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, tons (t)-C) and carbon dioxide absorption (CO, t-CO) of the trees in these parks. The results revealed that the estimated C and CO of these parks were 11,112.2 t-C and 41,219.4 t-CO, respectively. Of these values, 10,166.8 t-C and 37,753.1 t-CO were obtained for the group 1 trees (all observed species except palms), and 945.5 t-C and 3,466.3 t-CO were obtained for the group 2 trees (palms). The CO of the 25 parks was 83.6% of the estimated greenhouse gases (i.e., 49,279 t-CO 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-CO equivalent). To enhance the capacity of C sinks in dense urban landscapes, both tree C potential and park C efficiency should be simultaneously considered. The results of the linear mixed model and Kendall correlation analysis identified the variables influencing tree C 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 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.