Measurement of CO2 flux above a tropical rain forest at Pasoh in Peninsular Malaysia

This paper reports on the results of a short-term observation of CO2 flux above a tropical forest at Pasoh in Peninsular Malaysia, using the eddy covariance method with a closed-path CO2 analyzer, in March 1998. CO2 concentration profiles above and in a canopy were also measured. In the daytime, the time series of fluctuations in CO2 concentration above the forest drew the ramp pattern with a period of 2 min. This suggests that large-scale turbulent motions contribute to CO2 flux in the daytime. We obtained data on the CO2 flux for 6 days and CO2 storage flux under the flux measurement level for 3 days in this observation. The values of the CO2 flux fell within −1.0 to 0.5 mg CO2 m−2 s−1. Net ecosystem CO2 exchange (NEE) was estimated as the sum of the CO2 flux and the CO2 storage flux. Compared with the CO2 flux, the CO2 storage flux was relatively large in the early morning and the nighttime, therefore, the storage flux became important to estimate the NEE in those periods. The daily values of the NEE ranged from −2.08 to −2.74 g C m−2 per day. The results suggest that this tropical forest was a CO2 sink during the period. Although we tired to calculate the mass flow component proposed by Lee [Agric. For. Meteorol. 91 (1998) 39], the magnitudes of the mass flow obtained here were, from 5.20 to 12.55 g C m−2 per day, much larger than the magnitudes of the NEE.