References of "Heinesch, Bernard"
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See detailCarbon balance of an intensively grazed grassland in southern Belgium
Gourlez de la Motte, Louis ULg; Jérôme, Elisabeth; Mamadou, Ossénatou et al

in Agricultural and Forest Meteorology (2016), 228-229

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See detailDisentangling soil from plant methanol exchanges in a maize field: a first step
Bachy, Aurélie ULg; Mozaffar, Ahsan ULg; Aubinet, Marc ULg et al

Poster (2016, June)

This poster presents the current research done in order to disentangle soil from plant methanol exchanges in a maize field. Methanol exchanges were calculated at ecosystem-scale (therefore including both ... [more ▼]

This poster presents the current research done in order to disentangle soil from plant methanol exchanges in a maize field. Methanol exchanges were calculated at ecosystem-scale (therefore including both components). It bases on the following observation: methanol exchanges on bare soil (measured when maize was at germination stage) were as important as when plants were fast growing (and thereby, when the highest methanol plant methanol emissions were expected), and this under similar weather conditions. The goal of this poster is thus to understand why emissions were similar at these two periods. First, it addresses the question of the actual contribution of maize plants in methanol exchanges, by comparing up-scaled methanol exchanges measured on maize at leaf-scale (Mozaffar A.) to those measured at ecosystem-scale. Then, it investigates methanol exchanges mechanisms in order to evaluate how did soil methanol emissions evolve along the maize growing season. At the end of this poster, the hypothesis of decreasing soil methanol emissions along the maize growing season is proposed. [less ▲]

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See detailVingt ans de mesures des échanges de CO2 et de vapeur d'eau à l'Observatoire Terrestre de Vielsalm
Aubinet, Marc ULg; Vincke, Caroline; Heinesch, Bernard ULg et al

Article for general public (2016)

La séquestration du carbone via l'assimilation nette de CO2 par les écosystèmes terrestres varie fortement d'une année à l'autre. La compréhension plus fine de ce phénomène est nécessaire pour pouvoir ... [more ▼]

La séquestration du carbone via l'assimilation nette de CO2 par les écosystèmes terrestres varie fortement d'une année à l'autre. La compréhension plus fine de ce phénomène est nécessaire pour pouvoir prédire si les écosystèmes continueront à se comporter comme des puits de carbone ou si la séquestration va diminuer voire s'inverser complètement, transformant les écosystèmes en source de carbone. Pour mesurer les échanges nets de CO2, des chercheurs ont installé un "Observatoire Terrestre" dans une forêt à Vielsalm qui a permis de mettre en évidence les dynamiques journalière, saisonnière et interannuelle de la séquestration en carbone. La mesure simultanée de l'évapotranspiration réelle permet de plus d'évaluer la consommation en eau des espèces présentes. Les mesures effectuées durant 20 ans montrent que la forêt se comporte comme un puits de carbone. [less ▲]

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See detailAre BVOC exchanges in agricultural ecosystems overestimated? Insights from fluxes measured in a maize field over a whole growing season
Bachy, Aurélie ULg; Aubinet, Marc ULg; Schoon, Niels et al

in Atmospheric Chemistry and Physics (2016), 16(8),

Although maize is the second most important crop worldwide, and the most important C4 crop, no study on biogenic volatile organic compounds (BVOCs) has yet been conducted on this crop at ecosystem scale ... [more ▼]

