References of "Heinesch, Bernard"
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See detailNew Transfer Functions for Correcting Turbulent Water Vapour Fluxes
De Ligne, Anne ULg; Heinesch, Bernard ULg; Aubinet, Marc ULg

in Boundary-Layer Meteorology (2010), 137(2), 205-221

We address the problem of the high-frequency correction of water vapour fluxes measured by eddy covariance with a closed-path infrared gas analyser (IRGA). Different transfer functions are compared and ... [more ▼]

We address the problem of the high-frequency correction of water vapour fluxes measured by eddy covariance with a closed-path infrared gas analyser (IRGA). Different transfer functions are compared and evaluated at a forested (Vielsalm, Belgium) and an agricultural (Lonz,e, Belgium) site. Classical functions, usually applied to correct CO2 fluxes (Gaussian, Lorentzian), are found to be unsuited to water vapour cospectral corrections, being characterised by too sharp a decrease at high frequency. Two other functions characterised by a lower decreasing slope are found to better fit experimental transfer functions. They were calibrated and validated on experimental transfer functions and their dependency on air humidity is parameterised. On this basis, new correction coefficients are estimated. The coefficients are found to be larger than those based on the classical functions, even when the dependency of the latter on air humidity is taken into account. The difference amounts to 10 at the forested site and to 5 larger at the crop site. The study highlights the necessity of characterising the water transfer function shape and taking it into account in the correction factor at each site equipped with a closed path IRGA. [less ▲]

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See detailSpecies effect on the water use efficiency of a mixed forest of beech (Fagus sylvatica L.), Douglas fir (Pseudotsuga menziesii (Mirb.) Franco) and silver fir (Abies alba Mill.) in Belgium Ardennes
Soubie, Rémy; Heinesch, Bernard ULg; Aubinet, Marc ULg et al

Poster (2010)

Induced by climate change, intensity and frequency of droughts should be more important for the next century. How does water availability affect the physiology of woody plants at the species and stand ... [more ▼]

Induced by climate change, intensity and frequency of droughts should be more important for the next century. How does water availability affect the physiology of woody plants at the species and stand scale? Carbon and water vapour fluxes measurements of a mixed forest (deciduous and coniferous) were performed for over ten years by the eddy covariance method in Belgian Ardennes (Aubinet et al, 2001) as a part of the CarboEurope project. Whereas carbon fluxes have been analyzed in detailed and good estimations of the Net Ecosystem Exchange (NEE) and Gross Primary Production (GPP) were obtained, a thorough analysis of water vapour fluxes remains to be done. Improving analysis of water vapour fluxes and monitoring species transpiration will contribute to the estimation of the water use efficiency, WUE, at both the species and stand scale. The WUE well characterizes the vegetation productivity and ecosystem response to environmental factors. It also allows evaluating the sensitivity of temperate woody species to drought. The species concerned are beech (Fagus sylvatica L.), Douglas fir (Pseudotsuga menziesii (Mirb.) Franco) and silver fir (Abies alba Mill.). Since summer 2009 we monitor and analyze each species water use by measuring sap flow with the thermal dissipation method (Granier, 1987). Results at the species level will then be upscaled and compared to stand water vapour fluxes measurements obtained by the eddy covariance methodology. Transpiration of each species will be analyzed in relation with their own phenological and ecophysiological attributes, ecosystem soil and atmospheric conditions, to clarify among others their behaviour in case of water deficit. Data are actually analysed, the presented results will concern the 2009, and a part of 2010 growing season. [less ▲]

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See detailComparison of two drainage flow situations on a gentle forested slope
Heinesch, Bernard ULg; Yernaux, Michel ULg; Aubinet, Marc ULg

Poster (2010)

Drainage flows generated on a gentle slope in stable conditions were analysed at the forested site of Vielsalm (Belgium). Two distinct situations were encountered, one corresponding to vertical ... [more ▼]

