Multi-century times-since-fire and prior fire interval determine biomass carbon stocks in obligate-seeder eucalypt woodlands

Background Understanding the influence of fires on terrestrial carbon stocks is important for informing global climate models and underpinning land management-based carbon markets. Aims To quantify biomass carbon in south-western Australia’s Great Western Woodlands – the world’s largest extant Mediterranean-climate woodland – with time-since-fire and prior fire interval. Methods Plot-based measurement of live and dead tree and shrub size, woody debris volume and litter mass across a ~400-year chronosequence to calculate biomass carbon. Key results Biomass carbon increased with time-since-fire, reaching >65 Mg C ha−1, although the rate of increase declined in mature woodlands. Biomass carbon decreased after fire in these obligate-seeder woodlands, while a longer prior fire interval buffered carbon fluxes through retained large standing dead trees and fallen woody debris. Conclusions The current age class distribution of the ~95,000 km2 of eucalypt woodlands in the region may support ~0.453 Pg C. Further refinement of carbon estimates explicitly considering variation in woodland type and climate, a continuous woodland age distribution and soil carbon are required to underpin a carbon methodology. Implications Biomass carbon would be maximised by reducing the extent of bushfires impacting woodlands, focussing on existing mature stands that support the greatest carbon stocks.