Science Center Objects

Invasive annual grasses, such as cheatgrass (Bromus tectorum) and medusahead (Taeniatherum caput-medusae), are one of the most significant stressors to rangeland ecosystems in the western U.S. Their expansion and dominance across this area are the most damaging ecosystem agents on this iconic landscape.

Many invasive plants thrive in disturbed areas and are easily spread through various pathways and vectors. In the western U.S., disturbed landscape can take the form of areas changed by human development, improper grazing, and burned by wildfire. Roads and trails, and the vehicles that travel them, transmission corridors, and fuel breaks all serve as pathways and vectors that help spread these unwanted invaders. Once an invasive plant becomes established in an area, it can quickly spread across the landscape. Invasive plant species can become ecologically dominant, creating near-monocultures that result in reduced wildlife habitat, recreational opportunities, livestock forage, and altered fire regimes. Even after landscape disturbances are removed from areas dominated by these plants, these invasive annual grasses can remain the dominant plant.

grass seed head

Cheatgrass (Bromus tectorum) is the dominant exotic annual grass species on semi-arid rangelands of the western hemisphere. Photo by Justin L. Welty, USGS

Cheatgrass originated in Europe or Eurasia and medusahead in the Mediterranean region. Both were introduced to the U.S. in the mid- to late-1800's as a contaminant in seed and straw. Both species germinate in the fall and early spring, grow rapidly and in high numbers making them highly competitive with native species.

Plants native to the sagebrush landscape may not recover from disturbances that allow invasive annual grasses to over-run them, even decades later. In these areas, elimination of invasive annual grasses is very difficult because the limited number of remaining native plants are unable to produce seeds and seedlings that can compete with these invasive annual grasses. In addition, the thick thatch produced by annual grasses kills biological soil crusts (lichens, mosses and cyanobacteria) that once filled the soil interspaces between the native grasses and shrubs.

The conversion of a diverse native ecosystem to simple invasive grass-dominated ecosystems degrades the ecosystem processes leading to soil erosion, less water in the soil for plant growth, and changes in nutrient cycling, making a less productive land that is much harder to restore to what it was before the invasion.

Land managers are tasked with controlling cheatgrass and medusahead, but resources are limited for invasive plant management. They face difficult decisions on how to use their limited resources. Do they target high-risk pathways and vectors of invasion for efficiency, focus on specific invasive plant patches that are feasible to control, or treat the periphery of a large invasion to slow and contain the spread? Innovative approaches that capitalize on the targeted ecosystem’s resilience to disturbance and resistance to invasive plant invasion is needed to achieve long-term ecosystem conservation and restoration goals for invasive plant-dominated landscapes.

Researchers at the USGS have and continue to develop a wide variety of tools and systems, and answer questions, that help tribal, federal, state, industry, and private land managers design and implement sustainable rangeland practices along with effective restoration and rehabilitation projects. Studies focus on finding ways to control cheatgrass and medusahead through use of herbicides, soil bacteria, and targeted grazing. On-going research also answers questions about the resistance of an ecosystem to an invasive plant, including the suitability of the ecosystem’s climate and soils for establishment and persistence of the invasive plant, and the capacity of the native plant community to prevent increases in the invasive plant’s population through factors such as competition, herbivory, and ability of native plants, including biological soil crusts, to adapt to environmental conditions. They develop solutions to help land managers bolster or support the ecosystem's resilience, or ability to bounce back from a disturbance.

grass seed head

Medusahead (Taeniatherum caput-medusae) seed heads have long barbed “hairs” called awns that can cause injury to grazing animals. Photo by Justin L. Welty, USGS

Notable contributions include:

Exotic Brome-Grasses in the Western U.S. Edited and contributed to the authoritative source of information on exotic annual Bromus in arid and semi-arid ecosystems of the western U.S.

Indicators of Rangeland Health. Development of the best, most consistent, and comparable method to determine rangeland health. This method is widely used by multiple land management agencies and highly
valued by ranchers.

Right Seed at the Right Place and Time. Tests of seed sources used in BLM restoration efforts changed seed transfer guidelines and enhanced seeding success. Our data helps the BLM, the largest purchaser of
wildland seed globally, buy the right kind and amount of seed.

Conservation Efforts Database. Constructed a data system that helped the USFWS determine if stakeholder conservation efforts were enough to avoid an Endangered Species Act listing of the Greater sage-grouse. 

Restoration of biological soil crusts. Tests of species for restoration, impacts of grazing and fire are of interest to BLM, USFWS, and USFS managers to enhance restoration successes.


Browse the Publications and Data and Tools tabs to find USGS publications related to invasive annual grasses.

Check out the News tab for plain language descriptions of USGS studies and publications.

Click the Multimedia tab for pictures and maps.