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Y Brunet - One of the best experts on this subject based on the ideXlab platform.
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Wind-Flow Dynamics Over a Vineyard
Boundary-Layer Meteorology, 2014Co-Authors: Ali Chahine, Sylvain Dupont, Carole Sinfort, Y BrunetAbstract:Wind-flow dynamics has been extensively studied over horizontally uniform Canopies, but agricultural plantations structured in rows such as vineyards have received less attention. Here, the wind flow over a vineyard is studied in neutral stratification from both large-eddy simulation (LES) and in situ measurements. The impact of row structure on the wind dynamics is investigated over a range of wind directions from cross-row to down-row, and a typical range of row aspect ratio (row separation/height ratio). It is shown that the mean flow over a vineyard is similar to that observed in uniform Canopies, especially for wind directions from cross-row to diagonal. For down-row winds, the mean flow exhibits noticeable spatial variability across each elementary row-gap pattern, as the wind is channeled in the inter-row. This spatial variability increases with the aspect ratio. With down-row winds the turbulent structures are also more intermittent and generate larger turbulent kinetic energy and momentum flux. The displacement height and roughness length of the vineyard vary with the aspect ratio in a way similar to their variation with canopy density in uniform Canopies. Both parameters take smaller values in down-row wind flow, for which the canopy appears more open. The analysis of velocity spectra and autocorrelation functions shows that vineyard Canopies share similar features to uniform Canopies in terms of turbulent coherent structures, with only minor changes with wind direction.
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influence of foliar density profile on canopy flow a large eddy simulation study
Agricultural and Forest Meteorology, 2008Co-Authors: Sylvain Dupont, Y BrunetAbstract:Abstract The Advanced Regional Prediction System (ARPS) has been modified so as to simulate turbulent flow at very fine scale within and above vegetation Canopies using a large-eddy simulation (LES) approach. It is first shown that this new version of ARPS is able to reproduce accurately all essential features of turbulent flow over homogeneous Canopies. A sensitivity study of the flow to the morphology of the canopy, i.e. the density and vertical leaf-area (LAI) distribution, is then performed numerically over three types of Canopies with five levels of leaf-area index, from 1 to 5. This study confirms the universal characteristics of turbulent flow over vegetation Canopies, as previously observed from wind-tunnel and in situ experiments. It shows that the typical features of canopy flow become more pronounced as canopy density increases, and quantifies the extent to which differences in canopy morphology can explain the experimental variability observed between Canopies. This variability in turbulent characteristics is mostly visible in the subcanopy space, and depends significantly on the density of the upper foliated layers. The mean longitudinal separation Λ w between adjacent coherent structures has also been computed for each canopy using the wavelet transform and approximating the convection velocity of coherent structures as 1.8 times the average wind velocity at canopy top. Except for the sparsest Canopies, the analogy between the atmospheric flow near the top of a vegetation canopy and a plane mixing layer is well verified: Λ w is directly related to the shear length scale L s = U ( h ) / U ′ ( h ) , where h is canopy height, U mean velocity and U ′ is the vertical gradient d U / d z , in a way close to the prediction Λ w / h = 8.1 L s / h .
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Influence of foliar density profile on canopy flow: A large-eddy simulation study
Agricultural and Forest Meteorology, 2008Co-Authors: Sylvain Dupont, Y BrunetAbstract:The Advanced Regional Prediction System (ARPS) has been modified so as to simulate turbulent flow at very fine scale within and above vegetation Canopies using a large-eddy simulation (LES) approach. It is first shown that this new version of ARPS is able to reproduce accurately all essential features of turbulent flow over homogeneous Canopies. A sensitivity study of the flow to the morphology of the canopy, i.e. the density and vertical leaf-area (LAI) distribution, is then performed numerically over three types of Canopies with five levels of leaf-area index, from 1 to 5. This study confirms the universal characteristics of turbulent flow over vegetation Canopies, as previously observed from wind-tunnel and in situ experiments. It shows that the typical features of canopy flow become more pronounced as canopy density increases, and quantifies the extent to which differences in canopy morphology can explain the experimental variability observed between Canopies. This variability in turbulent characteristics is mostly visible in the subcanopy space, and depends significantly on the density of the upper foliated layers. The mean longitudinal separation Lambda(w) between adjacent coherent structures has also been computed for each canopy using the wavelet transform and approximating the convection velocity of coherent structures as 1.8 times the average wind velocity at canopy top. Except for the sparsest Canopies, the analogy between the atmospheric flow near the top of a vegetation canopy and a plane mixing layer is well verified: Lambda(w) is directly related to the shear length scale L-s = U(h)/U'(h), where h is canopy height, U mean velocity and U' is the vertical gradient dU/dz, in a way close to the prediction Lambda(w)/h = 8.1L(s)/h: (C) 2008 Elsevier B.V. All rights reserved.
