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Fire Behavior, Fuel Consumption, and Turbulence and Energy Exchange during Prescribed Fires in Pitch Pine Forests

USDA Forest Service, Northern Research Station, Silas Little Experimental Forest, 501 Four Mile Road, New Lisbon, NJ 08064, USA
USDA Forest Service, Northern Research Station, 3101 Technology Blvd., Suite F, Lansing, MI 48910, USA
USDA Forest Service, Northern Research Station, 180 Canfield Street, Morgantown, WV 26505, USA
BRE Centre for Fire Safety Engineering, School of Engineering, University of Edinburgh, Edinburgh EH93JL, UK
Worcester Polytechnic Institute, 100 Institute Road, Worcester, MA 01609, USA
Author to whom correspondence should be addressed.
Atmosphere 2020, 11(3), 242;
Received: 20 January 2020 / Revised: 17 February 2020 / Accepted: 27 February 2020 / Published: 29 February 2020
(This article belongs to the Special Issue Atmospheric Turbulence Processes and Wildland Fires)
Prescribed fires are conducted extensively in pine-dominated forests throughout the Eastern USA to reduce the risk of wildfires and maintain fire-adapted ecosystems. We asked how fire behavior and fuel consumption during prescribed fires are associated with turbulence and energy fluxes, which affect the dispersion of smoke and transport of firebrands, potentially impacting local communities and transportation corridors. We estimated fuel consumption and measured above-canopy turbulence and energy fluxes using eddy covariance during eight prescribed fires ranging in behavior from low-intensity backing fires to high-intensity head fires in pine-dominated forests of the New Jersey Pinelands, USA. Consumption was greatest for fine litter, intermediate for understory vegetation, and least for 1 + 10 hour wood, and was significantly correlated with pre-burn loading for all fuel types. Crown torching and canopy fuel consumption occurred only during high-intensity fires. Above-canopy air temperature, vertical wind velocity, and turbulent kinetic energy (TKE) in buoyant plumes above fires were enhanced up to 20.0, 3.9 and 4.1 times, respectively, compared to values measured simultaneously on control towers in unburned areas. When all prescribed fires were considered together, differences between above-canopy measurements in burn and control areas (Δ values) for maximum Δ air temperatures were significantly correlated with maximum Δ vertical wind velocities at all (10 Hz to 1 minute) integration times, and with Δ TKE. Maximum 10 minute averaged sensible heat fluxes measured above canopy were lower during low-intensity backing fires than for high-intensity head fires, averaging 1.8 MJ m−2 vs. 10.6 MJ m−2, respectively. Summed Δ sensible heat values averaged 70 ± 17%, and 112 ± 42% of convective heat flux estimated from fuel consumption for low-intensity and high-intensity fires, respectively. Surprisingly, there were only weak relationships between the consumption of surface and understory fuels and Δ air temperature, Δ wind velocities, or Δ TKE values in buoyant plumes. Overall, low-intensity fires were effective at reducing fuels on the forest floor, but less effective at consuming understory vegetation and ladder fuels, while high-intensity head fires resulted in greater consumption of ladder and canopy fuels but were also associated with large increases in turbulence and heat flux above the canopy. Our research quantifies some of the tradeoffs involved between fire behavior and turbulent transfer of smoke and firebrands during effective fuel reduction treatments and can assist wildland fire managers when planning and conducting prescribed fires. View Full-Text
Keywords: turbulence; energy fluxes; eddy covariance; prescribed fires; Pitch Pine; Pine Barrens; New Jersey turbulence; energy fluxes; eddy covariance; prescribed fires; Pitch Pine; Pine Barrens; New Jersey
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Clark, K.L.; Heilman, W.E.; Skowronski, N.S.; Gallagher, M.R.; Mueller, E.; Hadden, R.M.; Simeoni, A. Fire Behavior, Fuel Consumption, and Turbulence and Energy Exchange during Prescribed Fires in Pitch Pine Forests. Atmosphere 2020, 11, 242.

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