Smoldering combustion and plant recruitment.
Miyanishi, Kiyoko*,1, Hogan, Chad2, Johnson, Edward2, 1 University of Guelph, Guelph, ON, Canada2 University of Calgary, Calgary, AB, Canada
ABSTRACT- Post-fire seedling regeneration of most boreal forest trees is limited to areas of the forest floor from which most of the organic layer (duff) overlying the mineral soil has been consumed by smoldering combustion. Smoldering is a slow process, most of which occurs after passage of the flaming front. Thus, once duff is ignited by the flame, its smoldering occurs independently of the fire intensity. Past statistical regression studies have found duff moisture and sometimes duff depth to be significant factors in predicting the average decrease in duff depth. However, such regression models are highly site- and situation-specific and, more importantly, do not address the key issues of the areal extent and spatial patterning of duff removal that determine the availability of seedbed for successful seedling establishment. A more fruitful approach is to develop a spatially distributed physical process-based model of smoldering that can simulate propagation and extinction of smoldering to produce the patchy pattern of duff consumption observed in the forest following wildfires. The model being developed is entirely based on broad principles of physics and involves four stages of the smoldering process: heat transfer, vaporization of water, pyrolysis of duff to produce char, and oxidation of char. Previous physical models of smoldering had identified the fuel variables influencing the rate of smoldering. Some of these variables (e.g., bulk density, thermal conductivity, heat of combustion, heat of oxidation, etc.) would be relatively constant, both spatially and temporally, for duff within a given area while others (depth and moisture content) would be highly variable and thus play a more significant role in determining the patchiness of duff consumption. At this early stage of model development, using crude estimates of the constants, the results being generated have been found to be qualitatively consistent with empirical studies of duff consumption in boreal forest wildfires.
Key words: boreal forest, fire, post-fire regeneration, duff consumption
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