Water Balance Delineates the Soil Layer in Which Moisture Affects Canopy Conductance

Oren, Ram; Ewers, B. E.; Todd, Philip; Phillips, Nathan; Katul, Gabriel G.

doi:10.1890/1051-0761(1998)008[0990:wbdtsl]2.0.co;2

Cited by 137 publications

(88 citation statements)

References 83 publications

(101 reference statements)

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“…The highest water fluxes occur during and following rainfall events. If we assume that under these conditions, the top-soil is entirely saturated, the fluxes become of the same order of magnitude as the soil hydraulic conductivity at saturation, which has been estimated to be about 0.08 m 3 H 2 O m À2 soil day À1 (Oren et al 1998;Suwa et al 2004). In the upper soil layers (*5-6 cm) the largest CO 2 concentrations are about 10 4 lmol CO 2 mol À1 air ; which correspond to about 4 Â 10 5 lmol CO 2 m À3 H 2 O of dissolved CO 2 concentrations (see Eq.…”

Section: Co 2 Fluxes and Productionmentioning

confidence: 98%

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The effects of elevated atmospheric CO2 and nitrogen amendments on subsurface CO2 production and concentration dynamics in a maturing pine forest

et al. 2009

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Profiles of subsurface soil CO 2 concentration, soil temperature, and soil moisture, and throughfall were measured continuously during the years 2005 and 2006 in 16 locations at the free air CO 2 enrichment facility situated within a temperate loblolly pine (Pinus taeda L.) stand. Sampling at these locations followed a 4 by 4 replicated experimental design comprised of two atmospheric CO 2 concentration levels (ambient [CO 2 ] a , ambient ? 200 ppmv, [CO 2 ] e ) and two soil nitrogen (N) deposition levels (ambient, ambient ? fertilization at 11.2 g N m -2 year -1 ). The combination of these measurements permitted indirect estimation of belowground CO 2 production and flux profiles in the mineral soil. Adjacent to the soil CO 2 profiles, direct (chamber-based) measurements of CO 2 fluxes from the soil-litter complex were simultaneously conducted using the automated carbon efflux system. Based on the measured soil CO 2 profiles, neither [CO 2 ] e nor N fertilization had a statistically significant effect on seasonal soil CO 2 , the mineral soil over the study period. Soil moisture and temperature had different effects on CO 2 concentration depending on the depth. Variations in CO 2 were mostly explained by soil temperature at deeper soil layers, while water content was an important driver at the surface (within the first 10 cm), where CO 2 pulses were induced by rainfall events. The soil effluxes were equal to the CO 2 production for most of the time, suggesting that the site reached near steady-state conditions. The fluxes estimated from the CO 2 profiles were highly correlated to the direct measurements when the soil was neither very dry nor very wet. This suggests that a better parameterization of the soil CO 2 diffusivity is required for these soil moisture extremes.

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Section: Co 2 Fluxes and Productionmentioning

confidence: 98%

“…Site characteristics are described elsewhere (Oren et al 1998;Andrews and Schlesinger 2001) and only a brief description is provided here.…”

Section: Site Descriptionmentioning

confidence: 99%

The effects of elevated atmospheric CO2 and nitrogen amendments on subsurface CO2 production and concentration dynamics in a maturing pine forest

et al. 2009

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“…Vegetation plays an important role in movement of water across the landscape by exchanging water between the soil and the atmosphere via change in surface albedo and roughness [1], canopy water interception [2], and transpiration [3]–[5]; changing the hydro-mechanical properties of soil [6], [7]; and redistributing water laterally and vertically in soil profile via hydraulic redistribution [8]–[10]. On the other hand, survival and distribution of plants on a landscape depend on spatio-temporal patterns of soil water availability [11]–[14].…”

Section: Introductionmentioning

confidence: 99%

Spatial Distribution of Tree Species Governs the Spatio-Temporal Interaction of Leaf Area Index and Soil Moisture across a Forested Landscape

et al. 2013

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Quantifying coupled spatio-temporal dynamics of phenology and hydrology and understanding underlying processes is a fundamental challenge in ecohydrology. While variation in phenology and factors influencing it have attracted the attention of ecologists for a long time, the influence of biodiversity on coupled dynamics of phenology and hydrology across a landscape is largely untested. We measured leaf area index (L) and volumetric soil water content (θ) on a co-located spatial grid to characterize forest phenology and hydrology across a forested catchment in central Pennsylvania during 2010. We used hierarchical Bayesian modeling to quantify spatio-temporal patterns of L and θ. Our results suggest that the spatial distribution of tree species across the landscape created unique spatio-temporal patterns of L, which created patterns of water demand reflected in variable soil moisture across space and time. We found a lag of about 11 days between increase in L and decline in θ. Vegetation and soil moisture become increasingly homogenized and coupled from leaf-onset to maturity but heterogeneous and uncoupled from leaf maturity to senescence. Our results provide insight into spatio-temporal coupling between biodiversity and soil hydrology that is useful to enhance ecohydrological modeling in humid temperate forests.

