Extreme wildfire behaviour in 3-year-old fuels in a Western Australian mixed Eucalyptus forest

Summary

This paper describes the behaviour of an intense wildfire which burnt through three-year-old fuels in open forest of jarrah (Eucalyptus marginata), marri (E. calophylla) and karri (E. diversicolor) near Manjimup, W.A. The fire occurred during very dry fuel conditions which resulted from record high air temperatures (maximum 43.5°C) following a rainless period of twenty eight days. Fire danger at the time was Extreme, with a peak McArthur Forest Fire Danger Index of 65. The fire crowned extensively in mixed-aged jarrah/marri stands, and it is proposed that crown fire initiation was facilitated by the substantial component of sapling and pole-sized regrowth which provided a vertically continuous fuel structure. Concentrated spotting occurred up to 2km downwind of the fire, and an isolated spot fire developed 8km away. During an initial run under north-westerly winds the fire travelled 2.2km with an average forward rate of spread of 1300m/h, which is somewhat faster than predicted by either the Western Australian Forest Fire Behaviour Tables or the McArthur Forest Fire Danger Meter. The relatively low fuel loads in the area appear to have assisted in the rapid containment of the fire once burning conditions moderated.