Three-Year Variability Of Energy And Carbon Dioxide Fluxes At Clear-Cut Forest Site In The European Southern Taiga

Forest clearing strongly influences the energy, water and greenhouse gas exchange at the land sur face - atmosphere inter face. To estimate effects of clear cutting on sensible (H), latent heat (LE) and CO2 fluxes the continuous eddy covariance measurements were provided at the recently clear-cut area situated in the western part of Russia from spring 2016 to the end of 2018. The possible effects of surrounding forest on the air flow disturbances and on the spatial pattern of horizontal advection terms within the selected clear-cut area were investigated using a process-based 3D momentum, energy and CO2 exchange model. The modeling results showed a very low contribution of horizontal advection term into total turbulent momentum fluxes at flux tower location in case of the southern wind direction. The results of field flux measurements indicated a strong inter- and intra-annual variability of energy and CO2 fluxes. The energy budget is characterized by higher daily and monthly LE fluxes throughout the entire period of measurements excepting the first two months after timber harvest. The mean Bowen ratio (β=H/LE) was 0.52 in 2016, 0.30 - in 2017 and 0.35 - in 2018. Analysis of CO2 fluxes during the first year following harvest showed that the monthly CO2 release at the clear-cut area consistently exceeded the CO2 uptake rates. The mean net ecosystem exchange (NEE) in the period was 3.3±1.3 gC∙m-2∙d-1. During the second and the third years of the flux measurements the clear-cut was also a prevailed sink of CO2 for the atmosphere excepting short periods in June and in the first part of July when daily CO2 uptake was higher than CO2 release rates. The mean NEE rates averaged for the entire warm period of corresponding years were 1.2±2.3 gС∙m-2∙d-1 in 2017 and 2.8±2.5 gC∙m-2∙d-1 in 2018, respectively. The mean ratio between gross primary production (GPP) and ecosystem respiration (TER) was 0.58 in 2016, 0.84 - in 2017 and 0.74 - in 2018