Gridding Reconstruction of Cropland Spatial Patterns in Southwest China in the Qing Dynasty

On the basis of modern cropland spatial pattern,we designed a method to quantify the relationship among topography(including altitude and slope),production potential of climate(including light,temperature and water),population density and cropland spatial pattern.Then the method was used to reconstruct cropland spatial pattern with a resolution of 10 km by 10 km in Southwest China for 6 periods between 1661 and 1784 in the Qing Dynasty.The results are shown as follows.(1) As a whole,the changes of cropland spatial pattern in Southwest China can be described in two respects.One is the expansion of cultivated area,which are mainly distributed in the Sichuan Basin and the Yunnan-Guizhou Plateau.The grid cells with small cropland fractions(0~10%) decreased by 24.0% during the past 250 years.The other is enhancement of cultivation intensity,which are obvious in the Sichuan Basin and the central-eastern parts of Yunnan Province.The grid cells whose cropland fractions are relatively large(30%) increased by 10.3% during the past 250 years.(2) The process of cropland change in Southwest China in the Qing Dynasty can be divided into three periods.The cultivation recovery period(1661-1724)--the grid cells whose cropland fractions are small(0~10%) decreased by 11.4%;the slow cultivation expansion period(1724-1820)--the grid cells whose cropland fractions are small(0~10%) decreased by 7% while the grid cells with relatively large cropland fractions(30%) increased by 7%.The postwar abandonment of cropland in some parts of the study area and recovery period(1820-1911)--the grid cells whose cropland fractions are small(0~10%) decreased from 75.0% to 72.2% while the grid cells whose cropland fractions are relatively large(30%) increased from 9.1% to 10.9%.The results of correlation analysis indicate that the reconstruction is reasonable to some degree.