Canada Thistle, USDA/NRCS photoLake Trout, NPS photo, L.P. ParrattYellow Toadflax, NPS photo

Invasive species are those that are not native to a particular ecosystem and cause, or are likely to cause, harm to the health of the environment, humans, animals, or plants. Invasive species may compete with native species for food and habitat. This interferes with the growth, development, reproduction, and survival of native species.

Managers at Grant-Kohrs Ranch are managing invasive weeds such as spotted knapweed and leafy spurge as they try to sustain healthy plant communities representative of dry upland pasture and irrigated hayfields. In Glacier National Park, at least 127 non-native species of plants have been documented. Of the 765 acres at the Little Bighorn Battlefield National Monument approximately 445 acres have been encroached on by invasive plants.

The aquatic systems of the Crown of the Continent have been affected by invasive species as well. Introduced lake trout west of the divide compete with native bull trout for food resources. Non-native rainbow trout hybridize with native westslope cutthroat trout, causing adverse effects to their gene pool and reproductive success.

Resource managers keep a vigilant eye out for invasive species through ongoing monitoring and management on all park properties.