From UF/IFAS
In Summary:
Cogongrass can create heavy fuel loads that help fires spread faster and produce longer flames, according to a University of Florida study. The strongest effects appeared in late winter and early spring, when prescribed burning is common in the Southeast. Researchers say removing the invasive grass can help protect native vegetation and reduce potential fire risk.
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What is helping some Florida wildfires burn hotter and spread farther? A University of Florida study suggests cogongrass, an invasive grass that has spread across much of Florida and the Southeast United States, is adding more fuel to the landscape in wildfires.
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The invasive can create conditions that allow fires to spread faster and burn with longer flames to reach the tree canopy, particularly during Florida’s spring season.
The study published in Fire Ecology examined how cogongrass affects characteristics that influence fire behavior across different environmental and seasonal conditions.
Cogongrass forms dense patches that can displace native vegetation, reduce biodiversity, and alter ecosystems. Since its introduction in the 1930s, cogongrass has spread to almost every county in Florida, though it is most extensive in North and Central Florida.
This close-up shows a cogongrass inflorescence in a historic mine in Withlacoochee State Forest in west Central Florida, where cogongrass dominates the area.
Photo by Alan Ivory, UF/IFAS
“When you have cogongrass, you have greater fuel loads, so that means there’s more dead vegetation on the landscape that can fuel fires,” said Alan Ivory, a graduate student at UF’s West Florida Research and Education Center who led the study. “We found faster rates of fire spread and longer flame lengths, and we also found an increased likelihood of fire transitioning into the tree canopy.”
That transition, known as a crown fire, can present additional challenges for firefighters because fire moves from vegetation on the ground into the tree canopy.
“When you go from a ground fire to a crown fire, it becomes more difficult to suppress and requires more resources,” said Ivory.
The researchers also found that the effects of cogongrass on fire behavior varied by season. The greatest differences occurred during late winter and early spring, a period when prescribed fire is widely used across the Southeast.
That finding is particularly important in Florida, where prescribed fire is an important land management tool.
“The Southeast is a hot spot for prescribed fires, and Florida in particular is a model for prescribed fires across the country,” said Victoria Donovan, assistant professor of forest management at the UF/IFAS School of Forest, Fisheries, and Geomatics Sciences. “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 as well.”
The study also produced a surprising result. Ivory initially expected cogongrass to have its greatest effect on fire behavior during summer, when the grass is at its tallest and most vigorous. Instead, the researchers found that the plant’s moisture during this period helped suppress fire spread.
Donovan said the research also suggests that changing environmental conditions could influence how cogongrass affects fire behavior in the future.
“We found that cogongrass is more sensitive to changes in fuel moisture than native vegetation,” said Donovan. “When you have shifts in moisture dynamics, cogongrass is more responsive. 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.”
For homeowners and landowners, the findings add fire risk to the list of reasons to control cogongrass on their properties.
“Controlling cogongrass goes beyond just controlling biodiversity loss; it can reduce potential fire risk around your property as well,” Donovan said. “We have increasingly large wildfires and changing wildfire dynamics in the Southeast, and people are being encouraged to manage vegetation around their homes and create defensible space. Cogongrass is something that can elevate your potential fire risk.”
Cogongrass can spread through its extensive underground root system, making it particularly difficult to contain. Small pieces of its roots can establish new plants, and soil disturbance from activities such as timber harvest or construction can create opportunities for the grass to become established.
Residents can use citizen science resources such as iNaturalist and EDDMapS to see where cogongrass has been reported in their area. You can also see images of the plant on the UF/IFAS Center for Aquatics and Invasive Plants site.
“Invasive species can have an array of impacts,” Donovan said. “In this case, cogongrass is able to alter fire behavior, which adds another reason to be aware of and manage this invasive species.”
Key Points
- Cogongrass has spread to almost every Florida county.
- Its dense growth adds dead vegetation that can fuel fires.
- Researchers found faster fire spread, longer flames, and a greater chance of fire reaching tree canopies.
- The greatest differences from native vegetation occurred in late winter and early spring.
- Landowners can check reported sightings through iNaturalist and EDDMapS.
ABOUT UF/IFAS
The mission of the University of Florida Institute of Food and Agricultural Sciences (UF/IFAS) is to develop knowledge relevant to agricultural, human and natural resources and to make that knowledge available to sustain and enhance the quality of human life. With more than a dozen research facilities, 67 county Extension offices, and award-winning students and faculty in the UF College of Agricultural and Life Sciences, UF/IFAS brings science-based solutions to the state’s agricultural and natural resources industries, and all Florida residents.
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