Quantifying the 2023 sudden forest canopy dieback event in southeastern Australia using ground-based surveys and sentinel-2-derived live fuel moisture content

Extreme climatic events, particularly prolonged droughts and high-intensity wildfires, are becoming increasingly frequent, drawing attention to the compounding impacts of these events on forest ecosystems. Following a severe early-season drought, southeastern Australia experienced sudden and extensive forest canopy dieback between September and October 2023. In this study, we addressed two main objectives: (1) to develop a high-resolution canopy dieback prediction model for classifying the severity of the 2023 canopy dieback event, and (2) to analyze the key drivers of its spatial pattern. For objective 1, we selected and tested a suite of canopy moisture- and greenness-related variables from Sentinel-2A/2B data (10 m). A random forest model was trained using these variables, with a classification accuracy of 0.93. Live fuel moisture content (LFMC) emerged as the most significant predictor for predicting dieback, yielding a classification accuracy of 0.91 when using it alone. For objective 2, a SHAP analysis of the spatial drivers of dieback revealed that north-facing slopes and ridges experienced the highest canopy loss, while areas affected by the 2019–2020 megafires were significantly associated with more severe canopy dieback, suggesting a potential legacy effect that warrants further investigation. A time-series analysis from 2019 to 2023 identified multiple canopy dieback events coinciding with periods of drought and wildfire, highlighting a compounding stress cycle of drought–wildfire–drought. These findings underscore the robustness of the remotely sensed LFMC in predicting canopy dieback and highlight the importance of integrating climate, topographic, and disturbance factors into forest management to mitigate canopy dieback and enhance ecosystem resilience.