
• blue-green leaves
• inflorescence reddish when young
• reddish rhizomes

Himalayan blackberry

Rubus discolor

Family: Rosaceae

Himalayan blackberry was introduced from Asia by way of England. It prefers disturbed, open, upland sites. It is readily spread by birds and animals, as its fruits are delicious!

Characteristics:

• forms dense, shrubby thickets to two meters in height
• stems four-angled, with thick prickles
• leaves alternate, with five leaflets, white hairs on underside
• flowers white to pink
• fruits deep purple

English ivy

Hedera helix

Family: Apiaceae

English ivy is a familiar vine, often planted in yards. It thrives in the low-light conditions of Pacific Northwest forests, and is especially prevalent near settled areas. This vine often takes over the forest floor and climbs trees. It out-competes and ultimately kills many native plant species by shading them from light. It is not a good food source for wildlife, nor is it an effective erosion controller, as is commonly believed.

Characteristics:

• trailing, climbing vine
• leaves glossy, evergreen
• leaves palmate
• fruits white, round

English holly

Ilex aquifolium

Family: Aquifoliaceae

English holly is an escaped ornamental which often invades upland forests and the edges of wetland areas. Its bright red fruits are dispersed by birds. English holly often grows into a tall, thick-trunked tree. Male and female flowers are borne on separate trees.

Characteristics:

• leaves very stiff with sharp spines along tips and margins
• leaves dark, glossy green, leathery texture
• flowers small, creamy white
• fruits small, round, bright red

Purple loosestrife

Lythrum salicaria

Family: Lythraceae

Purple loosestrife is a perennial shrub that grows in both brackish or fresh wetland areas, preferring to "keep its feet wet" under a couple inches of water. It is a Eurasian native that has spread over much of North America through ornamental plantings. It can take over wetland areas, out-competing native plant species. It spreads easily by seed, cuttings and runners.

Characteristics:

• plant grows up to two meters high
• stems square
• leaves opposite, in threes, lance shaped, pointed, hairy
• flowers magenta, with crinkly petals, bloom August to September
• stamens in three distinct lengths within single flower

Scots broom

Cytisus scoparius

Family: Fabaceae

Scots broom is most often found in disturbed sites, but will invade other open areas. This plant contains a toxin that can adversely affect the heart and nervous system, causing severe reactions in children. When the seeds break apart, the pod halves contort in different directions, producing an audible snap.

Characteristics:

• shrub grows up to three meters tall
• branches five-angled, green
• leaves very small
• flowers bright yellow, similar in shape to a pea flower
• fruits black, flat pods