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Mark-recapture studies of northern quoll (Dasyurus hallucatus) were conducted in lowland savanna in Kakadu National Park during two periods: in 1985-87 when total mammal abundance was high, and in 1989-91 when total mammal abundance was low. Population characteristics from these studies are compared with results from a 1977-79 study in sandstone escarpment country 40 km to the south-east and from studies in a range of habitats on the Mitchell Plateau in the Kimberley. Populations in rocky country are most dense with animals often surviving two or three years. In contrast, populations in savanna are more sparse, with males and females rarely surviving beyond one mating season. While all populations seem to undergo an annual period of stress, it is the savanna populations that seem most vulnerable. An analysis of the distribution of northern quolls shows a 75% recent range reduction, from being widespread over much of northern Australia to six smaller rocky regions. Possible causes of the decline include cattle, cane toads and exotic disease.

Fire is a dominant feature of tropical savannas throughout the world, and provides a unique opportunity for habitat management at the landscape scale. We provide the background and methodology for a landscape-scale savanna fire experiment at Kapalga, located in Kakadu National Park in the seasonal tropics of northern Australia. The experiment addresses the limitations of previous savanna fire experiments, including inappropriately small sizes of experimental units, lack of replication, consideration of a narrow range of ecological responses and an absence of detailed measurement of fire behaviour. In contrast to those elsewhere in the world, Australia's savannas are sparsely populated and largely uncleared, with fires lit primarily in a conservation, rather than pastoral, context. Fire management bas played an integral role in the traditional lifestyles of Aboriginal people, who have occupied the land for perhaps 50 000 years or more. Currently the dominant fire management paradigm is one of extensive prescribed burning early in tbe dry season (May-June), in order to limit the extent and severity of fires occurring later in the year. The ecological effects of different fire regimes are hotly debated, but we identify geo-chemical cycling, tree demography, faimal diversity and composition, phenology, and the relative importance of fire intensity, timing and frequency, as critical issues. Experimental units ('compartments') at Kapalga are 15-20 km-catchments, centred on seasonal creeks that drain into major rivers. Each compartment has been burnt according to one of four treatments, each replicated at least three times: 'Early'-fires lit early in the dry season, which is the predominant management regime in the region; 'Late'-fires lit late in the dry season, as occurs extensively in the region as unmanaged 'wildfires'; 'Progressive'-fires lit progressively throughout the dry season, such that different parts of the landscape are burnt as they progressively dry out (believed to approximate traditional Aboriginal burning practices); and 'Unburnt'-no fires lit, and wildfires excluded. All burning treatments have been applied annually for 5 years, from 1990 to 1994. Six core projects have been conducted within the experimental framework, focusing on nutrients and atmospheric chemistry, temporary streams, vegetation, insects, small mammals, and vertebrate predators. Detailed measurements of fire intensity have been taken to help interpret ecological responses. The Kapalga fire experiment is multidisciplinary, treatments have been applied at a landscape scale with replication, and ecological responses can be related directly to measurements of fire intensity. We are confident that this experiment will yield important insights into the fire ecology of tropical savannas, and will make a valuable contribution to their conservation management.

No abstract

The distributions of 50 species of termites across five habitat types in Kakadu National Park are described. Open forests are riehest in speeies and monsoon forests are species-poor. The greatest diversity of termites is associated with infertile soils and is probably related to the enhanced role of termites in these nutrientimpoverished sites. Only the riehness of livewood feeders is associated with disturbance in the form of water buffalo impaet. Pew relationships with physical characteristics of the soil were apparent. Comparisons between continents suggest that lower termites are richer in Australia than on other continents. There are fewer species of soil-feeding termites, but only two of the four subfamilies ofthe higher termites (Termitidae) are present in Australia. There appears to be a eomplementary distribution of areas of high diversity of termites and native herbivorous mammals. This may be due to the ability of termites and other invertebrate groups to exploit low fertility systems and has profound implications for the size structure of the vertebrate community.

