Cooperatove Conservation Project

Fort Hunter Liggett Grasslands Restoration

Controlling a Thorny Problem: The Invasive Yellow Star Thistle

Location: Far West Region: California

Project Summary: A broad-based partnership is working to restore the grasslands and oak savannahs of Fort Hunter Liggett by controlling the invasive yellow star thistle.
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Spraying of Transline, a herbicide at Fort Hunter Liggett in the Long Valley area. (PHOTO BY ART HAZEBROOK)
Resource Challenge

Fort Hunter Liggett in California holds thousands of acres of grassland habitat and oak savannah within its borders, land that supports numerous species of vegetation and wildlife, including the second largest elk herd in the state. From a military perspective, these ecosystems offer quality training in a natural setting, typifying a Mediterranean-type climate. From a natural resources perspective, California’s grasslands and oak savannahs are declining in both amount and quality, threatening the animals and plants that depend upon them. Vernal pools, or seasonal wetlands, occur frequently in these grasslands, providing habitat for many species including the federally listed vernal pool fairy shrimp.

Since the non-native yellow star thistle was introduced to California in the 1800s, it has invaded 25 million acres of grasslands and oak savannah, crowding out native species and hampering soldier training. From the time it was discovered at the Fort, it spread to 20,000 acres in just 5 years. Besides overrunning native vegetation, the plant causes other problems: its thorns are sharp enough to rip clothing, the plant is toxic to horses, and cattle cannot eat the plant because it sticks in their throat. Worse, it’s prolific. Each plant produces about 5,000 seeds which can lay dormant for up to 5 years. 

Examples of Key Partners

Federal Agencies: U.S. Army West Coast Garrison (P), Fort Hunter Liggett Installation, Army Environmental Center; State Agencies: Monterey County Agriculture, San Luis Obispo County Department of Agriculture; non-government organizations: Rocky Mountain Elk Foundation; University of California-Davis, and Dow Agrochemical.

Results and Accomplishments

The Fort joined forces with State agencies and the Rocky Mountain Elk Foundation to control the yellow star thistle infestation.

Since 1999, about 4,800 acres have been treated successfully with a combination of prescribed fire, biological controls, and herbicides. The herbicide, developed by Dow Chemical, kills only the yellow star thistle, which allows safe aerial applications. It is applied for two consecutive years, supplemented by controlled fires to further stamp out the invader. In addition, plant-specific beetles and a fungus are being tested in the hope that they will substitute for the lack of natural enemies.

The Rocky Mountain Elk Foundation has awarded two grants to support yellow star thistle control, matched by funds from the Fort Hunter Liggett hunting program. Besides helping the Army clear Fort Hunter Liggett of yellow star thistle, the partners plan to assist farmers and ranchers in protecting and restoring their lands.


Weed control with a combination of a plant-specific herbicide, prescribed fire, and biological controls.

Project Contact
Joe DiTomaso
University of California, Davis



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