Fire-driven dynamic mosaics in the Great Victoria Desert, Australia - 1. Fire geometry

The dominant ground cover in the Great Victoria Desert is porcupine grass o r spinifex, a fire-prone perennial grass that grows in hummocks or tussocks . Lightning sets hundreds of wildfires annually in inland arid Australia, g enerating an ever changing spatial-temporal patchwork of habitats that diff er in their state of post-fire recovery. The spatial configuration of this patchwork is determined by the size, shape, frequency and inter-spatial rel ationships of fires, and is likely to play a vital role in the maintenance of the desert biota. Chronosequences of satellite imagery spanning the year s 1972-1991 are used to extract and describe the geometry of over 800 fires from fire scars. In the imagery study area, an average of 43 fires occur a nnually, fire size frequency distributions are roughly log-normal with mild right skew, with average area of 28 km(2), burning between 2 and 5% of the burnable landscape each year. Average fire return interval is estimated to be at least 20 years. These empirical findings are an important prerequisi te for developing a more sophisticated understanding of the dynamics of the fire cycle in this ecosystem.