Study On Landscape Ecological Risk Assessment Of Nanning City Based On Land Use Change

With the development of economy and society,the growth of population and the acceleration of urbanization,Nanning’s urban space has expanded rapidly,the regional land use landscape pattern has become more complex,and the fragmentation,separation and vulnerability of landscapes have intensified,and the ecological security of land in Nanning is facing severe challenges.Studying the evolution characteristics of land use landscape pattern in Nanning city and carrying out land use ecological risk assessment has important theoretical and practical significance for the protection of regional ecological environment,the sustainable use of land resources and the acceleration of the high-quality development of Nanning.This paper takes Nanning City as the research area,based on the land use data in 1990,2000,2010 and 2020,with the support of landscape ecology related theories and technical methods such as GIS,Fragstats,Geo Da,etc.,this paper firstly analyze the spatiotemporal evolution characteristics and driving factors of land use change in Nanning from 1990 to 2020,and the PLUS model was used to simulate and predict the land use pattern of Nanning City in 2030.Then,based on the optimal analysis granularity,the temporal and spatial change laws of Nanning’s landscape pattern were discussed.Finally,a landscape ecological risk assessment model was constructed through the landscape index,and the spatiotemporal distribution characteristics and spatial autocorrelation characteristics of landscape ecological risks in Nanning were analyzed,and corresponding management and control suggestions were put forward for different ecological risk areas.The main conclusions of the paper are as follows:(1)From 1990 to 2020,the changes in construction land,cultivated land,forest land and grassland in Nanning were relatively drastic,while changes in water areas and unused land were relatively moderate.In the past 30 years,the construction land and unused land showed an increasing trend and showed a growth rate,while the cultivated land,forest land,grassland and water area showed a decreasing trend and showed a slowdown;The land use level in Nanning is at a medium level,and the level of land use degree is gradually increasing under the influence of more frequent anthropogenic activities;the trajectory of the center of gravity of each land use type in Nanning changed and shifted to varying degrees;during the study period,a total of 1051.61 km~2of land use types in Nanning were transferred,among which construction land and unused land is characterized by net transfer in,while cultivated land,forest land,grassland and water area are characterized by net transfer out.Based on the PLUS model and the the land use data of Nanning City in 2010 and 2020,the land use pattern of Nanning City in 2030 is predicted,and the increase and decrease trend of various categories in 2020-2030 is consistent with that of 1990-2020,of which the construction land area is further increased,and the expansion of new construction land in the downtown area of Nanning and its surrounding areas is more obvious.These changes are mainly related to Nanning’s population growth,social and economic development,the acceleration of urbanization and the implementation of relevant policies.(2)Based on the optimal spatial analysis granularity of 60m,the land use landscape pattern of Nanning City from 1990 to 2030 was studied.The results show that:at the level of landscape type,the number of patches and patch density of construction land are the largest,and the degree of fragmentation is high.However,with the expansion of urban space and the improvement of transportation infrastructure,the shape of the patches tends to be regular and the degree of aggregation continues to increase.The boundary of cultivated land has the highest degree of fragmentation and irregular shape,and the forest land has always been the dominant landscape and the highest degree of aggregation.At the landscape level,from 1990 to 2030,the fragmentation degree of the overall landscape of Nanning increased,the contagion index continued to decrease,the aggregation degree of different patch types gradually weakened,and the shape of landscape patches gradually develops from an irregular and complex trend to a regular and simplistic one.With the development of regularization and simplification,the diversification level and richness of landscape types are continuously improved,and the changes in landscapes tend to be more complex and evenly distributed.(3)From 1990 to 2030,the overall ecological risk level of Nanning City will intensify,and the ecological environment will tend to be degraded.The area of low ecological risk areas and lower ecological risk areas decreased,and the area of medium ecological risk areas,higher ecological risk areas and high ecological risk areas increased.Among them,the ecological risk level of the main urban area of Nanning and its surrounding areas continued to decrease,and the landscape ecological risk level of most other areas increased.The landscape ecological risk index of Nanning City has significant spatial positive correlation characteristics and it shows a pattern of agglomeration distribution in space,mainly based on"high-high"agglomeration and"low-low"agglomeration,of which"high-high"agglomeration area is mainly distributed in Wuming District,Binyang County,Hengzhou City,Jiangnan District,Xixiangtang District and Long’an County,"low-low"agglomeration area is mainly concentrated in Mashan County,Shanglin County,Long’an County,Wuming District,Xingning District,Qingxiu District,Binyang County and Hengzhou City.The main urban area of Nanning City and its surrounding area are gradually transformed from a"high-high"agglomeration to a"low-low"agglomeration area.The distribution characteristics of the"low-high"agglomeration area and the"high-low"agglomeration area are not obvious.