Analysis of terrain gradient effects of land use change in Daqing River Basin

Dynamic evolution of land use is manifested in the continuous change of land use types in time or space. Previous studies reported that the land use type changes with terrain slope and surface undulation, showing an obvious gradient. Taking the Daqing River Basin of China as the research area, this study aims to analyze the terrain gradient of land use change using Landsat images in 1974, 1988, 2001, and 2019. The map of land use type was obtained in different periods using the object-oriented and the decision tree classification combined with a small amount of manual interpretation. The changing pattern of land use types was investigated in the topographic gradient, including the topographic undulation, slope, and topographic level. The driving forces were determined for the changes in the land use structure from the views of natural conditions, social economy, and government decision-making. The results are as follows. 1) There was a significant topographic gradient distribution of land use types. Construction land, arable land, and water bodies exhibited obvious advantages in low terrain gradient areas. The dominant distribution of grassland was in the middle and high terrain gradient areas, while that of forest land was mostly concentrated in high terrain gradient areas. 2) Two types included for the changed land use: the keeping-constant type and the changing-later type. The keeping-constant type included mainly cultivated land with low terrain gradient, and the forest land with high terrain gradient, whereas, the changing-later type distributed widely in middle-high and middle-low terrain gradient areas. The condition for the construction land that occupied farmland was becoming much more serious, while the dominant distribution of cultivated land had been expanding to higher terrain gradient areas. There was a downward trend in the dominant distribution of forest land, whereas, the cultivated land evolved from one-way transfer to two-way transfer, due mainly to the strategy implementation of the Returning Farmland to Forests and Grassland. 3) Large areas of land reclamation occurred in the foothills of Taihang Mountains during the economic backwardness period, due to the dual effects of the continuous decrease in precipitation and population growth. The cultivated land was converting into construction land, forest land, and grassland with the coordinated development in the Beijing-Tianjin-Hebei region. The contradiction between cultivated land and construction land was becoming increasingly sharp with the implementation of cultivated land protection policy. 4) Rational measures were needed for local conditions in the next stage of development. The plain areas with low topographic levels were for the cultivated land and construction land. Therefore, the speed that construction land encroached on cultivated land should be slowed, while the scale and structure of urban/rural construction land should be optimized to promote land-intensive development. The primary areas of soil erosion were concentrated in the sloping fields at the middle and low terrain levels in the foothills of Taihang Mountains, where the implementation of the Three-North Forest Protection Project and the Returning Farmland to Forests and Grassland needed to be strengthened. The scale of cultivated land should be strictly restricted in those medium and high terrain level mountainous areas. Simultaneously, nature reserves should be established under adequate consideration of ecological benefits. The finding can provide a scientific basis for the adjustment and optimization of the regional land structure. © 2021, Editorial Department of the Transactions of the Chinese Society of Agricultural Engineering. All right reserved.