Effects of Sydney Coastal Dry Sclerophyll Forest Litter on Fuels and Fire Behaviour in Hornsby Shire

Abstract

The research described in this thesis used empirical data to characterise the physical and chemical attributes of litter, a component of forest and woodland fuels that is particularly important for propagation of fire. Differences in the amounts, arrangement and flammability of components of litter were determined for Sydney Coastal Dry Sclerophyll Forest, a common vegetation type in the Sydney basin. Surface litter was investigated at study sites at Rofe Park, Hornsby Heights and Halls Creek, Arcadia, New South Wales, Australia. Data describing fuel load, structure and condition of surface litter were gathered using semi- quantitative (fuel hazard score, percent cover score, pin transect) and quantitative methods (surface litter depth, bulk density and soil moisture). Surface litter was sorted into fractions (e.g. whole leaves and twigs, partially and fully decomposed organic material) and used to determine which component or mixture of components were the most flammable. The Simplex Centroid Design method was used to determine optimum mixtures of fuel fractions and a General Blending Model was used to determine the best statistical model fit for flammability metrics (ignitability, combustability, consumability and sustainability). Flammability measures included time to ignition, burn to completion, vertical fuel height, rate of spread, volume consumed, and residual mass fraction. Allocasuarina littoralis drove flammability of litter mixtures. Twigs were the most flammable component in the litter without Allocasuarina littoralis from Halls Creek. Chemical analyses of litter fractions included total carbon and nitrogen. The data was optimised to find the maximum or minimum fit for the Simplex Centroid Design. Knowledge of fuel flammability can help inform management decisions about prioritising mitigation of fire risk.