Drainage flows generated on a gentle slope in stable conditions were analysed at the forested site of Vielsalm (Belgium). Two distinct situations were encountered, one corresponding to vertical convergence, characterised by a negative vertical velocity at the canopy top, the other corresponding to an equilibrium situation without any vertical movement. The causes of these two distinct flow patterns were analysed. Moreover, combined measurements of vertical velocity above the canopy and horizontal velocity divergence below the canopy were found to comply with the continuity equation: an acceleration of the horizontal flow was indeed observed in the trunk-space in convergence situations while not in equilibrium conditions. These measurements combined with those of the horizontal [CO2] gradient below the canopy were found to met the dilution hypothesis suggested by Aubinet et al.(2003): the horizontal [CO2] gradient was negative in convergence situations while slightly positive in equilibrium conditions. The existence of such patterns allows us to confirm the coherence of advection observations made at the site and help to better understand the mechanisms responsible of night flux exchanges at work in stable conditions in complex terrains. Nevertheless, difficulties were met when trying to obtain reliable estimates of the advection transport terms. The estimation of the vertical velocity in the trunk-space obtained by using the divergence measurements refuted the hypothesis of linearity of the vertical profile of vertical velocity, assumption usually used when computing vertical advection. This problem resulted in a great uncertainty on vertical advection which did not allowed to improve the night-flux estimation by adding advection terms to the turbulent flux and the storage. [less ▲]

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See detailClimate control of terrestrial carbon exchange across biomes and continents
Yi, Chuixiang; Ricciuto, Daniel; Li, Runze et al

in Environmental Research Letters (2010), 5(3),

Understanding the relationships between climate and carbon exchange by terrestrial ecosystems is critical to predict future levels of atmospheric carbon dioxide because of the potential accelerating ... [more ▼]

Understanding the relationships between climate and carbon exchange by terrestrial ecosystems is critical to predict future levels of atmospheric carbon dioxide because of the potential accelerating effects of positive climate-carbon cycle feedbacks. However, directly observed relationships between climate and terrestrial CO2 exchange with the atmosphere across biomes and continents are lacking. Here we present data describing the relationships between net ecosystem exchange of carbon (NEE) and climate factors as measured using the eddy covariance method at 125 unique sites in various ecosystems over six continents with a total of 559 site-years. We find that NEE observed at eddy covariance sites is (1) a strong function of mean annual temperature at mid-and high-latitudes, (2) a strong function of dryness at mid-and low-latitudes, and (3) a function of both temperature and dryness around the mid-latitudinal belt (45 degrees N). The sensitivity of NEE to mean annual temperature breaks down at similar to 16 degrees C (a threshold value of mean annual temperature), above which no further increase of CO2 uptake with temperature was observed and dryness influence overrules temperature influence. [less ▲]

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See detailHistory effect of light and temperature on monoterpenoid emissions from Fagus sylvatica L.
Demarcke, M.; Schoon, N.; Van Langenhove, H. et al

in Atmospheric Environment (2010), 44(27), 3261-3268

Monoterpenoid emissions from Fagus sylvatica L trees have been measured at light- and temperature-controlled conditions in a growth chamber, using Proton Transfer Reaction Mass Spectrometry (PTR-MS) and ... [more ▼]

Monoterpenoid emissions from Fagus sylvatica L trees have been measured at light- and temperature-controlled conditions in a growth chamber, using Proton Transfer Reaction Mass Spectrometry (PTR-MS) and the dynamic branch enclosure technique. De novo synthesized monoterpenoid Standard Emission Factors, obtained by applying the G97 algorithm (Guenther, 1997), varied between 2 and 32 mu g g(-1)DW h(-1) and showed a strong decline in late August and September, probably due to senescence. The response of monoterpenoid emissions to temperature variations at a constant daily light pattern could be well reproduced with a modified version of the MEGAN algorithm (Guenther et al., 2006), with a typical dependence on the average temperature over the past five days. The diurnal emissions at constant temperature showed a typical hysteretic behaviour, which could also be adequately described with the modified MEGAN algorithm by taking into account a dependence on the average light levels experienced by the trees during the past 10-13 h. The impact of the past light and temperature conditions on the monoterpenoid emissions from E sylvatica L was found to be much stronger than assumed in previous algorithms. Since our experiments were conducted under low light intensity, future studies should aim at confirming and completing the proposed algorithm updates in sunny conditions and natural environments. (C) 2010 Elsevier Ltd. All rights reserved. [less ▲]

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See detailANNUAL SCIENTIFIC REPORT PHASE II "Impact of Phenology and Environmental Conditions on BVOC Emissions from Forest Ecosystems" "IMPECVOC"
Dewulf, Jo; Joó, Eva; Steppe, Kathy et al

Report (2009)

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See detailEvaluation of the suitability of the land surface model JULES for climate impact studies in Belgian ecosystem
Van Den Hoof, Catherine; Aubinet, Marc ULg; Heinesch, Bernard ULg et al

Conference (2009, October)

