景观演化特征指数及其应用

随着中国城市化建设的快速推进,城市蔓延式增长和生态空间持续性萎缩成为普遍的现象,以地表硬化为主要特征的城市景观格局变化得到广泛关注,而景观扩张指数(Landscape Expansion Index, LEI)是测度这一现象的重要工具。但在新型城镇化背景下,由于大城市空间结构调整优化以及城市绿化率的提高,硬化地景观的收缩与消亡已成为城市景观演变的另一重要形式,因此亟需新的有效手段来刻画城市发展的新特征。在此背景下,本文在LEI指数的基础上,提出景观演化特征指数(Landscape Evolution Characteristic Index, LECI),尝试综合描述城镇化过程中硬化地景观斑块扩张与收缩的动态特征;并基于邻域特征计算的景观演化特征指数,包括景观演化模式识别指数(Landscape Evolution Pattern Index, LEPI)和景观演化规模指数(Landscape Evolution Area Index, LEAI),协同分析两个或多个时相景观格局演变过程中的斑块新生与消亡。本文将LECI指数应用于武汉都市发展区1990-2010年期间的城市硬化地景观演变过程中,与基于最小包围盒的景观扩张指数(LEI)对比分析,结果表明：①LEPI能准确识别不同规模和形状斑块的空间扩张模式,LEAI能够较好反映斑块扩张强度并表征景观扩张方向;②LEPI能有效识别城市景观演变中消亡斑块的湮灭模式,研究区内硬化地景观消亡现象明显加剧,可能与政府加强城市内部改造及绿化建设有关;③LECI指数变化分析发现,武汉都市发展区研究期内的城市景观扩张强度有所放缓,飞地式和边缘式空间增长构成斑块演变的主体,城市硬化地景观扩张模式在空间上呈现明显的梯度分异规律,随距主城区的远近呈现填充式/包围式、边缘式/邻接式到飞地式/孤立式的演替。

Landscape evolution characteristic index and application

With the rapid urbanization, urban sprawl growth and the contraction of ecological space have become a common phenomenon in China. Ground surface hardening is the main characteristic in urban landscape expansion, which has become widely concerned. Landscape expansion index (LEI) has been an important tool to describe and quantify this process. However, in the period of new urbanization, with the adjustment and optimization of urban internal structure and the improvement of urban greening rate, the shrinkage and extinction of hardened ground landscape have been another important form of urban landscape evolution. It is urgent to find a new and effective method to describe the emerging features of urban development. Therefore, a new landscape index based on the neighborhood characteristics of patches—landscape evolution characteristic index (LECI), including landscape evolution pattern index (LEPI) and landscape evolution area index (LEAI)—is proposed to comprehensively analyze the dynamic features of the landscape pattern. Collaborative analysis can be implemented by this index to recognize the expansion and shrinkage of the hardened landscape patches during the landscape pattern evolution in two or more periods. This index also can overcome the difficulty of LEI in identifying the pattern of special shaped patches. The LECI was applied to study the urban landscape expansion of metropolitan development area in Wuhan City during 1990-2010, and compared with LEI based on minimum bounding box. The results indicate that (1) LEPI can accurately identify the three modes of urban expansion—the infilling type, the edge-expansion type, and the outlying type, as well as for the isolated type, the adjacent type, and the surrounded type of urban shrinkage, and LEAI can perfectly reflect patch expansion/shrinkage intensity and landscape expansion/shrinkage direction; (2) Patch shrinkage of the hardened ground landscapes in the study area is clearly intensified. The recognition of shrinkage modes of these patches through LEPI can reveal the spatial distribution of urban ecological restoration and contribute to the construction of urban green infrastructure and residential land remediation; (3) Based on the analysis of LECI in the study area during 1990-2010, it was found that the speed of urban landscape expansion has been slowed but still rapid, and the outlying type and edge-expansion type are the dominant modes of patch change. As the distance from the central city increases, the spatial distribution pattern of different evolution modes is clearly distinctive, which are infilling/surrounded type, edge-expansion/adjacent type, and outlying/isolated type.