基于边际模型的中国城镇化演进对耕地影响极限研究

城镇化建设是支撑社会经济持续发展的国家战略,城镇化快速演进对耕地影响如何,关系到耕地保护红线目标能否实现及粮食安全,探索城镇化演进对耕地影响的极限规律具有重要现实意义。运用扩展Kaya恒等式及LMDI分解模型,测算了1997—2011年中国城镇化引致的耕地减少份额;借鉴经济学边际理论及边际效应模型,采用回归分析及高数求导方法,构建了边际耕地影响及边际耕地变化率测度模型;以边际耕地变化率时序数据为基础,借助EXCEL软件,通过作散点图并添加趋势线,构建了边际耕地变化率曲线,据此测算了城镇化演进对耕地影响最小的极限时刻。结果表明:①城镇化演进占用耕地面积由1997年的59.59万hm2下降至2011年的31.73万hm2,整体呈降幅态势,年均占用43.49万hm2;②边际耕地变化率指数由1997年的0.183 3下降至2011年的0.037 8,年均下降11%;③边际耕地变化率拟合曲线为开口向上的"U"形抛物线,其最低极值点大约出现在2010年。研究结果可为管理层科学编制土地利用规划及制定协调城镇化演进与耕地保护政策提供参考,也可为省域尺度的同类研究提供方法借鉴。

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.