CSIRO PUBLISHING www.publish.csiro.au/journals/ijwf International Journal of Wildland Fire, 2003, 12, 333–340 Fire impacts on surface heat, moisture and carbon fluxes from a tropical savanna in northernAustralia J. Beringer A,D , L. B. Hutley B , N. J. Tapper A , A. Coutts A , A. Kerley A andA. P. O’Grady B,C A School of Geography and Environmental Science, Monash University, PO Box 11A, Clayton, Vic. 3800, Australia. B Faculty of Science, Information Technology & Education, Charles Darwin University, Darwin, NT 0909,Australia. C Present address: CRC for Sustainable Forest Products, CRC/CSIRO, GPO Box 252-12, Hobart, Tas. 7001, Australia. D Corresponding author. Telephone: +61 3 9905 9352; fax: +61 3 9905 2948; email: jason.beringer@arts.monash.edu.au This paper is derived from a presentation at the conference ‘Fire and savanna landscapes in northern Australia: regional lessons and global challenges’, Darwin,Australia, 8–9 July 2002 Abstract. Savannas form a large fraction of the total tropical vegetation and are extremely fire prone. We measured radiative, energy and carbon exchanges over unburned and burned (both before and after low and moderate intensity fires) open forest savanna at Howard Springs, Darwin, Australia. Fire affected the radiative balance immediately following fire through the consumption of the grass-dominated understorey and blackening of the surface. Albedo was halved following fire of both intensities (from 0.12 to 0.07 and from 0.11 to 0.06 for the moderate and low intensity sites, respectively), but the recovery of albedo was dependent on the initial fire intensity. The low intensity fire caused little canopy damage with little impact on the surface energy balance and only a slight increase in Bowen ratio. However the moderate fire resulted in a comprehensive canopy scorch and almost complete leaf drop in the weeks following fire. The shutdown of most leaves within the canopy reduced transpiration and altered energy partitioning. Leaf death and shedding also resulted in a cessation of ecosystem carbon uptake and the savanna turned from a sink to a source of carbon to the atmosphere because of the continued ecosystem respiration. Post- fire, the Bowen ratio increased greatly due to large increases in sensible heat fluxes.These changes in surface energy exchange following fire, when applied at the landscape scale, may have impacts on climate through local changes in circulation patterns and changes in regional heating, precipitation and monsoon circulation. Additional keywords: surface energy exchanges; Howard Springs; albedo; fire intensity; eddy covariance; Northern Territory. Introduction Tropical savanna ecosystems account for 11.5% of the global landscape (Scholes and Hall 1996). Up to 75% of this land- scape burns annually (Hao et al. 1990) and 50% of all biomass burning in tropical regions originates from savannas (Hao and Liu 1994). The wet–dry tropics of northern Australia feature extensive tracts of savanna vegetation which occupy ∼2 mil- lion km 2 .This area is equivalent to 12% of the world’s tropical savanna estate, making this savanna biome of global signifi- cance. Fire is arguably the greatest natural and anthropogenic environmental disturbance in this region.Vast tracts are burnt each year by pastoralists, Aboriginal landholders and conser- vation managers (Russell-Smith et al. 2000; Williams et al. 2002). For example, in the relatively mild fire year of 1992, 74 000 km 2 (5.5% of the total land area) of the Northern Territory was burnt (Beringer et al. 1995), by far the largest proportion being savanna landscape. This ‘poor’ fire year consumed an estimated 29.5 × 10 6 tonnes of biomass and was associated with a likely release of more than 13 Tg of carbon products to the atmosphere (Beringer et al. 1995). Russell- Smith et al. (2000) provide an estimate of 244 000 km 2 and 242 000 km 2 for the total area of northern Australia (at least partially) burnt in 1997 and 1998, respectively. While extensive, these frequent savanna fires are of rel- atively low intensity when compared to the infrequent but intense fires of southern Australia (Williams et al. 1998, 2002). Fire intensity is seasonal, with early dry season fires of low intensity (<1000 kW m −1 ), causing minimal canopy damage, with intensity increasing as the dry season pro- gresses and fuel load accumulates and cures. However, by the late dry season and pre-monsoonal period (August–October), fire intensity can be an order of magnitude greater (Williams © IAWF 2003 10.1071/WF03023 1049-8001/03/030333