国内外大城市的城市森林时空变化对比研究

Temporal and spatial changes of urban forests in major cities in China and abroad

城市森林在减弱噪声、净化空气、调节城市气温等方面具有十分重要的作用。中国城市正处于快速发展阶段,对国内外大城市的城市森林现状及其时空变化进行对比分析可为中国城市森林的建设提供理论借鉴。跨区域城市森林对比研究的主要困难在于城市区域定义的差异导致不同城市之间可比性差。论文利用强度梯度法,基于夜间灯光影像及GlobeLand30地表覆盖产品,提取12个国内外大城市2000年和2010年的城市森林数据,探究其时空变化。结果表明,从现有城市森林量看,城市森林覆盖率及人均城市森林面积在发达国家城市中普遍偏高,而在亚洲发展中国家城市中非常低,例如纽约的人均城市森林面积高达316.5 m2,而上海、新德里和雅加达则低于2 m2。从时间变化看,2000—2010年城市森林面积增长率在发达国家城市中均小于70%,而在大部分发展中国家城市超过了100%。城市森林增加的最主要来源是城市面积扩张,减少的主要原因是转为硬化地面和城市草地。按照基于缓冲区分析得到的城市森林空间分布格局,这些城市可以分为3类:中心城区高、周边城区低(北京、首尔),中心城区低、周边城区高(广州、东京、圣保罗等),整个城区均低(上海、新德里、雅加达)。最后,基于对比结果为中国城市森林未来的发展提供了建议。

Increasing urbanization is a global phenomenon that has led to numerous urban problems,including noise,deteriorating air quality,and reduced biodiversity.Urban forests are able to effectively alleviate these problems through their ecosystem services.Therefore,in 2018,the theme of the World Forest Day is"Forests and Sustainable Cities";and China has started the assessment of"National Forest Cities"since 2004.Under this background,examining the distributions of urban forests in major Chinese cities and then comparing them with large foreign cities could help understand the current situation of Chinese urban forests and provide theoretical references for their management.The main difficulty in cross-regional urban forest research is that differences in urban definitions lead to poor comparability between cities.This study used the Defense Meteorological Satellite Program(DMSP)/Operational Linescan System(OLS)nighttime lighting image and the GlobeLand30 surface cover product to extract urban forest data of 12 major international cities(Beijing,Shanghai,Guangzhou,Tokyo,Seoul,New Delhi,Jakarta,Sao Paulo,Lagos,New York,London,and Moscow)in 2000 and 2010 based on the intensity gradient method and using ArcGIS tools,and examined their spatial and temporal changes.The results show that among the 12 cities,from the perspective of existing urban forests,urban forest coverage and per capita urban forest area are generally high in developed cities,while in Asian developing cities they are low.From the perspective of temporal change,the urban forest growth rate of cities in developed countries is mostly less than 70%,while in most cities of developing countries,it is more than 100%during 2000-2010.The major source of the increase is the expansion of urban area,while the decrease is mainly due to the conversion to artificial surface and urban lawn.According to the spatial distribution of urban forest coverage based on buffer analysis,these cities can be divided into three categories:low in the central area and high in the surrounding areas(Beijing and Seoul);low in the surrounding areas and high in the central area(Guangzhou,Tokyo,Sao Paulo,and so on);and low in the whole urban area(Shanghai,New Delhi,and Jakarta).Finally,based on the results of comparison,recommendations for the future development of urban forests in China are provided.