Effects of curing on grassfires: II. Effect of grass senescence on the rate of fire spread

Abstract

The capacity to predict fire dynamics in fuel beds comprised of live and dead fuel components is constrained by our limited understanding of the effects of live fuels on fire propagation. A field-based experimental burning program was conducted to specifically address the effect of the degree of curing, the proportion of dead fuels in the fuel bed, on fire propagation in grasslands. Experimental fires were conducted at two sites characterised by structurally distinct fuels with curing levels varying between 20% and 100%. Fire sustainability experiments showed that fire propagation can occur down to curing levels as low as 20%. Rate of fire spread varied between 41.7 and 102 m min–1 in fully cured fuels and between 2.8 and 43.5 m min–1 in partially cured grasslands. The degree of curing was found to be the best variable describing the damping effect of live fuels in a natural, senescing grassland. Live fuel moisture content by itself was not found to be related to the damping effect of live fuels on the rate of fire spread. Existing models for the effect of grass curing on fire behaviour presently used in Australia were found to under-predict the rate of forward fire spread in partially cured grasslands. A new curing relationship for southern Australian grasslands derived from the study results is proposed.