Trajectory analysis of agricultural lands occupation and its decoupling relationships with the growth rate of non-agricultural GDP in the Jing-Jin-Tang region, China

Urbanization leads to the expansion of construction land. The rapid and intense construction land expansion in the Jing-Jin-Tang (Beijing–Tianjin–Tangshan) region has had various impacts on the economic development and natural environments. Based on remote sensing images, trajectory analysis was used to depict the dynamic changes of land use types over past three decades and explore the impact of urban expansion on the environment. Adopting Tapio’s decoupling analysis, we considered the relationship between the rate of change in areas of agricultural land occupied by construction land (ALO) and the non-agricultural GDP (NAGDP) growth rate to determine and compare the ecological consequences and economic impacts of urban expansion between cities with different industrial structures in the region. Our results show that: (1) during the study period, expansion of construction land in Beijing, Tianjin and Tangshan increased first and then decreased. (2) Early in the study period, most of areas converted to construction land had originally been agricultural land, but this gradually changed to include more other land use types. (3) The expansion of construction land not only occupies a large amount of agriculture land and ecological land, but also aggravates urban ecological problems. (4) The decoupling state of Tianjin was more ideal compared with those of Tangshan and Beijing. (5) Finally, the rate of change in ALO area began to decrease over the study period, even though the NAGDP growth rate continually increased in the whole region, meaning that the decoupling states were moving in an ideal direction.