Mitigation of emissions from wildfires in Australia: potential for use of managed prescribed fire in eucalypt dominated vegetation, present and future. (Invited)

Species of Eucalyptus and other closely related genera dominate woodlands and forests in the moist regions of tropical and temperate Australia. Respectively, these savanna woodlands and open forests are highly fire prone, though fire regimes are fundamentally different due to inherent influences of weather, fuels, ignitions and terrain. Fuel reduction via prescribed burning is commonly used in both savanna woodlands and temperate, open forests with the intention of reducing the incidence, extent and intensity of wildfires and subsequent risk to human and environmental assets. The prospect of mitigation of greenhouse gas emissions from wildfires provides further impetus for extensive use of prescribed fire. This potential is dependent on a number of key factors, namely the efficacy of this fuel reduction technique and the relative difference in the intensity of prescribed fires and wildfires. We present a conceptual model of the potential for prescribed fire to mitigate emissions based on these key factors. Prescribed burning requires an outlay of emissions in return for a saving through a reduction in area burned and intensity of subsequent wildfires. If the reduction in area burned by wildfires, achieved through prescribed burning, is relatively small then the reduction in intensity of wildfires must be relatively large in order to achieve a net reduction in emissions. This is not the case if prescribed burning has a strong effect in reducing the size of wildfires. Contemporary data indicate that the effect of prescribed burning in reducing area burned by wildfires is high in savanna woodlands but relatively low in forests. Corresponding potential for mitigation of emissions is therefore high and low respectively. We tested this prediction for forests by estimating fire intensity and fuel consumption using a range of fuel accumulation models for south eastern Australian forests. The results indicate that at the level of effectiveness of prescribed fire achieved under contemporary management, fuel consumption and the volume of emissions may increase with increasing rates of prescribed burning. This has further implications for carbon storage in these forests. In eucalypt forests, current losses of carbon in wildfires appear to be offset by storage during the interval between wildfires. Future increases in the rate of intense wildfires as a result of climate change, have the potential to adversely disrupt this balance and pose a challenge to management. The ideal mix of management measures (i.e. prevention and suppression) required to counter the possibility of a degradation of significant carbon storage in Australian forests is yet to be resolved and will require a better understanding of how differing fuel treatment and suppression options can perform to best effect. By contrast the scope for management of emissions from fires in savanna woodlands is high, though their low potential for storage of carbon is also vulnerable to degradation by wildfires in the future.