Seasonal and interannual variability of CO2 above the moist tropical forest of southern Vietnam

The paper presents the results of a study of seasonal and interannual variability of CO2 concentration above the moist tropical forest in southern Vietnam. Experimental data were collected during year-long observation of CO2 directly in the forest from 2012 to 2017. All data were obtained through the use of an air intake tube, placed on a metal tower at a height of 46 m and connected to a Li-Cor 820 gas analyzer (Li-Cor Inc., USA) located in a building at the foot of the tower. The values of the concentration were recorded with a resolution of 1 second; for further analysis, all data was averaged to 0.5 h values. Statistical processing based on the Fourier analysis allowed to evaluate the main characteristics of the annual distribution of CO2 concentration, such as the amplitude and phase, as well as to analyze their variability over the years. The results of the study showed a presence of a well-determined annual course of CO2 concentration above the canopy of the moist tropical forest.