Toward biologically meaningful net carbon exchange estimates for tall, dense canopies: Multi-level eddy covariance observations and canopy coupling regimes in a mature Douglas-fir forest in Oregon

Thomas, Christoph; Martin, Jonathan G.; Law, B. E.; Davis, K. J.

doi:10.1016/j.agrformet.2013.01.001

Cited by 85 publications

(126 citation statements)

References 49 publications

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“…Most studies in forest sites reported that the drainage flows were restricted in the subcanopy layer, which characterized with relative open canopy and insignificant understory vegetation [8,13,21], or at the upper part of a long slope [39,40], or very gentle slope [39]. We did not detect the possible subcanopy wind maximum as many previous studies [13,28,31,41,42] due to only one observation point below canopy.…”

Section: Horizontal Wind Velocitycontrasting

confidence: 46%

“…For example, the height of wind velocity maximum on the low-angle (1.6°) side-wall of the floor of Utah's Salt Lake Valley occurred at 10 to 15 m height [20], but could reach 40 m in another slope in the same valley [48]. Most studies in forest sites reported that the drainage flows were restricted in the subcanopy layer, which characterized with relative open canopy and insignificant understory vegetation [8,13,21], or at the upper part of a long slope [39,40], or very gentle slope [39]. We did not detect the possible subcanopy wind maximum as many previous studies [13,28,31,41,42] due to only one observation point below canopy.…”

Section: Horizontal Wind Velocitymentioning

confidence: 99%

“…In valley topography, significant interplays between the flows on side-wall and the flows along the valley axis, down-valley flows differ dramatically from down-slope flows on isolated mountains [15]. When the observation was conducted at upper slope, the depth of nocturnal drainage flow was often limited to the first few meters above the ground in the trunk-space e.g., [8,13,39,40]. On the side-wall of a valley, the down-slope flow often started before sunset [23,49], and then speeded up and increased in depth with down-slope distance before mid-night [18,19,23].…”

Section: Horizontal Wind Velocitymentioning

confidence: 99%

“…One of the key factors that results in uncertainties in measuring scalar exchanges between the atmosphere and forests is the complexity of airflow above and within the forest canopy [4,[9][10][11]. Understanding mechanisms of airflow above and within a forest canopy provides a basis for interpreting nighttime CO2 fluxes above the forest canopy [10,[12][13][14].…”

Section: Introductionmentioning

confidence: 99%

“…Daytime coupling/decoupling of airflows above and below forest canopy was investigated for a few studies [10,13]. However, because of the site-specific wind regime, it needs more researches to gain a general perspective on canopy winds in a complex topography.…”

Section: Introductionmentioning

confidence: 99%

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Wind Regimes above and below a Temperate Deciduous Forest Canopy in Complex Terrain: Interactions between Slope and Valley Winds

Wang

2014

Atmosphere

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Abstract:The thermally driven wind over mountainous terrains challenges the estimation of CO2 exchange between forests and the atmosphere when using the eddy covariance technique. In this study, the wind regimes were investigated in a temperate deciduous forested valley at the Maoershan site, Northeast China. The wind direction above the canopy was preferentially up-valley in the daytime and down-valley in the nighttime, corresponding to the diurnal patterns of above-canopy temperature gradient and stability parameter. In both leaf-on and -off nighttime, a down-valley flow with a maximum velocity of 1~3 m•s −1 was often developed at 42 m above the ground (2.3-fold of the canopy height). However, the below-canopy prevailing wind was down-slope in the night, contrast to the below-canopy temperature lapse and unstable conditions. This substantial directional shear illustrated shallow slope winds were superimposed on larger-scale valley winds. As a consequence, the valley-wind component becomes stronger with increasing height, indicating a clear confluence of drainage flow to the valley center. In the daytime, the below-canopy wind was predominated down-slope due to the temperature inversion and stable conditions in the leaf-on season, and was mainly up-valley or down-slope in the leaf-off season. The isolation of momentum flux and OPEN ACCESSAtmosphere 2015, 6 61 radiation by the dense canopy played a key role in the formation of the below-canopy unaligned wind and inverse stability. Significant lateral kinematic momentum fluxes were detected due to the directional shear. These findings suggested a significant interaction between slope and valley winds at this site. The frequent vertical convergence / divergence above the canopy and horizontal divergence/convergence below the canopy in the nighttime / daytime is likely to induce significant advections of trace gases and energy flux.

