Abstract:

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.

Key words: urban forests, temporal and spatial changes, intensity gradient of nighttime lighting, major cities in China and abroad