Indigenous Knowledge and Seasonal Calendar Inform Adaptive Savanna Burning in Northern Australia

Indigenous fire management is experiencing a resurgence worldwide. Northern Australia is the world leader in Indigenous savanna burning, delivering social, cultural, environmental and economic benefits. In 2016, a greenhouse gas abatement fire program commenced in the savannas of south-eastern Arnhem Land in the Northern Territory, managed by the Indigenous Yugul Mangi rangers. We undertook participatory action research and semi-structured interviews with rangers and Elders during 2016 and 2019 to investigate Indigenous knowledge and obtain local feedback about fire management. Results indicated that Indigenous rangers effectively use cross-cultural science (including local and Traditional Ecological Knowledge alongside western science) to manage fire. Fire management is a key driver in the production of bush tucker (wild food) resources and impacts other cultural and ecological values. A need for increased education and awareness about Indigenous burning was consistently emphasized. To address this, the project participants developed the Yugul Mangi Faiya En Sisen Kelenda (Yugul Mangi Fire and Seasons Calendar) that drew on Indigenous knowledge of seasonal biocultural indicators to guide the rangers’ fire management planning. The calendar has potential for application in fire management planning, intergenerational transfer of Indigenous knowledge and locally driven adaptive fire management.

Seasonal fine fuel and coarse woody debris dynamics in north Australian savannas

Several studies have separately explored accumulation of the dominant fuels (grass, fine litter (<6mm diameter) and coarse woody debris (CWD, 6–50mm diameter)) in north Australian savannas. We report an analysis of two longitudinal datasets describing how these three fuel components covary in abundance throughout the year in eucalypt-dominated savanna over a rainfall gradient of 700–1700mm mean annual rainfall (MAR). Our observations concur generally with previous observations that litter accumulation results in a late dry season (LDS) peak in biomass, whereas cured grassy fuels typically are seasonally invariant, and CWD inputs are associated with stochastic severe wet season storms and dry season fires. The distinct LDS litter peak contributes significantly to the potential for LDS fires to be of higher intensity, burn more fuel per unit area and produce greater emissions relative to early dry season (EDS) fires. However, Australia’s current (2018) formal savanna burning emissions avoidance methodology erroneously deems greater EDS fine fuel (grass and fine litter) biomass in four of nine designated vegetation fuel types. The study highlights the need to develop seasonally dynamic modelling approaches that better account for significant seasonal variation in fine fuel inputs and decomposition.

Contemporary Aboriginal savanna burning projects in Arnhem Land: a regional description and analysis of the fire management aspirations of Traditional Owners

The growth of the carbon industry in Australia over the last decade has seen an increase in the number of eligible offsets projects utilising the savanna burning methods in northern Australia. Many of these projects are operated by Aboriginal people on Aboriginal lands utilising local Aboriginal knowledge and customary burning practice. The present paper reviews existing land management planning documents to describe the aspirations of Traditional Owners in relation to fire management at a regional scale in Arnhem Land. Available data collected in the course of savanna burning operations are then utilised to examine the extent to which the savanna burning projects are meeting these goals. There were six clear goals in relation to fire management within the planning documents across Arnhem Land. Traditional Owners want to: (1) continue the healthy fire management of their country; (2) see fewer wildfires; (3) protect biodiversity; (4) protect culturally important sites; (5) maintain and transfer knowledge; and (6) create a carbon abatement. The results from this paper suggest that although the savanna burning projects are annually variable, these goals are being met. Importantly, the present paper clearly communicates a description of contemporary fire management from the perspective of Traditional Owners at a broad regional scale.

Quantifying the relative importance of greenhouse gas emissions from current and future savanna land use change across northern Australia

