Assessing the Spatial Variability of Ecosystem Fluxes of Energy and Carbon Dioxide Above a Forest

When setting up a new eddy covariance flux system over tall canopy, the measurement height has to be decided mainly based on two criteria: 1) high enough to avoid influences on the measurements by the roughness layer; 2) low enough to ensure that the footprint does not extend beyond the fetch of interest. In this study, we performed a comparison of turbulent fluxes of carbon dioxide, latent and sensible heat using a one-year long dataset measured at two heights (23 and 33 m) over the 18 m tall forest ecosystem at Hyytiälä site in Finland. The goal was to assess the spatial variability and representativeness of flux measurements for different atmospheric stability regimes and wind direction sectors. Footprint modelling together with land use and vegetation maps is used to evaluate source/sink areas around the tower and to identify those critical conditions when the measured fluxes do not fully represent the target forest.