Although maize is the second most important crop worldwide, and the most important C4 crop, no study on biogenic volatile organic compounds (BVOCs) has yet been conducted on this crop at ecosystem scale and over a whole growing season. This has led to large uncertainties in cropland BVOC emission estimations. This paper seeks to fill this gap by presenting, for the first time, BVOC fluxes measured in a maize field at ecosystem scale (using the disjunct eddy covariance by mass scanning technique) over a whole growing season in Belgium. The maize field emitted mainly methanol, although exchanges were bi-directional. The second most exchanged compound was acetic acid, which was taken up mainly in the growing season. Bi-directional exchanges of acetaldehyde, acetone and other oxygenated VOCs also occurred, whereas the terpenes, benzene and toluene exchanges were small, albeit significant. Surprisingly, BVOC exchanges were of the same order of magnitude on bare soil and on well developed vegetation, suggesting that soil is a major BVOC reservoir in agricultural ecosystems. Quantitatively, the maize BVOC emissions observed were lower than those reported in other maize, crops and grasses studies. The standard emission factors (SEFs) estimated in this study (231 ± 19 µg m−2 h−1 for methanol, 8 ± 5 µg m−2 h−1 for isoprene and 4 ± 6 µg m−2 h−1 for monoterpenes) were also much lower than those currently used by models for C4 crops, particularly for terpenes. These results suggest that maize fields are small BVOC exchangers in north-western Europe, with a lower BVOC emission impact than that modelled for growing C4 crops in this part of the world. They also reveal the high variability in BVOC exchanges across world regions for maize and suggest that SEFs should be estimated for each region separately. [less ▲]

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See detailImpact of tillage on CO2 and N2O efflux in an agricultural crop
Lognoul, Margaux ULg; Theodorakopoulos, Nicolas ULg; Hiel, Marie-Pierre ULg et al

Poster (2016, April 20)

CO2 and N2O fluxes exchanged by a maize crop were measured from June to Octboer 2015 using a homemade automated system of dynamic closed chambers. We studied the impact of tillage (reduced and ... [more ▼]

CO2 and N2O fluxes exchanged by a maize crop were measured from June to Octboer 2015 using a homemade automated system of dynamic closed chambers. We studied the impact of tillage (reduced and conventional) on greenhouse gas emissions and nitrous oxide flux dynamics. [less ▲]

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See detailAre BVOC exchanges in agricultural ecosystems overestimated? Insights from fluxes measured in a maize field over a whole growing season
Bachy, Aurélie ULg; Aubinet, Marc ULg; Schoon, Niels et al

Conference (2016, April 18)

This oral communication aims to present the main outputs of the BVOC (Biogenic Volatile Organic Compounds) flux measurement campaign performed on a maize field in Belgium. It begins by highligthing the ... [more ▼]

This oral communication aims to present the main outputs of the BVOC (Biogenic Volatile Organic Compounds) flux measurement campaign performed on a maize field in Belgium. It begins by highligthing the interest of investigating BVOC exchanges on maize; then measurement techniques are briefly presented. The second half of the communication aims to present and discuss the main outputs of this measurement campaign (similar BVOC composition, lower exchange rate than other maize and cropland/grassland studies, significant importance of soil in ecosystem exchanges, strong differences between exchanges rates observed in this study and those used by up-scaling models). [less ▲]

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See detailCanopy proximity estimation and impact on long term turbulent fluxes above a heterogeneous forest
Hurdebise, Quentin ULg; Vincke, Caroline; De Ligne, Anne ULg et al

Poster (2016, April 18)

With the development of eddy covariance networks like Fluxnet, ICOS or NEON, long-term data series of carbon dioxide, water vapor and other gas exchanges between terrestrial ecosystems and atmosphere will ... [more ▼]

With the development of eddy covariance networks like Fluxnet, ICOS or NEON, long-term data series of carbon dioxide, water vapor and other gas exchanges between terrestrial ecosystems and atmosphere will become more and more numerous. However, long-term analyses of such exchanges require a good understanding of measurement conditions during the investigated period. Independently of climate drivers, measurements may indeed be influenced by measurement conditions themselves subjected to long-term variability due to vegetation growth or set-up changes. The present research refers to the Vielsalm Terrestrial Observatory (VTO) where fluxes of momentum, carbon dioxide, latent and sensible heat have been continuously measured by eddy covariance during twenty years. VTO is an ICOS site installed in a mixed forest (beech, silver fir, Douglas fir, Norway spruce) in the Belgian Ardennes. A multidisciplinary approach was developed in order to investigate the spatial and temporal evolution of several site characteristics: - displacement height (d) and relative measurement height (z-d) were determined using a spectral approach that compared observed and theoretical cospectra; - turbulence statistics were analyzed in the context of Monin-Obukhov similarity theory; - tree height during the measurement period was obtained by combining tree height inventories, a LIDAR survey and tree growth models; - measurement footprint was determined by using a footprint model. A good agreement was found between the three first approaches. Results show notably that z-d was subjected to both temporal and spatial evolution. Temporal evolution resulted from continuous tree growth as well as from a tower raise, achieved in 2009. Spatial evolution, due to canopy heterogeneity, was also observed. The impacts of these changes on measurements are investigated. In particular, it was shown that they affect measurement footprint, flux spectral corrections and flux quality. All these effects must be taken into consideration in order to disentangle long-term flux evolutions due to climate or phenology from changes resulting from measurement set-up changes. [less ▲]

