HEAT-BUDGET AND FIRE BEHAVIOR ASSOCIATED WITH THE OPENING OF SEROTINOUS CONES IN 2 PINUS SPECIES

We have constructed a heat budget for the transient heating of cones showing that there is a logarithmic relationship between the time (sec) to serotinous cone opening, releasing viable seeds, or cone ignition and temperature (degrees-K) in the convective column above a fire. The rate of opening at a given temperature is controlled by a thermal time constant which is the ratio of the thermal resistance of a cone to convection, to the heating capacity of a cone by conduction. The observed times to cone opening and ignition fit the logarithmic relationship as predicted by the heat budget model. In order to understand the fire behaviour that results in cone opening and ignition, we changed the variables of temperature and time to the fire behaviour variables of fire intensity (kW/m) and fire rate of spread (m/min). Cones borne high in the canopy open in fires with low rates of spread and high fuel consumption, where intensity = rate of spread x fuel consumption x heat of ignition, but not when the rate of spread is high and fuel consumption low.