| Cultivated land is the most fundamental natural resource to ensure human survival and social development and the fundamental guarantee for the stability of a country.In recent years,along with the increase in population and the rapid development of economy,urbanization and industrialization have been accelerated.In this context,a large amount of land is needed for urban construction.The main source of urban construction land is cultivated land,which leads to the encroachment of a large amount of cultivated land.The rapid development of industrialization intensifies soil pollution.As a result,a lot of cultivated land is no longer suitable for farming.However,due to the serious shortage of cultivated land reserve resources in China,it is difficult to supplement the occupied and polluted cultivated land.In addition,the state is vigorously promoting ecological policies such as returning farmland to forests,grasslands and lakes.Therefore,the spatial distribution of cultivated land shows an increasingly fragmented trend,and the decline in cultivated land area is getting worse.In response to the continuous reduction of cultivated land,it is particularly important to analyze the status quo and evolution process of cultivated land,explore the law and driving mechanism of cultivated land evolution,and provide relevant theoretical basis for cultivated land protection,and it is of great significance to ensure food security and promote the sustainable development of regional ecological environment and economic society.Taking Yangzhou City,a prefecture-level eity,as an example,based on the remote sensing image data of six phases in 1990-1995,1995-2000,2000-2005,2005-2010 and 2010-2015 and the landscape ecology,statistics and theories of other disciplines,this thesis used ArcGIS spatial analysis software and SPSS statistical software to analyze the status quo and change rules of cultivated land area under different scales and regions through the change rate of cultivated land use and the dynamic degree index of cultivated land change.The evolution characteristics of cultivated land landscape pattern in Yangzhou City were analyzed using the landscape index method.Nuclear density analysis was used to analyze the spatial distribution characteristics of the evolution degree of landscape pattern in Yangzhou City.The driving forces of cultivated land landscape evolution were analyzed using principal component analysis.The main conclusions are as follows:(1)From 1990 to 2015,on the whole,the cultivated land area in Yangzhou City continued to decrease,with the largest decrease in 2005-2010.In terms of region,except that the change rate and dynamic degree of cultivated land in Gaoyou city and Jiangdu District were higher than other districts and counties in 1995-2000,in other years,Hanjiang District and Guangling District with higher economic development level were significantly higher than other districts and counties.In terms of time,the cultivated land changed most dramatically from 2005 to 2010,with the change rate and dynamic degree of cultivated land higher than other periods.(2)The fragmentation of cultivated land landscape increased year by year and the landscape dominance decreased gradually,but it was still the dominant landscape in Yangzhou City.The complexity of landscape patch shape increased,the aggregation decreased,and the interference of human activities to the cultivated land landscape was getting stronger and stronger.The stability of cultivated land landscape also showed a decreasing trend year by year.Human activities promoted the gradual regularization of the distribution of cultivated land landscape and enhanced its anti-interference ability while damaging the cultivated land landscape.The cultivated land landscape pattern evolved the most dramatically during 2005-2010,followed by 1990-1995 and 1995-2005.After 2010,the trends such as cultivated land landscape fragmentation were effectively curbed.(3)Except that the sharp decrease and increase of cultivated land were mainly distributed in Jiangdu District and Gaoyou City during 1995-2000,such sharp decrease and increase distributed in Hanjiang District and Guangling District with high economic and social development levels in other years.(4)On a citywide scale,among the driving factors,the main driving factors affecting the evolution of cultivated land landscape in Yangzhou City were economy and people's lives.The influence of driving factors on the evolution of cultivated land landscape increased with time.After 2005,the influence increased rapidly and reached the maximum in 2015.(5)On a township scale,in the different years,the most influential factor on the evolution of cultivated land landscape was economy,followed by people's lives.In different regions,the regions with the higher comprehensive principal component values in different years were mainly distributed in Hanjiang District and Guangling District with high economic and social development levels. |
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