Eddy covariance measurements of CO2 and sensible and latent heat fluxes during a full year in a boreal pine forest trunk-space

The eddy covariance method was used to determine turbulent heat fluxes and CO2 flux below a boreal Scots pine canopy 3 m above the forest floor. Data were filtered using standard deviation of the vertical velocity as a measure of the turbulent mixing in the trunk space along with the non-stationary criterion. The turbulent transfer in the trunk space was dominated by large (15–100 m) intermittent eddies, which were detectable by the eddy covariance technique. Heat fluxes exhibited clear annual and diurnal course and amounted to 20%–30% of the fluxes above the canopy. The forest floor was a source of carbon all-year-round and the CO2 efflux was mainly controlled by soil temperature. Photosynthesis of the forest floor vegetation decreased daytime fluxes of CO2 by 1.0–1.5 µmol m–2 s–1 compared with nocturnal values (~3.0 µmol m–2 s–1). The eddy covariance method provided a similar daily cycle to the chamber method but there was a discrepancy between their mean levels.