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 (<6 mm diameter) and coarse woody debris (CWD, 6-50 mm 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 700-1700 mm 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.