Sylvain Dupont - One of the best experts on this subject based on the ideXlab platform.
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Wind-Flow Dynamics Over a Vineyard
Boundary-Layer Meteorology, 2014Co-Authors: Ali Chahine, Sylvain Dupont, Carole Sinfort, Y BrunetAbstract:Wind-flow dynamics has been extensively studied over horizontally uniform Canopies, but agricultural plantations structured in rows such as vineyards have received less attention. Here, the wind flow over a vineyard is studied in neutral stratification from both large-eddy simulation (LES) and in situ measurements. The impact of row structure on the wind dynamics is investigated over a range of wind directions from cross-row to down-row, and a typical range of row aspect ratio (row separation/height ratio). It is shown that the mean flow over a vineyard is similar to that observed in uniform Canopies, especially for wind directions from cross-row to diagonal. For down-row winds, the mean flow exhibits noticeable spatial variability across each elementary row-gap pattern, as the wind is channeled in the inter-row. This spatial variability increases with the aspect ratio. With down-row winds the turbulent structures are also more intermittent and generate larger turbulent kinetic energy and momentum flux. The displacement height and roughness length of the vineyard vary with the aspect ratio in a way similar to their variation with canopy density in uniform Canopies. Both parameters take smaller values in down-row wind flow, for which the canopy appears more open. The analysis of velocity spectra and autocorrelation functions shows that vineyard Canopies share similar features to uniform Canopies in terms of turbulent coherent structures, with only minor changes with wind direction.
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influence of foliar density profile on canopy flow a large eddy simulation study
Agricultural and Forest Meteorology, 2008Co-Authors: Sylvain Dupont, Y BrunetAbstract:Abstract The Advanced Regional Prediction System (ARPS) has been modified so as to simulate turbulent flow at very fine scale within and above vegetation Canopies using a large-eddy simulation (LES) approach. It is first shown that this new version of ARPS is able to reproduce accurately all essential features of turbulent flow over homogeneous Canopies. A sensitivity study of the flow to the morphology of the canopy, i.e. the density and vertical leaf-area (LAI) distribution, is then performed numerically over three types of Canopies with five levels of leaf-area index, from 1 to 5. This study confirms the universal characteristics of turbulent flow over vegetation Canopies, as previously observed from wind-tunnel and in situ experiments. It shows that the typical features of canopy flow become more pronounced as canopy density increases, and quantifies the extent to which differences in canopy morphology can explain the experimental variability observed between Canopies. This variability in turbulent characteristics is mostly visible in the subcanopy space, and depends significantly on the density of the upper foliated layers. The mean longitudinal separation Λ w between adjacent coherent structures has also been computed for each canopy using the wavelet transform and approximating the convection velocity of coherent structures as 1.8 times the average wind velocity at canopy top. Except for the sparsest Canopies, the analogy between the atmospheric flow near the top of a vegetation canopy and a plane mixing layer is well verified: Λ w is directly related to the shear length scale L s = U ( h ) / U ′ ( h ) , where h is canopy height, U mean velocity and U ′ is the vertical gradient d U / d z , in a way close to the prediction Λ w / h = 8.1 L s / h .