Habitat preferences of five species of small mammals were studied on a 6.6 ha trapping grid in heathland on an undulating, deep, sandy podzol at Cranbourne, Victoria. The 120 sites were sorted into groups using a polythetic, agglomerative, non-hierarchical clustering procedure with (i) floristic and (ii) structural data. The dispersion of 4051 trap captures over 28 months was studied in relation to these groupings. Rattus lutreolus showed no preference for any of the structural groups, but good differentiation was obtained with the floristic groups. Dispersion of R. lutreolus was related to a sedge-food index, and seasonal change in R. lutreolus dispersion was related to change in rainfall. The preference of R. rattus for areas of wet heath of high structural complexity was best revealed using the structural classification. The results for the other species tended to favour the floristic rather than structural groups. Pseudomys novaehoUandiae and Isoodon obesulus preferred dry heath of a younger successional stage. Mus musculus captures showed a preference for the dry heath generally. This preference was most pronounced in spring when the population was declining.The wet community species (R. lutreolus, R. rattus) tended to be food specialists and habitat generalists and the dry community species P. novaehoUandiae, I. obesulus, M. musculus), exhibited converse traits.

Because of its high frequency and generally low intensity, fire in tropical savannas appears to be a different phenomenon from that in other biomes. A recent study of fire in savanna at Munmarlary in northern Australia, analysed bv detrended correspondence analysis (DCA) concluded that different fire regimens resulted in t^eghgible changes in the vegetation, a conclusion crucial for fire management in the region.Here, we describe the short-term impact of an unusually intense fire in an area of tropical open forest. Tree and shrub mortality of 14.3% was recorded within 6 months of the fire, and the composition of the vegetation was changed because of differences between species in mortality rates, whtch ranged from 4 lo 90%. Analyses of variance (ANOVA) of DCA co-ordinates were unable to detect any change, however. DCA seems inappropriate for analysing vegetation changes after savanna fires, because the floristic changes, cotnpared with those in temperate fire-prone ecosystems, are subtle and multidirectional.Further, it is shown that rather large plot sizes (2-4 ha) are likely to be required to detect fire treatment differences even as great as about 20% of the mean, given the variability of savanna vegetation, and replicates that are likely to be limited in number. A possible solution is to measure the change over time in permanent plots, rather than attempting to detect treatment differences by sampling on a single occasion.

A general decline in populations of some savanna mammal species has occtirred since the mid-1980s in a fairly pristine national park environment in the Australian wet-dry tropics. Terrestrial native rodents have exhibited the greatest decline and marsupials the least. During the same period, waterholes have dried up and the previous strong association of mammals with riparian vegetation has diminished. A regional index of the level of groundwater was developed from 16 unexploited bores fi:om across the northern half of the Northern Territory. Predicted mean groundwater values over 28 years showed a strong increase throughout the 1970s and a similar decrease throughout the 1980s. Using data since 1986, strong correlations between mammal numbers and groundwater levels for the preceding two years, and much weaker relationships with rainfall, were obtained. In turn, the groundwater levels were best correlated with an eight-year running mean of rainfall for both Darwin and Alice Springs and an eleven-year running mean for the Southern Oscillation Index. Extrapolating backward in time, cumulative pressure variation at Darwin showed two extended periods of predicted low groundwater values, 1900s-1920s and 1940s. Both periods were preceded by the last records of a number of now-extinct mammals from central Australia. A third trough in the early 1960s suggests another period of extinction in central Australia, previously unappreciated due to the lack of survey work in the 1950s. Further, by this analysis, the past 20 years has been the best period for mammals since weather records commenced.Analysis of continental-scale distributions of mammals showed evidence of fluctuations suggesting rocky areas are important refuges for some species during periods of low groundwater levels. In contrast to those in savanna habitats, the mammals of the extensive wetland areas fluctuated in harmony with rainfall on a short-term basis except where habitat is flooded. It is the species which occur only in savanna but not also in rocky or wetland habitats which are most at risk.A number of other species-vulnerability characteristics were identified: riparian vegetation specificity; the degree to which they fall within the critical size range (35 g-5.5 kg); degree of semelparity; smallness of population size; and smallness of geographic range. Those savanna species with annual life histories strongly associated with riparian areas are likely to be in greatest jeopardy. The species which appear to be most vulnerable in northwestern Australia are Conilurus penicillatus, Mesembriomys gouldii, Mesenibriomys macrtirus, Antechinus bellus, Phascogale tapoatafa and Rattus ttmneyi.Our recent benign climatic history has coincided with the great public environmental awakening and upsurge in environmental research and management efforts.This historical accident has probably led us to overstate the negative effects of human impact and also our ability to change the course of biological history by ameliorating human impact. Our distorted view of these fac...