Climate-driven mangrove dieback and recovery: a case study in Albert and Leichhardt Rivers, Australia

Abstract

A severe dieback event occurred in 2015/2016 in the Gulf of Carpentaria, northern Australia, which was later attributed to El Nino-Southern Oscillation (ENSO) and unusually low sea levels associated with the lunar nodal cycle. However, the long-term drivers of mangrove changes, their resilience, and species-specific responses to these environmental events remain insufficiently understood. This study applies an integration of k-means clustering and random forest classification on the Landsat archive to address knowledge gaps regarding mangrove dynamics. Despite episodic dieback in 2002/2004 (9.1 km2), 2008 (2.9 km2), and 2015/2016 (8.1 km2), mangrove zones showed a net increase in area (+260%, from 21.4 km2 to 55.7 km2) and greenness (NDVI, +18%) over the period 1987-2023. These results indicate cyclical patterns of decline in extent and condition followed by rapid recovery. Landward edges, dominated by Avicennia marina, presented the lowest NDVI values during extreme negative ENSO phases, particularly when unusually low sea levels driven by the lunar nodal cycle further reduced tidal inundation. This pattern suggests greater vulnerability to water deficits and salinity stress in these zones. The mature R. stylosa dominated areas in the central zone of the mangrove forest remained stable throughout the study period, and significant progradation was observed at the seaward margins, dominated by A. marina, likely driven by sediment accretion during increased river discharge years. This highly dynamic mangrove forest demonstrates capacity to extend both landwards and seawards. However, as climate variability intensifies, particularly with more frequent extreme events and shifting tidal regimes projected with sea-level rise, understanding the long-term resilience of mangrove forests and their capacity to recover will be crucial for informing conservation strategies focused on specific zones and maintaining blue carbon stocks of mature mangrove forests.