中国生态退耕重要阶段耕地面积时空变化分析

为了兼顾生态退耕过程中的生态安全和食物安全，开展中国生态退耕政策实施重要阶段(1999—2008)的耕地时空变化特点的研究十分必要。根据各省市级耕地增减变化数据，利用分布重心计算模型和分区比较方法，探讨了中国耕地面积时空变化的总体特征。结果表明，从区域尺度分析，研究时段内耕地面积减少幅度排序为：西部＞东部＞中部；生态退耕政策实施的重要阶段可划分为2个时期：一是生态退耕前期，以耕地面积急剧减少、面积分布重心向东移动为特征；二是生态退耕后期，以耕地面积缓慢减少、面积分布重心向北迁移为特点；生态退耕、农业结构调整和建设用地占用所造成的耕地变化，对耕地面积分布重心迁移的影响较大。研究结果提示，建设用地占用优质耕地是制约中国耕地整体生产能力提高的重要因素，而耕地分布重心向北移动使生态退耕的成效面临挑战。

Spatio-temporal Changes in Cropland Area During Important Period of the Grain-for-Green Policy in China

It is necessary to carry out the study of spatio-temporal changes in cropland area during the important period of the grain-for-green policy (1999-2008) for food security and ecological security in China. The overall characteristics of spatio-temporal changes in cropland area were analyzed using gravity center model and regional comparison method based on the provincial-level cropland change data. The results showed that: the regional reducing order of cropland area was: west>east>central; the important period of the grain-for-green policy in China could be divided into two period: the early period was characterized by the sharp decline in cropland area and the movement of cropland distribution gravity center eastwards; the later period was characterized by the slow decline in cropland area and the movement of cropland distribution gravity center northwards; the movement of cropland distribution gravity center was largely affected by ecological de-farming, agricultural structural adjustment and expansion of construction land. The results implied that the expansion of construction land onto high quality cropland was an important factor restricting the overall productivity of cropland in China, and the movement of gravity center for cropland distribution northwards might reduce the effectiveness of the grain-for-green policy.