城市化和退耕还林草对中国耕地生产力的影响

Impacts of Cropland Transformation on Agricultural Production under Urbanization and Grain for Green Project in China

20世纪90年代以来的快速城市化进程和1999年开始启动的退耕还林草生态工程对耕地的分布与生产能力产生了重要影响。本研究应用由TM遥感影像获取的1980s-2000年与2000-2005年两个时间段耕地变化数据,结合以多时相遥感数据为主要数据源的耕地生产力光能利用率遥感模型估算两个研究时段耕地生产力变化特征,比较城市化与退耕还林草政策主导下两个时期耕地转移对各区域耕地生产力的影响。研究结果表明:两个研究时段因城市占用损失的耕地生产力占土地利用变化(LUCC)导致的耕地生产力减少总量比例均在60%以上。在20世纪90年代,全国新增耕地生产力总量比被占用耕地生产力高87%,耕地转移使中国耕地生产力增加。2000-2005年间,退耕还林草政策的启动和快速城市化进程对耕地的持续占用导致耕地生产力占补正平衡指数由前一时段的正平衡变为负平衡,转出耕地生产力总量比新增耕地生产力高31%,耕地转为林草地和建设占用损失的耕地生产力分别较前一时段提高57%和85%。城市化与退耕还林草政策等驱动因素作用下耕地开垦区与占用区的空间分布差异使得耕地生产力占补平衡状态和趋势呈现明显的区域分异。

In this study, the changes of agricultural production from cropland transformation in the periods of the late 1980s-2000 and 2000-2005 were estimated based on： 1） the cropland transformation results derived from Landsat TM imagery by artificial interpretation method, and 2） net primary productivity （NPP） data from the light use efficiency models of Global Production Efficiency Model （GloPEM） and Vegetation Photosynthesis Model （VPM）. Changes of regional grain production capacity were mainly from two aspects of cropland transformation： cropland conversion （e.g. urbanization, converting cropland into forest） and land reclamation （e.g. converting grassland into cropland）. The impacts of different cropland transformation types on agricultural production within the two periods were evaluated, a series of comparisons were conducted between the two periods as well as different regions. Results indicated that the agricultural production loss due to urban sprawl accounted for more than 60% during both stages （1980s-2000 and 2000-2005） in the total loss. In the first stage, generally, agricultural production increased evidently. The increased production from land reclamation was 87% higher than production decrease from cropland conversion. However, in the second stage （2000-2005） the agricultural production loss due to cropland conversion was 31% higher than the production increase from land reclamation, in other words, the production decrease due to cropland loss could not be compensated by limited land reclamation, as unban expansion and Grain for Green （GFG） project played an important role in cropland transformation since around 2000. Production losses from GFG project and urbanization were 57 % and 85 % higher than that in the previous stage, respectively. Due to GFG project, the states of agricultural production equilibrium changed from positive balance from the 1980s to 2000 into a negative balance during 2000-2005. the loss of agricultural production mainly occurred in Northeast China, Inner Mongolia, Yunnan and Zhejiang provinces from the 1980s to 2000, and then transferred to Inner Mongolia, Shaanxi, Gansu, Sichuan and Guizhou provinces from 2000 to 2005. The production loss due to urbanization mainly occurred in Jiangsu, Hebei, Anhui, Shandong, Henan and Guangdong provinces from the 1980s to 2000, then changed into provinces of Zhejiang, Guangdong, Shandong, Fujian and Jiangsu during 2000-2005. The land reclamation foci transferred from Northeast China to Northwest China in the two stages, the greatest contribution regions to agricultural production shifted from the Xinjiang Uygur Autonomous Region from the 1980s to 2000 into Heilongjiang Province during 2000-2005. Due to the cropland transformation from urbanization and GFG project, two thirds of provinces showed a significant change in agricultural production balance state in the two stages.