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Impact of Canopy Decoupling and Subcanopy Advection on the Annual Carbon Balance of a Boreal Scots Pine Forest as Derived From Eddy Covariance

Journal article
Authors Georg Jocher
John Marshall
Mats B. Nilsson
Sune Linder
Giuseppe De Simon
Thomas Hörnlund
Tomas Lundmark
Torgny Näsholm
Mikaell Ottosson Löfvenius
Lasse Tarvainen
Göran Wallin
Matthias Peichl
Published in Journal of Geophysical Research: Biogeosciences
Volume 123
Issue 2
Pages 303-325
ISSN 21698953
Publication year 2018
Published at Department of Biological and Environmental Sciences
Pages 303-325
Language en
Keywords Ecosystem respiration (R ) eco, Flux partitioning, Gap filling, Gross primary production (GPP), Net ecosystem CO exchange (NEE) 2, Pinus sylvestris
Subject categories Botany, Terrestrial ecology, Biological Sciences, Soil Science, Forest Science


Apparent net uptake of carbon dioxide (CO 2 ) during wintertime by an ∼ 90 year old Scots pine stand in northern Sweden led us to conduct canopy decoupling and subcanopy advection investigations over an entire year. Eddy covariance (EC) measurements ran simultaneously above and within the forest canopy for that purpose. We used the correlation of above- and below-canopy standard deviation of vertical wind speed (σ w ) as decoupling indicator. We identified 0.33 m s -1 and 0.06 m s -1 as site-specific σ w thresholds for above- and below-canopy coupling during nighttime (global radiation < 20 W m -2 ) and 0.23 m s -1 and 0.06 m s -1 as daytime (global radiation > 20 W m -2 ) σ w thresholds. Decoupling occurred in 53% of the annual nighttime and 14% of the annual daytime. The annual net ecosystem exchange (NEE), gross ecosystem exchange (GEE), and ecosystem respiration (R eco ) derived via two-level filtered EC data were -357 g C m -2 , -1,138 g C m -2 , and 781 g C m -2 , respectively. In comparison, both single-level friction velocity (u * ) and quality filtering resulted in ~ 22% higher NEE, mainly caused by ~ 16% lower R eco . GEE remained similar among filtering regimes. Accounting for changes of CO 2 storage across the canopy in the single-level filtered data could only marginally decrease these discrepancies. Consequently, advection appears to be responsible for the major part of this divergence. We conclude that the two-level filter is necessary to adequately address decoupling and subcanopy advection at our site, and we recommend this filter for all forested EC sites.

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