Using a geographical detector to identify the key factors that influence urban forest spatial differences within China

Increasing urbanization is a global phenomomen that has led to numerous urban problems, including air pollution and traffic noise. Urban forests are important, therefore, because they are able to effectively alleviate such unsustainable problems. Systematic analyses of spatial differences in urban forest coverage (UFC) and the factors that influence this cover type, however, need to be further explored within Chinese cities, especially on the basis of spatial data. The intensity gradient (IG) method was applied in this study to identify urban areas across China using Defense Meteorological Satellite Program (DMSP)/Operational Linescan System (OLS) data. Urban forests were then extracted from the global land cover dataset GlobeLand30 to enhance comparability of this land cover type between cities. The factors influencing spatial differences in UFC in 286 major Chinese cities were then detected using a geographical detector method, an approach which differs from the more traditional use of multiple regression as it better illustrates the explanatory power of variables and their interactions. The results of this study reveal that average UFC across China was 19.7 % in 2010 and that clear differences were present between south China (27.6 %) and north China (11.1 %). The factors underlying UFC differences between Chinese cities are complicated; data show that biogeoclimatic factors have exerted the greatest impact while the effects of socioeconomic factors have generally been weak. The impact of variables interacting with one another has also tended to be stronger than the influence of single factors. The results presented here also imply that there were no significant spatial differences in average UFC between cities with the title Chinese 'National Forest City' (NFC) and others.