Large-Scale Spartina alterniflora Removal Reshapes Coastal Wetland Vegetation with Short-Term Blue Carbon Losses in Yancheng Coastal Wetlands

Large-scale removal of the invasive salt-marsh plant Spartina alterniflora has become an important intervention for restoring native coastal wetland habitats. However, its effects on vegetation reorganization and blue carbon storage remain unclear because conventional before–after comparisons cannot readily separate management effects from background wetland dynamics. Following a large-scale S. alterniflora removal program in Yancheng Coastal Wetlands, China, we integrated Landsat and Sentinel observations (2009–2024), random forest classification, an LSTM–Land Change Modeler framework, and the InVEST Coastal Blue Carbon model to reconstruct vegetation trajectories and simulate a 2024 no-removal counterfactual. From 2010 to 2023, S. alterniflora expanded by 43.16%, Suaeda salsa declined by 78.95%, and Phragmites australis increased by 27.20%. The LSTM temporal-demand model estimated a 2024 S. alterniflora demand of 41.90 km2, whereas the intervention-defined management layer represented extensive post-removal surfaces and vegetation reorganization. Using the corrected 2023 landscape as a persistence-based carbon reference, carbon storage was 0.712 Tg C compared with 0.564 Tg C in the 2024 management layer, corresponding to a scenario difference of 0.148 Tg C (20.8%), 91.4% of which was attributable to biomass carbon. These findings reveal substantial short-term blue carbon losses and highlight the importance of rapid native vegetation recovery after invasive-species removal.