Wildfires tend to dominate headlines. Prescribed burns, also known as controlled burns, get less attention, but they’re certainly not uncommon—especially in the Southeast.
Landsat Enables Mapping of Fire Histories Across Florida
The Florida Forest Service issues permits for an average of 2 million acres of prescribed burns each year. That’s 16 times the annual prescribed burn acreage in California, according to the California Air Resources Board.
Today’s routine burning of parcels in the Southeast mimics historical practices that date back hundreds, even thousands, of years. These practices adapted the area’s trees, plants and wildlife to frequent fires.
In northern Florida today, frequent prescribed burning helps preserve longleaf pine forest habitats, where dozens of threatened and endangered species live alongside hunters’ prized northern bobwhite quail.
Knowing the history of these prescribed burns—and all fires—can help to optimally manage the land and identify habitat corridors. However, in areas of high private ownership, such as the Southeast, fire records may be incomplete or not kept at all. Assembling a historical record of fires across an entire State like Florida would seem impossible—to anyone but a remote sensing researcher.
A recent collaboration among fire and remote sensing scientists proved that it was, indeed, possible to show when and where fires had occurred across the landscape—even if they were just a few acres—thanks to the U.S. Geological Survey (USGS) Landsat satellite program.
Mapping Solution: Landsat Burned Area Product
Tall Timbers is a Florida research station known for its work in fire ecology and prescribed fires, and for helping recover the northern bobwhite quail population. Headquartered north of Tallahassee and just south of the Georgia border in the 436,000-acre Red Hills region of longleaf pine, Tall Timbers also serves as a conservation land trust. It protects more than 145,000 acres of private land from development. It also owns 13,000 acres of land.
When the Florida Fish and Wildlife Conservation Commission and the Peninsular Florida Landscape Conservation Cooperative learned from regional scientists that fire regime was an important indicator of biodiversity in various ecosystems, they engaged Tall Timbers experts to figure out how to map histories across the State for prescribed fires, which most fires there are, and for wildfires.
Joe Noble, the geospatial program lead at Tall Timbers, and Dr. Casey Teske, who worked with him on fire remote sensing projects before a recent move to the U.S. Fish and Wildlife Service, weighed options for the best method to go about mapping fires across a State with 42 million acres.
Considering most of the land is privately owned and recordkeeping is spotty, “using satellite data was a way to go across boundaries to understand this as a landscape process,” Teske said.
Some datasets may provide fire histories only for public lands, or for burned areas on a fairly large scale, or may exclude prescribed burns, but Noble and Teske fairly quickly concluded that a Landsat product would meet their need. The Landsat Burned Area product, a 30-meter resolution dataset derived from Landsat data and served as Landsat Analysis Ready Data produced at the USGS Earth Resources Observation and Science (EROS) Center, shows the extent of burns and the probability that an area has burned across the conterminous United States dating back to 1984.
Process of Mapping and Learning in Florida
To see how it would fare, Noble and Teske compared Burned Area product data with records of agencies with significant recorded histories of both wildfires and prescribed burns: Big Cypress National Preserve, Eglin Air Force Base, and Apalachicola National Forest.
They talked with land managers to understand characteristics of fires that had been missed by the Burned Area product—the types of fires and ecosystems.
“Management input is important for science to be relevant and helpful,” Teske said.
What they learned from the managers, they took to the team at the USGS Geosciences and Environmental Change Science Center who had originated Landsat Burned Area: Dr. Todd Hawbaker, the algorithm developer, and Dr. Melanie Vanderhoof, who supported the development and led the national validation of the product.
Hawbaker and Vanderhoof discovered that Burned Area’s threshold of burn extent was a little too conservative for Florida, so that was lowered slightly, Vanderhoof said.
Then the Burned Area product was applied for the years 2006-2018 over the entire State, a first for any State, and used to derive metrics of fire frequency, time since the last burn, year of the last burn, longest fire-free interval, time of year, and whether the fire happened during a growing or dormant season. Vanderhoof said land managers’ requests helped determine the metrics and the way they would be accessed.
“We’d never seen a wall-to-wall map of fire history in Florida, especially at that scale,” Teske said. She and Noble started giving presentations about the mapping and found that organizations were interested in comparing the map with their known histories. They recognized how well they matched up.
This type of mapping refutes an assumption that fire burns frequently and everything, said Dr. Morgan Varner, director of research at Tall Timbers.
“Their projections show that fire is really concentrated in a little more than a handful of areas. … Southeastern states have groups of basically superusers—a really strong collection of lands that we manage in a certain way with lots of fire,” Varner said.
Mapping Fire History for the Southeast and Beyond
Landsat’s archive of nearly 50 years sets it apart from other satellite data sources, Noble said. “It’s critical to this project and all subsequent projects that spin off this,” he said. “Without the history, we just couldn’t have done it. … History is the key. This ecosystem health doesn’t change overnight.”
Since completing the Florida study, Tall Timbers has contributed the same mapping method based on Landsat Burned Area, for years 1994-2019, to the Southeast FireMap project, an online map of fire history on public and private lands in portions of nine southeastern States. The project is funded by the U.S. Department of Agriculture (USDA) Natural Resources Conservation Service to support fire management.
The USGS now is working to scale up the derivation of fire history metrics for the conterminous United States for the years 1984-2020, Vanderhoof said.
“The idea is there might be different management priorities and issues in different regions across the country that these fire history metrics can inform,” she said. “The applications are probably most clearly useful and accurate in … habitat types that have a shorter fire-return interval.”
This information, which can help pinpoint high-quality habitats and areas in need of restoration, can help agencies and landowners prioritize their efforts. It’s invaluable for a conservationist trying to determine when and where to burn to maintain corridors of habitat, for a hunting plantation aiming to boost numbers of northern bobwhite quail, or for a land manager concerned about controlling wildfire fuels.
“It starts to get at, here’s how we can stabilize and ensure these areas can be burned in the future. Here’s how we could strategically focus conservation efforts that take advantage of the block of fire here. How do we build corridor-type conservation practices that ensure we can stabilize rare species that are dependent on that frequent fire?” Varner said.
“I love it that you can put everything into a model, and the thing that we can manage tends to be the factor that drives a lot of the diversity.”
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