Abstract
Fire severity varies with forest composition and structure, reflecting micrometeorology and the fuel complex, but their respective influences are difficult to untangle from observation alone. We quantify the differences in fire weather between different forest types and the resulting differences in modeled fire behavior. Collection of in-stand weather data proceeded during two summer periods in three adjacent stands in northern Portugal, respectively Pinus pinaster (PP), Betula alba (BA), and Chamaecyparis lawsoniana (CL). Air temperature, relative humidity and wind speed varied respectively as CL < PP < BA, PP < CL < BA, and CL < BA < PP. Differences between PP and the other types were greatest during the warmest and driest hours of the day in a sequence of 10 days with high fire danger. Estimates of daytime moisture content of fine dead fuels and fire behavior characteristics for this period, respectively, from Behave and BehavePlus, indicate a CL < BA < PP gradient in fire potential. High stand density in CL and BA ensured lower wind speed and higher fuel moisture content than in PP, limiting the likelihood of an extreme fire environment. However, regression tree analysis revealed that the fire behavior distinction between the three forest types was primarily a function of the surface fuel complex, and more so during extreme fire weather conditions.
Highlights
Wildfire severity in the Mediterranean basin and its corresponding socioeconomic and environmental impacts have reached unprecedented levels in the last decades due to changes in land use and land cover [1,2]
Differences in air temperature were small, and the greatest dissimilarities were between relative humidity in Betula alba (BA) and in the conifer stands, and amid wind speeds in Pinus pinaster (PP) and Chamaecyparis lawsoniana (CL)
Regarding temperature the three are ranked as PP is greater than CL and BA is greater than
Summary
Wildfire severity in the Mediterranean basin and its corresponding socioeconomic and environmental impacts have reached unprecedented levels in the last decades due to changes in land use and land cover [1,2]. Worsening of the fire problem is expected in the future, as the wildland-urban interface expands and extreme weather events become more frequent [2,7]. The fire environment can be defined as the conditions, influences and modifying forces that affect fire behavior characteristics such as rate of spread, flame size and heat release rate [8]. Three groups of variables shape the fire environment, respectively weather, fuel, and topography. Forest composition and structure influence both microclimatic conditions [9,10] and fuel structure and quantity [11], fire behavior and effects. Stand structure determines in-stand wind speed profile [12,13], solar radiation [10], and dead fuel moisture content [14,15].
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