Fuel consumption rates in resprouting eucalypt forest during hazard reduction burns, cultural burns and wildfires

Accurate estimation of emissions from biomass burning and their impact on carbon storage requires pre and post-fire plot measurement of fuel consumption across a range of forest types and fire severities, and this information is currently far from comprehensive in Australia or elsewhere. We measured fine and coarse fuels in 44 sites before and after 20 fires including cultural burns, hazard reduction burns and wildfires in resprouting dry sclerophyll (eucalypt) forests in the Sydney region of Australia. We compared consumption among the classes of fire severity and fire types. Most of the fires removed the great majority of fine litter and near surface fuels (mean 68% and 94% respectively) but a smaller and more variable percentage of other fine components and coarse fuels. Consumption was largely a function of pre-fire fuel levels. However, percentage consumption varied according to fire severity. Remaining fuel was negatively, and fresh fuel (i.e. immediate post-fire inputs) positively related to fire severity so that the two were in balance for litter, twigs and coarse woody debris. A higher proportion of twigs and coarse woody debris were consumed in hazard reduction and wildfires than in cultural burns, and more canopy and tree wood was consumed in wildfire than the other fire types. Total fuel consumption was 12.8 t ha−1 (13% of pre-fire) in cultural burns, 75.7 t ha−1 (27%) in hazard reductions, and 123.5 t ha−1 (38%) in wildfires. This was dominated by tree biomass consumption (69% of total). Our estimates for hazard reduction burns are higher than most previous studies from Australian forests, probably because our fires spanned a greater range of severities. Our study provides a benchmark for estimating fire emissions and carbon dynamics for the region and will contribute to improving predictions of the impact of hazard reduction burns on fire behaviour and smoke emissions.