Abstract
Fire-prone tropical savanna and grassland systems are a significant source of atmospheric emissions of greenhouse gases. In recent years, substantial research has been directed towards developing accounting methodologies for savanna burning emissions to be applied in Australia’s National Greenhouse Gas Inventory, as well as for commercial carbon trading purposes. That work has focused on woody savanna systems. Here, we extend the methodological approach to include tussock grasslands and associated Melaleuca-dominated open woodlands ( 1,000 mm/annum) regions of northern Australia. Field assessments under dry season conditions focused on deriving fuel accumulation, fire patchiness and combustion relationships for key fuel types: fine fuels − grass and litter; coarse woody fuels − twigs 6 mm diameter; and shrubs. In contrast with previous savanna burning assessments, fire treatments undertaken under early dry season burning conditions resulted in negligible patchiness and very substantial consumption of fine fuels. In effect, burning in the early dry season provides no benefits in greenhouse gas emissions and emissions reductions in tussock grasslands can be achieved only through reducing the extent of burning. The practical implications of reduced burning in higher rainfall northern Australian grassland systems are discussed, indicating that there are significant constraints, including infrastructural, cultural and woody thickening issues. Similar opportunities and constraints are observed in other international contexts, but especially project implementation challenges associated with legislative, political and governance issues.
Highlights
It is widely recognized that, together with interactions with seasonal moisture availability, nutrients and herbivory, fire regimes play a critical role in modifying the floristic composition, vegetation structure and dynamics of tropical savanna and associated grassland systems (Scholes and Archer 1997; Bond 2008; Lehmann et al 2011)
Pyrolized fuel is the product of: the area exposed to fire, taking into account spatial patchiness, x the accumulated fuel load (FA) x the burning efficiency (BEF), defined as the mass of fuel exposed to fire that is pyrolized
Sample plots were dominated by perennial graminoids (Figure 2), characteristic of open grassland systems in Cape York Peninsula (Queensland Herbarium 2009)
Summary
It is widely recognized that, together with interactions with seasonal moisture availability, nutrients and herbivory, fire regimes play a critical role in modifying the floristic composition, vegetation structure and dynamics of tropical savanna and associated grassland systems (Scholes and Archer 1997; Bond 2008; Lehmann et al 2011). It is recognized that fire regimes in tropical savanna and grassland systems have substantial effects on carbon stocks and dynamics in living biomass components and associated dead fractions In addition to effects of fire regimes on biomass/carbon stocks, fire-prone savanna and grassland systems are a globally significant source of annual greenhouse gas (GHG) emissions. As the only Tier 1 country with substantial savanna coverage, includes savanna burning emissions in its National Greenhouse Gas Inventory (NGGI); typically accountable GHG emissions annually contribute ~3% of Australia’s NGGI (ANGA 2011). Accountable greenhouse gas emissions from Australian savanna burning are predominantly associated with anthropogenic ignition sources (Russell-Smith et al 2007)
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