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See detailImpact of tillage on N2O and CO2 efflux in an agricultural crop
Lognoul, Margaux ULg; Theodorakopoulos, Nicolas ULg; Hiel, Marie-Pierre ULg et al

Poster (2016, April)

In an experiment conducted in the Belgian loess belt between June and October 2015, the effect of two tillage treatments (CT - conventional tillage and RT - reduced tillage) on CO2 and N2O fluxes ... [more ▼]

In an experiment conducted in the Belgian loess belt between June and October 2015, the effect of two tillage treatments (CT - conventional tillage and RT - reduced tillage) on CO2 and N2O fluxes exchanged by a maize crop were compared. Fluxes were measured using two fully automated sets of dynamic closed chambers, allowing a 4.5h temporal resolution. Soil water content and temperature were also monitored as well as pH, total N (TN) and total organic C (TOC) content. [less ▲]

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See detailAnnual dynamics of pCO2 within bulk sea ice and related CO2 fluxes at Cape Evans (Antarctica)
Van Der Linden, Fanny ULg; Champenois, Willy ULg; Heinesch, Bernard ULg et al

Poster (2016, February 26)

Sea ice is a biome actively participating in the regional cycling of CO2 as both a source and a sink at different times of the year. In the frame of the YROSIAE project (Year-Round Ocean-Sea-Ice ... [more ▼]

Sea ice is a biome actively participating in the regional cycling of CO2 as both a source and a sink at different times of the year. In the frame of the YROSIAE project (Year-Round Ocean-Sea-Ice-Atmosphere Exchanges), annual dynamics of sea ice pCO2 was compared with CO2 fluxes measured by automated accumulation chambers at Cape Evans (Ross Island, Antarctica). Results confirmed a general trend of brine pCO2 supersaturation with respect to the atmosphere during the late winter (concentration of dissolved inorganic carbon - DIC - in brine and brine expulsion in the brine skim) leading to CO2 degassing, and undersaturation during the spring (carbon-uptake by autotrophs and brine dilution) leading to atmospheric CO2 uptake. Despite high primary production at the bottom of the ice in spring, DIC profiles suggest that sea ice as a whole appears to be net heterotrophic. Still, sea ice absorbs CO2 from the atmosphere, as a result of physical processes. Some variability in the CO2 fluxes (both in magnitude and sign) could not be explained by variability in sea ice pCO2 but rather seemed driven by variability in atmospheric conditions and sea ice surface properties. For instance, in late spring, CO2 fluxes showed a diurnal variability (from CO2 degassing to uptake) related to atmospheric temperature variations. Large and episodic CO2 fluxes were systematically positively correlated with strong wind events, and large CO2 degassing was observed over thin, wet and salty snow cover. [less ▲]

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See detailAnnual dynamics of pCO2 within bulk sea ice and related CO2 fluxes at Cape Evans (Antarctica)
Van Der Linden, Fanny ULg; Champenois, Willy ULg; Heinesch, Bernard ULg et al

Poster (2016, February 12)

Sea ice is a biome actively participating in the regional cycling of CO2 as both a source and a sink at different times of the year. In the frame of the YROSIAE project (Year-Round Ocean-Sea-Ice ... [more ▼]

