Invasive Species in the Pacific Northwest

Invasive Species Impact Cultural Resources

Organisms moved and introduced to new areas around the globe can become invasive. Once established, these organisms negatively impact our natural and cultural resources if left uncontrolled.

Native species in Washington state are threatened by invasive plants, animals, insects, and pathogens. Invasive species threaten Washington’s biodiversity and can negatively impact the environment, economy, and ecosystem health. Invasives can be easily spread by wind, water, animals, and humans which assist them through equipment, trade, and travel.

Invasive species

  • Outcompete with native species for resources and can result in native species decline and further impact threatened or endangered species.
  • Decrease biodiversity
  • Degrade natural habitats by changing the habitat or reducing the presence of native species.
  • Destabilize soil and alter hydrology
  • Hinder recreation activities such as boating, fishing, hunting, and hiking.
  • Increase the frequency and intensity of wildfire. Some invasive plants can burn more quickly and readily spread fires faster.
  • Interfere with industries like agriculture, timber, seafood, and aquaculture operations.
  • Costs Americans billions of dollars yearly to control and more money is lost from reduced agricultural productivity, public utility operations, native fisheries, and tourism.
  • Increase the frequency of livestock poisoning. Toxic and noxious weeds can be highly aggressive and take over pasture areas where livestock feed.
  • Loss of culturally and socially significant organisms

Below is a list of critical ecosystems with examples of invasive species affecting Tribal lands in Washington.

Invaded wetland
Reed Canary Grass
Reed canary grass is an invasive noxious weed found in wetlands, ditches, pastures, and on shorelines across Washington State. It can clog up streams and ditches, which increases flooding and blocks passage for salmon and other fish. Control is recommended, especially in areas where wetlands are being restored.
Scotch Broom
Scotch Broom
Scotch broom is a bushy shrub that can grow up to six feet tall. It is invasive to hillsides, pasture, forest clearings, and dry waterways in Idaho, Montana, Utah, and much of the east and west coasts of the North America. While thriving in sandy sunlit areas, it does not tend to survive well in barren or cold areas. The presence of Scotch Broom affects wildlife habitat and out-competes native vegetation in the area.
Tansy Ragwort
Tansy Ragwort
Tansy ragwort is an invasive noxious weed and a threat to livestock and agriculture because all plant parts are toxic. It is most often found in disturbed areas and can invade any soil type across the Pacific Northwest. While commonly avoided by animals, it may go undetected when mixed with hay, affecting the health of livestock and other grazing animals.

Pressing Issues in the Pacific Northwest

Forest Ecosystems

The introduction of invasive species into native forest ecosystems creates challenges for forest communities. As non-natives are introduced, the structure and composition of native plant communities are altered. The loss of an organism or the loss of its ability to function ecologically correct can change the forest landscape and how organisms interact.

English ivy growing on trees

English Ivy (Hedera helix) over growing trees

English Ivy is aggressive and is a threat to forest ecosystems. Vines are capable of climbing up trees, as shown above, and can decline the health of the tree by enveloping the trunk and branches, blocking photosynthesis, and create a hazard tree in storms due to the weight of the ivy. Ivy can outcompete understory plants and block new plants from establishing due to its aggressive nature.

Invasive organisms’ impact on forest ecosystems include:

  • Loss of tree canopy
  • Weakened ecological integrity
  • Destruction of wildlife habitat
  • Reduced ecological services
  • Decreased ecological health
  • Reduced wood supply and wood quality
  • Threaten urban forests

Aquatic Ecosystems

Aquatic invasive species can be found in streams, wetlands, rivers, bays, and the coast and can exist at a variety of depths. Human travel has dispersed species much further than their native range, or how far they can travel which has resulted in the introduction of many aquatic invasive species. Once established, invasive species are nearly impossible to eradicate, and they can threaten the waterway and the communities existing within them.

invasive aquatic plant species

Aquatic Ecosystems

Invasive organisms’ impact on aquatic environments include:

  • Reduced fisheries production
  • Decreased water availability
  • Block transportation
  • Choke irrigation canals
  • Degrade water quality
  • Obstructing water supply pipelines

Rangeland Ecosystems

Rangelands can become overgrown with toxic and noxious weeds that can cause serious harm or even death to grazing animals. Many non-natives that are toxic to livestock are highly aggressive and can spread and reproduce quickly to take over pastures and rangelands.

Tansy ragwort blooming

Tansy Ragwort (Jacobaea vulgaris)

This invasive is a class B noxious weed, an invasive with mandatory control, and is known to cause losses for pasture grazing animals. The entire plant whether it is alive or dried is toxic to equines, cattle, sheep, goats, alpaca, and llama and can cause poisoning that may lead to conditions that are irreversible or death.
Image from Washington State Noxious Weed Control Board

Invasives organisms’ impact on rangelands include:

  • Declined pasture conditions
  • Degraded water
  • Negative economic impact
  • Grazing animals may ingest toxic plants which can result in:
    • Death
    • Reduced productivity
    • Deformed newborns
    • Loss of dairy or milk quality

Additional WSU Resources:


WSU Extension Forestry – Invasive Forest Weeds Resources

Aquatic Ecosystems

WSU Extension Aquatic Invasive and Noxious Plants


WSU Veterinary Microbiology and Pathology Research – Elk Hoof Disease

Prairies and range lands

WSU Weeders of the West Blog


WSU Biological Control (Biocontrol)