城市扩张对北京市城乡结合部自然和农业景观的影响——以昌平区三镇为例

The impact of the urban sprawl on natural and agricultural landscape at the urban-rural interface of Beijing: taking three towns of Changping District for example

城乡结合部自然和农业生态系统是确保城市生态安全的重要基础。研究快速城市化背景下城乡结合部自然和农业景观的时空演变规律和驱动因素,能够为相关规划的编制和保护政策的制定提供科学支撑。以北京市三个典型的城乡结合部乡镇为例,通过对1999、2004和2010年三期SPOT遥感影像的解译,获取三镇三个时期土地利用/覆盖(Land Use/Land Cover,LULC)数据。在此基础上,借助Arc GIS空间叠加功能和土地利用转移矩阵,分析1999—2010年三镇LULC的时空变化特征;并通过空间自相性和景观连通性分析,研究近十年来三镇建设用地的空间聚集特征以及自然和农业景观空间连通性的变化,分析城市扩张对三镇自然和农业景观格局和稳定性的影响。最后,采用定量和定性相结合的方法,分析三镇自然和农业景观变化的驱动力。结果表明,1999—2010年三镇经历了剧烈的LUCC过程,建设用地、林地和草地面积大幅增加,伴随的是农业用地和水域面积的急剧减少。各种土地利用类型之间都存在着相互转移,特别是农业用地向建设用地、林地和草地,以及林地向建设用地转移明显。新增建设用地大多通过侵占原有建设用地周边的农业用地和林地,而实现"成片蔓延式"扩张;并造成了三镇自然和农业景观连通性的急剧下降,危及到该区域生态系统结构的完整性和功能的持续性。社会经济发展、土地利用规划、公共政策等共同决定着三镇LUCC的结构、规模和空间分布,是三镇自然和农业景观格局演变的主要驱动力。

Natural and agricultural landscape at the urban-rural interface is the important foundation to ensure the urban ecological security. Studying the spatio-temporal evolution of natural and agricultural landscape and its driving forces at the urban-rural interface in the context of the rapid urbanization can provide scientific support for some protection policies formulation and implementation. This paper investigates the spatial pattern of land use/land cover （LULC） in three typical townships at the urban-rural interface of Beijng by interpreting the 1999, 2004 and 2010 SPOT images. One this basis, with ArcGIS spatial overlay function and land use transition matrix, this paper tries to further investigate the spatio-temporal evolution of LULC in the study area. At the same time, the spatial autocorrelation of build land and the landscape connectivity of natural and agricultural land are measured to analysis the impact of urban sprawl on the pattern and stability of natural and agricultural ecosystems. Finally, using a combination of quantitative and qualitative methods, the driving forces of the change of natural and agricultural landscape in the study area are analyzed. The results show that, from 1999 to 2010, the town experienced a dramatic process of LUCC; build land, woodland and grassland substantially increased, accompanied by a sharp reduction of agricultural land and water area. There is dramatic mutual transfer between the various land use types, especially from agricultural land to build land, woodland, grassland, and from woodland to build land. Most of the new build land located in the neighbourhood of the existing build land, implying that the existing built-up areas have a greater influence on urban expansion. The rapid expansion of build land caused the sharp decline of the landscape connectivity of natural and agricultural land, and endangering the structural integrity and the functional stability of ecosystem in the study area. Socio-economic development, land use planning and public policy which jointly determined the LUCC structure, size and spatial distribution, were the main driving forces of pattern evolution of natural and agricultural landscape in the three towns.