Temporal And Spatial Variations Of Landscape Pattern Vulnerability In The Yellow River Delta

The Yellow River Delta is one of the three largest deltas in China.It contains important wetland ecosystems,providing important habitats for rare and endangered bird species,and thus plays an important role in ecological environmental protection and national economic development.At the same time,the Yellow River Delta has a fragile ecological environment due to its special sedimentary environment.In recent years,due to the increasing impact of human activities,its surface landscape has undergone complex and drastic changes,resulting in threats to the ecological environment,reduced land use benefits,and increased vulnerability of landscape patterns.In view of the strong scale-dependence of the vulnerability of landscape pattern,it is of great significance to carry out research on the spatio-temporal changes of the landscape pattern and its vulnerability of the Yellow River Delta based on the selection of the most suitable spatial analysis scale.This paper takes the Yellow River Delta as the research area,and uses Landsat remote sensing images in 1998,2005,2012 and 2018 as the data source.The coefficient of variation method and the inflection point identification method are applied to determine the best spatial analysis granularity of the study area from the perspective of landscape level and type level;semivariogram and other geostatistical methods are used to determine the best spatial analysis range in the study area;On this basis,according to the changes in the landscape index during the study period,the changes in the landscape pattern of the Yellow River Delta are analyzed,and according to the change of the landscape pattern vulnerability index,the temporal and spatial evolution law and spatial correlation characteristics of the landscape pattern vulnerability of the Yellow River Delta are analyzed.The main conclusions are as follows.(1)From 1998 to 2018,the unused land,tidal flats,salt pans,aquaculture ponds,and construction land in the Yellow River Delta have changed significantly.Among them,the transfer-in area of construction land is the largest,and the transfer-out area of unused land is the largest.From 1998 to 2005,the dynamic range of landscape changes was relatively small,and the main types of landscape that changed were construction land,salt pans and breeding ponds,especially the conversion of unused land to cultivated land;The unused land,salt pans and breeding ponds experience large dynamic changes from 2005 to 2012,and the area of salt pans and breeding ponds increased rapidly;From 2012 to 2018,the dynamic range of changes in various landscape types was relatively obvious,especially the changes in cultivated land,waters,construction land,tidal flats,salt pans,and breeding ponds.(2)The optimal granularity for spatial analysis of landscape patterns in the Yellow River Delta is 220 m.The analysis of landscape indices showed that,from the perspective of landscape level,,the landscape of the Yellow River Delta has been fragmented in the past 20 years,accompanied by the complexity of the boundary of the landscape types and the strengthening of the connectivity between the landscape types..From the perspective of type level,the largest patch index of cultivated land was larger,indicating that the cultivated land was the main landscape type,and the patch cohesion index was higher and the connectivity was stronger;The patch shape index of construction land was larger,and the landscape shape tended to be more complicated,while the patch shape index of forest and grassland was lower with relatively simple landscape shape;The agglomeration index of cultivated land,salt pans,breeding ponds,and tidal flats was relatively high,indicating that the concentration of landscape types was relatively strong.(3)The most suitable landscape analysis range for the Yellow River Delta is a 3×3 km grid,based on which the landscape vulnerability of the Yellow River Delta was analyzed.Results showed that the landscape vulnerability of the Yellow River Delta has been strengthened during 1998-2018,and the landscape vulnerability has gradually increased from inland to coastal.High-vulnerability areas were mainly distributed in the northern and eastern coastal areas,and low-vulnerability areas are widely distributed in the central and southwestern regions.The main reason for the higher vulnerability of the landscape pattern is that the landscape pattern of the high-vulnerability area was mainly composed of unused land,tidal flats,salt pans,and breadingponds,which made the higher dominance of single landscape type and led to increased landscape sensitivity and lower diversity.Besides,the uneven spatial distribution of landscape types could also lead to low landscape adaptability.(4)The spatial autocorrelation analysis of the landscape pattern vulnerability in the study area found that Moran's I coefficients have been increasing year by year,with 0.344,0.354,0.365,and 0.399,respectively.The spatial aggregation effect was becoming more and more obvious,and the spatial positive correlation was significant.The local autocorrelation analysis found that the spatial difference of the vulnerability index of the landscape pattern in the study area was significant,and mainly in the form of "high-high" aggregation and "low-low" aggregation.During the study period,indicating that the spatial correlation of the vulnerability of the Yellow River Delta landscape pattern has increased.