Comparison of fire patterns and fire frequency in two tropical savanna bioregions

Fire is a significant determinant of vegetation structure in Australia's savannas and has been implicated in the decline of many species. Identifying the patterns of fire in the landscape is fundamental to understanding vegetation dynamics but variation over time and space makes generalization difficult and specific management recommendations elusive. In order to improve the knowledge base for fire management in tropical savannas, we investigated interregional variation in fire patterns in two Queensland bioregions, the Mount Isa Inlier (MII) and CapeYork Peninsula (CYP), over a 5-year period (1999-2003). Remotely sensed satellite data were used to identify burnt areas on a monthly basis for the western half of the CYP bioregion and about two-thirds of the smaller MII. Fire scars were mapped from JPEG-compressed, low-resolution Landsat images using geographical information system technology and data were investigated to determine annual burning patterns. Patterns were interpreted with regard to meteorological information and recent fire history. The area burnt per annum on western CYP was generally an order of magnitude greater than the area burnt on the MII. In the biggest fire year, nearly 74% (5 295 098 ha) of the CYP landscape burnt, compared with 35% (1 770 771 ha) of the MII landscape. The minimum percentage of the CYP study area burnt in 1 year between 1999 and 2003 was 43.1%, compared with 1.6% for the MII. The reliability and amount of seasonal rainfall was a strong determinant of differences in time of fire occurrence and area burnt between regions. Widespread wildfires were significantly related to above average rainfall in the preceding 12 months in the Mt. Isa area but not in CYP. Rainfall also affected fire frequency. Predictable wet season rainfall on CYP allowed for a biennial fire return interval, while on the semiarid MII, the average fire return interval was 5 years or longer. We conclude that the fire patterns in the semiarid MII are similar to those reported for and Australia, while fire patterns in western CYP are comparable with other mesic savanna areas.