Fuel types and crown fire potential in Pinus halepensis forests

Abstract

There is a lack of knowledge to identify and classify forest structures according to the risk of crown fires, especially in Mediterranean regions. In this study, for the first time, we use real information, obtained after a wildfire that burnt under extreme meteorological conditions, to classify forest structures of Pinus halepensis into fuel types as a function of crown fire potential. We identified fourteen forest structures which characterize many forest types in Western Mediterranean areas depending on canopy closure, number of tree layers, percent of each tree layer and overall tree density. By using the pattern of fire types that burnt the most numerous forest structures, we have identified four fire hazard groups of forest structures which are considered different fuel types. The first two had the lowest risk of active crown fires and they differed in the proportion of surface fires and passive crown fires. The third fuel type was the threshold between structures with low and high extreme fire behavior; while the fourth had a high risk of active crown fires. Firefighters and forest managers who are demanding this kind of schema, will test and upgrade this classification of fuel types in function of crown fire potential during future wildfires.

Fuel Classes in Conifer Forests of Southwest Sichuan, China, and Their Implications for Fire Susceptibility

“…FT6 would benefit from the removal of some "ladder fuels" to reduce the canopy density. This could be effective in stopping passive crown fires and preventing the start of new fires, especially if it was combined with patchy canopy and vertical layer management [13,14,29].…”

“…Firstly, this strategy can be effective to stop passive crown fires and also prevent new fires when combined with surface/crown patchiness, understory management and "ladder fuel" management. Several measures can be taken to achieve this goal, such as reducing surface fuel (needles, leaves, grass, dead and down branch wood) [46], and reducing the amount of ladder fuels (small trees and shrubs) [14,28,29]. The pruned plant material can be masticated or chipped and left on site, which is an option an increasing number of forest managers are using [24,28].…”

“…Treatments to reduce crown fire susceptibility often focus on reducing canopy fuels and interrupting the surface-canopy fuel continuum. Combining this with a lower vertical and horizontal continuity makes the transition to crown fire more difficult [29]. Horizontal patchiness of the canopy will reduce the spread of fire within the canopy layer [29], using measures such as cleaning up litter (active fuel and fine fuel) [24], increasing canopy gaps [48], and decreasing tree density [28].…”

“…We used the custom fuel model and set many parameters (surface fuel loading, crown fuel density of each plot, moisture content, heat content values, canopy base height, wind speed and slope). According to the simulated effects of the fire on the plot and the neighboring plot, we distinguished three fire types (surface fires, passive crown fires, and active crown fires) by Alvarez's [29] criterion.…”

“…The initial classification of stands was based on site specific data including elevation, slope, and aspect. Total height and the height to the live crown base were measured with a hypsometer laser Vertex III [29]. The canopy closure in each plot was estimated using a spherical densitometer [30], and the slope was measured with a forest compass [31].…”