Urban Expansion’s Effects On Habitat Quality And Spatial Optimization In Densely Populated Areas Of The Yellow River Basin

The Yellow River Basin is both an ecological barrier protection zone and an important economic development zone,and the densely populated areas in the basin have the most intense human activities and the most prominent conflicts in the "human-land" relationship.The rapid development of socio-economic and urban expansion has exacerbated the dysfunction of ecosystems and destruction of natural habitats,resulting in a significant reduction of ecological restoration functions and habitat carrying capacity.The study takes the densely populated areas in the Yellow River Basin as typical case areas,which is important for exploring the future urban development planning and habitat quality conservation in the Yellow River Basin.This paper systematically compares the current research progress at home and abroad.Supported by the relevant research theories,the intensity of urban expansion is comprehensively evaluated with the help of multi-source remote sensing data and land-use change data.Then,we use landscape index,land transfer matrix,In VEST model and FLUS model to explore the characteristics and patterns of spatial and temporal changes of urban expansion in the Yellow River Basin and its impact on habitat quality,simulate and predict the trends of urban land use and habitat changes in the Yellow River Basin in 2030,and explore the conflicts between urban expansion and habitat quality protection in densely populated areas under different scenarios.Finally,this paper optimizes the spatial suitability of urban development pattern and habitat quality distribution based on the MCR model.The results of the study are as follows.(1)The impact of urban expansion on habitat quality in the Yellow River basin changed significantly from 1990 to 2018,with the area of urban land increasing by 79.8% and the total area of habitat patches decreasing by 5.2%.Habitat quality is best in the areas where woodlands and grasslands are located in the basin,and habitat quality is worst in urban patches of land,mainly due to the large occupation of grasslands by construction land and arable land,and the increase in the area of construction land patches and the aggregation of patches makes the habitat quality within the towns decreasing year by year.The expansion rate of towns in densely populated areas has a particularly obvious impact on habitat quality,showing a spatial pattern of "high and low outside",with the Xi’an-Taiyuan dense zone having the fastest expansion rate and the most serious habitat degradation,and the mean habitat quality decreasing by 3.9%.The average habitat quality decreased by 3.9%.High-grade habitat patches in the dense area are easily transformed into low-grade patches,which aggravates the reduction of high-grade habitat area and makes the habitat quality grade extremely unstable.(2)The influence of socio-economic factors on habitat quality is stronger than that of natural environmental factors.Among them,population density and distance from roads are the dominant factors leading to habitat fragmentation,while GDP,slope and precipitation can provide favorable development space for habitat quality and promote the development of high-quality habitat patches.Urban expansion produces different results under different environmental characteristics in the future,set up a multi-scenario model,combined with FLUS model and Markov model simulation to predict the impact of urban expansion on habitat quality in the Yellow River basin,simulated land use in 2018 compared with the actual,the final overall accuracy of 89.23%,kappa coefficient of 0.862,the simulation accuracy and reliability meet the requirements.(3)Under the development scenario without habitat constraint,the predicted areas of cropland,forest land and construction land in the Yellow River basin in 2030 all increased significantly,and the area of construction land was 1.13 times larger than that in 2018,with an expansion rate of 11.8%.The mean value of habitat quality decreased by 1.8% compared to the mean value of habitat quality in 2018,the lower-grade patches of habitat quality increased by 10.1%,and the medium-grade patches of habitat quality decreased by 9.4%,with urban expansion having the greatest impact on the lower-grade patches of habitat quality.With the habitat-constrained development scenario,all types of land use types receive the constraints of habitat development conditions,making the area of natural habitat patches continue to rise,and the expansion of construction land is constrained,but the area of patches is also slowly increasing.The predicted area of grassland in the Yellow River Basin in 2030 grows most rapidly,1.01 times more than in2018,and the area of land for construction is 1.07 times more than in 2018.The mean value of habitat quality was 0.6% lower than the mean value of habitat quality in 2018,and the standard deviation of habitat quality decreased by 6.3%.(4)Different habitat grade patches in densely populated areas under no habitat constraint had different degrees of increase or decrease in different regions,with the most increase in medium grade patches of habitat quality in the densely populated area of Lanxi,which increased by 18.2%,and a 4.7% decrease in high and higher grade patches of habitat quality in the densely populated area of Xi’an-Taiyuan.Habitat quality medium-grade patches increased by 14.3% due to scenario-setting constraints,and medium-grade habitat patches were on a continuous rise.The mean habitat quality in densely populated areas with restrictive conditions showed an overall small increase and the standard deviation of habitat quality showed a small decrease,and the habitat quality rebounded when natural habitats were protected.(5)The ecological source lands in the Yellow River basin are mainly distributed in the western and southern parts of the basin,and the source land patches are larger in area,while the eastern part is sparser.The ecological minimum cumulative resistance surface in the high value area of ecological source lands is distributed in clusters,and the ecological minimum cumulative resistance surface in the low value area occupies a large area.In the unconstrained scenario,the low-value areas of the minimum cumulative resistance surface of the construction source land are mainly distributed in the densely populated areas,and the contribution of rural settlements and other construction land to the minimum cumulative resistance surface is smaller in the constrained scenario,and they are scattered in the urban land area in a dotted pattern,showing sporadic spatial clustering.