5. Conclusions

The results from this study demonstrate that it is feasible to extract native and invasive species in the Yellow River Delta region based on phenological characteristics of vegetation and spectral features of satellite remote sensing images. May and October are important periods for extracting the P. australis community and the S. alterniflora community, respectively, in the Yellow River Delta or in the coastal wetlands in North China. The landscape characteristics and spectral characteristics of the two communities are not much different and are difficult to distinguish.
The accuracy of different vegetation community in this area can be improved by taking into consideration both the vegetation phenology and the spectral features of remote sensing images. The Sentinel-2 images with red edge bands have obvious advantages in vegetation community extraction as compared to Landsat-8 images. The P. australiscommunity in the study area is the dominant species, and its multi-year landscape index is stable. The spatial distribution of S. salsais discrete, the degree of aggregation is low, and the area is decreasing. The landscape index of the S. alterniflora community showed a trend of increasing year by year, but the degree of fragmentation decreased, indicating that the expansion pattern of theS. alterniflora community became spatially continuous, more regularized and aggregated overtime.
The findings from this study advanced understanding of the spatial distribution and spatiotemporal variation characteristics of native and invasive plant species, and the expansion mechanism of S. alterniflora and other species in the study area, and provide a basis for making scientifically sound decision for management and the controlS. alterniflora invasion. It will contribute to the ecological restoration and the protection of species diversity of the entire Yellow River Delta in China. In addition, the research findings have important theoretical and scientific value for the ecological environment protection and sustainable development of the worldwide estuary wetland ecosystem.