The carbon balance of a managed boreal landscape measured from a tall tower in northern Sweden

Boreal forests exchange large amounts of carbon dioxide (CO₂) with the atmosphere. A managed boreal landscape usually comprises various potential CO₂ sinks and sources across forest stands of varying age classes, clear-cut areas, mires, and lakes. Due to this heterogeneity and complexity, large uncertainties exist regarding the net CO₂ balance at the landscape scale. In this study, we present the first estimate of the net CO₂ exchange over a managed boreal landscape (∼68 km²) in northern Sweden, based on tall tower eddy covariance measurements. Our results suggest that from March 1, 2016 to February 28, 2018, the heterogeneous landscape was a net CO₂ sink with a 2-year mean uptake of −87 ± 6 g C m⁻² yr⁻¹. Due to an earlier and warmer spring and sunnier autumn, the landscape was a stronger CO₂ sink during the first year (−122 ± 8 g C m⁻²) compared to the second year (−52 ± 9 g C m⁻²). Footprint analysis shows that 87% of the CO₂ flux measurements originated from forests, whereas mires, clear-cuts, lakes, and grassland contributed 11%, 1%, 0.7%, and 0.2%, respectively. Altogether, the CO₂ sink strength of the heterogeneous landscape was up to 38% lower compared to the sink strength of a mature stand surrounding the tower. Overall, this study suggests that the managed boreal landscape acted as a CO₂ sink and advocates tall tower eddy covariance measurements to improve regional carbon budget estimates.