生态退耕前后张家口市耕地变化及影响因素识别

耕地变化与相关土地政策密切相关,为揭示生态退耕政策实施前后,耕地变化特征及其影响因素的差异性,该研究以北方农牧交错区——张家口市为例,分析了生态退耕前后（1989—2000年和2000—2015年）耕地变化特征。在此基础上,应用多项Logistic回归模型研究了耕地变化的影响因素。研究结果表明：1）耕地面积由1989年的1 090 031.02 hm²减少到2015年的924 647.32 hm²,持续减少了15.17%,特别是生态退耕后,耕地减少速度加快;但耕地仍然集中分布在张北县、康保县、沽源县。2）生态退耕前后,耕地转出与转入并存。与生态退耕前相比,生态退耕后耕地转换变化总面积增加121 695.72 hm²,其中转出面积增加占88.72%;耕地主要转换去向由草地（17 063.59 hm²）、建设用地（9 007.00 hm²）、林地（8 932.72 hm²）和园地（5 981.19 hm²）,变为林地（51 902.41 hm²）、园地（40 311.23 hm²）、草地（32 292.66 hm²）和建设用地（23 152.11 hm²）。3）生态退耕前后,耕地转换变化的影响因素不同。退耕前,海拔和坡度分别是耕地转为园地、林地和转为草地、建设用地的主导因素;退耕后,耕地转化的影响因素多样化,海拔仍是耕地向园地转换的主导影响因素,人均GDP变化和到最近道路距离分别成为耕地转为林地、草地和转为建设用地的首要因素。基本农田保护区和自然保护区对耕地转为园地、林地和草地也起着重要作用。研究结果能为张家口市耕地保护、生态环境保护及经济社会协调发展提供科学依据。

Changes in Cultivated Land and Influencing Factors before and after the Implementation of Grain forGreen Project in Zhangjiakou City

The Grain for Green Project (GGP) started in Zhangjiakou city, Hebei Province, China in 2000. As an important artificial landscape, cultivated land has functions of ensuring national food security and meeting the needs of urbanization and ecological environment construction land. It is necessary to pay more attention to the differences of cultivated land change and the influencing factors before and after GGP due to the influence of related land policies. By integrating satellite images, geospatial data and socio-economic statistic data, we characterized spatio-temporal dynamics of cultivated land change and micro spatial affecting factors of cultivated land change in Zhangjiakou city before and after GGP (1989-2000 and 2000-2015). This region is located in the farming-pastoral ecotone in North China facing contradictions of developing economy, protecting cultivated land and restoring ecology. The major findings were that cultivated land area continued decreasing from 1 090 031.02 hm² in 1989 to 924 647.32 hm² in 2015, especially after GGP, the rate of cultivated land decreased at annual change rate of -0.84%, totally 132 426.91 hm² cultivated land lost; however, spatial pattern of cultivated land did not change, concentrated in Zhangbei, Kangbao and Guyuan. GGP had accelerated cultivated land conversion speed. Compared with before GGP (1989-2000), conversion area increased 121 695.72 hm² after GGP. Also, the rank of cultivated land conversion type changed remarkably. Cultivated land mainly converted to grassland, construction land, forestland and orchard land before GGP with conversion area of 17 063.59, 9 007.00, 8 932.72 and 5 981.19 hm², respectively, and mainly converted to forestland, orchard land, grassland and construction land after GGP with conversion area of 51 902.41, 40 311.23, 32 292.66 and 23 152.11 hm², respectively. Before GGP, altitude was the leading factor for cultivated land converting to orchard land and forestland, and slope affected most evidently on the conversions from cultivated land to grassland and construction land. After GGP, while altitude remained the dominant factor affecting the conversion from farmland to orchard land, per capita GDP was the most important factor for conversions of cultivated land to forestland and grassland and distance to the nearest road was the significant factor for conversion of cultivated land to construction land. In addition, China’s specific land control policy (prime cropland protection and nature reserves) had an important influence on the conversion of farmland to orchard land, forestland and grassland. In order to protect food and ecology security, the following measures could be taken in Zhangjiakou city: continue to return cultivated land on steep slope and serious desertification regions to forests or grassland moderately, construct ecological farmland which emphasizes farmland system production and ecology safety, establish a differential mechanism for returning farmland to compensation and develop the follow-up industry after GGP. The research results will provide an objective basis for cultivated land protection, ecological protection and socio-economic coordinated development, as well as a scientific reference for similar regions.