Net Exchange of CO
            <sub>2</sub>
            in a Mid-Latitude Forest

Wofsy, Steven C.; Goulden, Michael L.; Munger, J. William; Fan, Song‐Miao; Bakwin, P.; Daube, Bruce C.; Bassow, S. L.; Bazzaz, F. A.

doi:10.1126/science.260.5112.1314

Cited by 831 publications

(550 citation statements)

References 22 publications

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“…The forest is 50-70 years old and contains a mixture of red oak, red maple, and hemlock with an average tree height of 24 m. The site has been equipped with a suite of radiation and turbulent flux measurements since 1991 [Wofsy et al, 1993;Moore et al 1996]. The long-term turbulent exchange, such as latent heat and 6 CO 2 fluxes, and radiation and ground heat flux measurements sampled every 30 min at EMS provide us the opportunity to investigate processes of evapotranspiration, CO 2 uptake, and photosynthesis [Min, 2005].…”

Section: Mlse and Harvard Forestmentioning

confidence: 99%

Remote sensing of evapotranspiration and carbon uptake at Harvard Forest

Min

Lin

2006

Remote Sensing of Environment

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Section: Mlse and Harvard Forestmentioning

confidence: 99%

Remote sensing of evapotranspiration and carbon uptake at Harvard Forest

Min

Lin

2006

Remote Sensing of Environment

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“…Harvard Forest soils are acidic and originate from sandy loam glacial till (Allen, 1995). Measurements presented in this study were made from November 2010 to March 2012 at the Environmental Measurement Station (EMS) (Wofsy et al, 1993), located in the Prospect Hill tract of Harvard Forest. The station is surrounded for several kilometers by moderately hilly terrain and forest that has been relatively undisturbed since the 1930s.…”

Section: Measurement Sitementioning

confidence: 99%

“…The relevant eddy-derived quantity to compare to surfacebased chamber measurements is the u * -filtered (Sect. 3.3) nocturnal net ecosystem exchange (NEE), which accounts for the time lag between CO 2 emitted by respiration and its release from storage from beneath the canopy (storage in the sense of Wofsy et al, 1993). The mean chamber flux was approximately 2 times higher than NEE at night over the weeklong summer example period (Fig.…”

Section: Comparing Eddy Covariance and Chamber Co 2 Flux Measurementsmentioning

confidence: 99%

Ecosystem fluxes of hydrogen: a comparison of flux-gradient methods

et al. 2014

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Abstract. Our understanding of biosphere-atmosphere exchange has been considerably enhanced by eddy covariance measurements. However, there remain many trace gases, such as molecular hydrogen (H 2 ), that lack suitable analytical methods to measure their fluxes by eddy covariance. In such cases, flux-gradient methods can be used to calculate ecosystem-scale fluxes from vertical concentration gradients. The budget of atmospheric H 2 is poorly constrained by the limited available observations, and thus the ability to quantify and characterize the sources and sinks of H 2 by fluxgradient methods in various ecosystems is important. We developed an approach to make nonintrusive, automated measurements of ecosystem-scale H 2 fluxes both above and below the forest canopy at the Harvard Forest in Petersham, Massachusetts, for over a year. We used three flux-gradient methods to calculate the fluxes: two similarity methods that do not rely on a micrometeorological determination of the eddy diffusivity, K, based on (1) trace gases or (2) sensible heat, and one flux-gradient method that (3) parameterizes K. We quantitatively assessed the flux-gradient methods using CO 2 and H 2 O by comparison to their simultaneous independent flux measurements via eddy covariance and soil chambers. All three flux-gradient methods performed well in certain locations, seasons, and times of day, and the best methods were trace gas similarity for above the canopy and K parameterization below it. Sensible heat similarity required several independent measurements, and the results were more variable, in part because those data were only available in the winter, when heat fluxes and temperature gradients were small and difficult to measure. Biases were often observed between flux-gradient methods and the independent flux measurements, and there was at least a 26 % difference in nocturnal eddy-derived net ecosystem exchange (NEE) and chamber measurements. H 2 fluxes calculated in a summer period agreed within their uncertainty and pointed to soil uptake as the main driver of H 2 exchange at Harvard Forest, with H 2 deposition velocities ranging from 0.04 to 0.10 cm s −1 .

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“…The technique is closely related to physiological and ecological processes and can reflect the seasonal and interannual variability of carbon fluxes (Baldocchi et al, 2001;Chen et al, 2013). Since being established in the early 1990s, eddy covariance flux towers have provided continuous measurements of the ecosystemlevel net exchange of carbon (Wofsy et al, 1993). The FLUXNET is the global network of flux towers (Baldocchi et al, 2001).…”

Section: Introductionmentioning

confidence: 99%

Regional representativeness assessment and improvement of eddy flux observations in China

Zhang

Gao

et al. 2015

Science of The Total Environment

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• The network of flux towers performed well in representing the environment of more than half of China.• The towers in wetlands and barelands were poorly represented.• Representativeness increased with towers added in forests, grasslands, wetlands and barelands.• Substantial gains in representation were achieved by adding new towers on the Tibet Plateau. Both the amounts of data describing the site-scale carbon flux at a high temporal and spatial resolution collected in China and the number of eddy covariance flux towers have been increasing during the last decade. To correctly upscale these fluxes to the regional and global level, the representativeness of the current network of flux towers must be known. The present study quantifies the representativeness of the flux network for the regional carbon exchange. This analysis combined the total solar radiation, air temperature, vapor pressure and the enhanced vegetation index to indicate the environmental characteristics of each 1-km pixel cell and flux tower. Next, the Euclidean distance from each pixel to the tower was calculated to determine the representativeness of the existing flux towers. To improve the regional representativeness, additional tower locations were pinpointed by identifying and clustering the underrepresented areas. The existing network of flux towers performed well in representing the environmental conditions of the middle and the northeastern portions of China. The wellrepresented areas covered 60.9% of the total areas. The towers in croplands and grasslands represented the vegetation types well, but the wetlands and barelands were poorly represented. The representativeness of the flux network increased with the addition of nine towers located in forests, grasslands, wetlands and barelands. The representativeness of 27.5% of the land areas improved. In addition, the well-represented areas were enlarged by 15.2%. Substantial gains in representation were achieved by adding new towers on the Tibet Plateau. The representativeness of the northwest and southwest was improved less significantly, suggesting that more towers are required to capture certain ecosystem behaviors. a b s t r a c t a r t i c l e i n f o

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Net Exchange of CO ₂ in a Mid-Latitude Forest

Cited by 831 publications

References 22 publications

Remote sensing of evapotranspiration and carbon uptake at Harvard Forest

Remote sensing of evapotranspiration and carbon uptake at Harvard Forest

Ecosystem fluxes of hydrogen: a comparison of flux-gradient methods

Regional representativeness assessment and improvement of eddy flux observations in China

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Net Exchange of CO 2 in a Mid-Latitude Forest

Cited by 831 publications

References 22 publications

Remote sensing of evapotranspiration and carbon uptake at Harvard Forest

Remote sensing of evapotranspiration and carbon uptake at Harvard Forest

Ecosystem fluxes of hydrogen: a comparison of flux-gradient methods

Regional representativeness assessment and improvement of eddy flux observations in China

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Product

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Net Exchange of CO ₂ in a Mid-Latitude Forest