Invasive Species Information

What is an invasive species?

There is more than one definition for “invasive species” as you may have noticed, if you’ve already done any research. In general, an invasive species is a plant introduced to an area from another part of the world (i.e., non-native), spreading aggressively and negatively impacting native species and overall ecosystem function. There are also invasive animal species, but LEAD focuses on plants.

What is a noxious weed?

volunteers on a wooded roadside looking at plants two volunteers pose by a bush of ivy near some trees

Some invasive plants are categorized as “noxious weeds” which means they are aggressive enough to be harmful to environmental or human health or well-being, but they also have the potential to be eradicated or controlled within Washington. They are harmful because they reduce crop yields, destroy native plant and animal habitat, damage outdoor recreational opportunities, clog waterways, lower land values, create erosion problems and fire hazards, and (sometimes) poison humans and livestock. Unlike invasive species, noxious weeds are legally defined in Washington State, with an obligation on the land-owner to control the plant to some degree depending on its classification (A, B, or C). Some invasive plants are not worthwhile to attempt removing (e.g, Hedge Bindweed), so they are not listed as noxious weeds.

Common Invasive Species:

Himalayan Blackberry (Rubus armeniacus, R. procerus, R. discolor):

A blackberry vine with bunches of leaves and thorns

LEAD focuses a lot of effort every year on this difficult plant, especially at the Outback Farm. Himalayan blackberry has 5 leaflets with white undersides, typically growing vertically its first year, then sprawling and producing berries its second year. The plant reproduces by seed (dispersed by birds such as robins and other thrushes), but also sprouts from the roots. This root reproduction strategy is what helps make the plant so successful (and so difficult to permanently remove!), because even when the entire above-ground plant parts are removed from the scene, new suckers can sprout from the roots the following year, and it can be quite a challenge to remove the entire root. To remove Himalayan blackberry, we typically cut off the majority of above-ground shoots (aka “canes”) down to just above where the shoots emerge from the ground. Then with the root more accessible, we dig down about 6-10 inches to expose the swollen root crown containing much of the plant’s stored nutrients, and remove this structure. This sometimes requires severing it from other roots growing out of it that connect to other plants.Another invasive blackberry with similar growing habit and impact, though less locally common, is Evergreen Blackberry (aka “Cut-Leaf Blackberry”). Sometimes you see the Himalayan and Evergreen blackberry species growing alongside each other. When removing these stubborn plants, be sure to look out for our native blackberry species, Trailing Blackberry. This plant is typically smaller than the invasive species, with only 3 leaflets lacking whitish undersides, found growing low along the ground and often creating a carpet of prickles. Don’t remove this one! It is supposed to live here….and its little berries are delicious too!

English Ivy (Hedera helix):

a forest of trees with evergreen ivy growing near their roots a bush of light green ivy leaves, shaped like angled hearts

English ivy is another very common invasive species in the Pacific Northwest, originally introduced from Europe because of the lovely way it adorns buildings. It is an evergreen vine that creeps along the forest floor preventing other plants from accessing sunlight. It also climbs up trees and its weight makes them vulnerable to toppling over, especially in heavy winds. Ivy reproduces both by seed and by sprouting from its stolons (horizontal roots). It can often be removed without the need for tools; pulling out the trailing plants by these roots will often do the job. It is best to prioritize removing any ivy from trees before groundcover ivy, and this can be done by cutting the ivy at hip-height all around the tree to cut if off from its roots (the ivy above the cut will die), and then removing everything rooting in the soil by pulling or digging it out as described above. Pulled plants should be removed from the site because they could otherwise re-root and grow back!

Scotch Broom (Cystisus scoparius):

shrubs with green stems and yellow flowers grouped together close-up of small yellow flowers on a green stem with tiny leaves

Scotch broom is an invasive shrub in the pea family, introduced in the mid-1800s from… (you guessed it!) western Europe. It was actually first introduced to the northwest in nearby Victoria, B.C. as a garden ornamental, admired for its cheerful yellow flowers. Scotch broom especially likes to grow in open sunny areas, such as roadsides and in recently logged areas, establishing itself quickly and outcompeting native plant seedlings. Scotch broom reproduces vigorously via seed dispersal, and these long-lived seeds are often transported unwillingly by shoes, vehicle tires, and animals. It is best to remove the plant outside of its reproductive season to avoid accidentally aiding its reproductive efforts. Broom is another plant that requires complete root removal, otherwise new plants will resprout from the root. The root can be difficult to remove completely, but is done with a shovel or even better with a weed wrench, using this leverage to pull out the entire root structure after trimming off the bulk of the plant for easier root access.

English Holly (Ilex aquifolium):

green leaves with pointed edges surround a grouping of red drupes

Herb Robert (Geranium robertianum):

bush of green leaves with small, pink, five-petalled flowers

Knotweeds (Polygonum sp.):

A bush of large leaves with branched stems covered in ochrea

Hedge Bindweed (aka Morning Glory) (Calystegia sepium):

dark green leaves with a white round flower in the center

Reed Canary-Grass (Phalaris arundinacea):

a field of grass with dark green at its roots, turning brown near the top

Yellow Archangel (Lamiastrum galeobdolon):

a grouping of leaves with a spotted white  pattern shaping the leaf's edge

Other non-natives you may see often but are not as threatening:

  • Creeping buttercup
  • Canada Thistle and Bull Thistle
  • Teasel
  • Tansy ragwort

Recommended Web Resources:

The Washington State Noxious Weed Control Board determines which plants are included on the list. The Whatcom County Noxious Weed Control Board website is another great resource for learning more about common invasive plants in our area. The Pacific Northwest Invasive Plant Council is a non-governmental organization working to educate the public, collaborate to provide solutions, and also provide research and volunteer opportunities for anyone interested. They have an informative website and a nice discussion about our role in managing invasive species in the long-term.

Questions to Contemplate:

  • Why does LEAD remove invasive plants manually instead of using a much easier and quicker chemical herbicide treatment?
  • Why does LEAD remove some plants with desirable qualities, such as Himalayan blackberry with its yummy berries?
  • Why should we even care? Won't evolution just take its course in the long-term and nature will have her way no matter what we do?
  • What would be the consequences if nobody did anything?