Releases of the greenhouse gases carbon dioxide (CO2) and methane (CH4) from thawing permafrost are expected to be among the largest feedbacks to climate from arctic ecosystems. However, the current net carbon (C) balance of terrestrial arctic ecosystems is unknown. Recent studies suggest that these ecosystems are sources, sinks, or approximately in balance at present…. More

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Similar nonsteady-state automated chamber systems were used to measure and partition soil CO2 efflux in contrasting deciduous (trembling aspen) and coniferous (black spruce and jack pine) stands located within 100km of each other near the southern edge of the Boreal forest in Canada. The stands were exposed to similar climate forcing in 2003, including marked… More

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The interannual and seasonal variability of gross ecosystem photosynthesis (P), ecosystem respiration (R) and evapotranspiration (E), and their relationships to environmental factors were used to explain changes in net ecosystem productivity (FNEP) at the onset of, during, and following a 3-year-long (2001–2003) drought in a mature boreal aspen stand in central Saskatchewan, Canada. The forest… More

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Aerodynamic canopy height (ha) is the effective height of vegetation canopy for its influence on atmospheric fluxes and is a key parameter of surface‐atmosphere coupling. However, methods to estimate ha from data are limited. This synthesis evaluates the applicability and robustness of the calculation of ha from eddy covariance momentum‐flux data. At 69 forest sites,… More

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It is necessary to partition eddy covariance measurements of carbon dioxide exchange into its offsetting gross fluxes, canopy photosynthesis, and ecosystem respiration, to understand the biophysical controls on the net fluxes. And independent estimates of canopy photosynthesis (G) and ecosystem respiration (R) are needed to validate and parametrize carbon cycle models that are coupled with… More

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We monitored sap flow and estimated diurnal changes in transpiration rates of two trembling aspen (Populus tremuloides Michx.) stands, located in the southern boreal forest and aspen parkland of Saskatchewan, Canada. In both stands during the peak growing season (June and July), sap flow during the day (0700–1700 h local time) increased linearly with vapor… More

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Tower and aircraft data from a number of field studies are analyzed to: (1) estimate the roughness lengths for local and area-averaged momentum fluxes over various surface types; (2) examine the applicability of the ψ-stability formulations of Paulson and Dyer for momentum fluxes; (3) investigate the possibility that tower flux measurements over tall vegetation are… More

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Using a helicopter-mounted portable spectroradiometer and continuous eddy covariance data we were able to evaluate the photochemical reflectance index (PRI) as an indicator of canopy photosynthetic light-use efficiency (LUE) in four boreal forest species during the Boreal Ecosystem Atmosphere experiment (BOREAS). PRI was calculated from narrow waveband reflectance data and correlated with LUE calculated from… More

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