Effects Of Spartina Alterniflora Invasion On Quality Of The Red-crowned Crane(Grus Japonensis)Wintering Habitat On Yancheng Tidal Wetland

China's yellow?Bohai?sea migratory bird habitat,which was listed in the world heritage list in July 2019,is not only one of the remaining original coastal wetland types with international significance for conservation,but also the largest overwintering habitat for the west line migratory population of wild Red-crowned cranes in the world.It plays an important strategic role in global biodiversity protection.The red-crowned crane has been listed as a global endangered species by IUCN for nearly 20 years,which is of great value in biodiversity conservation.The number of wintering red-crowned crane here was up to more than 1000,accounting for 60%of the world's total wild population and 80-90%of wintering population in China.Affected by the invasion of Spartina alterniflora since 2000,the landscape structure and function of the regional wetland have changed greatly.This led to the serious fragmentation of the wintering habitat of red-crowned cranes and the shrinking of the living area.The wintering population originally distributed in the coastal wetland of Jiangsu Province from north to south gradually gathered in the core area of Yancheng National Nature Reserve.Meanwhile,the population number showed a continuous decreasing trend.In this context,it is an important scientific problem to study the effect of the invasion of Spartina alterniflora on the overwintering habitat structure and quality of red-crowned cranes.Therefore,this paper is based on the theories of landscape ecology,geography,environmental science,remote sensing,geographic information system and mathematical modeling.Taking Yancheng muddy tidal flat wetland as a case study,it analysed the spatial characteristics of habitat selection by using the field data and remote sensing data.And it identified the basic pattern of Spartina alterniflora expansion,and expounded the influence of expansion on the wintering habitat structure of red-crowned cranes.The basic model of the expansion of Spartina alterniflora was established to explain the influence of the expansion on the overwintering habitat structure of the red-crowned crane.The habitat quality assessment model of the wintering red-crowned cane was established from the perspective of ecological process,and then revealed the impact of the invasion of Spartina alterniflora on the habitat quality.Through the studies,this paper mainly found the following conclusions:?1?The overwintering distribution and habitat selection of red-rowned cranes were obvious.During the wintering periods of 2014-2015,2015-2016 and 2016-2017,the frequency of red-crowned cranes appeared in Suaeda salsa marsh was 44.20%,42.82%and 43.71%,respectively.They appeared in Phragmites australis marsh after harvest at frequencies were 36.72%,39.63%and 38.05%in artificially managed region,and12.80%,13.30%and 12.26%in natural conditional Phragmites australis,respectively.In these three years,the distribution proportion of red-crowned cranes in Spartina marsh were less than 3%.The distribution in aquaculture pond was up to 5.55%,and only 3.67%in the mudflat in 2016.The wintering red-crowned cranes had positive selectivity to Suaeda salsa marsh(₄)=0.4282?0.4420)and Phragmites australis after harvest(₄)=0.3672?0.3963)in artificially managed region,natural habitat,but negative selectivity to Phragmites australis in natural conditional region,Spartina alterniflora,aquaculture pond and mudflat.It was concluded that the Suaeda salsa and reed stubble in artificially managed region were suitable or preferred habitats for the red-crowned cranes.?2?The landscape pattern of Spartina alterniflora changed obviously in time and space.There were three patterns of invading native Suaeda.Since the introduction in1985,the Spartina alterniflora in the core area of YNNR had expanded from sparse community to continuous strip and the area increased to 33.81 km² in 2006.In recent years,the expansion rate of Spartina alterniflora had become slower,with an area of45.95 km² in 2015.From 2000 to 2015,the average annual expansion area of Spartina alterniflora was 1.53 km2.The number of patches increased dramatically,and the landscape shape became complex.In addition,the main invasion orientation of Spartina alterniflora had gradually shifted.The direction was seaward to occupy mudflats in the initial stage.Then,it changed to the landward direction to occupy the habitat of Suaeda salsa.Suaeda salsa was not only the original habitat of the region,but also the preferred habitat for the overwintering red-crowned cranes.The spatial expansion of Spartina alterniflora significantly affected the habitat structure of Suaeda salsa.The area of Suaeda salsa decreased from 45.89 km² in 1980 to 22.36 km² in 2015,and the average width decreased year by year to 1.64 km in 2015.The main impact of marginal invasion was the area reduction and the internal patches invasion led the aggravation of fragmentation trend in Suaeda salsa.Tidal creek-leading invasion resulted in the area reduced and linear partition.?3?The quality of wintering habitat of red-crowned cranes had spatial differentiation.Based on the functional factors of habitat quality?habitat type,benthic biomass,vegetation coverage,distance to water source,topography?,the assessment model of wintering habitat quality of red-crowned crane was established.The results show that the habitat type factor had the largest contribution rate to the habitat quality,which was the main limiting factor to the occurrence probability of red-crowned crane.It followed by the vegetation coverage and benthic biomass,and the water source distance has a low impact on the overwintering habitat.From the perspective of space,the high-quality wintering habitat of red-crowned crane was mainly distributed in the Suaeda marsh in the natural succession area and presented the fragmentation.The reed stubble habitat after harvesting in the artificial management area was relatively high-quality habitat.Most of the reed marshes in the natural condition area were medium-quality habitat,while the Spartina marsh,tidal flat and aquaculture ponds were mostly low-quality habitats.?4?Suggestions on habitat protection and management of red-crowned cranes were put forward.Based on the aspects of biology and environment,a conceptual model of quality management was constructed from the food availability and food richness of red-crowned cranes.It was proposed that proper harvesting and management of reed could change the height and coverage of vegetation,which could be used as an important supplementary habitat for the overwintering cranes.In addition,the restoration of the habitat structure of Suaeda salsa and the control of the community of Spartina alterniflora are important problems to protect the habitat of red-crowned cranes.