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Invasive grasses in a wetland area next to the Golden Hoof farm in Boulder on Sept. 30.
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Invasive grasses have changed the landscape of America’s open spaces, out-competing native species in areas across the country.

As a result, according to a new study from The Cooperative Institute for Research in Environmental Sciences at the University of Colorado Boulder, these aggressive plants have increased the likelihood of wildfire by anywhere from 27% to 230%.

“This work shows that invasive species are one of the big three ways that people are changing fire regimes,” said senior author Bethany Bradley, a terrestrial ecologist at the University of Massachusetts Amherst. “Climate change more than doubles the likelihood of fire, human ignitions triple the fire season, and now we can add invasive species fueling fires.”

In Boulder County, the main offender is cheatgrass, which was likely introduced to the area alongside agriculture and ranching, according to the U.S. Forest Service. As those industries dwindled, cheatgrass thrived and created a significant wildfire threat, increasing fire danger by 29%, according to Chelsea Nagy, a terrestrial ecologist at The Cooperative Institute for Research in Environmental Sciences, who co-authored the study.

“Cheatgrass expansion has dramatically changed fire regimes and plant communities over vast areas of western rangelands by creating an environment where fires are easily ignited, spread rapidly, cover large areas, and occur frequently,” the U.S. Forest Service Fire Effects Information System reports.

It also has an effect on the biodiversity of the areas.

“It’s changing the composition of those areas, which causes a whole cascade of problems in terms of wildlife habitat,” Chris Wanner, a forest ecologist for Boulder’s Open Space and Mountain Parks.

In response to the growing threat, Boulder County Parks and Open Space, as well as Boulder Open Space and Mountain Parks, were some of the early adopters of integrated weed management practices, which included prescribed fire, mowing, and grazing, along with the use of herbicides.

While the use of herbicides has become increasingly disparaged by the public in light of several studies reporting significant health and environmental concerns, Therese Glowacki, the resource management manager for Boulder County Parks and Open Space, said those effects can be mitigated with new herbicides and careful application.

On the other hand, she said trying to eliminate cheatgrass, and thereby mitigate fire risk from all 60,000 acres Boulder County Parks and Open Space manages using only natural processes, simply isn’t effective.

Boulder Open Space and Mountain Parks deployed cattle to graze the tall oat-grass infestation that sprung up around Eldorado Springs, but since the cows eat both native and invasive grass species, they are less effective at eradicating an alien species, especially one as pervasive as cheatgrass. The practice of grazing is also far less precise with one cow only able graze up to an acre a month, hindering the ability to attack an invasive species when its germinating.

In an attempt to improve this practice and thereby stave off the use of herbicides, Glowacki remembers a study Boulder County Parks and Open Space partnered with Colorado State University on, in which they attempted to train cattle to only eat noxious weeds. It didn’t work.

Both the city and county also use prescribed fires to fight noxious weeds, but because cheatgrass germinates in the early spring, it’s difficult to start a prescribed burn capable of killing the seeds. If the burn takes place in the late fall, as is normally the case, the cheat grass’s seeds are already on the ground and can survive a fire.

In fact, because cheatgrass germinates before many of the native species, fire actually serves to propagate the plant, allowing it to better ‘cheat’ the native species out of resources and nutrients early on in the growing season.

“Years ago we were trying to use fire to target cheatgrass and the goal was if you could burn the cheatgrass before it had gone to seed, over time you could deplete the seed source,” Glowacki said. “What we found was that we often didn’t have the right weather conditions to be burning at the time.”

In the face of rising temperatures that are already driving up fire risk, herbicides were the last option for eliminating the dense cheatgrass.

In search of the most effective, least toxic herbicide, Boulder County Parks and Open Space initiated a study along with Colorado State University to test a new chemical called Esplanade, which was developed to attack grasses in almond orchards in California.

After one application four years ago, the cheatgrass has yet to return and in its place the native species are flourishing, bringing back many of the pollinators and wildlife as well.

“We saw immediate results,” Glowacki said. “There is no cheatgrass out there, which also gets rid of the thatch that forms when the cheatgrass dies and acts as a fuel. From a fire management perspective, if you can get rid of that thatch, it’s basically substituting for a prescribed burn, allowing the natives to have all of the moisture and nutrients they need.

“So we are having a flush of natives come back once we treat it. And, because cheatgrass seeds are only viable for three or four years we’re hoping we can deplete the seed source of cheatgrass all together.”

While only seven ounces of Esplanade is used per acre of cheatgrass, there is still opposition to its use, including Dr. Mary Mulry with the group, GMO Free Boulder.

However, by incorporating the data within the Cooperative Institute for Research in Environmental Sciences new study, Chelsea Nagy, a terrestrial ecologist at The Cooperative Institute for Research in Environmental Sciences, who co-authored the study, said fire modeling could be improved to pinpoint hazardous areas, allowing land managers to apply the herbicide in only the most critical areas.

“Many different groups are working on fire modeling, but to a large extent they don’t include invasive species,” she said. “If that’s incorporated, we could do a better job predicting where fires occur and if you know of a high invaded area you can specially target it.”

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