北京市近二十年景观破碎化格局的时空变化

基于1993—2013年3期时间序列的遥感影像获得的一、二级景观类型的土地覆盖数据,利用移动窗口法和空间主成分分析法研究景观破碎度空间分布格局和破碎化过程。结果表明:北京市正处于快速城市化阶段,20年间其建设用地面积增加了1000.8 km~2,增长47.14%,而耕地面积减少21.86%;全市破碎化程度增加,其中,景观斑块总数增加了15.26%,而景观斑块的平均面积缩小了15.35%,景观形状指数(LSI)从88.426增加到98.897;北京市景观破碎化格局的空间异质性较大,但没有方向性偏好,却表现了"两极化"发展趋势,其中,高破碎化区域和低破碎化区域的面积增加,中等破碎化的区域面积减少,核心大城区和山区的景观破碎度降低,而新兴城区和郊区的景观破碎度增大;北京市景观破碎化格局的距离效应显著,呈现倒"U"型二次函数关系,其中,2013年的破碎度距离函数为:Y_3=0.1767+0.02898X_3-0.0005167X_3~2,距城市中心20—35 km处的城郊交错区景观破碎化程度最高。景观破碎化格局的分析有助于了解大城市快速发展阶段的景观格局演变规律,为城市生物多样性保护、绿地廊道维护和生态文明城市建设提供理论依据。

Spatial-temporal changes of landscape fragmentation patterns in Beijing in the last two decades

Landscape fragmentation is a major factor for ecological and environmental degradation, and it has serious impacts on rapidly urbanized regions. Over the last 20 years, urbanization in Beijing has substantially changed the surface landscape, and deeply influenced the landscape heterogeneity. However, much of the current research on the landscape fragmentation in Beijing City has focused primarily on simple landscape indexes, and only a few studies have investigated the complexity and dynamics of fragmentation characteristics on the temporal and spatial patterns. Therefore, the combined use of remote sensing-based technology to classify land use cover, employing the moving windows method of landscape metrics, and the spatial principal components analyses method have provided an useful comprehensive understanding of the spatial-temporal characteristics and changes in landscape fragmentation patterns. In this study, we were mainly concerned with landscape fragmentation during the rapid urbanization in Beijing City, throughout 1993, 2003 and 2013 based on RS and GIS. The LUCC results, which were obtained from Landsat TM/ETM, have been divided into two grades, including six classes in first grade and 19 classes in second grade. We have fully integrated the two grades of LUCC results to analyze landscape fragmentation, combined with the moving windows method and the spatial principal components analyses method. Additionally, we use transfer-matrix and distribution pattern maps to describe the course of urbanization in Beijing City. Based on the results of our study, we concluded that, there were many changes in landscape structure and pattern during the rapid urbanization in Beijing, and the dominant change was construction land, which increased by 47.16%. At the same time, farmland area has decreased by 21.86%. Landscape fragmentation indices also changed over time during this stage, the landscape patch number was increased from 20,986 to 24,765, the average area of landscape patches has reduced by 15.35%, landscape connectivity index (CONNECT) has decreased from 0.1316 to 0.1271, and landscape shape index (LSI) has increased from 88.426 to 98.897. This indicates that, in the process of rapid urbanization, landscape fragmentation has increased in Beijing City. The spatial distribution fragmentation pattern revealed substantial heterogeneity and complexity, which primarily has the following outcomes: a polarizing trend, in which locations show increased dissimilarity. The fragmentation index of urban center and mountainous regions has continued to decrease, but the fragmentation index of emerging urban and suburban regions has increased. The gross area of high fragmentation and low fragmentation has expanded. We find that urbanization is the main factor in the change of landscape fragmentation patterns, and the dramatically changed region lies in the urban-rural ecotone, where construction land has rapidly increased. There was hardly a directional preference in the fragmentation pattern. However, it has a distinct distance effect; the landscape fragmentation index first increases with increasing distance, and then decreases in an inverted "U" type function. Also, the landscape fragmentation showed a "layer ring structure" model for urban development in Beijing. The landscape fragmentation index reaches a maximum when the distance at range of 20 to 35 km. This study could provide both reference and guidance for land use management and ecological environment protection for rapidly developing areas. Also, the multifaceted research approach toward landscape patterns and their ecological processes must be explored.