Quantifying the impacts of Australian bushfires on native forests and gray-headed flying foxes

Abstract

Climate change is increasing the frequency and intensity of wildfires in many regions of the world. Changing fire regimes have been shown to delay vegetation recovery and shift distribution of ecosystems, increasing the importance of understanding the short-and long-term impacts of these changes. The unusually severe 2019–2020 Australian bushfire season has been linked to climate change and the impacts on wildlife and ecosystems are still being studied. We use remotely sensed thermal data to assess the differences between annual fire seasons from 2012 to 2019 in eastern Australia to understand the unique characteristics of the 2019–2020 anomalous fire season. We use spatial and temporal monitoring data of the vulnerable gray-headed flying fox (Pteropus poliocephalus) and its habitat to examine evidence for fire impacts on these important forest pollinators. We analyze roost occupancy in response to a previous fire season and use these results to identify roosts that are particularly affected by the 2019–2020 fires. During the 2019–2020 anomalous fire season, mega-fires, defined as contiguous fires over 10,000 hectares (ha) each, burned over 60% of the total affected area and occurred mostly in forested areas. This is in contrast to previous fire seasons in which smaller, scattered fires burned mostly non-forested areas. While we found little evidence that gray-headed flying fox reacted directly to fires in a previous season, unburned winter habitat was a key predictor of roost occupancy. The 2019–2020 anomalous fire season burned nearly ten times the amount of total habitat (33.7%) across the gray-headed flying fox range compared to the previous season. Critical winter habitats, including a species in fire refugia, were also substantially more burned in the anomalous fire season. Much of the winter habitat that burned in the anomalous fire season was within high or extreme severity fires (41.7%), causing substantial canopy consumption of these species. This work highlights the utility of remotely sensed thermal data for rapidly mapping fire impacts to wildlife and vegetation and highlights areas of habitat key for the conservation of these vulnerable populations.