Carbon sink capacity of public parks and carbon sequestration efficiency improvements in a dense urban landscape

In Bangkok, the crowded capital of Thailand, the capacity of 25 public parks as carbon (C) sinks was determined from the aboveground C sequestration (C-seq, tons (t)-C) and carbon dioxide absorption (CO2abs, t-CO2) of the trees in these parks. The results revealed that the estimated C-seq and CO2abs of these parks were 11,112.2 t-C and 41,219.4 t-CO2, respectively. Of these values, 10,166.8 t-C and 37,753.1 t-CO2 were obtained for the group 1 trees (all observed species except palms), and 945.5 t-C and 3,466.3 t-CO2 were obtained for the group 2 trees (palms). The CO2abs of the 25 parks was 83.6% of the estimated greenhouse gases (i.e., 49,279 t-CO2 equivalent) absorbed by all green areas in Bangkok, but this amount was trivial and approximately 0.1% of the greenhouse gases emitted by the city (i.e., 46.44 million t-CO2 equivalent). To enhance the capacity of C sinks in dense urban landscapes, both tree C-seq potential and park C-seq efficiency should be simultaneously considered. The results of the linear mixed model and Kendall correlation analysis identified the variables influencing tree C-seq potential, i.e., tree group, species diversity, tree density, and tree diameter at breast height. Based on the preliminary baseline proposed in this study, identifying appropriate specifications for tree planting and park management planning could improve park C-seq efficiency. In each park, the diverse tree subgroup species should be planted, and proportions of green area and tree density should be managed to meet relevant baseline values.