The clearing and burning of tropical savanna leads to globally significant emissions of greenhouse gases (GHGs); however there is large uncertainty relating to the magnitude of this flux. Australia's tropical savannas occupy the northern quarter of the continent, a region of increasing interest for further exploitation of land and water resources. Land use decisions across this vast biome have the potential to influence the national greenhouse gas budget. To better quantify emissions from savanna deforestation and investigate the impact of deforestation on national GHG emissions, we undertook a paired site measurement campaign where emissions were quantified from two tropical savanna woodland sites; one that was deforested and prepared for agricultural land use and a second analogue site that remained uncleared for the duration of a 22-month campaign. At both sites, net ecosystem exchange of CO2 was measured using the eddy covariance method. Observations at the deforested site were continuous before, during and after the clearing event, providing high-resolution data that tracked CO2 emissions through nine phases of land use change. At the deforested site, post-clearing debris was allowed to cure for 6 months and was subsequently burnt, followed by extensive soil preparation for cropping. During the debris burning, fluxes of CO2 as measured by the eddy covariance tower were excluded. For this phase, emissions were estimated by quantifying on-site biomass prior to deforestation and applying savanna-specific emission factors to estimate a fire-derived GHG emission that included both CO2 and non-CO2 gases. The total fuel mass that was consumed during the debris burning was 40.9 Mg C ha−1 and included above- and below-ground woody biomass, course woody debris, twigs, leaf litter and C4 grass fuels. Emissions from the burning were added to the net CO2 fluxes as measured by the eddy covariance tower for other post-deforestation phases to provide a total GHG emission from this land use change. The total emission from this savanna woodland was 148.3 Mg CO2-e ha−1 with the debris burning responsible for 121.9 Mg CO2-e ha−1 or 82 % of the total emission. The remaining emission was attributed to CO2 efflux from soil disturbance during site preparation for agriculture (10 % of the total emission) and decay of debris during the curing period prior to burning (8 %). Over the same period, fluxes at the uncleared savanna woodland site were measured using a second flux tower and over the 22-month observation period, cumulative net ecosystem exchange (NEE) was a net carbon sink of −2.1 Mg C ha−1, or −7.7 Mg CO2-e ha−1. Estimated emissions for this savanna type were then extrapolated to a regional-scale to (1) provide estimates of the magnitude of GHG emissions from any future deforestation and (2) compare them with GHG emissions from prescribed savanna burning that occurs across the northern Australian savanna every year. Emissions from current rate of annual savanna deforestation across northern Australia was double that of reported (non-CO2 only) savanna burning. However, if the total GHG emission, CO2 plus non-CO2 emissions, is accounted for, burning emissions are an order of magnitude larger than that arising from savanna deforestation. We examined a scenario of expanded land use that required additional deforestation of savanna woodlands over and above current rates. This analysis suggested that significant expansion of deforestation area across the northern savanna woodlands could add an additional 3 % to Australia's national GHG account for the duration of the land use change. This bottom-up study provides data that can reduce uncertainty associated with land use change for this extensive tropical ecosystem and provide an assessment of the relative magnitude of GHG emissions from savanna burning and deforestation. Such knowledge can contribute to informing land use decision making processes associated with land and water resource development.

Quantifying the relative importance of greenhouse gas emissions from current and future savanna land use change across northern 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 occupy over 25 % of the continental land mass and have a potential to significant influence the national greenhouse gas budget, particularly because they are the focus of likely agricultural expansion. To investigate the role of deforestation on GHG emissions, a paired site approach was used. The CO2 exchange was measured from two tropical savanna woodland sites, one that was cleared, and a second analogue site that remained uncleared for a 22 month observation period. At both sites, net ecosystem exchange (NEE) was measured using the eddy covariance (EC) method. Observations at the cleared site was continuous before, during and after the clearing event, providing high resolution data that tracked CO2 emissions through multiple phases of land use change. At the cleared site, post-clearing debris was allowed to cure for 6 months and was subsequently burnt, followed by extensive soil preparation for cropping. Emissions were estimated from the debris fire by quantify the on-site biomass prior to clearing and applying savanna-specific emissions factors to estimate a fire-derived GHG emission. This was added to net CO2 fluxes as measured by the eddy covariance tower giving a total GHG emission of 154 Mg CO2-e ha−1 from a savanna woodland with a total fuel load (above- and below- ground woody debris, course woody debris, litter plus C4 grass fuel) of 40.9 Mg C ha−1. This emission was dominated by debris combustion from the fire event, which was 83 % of the total emission, the remained from soil emissions and decay of debris during the curing period prior to burning. Soil disturbance from ploughing and site preparation for cropping was responsible for almost 10 % of the total emission. Fluxes at the uncleared site were tracked using an additional flux tower for 668 days and over this period, cumulative NEE was −2.1 Mg C ha−1, a net carbon sink. Estimated emissions for this savanna type were then upscaled to provide estimates of the magnitude of emissions from any future deforestation. At current rates of deforestation, savanna burning is as significant a source of GHG emissions as deforestation, with fire emissions occurring every year across this savanna biome. However, expanded deforestation could exceed fire emissions and a clearing scenario was examined which suggested clearing over and above current rates could add up to 5 % to Australia’s national GHG account, depending on the annual rate of deforestation. This bottom-up study provides data that can reduce uncertainty associated with land use change for this extensive tropical ecosystem and provide an assessment of the relative magnitude of GHG emissions from savanna burning and deforestation as well as informing northern land use decision making processes.