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UMass study: Invasive grasses are contributing to wildfires across US

A firefighter dragged a hose closer to battle a grass fire on East Cypress Road in Knightsen, Calif. UMass researchers say invasive grasses may be promoting wildfires across the United States.Carlos Fajardo/San Jose Mercury News/San Jose Mercury News via AP

A new study from University of Massachusetts says invasive grasses may be contributing to wildfires across the United States.

And one of the researchers involved says it’s likely they are playing a role, too, in the blazes currently raging across the California landscape.

“It wouldn’t suprise me,” said Bethany Bradley, an associate professor at UMass who is the senior author of a paper published Monday in the journal PNAS.

She said researchers didn’t know exactly which grasses were involved in the affected parts of California, but said, “We know, for a couple of fires, the grass has been implicated.”


The team, which included members from the University of Colorado-Boulder, looked at 12 invasive grasses and their impact on fires in 29 US ecoregions encompassing more than a third of the area of the continental US.

The researchers combined information on wildfires from satellites and government fire records with information on “abundant grass invasion to test for differences in fire regimes between invaded and nearby ‘uninvaded’ habitat,” the study said.

Researcher Emily Fusco examining a burned hillside of buffelgrass in Arizona.UMass Amherst/Bradley Lab

Eight species were associated with significantly higher rates of fire occurrence, with two species associated with more than a tripling of the rate. Six of the eight species were associated with significantly higher fire frequency, with two species more than doubling the rate, researchers said.

The researchers conducting the “pyrogeographic” study said one of the grasses, cheatgrass, was long known as a fire promoter, but their study found that at least seven other invasive grasses were increasing wildfire risk. Most of the previous work on the subject has also been done on a smaller scale, the researchers said.

The suspects include cogon grass in the Southeastern pine forests, buffelgrass in the desert Southwest, and Japanese stiltgrass in Eastern temperate forests, researchers said. “These regions are all ecologically distinct, and these grasses seem to be impacting fire in all of them,” post-doctoral researcher and lead author Emily Fusco said in a statement.


The study found that “the significant differences in fire regimes, coupled with the importance of grass invasion in modeling these differences, suggest that invasive grasses alter US fire regimes at regional scales. As concern about US wildfires grows, accounting for fire-promoting invasive grasses will be imperative for effectively managing ecosystems.”

“Managing existing grass invasions and preventing future introductions presents a key opportunity to remediate the ecological and economic consequences of invasive species and fire,” the study said.

Carla D’Antonio, an environmental studies professor at the University of California Santa Barbara whose research interests include invasive grasses and their impact on the grass fire cycle, said the study was important “because it helps to document what we have suspected for a few decades — that invasive grasses are playing a role in changing the fire cycle across a variety of environments.”

“This paper capitalizes on big data, breakthroughs in accessing and analyzing data across big areas, and includes a big geographical area. The latter is important in showing this is not a problem isolated to the West or Hawaii,” two areas that have been previously studied, she said.

D’Antonio also said it was possible invasive grasses are playing a role in the ignition and spread of the wildfires currently plaguing California.

The grasses tend to be abundant along roadways and power line right-of-ways, which are both places were fires commonly start, she said. The grasses can also be found near homeless encampments, where the fires occasionally start, she said in an e-mail.


Once a fire starts, embers can travel a great distance. If they land in dry grass, they can almost immediately ignite and accelerate the spread of the fire, she said. Some of the areas in California that have burned have seen multiple fires in recent decades “and thus have partially converted to invasive grass dominance. Once invasive grasses dominate, the likelihood of future fire in these high wind corridors is much increased.”

Bradley said in the statement that invasive grasses add to the other ways in which humans are responsible for wildfires. “Climate change more than doubles the likelihood of fire, human ignitions triple the fire season and now we can add invasive species fueling fires,” she said.

“Although climate change has received considerable attention as a factor in altered fire regimes, invasive grasses are similarly important,” the study said.

Fusco said one of the things the study highlighted was that “in the places affected, fire management and invasive species management need to be done together, and where these managers are distinct groups, they would benefit from closer collaboration. And, looking at future fire risk modeling, we should definitely be including invasive grasses, and their likely spread, in the mix.”

Bradley noted in a telephone interview that one of the species, Japanese stiltgrass, could be headed our way from the mid-Atlantic. She said it is “just emerging in Massachusetts.”