Synergistic effects of urban forest on urban heat island-air pollution-carbon stock in mega-urban agglomeration

Urban forests provide multiple ecosystem services from mitigation of urban heat island and air pollution to multi-dimensional human well-beings. However, extensive studies focus on the singular contribution of urban forests to cooling, clean air and increase carbon sequestration. This study combined multi-source data and geostatistical methods to quantify the spatiotemporal effects of urban forests on the spatial interactions between surface urban heat island (SUHI), PM2.5, and carbon stock (i.e., synergistic effects) and its mechanisms in the mega-urban agglomeration of Guangdong–Hong Kong–Macao Greater Bay Area. Results showed that urban forest evolution was spatiotemporally coupled with the patterns of PM2.5, SUHI, and carbon stock in 2000–2020. 80 % of the urban forest landscape indices demonstrated significant positive effects on cooling–clean air–increase carbon sequestration, with much higher (on average 2.98 times) influence than for each single environmental variable. In addition, patch dominance explained an average of 60.55 % of the synergistic effects, and its control zone rapidly expanded spatially by 54.3 %. In contrast, the influence of cover rate diminished, with q value and control zone proportion decreasing by 18.87 % and 26.61 %. Moreover, the contributions of anthropogenic factors to synergistic effects were 1.2–3.8 times higher than the natural factors. This study established an urban ecosystem service framework, thereby providing crucial information and decision support for effective urban forest management. [Display omitted] •Quantify cooling—clean air—carbon sequestration synergistic effect of urban forest.•80 % of the urban forest landscape indices show significant positive effects.•Dominant role of urban forest richness replaced by patch marginalization.•Anthropogenic factors played a more important role than natural factors.•Establish urban ecosystem service synergy framework with nature-based solutions.