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Influence of foliar density profile on canopy flow: A large-eddy simulation study
Agricultural and Forest Meteorology, 2008Co-Authors: Sylvain Dupont, Y BrunetAbstract:The Advanced Regional Prediction System (ARPS) has been modified so as to simulate turbulent flow at very fine scale within and above vegetation Canopies using a large-eddy simulation (LES) approach. It is first shown that this new version of ARPS is able to reproduce accurately all essential features of turbulent flow over homogeneous Canopies. A sensitivity study of the flow to the morphology of the canopy, i.e. the density and vertical leaf-area (LAI) distribution, is then performed numerically over three types of Canopies with five levels of leaf-area index, from 1 to 5. This study confirms the universal characteristics of turbulent flow over vegetation Canopies, as previously observed from wind-tunnel and in situ experiments. It shows that the typical features of canopy flow become more pronounced as canopy density increases, and quantifies the extent to which differences in canopy morphology can explain the experimental variability observed between Canopies. This variability in turbulent characteristics is mostly visible in the subcanopy space, and depends significantly on the density of the upper foliated layers. The mean longitudinal separation Lambda(w) between adjacent coherent structures has also been computed for each canopy using the wavelet transform and approximating the convection velocity of coherent structures as 1.8 times the average wind velocity at canopy top. Except for the sparsest Canopies, the analogy between the atmospheric flow near the top of a vegetation canopy and a plane mixing layer is well verified: Lambda(w) is directly related to the shear length scale L-s = U(h)/U'(h), where h is canopy height, U mean velocity and U' is the vertical gradient dU/dz, in a way close to the prediction Lambda(w)/h = 8.1L(s)/h: (C) 2008 Elsevier B.V. All rights reserved.
A. J. Hall - One of the best experts on this subject based on the ideXlab platform.
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Canopy nitrogen distribution and the photosynthetic performance of sunflower crops during grain filling — a quantitative analysis
Oecologia, 1995Co-Authors: D. J. Connor, V. O. Sadras, A. J. HallAbstract:Measurements of the profiles of leaf area and leaf nitrogen were made on five occasions from midflowering to maturity (53, 61, 70, 78 and 83 days after emergence, DAE) in sunflower crops grown at contrasting density (2.4 and 4.8 plants m^-2) and nitrogen supply (0 and 5 g N m^-2 at emergence) in the summer in Buenos Aires, Argentina. As the crops matured, nitrogen was withdrawn unequally from all leaf positions and leaves senesced from the bases of the Canopies. A model was used to estimate the daytime net photosynthesis (P_c) of Canopies of defined leaf area and nitrogen content under the observed conditions of temperature and irradiance. Comparisons were made between the observed profiles of leaf nitrogen and those that would maximise P_c (the optimal profiles). The observed nitrogen profiles were sub-optimal at mid-flowering, except in the low-density, low-nitrogen treatment. The differences were most marked in the high-nitrogen treatments which held ‘excessive’ nitrogen in their lower Canopies. As the Canopies matured and nitrogen was mobilised to the grain, leaf area index and total nitrogen content decreased and optimal profiles changed shape from exponential to linear. During this period observed profiles became more optimal. There was, however, little difference in P_c between observed and optimal profiles. The maximum difference was 3.2% observed in the low-density, high-nitrogen treatment at DAE 53. The comparison of actual and optimal profiles as leaf nitrogen content (mg N) in addition to the more commonly used specific leaf nitrogen (SLN, g N m^-2 leaf) explains this result because relatively large changes inSLN in the small leaves at the top of Canopies have little effect on P_c. The study shows that leaf nitrogen content is an appropriate basis for comparison of canopy nitrogen profiles in sunflower.
Joy Zedle - One of the best experts on this subject based on the ideXlab platform.
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relationships between canopy complexity and germination microsites for phalaris arundinacea l
Oecologia, 2002Co-Authors: Roberto Lindigcisneros, Joy ZedleAbstract:Microsites that prevent seed germination are critical for slowing the invasion of native plant communities by aggressive, clonal species. A suitable model for study is the clonal grass, Phalaris arundinacea, which reproduces prolifically from seed and is spreading into wetlands across temperate North America. Knowing that light conditions control its seed germination in the laboratory and that light varies with canopy complexity in a Wisconsin fen, we tested multiple attributes of microsites under spatially and temporally dynamic Canopies (namely, presence/absence of a matrix species, number of species in the canopy, plus indirect effects of three soil water levels) for their control of germination in microcosms. Our 6-species Canopies + the matrix of Glyceria striata had the densest cover and reduced P. arundinacea germination to 1.9%, compared to 7.3% for 1-species Canopies + the matrix. After selectively removing canopy components, germination increased to 36.1% for 6-species and 33.0% for 1-species Canopies. Comparing Canopies with each of the six species, germination declined in relation to increasing leaf width. Given moist soil, P. arundinacea germination microsites are determined by canopy complexity, which affects light penetration, which in turn determines germination rate.
