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Cheatgrass implicated in Great Basin fire regime

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Satellite images help pinpoint land-cover and fire patterns

By Summit Voice

FRISCO — Along with global warming, new research suggests that invasive cheatgrass is a significant factor in the proliferation of more intense fires in the intermountain West, and specifically in the Great Basin.

“Although this result has been suspected by managers for decades, this study is the first to document recent cheatgrass-driven fire regimes at a regional scale, the scientists wrote, describing the study that relied partly on satellite images captured between 2000 and 2009 to create a detailed land-cover map of the Great Basin.

The study was led by Penn State University fire expert Jennifer Balch. Bethany Bradley, a biogeographer at the University of Massachusetts Amherst, brought her expertise in remote sensing and spatial analysis to the study.

Bradley, Balch and the other co-researchers said that, during the past 10 years, cheatgrass fueled most of the largest fires, influencing 39 of the largest 50. Also, fires in grass-covered lands were on average significantly larger than the average fire size on lands dominated by other types of vegetation such as pinyon-juniper, montane shrubland and cultivated areas.

Data also suggest that cheatgrass plays a role in more frequent fires.

“From 2000 to 2009, cheatgrass burned twice as much as any other vegetation,” Balch said.

“One of the tricky things about fires in the West is high year-to-year variability,” Bradley said. “Grass fires tend to occur the year after a wet year, because there is plenty of dry, standing biomass ready to be burned. So trying to figure out this fire relationship you need to have a time series with enough fire years to produce a strong signal. With a full decade of data, we were able to capture the relationship.

“Cheatgrass leaves a continuous cover, which is why it may burn more frequently. The native vegetation in such dry landscapes is often shrubby and separated by bare soil, which can stop a fire, but cheatgrass forms a continuous fuel,” she added.

Balch explained that one of the consequences of more widespread cheatgrass fires is that landscapes dominated by it have a shorter fire-return interval, the time between fires in a region. For cheatgrass-dominated areas it is 78 years, compared to a 196-year interval in areas dominated by another species such as sagebrush.

“What’s happening is that cheatgrass is creating a novel grass-fire cycle that makes future fires more likely,” she explained. “Fire promotes cheatgrass and cheatgrass promotes fires. And cheatgrass-influenced fires create a difficult management challenge.” They can threaten agricultural lands, residential areas as well as habitat for vulnerable native wildlife.

The new information from this study will be useful to management agencies in the West, Bradley said.

“Managers have until now been trying to model fire risk under future climate and development conditions without any information on cheatgrass’s influence. So now they have one more tool to introduce more information and accuracy into their models.”

In the future, the research team hopes to use this regional approach to learn more about how different landscape types such as shrub, forest and wetland ecosystems respond to climate on a yearly basis.

“Using remote sensing we can relate climate conditions to fire response and ecosystem phenology over time, and potentially predict how those ecosystems might be affected by consistently warming temperatures in the future,” Bradley said.

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