Invasive Plant Species

Spotted knapweed in a road ditch
Spotted knapweed (Centaurea stoebe L. subsp. micranthos)

NPS Photo

One of the biggest threats to national parks and other natural areas is the invasion of non-native plant species, also known as invasives and exotics. Exotic invasive plants cover approximately 1.4 million acres of NPS lands and waters. Responding quickly to new invasions and controlling existing infestations of invasive plants are important functions of Crater Lake National Park’s Invasive Vegetation Management (IVM) program.

Before needing a rapid response or effective control measures the first goal of IVM is to prevent the introduction of non-native species. This protects and maintains the integrity of the park’s diverse native flora.

While Crater Lake National Park is threatened by invasive plants, there are areas in the park that are still composed entirely of native plant species. The park’s high elevation and copious snowfall assist in minimizing human and natural disturbances that may introduce invasive plants with negative long-term impacts.
A combined photo of bull and Canada thistles which are invasive plants in the park.
Both the bull thistle (Cirsium vulgare) and the Canada thistle (Cirsium arvense (L.)) are invading areas of the park.

NPS Photo

A Few Invasives

Dyer’s woad was first cultivated for its dye. It became invasive when introduced to western states as a contaminant in alfalfa seed.
Canada thistle accidentally arrived through farm seed shipments as early as 1600. It crowds out native species reducing the yield of native plants.
Spotted knapweed was accidentally introduced into North America in contaminated alfalfa and clover seed in the late 1800s.
St. John's wort was Introduced as an ornamental and as a medicinal herb. It is toxic to cattle.
Bull thistle can form dense thickets, displacing native vegetation. Introduced around late 1800's and is now found in all 50 states.
St. Johns wort and dyer's woad are invasive plant species that grow in the park.
St. Johns wort (Hypericum perforatum L.) and dyer's woad (Isatis tinctoria L.) are two invasive species found growing in the park.

NPS Photo

Invasive species do not arrive with natural controls that keep their population in check. Invaders crowd out native species and reduce their habitats. This has cascading negative impacts on pollinators and wildlife that depend on native plants for food and shelter.

The seeds of invasive plant species can “hitchhike” on your boots, clothing, gear, and even your pets! Help protect the Park’s native ecosystems by brushing seeds and soil off your footwear and equipment before leaving home.

Boot brush stations are located at Cleetwood Cove, Garfield Peak, and at the south Pacific Crest Trail trailheads, giving trail-goers one last chance to brush any seeds or soil off of boots that may harbor invasive species.

Last updated: March 25, 2019

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Crater Lake National Park
PO Box 7

Crater Lake, OR 97604


541 594-3000

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