Understanding variability in heat yields of wet sclerophyll forest fuels

Abstract

Background: Fireline intensity is important for understanding fire behaviour. Heat yield – the amount of energy released by fuels, calculated by subtracting energy lost by vaporising moisture from a fuel’s calorific value – is considered the least variable component of fireline intensity. Recent work suggests it may be more variable than assumed, though how it varies between fuels and seasons remains unclear. Aims: This study aims to determine how heat yields vary between fuels and seasons in terms of calorific values, hydrogen content and fuel moisture. Methods: We sampled common wet sclerophyll forest fuels over a year, measuring their moisture content. We determined their calorific value with bomb calorimetry, and hydrogen content with elemental analysis. Key results: Fuel heat yields varied substantially between species and seasons, with some species having large seasonal variations. The heat yields of live fuels were significantly lower than dead fuels. Conclusions: Heat yields are highly variable between fuels. Accounting for species composition and seasonal variation may be important for accurately estimating heat yield at the forest-stand scale. Implications: Heat yields are more variable than previously assumed and have been overestimated in some models. This could have implications for fireline intensity.