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“…Mean annual precipitation at the site is 1140 mm, and mean annual temperature is 15.5°C. Soils are acidic Hapludalf, with a clayey loam in the upper 0.3 m, and a clay pan below, minimizing drainage [Oren et al, 1998]. The local topographic variations are sufficiently small (<5% slopes) such that their impact on micrometeorological flux measurements can be neglected.…”

Section: Study Site and Datamentioning

confidence: 99%

“…For simplicity, we used g a in the canopy instead of modeling g a for the forest floor separately as forest floor evaporation is a minor component of LE [Oren et al, 1998]. LE x is the potential latent heat flux limited by soil exfiltration modeled as…”

Section: Appendix C: Modeling Long Wave Radiationmentioning

confidence: 99%

Energy, water, and carbon fluxes in a loblolly pine stand: Results from uniform and gappy canopy models with comparisons to eddy flux data

et al. 2009

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[1] This study investigates the impacts of canopy structure specification on modeling net radiation (R n ), latent heat flux (LE) and net photosynthesis (A n ) by coupling two contrasting radiation transfer models with a two-leaf photosynthesis model for a maturing loblolly pine stand near Durham, North Carolina, USA. The first radiation transfer model is based on a uniform canopy representation (UCR) that assumes leaves are randomly distributed within the canopy, and the second radiation transfer model is based on a gappy canopy representation (GCR) in which leaves are clumped into individual crowns, thereby forming gaps between the crowns. To isolate the effects of canopy structure on model results, we used identical model parameters taken from the literature for both models. Canopy structure has great impact on energy distribution between the canopy and the forest floor. Comparing the model results, UCR produced lower R n , higher LE and higher A n than GCR. UCR intercepted more shortwave radiation inside the canopy, thus producing less radiation absorption on the forest floor and in turn lower R n . There is a higher degree of nonlinearity between A n estimated by UCR and by GCR than for LE. Most of the difference for LE and A n between UCR and GCR occurred around noon, when gaps between crowns can be seen from the direction of the incident sunbeam. Comparing with eddy-covariance measurements in the same loblolly pine stand from May to September 2001, based on several measures GCR provided more accurate estimates for R n , LE and A n than UCR. The improvements when using GCR were much clearer when comparing the daytime trend of LE and A n for the growing season. Sensitivity analysis showed that UCR produces higher LE and A n estimates than GCR for canopy cover ranging from 0.2 to 0.8. There is a high degree of nonlinearity in the relationship between UCR estimates for A n and those of GCR, particularly when canopy cover is low, and suggests that simple scaling of UCR parameters cannot compensate for differences between the two models. LE from UCR and GCR is also nonlinearly related when canopy cover is low, but the nonlinearity quickly disappears as canopy cover increases, such that LE from UCR and GCR are linearly related and the relationship becomes stronger as canopy cover increases. These results suggest the uniform canopy assumption can lead to underestimation of R n , and overestimation of LE and A n . Given the potential in mapping regional scale forest canopy structure with high spatial resolution optical and Lidar remote sensing plotforms, it is possible to use GCR for up-scaling ecosystem processes from flux tower measurements to heterogeneous landscapes, provided the heterogeneity is not too extreme to modify the flow dynamics.

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Water Balance Delineates the Soil Layer in Which Moisture Affects Canopy Conductance

Cited by 137 publications

References 83 publications

The effects of elevated atmospheric CO2 and nitrogen amendments on subsurface CO2 production and concentration dynamics in a maturing pine forest

The effects of elevated atmospheric CO2 and nitrogen amendments on subsurface CO2 production and concentration dynamics in a maturing pine forest

Spatial Distribution of Tree Species Governs the Spatio-Temporal Interaction of Leaf Area Index and Soil Moisture across a Forested Landscape

Energy, water, and carbon fluxes in a loblolly pine stand: Results from uniform and gappy canopy models with comparisons to eddy flux data

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