Although biomass burning of savannas is recognised as a major global source of greenhouse gas emissions, quantification remains problematic with resulting regional emissions estimates often differing markedly. Here we undertake a critical assessment of Australia’s National Greenhouse Gas Inventory (NGGI) savanna burning emissions methodology. We describe the methodology developed for, and results and associated uncertainties derived from, a landscape-scale emissions abatement project in fire-prone western Arnhem Land, northern Australia. The methodology incorporates (i) detailed fire history and vegetation structure and fuels type mapping derived from satellite imagery; (ii) field-based assessments of fuel load accumulation, burning efficiencies (patchiness, combustion efficiency, ash retention) and N : C composition; and (iii) application of standard, regionally derived emission factors. Importantly, this refined methodology differs from the NGGI by incorporation of fire seasonality and severity components, and substantial improvements in baseline data. We consider how the application of a fire management program aimed at shifting the seasonality of burning (from one currently dominated by extensive late dry season wildfires to one where strategic fire management is undertaken earlier in the year) can provide significant project-based emissions abatement. The approach has wider application to fire-prone savanna systems dominated by anthropogenic sources of ignition.

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Distributions of¯ying-fox (Pteropus alecto and P. scapulatus) were examined in relation to use of habitat in the essentially natural landscape of northern Australia. There were differences between the species in terms of the vegetation used for roosting and foraging, which were related to the reproductive cycle and seasonal variation in temperature, rainfall and the availability of preferred foods. Important habitats of P. alecto varied seasonally and included¯oodplain, mangrove, monsoon rainforest, Melaleuca open-forest, and Eucalyptus miniata/E. tetrodonta open-forest and woodland. The minimum scale at which conservation of P. alecto should be attempted is in the order of 5000 km 2 , based on seasonal patterns of habitat use. The size of this area will make conservation via traditional reserves dif®cult and conservation of important habitats outside reserves will be needed. Habitats protected for the bene®t of P. alecto will also bene®t P. scapulatus but because P. scapulatus is more mobile, displays greater yearly variation in distribution and is less well understood than P. alecto, appropriate conservation actions are less certain.

In this study, systematic variation in tree morphology across a rainfall gradient in Australia's tropical savanna biome and its implications for carbon stocks and dynamics were quantified. The aim was to support efforts to manage fire regimes to increase vegetative carbon stocks as a greenhouse gas mitigation strategy. The height of trees for a given trunk diameter declines with decreasing rainfall from 2000 to 300 mm and increasing dry season length across the Australian savanna biome. It is likely that increasing dry season length is the main driver of this decline rather declining rainfall per se. By taking account of the response of total basal area to rainfall and soil type, stand structure, and tree height and diameter relationships, the carbon stocks in live trees were estimated to decline from about 34 t ha−1 in the wetter savannas to 6 t ha−1 in the drier savannas. These values are broadly consistent with field‐based estimates. Because of the declining ratio of height to trunk diameter, trees of a given diameter in drier regions will be more likely to be killed by fires of a given intensity than trees in wetter regions. Thus single fires of given intensity are likely to have a greater proportionate impact on live tree carbon stock in drier savannas, but a much greater absolute impact in wetter savannas due to the greater total carbon stock. Projected decreases in early wet season rainfall under climate change scenarios, despite projections of little change in total precipitation in northern Australia, may lead to decreased carbon stock in live trees through two mechanisms: a reduction in total basal area and decreases in tree height for given trunk diameters.