Invasive Species

Native Species vs. Invasive Species

Scotch Broom

Native or indigenous plants or animals are ones that were present in the Pacific Northwest historically prior to European-American settlement. Non-native (exotic, alien or introduced) plants or animals, on the other hand, are ones that were brought to the Pacific Northwest by humans, either deliberately or by accident.

Invasive species are ones that are non-native and which thrive and spread aggressively outside their natural range. Some invasive species can become serious problems that threaten water quality, drive away native wildlife, crowd out native plants and create fire hazards.

Oregon Public Broadcasting has an excellent program The Silent Invasion giving some history and explanation of the problem with invasive species.

Identification of Invasive Species

The first step in detecting invasive species is knowing what to look for. Start with the natural environment you know best – your own property. Familiarize yourself with the native species that should be there as well as the plants on the “watch list” of invasive species that are threatening to invade (or have already invaded) the Pacific Northwest. There are many helpful guides, both in print and online.

The Oregon State Noxious Weed List lists all the plants classed as noxious weeds (slightly different than invasive species, but still ones to look out for) with links to pictures and descriptions of each one. King County (Washington) also has an excellent source to identify invasive species with their weed photo index.

To learn about the native species that are likely to be on your property, check the King Country Native Plant Guide. You can search through pictures or a list of species, and even create your own custom native plant list for reference. There are also many books available on Pacific Northwest native plants.

Removal of Invasive Species

If you are trying to get rid of existing invasive species, you have several options depending on what type of plant(s) you have and your philosophy on dealing with them.

Smaller plants can be “weeded” by manually pulling them out of the ground; larger plants and trees can also be manually removed with the right tools. It takes hard work, a good pair of gloves and persistence, but it will work. Do not put invasive species in your compost pile; composting will not kill the seeds of all invasive species.  In fact, you might be giving them very fertile ground, enabling them to sprout and grow! The 4-part series on Physical Methods to Manage Invasive Plants by the National Wildlife Refuge System for some directions.

Using chemical herbicides to kill invasive species is another option. Herbicide Advice for Homeowners has general information about different methods for using herbicides and general removal tips. For the complete guide, see the Pacific Northwest Weed Management Handbook, available in print or online.

For seed-bearing annuals, you can slow or stop the invasion by deadheading flowers before they have a chance to produce seeds for the next crop of plants.

Burning and biological controls (such as the cinnabar moth to control tansy) are other options.

Repopulating with Native Plants

Native Douglas Fir

As your invasive species are removed, you can find native replacements at native plant nurseries. The Invasive Species: What Gardeners Need to Know brochure is an excellent resource for selecting non-invasive plants as replacements.

As your native plant population grows and any invasive plant species are controlled, the population of native wildlife is likely to increase as they will have the natural habitat they need.

Additional Resources for Identifying and Removing Invasive Species


Special thanks to Oregon Department of Fish and Wildlife & OSWA Member Kristin Ramstead for images used on this page.

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