UMass Amherst Biogeographer to Lead Study on Wildfire Risk Caused by Invasive Grass Species

carbon grass map
Some of the invasive grasses Bradley and colleagues expect to study are buffelgrass that has invaded southeast Arizona; giant cane that has invaded southeast Texas; cogongrass that has invaded Florida, Alabama and Mississippi; red brome that has invaded the Mojave Desert and the Las Vegas area and reed canarygrass that has hybridized with a native grass and invaded areas in Minnesota and Maine.
sagebrush loss
In the western United States, cheatgrass invasion and the fires that follow leads to 90 percent loss of above-ground biomass, as sagebrush (left) burns and cheatgrass monoculture (right) takes over.

AMHERST, Mass. – Invasive plant expert Bethany Bradley at the University of Massachusetts Amherst has received a three-year, $389,975 grant from the National Science Foundation (NSF) to create the first comprehensive assessment of how more than two dozen non-native, invasive grasses may alter fire patterns and carbon storage across ecosystems in the contiguous United States.

Bradley will team up with her collaborator of seven years, geographer Jennifer Balch at the University of Colorado Boulder, Balch’s postdoctoral researcher Chelsea Nagy and Bradley’s graduate student Emily Fusco for the work, supported by NSF’s Geography Spatial Sciences program.

Bradley says, “This study builds on our work with cheatgrass, which strongly increases risk of wildfire. But, ecologists and managers have reported suspected links between invasive grasses and fire for at least 30 additional species in the continental U.S. Our analysis will test whether we can see similar increases in fire associated with these other invasive grass species.”

The researchers will combine spatial information about the location of invasive grass abundance with satellite-derived fire perimeters to look for influence of invasive grasses on fire. Bradley adds, “We know where fires are burning and we have compiled quite a bit of information about the invaded range of these grasses. We overlay the two sets of data to try to answer whether the presence of the invasive grasses is associated with more frequent or larger fires.”

Some of the invasive grasses they expect to study are buffelgrassthat has invaded southeast Arizona; giant cane that has invaded southeast Texas; cogongrass that has invaded Florida, Alabama and Mississippi; red brome that has invaded the Mojave Desert and the Las Vegas area and reed canarygrass that has hybridized with a native grass and invaded areas in Minnesota and Maine.

Bradley says many of these grass species have been deliberately introduced either as ornamentals or as biofuels. “We recognize that ornamental plants and biofuels are important, but it’s a pretty big tradeoff if you’re going to get increased fire risk and harm native ecosystems and threaten homes and livelihoods.”

Another question the scientists will try to answer is whether fire-prone invasive grasses are reducing native vegetation cover and thus carbon storage. Because they are bigger, trees and shrubs store more carbon that grasses can, including in their roots.

Bradley notes, “If grasses come in and stop the natural succession of the southern pine ecosystem, for example, we could end up with ecosystems dominated by cogongrass instead of trees. This is happening with cheatgrass in the West, which is interrupting the succession of native shrubs and causing huge losses in ecosystem carbon storage.”

She adds, “The native trees and shrubs might be able to come back if we could remove the cheatgrass and fires, but once those are established, it’s extremely costly and time intensive to restore.”

In the first of four steps of the researchers plan, they will conduct a spatial analysis to evaluate how extensive the invasive grass coverage is. In the second phase, they will model, or predict, what the potential spread of the invasive species may look like in the lower 48 states over time and produce a series of maps to illustrate this.

Third, they will conduct field studies including a carbon budget analysis of three invasive species that will serve as case studies. The carbon budget will estimate what, if any, carbon losses are associated with the loss of larger plants in each area.

“We have very little understanding of how fire-prone invasive grasses alter both above- and below-ground carbon storage. This part of the study will help us understand how invasive grasses and fire could contribute to carbon emissions from ecosystems, which affects atmospheric CO2 and climate change,” Bradley explains. In the final step, she and colleagues will produce a national-scale estimate of potential losses that may be related to as many as 30 species of invasive grasses.

The researchers note that “by exploring how invasive grasses impact wildfire, the project will expand basic understanding of how invasive species affect the ways in which ecosystems function. By quantifying changes in carbon stocks associated with invasion and fire, the project will provide a national estimate of how the grass-fire cycle affects ecosystem carbon storage.” They also hope to provide new perspectives, insights and information on managing and controlling fire-prone invasive grasses.

Their technical tools will include a comprehensive database of fire-prone invasive grass occurrence locations with fire data gathered using satellite-based moderate-resolution imaging spectro-radiometer (MODIS) and visible infrared imaging radiometer suite (VIIRS) sensors to identify invasive grasses that are altering regional fire cycles. For modeling the potential range of invasive grass infestations they will use parameter-elevation relationships on independent slopes model (PRISM) climate data, shuttle radar topography mission (SRTM) topography data, and MODIS and U.S. Geological Survey phenology vegetation products as predictors.

As the lead institution, UMass Amherst is projected to receive $224,146 of the total NSF grant and subcontractor University of Colorado Boulder will receive $165,000.