Abstract:
The probability of wildfires, or prescribed fires, occurring in mallee rangelands, is strongly dependent on availability of adequate grass fuel loads. Grass fuels comprise two major elements, a perennial component dominated by the hummock species Triodia scariosa (porcupine grass) and an ephemeral component dominated by the annual/biemial tussock species Stipa nitida (speargrass). Population dynamics and abundance of both fuel elements are, in turn, strongly influenced by rainfall regime, particularly during the seedling recruitment phase. This paper records data on the spatial distributions of different fuels, plant architecture and post-fire seedling recruitment and survivorship of T. scariosa, obtained during field studies on contrasting mallee sites in western New South Wales. In addition, rainfall data extending over c. 100 years were used in a water balance study at one mallee site (Pooncarie); while similar rainfall data were analysed for three mallee sites (Pooncarie, Ivanhoe and Mount Hope) using a filter technique to examine quasi- periodicities of rainfall and potential correlations with known wildfire seasons in the past. Precipitation records from the Meteorological Districts of western New South Wales, and from various towns in the area, were analysed as well. All data sets exhibited strong coherence and the resulting filter curves resembled each other closely, with peaks reflecting 'above-average rainfall' and troughs 'below-average rainfall or drought'- the latter often being associated with El NiiiolSouthern Oscillation events. The management implications of these phenomena, particularly as they relate to major drought events, are discussed in the context of vegetation manipulation based on prescribed fire.