A marginal model-based study of the ultimate influence of China's urbanization evolution on cropland

Urbanization is a national strategy support for sustainable socio-economic development, which has become an inevitable way of achieving modernization in China. The process of urbanization is closely related with changes in land use. Proposed by the report delivered at the 18th National Congress of the Communist Party of China (CPC), China should continue to promote the process of urbanization. The influence of rapid evolution of urbanization on cropland is related with cropland protection and food security. It is therefore of great practical significance to explore the ultimate effect of the laws of urbanization evolution on cropland so as to formulate cropland protection policies in relation to efficient management of the evolution of urbanization in China. The extended Kaya Identity and Logarithmic Mean Divisia Index (LMDI) decomposition models were used to estimate the proportion of dwindling of cropland caused by China's urbanization from 1997 to 2011. In reference to the marginal theory and marginal effect model, the decreasing proportion of croplands due to urbanization evolution was used as the dependent variable and the level of urbanization used as the independent variable to establish the marginal cropland influence model in SPSS software and regression analysis. By using time as independent variable, marginal change rate of cropland as dependent variable, a curve of marginal influence change rate of China's urbanization evolution on cropland was constructed. Then based on the curve, the ultimate moment of minimum urbanization evolution influence on cropland was estimated. The results showed that with evolution of urbanization, the area of land under cropland fell, dropping from 595 900 hm² in 1997 down to 317 300 hm² in 2011. The annual average trend of decline was 434 900 hm². The marginal change rate of cropland dropped from 0.183 3 in 1997 to 0.037 8 in 2011, and with an annual average of 11%. The curve best fitting marginal change rate of cropland was a U-shaped parabola with the minimum point in 2010, which meant year 2010 was the ultimate time of urbanization influence on cropland. The results not only provided reference for the scientific formulation and management of land use and the coordination of evolution of urbanization policies and cropland protection, but also provided the way for similar studies at provincial scale.