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Summary 1.A fire history (1980 to the present) developed for Kakadu National Park, derived mostly from manual interpretation of LANDSAT MultiSpectral Scanner (MSS) imagery, was used as the temporal basis for undertaking rapid assessment of the effects of fire regimes on floristically diverse vegetation containing many regionally endemic species, occupying sandstone formations of the Arnhem Plateau, monsoonal northern Australia. 2. Three broad vegetation types were identified through TWINSPAN classification of floristic composition at 108 sample plots: AIIosyrzcavpia-dominated closed forest; open forest/woodland savanna with an annual grass understorey; and open shrubby heath interspersed with perennial hummock grasses. All sampled vegetation occurred on freely draining, oligotrophic substrates derived from sandstone parent materials; grazing and browsing of sampled vegetation were not significant factors. 3. The three fire frequency parameters derived from the assembled fire history ('years unburnt', 'fire frequency', 'shortest interfire interval') were autocorrelated. Correlative analyses between vegetation structure and soil nutrient variables, and 'years unburnt', demonstrated generally increasing shrub densities, fuel loads and soil fertilities with increasing time since last burnt. Identified limitations in assembled data included: substantial between-plot structural variation for respective vegetation types, reflecting diverse ecological and fire histories of individual plots; and inability to describe accurately the important fire regime variable 'fire intensity' from the imagery used. 4. Assessment of the reproductive maturity of obligate seeder shrub species indicated that, whereas vegetation at some sites could tolerate burning after 3-year intervals without loss of floristic diversity, many species required fire-free intervals of more than 5 years, particularly those occupying harsher, rocky sites. In contrast, fine grass and litter fuels were sufficient to support intense fires in all representative situations under late dry season climatic conditions within 1-3 years of having been burnt previously. 5. Published fire history data for the period 1980-94 show that 40% of vegetation occupying sandstone-derived landforms in Kakadu National Park have been burnt at frequencies of at least 1 in 3 years; such fire frequencies evidently cannot be sustained without substantial loss of obligate seeder species, comprising 54% of the sampled shrubby heath flora.

LANDSAT Multi-Spectral Scanner imagery was used to determine aspects of the fire regimes of Kakadu National Park (in the wet-dry tropics of Australia) for the period 1980-1995. Three landscape types recognized in this Park were Plateau, Lowlands and Floodplain. Areas burned in early and late dry seasons each year were documented using a Geographical Information System. Regression analyses were used to examine time trends in the areas burned each year and the interrelationships between early and late dry season burning. The proportions of landscapes having different stand ages (years since fire), and the proportions having had different fire intervals, were compared with results expected from the simplest random model (i.e. one in which the probability of ignition at a point [PIP] burning annually was constant). Using overlays of successive stand-age maps, PIP could be calculated as a function of stand age. The Lowlands burned extensively each year; the areas burned by late dry season fires adding to those burned in the early dry season such that around 50-60% of the total area burned annually. Early dry season fires have lower intensities than late dry season fires, on average. Using a theoretically constant PIP and the mean proportion burned per year as the only input, predictions of areas burned as a function of stand age and fire interval were reasonable when compared with the empirical data, but best for the Lowlands landscape. PIP functions for Lowlands and Floodplains had negative slopes, an unexpected result. The nature of these PIP functions may reflect heterogeneity in fire proneness of the various vegetation types within landscapes. The scale of measurement, the scale of variation in vegetation types within a landscape, and the accuracy of the determination of burned areas, are constraints on the accuracy of fire-interval and seasonality determination perceived from an analysis of satellite data.

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