Tree Mortality and Carbon Emission as a Function of Wildfire Severity in South-Eastern Australian Temperate Forests

Disturbance trends over recent decades indicate that climate change is resulting in increased fire severity and extent in Australia’s temperate Eucalyptus forests. As disturbance cycles become shorter and of greater magnitude empirical measurements are required to identify changes in forest carbon stock and emissions. However, there is scant evidence in the literature based on careful monitoring of tree mortality and distribution of carbon in live and dead vegetation.The 2019/2020 wildfires burnt around 6 to 7 million hectares of mainly temperate forest in south-east Australia, with estimates of CO 2 emissions ranging 97 - 130 tonnes CO 2 ha -1 . Our research sites in eastern Victoria, that were measured prior the wildfires, were burnt in January 2020 with varying fire severities. Here we quantify the impact of fire severity on tree mortality, carbon loss and carbon redistribution and assess implications for future carbon storage in temperate Eucalyptus forests.Moderate to high severity fire resulted in almost 100% understorey mortality and about 20-30% overstorey mortality, with smaller diameter trees accounting for most losses. Total aboveground carbon lost was 15% in high severity fire and 14% in low/moderate severity wildfire. A greater percentage of carbon was redistributed from live to dead standing trees in high severity compared to moderate severity fires. At our research sites, wildfires emitted about 46 Mg C ha -1 equivalent to about 166 Mg CO 2 ha -1 .Extrapolating our findings to the landscape scale revealed that 38.58 Tg C or 98 Mg CO 2 ha -1 was lost to the atmosphere from the 1.4 million ha of area in eastern Victoria burnt in 2019-2020 wildfires, equating to about 20% of Australia’s total net annual emissions