| China’s urbanization has achieved great results,but the phenomenon of rural hollowing has also emerged,which directly leads to a large number of farmlands abandonment,and forms certain obstacles to food security and industrial development.As a main grain production area and high-quality farmland protection area of the country,as well as a major labor export province,Sichuan is with prominent rural hollowing,mainly in hilly and mountainous regions surrounding the basin.The problem of regional farmland abandonment cannot be ignored,especially when it is related to food security,rural economic development,precise poverty alleviation,establishment of regional farmland rotation system,sticking to the red line of farmland protection,and implementation of strategic decision of storing grain in the land.But there are still many problems to be discussed.Such as what kind of technical methods can be used to collect statistics of abandoned farmland areas in Sichuan Province?Is there a rule of territorial differentiation in abandoned farmland?Does the problem of different study scales of geography exist in the abandoned farmland?What are the internal causes and mechanisms of abandoned farmland?How to carry out dynamic monitoring of abandoned farmland?And what are the most effective methods to control the abandonment of farmland?The solution of the above problems can provide technical support for the general survey of farmland abandonment in similar areas,data reference and evidence for the problem of food security,reference for the systematic research of abandoned farmland,guidance for the spatial pattern of rotation of farmland in Sichuan Province and similar areas,and enlightenment for carrying out the research of farmland protection and formulating the farmland protection measures and strategies in different regions.Due to the influence of cloud,light and other conditions in Sichuan Basin and southwest hilly area,quality and quantity of land surface information obtained from traditional remote sensing images are relatively low.At the same time,because of the influence of unique topography,the mountainous and hilly regions around Sichuan Basin are with a high degree of fragmentation.So it is difficult to identify abandoned farmland by low-resolution remote sensing survey.Based on the comparative analysis of satellite remote sensing image with resolution of 5.8m and 2m and UAV remote sensing image with resolution of 12cm,it is found that the visual interpretation of remote sensing image data with resolution of 5.8m cannot distinguish whether the farmland is abandoned or not;but the image with resolution of 2m and 12cm can solve this problem at the scale of patch and plot.However,some of the farmland cannot be correctly interpreted by visual method for the influence of plant growth and water content of underlying surface.In additon,the 12 cm resolution UAV image is greatly influenced by the training samples.Therefore,in the study of abandoned farmland on provincial scale,field survey methods were used to obtain spatial information based on high-resolution remote sensing images.Firstly,the author selected Tanshanpu village of Shunqing District,Nanchong City as the experimental site to carry out the investigation of abandoned and cultivated farmland.In all,1379 abandoned farmland plots(including 569 paddy fields and 810 dry lands),770 uncultivated farmland plots(302 paddy fields and 468 dry lands)were obtained,which accumulated experience for the follow-up steps.After that,501 survey sample areas(1km~2 of each)were randomly selected in Sichuan Province to carry out the land type survey of abandoned farmland patchs and their influencing factors.A total of 9895 abandoned farmland patchs(3880in paddy field,6015 in dry land),15276 cultivated farmland patchs(6104 in paddy field and 9172 in dry land)were obtained,and the provincial scale abandoned farmland patchs database was constructed.Then,based on the high-resolution remote sensing image,the author selected typical case areas to carry out village scale abandoned farmland patch survey,and obtained 537 abandoned farmland patchs(264 paddy fields and 273 dry lands),730 cultivated farmland patchs(161 paddy fields and 569 dry lands),1044 abandoned farmland patchs(413 paddy fields and 631 dry lands),860 in Jinyuan and Baoping respectively(224 paddy fields and 636 dry lands),and the geographic information database of abandoned agricultural patchs in villages and towns were constructed.Then,two typical case villages were selected to collect the information of abandoned farmland and farmers.For Tiantang,a village located in the mountainous area around the basin of Jiangshi Township,Jian’ge County,Guangyuan City,398abandoned farmland plots(149 paddy fields and 249 dry lands)and 2390 uncultivated farmland plots(733 paddy fields and 1657 dry lands)were obtained,and for Fenghuang,a village located in the hilly area of the basin of Langchi Town,Yingshan County,Nanchong City,930 abandoned farmland plots(212 paddy fields and 718 dry lands)and 1651 cultivated farmland plots(714 paddy fields and 937 dry lands)were obtained,and a database of abandoned farmland plots was constructed at the scale of contracted plots for rural households.Finally,based on the above-mentioned geospatial and DEM data,six methods such as spatial exploratory data analysis,cold and hot spot analysis,spatial autocorrelation analysis,fractal analysis,geographic concentration analysis,and nuclear density analysis were used to study the spatial heterogeneity of