Crown fire behaviour in a northern jack pine – black spruce forest

Abstract

This paper reports on the behaviour of 10 experimental crown fires conducted between 1997 and 2000 during the International Crown Fire Modelling Experiment (ICFME) in Canada's Northwest Territories. The primary goal of ICFME was a replicated series of high-intensity crown fires designed to validate and improve existing theoretical and empirical models of crown fire behaviour. Fire behaviour characteristics were typical for fully developed boreal forest crown fires, with fires advancing at 15-70 m/min, consuming significant quantities of fuel (2.8-5.5 kg/m 2 ) and releasing vast amounts of thermal heat energy. The resulting flame fronts commonly extended 25-40 m above the ground with head fire intensities up to 90 000 kW/m. Depth of burn ranged from 1.4-3.6 cm, representing a 25%-65% reduction in the thickness of the forest floor layer. Most of the smaller diameter (<3.0 cm) woody surface fuels were consumed, along with a significant proportion of the larger downed woody material. A high degree of fuel consumption occurred in the understory and overstory canopy with very little material less than 1.0 cm in diameter remaining. The documentation of fire behaviour, fire danger, and fire weather conditions carried out during ICFME permitted the evaluation of several empirically based North American fire behaviour prediction systems and models.Résumé : Cet article traite du comportement de 10 feux de cime expérimentaux provoqués entre 1997 et 2000 dans le cadre de l'Expérience internationale de modélisation des feux de cimes (EIMFC) dans les Territoires du Nord-Ouest au Canada. Le principal objectif de cette expérience consistait à reproduire une série de feux de cime de forte intensité conçus pour valider et améliorer les modèles théoriques et empiriques existants de comportement des feux de cime. Les caractéristiques du comportement des feux de cime étaient typiques des feux de cime en forêt boréale mature, où les feux progressent à 15 à 70 m/min, en consumant d'importantes quantités de combustibles (2,8 à 5,5 kg/m 2 ) et génèrent de fortes quantités d'énergie thermique sous forme de chaleur. Les fronts de flamme qui en résultent s'élevaient géné-ralement à 25 à 40 m au-dessus du sol avec des intensités à la tête du feu allant jusqu'à 90 000 kW/m. La profondeur de brûlage variait de 1,4 à 3,6 cm, ce qui représentait une réduction de 25 % à 65 % de l'épaisseur de la couverture morte. La plupart des combustibles de surface de plus petit diamètre (<3,0 cm) ont été consumés de même qu'une importante proportion du plus gros matériel ligneux au sol. Il y a eu une forte consommation de combustibles dans le couvert des étages inférieur et supérieur où il restait très peu de matériaux d'un diamètre inférieur à 1,0 cm. La documentation du comportement du feu, le danger de feu et les conditions météorologiques propices aux incendies forestiers ont permis d'évaluer plusieurs systèmes et modèles empiriques nord-américains de prédiction du comportement des feux.[Traduit par la Rédaction] Stocks et al. 1560

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

“…The low fuel strata gap, the heavy available surface fuel load and the substantial height of the surface fuel bed that characterize Aleppo pine fuel complexes, increase dramatically the likelihood of crown fire initiation. Active crown fire rate of spread, fireline intensity and flame length in Aleppo pine stands were found similar to values reported in typical active crown fires in the International Crown Fire Modelling Experiment, where the rate of crown fire spread ranged from 15.8 to 69.8 m/min, the fire intensity from 20 000 to 100 000 kW/m and the flame front was 2−3 times the mean stand height [76]. Under extreme burning conditions, active crown fire rate of spread was even observed in Aleppo pine stands with CBD lower than Agee's threshold value (0.10 kg/m 3 ) [1], as the simulation results indicated.…”

“…CBD was computed using only the available canopy biomass (needles and branches < 0.63 cm). This biomass aggregation best represents the fuels that are available for consumption in most crown fires [76]. The CBD distribution in the fuel profiles of Aleppo pine stands indicate values which would readily support the propagation of active crown fires [1,6,25,41].…”

“…The new physical model overestimated the crown fire rate of spread and required large computation time. On the contrary, the Cruz et al [22,25] model adequately predicted the crown fire rate of spread in most cases [76]. The ICFME is the only extensive evaluation of crown fire models published so far.…”

“…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.…”

“…Furthermore, all the existed fully operational models were evaluated against high intensity experimental crown fires [76]. The experimental dataset was comprised of eleven experimental crown fires in a mature Pinus banksiana stand with a substantial Picea mariana understory.…”