城市化背景下景观破碎化及连接度动态变化研究——以昆明市为例

城市化不仅改变景观类型和组成,也导致空间形态变化与自然生境连接度的降低,刻画不同城市化过程中人工表面、耕地与自然生境的空间关系对于研究其景观生态效应,尤其是对不同景观之间的相互作用以及结构和功能的变化具有重要意义。以云南省昆明市为研究区,分析了1990—2015年城市扩张导致的破碎化与形态变化对景观连接度的影响。利用城市破碎指数(UFI)刻画景观破碎水平,进一步基于形态学空间格局分析(MSPA)得到耕地和自然生境的七类景观形态要素(核心、岛状斑块、桥接、环岛、孔隙、边缘和支线),选取了3种边缘宽度比较边缘宽度对景观形态的影响差异,然后通过概率连接度指数(PC)和斑块重要值(dPC)评估景观连接度的变化。在4 km×4 km的网格基础上计算平均UFI和dPC,利用三维曲面分析不同变量之间的相关性。结果表明:过去25年间,昆明市人工表面不断扩大,占用大量耕地并导致景观破碎度的增加,速率呈逐年增加的趋势;MSPA结果显示,耕地表现出持续稳定的消减,自然生境景观形态类型前期变化不大,2010年后有较大幅度改变,表现出从稳定、波动到破碎的过程,不同边缘宽度下存在显著差别,边缘宽度越大则连接度变化越为明显,表明城市化对小型绿色斑块影响较大;斑块重要值与UFI的变化表现出一致性,变化集中于东部地区,随着UFI的增加景观连接度逐年降低;相关性分析显示,随着破碎度的增加,景观连接度经历了从波动到稳定下降的过程。总体上,昆明市城市化造成耕地的持续减少,虽未造成大面积自然生境丧失,但在一定程度上降低了连接度,需要从空间格局上加以管控,避免对整体景观连接度产生负面影响。

Changes of landscape fragmentation and connectivity with urbanization: a case study of Kunming City

Urbanization can not only change the landscape types and composition, but also change the spatial morphology and decrease the natural habitat connectivity. Depicting the spatial relationship between artificial surface, arable land and natural habitat is of great significance to examine the landscape ecological effects, especially for the interaction between different landscapes and changes of structure and function. The effects of fragmentation and morphological changes on landscape connectivity with urban expansion of Kunming City, Yunnan Province in 1990-2015 were analyzed in this study by using the urban fragmentation index (UFI) to depict the level of landscape fragmentation. Based on morphological spatial pattern analysis (MSPA), seven landscape morphological elements (core, islet, bridge, loop, perforation, edge, and branch) of arable land and natural habitat were obtained. Three edge widths were selected to compare the influence of edge widths on the landscape morphology. The landscape connectivity changes were evaluated by probability of connectivity (PC) and importance value of patches (dPC). The average UFI and dPC were calculated on the grid of 4 km×4 km, and the correlation among different variables were analyzed by the three-dimensional curved surface graph. The results showed that the artificial surface in Kunming has been expanding, occupying a large amount of arable land. The annual increase rate of landscape fragmentation has been increasing in the past 25 years. The results of MSPA indicated that the arable land showed a continuous and stable declining trend, and the landscape morphology of natural habitat showed little change from 1990 to 2010. After 2010, there has been a dynamic process from stability to fluctuation and then to fragmentation. There were significant differences between different edge widths. The wider the edge width was, the more obvious the change of connectivity was. This fact indicated that urbanization had a more serious impact on small green patches. The change of dPC was consistent with that of the UFI, and the change was concentrated in the eastern region of Kunming. With the increase of the UFI, the landscape connectivity decreased year by year. The correlation analysis showed that the landscape connectivity experienced a process from fluctuation to steady decline with the increase of fragmentation. In general, the urbanization of Kunming has caused continuous reduction of arable land. Although the loss of large-scale natural habitat has not been caused by the urbanization, the connectivity has been reduced to a certain extent. It is necessary to control the spatial pattern to avoid the negative impact of the urbanization on the overall landscape connectivity.