| Cultivated land is the basis for human survival and development.Entering the21st century,with the process of urbanization in my country,the number of people working in agriculture is decreasing,and it is gradually showing an aging state.Most arable land in rural areas has been abandoned.The abandonment of arable land has seriously affected my country’s food security.To maintain sustainable agricultural development,we must first ensure the quantity and quality of arable land.Therefore,mastering the amount and distribution of abandoned land and taking timely re-cultivation measures are an important part of the country’s sustainable development.Because of the steep terrain and difficult planting in the low mountain and hilly areas,the abandonment phenomenon is the hardest-hit area in the country,and there are currently few studies on the abandonment of the hilly areas.Chongqing Dazu District is a transitional zone between mountain and plain.It is located in the westernmost part of Chongqing and connects with Sichuan.It has a special geographical location and serious abandonment.The need for re-cultivation of abandoned land is urgent.Therefore,this paper takes Chongqing Dazu District as the research area,uses Sentinel 2 and Landsat8,Landsat5 series of images as remote sensing data sources,and extracts the abandoned land parcels in Dazu District during the three periods from2010 to 2020 based on the decision tree classification method and the annual land transfer method.Studying the situation of re-cultivation of abandoned land in the study area during the past ten years.Using the extraction results of abandoned land,combined with 6 factors such as DEM,slope,irrigation distance,transportation convenience,cultivation radius,and patch area,a micro-recoverability study of the current abandoned land in the study area in 2020 is carried out.Select the appropriate landscape index to analyze the spatial distribution of abandoned land in each region in2020 and obtain the distribution law of abandoned land.Correlation analysis and multiple regression analysis were made between the landscape index and the micro-recoverability index of abandoned land in 2020,Obtaining the macro-recoverability model of abandoned land in Dazu District and Calculate the re-cultivability values of 21 towns and central urban areas in the study area respectively.In the previous studies on the spatial pattern of abandoned land,they were all qualitative forms,and most of the studies were based on the spatial distribution characteristics of abandoned land.This article innovatively proposes to study abandoned land in a quantitative manner,and introduces the concept of re-cultivability.In terms of spatial pattern,it provides a more in-depth study of cultivated land abandonment,and provides reference and technical support for the restoration of abandoned land in the research area.The main results of this research are as follows:(1)Extracting land use classification information on the basis of analyzing abandoned land spectral characteristics,vegetation index characteristics,ISODATA classification and topographic characteristics,the accuracy of each image extracted by the decision tree classification method is greater than 80%.The Kappa coefficients are all greater than 0.7,indicating that the grass and bare soil can be extracted well,and the extraction accuracy of abandoned land is high.Among them,the three-year remote sensing image from 2018 to 2020 is sentinel 2 data,which is 10 m due to its high spatial resolution.the classification accuracy is improved.Improved classification accuracy,can successfully extract abandoned land with small patch area.Therefore,compared with 2011 and 2016,the number of abandoned land parcels in 2020 will be more and more accurate.(2)During the ten years from 2010 to 2020 in Dazu District,the restoration of abandoned land in three periods was good:1.The total area of abandoned land in2011 was 51.59 km~2,accounting for 12.14%of the total cultivated area;the total area of abandoned land in 2016 was 31.47 km~2,accounting for The ratio is 7.41%;the total abandoned area in 2020 is 26.33 km~2,accounting for 6.19%.2.The overall restoration of abandoned land in the past ten years is relatively good:from 2011 to 2016,the area of restoration was 31.47 km~2,with a coverage rate of 61.08%,and the newly abandoned area was 11.35 km~2;from 2016 to 2020,the area of restoration was 19.98km~2.,The re-cultivation rate was 54.78%,and the newly abandoned area was 14.84km~2;from 2011 to 2020,the re-cultivation area was 37.27 km~2,the re-cultivation rate was 72.23%,and the abandoned newly-increased area was 12.01 km~2.3.Abandoned land in the study area during the ten years from 2010 to 2020,the duration of abandonment of abandoned land:The total area of abandoned land that lasted for 1-5years was 53.3 km~2,accounting for 81.2%of the total area of all abandoned land in the ten years.The total area of abandoned land that lasted for 6-9 years was 9.39 km~2,accounting for 14.3%of the total area of all abandoned land,and the total area of abandoned land that lasted for 10 years was 2.95 km~2,accounting for 4.5%.4.For the study of abandoned land in 2020,most of the abandoned land is small in area,less than 0.5 hm~2,the number of blocks is 9748,and the total area is 21.62 km~2,accounting for 82.11%of the total area of all abandoned land in 2020;patch area;0.5-1 hm~2,accounting for 9.8%,greater than 1 hm~2,accounting for 8.09%.(3)In 2020,most of the abandoned land parcels have a high micro-recoverability index,and the difficulty of recovery is relatively small.Six factors such as DEM,slope,irrigation distance,transportation convenience,cultivation radius and patch area are related to the recultivability of abandoned land factors.Among them,DEM,slope,irrigation distance,tillage radius and patch area factors are negatively correlated with the cultivability of abandoned land,and transportation convenience is positively correlated with the cultivability of abandoned land.Using the principal component analysis method to determine the weight of the 6factors,the micro-recoverability index of abandoned land can be calculated,and the index is divided into five levels according to size,representing the difficulty of recultivating each abandoned land.(4)Dazu District will have three levels of macroscopic re-cultivation of abandoned land in each region in 2020,which are easy,medium and difficult.Correlation analysis results between the selected landscape index and the microscopic cultivability index of abandoned land:CA,NP,AREA＿MN,AREA＿MD,PR,and SHDI are negatively correlated with the cultivability index of abandoned land,while PD,PRD,and CONTAG are positively correlated.Among them,NP,AREA＿MN,CONTAG,SHDI,CA have a greater correlation with the recultivability index of abandoned land.In the area,the smaller the number of abandoned land,the smaller the total area of??abandoned land,and the more regular the distribution.The smaller the overall fragmentation,the fewer the microscopic re-cultivation index levels of abandoned land,and the less manpower and material resources need to be re-cultivated.The regional macroscopic cultivability is divided into five levels:high cultivability(8-10),high cultivability(6-8),general cultivability(4-6),low cultivability Re-cultivation(2-4),low re-cultivation(0-2).In 2020,22 areas in Dazu District will have a re-cultivability value between 3-9,5 towns have low re-cultivability,9 towns have general re-cultivability,and 8 towns have high re-cultivability. |
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