摘要:城市林木树冠覆盖（urban tree canopy，UTC）既是衡量一个城市生态状况的标志性指标，也是衡量森林城市建设成就的关键指标，其中的潜在林木树冠覆盖（possible urban tree canopy，简称PUTC）又与城市森林建设目标的科学制定息息相关。在国外文献与实践案例研究的基础上，以北京市六环外1km以内范围为研究对象，利用2002和2013年的0.5m分辨率航、卫片影像，通过其解译的地表覆盖数据，对其两个年度的潜在林木树冠覆盖的区域分布和动态变化进行分析，并利用人口密度、道路密度和现实林木树冠覆盖率等指标，以村（社区）为单元对其潜在林木树冠覆盖的优先度进行了分析评价。结果显示，11年间，研究区域的PUTC从40882.18hm²减少到了18845.82hm²，空间分布也呈现出沿环路越是靠近城市中心区域，其分布也越少的格局，从其类型上看，随着时间的推移，其类型的丰富度也越来越低，到2013年，则呈现出荒草地类型绝对占优的格局。PUTC的斑块数量从109892个减少为7793个，但斑块平均面积从2002年的0.37hm²增加到了2013年的2.36hm²，斑块大小格局也从2002年的小斑块占绝对优势演变为各种类型"平分秋色"的状况。以PUTC为核心的村（社区）区域潜力评价结果显示，整个研究区域在2002年时低潜力和中潜力区域范围最大，分别占到了研究区域的32.39%和28.83%，2013年时潜力格局改变为极低潜力和低潜力区域面积最大，分别占研究区域总面积的25.83%和50.94%。极高优先度和高优先度区域应该是北京城市未来重点发展城市森林的区域，目前的潜在优先度评价结果表明，其面积占比分别达到了研究区域面积的13.11%和41.79%，其中极高优先度区域主要分布在构成城市核心区的东城区和西城区，因此北京城区未来的林木树冠发展策略应该走植被潜在斑块与不透水地表潜在斑块共同开发之路。



Abstract:Urban tree canopy (UTC) is not only a landmark index to measure the ecological condition of a city, but also a key index to measure the achievement of forest city construction.The possible urban tree canopy (PUTC) is closely related to the formulation of scientific urban forest construction objectives.On the basis of foreign literatures and practical case studies,this paper analyzed the regional distribution and dynamic changes of PUTC within 1 km outside the 6th Ring Road in Beijing by using surface canopy interpretation data of 0.5 m resolution aerial and satellite images in 2002 and 2013.In addition, the priority of PUTC in village (community) was analyzed and evaluated by using population density, road density, and existence urban tree canopy coverage.The results showed that,during the 11 years, the PUTC in the study area decreased from 40882.18hm² to 18845.82hm². Its spatial distribution showed that the more urban centers along the loop, the less the distribution.Moreover,as time goes on, the richness of PUTC types was also getting lower and lower. By 2013, the grassland types have occupied the absolute advantage.The number of PUTC patches decreased from 109892 to 7793, but the average patch area increased from 0.37 hm² in 2002 to 2.36 hm² in 2013. The patch size pattern also changed from the absolute dominance of small patches in 2002 to a more equal situation of various types.The PUTC assessment showed that the whole study area was dominated by low and medium potential areas in 2002, accounting for 32.39% and 28.83%, respectively. In 2013, the potential pattern changed to the region with the largest area of severe low potential and low potential areas, accounting for 25.83% and 50.94%, respectively. This obviously indicated that the severe high priority and high priority areas should be the key areas for Beijing to develop urban forests in the future. The current results of potential priority assessment showed that the proportion of the severe high priority area and high priority areas reached 13.11% and 41.79%, respectively. The severe high priority areas were mainly distributed in the eastern and western urban core areas. Therefore, the future development strategy of forest canopy in Beijing urban area should take the road of joint development of the possible urban tree canopy patches and potential patches on impervious surface.





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