UM Research Studies Relationship Between Sheep-Grazing, Native Plant Recovery

February 07, 2018

The City of Missoula uses sheep to help restore grasslands.MISSOULA – New research by University of Montana alumna Eva Masin and restoration ecology Professor Cara Nelson is examining the effectiveness of using domestic sheep to control nonnative invasive plants.

Masin, who holds a master’s degree in resource conservation, and Nelson investigated how managing weeds through sheep-grazing affects native plant recovery in one of the first studies on sheep and native plants in North America.

“Restoring native plant cover is often the underlying objective behind removal of nonnative invasive plants, not simply controlling the weeds,” Nelson said. “This study helps managers make decisions about when and how to use sheep-grazing as a restoration tool.”

The City of Missoula uses sheep as part of its arsenal of tools to combat invasive plants on the city’s conservation properties. Masin, Nelson and coauthor Morgan Valliant, conservation lands manager for the City of Missoula, set up research plots on the grassland hills above Missoula before setting 400 sheep and five goats free to roam and forage.

The team found that although the sheep grazed on a higher percentage of nonnative than native forbs – plants other than grasses – they did eat natives, and their consumption of natives increased with the decreasing availability of the targeted nonnative plants.

“We found that sheep will eat a larger variety of nonnatives than previously thought, including another problem – invasive sulphur cinquefoil,” Masin said. “But the timing and duration of grazing are very important.”

Active monitoring is required throughout the grazing period to ensure that animals are moved once target weed-removal levels are reached, but before damage occurs to native plants.

Although the City of Missoula has used sheep on the hillsides around the Missoula Valley for more than a decade, not much is known about incorporating sheep-grazing into a restoration program.

“There’s been a fair amount of research on how sheep-grazing can control a handful of problematic invasive weeds, but reducing weeds is often the easiest part of a project like this,” Valliant said.

Valliant said previously most information on using sheep to help restore native plants came from research conducted on city open space lands.

“Eva’s research, and our partnership with the University of Montana, has certainly helped us better understand the non-target effects of this form of weed control,” Valliant said.

The study will be published in the journal Range Ecology and Management in March 2018 and is available online via Science Direct at

For more information on the research, call Masin, library specialist at the U.S. Forest Service Rocky Mountain Research Station Fire Sciences Lab, at 406-329-4820 or email or call Valliant at 406-552-6263 or email


Contact: Cara Nelson, UM associate professor of restoration ecology, 406-243-6066,