Abstract
Suaeda salsa (L.) Pall. (S. salsa) acts as a pioneer species in coastal wetlands due to its high salt tolerance. It has significant biodiversity maintenance, socioeconomic values (e.g., tourism) due to its vibrant color, and carbon sequestration (blue carbon). Bohai Bay region, the mainly distributed area of S. salsa, is an economic intensive region with the largest economic aggregate and population in northern China. The coastal wetland is one of the most vulnerable ecosystems with the urbanization and economic developments. S. salsa in Bohai Bay has been changed significantly due to several threats to its habitat in past decades. In this paper, we analyzed all available archived Landsat TM/ETM+/OLI images of the Bohai Bay region by using a decision tree algorithm method based on the Google Earth Engine (GEE) platform to generate annual maps of S. salsa from 1990 to 2020 at a 30-m spatial resolution. The temporal-spatial dynamic changes in S. salsa were studied by landscape metric analysis. The influencing factors of S. salsa changes were analyzed based on principal component analysis (PCA) and a logistic regression model (LRM). The results showed that S. salsa was mainly distributed in three regions: the Liao River Delta (Liaoning Province), Yellow River Delta (Shandong Province), and Hai River Estuary (Hebei Province, Tianjin). During the past 31 years, the total area of S. salsa has dramatically decreased from 692.93 km2 to 51.04 km2, which means that 92.63% of the area of S. salsa in the Bohai Bay region was lost. In the 641.89 km2 area of S. salsa that was lost, 348.80 km2 of this area was converted to other anthropic land use categories, while 293.09 km2 was degraded to bare land. The landscape fragmentation of S. salsa has gradually intensified since 1990. National Nature Reserves have played an important role in the restoration of suitable S. salsa habitats. The analysis results for the natural influencing factors indicated that precipitation, temperature, elevation, and distance to the coastline were considered to be the major influencing factors for S. salsa changes. The results are valuable for monitoring the dynamic changes of S. salsa and can be used as effective factors for the restoration of S. salsa in coastal wetlands.
Highlights
Wetlands are often recognized as nature-based solutions that can provide a variety of comprehensive services that are of social, economic, and environmental value to humans [1].Coastal wetlands are located where ocean and land are interspersed, and they are sensitive to external stresses and are vulnerable to human activities [2]
The results showed that the overall trends of the S. salsa areas in the Bohai Bay region were consistent with the trend of the S. salsa area in the Yellow River Delta (Figure 5)
Monitoring the dynamic changes in S. salsa distributions at the regional scale is meaningful for coastal wetland conservation
Summary
Coastal wetlands are located where ocean and land are interspersed, and they are sensitive to external stresses and are vulnerable to human activities [2]. Coastal populations and wetlands have been intertwined for centuries and have experienced intense and varied human impacts [3]. Many studies have been carried out on the restoration [5], evaluation, management, evolution mechanisms [6], biomass, and carbon storage in coastal wetlands [7]. Vegetation changes can provide good indicators for understanding and evaluating the status of coastal wetlands. Some studies have found that the global vegetation densities in wetlands are decreasing due to climate change and the impacts of interference from human activities [8]
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