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See detailMeasuring air-ice CO2 fluxes in the Arctic
Heinesch, Bernard ULg; Yernaux, Michel; Aubinet, Marc ULg et al

in FluxLetter: the Newsletter of FLUXNET (2009), 2(2), 9-10

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See detailMesures de flux dans le grand Nord
Heinesch, Bernard ULg; Yernaux, Michel

in FACtuel (2009), 7

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See detailCO2 fluxes exchanged by a 4-year crop rotation cycle
Aubinet, Marc ULg; Moureaux, Christine ULg; Bodson, Bernard ULg et al

Poster (2009, April)

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See detailSurvey of air-ice ocean carbon dioxyde exchange over arctic sea-ice
Heinesch, Bernard ULg; Aubinet, Marc ULg; Carnat, Gauthier et al

Conference (2009)

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See detailExceptional Carbon Uptake In European Forests During The Warm Spring Of 2007: A Data-Model Analysis
Delpierre, N.; Soudani, K.; Kostner, B. et al

in Global Change Biology (2009), 15(6), 1455-1474

Temperate and boreal forests undergo drastic functional changes in the springtime, shifting within a few weeks from net carbon (C) sources to net C sinks. Most of these changes are mediated by temperature ... [more ▼]

Temperate and boreal forests undergo drastic functional changes in the springtime, shifting within a few weeks from net carbon (C) sources to net C sinks. Most of these changes are mediated by temperature. The autumn 2006-winter 2007 record warm period was followed by an exceptionally warm spring in Europe, making spring 2007 a good candidate for advances in the onset of the photosynthetically active period. An analysis of a decade of eddy covariance data from six European forests stands, which encompass a wide range of functional types (broadleaf evergreen, broadleaf deciduous, needleleaf evergreen) and a wide latitudinal band (from 44 degrees to 62 degrees N), revealed exceptional fluxes during spring 2007. Gross primary productivity (GPP) of spring 2007 was the maximum recorded in the decade examined for all sites but a Mediterranean evergreen forest (with a +40 to +130 gC m(-2) anomaly compared with the decadal mean over the January-May period). Total ecosystem respiration (TER) was also promoted during spring 2007, though less anomalous than GPP (with a +17 to +93 gC m(-2) anomaly over 5 months), leading to higher net uptake than the long-term mean at all sites (+12 to +79 gC m(-2) anomaly over 5 months). A correlative analysis relating springtime C fluxes to simple phenological indices suggested spring C uptake and temperatures to be related. The CASTANEA process-based model was used to disentangle the seasonality of climatic drivers (incoming radiation, air and soil temperatures) and biological drivers (canopy dynamics, thermal acclimation of photosynthesis to low temperatures) on spring C fluxes along the latitudinal gradient. A sensitivity analysis of model simulations evidenced the roles of (i) an exceptional early budburst combined with elevated air temperature in deciduous sites, and (ii) an early relief of winter thermal acclimation in coniferous sites for the promotion of 2007 spring assimilation. [less ▲]

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See detailCarbon sequestration by a crop during a four year rotational cycle
Aubinet, Marc ULg; Moureaux, Christine ULg; Bodson, Bernard ULg et al

in Agricultural and Forest Meteorology (2009), 149

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See detailVOC and ozone fluxes from a pine forest in the north of Belgium
Eerdekens, Guenther; Gielen, Bart; Neirynck, J. et al

Poster (2009)

Plants release large amounts of carbon as Volatile Organic Compounds (VOCs) into the atmosphere. These VOCs play an important role in the chemistry of the troposphere as they can be involved in the ... [more ▼]

Plants release large amounts of carbon as Volatile Organic Compounds (VOCs) into the atmosphere. These VOCs play an important role in the chemistry of the troposphere as they can be involved in the mechanisms of ozone and aerosol formation. The key mechanisms underneath biogenic VOC emissions are still not well understood, leading to large uncertainties in BVOC inventories on global and regional scales. Measurements of VOCs, ozone and micro-meteorology are conducted at the ‘De inslag’, a 80-year old mixed pine–oak forest located in the Campine region near Antwerp, Belgium. The forest site is a level-II plot of the European Programme of Intensive Monitoring Forest Ecosystems and is part of the Carboeuro and Nitroeurope-flux research network. The site is equipped with a flux tower that reaches above the 23m canopy. A Proton Transfer Reaction Mass Spectrometer and a Fast Ozone analyser allow determining VOC and ozone fluxes by Eddy Covariance. An analytic footprint model is used to exclude non-forest fluxes. In this study, we will test the accuracy of this footprint model with anthropogenic tracers (benzene and toluene). [less ▲]

