Spatial–Temporal Change in Paddy Field and Dryland in Different Topographic Gradients: A Case Study of China during 1990–2020

Abstract

As a country with a vast area and complex terrain, the differentiation between paddy field and dryland under different topographic gradients in China is difficult. Based on a land-use grid data set with an accuracy of 1 km, this study applied the Topographic Potential Index and used land-use transition matrices and landscape analysis to compare the change in dryland and paddy field in China from 1990 to 2020 at different elevations, slopes, and slope aspects. The results indicate that paddy field and dryland were mostly distributed in areas with better photothermal conditions. However, in recent years, the paddy field and dryland on the “sunny” slope decreased. Specifically, the area of paddy field and dryland on the southeast, south, and southwest slopes decreased, while they increased on the northwest, north, and northeast slopes. From 1990 to 2020, land conversion among paddy field, dryland, and other land use was mostly concentrated in the third ladder (<500 m elevation) of China. However, the changes in paddy field and dryland have now become active on the second ladder of China. Moreover, the change from other land to dryland on the second ladder accounted for nearly 50% of the country’s change from other land to dryland. Paddy fields and drylands in areas with low elevation and low slopes were reduced, whereas those with higher elevation and higher slopes increased, indicating that the arable land in mountainous areas increased. This indicates that the topographic conditions of arable land that become worse may aggravate soil erosion in the planting process. The landscape fragmentation of paddy field and dryland increased. Compared with paddy field, the dryland was more aggregated, the shape was more complex, and the land plots were more fragmented. As a result, paddy field and dryland show significant differences in their spatial–temporal pattern, landscape characteristics, and land-use changes, and these results can provide an important reference for the sustainable utilization of arable land resources.