Changes in net ecosystem exchange of CO₂, latent and sensible heat fluxes in a recently clear-cut spruce forest in western Russia: results from an experimental and modeling analysis

Ecosystem carbon dioxide, energy, and water fluxes were measured using eddy covariance in a fresh clear-cut surrounded by a mixed spruce-birch-aspen forest in the boreal zone of European Russia. Measurements were initiated in spring 2016 following timber harvest and continued for five months. The influence of surrounding forest on air flow and turbulent fluxes within the clear-cut were examined using a process-based two-dimensional (2D) hydrodynamic turbulent exchange model. The clear-cut was a source of CO₂ to the atmosphere prior to onset of vegetation growth during early spring. During this period the mean daily latent ( LE ) and sensible ( H ) heat fluxes were very similar and the Bowen ratio ( β = H/LE ) averaged about 1.0. Daily net ecosystem exchange of CO₂ ( NEE ) was around 0 gC m⁻² d⁻¹ following onset of vegetation growth from mid-spring through summer, while β declined to 0.6–0.7. There was strong diurnal variability in NEE , LE and H over the measurement period that was governed by solar radiation and temperature as well as the leaf area index (LAI) of regrown vegetation. Modeled vertical CO₂ and H₂O fluxes along a transect that crossed the clear-cut and coincided with the dominate wind direction showed that the clear-cut strongly influenced turbulent fluxes within the atmospheric surface layer. Furthermore, modeled atmospheric dynamics suggested that the clear-cut had a large influence on turbulent fluxes in the downwind forest, but little impact on the upwind side. An aggregated approach including field measurements and process-based models can be a useful approach to estimate energy, water and carbon dioxide fluxes in non-uniform forest landscapes. (letter)