Spatiotemporal dynamics of salt marsh vegetation and phenological response to environmental factors in a high-latitude estuary in China

• Phragmites australis and Suaeda salsa areas increased 94% and 125% respectively in Liao River Estuary (2018-2023). • Both species showed phenological advances, with SOS, POS, EOS shifts of 22.5–38 days between min-max values. • Earlier phenology in upper estuary vs. 40-50-day delay in lower estuary showed spatial heterogeneity. • Strong correlations found between vegetation dynamics and summer discharge, winter precipitation, and previous-year precipitation. Coastal salt marshes are essential to the ecological balance of coastal environments because they contribute significantly to ecosystem services, such as carbon sequestration, biodiversity conservation, and flood regulation. Understanding the spatiotemporal changes of salt marsh vegetation in coastal wetlands and the responses to influencing factors are critical in coastal wetlands. This study investigates the driving factors and response mechanisms of Phragmites australis ( P. australis ) and Suaeda salsa ( S. salsa ) in the Liao River Estuary (LRE)wetland from 2018 to 2023. We analyzed the spatiotemporal dynamics of vegetation distribution and phenological characteristics using multi-source remote sensing data and machine learning techniques. Google Earth Engine (GEE) was utilized due to its powerful ability to integrate diverse satellite data, enabling the large-scale and long-term wetland vegetation monitoring. The results reveal that the P. australis and S. salsa areas increased by 94 % and 125 % from 2018 to 2023, indicating significant vegetation recovery. Both species exhibited phenological advances from 2018 to 2023, with shifts of 22.5–38 days at the start of season (SOS), peak of season (POS), and end of season (EOS). Phenological events occurred earlier in the upper estuary, with a 40–50-day delay in the lower estuary. Strong correlations were found between vegetation dynamics and hydrological/climatic variables, especially summer discharge (14.6 %) and winter precipitation (12.6 %) for S. salsa and previous-year precipitation (8.9 %) for P. australis . These results highlight the critical role of hydrological and climatic factors in driving vegetation changes, providing valuable insights for wetland restoration, management, and adaptation to changing environmental conditions.