The impact of dynamic change of cropland on grain production in Jilin

The quantity and quality changes of cropland in Jilin province are analyzed by combining the statistics from 1949 to 1999 and land-use maps interpreted from TM images in 1986 and in 2000. In general, the decreasing trend of the cropland in Jilin province was derived from the statistic data in 1949-1999. While since 1983, the cropland area has increased slightly, because of the conversion from other land-use types to cropland. It is showed that the net increase of cropland was about 43.40×10 4 ha. While the quality change of the cropland can be seen from that mainly caused by the conversion from forestland, grassland to cropland and the change mainly took place in the west, where it is ecologically fragile. According to the spatial distribution model, the centroids' move of the cropland and the grain production are calculated, whose directions are not consistent. The impact of the dynamic change of the cropland on food security is further analyzed.

2008—2017年陕西地级城市经济影响力时空分异

城市经济对城市的定位、发展具有重要意义,随着城市的发展,各城市之间经济影响力的差异逐渐显现,探索其时空分布特征及驱动机制,可以为城市规划定位、政策制定等提供依据。文章基于陕西省地市级城市经济的时空分异性,运用主成分分析法,对2008—2017年陕西省城市经济影响力进行测算并分析。研究结果表明:①陕西省各市经济影响力随时间推移逐年提升,各市增速不同,总体稳定,局部变动;②自然、资本和政策共同驱动着城市经济的变化,与城市经济影响力得分显著正相关;③2008—2017年陕西省城市经济影响力热点区和冷点区呈现出明显的空间异质性,冷点区主要分布在陕南,西安市以7.285居热点区第一位,榆林(2.337)次之;④2008与2017年趋势面在东西、南北两个方位均呈现倒U型趋势,凸显西安市作为陕西省经济中心的影响力。