Effects of Changes in Hydrological Connectivity Induced by Spartina alterniflora Invasions on Suaeda salsa Community Evolution in Yellow River Estuary Wetland, China

Spartina alterniflora invasions seriously threaten the structure and functions of coastal wetlands in China. In this study, the Suaeda salsa community in the Yellow River Estuary wetland was monitored using long-term Landsat satellite images acquired from 1997 to 2020 to quantify the impact of changes in hydrological connectivity induced by S. alterniflora on neighboring vegetation communities. The results showed that S. alterniflora rapidly expanded in the estuary area at a rate of 4.91 km²/yr from 2010 to 2020. At the same time, the hydrological connectivity of the area and the distribution of S. salsa changed significantly. Small tidal creeks dominated the S. alterniflora landscape. The number of tidal creeks increased significantly, but their average length decreased and they tended to develop in a horizontal tree-like pattern. Affected by the changes in hydrological connectivity due to the S. alterniflora invasion, the area of S. salsa decreased by 41.1%, and the degree of landscape fragmentation increased from 1997 to 2020. Variations in the Largest Patch Index (LPI) indicated that the S. alterniflora landscape had become the dominant landscape type in the Yellow River Estuary. The results of standard deviation ellipse (SDE) and Pearson’s correlation analyses indicated that a well-developed hydrological connectivity could promote the maintenance of the S. salsa landscape. The degradation of most S. salsa communities is caused by the influence of S. alterniflora on the morphological characteristics of the hydrological connectivity of tidal creek systems.