Impact of the Black Summer Bushfires on Coastal Wetlands of Wonboyn Lake, NSW

<p dir="ltr">The 2019 / 2020 bushfires were the largest fire event in Australia’s recorded history, resulting in over 5.6 million hectares of land burnt in New South Wales alone, including extensive damage to mangroves and saltmarsh. This project focussed on Wonboyn Lake of NSW and assessed the coastal wetland vegetation dynamics pre-fire, extent of coastal wetland vegetation impacted post-fire, and quantifying the recovery of such vegetation post-fire. The study further produced a fire risk mapping method, examining the likelihood of a highly intense fire occurring (HIFO) across the catchment. While Wonboyn supports a relatively small area of mangroves in comparison to other estuaries, it supports a substantial area of saltmarsh. This study utilised remotely piloted aircraft surveys using spectral and LiDAR sensors, in-field elevation data collection, and remotely sensed datasets, that were processed using various analytical approaches. Pre-fire coastal wetland dynamics mapping indicated a generally stable state of vegetation extents, with saltmarsh area declining as mangrove area increased in 2013 and 2018, suggesting the encroachment of mangroves into saltmarsh as a result of sea level rise. Saltmarsh communities across the lake were comprehensively impacted by fire, with ~77% (34 ha) of the total saltmarsh population recorded as burnt in 2020. Mangrove populations were less affected immediately post-fire, with ~3% (45 m²) of the total 2020 mangrove population recorded as dead. Dead mangrove cover increased to 1016 m² in 2023. Saltmarsh made a major recovery within one year post fire, with complete recovery observed by 2023. While mangrove mortality increased to 2023, recovery was slow with some recruitment of seedlings observed. The HIFO map visualises area’s most at risk within the Wonboyn catchment. Fire risk was observed to increase on westerly aspects and where elevation declines. Validation of the map against fire frequency shows promising results, where high and low thresholds overlap appropriately. Overall, this study provides important insights into the impact fires have on coastal wetland vegetation structure and recovery following a severe fire. Future research should consider monitoring implications the extended recovery of coastal wetlands has on other physical properties such as tidal frame positioning and soil structure. Consideration into the maps production and validation should also be undertaken, where a multiplicative method and comprehensive validation approach may improve map accuracy, allowing for future applications in management.</p>