Coastal salt marsh changes in China: Landscape pattern, driving factors, and carbon dynamics

• Mean center, standard deviational ellipse, and landscape indices of salt marsh species in China varied between 1985 and 2019. • Human disturbance dominated changes in salt marsh species distribution. • Salt marsh changes in China resulted in net emission of 68.1 Mt CO 2 during 1985–2019. • Highest CO 2 emission occurred as a result of Phragmites australis losses, and in Shandong Province. • CO 2 sequestration occurred mostly due to introduction and expansion of Spartina alterniflor a. Coastal salt marshes provide critical ecological services, including carbon sequestration. However, the landscape patterns, driving factors, and carbon dynamics associated with salt marsh losses and gains remain insufficiently explored, which is vital for effective restoration. This study conducted a comprehensive analysis of these aspects across China, with a focus on species-specific differences. Based on historical salt marsh data, landscape analysis was applied for identifying the spatiotemporal characteristics of changes. XGBoost algorithm was used for driving factor analysis. Carbon dynamics derived from salt marsh changes were estimated with statistical calculation. Our results indicated that the distribution patterns of salt marshes, as indicated by mean center, ellipse area, and landscape indices, varied significantly from 1985 to 2019, particularly between 2005 and 2010. Native species, such as Phragmites australis and Suaeda salsa , experienced significant losses with a 72 % reduction, while exotic species Spartina alterniflora showed substantial gains with a 680-fold. Human disturbances emerged as the primary driver of these changes, with mean temperature and precipitation influencing certain regions and years. Overall, salt marsh changes resulted in a net emission of 68.1 Mt CO 2 , with the highest emission in Shandong and linked to the loss of Phragmites australis . Conversely, carbon sequestration equivalent to 11.1 Mt CO 2 mainly resulted from the expansion of Spartina alterniflora , with Shanghai contributing the most. This species-specific and site-specific analysis of landscape patterns, drivers, and carbon dynamics in China could enhance our understanding of salt marsh changes and offer valuable insights for targeted restoration efforts at both local and national levels.