Spatiotemporal pattern change of cultivated land in Weibei Dryland of Shaanxi Province

Cultivated land is an irreplaceable natural resource for food security and social stability, even human survival. However, a drastic change in the spatial distribution of occupied cultivated land has caused tremendous pressure on agricultural production and the ecological environment. It is necessary to carry out long-term dynamic monitoring for the spatial distribution of cultivated land on a regional scale in the sustainable development of the natural resource. Taking the Weibei Dryland in Shaanxi Province of China as research area, this study aims to investigate the spatial distribution and change trends of farmland since 1995. Digital elevation model (DEM) data was selected at the township-level administrative divisions in six years (1995, 2000, 2005, 2010, 2015, and 2020). ArcGIS 10.6 platform was used for the net change rate of arable land and the dynamics degree, as well as the shift of gravity center and standard deviational ellipses of cultivated land. GeoDa 1.14 software was selected for the plot of local spatial autocorrelation and laser interferometer space antenna (LISA) in the areal proportion. The results showed that: 1) The total area of cultivated land in the Weibei arid highland decreased by 5.58% in 2020, compared with 1995. Specifically, the area of cultivated land decreased by 730.47 km2, while the net loss area of cultivated land continued to expand over the past 25 years. The dynamic degree of cultivated land change maintained at a medium level, where the stability of cultivated land resources weakened in the whole region, particularly relatively low in the northern high plain. 2) The gravity center of cultivated land shifted generally in the northeast direction. Specifically, the moving distance was 17 160.84 m, while the migration rate increased from 165.34 m/a to 1 303.78 m/a. There was a "slow (1995-2000) and accelerating (2000-2020)" variation in the migration speed for the gravity center of cultivated land. The spatial pattern of the standard deviational ellipse shifted also to the northeast in the cultivated land, where the ellipse area increased by 1 904.93 km2. Nevertheless, there was a decreasing trend of cultivated land area only from 2015 to 2020, while the spatial distribution of cultivated land tended to be scattered. The scattering rate of cultivated land was stable, due mainly to the implementation of the ditch reclamation project in Yan'an City. 3) There was a significant difference in the local spatial autocorrelation heterogeneity of area ratio in the cultivated land from 1995 to 2020, ranging from 0.273 to 0.529. Most regions showed an aggregation state of high-high value (HH) or low-low value (LL). The high-high-type areas were concentrated in the southeast of the study area. In the LISA frequency geo-spectrum, the proportion of stable and low-frequency regions were 89.58% in total, indicating a relatively stable pattern of cultivated land. The transition mode was mainly from "low-low" and "low-high" aggregation to stable in the regions with the medium and high frequency. The spatial pattern attenuated more obviously in some cultivated land. Therefore, a combination of the LISA frequency map, the barycenter model, standard deviation ellipse, and spatial autocorrelation can be expected to systematically explore the variation trend of regional spatial patterns in real time. The finding can provide a scientific basis for the optimization of spatial layout in farmland protection. © 2021, Editorial Department of the Transactions of the Chinese Society of Agricultural Engineering. All right reserved.