It’s Invasive Species Awareness Week! 

February 24, 2025 – Yosemite National Park officials announce that it’s Invasive Species Awareness Week!

Invasive species are species that have the ability to negatively affect ecosystems. At Yosemite, yellow star-thistle (Centaurea solstitialis) is one of the park’s peskiest invasive plants. Already widespread throughout California, this weed has become well-established in the Sierra Nevada foothills and is slowly trying to spread eastward into the park. 

Wherever yellow star-thistle grows, it takes over the area and pushes other vegetation out. One single plant can disperse up to 150,000 seeds in a single season. Lightweight seeds carried on the wind get stuck to clothing, shoes, vehicle tires, and animal fur like horses and dogs. Those seeds then get dropped on the sides of roads or in the park, taking root easily and refusing to leave once grown.

In 2023, invasive plant crews treated many previously known yellow star-thistle infestations in Yosemite National Park and El Portal Administrative Site. After several years, yellow star-thistle density has undergone drastic reductions. And you can help, too! Check your boots, clothing, and pets for hitchhiking seeds, or volunteer to help with invasive plant removal in the summer.

Yellow star-thistle isn’t the only invasive plant in Yosemite. Vegetation crews and volunteer groups work hard throughout the year to remove plants like the Himalayan blackberry, common velvet grass, Italian thistle, spotted knapweed, and more. To learn more about invasive plants in the park, visit: https://www.nps.gov/yose/learn/nature/invasive-plants.htm.

Source & photos: NPS