Garry D. Cook

Reliability of biomass burning estimates from savanna fires: Biomass burning in northern Australia during the 1999 Biomass Burning and Lightning Experiment B field campaign

[1]xa0This paper estimates the two-daily extent of savanna burning and consumption of fine (grass and litter) fuels from an extensive 230,000 km2 region of northern Australia during August-September 1999 encompassing the Australian continental component of the Biomass Burning and Lightning Experiment B (BIBLE B) campaign [Kondo et al., 2002]. The extent of burning for the study region was derived from fire scar mapping of imagery from the advanced very high resolution radiometer (AVHRR) on board the National Oceanic and Atmospheric Administration (NOAA) satellite. The mapping was calibrated and verified with reference to one Landsat scene and associated aerial transect validation data. Fine fuel loads were estimated using published fuel accumulation relationships for major regional fuel types. It is estimated that more than 43,000 km2 was burnt during the 25 day study period, with about 19 Mt of fine (grass and litter) fuels. This paper examines assumptions and errors associated with these estimates. It is estimated from uncalibrated fire mapping derived from AVHRR imagery that 417,500 km2 of the northern Australian savanna was burnt in 1999, of which 136,405 km2, or 30%, occurred in the Northern Territory study region. Using generalized fuel accumulation equations, such biomass burning consumed an estimated 212.3 Mt of fine fuels, but no data are available for consumption of coarse fuels. This figure exceeds a recent estimate, based on fine fuels only, for the combined Australian savanna and temperate grassland biomass burning over the period 1990–1999 but is lower than past estimates derived from classification approaches. We conclude that (1) fire maps derived from coarse-resolution optical imagery can be applied relatively reliably to estimate the extent of savanna fires, generally with 70–80% confidence using the approach adopted here, over the major burning period in northern Australia and (2) substantial further field assessment and associated modeling of fuel accumulation, especially of coarse fuels, is required.

Variation in vegetative water use in the savannas of the North Australian Tropical Transect

Abstract The decline in tree density on sandy soils in savannas is highly correlated with declining mean annual rainfall along the North Australian Tropical Transect (NATT). We re-analyse various data on water use by individual trees and argue that a common relationship can be used to estimate annual water use by tree stands along the NATT from ca. 600 mm mean annual rainfall to at least 1600 mm. Where rainfall is less than 600 mm, trees of a given size use less water than at sites where rainfall is higher. We use these relationships to relate water use at the stand scale with mean annual rainfall along the NATT. From this we show that the empirical data imply that the minimum depth of sandy soil that needs to be exploited by trees declines with increasing aridity along the NATT from more than 5 m to less than 1 m. This finding is consistent with other observations and the pattern that with increasing aridity, an increasing proportion of rainfall coming from isolated storms rather than from periods of extended monsoon activity. Abbreviation: NATT = North Australian Tropical Transect.

Carbon accounting, land management, science and policy uncertainty in Australian savanna landscapes: introduction and overview

ACooperative Research Centre for Tropical Savannas Management, CSIRO Sustainable Ecosystems, PMB 44 Winnellie, NT 0810, Australia. BCooperative Research Centre for Tropical Savannas Management, Charles Darwin University, Darwin, NT 0909, Australia. CCooperative Research Centre for Greenhouse Accounting, GPO Box 475, Canberra, ACT 2601, Australia. DQueensland Department of Natural Resources and Mines, 80 Meiers Road, Indooroopilly, Qld 4068, Australia. EBiodiversity Conservation, Department of Natural Resources, Environment and The Yartz, PO Box 496, Palmerston, NT 0831, Australia. FCSIRO Publishing, PO Box 1139, Collingwood, Vic. 3066, Australia. GCorresponding author. Email: dick.williams@csiro.au

Stable Isotope Signatures and Landscape Functioning in Banded Vegetation in Arid-Central Australia

We examined how the measurement of stable carbon and nitrogen isotopes in soils, vegetation and invertebrates can contribute to understanding landscape processes in mulga Acacia aneura ecosystems characterised by alternating wooded groves and intergroves. Our analyses showed that greater leakiness of water from intergroves at the landscape scale tended to promote more conserving physiology at the plant scale. Thus isolated mulga trees in intergroves probably have higher water use efficiency than those in groves. Both trees and grasses in the intergroves have a greater reliance on recycled nitrogen than plants in the groves for which recently fixed N was a substantial source. Grasses in the intergroves had higher N concentrations than those in the groves despite the soil having lower N concentrations. A lack of variation in the isotopic signature of surface soil N suggested that the lower N concentrations in soils of intergroves than groves is due to lower rates of input and not shorter residence times. Stable isotopic signatures of invertebrates showed a diversity of feeding strategies amongst termite species and indicated symbiotic N fixation in two species. There was no relationship between the dependence on N fixation and the habitat preference or diet of termites. Our results suggest that with cautious interpretation, stable isotope signatures could contribute to understanding other ecosystems where patch-interpatch functioning is an important landscape process.