Sea ice is a biome actively participating in the regional cycling of CO2 as both a source and a sink at different times of the year. In the frame of the YROSIAE project (Year-Round Ocean-Sea-Ice-Atmosphere Exchanges), annual dynamics of sea ice pCO2 was compared with CO2 fluxes measured by automated accumulation chambers at Cape Evans (Ross Island, Antarctica). Results confirmed a general trend of brine pCO2 supersaturation with respect to the atmosphere during the late winter (concentration of dissolved inorganic carbon - DIC - in brine and brine expulsion in the brine skim) leading to CO2 degassing, and undersaturation during the spring (carbon-uptake by autotrophs and brine dilution) leading to atmospheric CO2 uptake. Despite high primary production at the bottom of the ice in spring, DIC profiles suggest that sea ice as a whole appears to be net heterotrophic. Still, sea ice absorbs CO2 from the atmosphere, as a result of physical processes. Some variability in the CO2 fluxes (both in magnitude and sign) could not be explained by variability in sea ice pCO2 but rather seemed driven by variability in atmospheric conditions and sea ice surface properties. For instance, in late spring, CO2 fluxes showed a diurnal variability (from CO2 degassing to uptake) related to atmospheric temperature variations. Large and episodic CO2 fluxes were systematically positively correlated with strong wind events, and large CO2 degassing was observed over thin, wet and salty snow cover. [less ▲]

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See detailLINKING CATTLE GRAZING BEHAVIOR TO METHANE AND CARBON DIOXIDE DYNAMICS
Blaise, Yannick ULg; Lebeau, Frédéric ULg; Andriamandroso, Andriamasinoro ULg et al

in Communications in Agricultural and Applied Biological Sciences (2016, February), 81(1), 107-112

Various methods are presently used to measure methane (CH4) emissions of ruminants on pasture. Those measurements are essential to evaluate nutritional strategies to mitigate enteric CH4 emissions as well ... [more ▼]

Various methods are presently used to measure methane (CH4) emissions of ruminants on pasture. Those measurements are essential to evaluate nutritional strategies to mitigate enteric CH4 emissions as well as addressing the selection of low producing individuals. On pasture and in the barn, variations in CH4 emissions are observed depending on the time of the day. However, no studies have been made to link these diurnal fluctuations to behavioural phases, especially on pasture. The aim of this study was to understand the individual dynamics of CH4 production and their links to the grazing behaviour. For this purpose, a new tool was specifically developed. Five red-pied dry cows were equipped with infrared CH4 and carbon dioxide (CO2) sensors measuring concentrations in the exhaled air at 4 Hz. The animals were equipped with a heart rate belt (HR) and motion sensors to detect their feeding behaviours (grazing vs. rumination) for periods of 8 h/d. Wind speed (WS) was also monitor to verify interference with sampled gas concentrations. Results showed that using the CH4:CO2 ratio reduced the interference with WS that was observed on raw CH4 and CO2 concentration signals. CH4:CO2 ratio average over 5 min periods indicated that CH4 emissions were lower during grazing than rumination (P<0.01). The eructation frequency during grazing (0.48 eructation/min, P<0.01) was also lower than during rumination (0.65 eructation/min). HR was higher during grazing that rumination. Because HR is usually linked to metabolic CO2 production intensity, hence influencing the denominator of the CH4:CO2 ratio, further investigation should focus on the quantification of changes in fermentative and metabolic CO2 emissions along the day to estimate total CH4 production more accurately and the relationship between CH4 emissions patterns and post-feeding times. [less ▲]

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See detailOUTDOOR MEASUREMENT OF CATTLE METHANE EMISSIONS USING THE EDDY-COVARIANCE TECHNIQUE IN COMBINATION WITH GEOLOCALIZATION DEVICES
Dumortier, Pierre ULg; Andriamandroso, Andriamasinoro ULg; Aubinet, Marc ULg et al

Poster (2016, February)

Methane emissions account for 8% of the EU-15 GHG emissions and livestock generates approximately half of these emissions [1]. In order to improve emissions reporting and properly test mitigation options ... [more ▼]