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See detailAn analysis of the random error affecting CO2 fluxes measured by eddy covariance
Laffineur, Quentin ULg; Heinesch, Bernard ULg; Aubinet, Marc ULg

Poster (2009)

This study focuses on random errors associated with eddy covariance flux measurements. This error is heteroscedastic, increases linearly with the flux magnitude and the error on CO2 flux decreases with ... [more ▼]

This study focuses on random errors associated with eddy covariance flux measurements. This error is heteroscedastic, increases linearly with the flux magnitude and the error on CO2 flux decreases with increasing wind speed. As random errors accumulate in quadrature, they are less critical than systematic errors as far as flux sums are concerned. On the other hand it may affect significantly half-hour data and pose problem for modelling or analysis of flux response to environmental parameters. It is therefore useful to characterize the site and the specific conditions under which the random error is the most important. The random error on CO2 flux was computed at two sites, one cropland and one forested site, by using the daily differencing approach (DDA, Hollinger and Richardson 2005). Relationships with flux and wind speed were compared between different periods (day vs. night, growing season vs. rest of the year) and for different flux computation methods. First, an increase of random error with decreasing wind speed was observed at low speed. This effect was not observed during the rest period at the cropland site and disappears when a high-pass filtering is applied to the data. It may be explained by two processes: on one hand, the below canopy air layer is less efficiently mixed which can create large flux variations when CO2 sources and sinks are separated. On the other hand, mesoscale motions may exceed small-scale turbulence at low wind speed. At similar wind speeds, the random error was lower at the cropland than at the forested site, which can be due to either process: indeed, at the cropland site, the distance between CO2 sources and sinks is smaller which reduce the low mixing effect but the site is also more flat and homogeneous which reduce the impact of mesoscale movements. The possibility of mesoscale movement impact is supported by the fact that the effect disappears when applying a high pass filtering. The random error was also found sensitive to the computational method: in particular it is larger when the flux is computed using the block average rather than the running mean, it increases when storage is taken into account and decreases when data are filtered by applying stationarity screening or u* filtering. [less ▲]

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See detailAn analysis of the random error affecting CO2 fluxes measured by eddy covariance.
Laffineur, Quentin ULg; Heinesch, Bernard ULg; Aubinet, Marc ULg

Poster (2009)

This study focuses on random errors associated with eddy covariance flux measurements. This error is heteroscedastic, increases linearly with the flux magnitude and the error on CO2 flux decreases with ... [more ▼]

This study focuses on random errors associated with eddy covariance flux measurements. This error is heteroscedastic, increases linearly with the flux magnitude and the error on CO2 flux decreases with increasing wind speed. As random errors accumulate in quadrature, they are less critical than systematic errors as far as flux sums are concerned. On the other hand it may affect significantly half-hour data and pose problem for modelling or analysis of flux response to environmental parameters. It is therefore useful to characterize the site and the specific conditions under which the random error is the most important. The random error on CO2 flux was computed at two sites, one cropland and one forested site, by using the daily differencing approach (DDA, Hollinger and Richardson 2005). Relationships with flux and wind speed were compared between different periods (day vs. night, growing season vs. rest of the year) and for different flux computation methods. First, an increase of random error with decreasing wind speed was observed at low speed. This effect was not observed during the rest period at the cropland site and disappears when a high-pass filtering is applied to the data. It may be explained by two processes: on one hand, the below canopy air layer is less efficiently mixed which can create large flux variations when CO2 sources and sinks are separated. On the other hand, mesoscale motions may exceed small-scale turbulence at low wind speed. At similar wind speeds, the random error was lower at the cropland than at the forested site, which can be due to either process: indeed, at the cropland site, the distance between CO2 sources and sinks is smaller which reduce the low mixing effect but the site is also more flat and homogeneous which reduce the impact of mesoscale movements. The possibility of mesoscale movement impact is supported by the fact that the effect disappears when applying a high pass filtering. The random error was also found sensitive to the computational method: in particular it is larger when the flux is computed using the block average rather than the running mean, it increases when storage is taken into account and decreases when data are filtered by applying stationarity screening or u* filtering. [less ▲]

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See detailFINAL REPORT PHASE I "Impact of Phenology and Environmental Conditions on BVOC Emissions from Forest Ecosystems” «IMPECVOC»
Steppe, Kathy; Šimpraga, Maja; Verbeeck, Hans et al

Report (2008)

Detailed reference viewed: 27 (5 ULg)