The spatio-temporal dynamics of salt marsh vegetation for Chongming Dongtan National Nature Reserve, Shanghai

Salt marsh vegetation is one of the most important components of coastal wetlands, and its evolution and dynamics have direct influences on the ecosystem service and value of wetlands. Based on analyses and interpretation of four Landsat TM remotely sensed images, integrated with historical data and field surveys, this study investigated the spatio-temporal dynamics of salt marshes at Chongming Dongtan National Nature Reserve for the period 1998-2005. The results showed that the total area of salt marsh increased from 2478.32 hm² in 1998 to 4687.74 hm² in 2005 along with the expansion and accretion of tidal flats in the natural reserve. Results also indicated that Spartina alterniflora expanded at a much faster rate than the native species Scirpus mariqueter and Phragmites australis. In less than 10 years, the area of S. alterniflora increased from the initial introduction to 1283.4 hm² by 2005 and it had formed a large area of mono-dominant community. During this same period, the area of the P. australis community decreased significantly, mainly due to the influences of wetland reclamations in 1998 and 2001, and the invasion of S. alterniflora. S. alterniflora expanded very quickly in the nature reserve due to its stronger competitive capacity and wider ecological niche, and the rapid accretion of intertidal flats which provided more suitable habitat. It can be concluded that the range expansion of exotic S. altemiflora poses a potential threat to local ecosystems, and measures should be taken for the management and control of this invasive species at the nature reserve.