21st Century Fire Ecology in the South

Using high resolution infrared thermography to understand prescribed fire in longleaf pine ecosystems

The infrared thermography platform developed by Forest Service researchers consists of a thermal imagery system combined with a pan-tilt system that allows high resolution images to be taken from directly over study plots. Photo by U.S. Forest Service.
The infrared thermography platform developed by Forest Service researchers consists of a thermal imagery system combined with a pan-tilt system that allows high resolution images to be taken from directly over study plots. Photo by U.S. Forest Service.

U.S. Forest Service researchers are using an array of high technologies — high resolution infrared thermography, LiDAR, and photogrammetry — to reach a new level of understanding of the interactions among fuels, fire, and plant diversity that underlie the successful use of prescribed fire in longleaf pine ecosystems.

The longleaf pine forests that once covered over 90 million acres in the South include some of the most species-rich plant communities outside of the tropics, with most of this diversity in the groundcover. Besides harboring many rare plant species, the groundcover provides habitat for birds and animals distinct to longleaf pine ecosystem and produces fuel for the surface fires that keep the system healthy.

Though it’s widely accepted that prescribed fire promotes the diversity of longleaf pine understory plants, exactly how this happens is not well understood, partly because there’s been so little research linking fire behaviors such as combustion and heat transfer to fire effects on trees and understory plants.

Scientists at the Forest Service Southern Research Station (SRS) Center for Forest Disturbance Science — Fire Science team leader Joe O’Brien , project leader Scott Goodrick, and Louise Loudermilk — are using infrared thermographic technology at high spatial and temporal resolution to test hypotheses about the interactions among tree canopy structure, fuels, fire behavior, and fire effects in longleaf pine forest ecosystems. They are combining these measurements with other high-tech measurements such as LiDAR and 3D digital rendering to capture important elements of forest structure and fuels.

Example of data collected by imagery system, with the colors representing fire temperature. The top frame, taken 25 seconds after fire enters the plot, shows the flaming phase of combustion. The second frame, taken 3 minutes later, shows the smoldering combustion of pine cones that release much more energy than the fine fuels that drive combustion in the first frame. The team is investigating how these patterns of energy release affect the plant communities within the plots. Image by U.S. Forest Service.
Example of data collected by the imagery system, with the colors representing fire temperature. The top frame, taken 25 seconds after fire entered the plot, shows the flaming phase of combustion. The second frame, taken 3 minutes later, shows the smoldering combustion of pine cones, which release much more energy than the fine fuels that drove combustion in the first frame. The team is investigating how these patterns of energy release affect the plant communities within the plots. Image by U.S. Forest Service.

Using cameras that detect radiation in the long-infrared range of the electromagnetic spectrum, the scientists can produce images that capture variations in temperature and display the data in brilliant colors. Long-wave thermography is particularly useful for this research because the long-wave part of the infrared spectrum is the most sensitive to radiation emitted when surfaces such as fuels and plants are heated by fire.

“We’re looking specifically at how variations in the energy released by burning cones and woody fuels might allow such a high diversity of plant species to coexist in the very uniform soil environment in many longleaf pine forests,” said O’Brien. “By explicitly testing ecological theories on how plant communities respond to fire, the work that we’re doing is poised to revolutionize the fundamental understanding of fire behavior and the connection between fire behavior and fire effects.”

SRS researchers use the high resolution infrared thermography platform they’ve developed as part of a larger U.S. Department of Defense Strategic Environmental Research and Development Program (SERDP) study being conducted at Eglin Air Force Base (Eglin AFB) in northwest Florida, with Joe O’Brien as principal investigator on a $2.3 million grant. The team consists of researchers from the University of Nevada-Reno, the Forest Service Rocky Mountain Research Station and the University of Montana. Study researchers are investigating both the mechanisms driving patterns of plant diversity across the Eglin AFB landscape and how to best model and measure biological diversity.

The team measured over 29 operational fires at Eglin AFB over the last three years. The research funded by SERDP builds on knowledge gained during the RxCADRE (Prescribed Fire Combustion and Atmospheric Dynamics Experiment). Multidisciplinary RxCADRE teams converged on Eglin in 2008, 2011, and 2102 to set both large and small fires, and to collect wildland fire data in six integrated core science areas – fuels, meteorology, fire behavior, energy, smoke emissions, and fire effects. The high resolution infrared thermography methods developed by SRS researchers have been critical for collecting data on fire behavior and fire effects.

The January issue of the International Journal of Wildland Fire is entirely devoted to RxCADRE measurements, datasets, and preliminary results, and includes an article by O’Brien and fellow scientists on the techniques they developed.  O’Brien and Loudermilk are also co-authors on an article about measurements of fire radiative density and surface fuel consumption.

Read more about the findings from RxCADRE reported in the International Journal of Wildland Fire.

For more information, email Joe O’Brien at jjobrien@fs.fed.us.

 Access the latest publications by SRS scientists.

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