abandoned farmland in four different scales,that is province,county,township and plot,respectively.And the impact mechanism of abandoned farmland in county,village,farmer and plot scale was judged by regression analysis.The innovative achievements of this thesis are as follows:(1)Through this study,the author explored a suitable method for different geographical scales to solve the spatial pattern of abandoned farmland.On provincial scale,due to the data unavailability,abandonment rate should be calculated by the method of random sampling,and then the spatial pattern of abandonded farmland of this scale should be analyzed based on variation function,spatial exploration analysis and cold hot spot calculation.For county scale,the spatial interpolation can be conducted according to the abandonment rate of random samples,and then spatial autocorrelation analysis can be selected to evaluate its spatial difference.Specific to township and village scale,the study is with more details.Therefore,the acquisition of plot is more suitable to select geographic concentration and nuclear density detection to find the concentrated area of abandoned farmland.As for plot or patch scale,they are more suitable by fractal theory and statistical calculation to determine the spatial heterogeneity of plot and pacth abandonment based on concentration analysis of spatial interference factors.(2)Carry out the study on the spatial pattern of abandoned farmland on the provincial scale is the supplement and improvement of this field in China.In the study of abandoned farmland,scholars mainly took geomorphic type area,country,county,town and village as the research scale.In recent studies,no scholars at home and abroad have ever carried out the research work on abandoned farmland in the provincial scale and plains.As a main grain producing area,Sichuan Province has five geomorphic types of plateau,mountain,plain,hill and parallel mountain valley.So the study on abandoned farmland in Sichuan Province can made up for the lack of research on the default domain scale and the plain geomorphic type area.At the same time,this study can help to improve and summarize the spatial characteristics of abandoned farmland in different geomorphic types.The results showed,in east Sichuan Province,the farmland in the basin hills was seriously abandoned,followed by the mountain areas around the basin.while the farmland in Chengdu Plain and the mountain areas in the southwest was relatively low,and the farmland in the plateau of the west was relatively random.The degree of abandonment of paddy field and dry land was slightly different among geomorphic units.(3)The study on spatial heterogeneity and formation mechanism of farmland abandonment based on the scale of province,county,village,farmer and plot was a new attempt to study multi-scale geographic information science under the guidance of system theory.Taking high-resolution remote sensing image as the data source,the field survey of abandoned farmland was carried out to obtain large sample data of abandoned farmland.It was a new attempt to study the spatial heterogeneity of abandoned farmland in different scales and discuss its formation mechanism,which was supported by geographic information technology.Furthermore,it also improved the regional unit and research system of abandoned farmland.Under the influence of research scale,the spatial pattern characteristics and driving mechanism of abandoned farmland in different scales were different.On the provincial scale,there were regional spatial differences in abandoned farmland of Sichuan Province,just like the geomorphic division;on the county scale,the county agglomeration characteristics of paddy field,dry land and comprehensive abandoned farmland were more detailed than the provincial scale,and slightly different from the cold hot spots of the abandonment rate on the provincial scale;on the township village scale,there were spatial differences between the villages;on the plot scale in degree,abandoned farmland was disturbed by its own topography,irrigation,commuting distance and other family economic factors,showing spatial differentiation characteristics.(4)The shortage of spatial pattern analysis of abandoned farmlands is made up,and their spatial pattern characteristics are systematically summarized.At present,the spatial pattern of abandoned farmland is analyzed from the perspective of geographical space,while the quantitative analysis of the spatial pattern of abandoned farmland by domestic scholars is deficiency.Based on the systematic analysis of the topographical factors(altitude,slope,aspect)and spatial disturbance factors of abandoned farmland,it was found that the patchs of abandoned farmland in Sichuan Province were affected by their own topographical conditions and surrounding land types.It showed that the abandonment rate of farmland raised gradually with the increase of terrain gradient;it raised successively from sunny slope,semi sunny slope and semi shady slope;within200m of the adjacent road,the abandonment rate raised gradually with the increase of distance from the road;within 0-600m of the water system,the abandonment rate of dry land was higher than that of paddy field;and within 0-250m of the residential area,it was higher with the distance from the residential area.The increase of the distance between the residential area and the dry land showed that the closer to the forest land,the higher the rate of abandonment. |
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