Document: MAT-3-68-24

Effects of deciduous and conifer fuels on predicted fire extinction in the mixedwood boreal forest.

DICKINSON, M.B.* and E.A.JOHNSON

University of Calgary, Calgary, Alberta, Canada. ¹

Abstract:
Deciduous and conifer fuels are thought to differ in their effects on fire extinction. To test this expectation, we used a semi-empirical model to estimate the probability that fires would go out over a range of fuel moisture conditions. In the model, extinction is determined by a ratio of heat sources to heat sinks. Fuel particle low heats of combustion and surface-area-to-volume ratios and fuel loading and depth affect the heat source. The heat required to complete fuel pyrolysis determines the heat sink. Part of the heat sink is accounted for by the heat required to vaporize water which is dependent on fuel moisture calculated from weather records. In stands >30 years old (i.e., >30 years since the last fire), fires were predicted to go out with a probability of 1 on 25% of days in deciduous-dominated stands and 15% of days in conifer-dominated stands during the 1955 to 1998 fire seasons. Consistent with these results, fuel loadings and surface-area-to-volume ratios were lower in deciduous-dominated stands. Though deciduous fuels may inhibit fire spread in older stands during moist periods, in stands <=12 years old, the probability of fire extinction dropped with the amount of deciduous basal area. This result suggests that fuels accumulate more rapidly where regrowth after fire has a large deciduous component. We conclude that during dry periods, only the youngest stands will not carry a fire, but during moist periods, fuel variability becomes increasingly important in determining where on the landscape a fire will or will not spread.

Keywords: fire extinction, fuel characteristics, boreal forest, fire ecology, forest disturbance, landscape ecology.

This abstract is being presented at: 2:45 PM in session:
Oral Session #35: Fire Ecology.