Pattern change of the coastal wetland system and its dynamic impact on the habitat of red-crowned cranes in Yancheng, Jiangsu Province

Abstract

The Yancheng coastal wetland in Jiangsu province, as a UNESCO (United Nations Educational, Scientific and Cultural Organization) natural heritage site with an area of 2687 km², is one of the most important habitats for the overwintering of red-crowned cranes in Asia. In recent decades, due to the combined effects of intensive human activities in sectors, such as industry, agriculture, aquaculture, and urbanization, the pattern of coastal wetland system and the suitable habitat for red-crowned cranes have changed dramatically. Therefore, the spatio-temporal variation pattern of coastal wetland system must be identified, and its key impact factors must be explored to protect the coastal wetland and conserve its biodiversity. Currently, research on land cover changes in the Yancheng coastal wetland is insufficient for species habitat monitoring. Thus, further study on the suitable habitat for red-crowned cranes in a long-term and large regional scale is warranted.In this study, multi-temporal and multi-source remote sensing data, such as Landsat TM/OLI data during 1989 to 2019 and Sentinel-2 data in 2019, were used to analyze the features of spatio-temporal variation in the Yancheng coastal wetland. First, the classification system and image interpretation symbols of the study area were established to draw the maps of classification and transfer distribution in six periods from 1989 to 2019. Then, the structural and functional connectivity of the suitable habitat for red-crowned cranes were evaluated on the basis of the species diffusion ability. Finally, the key ecological nodes for the overwintering of red-crowned cranes were evaluated.Results show that the eco-environment of natural wetland has degraded rapidly, with an area loss of 49.46%. Contrastingly, the artificial wetland increased by 69.24%, which was mainly realized by occupying the natural wetland and reclaiming the tidal flat. The center of reclamation tended to migrate from north to south and from coastal land to sea. The area of seepweed saltmarsh and alkaline land as suitable habitat decreased by 489.10 km², with a proportion decreased from 19.88% in 1989 to 4.36% in 2019. As for structural connectivity, our results reveal that the connectance index of suitable habitat patches decreased from 1.83 to 1.30, showing a downward trend. The distance between the patches increased and the fragmentation intensified. Concurrently, the estimations of functional connectivity index demonstrate that the integral and probability indexes of connectivity in 2019 are less than 0.01. The functional connectivity decreased, and the connection network was generally broken with only a small part of the connection network with high betweenness centrality index. They exist in the core area of UNESCO natural heritage site and the Tiaozini region. They are also the key ecological nodes for the habitat of red-crowned cranes.In summary, the connectivity of the suitable habitat for red-crowned cranes has decreased sharply because of land cover changes in the UNESCO natural heritage site-Yancheng coastal wetland in the past 30 years. However, the habitat for red-crowned cranes has been greatly improved since the core area has reverted aquaculture pond and cultivated land to natural wetland in 2014. In addition to enhancing the scientific conservation of the existing suitable habitat, such as the core area of UNESCO natural heritage site and Tiaozini region, the key ecological nodes in the natural wetland should be restored to improve the connectivity among the habitat patches.