Northeast China has undergone large-scale cultivation of agricultural land, accompanied by internal restructuring of paddy fields and rain-fed farmland. Such a land change process has an obvious impact on the ecosystem. However, the quantitative effects of long-term cultivation of land/internal structure on the eco-environment are still lacking in the Heilongjiang region, China’s ecological barrier and grain base. To address this academic issue, the integrated method of land update technology, dynamic tracking, remote sensing classification, and improved ecosystem services were applied using satellite imagery and land products. Through satellite monitoring, the area of cultivated land changed from 127,221.71 to 173,665.12 km2, with an increment of 46,443.41 km2, expanding the central–northern parts and the eastern part over the past half-century. In different regions, all cities have undergone varying degrees of reclamation rate expansion ranging 0.71–29.62%. Regarding the structure, a quarter of the study area was covered by rain-fed farmland (25.29%), but the cultivation level of paddy fields (2.83%) was very low in 1970; after that, only a 13.08% increment in rain-fed farmland but a high increase of 246.14% in paddy fields was monitored from 1970 to 2020. Meanwhile, the source area of cultivated land was 59,271.48 km2, with 60.41% from forest and grassland of the agricultural-forestry ecotone. Its destination area was 12,827.11 km2, and 78.49% of the total was converted to construction land, forest, and grassland. From 1970 to 2020, the evaluated ecosystem service changed from 15,575.87 to 12,495.72 × 108 yuan, showing a total loss of 3080.15 × 108 yuan and an annual turnover rate of 0.40%. An important calculation indicated that the expansion and shrinkage of cultivated land led to a 2303.46 × 108 yuan loss, which means that three-quarters (i.e., 74.78%) of ecosystem service loss was caused by cultivated land changes. Another key finding was that a large transformation of wetland into paddy fields brought about the huge loss of 847.85 × 108 yuan; by contrast, the process of extensive rain-fed farmland turning into paddy fields was only a small change of 3.38 × 108 yuan. Considering the ecological loss caused by cultivated land, the projects of returning farmland to forests and wetland protection should be implemented. This study provided important references for land system monitoring and environmental impact assessment in high-latitude regions around the world.
Yin et al. (Sun,) studied this question.