PS 22-27 - Carbon stocks by forest types in tropical rainforests of Brunei Darussalam

Background/Question/Methods

More than half of the carbon stocks in terrestrial ecosystems are stored in tropical rainforests, which are highly vulnerable to anthropogenic activities. Southeast Asian tropical rainforests have lost vast carbon stocks by deforestation compared to other tropical rainforests (annual deforested area rate in Southeast Asia: 0.91% vs globally: 0.52%). These tropical rainforests are diverse and comprise of several forest types, each of them containing a distinct amount of carbon stock. To accurately respond to changes presented by climate change, the monitoring and quantification of carbon stocks by forest types is crucial. This study estimated the carbon stocks of each carbon pool (biomass, litterfall, and soil) in mixed dipterocarp forests (MDF), heath forests (HF), and peat swamp forests (PSF) in Brunei Darussalam. Specifically, the carbon stocks in biomass (diameter at breast height (DBH) ≥ 1cm), litterfall, and soil (0-10cm, 10-20cm, and 20-30cm) were estimated by using allometric equations and sampling methods for each component.

Results/Conclusions

The total carbon stocks of MDF, HF, and PSF were 495.9 t C ha^-1, 252.6 t C ha^-1, and 325.9 t C ha^-1, respectively. The biomass carbon stocks in MDF (449.2 t C ha^-1) were approximately two folds higher than HF (167.6 t C ha^-1) and PSF (220.1 t C ha^-1). Emergent trees with DBH of over 70 cm partially contributed to the difference in values, as they account for 63.8% of stems in MDF, but only 18.7% and 9.7% in HF and PSF, respectively. The litterfall carbon stocks were not different between the three forest types. The soil carbon stocks were higher in HF (81.4 t C ha^-1) and PSF (102.8 t C ha^-1) than MDF (43.1 t C ha^-1), likely due to the presence of peat in HF and PSF. The higher soil carbon stocks in HF and PSF highlights the necessity for further studies of deeper soil, over 30 cm depth, to verify potential soil carbon stocks in Southeast Asian rainforests. In conclusion, emergent tree density and soil depth should be considered along with forest types. These results provide importance information to increase understanding of the carbon stocks in tropical rainforests of Southeast Asia.