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Spatiotemporal characteristics of landscape change in the coastal wetlands of Yancheng caused by natural processes and human activities

ZHANG Huabing1,2,3,LIU Hongyu1,2,,HAO Jingfeng1,2,LI Yufeng1,2 1 College of Geography,Nanjing Normal University,Nanjing 210046,China 2 Key Laboratory of Environment Change and Ecology Construction in Jiangsu Province,Nanjing 210046,China 3 College of Urban and Resource Environment,Yancheng Teachers University,Yancheng 224002,China  
Wetlands are one of most important ecological systems on earth.Their unique ecosystem function has led to them been sometimes called "the earth′s filtration system".Coastal wetland is an important type of wetland,which is not only a rare ecosystem but is also often found in areas disturbed human activities.Landscape changes have become the most significant feature of this fragile zone.Landscape changes inevitably have effects on material circulation and energy flow within the coastal wetland ecosystems,which alter the landscape ecological processes,as well as the coastal wetland pattern and function.In this study,Yancheng coastal wetland was chosen as the study area.The Yancheng coastal wetland,located in the east of Jiangsu Province,is one of the largest mudflats in China and represents one of the most rapidly changing landscapes in the world.Changes to coastal landscapes can have natural causes or result from human activities;the pattern of change greatly differs between the two.We focused on the core area of Yancheng Nature Reserve.This area was divided into two parts based on the type of landscape change: change in the northern area being characterized as from human activities,and that in the southern area characterized as from natural causes.We used remote sensing digitized data from 1987,1997 and 2007,and applied GIS techniques and methods of landscape ecology to analyze the temporal and spatial changes in landscape pattern caused by natural processes and human activities.In the area affected by human activities,from 1987 to 2007,the landscape pattern was characterized by greater fragmentation,higher dominance and less landscape diversity than those of the other area.The mean vegetation patch area decreased from 205.31 hm2 to 55.60 hm2 and the landscape diversity index from 1.4284 to 1.2928 while the landscape dominance index increased from 0.3634 to 0.7766.This landscape change resulted in degraded and heterogeneous strips of wetlands.The wetlands showed a one-direction succession from land to sea in the period between 1987 and 1997 but the landscape exhibited a multi-directional succession from 1997 to 2007.In the area that was affected only by natural processes,from 1987 to 2007,the landscape pattern was characterized by greater diversity and less dominance than those of the other area.The landscape dominance index decreased from 0.4844 to 0.3164 while the landscape diversity index increased from 0.9019 to 1.4754.Strips of wetland development were more evident and there was a one-direction succession from land to sea between 1987 and 2007.The geomorphic deposit process and the succession of plant communities adapting to environmental changes were fundamental factors driving the landscape dynamics of the area not affected by human activities.Whereas human activity,such as dyke construction,was the important driving force behind the changes in landscape pattern in the area with human activities.Through identifying the rules of landscape changes caused by different factors in the Yancheng coastal wetland,we can form a scientific basis for the sustainable exploitation of the coastal wetlands,ensuring protection of the wetland resources while simultaneously achieving social and economic sustainable development in the Yancheng coastal region.
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