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Section: Horizontal Wind Velocitycontrasting

confidence: 46%

Section: Horizontal Wind Velocitymentioning

confidence: 99%

Section: Horizontal Wind Velocitymentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Wind Regimes above and below a Temperate Deciduous Forest Canopy in Complex Terrain: Interactions between Slope and Valley Winds

Wang

2014

Atmosphere

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Observations of ¹⁴CO₂ in ecosystem respiration from a temperate deciduous forest in Northern Wisconsin

et al. 2015

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The 14 CO 2 composition of plant and soil respiration can be used to determine the residence time of photosynthetically fixed carbon before it is released back to the atmosphere. To estimate the residence time of actively cycled carbon in a temperate forest, we employed two approaches for estimating the Δ 14 CO 2 of ecosystem respiration (Δ 14 C-R eco ) at the Willow Creek AmeriFlux site in Northern Wisconsin, USA. Our first approach was to construct nighttime Keeling plots from subcanopy profiles of Δ 14 CO 2 and CO 2 , providing estimates of Δ 14 C-R eco of 121.7‰ in June and 42.0‰ in August 2012. These measurements are likely dominated by soil fluxes due to proximity to the ground level. Our second approach utilized samples taken over 20 months within the forest canopy and from 396 m above ground level at the nearby LEF NOAA tall tower site (Park Falls, WI). In this canopy-minus-background approach we employed a mixing model described by Miller and Tans (2003) for estimating isotopic sources by subtracting time-varying background conditions. For the period from May 2011 to December 2012 the estimated Δ 14 C-R eco using the Miller-Tans model was 76.8‰. Together, these Δ 14 C-R eco values represent mean R eco carbon ages of approximately 1-19 years. We also found that heterotrophic soil-respired Δ 14 C at Willow Creek was 5-38‰ higher (i.e., 1-10 years older) than predicted by the Carnegie-Ames-Stanford Approach global biosphere carbon model for the 1 × 1 pixel nearest to the site. This study provides much needed observational constraints of ecosystem carbon residence times, which are a major source of uncertainty in terrestrial carbon cycle models.

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Turbulent mixing and removal of ozone within an Amazon rainforest canopy

et al. 2017

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Simultaneous profiles of turbulence statistics and mean ozone mixing ratio are used to establish a relation between eddy diffusivity and ozone mixing within the Amazon forest. A one‐dimensional diffusion model is proposed and used to infer mixing time scales from the eddy diffusivity profiles. Data and model results indicate that during daytime conditions, the upper (lower) half of the canopy is well (partially) mixed most of the time and that most of the vertical extent of the forest can be mixed in less than an hour. During nighttime, most of the canopy is predominantly poorly mixed, except for periods with bursts of intermittent turbulence. Even though turbulence is faster than chemistry during daytime, both processes have comparable time scales in the lower canopy layers during nighttime conditions. Nonchemical loss time scales (associated with stomatal uptake and dry deposition) for the entire forest are comparable to turbulent mixing time scale in the lower canopy during the day and in the entire canopy during the night, indicating a tight coupling between turbulent transport and dry deposition and stomatal uptake processes. Because of the significant time of day and height variability of the turbulent mixing time scale inside the canopy, it is important to take it into account when studying chemical and biophysical processes happening in the forest environment. The method proposed here to estimate turbulent mixing time scales is a reliable alternative to currently used models, especially for situations in which the vertical distribution of the time scale is relevant.

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Toward biologically meaningful net carbon exchange estimates for tall, dense canopies: Multi-level eddy covariance observations and canopy coupling regimes in a mature Douglas-fir forest in Oregon

Cited by 85 publications

References 49 publications

Wind Regimes above and below a Temperate Deciduous Forest Canopy in Complex Terrain: Interactions between Slope and Valley Winds

Wind Regimes above and below a Temperate Deciduous Forest Canopy in Complex Terrain: Interactions between Slope and Valley Winds

Observations of ¹⁴CO₂ in ecosystem respiration from a temperate deciduous forest in Northern Wisconsin

Turbulent mixing and removal of ozone within an Amazon rainforest canopy

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Toward biologically meaningful net carbon exchange estimates for tall, dense canopies: Multi-level eddy covariance observations and canopy coupling regimes in a mature Douglas-fir forest in Oregon

Cited by 85 publications

References 49 publications

Wind Regimes above and below a Temperate Deciduous Forest Canopy in Complex Terrain: Interactions between Slope and Valley Winds

Wind Regimes above and below a Temperate Deciduous Forest Canopy in Complex Terrain: Interactions between Slope and Valley Winds

Observations of 14CO2 in ecosystem respiration from a temperate deciduous forest in Northern Wisconsin

Turbulent mixing and removal of ozone within an Amazon rainforest canopy

Contact Info

Product

Resources

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Observations of ¹⁴CO₂ in ecosystem respiration from a temperate deciduous forest in Northern Wisconsin