Fuel and fire behaviour in semi-arid mallee-heath shrublands

An experimental burning program was set up in South Australia aimed at characterizing fuel dynamics and fire behaviour in mallee-heath woodlands. Fuel complexes in the experimental area comprised mallee and heath vegetation with ages (time since fire) ranging from 7 to 50 years old. Dominant overstorey mallee vegetation comprised Eucalyptus calycogona, E. diversifolia, E. incrassate and E. leptophylla. A total of 66 fires were completed. The range of fire environment conditions within the experimental fire dataset were: air temperature 15 to 39°C; relative humidity 7 to 80%; mean 10-m open wind speed 3.6 to 31.5 km/h; Forest Fire Danger Index 1.7 to 46. Total fuel load ranged from 0.38 kg/m2 in young (7-year old) mallee to 1.0 kg/m2 in mature stands. Fire behaviour measurements included rate of spread, flame geometry, residence time and fuel consumption. Measured rate of spread ranged between 0.8 and 55 m/min with fireline intensity between 144 and 11,000 kW/m. The dataset provided insight into the threshold environment conditions necessary for the development of a coherent flame front able to overcome the fine scale fuel discontinuities that characterise the semi-arid mallee-heath fuel types and support self-sustained fire propagation. The data also provided a better understanding of the variables determining the behaviour of selfsustained fires, including rate of fire spread, flame dimensions, crowning and spotting activity.