Black summer bushfires caused extensive damage to estuarine wetlands in New South Wales, Australia

Abstract

Summary There is now considerable evidence that, as the climate continues to warm, bushfires are becoming more common and severe, particularly in regions such as south‐eastern Australia. The extraordinary Australian bushfires over the summer of 2019/2020 resulted in the burning of habitats such as highland peat swamps and intertidal estuarine wetlands over unprecedented spatial scales. Across New South Wales, these bushfires affected 183 ha of saltmarshes and 23 ha of mangroves in 19 estuaries. The percentage of fire‐affected saltmarsh ranged from 51% to 81% in the worst impacted estuaries, although typically ≤15% of mapped saltmarsh was damaged. Just over 50% of mangroves were burnt in Wonboyn Lake (although this constituted <0.2 ha), whereas in all other estuaries, ≤5% of mangroves were burnt. At the state‐wide scale, the likelihood of saltmarshes being affected by fire was unrelated to adjacent terrestrial vegetation; however, mangroves adjacent to burnt wet sclerophyll forest were more likely to burn than not. Burnt mangroves were almost exclusively associated with extreme or high severity fires in adjacent terrestrial vegetation, yet saltmarshes were also impacted in some cases by moderate or low‐intensity fires. Many species of saltmarsh plants had re‐sprouted or germinated after 6–24 months, but the extent of any recovery or changes in species composition were not quantified. The majority of fire‐affected mangrove trees appeared to be dead 24 months after the fires, despite observations of epicormic growth on some trees after six months. Bushfire impacts to estuarine wetlands are likely to become more frequent and results from our work can help target hazard reduction burning that might be considered for minimising damage to mangroves. More work is required to better understand potential longer term impacts and the capacity for natural recovery of estuarine wetlands from bushfires.

Impacts of Climate Change on Marine Foundation Species

“…Indeed, in China (He et al 2017) and the United States (Silliman et al 2005), severe drought has weakened marsh plants (e.g., Spartina alterniflora and Suaeda salsa), increased top-down control by common grazers, and led to runaway die-offs of marsh ecosystems due to the interaction of drought and overgrazing (Silliman & Bertness 2002, Silliman et al 2005. While fire has been used as a salt marsh management tool to prevent woody plant invasion and manage cattle impacts (Williams-Jara et al 2022), the increasing intensity and frequency of wildfires and bushfires are of growing concern because of the fires' physical impacts on plant condition (Glasby et al 2023), soil structure (Smith 2001), and invertebrate communities (Ross et al 2019).…”