A LANDSAT MSS-derived fire history of Kakadu National Park, monsoonal northern Australia, 1980-94: seasonal extent, frequency and patchiness.
Abstract
A 15-year fire history (1980-94) was assembled for Kakadu National Park, a 20 000 km2 World Heritage property in monsoonal northern Australia, based on interpretation of LANDSAT MSS imagery sampled at least three times over the 7-month dry season. Detailed ground-truthing was undertaken at the end of the early dry season period (May-July) for both 1993 and 1994; ground-truth data were not available for previous years. Overall agreement was greater than 80% in both years. In sum, these data inspire a relatively high degree of confidence in the interpreted fire history of the Park for any one year, at least at the landscape and habitat scales examined here. An average of 46% of the Park was found to be burnt each year over the 15 years of records, with 25% burnt in the early, and 21% burnt in the late, dry season. The data indicate a pronounced shift from a fire regime dominated by late (typically more intense and potentially extensive) dry season fires up until the mid-1980s, to one dominated by early (typically of low intensity and patchy) dry season fires subsequently. Whereas an average of 55% of lowland savanna habitats has been burnt annually, 28% of habitats occupying both sandstone plateau and riverine landforms have been burnt each year. The great majority of burning in relatively fire-sensitive sandstone habitats continues to be in the late dry season. Data indicate a marked increase in the extent of burning on floodplains, and in associated fire-sensitive Melaleuca forests and lowland rain forests, from 1990: this increase is attributed to increased herbaceous fuel loads associated with the removal of feral Asian water buffalo. Proximity analyses indicate that slightly more early dry season burning has been undertaken close to roads, and at greater distances from settlements: no proximity differences were discernible for fires late in the dry season. Burning has been concentrated close to lowland drainage lines, both in the early and late dry season. Lowland savanna sites are burnt on average 3 out of 5 years. In contrast, the majority of sandstone plateau and riverine floodplain sites have burnt on average 0-4 times and 0-3 times, respectively, over the 15 years of records. The median size of contiguously burnt areas (patches) has been declining steadily over the 15 years of records, from upwards of 300 ha initially to c. 60 ha in 1994. It is concluded that although the assembled data are imperfect in that they under-represent wet season burns and very small fires, are prone to positional errors of up to c. 300 m, and because little confidence can be placed in the sequential fire histories for any 1-ha site, they afford an effective means by which the Park's fire management programme can be monitored, its problems identified, and its needs assessed. The demonstrable utility of this programme has led to its recent extension on other significant properties in monsoonal northern Australia.