Efficacy of eastern Australian rainforests and topography as fire refugia under anthropogenic climate change

Abstract

Background: The 2019-20 Australian bushfire season was the most environmentally detrimental bushfire season on record. The extreme heat and drought exposed normally fire-resistant communities to uncharacteristically dry fuel loads and abnormally high severity burning. In eastern Australia this included mesic rainforest environments (including the World Heritage listed Gondwana Rainforests of Australia), which are often highly sensitive to fire, contain high biodiversity values, are critical habitat for threatened species, embody distinct endemism, provide valuable ecosystem services and are critical for terrestrial carbon storage. East coast rainforests are also highly fragmented, with less than half of pre-European levels remaining. Increases in fire frequency and intensity associated with climate change may threaten these already fragmented rainforest environments. This study considers the efficacy of rainforest refugia under a heightened bushfire climate, via spatial analysis of burn extent, burn severity and topographic characteristics for rainforests during the 2019-20 bushfire season within the Eastern Australian Temperate and Subtropical Forests Conservation Management Zone.Results: Burn severity, vegetation and elevation datasets were merged and analysed across mid-eastern Australia. A significant portion of rainforest was fire affected across the study area (~17%), with ~5% burnt to a high or very high severity. Elevation, topographic position (i.e. valleys), slope and aspect all contributed to maintaining rainforest fire refugia. The study resulted in a mapping product that can be utilised by researchers and protected area managers to locate and assess burnt rainforest in mid-eastern Australia.Conclusions: This study enables the identification of rainforest fire refugia and threatened rainforest communities for future research and conservation efforts in eastern Australia. The results also demonstrate the potential of climate change to enact widespread rainforest declines, with potentially dire consequences for biodiversity and ecosystem services. This event and recurrent fire events may enact positive climate feedback systems by enabling pyrophytic vegetation expansion and converting rainforest carbon pools into a carbon source.