Methane emissions account for 8% of the EU-15 GHG emissions and livestock generates approximately half of these emissions [1]. In order to improve emissions reporting and properly test mitigation options, techniques for measuring methane emissions from cattle must be developed and adapted to each management system. Among available micrometeorological methods, the use of eddy-covariance is still in its infancy [2] and its relevance and robustness for cattle flux estimation has still to be proved. On one hand, it is well adapted to seasonal grazing systems, is non-invasive, needs little animal handling and allows detection of daily emission patterns. On the other hand, it has the drawback of requiring cattle geo-localization and long periods of measurements (typically one month). In this study, we combined measured CH4 fluxes with a footprint model [3] and cattle positions (GPS devices) over several one-month campaigns at key periods in the grazing season in order to obtain CH4 emissions per cow at herd scale. Accelerometers were also added to the system for behaviour detection, opening the possibility of linking emissions to feeding behaviour. Measurements were performed and are still ongoing at the Dorinne Terrestrial Observatory in 2014/2015. The first campaign provided a mean emission per cow of 65±6 kg CH4.LSU-1.year-1. Cattle emission pattern was tightly linked with behaviour pattern, emissions being higher during and shortly after grazing (i.e. at dawn and dusk). Uncertainties linked to the method will be discussed and quantified (footprint model validity, geo-localization precision, eddy covariance corrections and filtering specificities linked to CH4 measurements). Compilation of data from multiple campaigns will allow quantification of the effects of forage quality, animal weight and lactating state on emissions per cow. [less ▲]

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See detailHigh rate monitoring CH4 production dynamics and their link with behavioral phases in cattle
Blaise, Yannick ULg; Lebeau, Frédéric ULg; Andriamandroso, Andriamasinoro ULg et al

in EAAP – 67 th Annual Meeting, Belfast 2016 (2016)

Microbial fermentation in the rumen produces methane (CH4) which is a loss of energy for ruminants and also contributes to global warming. While the respiration chamber is the standard reference for CH4 ... [more ▼]

Microbial fermentation in the rumen produces methane (CH4) which is a loss of energy for ruminants and also contributes to global warming. While the respiration chamber is the standard reference for CH4 emissions quantification, daily CH4 production dynamics can be measured only by steps of 30 min and measurements on pasture are impossible. The alternative method using SF6 as tracer gas can be applied for grazing animals but provides average CH4 production values over at least several hours, making it impossible to measure short term dynamics of rumen CH4 production with changing animal behavior along the day. Newly developed methods using CO2 as internal tracer gas extrapolate CH4 emissions from few short measurements. However, both CO2 and CH4 emissions fluctuate during the day depending on the behavior and the post-feeding times questioning the validity of this method. Therefore, an innovative device was developed to monitor at a high rate CH4 and CO2 emission dynamics in order to investigate the link between CH4 dynamics and the animal behavior on pasture. Preliminary results showed the ability of the device to record differences in CH4:CO2 ratios and eructation frequencies according to the individual and the behavior. Results from complementary experiments in barn with animals fed contrasting diets regarding CH4 production (with and without linseed) and on pasture with different forage allowance will be presented in order to highlight how post-feeding time and grazing behavior impact CO2 and CH4 emission dynamics along the day. [less ▲]

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See detailUnexpected sensitivity of the annual net ecosystem exchange to the high frequency loss corrections in a grazed grassland site in Belgium
Mamadou, Ossénatou ULg; Gourlez de la Motte, Louis ULg; De Ligne, Anne ULg et al

Poster (2016)

The eddy covariance technique is widely used to measure CO2 and other gas fluxes. However, eddy covariance fluxes are affected by systematic errors that must be corrected. Among them, high frequency loss ... [more ▼]