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phalaris arundinacea seedling establishment effects of canopy complexity in fen mesocosm and restoration experiments
Botany, 2002Co-Authors: Roberto Lindigcisneros, Joy ZedleAbstract:Phalaris arundinacea L. (reed canary grass) is a major invader of wetlands in temperate North America; it creates monotypic stands and displaces native vegetation. In this study, the effect of plant Canopies on the establishment of P. arundinacea from seed in a fen, fen-like mesocosms, and a fen restoration site was assessed. In Wingra Fen, Canopies that were more resistant to P. arundinacea establishment had more species (eight or nine versus four to six species) and higher cover of Aster firmus. In mesocosms planted with Glyceria striata plus 1, 6, or 15 native species, all Canopies closed rapidly and prevented P. arundinacea establishment from seed, regardless of the density of the matrix species or the number of added species. Only after gaps were created in the canopy was P. arundinacea able to establish seedlings; then, the 15-species treatment reduced establishment to 48% of that for single-species Canopies. A similar experiment in the restoration site produced less cover of native plants, and P. a...
Marion Durand-gillmann - One of the best experts on this subject based on the ideXlab platform.
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Asymmetric competition increases leaf inclination effect on light absorption in mixed Canopies
Annals of Forest Science, 2013Co-Authors: Guillaume Simioni, Marion Durand-gillmannAbstract:• Context The effects of leaf inclination on plant light capture, growth, and water balance of monospecific Canopies are well documented, but we still lack information on such effects in the case of multispecific Canopies. • Aims We investigated the effects of leaf inclination on the absorption of photosynthetically active radiation (PAR) of a mixed forest. • Methods We ran a 3D mechanistic radiation transfer model for a Mediterranean forest where Pinus halepensis makes the upper strata while Quercus ilex occupies the lower strata. As factors, we included (1) the distributions of leaf inclinations that ranged from vertical to horizontal (including the actual inclinations), (2) the fraction of diffuse light, sun position, and leaf area index (LAI), and (3) the Pinus/Quercus LAI ratio. • Results Simulated PAR absorption was more than twice as sensitive to leaf inclination in oaks than in pines because oaks depended on PAR transmitted below the pine layer. The extent of the effect depended on season, fraction of diffuse light, LAI, and vegetation spatial structure. None of the observed inclinations maximized PAR absorption, suggesting a trade-off with water economy. • Conclusion Erroneous assumptions about leaf inclination lead to larger errors when modelling heterogeneous, mixed Canopies. This also highlights potential caveats when using models that do not account for the spatial structure of Canopies.
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Asymmetric competition increases leaf inclination effect on light absorption in mixed Canopies
Annals of Forest Science, 2013Co-Authors: Guillaume Simioni, Marion Durand-gillmann, Roland HucAbstract:The effects of leaf inclination on plant light capture, growth, and water balance of monospecific Canopies are well documented, but we still lack information on such effects in the case of multispecific Canopies. We investigated the effects of leaf inclination on the absorption of photosynthetically active radiation (PAR) of a mixed forest. We ran a 3D mechanistic radiation transfer model for a Mediterranean forest where Pinus halepensis makes the upper strata while Quercus ilex occupies the lower strata. As factors, we included (1) the distributions of leaf inclinations that ranged from vertical to horizontal (including the actual inclinations), (2) the fraction of diffuse light, sun position, and leaf area index (LAI), and (3) the Pinus/Quercus LAI ratio. Simulated PAR absorption was more than twice as sensitive to leaf inclination in oaks than in pines because oaks depended on PAR transmitted below the pine layer. The extent of the effect depended on season, fraction of diffuse light, LAI, and vegetation spatial structure. None of the observed inclinations maximized PAR absorption, suggesting a trade-off with water economy. Erroneous assumptions about leaf inclination lead to larger errors when modelling heterogeneous, mixed Canopies. This also highlights potential caveats when using models that do not account for the spatial structure of Canopies.