Investigating carbon dioxide absorption by urban trees in a new park of Bangkok, Thailand.

Background: Trees remove atmospheric carbon dioxide through photosynthesis, hereafter CO₂ absorption (A). Despite growing urban green areas, only a few studies have quantified A of urban trees and assessed their dynamical changes with varying atmospheric conditions. Hence, we investigated A in nine dominant tree species in a new park of Bangkok.

Results: Results revealed that A of two tree species (Millingtonia hortensis and Afzelia xylocarpa) significantly increased with vapor pressure deficit (VPD) until it reached a maximum and declined when VPD decreased, with no seasonal difference. Five of them (Dalbergia cochinchinensis, Tabebuia rosea, Lagerstroemia floribunda, Dipterocarpus alatus and Bauhinia purpurea) exhibited different response patterns of A to VPD between wet and dry seasons. In contrast, the A of two tree species (Samanea saman and Homalium tomentosum) did not respond to changing VPD in either season.

Conclusions: Comparing planting scenarios of insensitive (i.e. no response to VPD) versus sensitive (i.e. significant response to VPD) species, we found that planting a mixture of sensitive and insensitive tree species would improve the park's capacity of A across seasons, allowing climate change adaptation to adverse environmental impacts such as droughts and the urban heat island effects, and would increase biodiversity. Additionally, planting insensitive tree species would significantly increase the capacity of the park for CO₂ mitigation. These findings are useful for those who design parks and expand urban green areas to fully benefit ecosystem services from trees.