Assessing crown fire potential by linking models of surface and crown fire behavior

Abstract

You may order additional copies of this publication by sending your mailing information in label form through one of the following media. Please specify the publication title and series number. Fire managers are increasingly concerned about the threat of crown fires, yet only now are quantitative methods for assessing crown fire hazard being developed. Links among existing mathematical models of fire behavior are used to develop two indices of crown fire hazard-the Torching Index and Crowning Index. These indices can be used to ordinate different forest stands by their relative susceptibility to crown fire and to compare the effectiveness of crown fire mitigation treatments. The coupled model was used to simulate the wide range of fire behavior possible in a forest stand, from a low-intensity surface fire to a high-intensity active crown fire, for the purpose of comparing potential fire behavior. The hazard indices and behavior simulations incorporate the effects of surface fuel characteristics, dead and live fuel moistures (surface and crown), slope steepness, canopy base height, canopy bulk density, and wind reduction by the canopy. Example simulations are for western Montana Pinus ponderosa and Pinus contorta stands. Although some of the models presented here have had limited testing or restricted geographic applicability, the concepts will apply to models for other regions and new models with greater geographic applicability. Fort Collins Service Center

Canopy fuel characteristics and potential crown fire behavior in Aleppo pine (Pinus halepensis Mill.) forests

“…Since conifer needles are the main aerial fuels consumed during a crown fire [79], crown fuel properties are based on the quantification of live needle foliage. Nevertheless, current research efforts state that in certain fuel complexes, other fuel categories, such as the fine twigs, may significantly contribute to the heat released from the flaming zone of a crown fire [19,70,76]. Although numerous studies correlate crown or foliage biomass with tree dendrometric characteristics [13,37,46,51,53,55,56], only few studies measure crown fuel load by diameter size class at tree level [15,39,40,73] and at stand level [9,23], as it is required in crown fire behavior modeling.…”

“…In recent studies, the term "crown" is applied to describe aerial fuels at the tree level and "canopy" at the stand level [23]. Computer systems and models that simulate crown fire behavior need a quantitative description of the canopy fuels; available canopy fuel load (CFL), canopy bulk density (CBD) and canopy base height (CBH) [31,32,70].…”

“…CBD, measured in kg/m 3 , is the dry weight of the available canopy fuel load per unit of canopy volume [70]. CBD is a target value for assessing the spread of active crowning in conifer stands [44,70].…”

“…Until recently, fuel complex characterization has been limited to surface fuel beds [10,27], due to the restricted applicability of fire behavior simulation models only to surface fuels [11,16]. The development of fire behavior models and systems designed to predict crown fire behavior [24,25,31,32,70,79,80] made necessary the measurement of canopy fuel data. Recently, the risk of wildland fire as a forest stand management optimization problem was analyzed [34,35].…”

“…They are also responsible for the largest proportion of the overall area burned in large fires in coniferous forests, worldwide [2,36]. The importance of crown fire behavior prediction in assessing fire potential has made it a prerequisite for evaluating the effectiveness of fuel management treatments during fire prevention planning [33,44,70,72].…”