Radiant heating rapidly increases litter flammability through impacts on fuel moisture

Jesse K Kreye,Jeffrey M Kane,J Morgan Varner,J Kevin Hiers

doi:10.1186/s42408-020-0067-3

Abstract

BackgroundLitter is the predominant fuel that drives surface fire behavior in most fire-prone forest and woodland ecosystems. The flammability of litter is driven by fuel characteristics, environmental factors, and the interactive effects of the two. Solar radiation can influence litter flammability through its effect on fuel moisture and temperature. The direct influence of radiative heating on flammability, however, is poorly understood and the interactive effects of forest structure, composition, fuels, and micrometeorology may have fine-scale ecological consequences in fire-dependent ecosystems.ResultsIn this study, we measured laboratory flammability of two dominant southeastern USA litter fuels—Pinus palustris Mill. and Quercus stellata Wangenh.—and evaluated the interactive effects of fuel moisture and infrared radiation. Heating of litter fuels increased their flammability primarily through enhanced litter drying. Heated litter quickly became more flammable than unheated litter when fuels were undergoing drying after saturation, a result of more rapid moisture loss. Litter mass did not change the effect of heating on drying rates, but heavier fuels burned with greater flammability.ConclusionsInteractions among surface fuels, overstory structure, and solar heating may be important in understanding fine-scale heterogeneity in both fire behavior and effects, with strong implications toward increasing the effectiveness of prescribed burning.

Highlights

The role of fire as an ecological process has been well recognized in many fire-dependent ecosystems
An unappreciated mechanism in the variability of fire behavior may be the interactive effects of canopy cover and surface fuel characteristics on fuel moisture and flammability (Varner et al 2015, Kreye et al 2018a, 2018b)
Solar impacts are often assumed to influence factors related to fire behavior (Bradshaw et al 1983), the more rapid response of litter flammability to drying under infrared heating highlights how quickly flammability increases when fine fuels are drying under exposure to infrared radiation

Summary

Introduction

The role of fire as an ecological process has been well recognized in many fire-dependent ecosystems. Interactions among fuels, vegetation, and micrometeorological conditions may influence fire behavior at fine scales and subsequently affect plant diversity (Hiers et al 2009; Dell et al 2017). Forest structure and composition affect forest floor shading patterns as well as the composition of surface fuels The role of these factors in the variability of fire behavior and effects at fine scales may influence vegetation patterns or species diversity in fire-prone landscapes. An unappreciated mechanism in the variability of fire behavior may be the interactive effects of canopy cover (i.e., shading) and surface fuel characteristics (e.g., composition and mass) on fuel moisture and flammability (Varner et al 2015, Kreye et al 2018a, 2018b). The direct influence of radiative heating on flammability, is poorly understood and the interactive effects of forest structure, composition, fuels, and micrometeorology may have fine-scale ecological consequences in fire-dependent ecosystems

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