Fuel Dynamics and Fire Spread in Spinifex Grasslands of the Western Desert

Spinifex grasslands, characterised by the dominance of perennial hummock grasses of the genus Triodia, cover some 43% of Western Australia. The combination of the physical structure of the vegetation and the often extreme weather conditions makes spinifex grasslands highly flammable. Historically, lightning and burning by Aboriginal people maintained much of the grasslands as a fine-grained mosaic of vegetation at different seral stages providing diverse habitats. Where traditional Aboriginal burning has ceased, large summer wildfires have reduced habitat diversity. In many areas there is a need to reintroduce anthropogenic burning to re-establish habitat diversity at finer scales as well as to protect human life, property and cultural values. An understanding of fuel dynamics and fire behaviour is fundamental to managing fire in these landscapes. Spinifex grasslands have the potential to re-burn 5-7 years after fire, depending on rainfall, but can take 18-20 years to reach full maturity as a fuel. Because of the discontinuous nature of the vegetation, there are thresholds of combinations of fuel load, fuel moisture and wind speed that need to be exceeded before fire will spread. Once thresholds have been exceeded, fires have the potential to spread rapidly, especially under high wind speeds. In this paper we present a revised empirical model for predicting threshold fuel and weather conditions for fire initiation and subsequent rate of spread over a broad range of fuel and weather conditions.