Direct measurements of the seasonality of emission factors from savanna fires in northern Australia

Abstract

[1] Current good practice guidelines for national greenhouse gas inventories requires that seasonal variation in emission factors from savanna fires be considered when compiling national accounts. African studies concluded that the emission factor for methane decreases during the dry season principally due to curing of the fuels. However, available data from Australian tropical savannas shows no effect of seasonality on emission factors, consistent with observations that the fine fuels appear to cure fully soon after the start of the fire season. To test whether the seasonality in greenhouse gas emission factors reported for Africa also occurs in Australia, methane and nitrous oxide emission factors were measured in early and in late dry season fires in Western Arnhem Land, a region typical of much of the northern Australia savanna zone. We found no significant seasonality in methane emission factors, but there was substantial variation in emission factors associated with inter-fire differences in vegetation and fuel. This variation could be explained almost completely by combustion efficiency. Nitrous oxide emission factors were not related to combustion efficiency but showed some variation across vegetation and fuel size class. Both methane and nitrous oxide emission factors were consistent with previous work in northern Australia and with some published values from Africa. The absence of a significant seasonal trend in emission factors indicates that savanna fire emissions in northern Australia can be managed by strategic prescribed burning.

Rapid response of habitat structure and aboveground carbon storage to altered fire regimes in tropical savanna

“…These patterns are consistent with the trend of lower greenhouse gas emissions under early dry season fires, relative to late fires (Meyer et al, 2012) and point to the importance of available fuel load and its characteristics (greater herbaceous volume and lower moisture content late in the dry season) in understanding fire induced structural change in savannas. Murphy et al (2013) suggested that the moderation of fire regimes in northern Australia is likely to increase carbon storage 5 in woody biomass, but the extent to which woody biomass can increase in these savannas is highly uncertain.…”

“…There are widespread concerns that such fire regimes are linked to dramatic declines in faunal populations, through the removal of ground layer vegetation (Lawes et al, 2015;Legge et al, 2015;Woinarski et al, 2015). Methane and nitrous oxide emissions from savanna fires are included in Australia's national greenhouse-gas accounts, and are responsible for approximately 3% of total accountable greenhousegas emissions (Meyer et al, 2012). There is considerable interest in reducing the frequency and intensity of fires in northern ii) how vegetation structural diversity and carbon storage respond to increasing fire frequency; and iii) the structural impact of higher-intensity, late-season fires compared to early-season fires.…”

Can savanna burning projects deliver measurable greenhouse emissions reductions and sustainable livelihood opportunities in fire-prone settings?

“…Particular methodological challenges are to ensure that the application is supportive of local cultural practices and requirements, and that mitigating early dry season fire management activities actually reduce emissions-i.e. are conducted when fuels are fully cured rather than still being moist which would result in higher CH 4 emissions (Meyer et al 2012). A first step therefore is to work with local communities to assess the applicability of, and where practicable appropriately modify, the model.…”

“…An essential premise underlying Australia's recently developed savanna burning methodology (Russell-Smith et al 2009a;DCCEE 2012;Meyer et al 2012) is that reductions in fire frequency result in reduced GHG emissions because more of the fuel biomass (mostly grass and leaf litter) is decomposed biologically through pathways that, compared with savanna fires, produce lower relevant emissions per unit biomass consumed (Cook and Meyer 2009). In unburnt north Australian savannas, emissions of CH 4 and N 2 O arising from biological decomposition pathways are likely to be less than 10 % than that from fire (Cook and Meyer 2009;Jamali et al 2011).…”

Biomass burning emissions in north Australia during the early dry season: an overview of the 2014 SAFIRED campaign

“…In Australia approximately 550 000 km 2 of tropical and arid savannahs burn each year (Meyer et al, 2012;RussellSmith et al, 2007), representing 7 % of the continent's land area. In the tropical north of Australia, the fires during the early dry season in May/June consist of naturally occurring and accidental fires, as well as prescribed burns under strategic fire management practice to reduce the frequency and intensity of more extensive fires in the late dry season in October and November (Andersen et al, 2005).…”