Land Use Change In Australia’s Tropical Savanna Woodlands: Greenhouse Gas Emissions From Deforestation And Conversion To Agriculture

Wednesday, 16 December 2015
Poster Hall (Moscone South)
Lindsay B Hutley1, Mila Bristow1,2, Jason Beringer3, Stephen L Livesley4 and Stefan K Arndt4, (1)Charles Darwin University, Casuarina, NT, Australia, (2)Northern Territory Government, Department of Primary Industry and Fisheries, Darwin, Australia, (3)University of Western Australia, Crawley, WA, Australia, (4)The University of Melbourne, Ecosystem and Forest Sciences, Melbourne, Australia
Clearing and burning of tropical savanna leads to globally significant emissions of greenhouse gases (GHG), although there is large uncertainty relating to the magnitude of this flux. Australia’s tropical savannas are 12% of global savanna extent and are largely intact; however there is currently a focus on agricultural expansion across northern Australia involving clearing for primary production. Eddy covariance and soil chamber methods were used over almost 2 years to quantify CO2 and non-CO2 fluxes from savanna that was cleared and prepared for agriculture (CS). Fluxes from an uncleared site (UC) were also monitored. Carbon fluxes from both sites were similar (NEE -0.23 Mg C ha-1 month-1) for the 5.4 months prior to clearing, a period spanning the late dry to mid-wet season. Fluxes were monitored for a further 17 months through a dry-wet-dry climate cycle and phased land use change which included clearing and a debris curing phase, followed by burning and soil preparation for cropping. Over this period (excluding the managed fire), the CS site was a source of +0.43 Mg C ha-1 month-1 compared to a net sink at the UC site of -0.05 Mg C ha-1 month-1. Woody debris from clearing (30.9 Mg C ha-1) was removed from the site via burning in the late dry season and emission factors were used to calculate emissions of CO2, CH4 and N2O which totalled 138.0 Mg CO2-e ha-1. Over the 17 months of monitoring this land transformation, emissions were +9.7 Mg CO2-e ha-1 month-1 compared to a sink of -0.17 Mg CO2-e from the UC site. Using these emissions and LUC scenarios at catchment to regional scales suggest proposed clearing for agriculture could significantly increase the region’s fire-dominated GHG emissions. These data are essential for both land-atmosphere models as well as decision support tools that inform trade-offs between greenhouse gas accounting, conservation and development goals.