Effects Of Beach Expansion And Poplar Ecological Retreat On Habitat Suitability Of Migratory Birds In Dongting Lake Wetland

Human activities are changing the original land cover on a larger scale,and the loss and degradation of wetlands in this process is shocking.Wetland is a key habitat for many organisms,especially rare animals and plants.Monitoring its land cover change is of great significance for biodiversity conservation.As one of the most important lake wetlands in China,Dongting Lake is an important wintering place for migratory birds in the world,which is very important for the migration of migratory birds in East Asia.After reclaiming farmland from the lake was stopped in 1978,the scope of the lake remained basically stable.However,some changes were still taking place inside the lake.First,the beach area of Dongting Lake was still changing because of sediment scouring and silting.Second,the eastern cottonwoods(Populus deltoides)were introduced and planted on a large scale in the 1970s and the Poplar Ecological Retreat project in 2017 significantly affected the vegetation coverage of Dongting Lake.Third,the construction of large dams in the upper reaches of the Yangtze River significantly affected the hydrological conditions of Dongting Lake.All these will affect the migration and wintering of migratory birds in Dongting Lake.At present,some studies have explored the impact of dam construction and poplar planting on migratory birds.However,few people pay attention to the impact of Dongting Lake beach expansion and Poplar Ecological Retreat on them.In order to quantify these impacts,we collected satellite images of Dongting Lake Wetland from 1979 to 2019,explored the land cover changes of Dongting Lake through interpretation,and added other typical habitat indicators(including altitude,slope and human disturbance)affecting the foraging and habitat of migratory birds,The habitat suitability index model is used to calculate the overwintering habitat suitability of the four most important migratory bird guilds in Dongting Lake(Anatidae,Scolopacidae,Ardeidae and Laridae)in the past 40 years.The suitability is divided into four grades:poorly(0-25),generally(25-50),moderately(50-75)and highly(75-100).Using a variety of analysis methods such as difference analysis and correlation analysis,this paper discusses the impact of beach expansion and Poplar Ecological Retreat on the habitat suitability of migratory birds in Dongting Lake.The time interval of section of beach expansion is 1979-2019,which is divided into four stages:1979-1989(1980s),1990-1999(1990s),2000-2009(2000s)and 2010-2019(2010s);The time interval of section of Poplar Ecological Retreat is 2014-2019,which is divided into two stages:2014-2016(before Poplar Ecological Retreat)and 2017-2019(after Poplar Ecological Retreat).The main conclusions of this study are as follows:(1)The beach of Dongting Lake expanded rapidly before 2003,with an average annual expansion area is 26.51km2.This is due to the continuous deposition of sediment in Dongting Lake before that.After 2003,the beach expansion tended to stop.This is because after the operation of the Three Gorges Dam,the sediment entering the Dongting Lake has been reduced and the balance of erosion and deposition has been basically realized.(2)For Anatidae and Ardeidae,the increase of grassland in the early stage of beach expansion can improve the habitat suitability,but this benefit will soon disappear with the evolution of grassland into reed and forest land.In general,because the area of grassland and shallow water area has not changed significantly,the expansion of beaches has little impact on their habitat suitability.(3)For Scolopacidae and Laridae,because of the expansion of the beach,the mudflat has been transformed into grassland and reed successively.In addition,after the operation of the Three Gorges Dam,the deep-water area of Dongting Lake in winter was expanded.The area of mudflats has been decreasing,which has seriously reduced their habitat suitability.Compared with the 1980s,the high grade of total habitat area,mean patch size and largest patch index of Scolopacidae decreased by 61.2%,71.4%and 43.4%respectively in 2010s,while those of Laridae decreased by 51.7%,57.6%and 48.6%respectively.(4)After the implementation of Poplar Ecological Retreat,the area of poplar in Dongting Lake wetland decreased significantly.Compared with 2016,the area of poplar in 2019 decreased by 98 km2.(5)According to the results of Pearson correlation analysis,the area of poplar was significantly negatively correlated with the area of moderate grade habitat of Anatidae and Ardeidae,and significantly positively correlated with the area of general grade habitat.Poplar Ecological Retreat improved the habitat suitability of Anatidae and Ardeidae.(6)There was no significant change in the habitat indexes of different grades of Scolopacidae and Laridae with the reduction of poplar area.This shows Poplar Ecological Retreat had no significant impact on the habitat suitability of Scolopacidae and Laridae.The conclusions of this research can provide reference for understanding the living conditions of migratory birds in Dongting Lake wetland,determining priority conservation areas and maintaining wetland biodiversity.