| Changchun is located in the central Jilin province,covering with typical black soil.This region is characterized by high grain production and fertile soils.Nevertheless,Changchun,as the provincial capital and the most developed area in the province,is also in enormous demand of built-up land and of a relatively vulnerable ecological security.Its ecological security concerns regional stability and social sustainable development.Along with the rapid urbanization,increased population and prominent human-land conflict,anthropogenic activities have profoundly reshaped the components and spatial pattern of cultivated landscape.Moreover,the land ecosystem of Changchun has been suffering from the intensive development and utilization and other ambient pressures.A majority of cultivated lands covered with black soil are going through severe quantity loss,evident degradation and pollution and function declines of ecosystem service.The conservation of black soil resources and regional ecological security requires a guarantee method.Thus,this thesis performed an evolution analysis of black soil cultivated landscape pattern in the main urban districts of Changchun in order to contribute to the establishment of landscape security pattern system and sustainable use of black soil resources.The main urban districts of Changchun,which are composed of Chaoyang District,Nanguan District,Erdao District,Kuancheng District and Luyuan District,were selected as the study area.Cultivated lands covered with typical black soil in the study area were selected as the object of study.Land use data in the main urban districts of Changchun and statistics of yearbooks from 2009 to 2014,along with spatial analysis method in GIS and Fragstats techniques,were used to analyze the quantity,spatial distribution and evolution of landscape pattern metrics of cultivated land based on the theory of landscape ecology.In addition,a quantitative assessment and dynamic analysis were employed for the landscape ecological security in the study area.The results indicate the following,(1)There was a decrease in the total area of cultivated land covered with black soil every year between 2009 and 2014.The total area decreased from 429.474 km2 in 2009 to 372.429 km2 in 2004,57.045km2 of cultivated land covered with black soil were converted.Meanwhile,the change in cultivated land per capita was in accord with the total,and it decreased from 0.000133 km2 per capita in 2009 to 0.000114km2 per capita in 2014,which indicated a rapid urban sprawl rate and the massive occupation of cultivated land resources.Moreover,the dry land dominated in the cultivated land structure and distribution of irrigable land and paddy field was relatively less in the study area.A large area of converted irrigable lands were located in Nanguan District and most of converted paddy fields were located in Luyuan District.Moreover,most of the converted cultivated lands were located in Kuancheng District,which was also the district where cultivated land area was less than the others.It indicated that the spatial development direction of Changchun urban built-up area between 2009 and 2014 was towards the northeast.The land use change rate and the dynamic degree of cultivated land in the study area were both negative values.It rose from-3.463% between 2009 and 2010 to-0.336% between 2013 and 2014,which indicated that the conversion rate of cultivated land was decreasing.The ratio of converted cultivated land area to the added is 62.3:1,the cultivated land loss is evident.Moreover,a majority of cultivated lands were occupied for construction purposes.Thus,the urban sprawl is seriously challenging the black soil conservation and leading to severe cultivated land loss.The cluttered distribution of cultivated land pattern is contributing to the protection of cultivated land resources.(2)According to the measurements of cultivated landscape metrics,this thesis performed an evolution analysis of the landscape pattern of cultivated land covered with black soil in the main urban districts of Changchun.The area weighted mean shape index(AWMSI),fractal dimension(FRAC),fractal dimension(F),division(D),patch density(PD)and edge density(ED)were 0.276,1.278,0.665,0.317 and 0.286,respectively,and they rose to 0.295,1.283,0.708,0.351 and 0.305,respectively.The increasing index values indicated that cultivated land patches were growing more irregular,complex and fragmented.Moreover,landscape metrics in Kuancheng District,Erdao District and Nanguan District were relatively higher,which was mainly attributed to that northeast and east were the dominant development direction for the urban built-up area.In addition,due to the rapid urban sprawl and intensified road networks,most of the index values were elevated and more imbalanced between regions.There is a decrease in the stability of cultivated landscape pattern.(3)The change of cultivated landscape pattern contributes to the significant differences between landscape ecological security in different space and time.The landscape ecological security of area at the east side was much lower than the west.The assessment value of landscape ecological security decreased from 0.593 in 2009 to 0.534 in 2014.The cultivated landscape vulnerability increased with the decrease in landscape ecological security,and the variations were prominent.The area of lower landscape ecological security levels such as level I and level II increased between 2009 and 2014,and the area of higher landscape ecological security level like level III was shrinking.The area of level III was mostly located in the north,the central and the southeast of the study area.The spatial center of landscape ecological security in the study area was moving towards southwest,and the displacement distance is 1621.795 m from 2009 to 2014.It indicates that the landscape ecological security of the eastern part and the northern part is lower than that of the western and the northern part.In a context of Changchun-Jilin integration,the built-up area is sprawling towards the northeast,the east and the northwest.Thus,a large quantity of cultivated land covered with black soil was occupied,and the increase in landscape corridors has damaged the intrinsic cultivated landscape in the peri-urban area.For this reason,the ability against potential ecological risk and landscape security have both been destructed. |
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