中国超大城市土地利用状况及其生态系统服务动态演变

随着城市的快速发展,城市用地及其生态服务功能也在不断发生变化。近十几年间,中国城市发展迅速,超大规模城市的土地利用以及生态系统服务动态演变的一般特征以及差异值得关注。研究以中国1995年非农业人口超过200万的9个超大城市为研究对象(包括上海、北京、天津、重庆、南京、西安、哈尔滨、武汉和广州),对各城市不同用地类型在1995年至2008年这一阶段的利用动态度进行分析。然后以用地结构和谢高地等^1]提出的大陆生态系统服务价值当量表为基础估算了城市土地生态系统服务价值,并且对城市土地利用结构与生态系统服务之间的关系进行了分析。最后为证明研究结果可信,对每种用地类型对单位面积生态系统服务价值系数的依赖性进行了敏感性分析。结果表明,9个超大城市用地结构变化趋势总体一致, 主要缩减地类为农田和水体,增长地类为建设用地、林地和城市绿地。单位面积生态系统服务价值量1995年总体范围为4996-8854元/hm²,排序为广州>武汉>哈尔滨>南京>西安>天津>北京>上海>重庆,2008年范围为4746-8777元/hm²,排序为广州>哈尔滨>西安>上海>重庆>北京>武汉>南京>天津,各城市均值由1995年的7189元/hm²降到2008年的6987元/hm²。人均享有生态系统服务价值量1995年总体范围为284-7983元/人,排序为哈尔滨>西安>北京>广州>武汉>南京>天津>重庆>上海,2008年范围为305-4538元/人,排序为哈尔滨>重庆>西安>广州>武汉>北京>南京>天津>上海,各城市平均值由1995年的1677元/人降到2008年的1230元/人。超大城市土地生态系统服务动态演变的一致特征是人均享有生态系统服务价值下降,主要减弱的生态系统服务为水文调节和粮食生产,增强的服务为娱乐文化和废物处理,而单位面积生态系统服务价值与生态系统服务结构9个城市之间存在差异。敏感性分析结果显示所有土地类型的敏感度指数皆小于1,证明研究结果可信。研究结果说明城市可持续发展主要面临的问题之一是建设用地无序扩张和各类生态用地的配置不均衡,可为中国迅速城市化的新兴大型城市的生态建设提供参考和指导。

Dynamics of land use and its ecosystem services in China's megacities

With rapid urban development, land use and its ecosystem services in large cities change accordingly. During the latest decades, urban development boomed in China. Researchers and decision makers have increasingly paid attentions to the characteristics and variations of land use and its ecosystem services among megacities. We conducted the current study to understand the dynamics of land use and its ecosystem services in China's megacities. We firstly analyzed changes in land use in nine cities with over two million nonagricultural inhabitants (in 1995), including Shanghai, Beijing, Tianjin, Chongqing, Nanjing, Xian, Harbin, Wuhan and Guangzhou. We then modified the criteria proposed by Xie et al^1] in 2010 regarding to the equivalent values per unit area of land ecosystem services and used the modified version to translate land uses in the nine surveyed cities into values of ecosystem services. In addition, we examined the relationship between urban land use structure and ecosystem services. To test the reliability of the results, sensitivity analysis was conducted to examine the dependency of each class of land use on the coefficient of ecosystem service values per unit area. The results showed generally similar trends of land use structure changes among the surveyed megacities. Reduced land types mainly included cultivated land and water area. In contrast, lands were increasingly used for construction, urban greening and forest. The values of ecosystem services per unit area differed among the nine cities. It ranged from 4 996 to 8 854 Yuan/hm² in 1995 with the highest value in Guangzhou followed by Wuhan, Harbin, Nanjing, Xian, Tianjin, Beijing, Shanghai and Chongqing. The range in 2008 was from 4 746 to 8 777 Yuan/hm² and the descending rank was Guangzhou, Harbin, Xian, Shanghai, Chongqing, Beijing, Wuhan, Nanjing and Tianjin. The average value of ecosystem services per unit area across the nine surveyed cities dropped to 6 987 Yuan/hm² in 2008 from 7 189 Yuan/hm² in 1995. Per capita values of ecosystem services across the megacities dropped. It ranged from 284 Yuan to 7 983 Yuan in 1995 with a descending rank of Harbin, Xian, Beijing, Guangzhou, Wuhan, Nanjing, Tianjin, Chongqing and Shanghai. The rank in 2008 changed into Harbin, Chongqing, Xian, Guangzhou, Wuhan, Beijing, Nanjing, Tianjin and Shanghai with a range from 305 to 4 538 Yuan. The average per capita value of ecosystem services was 1 677 Yuan in 1995 which decreased to 1 230 Yuan in 2008. Hydrological regulation and food production were the first two weakened services. The services of culture, entertainment and waste disposal were, however, improved. The sensitivity analysis showed less dependency (<1) for all classes of land uses in both 1995 and 2008, which indicated high reliability of our results. We suggested disordered expansion of construction lands and imbalance of ecological lands as main problems impeding the harmonious urban development. Given the similar social environment across the Chinese mainland, the findings in our study might have important implications for the sustainable development of other rising cities.