| Urban green patch is an important part of urban ecosystem,and changes in its total amount and spatial pattern are closely related to urban construction and development.In order to further explore the temporal and spatial evolution pattern and influencing factors of green patches in the main urban area of Nanjing from 1990 to 2020,this paper obtained 4 high-resolution remote sensing images in the past 30 years,and used the support vector machine(SVM)classification method to interpret the remote sensing images.Extracted with green spot classification.Based on the quantitative,spatial and driving indicators of green patches,this paper analyzes the area(TA),number(NP)and fragmentation index(Fi)of green patches in the main urban area from1990 to 2020 from the two dimensions of time series and space.At the same time,with the help of exploratory regression analysis,14 explanatory variables in social economy,natural environment and urban construction affecting the evolution of green patches were screened out,and the GWR geographically weighted regression model was constructed to discuss the years1990-2000 and 2000-2010 respectively.And the temporal and spatial differentiation characteristics of Y1 green spot reduction rate(RRP)and Y2 green spot fragmentation index change value(VPF)driving factors in three periods from 2010 to 2020.The regression results show that compared with the traditional linear least squares OLS regression model,the AICc value of the GWR model is lower than 3.The model can better eliminate the influence of spatial non-stationarity and has a stronger interpretation of spatial heterogeneity.The main conclusions of the study are as follows:(1)Time series evolution: From 1990 to 2020,the green patches in the main urban area of Nanjing showed a trend of "first decrease and then increase,and the degree of fragmentation intensified".The green spot area decreased from 137.32km~2 in 1990 to 92.45km~2 in 2010,the overall green spot reduced by 32.68%,and the reduction rate gradually accelerated.In 2020,the area of green patches ushered in the first increase,with an area of 113.62km~2,an increase of 22.78%.At the same time,the number of green patches continued to increase,resulting in a gradual increase in the degree of fragmentation in the main urban area.Combining with the structural evolution of green patches,it can be seen that the number and area of green patches of grades I to III increased at the same time;The structure of green patches is developing and evolving towards the pattern of "decreasing layer by layer".The main urban area of Nanjing has transformed from large green patches to small and medium green patches,forming a "complementary" state in space,which explains Nanjing to a certain extent.The principle behind the fragmentation of green patches is that green patches in the main urban area show complex bidirectional flow characteristics.(2)The spatial pattern is evolving: The standard deviation ellipse(SDE)analysis results show that the fluctuation range of the green spot gravity center in the main urban area is maintained at 118.79°～118.81°E,32.04°～32.07°N,and presents a “northeast-southwest-central”pattern.The migration trend of the green spot is more consistent with the migration trend of the green spot along the coastline.The proportion of the semi-axis of the SDE length increases gradually,indicating that the centripetal force of the green spot distribution in the main urban area is gradually increasing,while the change of the SDE area indicates that the spatial distribution range of the green spot in the main urban area has experienced a state of gradual reduction and later expansion;global Moran’s I index analysis The results show that there is a spatial autocorrelation between the green spot reduction rate(RRP)and the change value of the fragmentation index(VPF)in the main urban area of Nanjing from 1990 to 2020,the average distribution of Moran index is 0.21～0.56,and the Z score is 4.5～4.8,the space presents a "clustering" pattern;the local spatial autocorrelation results show that the clustering trend of the green spot fragmentation index(VPF)in the past 30 years is more obvious than the green spot reduction rate(RRP),and the cold value area Distributed in the core scenic area;from the street evolution model,from 1990 to 2020,the “DDI(decrease-decrease-increase)” and “DII(decrease-increase-increase)” evolution models accounted for 48.78% and 43.90% of the main urban area,respectively.,and the rest of the evolution patterns only accounted for 2.44%.The overall evolution of green patches showed a trend of "decreasing and then increasing",and the DDI patterns were concentrated in the main urban area and outside the old urban area,and the IDI patterns were more distributed in the main urban area.(3)In the study of related factors: the analysis results of the GWR model show that the overall explanatory power of urban construction factors on the Y1 green spot reduction rate(RRP)is stronger,and the “construction land area and water body area” have a stronger effect on the green spot reduction in the main urban area of Nanjing.The rate showed an obvious inhibitory effect;while socioeconomic factors and natural environment factors had a more significant influence on the change value of Y2 green spot fragmentation index(VPF),socioeconomic factors played a dominant role,followed by natural environment factors,and the influencing factors There are significant differences in space. |
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