Understanding variability in heat yields of wet sclerophyll forest fuels

Wey Yao Wong; Jane Cawson; Thomas Duff; Patrick Lane; Gary Sheridan

doi:10.1071/WF24227

RESEARCH ARTICLE (Open Access)

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Understanding variability in heat yields of wet sclerophyll forest fuels

Wey Yao Wong

^A ^* , Jane Cawson

^B , Thomas Duff

^C , Patrick Lane ^A and Gary Sheridan

^A

+ Author Affiliations

- Author Affiliations

^A School of Agriculture, Food and Ecosystem Sciences, Faculty of Science, University of Melbourne, Parkville, Vic 3010, Australia.

^B School of Agriculture, Food and Ecosystem Sciences, Faculty of Science, University of Melbourne, Burnley Campus, 500 Yarra Boulevard, Richmond, Vic 3121, Australia.

^C Country Fire Authority, 8 Lakeside Drive, Burwood East, Vic 3151, Australia.

^* Correspondence to: weyw@student.unimelb.edu.au

International Journal of Wildland Fire 34, WF24227 https://doi.org/10.1071/WF24227

Submitted: 13 January 2025 Accepted: 12 July 2025 Published: 20 August 2025

© 2025 The Author(s) (or their employer(s)). Published by CSIRO Publishing on behalf of IAWF. This is an open access article distributed under the Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License (CC BY-NC-ND)

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.

Keywords: calorimetry, energy release, fireline intensity, fuel, fuel moisture, heat of combustion, mountain ash, wildfire.

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