Multiple methods reveal the carbon stock potential of young reforested mangroves in Quanzhou Bay Nature Reserve, China

• Carbon sequestration in early afforestation was estimated via an allometric biomass model, with area changes tracked using NDVI analysis. • A phased evaluation was proposed that integrates multiple methodologies to enhance the accuracy of mangrove carbon sequestration assessments. • These findings provide valuable insights into improving the scientific basis of carbon offset verification and informing risk assessment in blue carbon trading schemes. Mangrove reforestation has emerged as a critical component in blue carbon, with its carbon sequestration potential receiving increasing attention. However, most existing studies have focused on mature mangrove stands and adopted generalized assessment approaches, often ignoring the dynamics of plant growth, thereby raising concerns about the accuracy and reliability of carbon sequestration estimations. In this study, a site-based was assessed in a juvenile mangrove reforestation experimental area within the Quanzhou Bay Estuarine Wetland Natural Reserve from December 2022 to 2024, using three complementary models to evaluate early-stage carbon accumulation. Model I applied species-specific allometric equations suitable for saplings (basal diameter < 4 cm); Model II employed general equations commonly used for estimating biomass in more mature stands (DBH ≥ 4 cm); and Model III assessed vegetative expansion using NDVI-based remote sensing. The results revealed the cumulative carbon stock ranging from 45.34 to 158.84 t C, corresponding to a CO 2 sequestration potential of 166.25 to 582.41 t CO 2 . Moreover, based on biomass increments, annual carbon sequestration rates were calculated for five species and two reforestation strategies (mixed vs. monoculture forests). Under Model I, sequestration rates increased from 9.58 to 24.74 t C yr −1 in mixed forests and from 3.73 to 7.52 t C yr −1 in monocultures. Model II produced consistently higher estimates, with mixed forests rising from 8.96 to 27.23 t C yr −1 and monocultures from 28.38 to 35.18 t C yr −1 . These trends highlight accelerated carbon accumulation during the second year and variation between models and planting strategies. Cumulative carbon stocks increased significantly in the second year, and Kandelia obovata contributed the highest species-level carbon stock. Statistical analysis also showed that mixed forests (Area A) consistently outperformed monocultures forests (Area B) in biomass accumulation ( p -value < 0.0001), but NDVI failed to reflect these differences. The result was highlighting its limitations in detecting early-stage structural complexity. These findings suggest that Model I is more appropriate for evaluating biomass accumulation during the juvenile phase, and that reliance on NDVI alone may underestimate early-stage carbon stock. Overall, a phased evaluation was proposed that integrates multiple methodologies to enhance the accuracy of mangrove carbon sequestration assessments in this study. This approach holds promise for improving the scientific basis of carbon offset verification and informing risk assessment in blue carbon trading schemes.