Effect of recent fuel reduction treatments on wildfire severity in southeast Australian Eucalyptus sieberi forests

Abstract

Climate change is increasing the area of seasonally dry forests burnt by wildfire in many parts of the world, compelling a revision of management strategies to reduce risk and improve the resilience of forest ecosystems. While prescribed burning is a common strategy used to reduce bushfire risk, mechanical thinning has not been as widely applied in Australia’s temperate forests in comparison with the USA and Europe. In this study we report results from a prescribed burning and mechanical thinning experiment in a 37-year-old naturally regenerated Eucalyptus open forest that was burnt through by wildfire in January 2020, providing an opportunity to determine how pre-wildfire fuel status and burning and thinning treatments influenced wildfire severity.Fuel hazard assessments in the experimental forest, made prior to the wildfire, indicated that untreated forest, and thinned forest, had very high to extreme fuel hazard scores, while forests treated with prescribed burning, or with thinning plus burning, had low fuel hazard scores. These fuel hazard scores explained more than 70% of the variation in wildfire severity, indicating that the fire was largely fuel driven and responsive to fuel reduction measures.Forest areas treated with thinning only recorded extreme fuel hazard, largely due to the increase in forest floor residues, which were ignited by the wildfire resulting in a high fire severity ranking. Forest areas treated with thinning and prescribed burning, or with high intensity prescribed burning, did not ignite from the advancing front of the wildfire, clearly demonstrating the effectiveness of fuel reduction management under low to moderate forest fire danger weather.Fuel hazard reduction benefits extend for at least three years after the application of fuel modification treatments in Eucalyptus sieberi forests. The results from this forest experiment demonstrate that the active management of fuels, including thinning with prescribed burning, can reduce wildfire risk and fire severity.