Areal Extent, Species Composition, and Spatial Distribution of Coastal Saltmarshes in China

Coastal saltmarshes are key ecosystems with important ecological functions. Yet, they have experienced a widespread decline. Due to their importance, the conservation and restoration of saltmarshes are globally shared objectives, including China. Despite multiple local studies, nationwide information about saltmarshes in China is scarce. Thus, we used remote sensing to delineate the spatial distribution and areal extent of saltmarshes along coastal China and resolve their species composition. By interpreting 10 m spatial resolution Sentinel-2 images on Google Earth Engine, assisted with field survey and literature search, a total of 118 010 ha of saltmarshes were delineated in coastal China in 2019. Seven typical saltmarsh species were identified, with <i>Phragmites australis</i>, <i>Spartina alterniflora,</i> and <i>Scirpus mariquater</i> as dominant species, accounting for 95.5&#x0025; of total saltmarsh extent, while <i>Suaeda salsa</i>, <i>Tamarix chinensis</i>, <i>Cyperus malaccensis,</i> and <i>Sesuvium portulacastrum</i> were present in limited abundance. The <i>P. australis</i> and exotic species <i>S. alterniflora</i> grow along almost all coastal provinces, but <i>P. australis</i> dominates in the north while <i>S. alterniflora</i> dominates in the middle part of coastal China. <i>Suaeda salsa</i> occurs mainly in the north and has suffered large losses. <i>Tamarix chinensis</i> is abundant in Shandong province, <i>S. mariquater</i> in the Yangtze River delta, <i>C. malaccensis</i> in Guangdong and Guangxi provinces, and <i>S. portulacastrum</i> in Taiwan. The exotic species <i>S. alterniflora</i> expanded extensively along the coast and its expansion rate continues to increase. The results provided conform a much-needed baseline for future monitoring efforts and the assessment of progress in the conservation and restoration projects toward recovering saltmarshes in China.