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Research Shows that the Risk of Wildfire Spread Rises with Replacement of Grasses by Trees and Shrubs.


Comparison of maximum potential spot fire distance under set fire (8 and 32 km/h) versus wind speeds (8, 32, 64, 97 and 129 km/h) relative to the grassland condition (yellow), and juniper overtaking the grassland (in orange), and the state of juniper forests (in red) in experimental landscapes of the Lewis Valley. Column 1 shows a landscape representation of changes in potential future fuel exposure relative to maximum fire distance from burning units in Loess Canyons if all grassland (yellow), all creeping meadow juniper (orange), and all woodland (red). Column 2 focuses on changes in maximum spot fire distance for a single burning unit, where black lines represent the perimeter of potential spot fire exposure and colored lines represent maximum spot fire distance if the burning unit was a turf (yellow), wood infiltrate turf (orange ), or Forest (red). Column 3 lists the maximum firing distances for each encroachment scenario. Green areas in the maps represent receptive fuels while gray areas represent non-receivable fuels (urban, agricultural, water, and arid regions) (52). Maps were created using ArcGIS (45). credit: Plus one (2023). DOI: 10.1371/journal.pone.0283816

Across the United States over the past decade, an average of more than 61,000 wildfires have burned about 7.2 million acres annually. Once a wildfire begins to spread, the firefighting task is compounded by problems such as spot fires, where winds carry sparks up high and new fires start outside the perimeter of the original fire. The greater the potential distance of a fire, the more difficult it is to detect, control and extinguish wildfires.

A new study published in Plus one, led by Victoria Donovan, a University of Florida Department of Forestry researcher, found that because woody plants such as shrubs and trees replace herbaceous plants such as grasses, localized fires can occur far from the fire’s original perimeter. This “timber encroachment” is not only a major issue in the grasslands where the study is taking place, but also in wetlands and savannah systems such as longleaf pine, an important ecosystem in Florida.

said Donovan, associate professor in the School of Forestry, Fisheries, and Geomatics at the UF/IFAS West Florida Research and Education Center in Milton, Florida. “It is not usually because the flames from a wildfire reach a house, but that embers from that fire fall on roofs, travel through the home’s ventilation systems, or land on some other combustible material in or near the house, and ignite the house from there .re a major concern for structural damage.”

Donavan’s study suggests that described fire, which is commonly used in Florida to control the growth of woody plants, can help reduce spot fires.

The study looked at three phases of woodland encroachment: the first is a largely grassy area, the second is pasture with new forest growth, and the third is dense forest. The research was modeled using mathematical fire simulation software considering different conditions in the experimental landscape of the Loess Valley in southern Nebraska. Donovan conducted this study as a researcher at the University of Nebraska-Lincoln.

“Our study shows that the risk of a localized fire is much lower when you’re burning under the atmospheric conditions used for a prescribed fire, regardless of the stage of encroachment, compared to waiting for the more extreme conditions we can see during a wildfire,” Donovan said. . “This tells us that using fire early to control encroachment and reduce fuel load is safer than waiting for a wildfire to occur.”

Wood trespassing safety concerns extend beyond buildings and residents to also include firefighters fighting the fire.

“It’s not just fire distance that increases wildfire risk from log creep,” Donovan said. “Shrubs and trees can grow much taller than grass.” “Think of putting out a campfire on the ground by pouring water on it, and compare that to trying to put out a fire on top of you.”

She said the concerns are universal and reveal similarities regardless of the type of land where wildfires occur.

“We’re seeing the same kind of problem here in Florida, where putting out fires has led to a lot of bush encroachment,” Donovan said. “This creates these really dense forests rather than the open savanna systems that we would historically have with more frequent fire.”

Florida has become a model for arson described across the country, she added, though there is still reluctance among some private landowners. Donovan warns: “Using prescribed fire as an operation to control wood encroachment has far fewer risks than allowing loggers to encroach and wait for wildfires.”

“Across the country, the data has shown that fire is inevitable,” she adds. “Using described fire allows us to decide what we want a lot of that fire to look like.”

more information:
Victoria M. Donovan et al, fire spot distance increases disproportionately for wildfires compared to fires described as transition of grassland to Juniperus forest, Plus one (2023). DOI: 10.1371/journal.pone.0283816

Provided by the University of Florida

the quote: Study: Wildfire Risks Increase as Trees and Shrubs Replace Grasses (2023, May 18), Retrieved May 18, 2023 from https://phys.org/news/2023-05-wildfire-trees-shrubs-grasses. html

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