Fire-related threats and transformational change in Australian ecosystems

Aim: Megafire events generate immediate concern for wildlife and human well-being, but their broader ecological impacts likely extend beyond individual species and single fire events. In the first mechanistic study of fire effects focussed on ecosystems, we aimed to assess the sensitivity and exposure of ecosystems to multiple fire-related threats, placing impacts in the context of changing fire regimes and their interactions with other threats. Location: Southern and eastern Australia. Time period: 2019-2020. Major species studied: Australian ecosystems. Methods: We defined 15 fire-related threats to ecosystems based on mechanisms associated with: (a) direct effects of fire regime components; (b) interactions between fire and physical environmental processes; (c) effects of fire on biological interactions; and (d) interactions between fire and human activity. We estimated the sensitivity and exposure of a sample of 92 ecosystem types to each threat type based on published relationships and spatial analysis of the 2019-2020 fires. Results: Twenty-nine ecosystem types assessed had more than half of their distribution exposed to one or more threat types, and only three of those were listed as nationally threatened. Three fire-related threat types posed the most severe threats to large numbers of ecosystem types: high frequency fire; pre-fire drought; and post-fire invasive predator activity. The ecosystem types most affected ranged from rain forests to peatlands, and included some, such as sclerophyllous eucalypt forests and heathlands, that are traditionally regarded as fire-prone and fire-adapted. Main conclusions: Most impacts of the 2019-2020 fires on ecosystems became apparent only when they were placed in the context of the whole fire regime and its interactions with other threatening processes, and were not direct consequences of the megafire event itself. Our mechanistic approach enables ecosystem-specific management responses for the most threatened ecosystem types to be targeted at underlying causes of degradation and decline.