Changes in behaviour of fire in dry eucalypt forest as fuel increases with age

Abstract

This paper describes the conduct and results of a series of high-intensity experimental fires in dry eucalypt forest under summer conditions of high fire danger. Simultaneous experimental fires were conducted at two locations with contrasting understorey and fuel structures that had developed over periods of 2–22years after prescribed burning. Fuel characteristics (load, height, and visual scores that gave a numerical rating of structure) and wind speed were correlated with fire spread, flame height, firebrand density and spotting distance, all of which increased with time since the last fire. The near-surface layer was the dominant stratum affecting headfire rate of spread during these experiments and provided a common descriptor for fuel types that were visually very different because of the characteristics of the understorey shrubs. Visual hazard scores that reflected the quantity and arrangement of surface and near-surface fuel were more strongly correlated with most fire behaviour variables than were the corresponding fuel load variables. Visual ratings of fuel structure should be suitable to include in algorithms to predict fire behaviour and fire threat.