快速城市化地区景观可达性及其对林地的影响——以深圳市宝安区为例

Landscape accessibility and its effect on forest-cover change in quickly urbanizing area:a case study of Baoan,Shenzhen

以深圳市宝安区为工作区，利用基于1988，2003年期间的3景TM卫星影像数据得到的景观分类制图和DEM、道路等GIS数据，通过构建一个涵盖高程、道路和建设用地密度影响的综合可达性评估指数，研究了工作区内景观可达性动态特征及其对林地植被变化的影响。结果表明：（1）研究时段内工作区景观整体可达性程度显著提高，低水平可达性区域面积比重显著下降，中、高水平可达性区域面积比重普遍提高；（2）全区林地面积比重下降了10％以上，低水平可达性区域内林地比重受建设用地扩张影响持续下降，中、高水平可达性区间的林地面积比重则因城市生态建设工作逐步受到重视而呈先降后升的变化格局，表明快速城市化地区林地动态变化不仅受道路、高程及建设用地扩展影响，政府政策性调控也起到了重要的作用。

Accessibility analysis has played an important role on the research of land-cover change, but the early studies mainly focused on the metropolitan accessibility problems in urban planning and urban-traffic geography researches. This study evaluates the relationship between landscape accessibility and forest-cover change in Baoan, Shenzhen, in order to explain the motivity and process of forest-cover change, and provides scientific basis for the forest protection policies making. Landsat Thematic Mapper （TM） satellite imagery of 1955, 1996,2003 was used to create three single date classification, together with DEM and road information of Baoan, we created a compound-accessibility evaluation index based on DEM, distance to the nearest road and buildup area density, and the whole study area can be divided into 7 accessibility grades from the least reachable area to the most easily reachable area. The following conclusions are drawn from this research ： （ 1 ） The accessibility of the whole study area has increased significantly from 1988 to 2003, with the low accessibility areas declined and the high accessibility areas increased. Since 1955, the accessibility grades have experienced great changes except accessibility grade 1 and grade 7, especially the area reservation ratio of grade 3 - 5 is below 50% ; （2） The enhancement of accessibility in the study area will result in the increase of deforestation directly without the strict government policies. Besides, the continuous loss of forest-cover in the low accessibility area will result in the landscape fragmentation in space as well as the decline of forest-cover rate in the study area, which will block the forest protection work there; （3） In the low accessibility areas, forest-cover is decreasing consistently while in the secondary and high accessibility areas,forest- cover has experienced complex changes, which decreased during 1988 - 1996 but the trends reversed during 1996- 2003, mostly because the government promote reforestation in the build-up areas to improve the eco-environment of the city. It means that in the fast urbanization area,forest-cover change is not only influenced by accessibility but also the economic profits drive and government policies control.