Science1 publisher2 min readPublished
Invasive cogongrass lets Florida fires run faster and reach the canopy in early spring
University of Florida researchers report that cogongrass, now in almost every Florida county, makes fires spread faster with longer flames. The effect peaks in late winter and early spring, so controlling the grass now belongs in wildfire planning for burn crews and homeowners.
The Scientist · Science desk
What happened
- Lead author Alan Ivory, a UF graduate student, said infested ground carries greater fuel loads, meaning more dead vegetation is available to burn.
- Fires burning through cogongrass were also more likely to move from the ground into the tree canopy, according to the study team.
- Ivory expected the grass to matter most in summer, when it is tallest, but moisture in the plant at that time helped suppress fire spread.
- Cogongrass, introduced in the 1930s, is most extensive in northern and central Florida.
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Why it matters
- decision Burn planners working infested stands in late winter and early spring, the Southeast's main prescribed-fire window, are setting fires when the grass alters fire behavior most.
- exposure Donovan says the grass can raise a property's fire risk, so clearing it becomes part of defensible-space work for homeowners and landowners.
- constraint Root fragments start new plants, so timber harvests, construction and other soil-disturbing work can widen the ground where fire risk is elevated.
Phys.org's account of the paper in Fire Ecology describes a study of how cogongrass changes "characteristics that influence fire behavior across different environmental and seasonal conditions" [1][3]. Victoria Donovan, an assistant professor of forest management at the UF/IFAS School of Forest, Fisheries, and Geomatics Sciences, describes the comparison as cogongrass against native vegetation [12]. The account gives the direction of each effect but not its size, the number of sites, or whether fire behavior was observed in test burns or modeled from measured fuels. Those details decide whether "longer flame lengths" [7] means a modest change or a different kind of fire.
The canopy result matters most to the people who fight fires. "When you go from a ground fire to a crown fire, it becomes more difficult to suppress and requires more resources," said Alan Ivory, the UF graduate student who led the study [8]. Florida also relies on fire set on purpose [18]. "The Southeast is a hot spot for prescribed fires, and Florida in particular is a model for prescribed fires across the country," Donovan said [10]. She added: "We use prescribed fire to enhance our ecosystems and the services that they provide to people, but we also use prescribed fire to reduce wildfire risk." [17]
I'd give the seasonal pattern the most weight. Its summer half contradicted the lead author's own prediction, and a result that overturns the hypothesis is harder to explain away as expectation [11]. It also lines up with a second finding. "We found that cogongrass is more sensitive to changes in fuel moisture than native vegetation," Donovan said [12]. In summer that sensitivity worked against fire, because the plant's moisture held spread down [11]. Donovan extended the moisture result to a warmer climate. "What that potentially means is that under future climate projections, there could be stronger impacts of cogongrass on fire behavior as we see more intense drying periods and warmer temperatures," she said [13].
Residents can check where cogongrass has been reported near them on the citizen-science platforms iNaturalist and EDDMapS [16]. The UF/IFAS Center for Aquatic and Invasive Plants posts images of the plant for identification [16].
What to watch
- The effect sizes in the Fire Ecology paper: how much faster spread and how much longer flames are in cogongrass than in native vegetation, and across how many sites.
- Whether Florida burn managers change timing or pre-treat cogongrass before late-winter and early-spring prescribed burns in infested stands.
- Field records of wildfires and prescribed burns in infested stands showing whether canopy transitions happen as often as the study suggests.