Empirical determination of the carbon impacts of urban forest management in Hong Kong : removal of Acacia confusa and Leucaena leucocephala

Abstract

Urban trees contribute to decarbonisation. However, the removal of trees may release the stored carbon within them. In Hong Kong, Acacia confusa and Leucaena leucocephala are being removed, but with unknown carbon impacts. This industry-academia-government collaborative research aimed to: (1) report the amount of carbon stored inside Acacia confusa and Leucaena leucocephala harvested from slopes; (2) estimate the carbon storage of a tree using dendrometric measurements; and (3) explain the variation in carbon content percentage of urban trees with respect to tree species, part of the tree, and position within the part. 10 Acacia confusa and 10 Leucaena leucocephala were harvested during March–September, 2023. Each tree was weighed for carbon storage estimation. Results showed that Acacia confusa had higher mean wood volume, biomass and carbon storage than Leucaena leucocephala. The mean carbon content of the analysed samples (45.53−52.58%) were mostly significantly different from 50%. But the difference may become insignificant depending on how volatile carbon loss was controlled. Diameter at breast height (mm) was a significant predictor of carbon storage (kg) for both Acacia. confusa (β = 0.9574) and Leucaena leucocephala (β = 0.3909). Significant interaction between tree species and tree part on carbon content percentage was confirmed. This research demonstrated the impacts of past arboricultural decisions on present decarbonisation plans.