Changes in vegetation front and evolution trend of landscape pattern of tidal salt marsh wetland in Yancheng in recent 40 years

The tidal salt marsh in the core area of Jiangsu Yancheng Rare Bird Nature Reserve has currently been less affected by human but mainly by natural marine dynamics (waves, tides, sea level, and so on) and local primitive organisms. To understand the changes at the front edge of the salt marsh and in the wetland area, and the landscape evolution of the wetland, the Landsat serial images from 1984 to 2021 were analyzed using remote sensing technology and geographic information technology, combined with various methods (threshold segmentation, Otsu algorithm, and unsupervised classification). Results show that first, from 1984 to 2006, the front edge showed a trend of full seaward advancement. In 2008, the front edge began to show a pattern of "north-south siltation and central erosion"; from 2014 to 2021, the central part of the front edge in the core area tended to be stable. Secondly, the landscape organisms in the core area included mainly intergrass, alkali ponies, reeds and aquaculture ponds. The area of intergrass is positively correlated with time, the area of alkali canopy increased first and then decreased, and the area of reed was influenced by alkali canopy and intergrass, showing a decrease first and then an increase. The area of culture pond increased first and then decreased until it was completely banned by the government. Thirdly, The change of salt marsh front edge in the core area wetlands tended to be consistent with the change of intergrass area in the core area. From 1984 to 2014, the salt marsh front edge had been advancing seaward with the area of intergrass increasing, and then stabilized after 2014.