The eddy covariance technique is widely used to measure CO2 and other gas fluxes. However, eddy covariance fluxes are affected by systematic errors that must be corrected. Among them, high frequency loss corrections are particularly important in this regard, especially when using a closed-path infrared gas analyzer. In this study, we compared three approaches to do these corrections for CO2 fluxes and evaluated their impact on the carbon balance an intensively grazed grassland site in Belgium . In the first approach, the computation of correction factors was based on the measured sensible heat cospectra (‘local’ cospectra), whereas the other two were based on theoretical models (Kaimal et al., 1972). The correction approaches were validated by comparing the nighttime eddy covariance CO2 fluxes corrected with each approach and in situ soil respiration measurements. We found that the local cospectra differed from the Kaimal theoretical shape, although the site could not be considered ‘difficult’ (i.e., fairly flat, homogeneous, low vegetation, sufficient measurement height), appearing less peaked in the inertial subrange. This difference greatly affected the correction factor, especially for night fluxes. Night fluxes measured by eddy covariance were found to be in good accord with in situ soil respiration measurements when corrected with local cospectra and to be overestimated when corrected with Kaimal cospectra. As the difference between correction factors was larger in stable than unstable conditions, this acts as a selective systematic error and has an important impact on annual fluxes. On the basis of a 4-year average, at DTO the errors reach 71-150 g C m-2 y-1 for net ecosystem exchange (NEE), 280-562 g C m-2 y-1 for total ecosystem respiration (TER) and 209-412 g C m-2 y-1 for gross primary productivity (GPP), depending on the approach used. We finally encourage site PIs to check the cospectrum shape at their sites and, if necessary, compute frequency correction factors on the basis of local cospectra rather than on Kaimal cospectra. [less ▲]

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See detailCarbon balance of an intensively grazed grassland in southern Belgium
Gourlez de la Motte, Louis ULg; Jérôme, Elisabeth; Mamadou, Ossénatou ULg et al

Poster (2016)

Grasslands are an important component of the global carbon balance but their carbon storage potential is still highly uncertain. Especially, the impact of weather variability and management practices on ... [more ▼]

Grasslands are an important component of the global carbon balance but their carbon storage potential is still highly uncertain. Especially, the impact of weather variability and management practices on grassland carbon budgets need to be assessed. This study investigates the carbon balance of an intensively managed permanent grassland in southern Belgium and its uncertainties by combining 5-years of eddy covariance measurements and other organic carbon exchanges estimates. The specificities of this study lie in: (i) the age of the pasture, which has probably been established since more than one century; (ii) the intensive character of the management with a mean grazing pressure larger than 2 livestock unit ha-1 and stocking cycle including stocking and rest periods, (iii) the livestock production system, typical of Wallonia, farming intensively Belgian Blue breed of cattle in order to produce meat. The results showed that, despite the high stocking rate and the old age of the pasture and the high stocking rate, the site acted as a relatively stable carbon sink from year to year with a 5-year average Net Biome Productivity of ‒173 [‒128 ‒203] g C m-2 yr-1. The carbon sink behavior of the pasture was directly increased by management practices through food complementation and organic fertilization and indirectly by mineral fertilization. The relatively low carbon budget inter-annual variability could be explained both by: (i) grazing management of the farmer that regulated Growth Primary Productivity by adapting the stocking rate to the Leaf Area Index which itself depends on weather conditions, (ii) carbon imports through food complements only when grass regrowth was not sufficient to feed the cattle. An exception occurred when low temperatures at the beginning of the year and a prolonged snow period provoked a delay in grass growth and therefore Growth Primary Productivity that could not be completely offset during the rest of the year. The results suggest that management practices that tend to optimize forage availability for meat production could contribute to maintaining a carbon sink. [less ▲]

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See detailPhénologie des hêtres dans une forêt ardennaise: comparaison de méthodes de suivi et relations avec les flux de CO2
Hurdebise, Quentin ULg; Vincke, Caroline; De Ligne, Anne ULg et al

Poster (2015, November 18)

Bien caractériser la phénologie des essences forestières dans un contexte climatique changeant est indispensable. Dans cette optique, confronter les différentes sources d’informations phénologiques ... [more ▼]

Bien caractériser la phénologie des essences forestières dans un contexte climatique changeant est indispensable. Dans cette optique, confronter les différentes sources d’informations phénologiques (relevé de terrain, modélisation, capteurs de rayonnement, caméra phénologique, satellite, eddy covariance…) est une démarche essentielle. Les différences et la complémentarité de ces sources d’informations ont été mises en évidence en utilisant les données provenant d’une forêt mixte de l’Est de la Belgique, principalement composée de hêtres. Par ailleurs, ces informations ont été utilisées pour étudier l’influence de la phénologie des hêtres sur les échanges annuels de CO2 de ces derniers. [less ▲]

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