References of "Heinesch, Bernard"
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See detailEvapotranspiration amplifies European summer drought
Teuling, Adriaan J.; Van Loon, Anne F.; Seneviratne, Sonia Isabelle et al

in Geophysical Research Letters (2013)

Drought is typically associated with a lack of precipitation, whereas the contribution of evapotranspiration and runoff to drought evolution is not well understood. Here, we use unique long-term ... [more ▼]

Drought is typically associated with a lack of precipitation, whereas the contribution of evapotranspiration and runoff to drought evolution is not well understood. Here, we use unique long-term observations made in four headwater catchments in Central and Western Europe to reconstruct storage anomalies and study the drivers of storage anomaly evolution during drought. We provide observational evidence for the ‘drought-paradox’ in that region: a consistent and significant increase in evapotranspiration during drought episodes which acts to amplify the storage anomalies. In contrast, decreases in runoff act to limit storage anomalies. Our findings stress the need for the correct representation of evapotranspiration and runoff processes in drought indices. [less ▲]

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See detailImpact of diffuse light on isoprene and monoterpene emissions from a mixed temperate forest
Laffineur, Quentin ULg; Aubinet, Marc ULg; Schoon, Niels et al

in Atmospheric Environment (2013), 46(74), 385-392

This study investigated the impact of diffuse light on canopy scale emission of isoprene and monoterpenes measured continuously above a mixed temperate forest, using the disjunct eddy-covariance by mass ... [more ▼]

This study investigated the impact of diffuse light on canopy scale emission of isoprene and monoterpenes measured continuously above a mixed temperate forest, using the disjunct eddy-covariance by mass scanning technique with a proton transfer reaction-mass spectrometer (PTR-MS) instrument. To assess this impact, the relationship between emissions/radiation and emissions/gross primary production (GPP) under clear sky and cloudy conditions were analysed. Under cloudy conditions (high proportion of diffuse radiation), the isoprene and monoterpene fluxes were enhanced compared to clear sky conditions (low proportion of diffuse radiation) at equivalent temperature and above-canopy total radiation. The whole-canopy enzymatic activity of the metabolic isoprene production pathway, however, was suggested to be lower under cloudy conditions than under clear sky conditions at equivalent temperature. The mechanisms behind these observations are probably linked to the better penetration of diffuse radiation in the canopy. Shade leaves/needles receive more radiation in cloudy conditions than in clear sky conditions, thereby inducing the observed effects. [less ▲]

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See detailLong term measurements of volatile organic compounds exchanges above a maize field at Lonzee (Belgium)
Bachy, Aurélie ULg; Aubinet, Marc ULg; SALERNO, Giovanni ULg et al

in Communications in Agricultural and Applied Biological Sciences (2013, February), 78(1), 127-132

VOC (volatile organic compounds) include a wide set of molecules which are mostly emitted by the plants. Atmospheric scientists are strongly interested in these compounds because of their important role ... [more ▼]

VOC (volatile organic compounds) include a wide set of molecules which are mostly emitted by the plants. Atmospheric scientists are strongly interested in these compounds because of their important role in the atmospheric chemistry and their final impact on air pollution and climate change. Evaluation of current and future VOC emissions is thus necessary and requires a comprehensive understanding of VOC production and exchange dynamics under a wide panel of climatic conditions and ecosystems. Forest and non pastured grasslands have been largely studied for the last decade. However, knowledge about VOC fluxes from croplands remains scarce. Our study focuses on the VOC exchanges between a maize field and the atmosphere. It is incorporated in a wider project that aims to study VOC fluxes from two croplands (maize and winter wheat) and a pastured grassland. VOC fluxes have been measured on a maize field during the whole growing season using a micrometeorological method (eddy covariance). While first results show half-hourly bidirectionnal exchanges among all the preselected compounds, in average methanol stands for the greatest emitted VOC, followed by green leaf volatiles, and acetic acid is the greatest taken up VOC. Small isoprene and monoterpenes fluxes are also observed. A diurnal pattern is found for all those VOC, with greater emission/uptake during the day, suggesting a flux dependence on environmental parameters. These environmental controls will be further investigated [less ▲]

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See detailMéthodologie de calcul des flux turbulents : Corrections de fréquence
Heinesch, Bernard ULg

Conference (2013, January 29)

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See detailMéthodologie de calcul des flux turbulents : rotation du système de coordonnées
Heinesch, Bernard ULg

Conference (2013, January 28)

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See detailPhysical and biogeochemical properties in landfast sea ice (Barrow, Alaska): insights on brine and gas dynamics across seasons
Zhou, Jiayun ULg; Delille, Bruno ULg; Eicken, H. et al

in Journal of Geophysical Research (2013), 118(6), 3172-3189

The impacts of the seasonal evolution of sea-ice physical properties on ice-ocean biogeochemical exchanges were investigated in landfast ice at Barrow (Alaska) from January through June 2009. Three stages ... [more ▼]

The impacts of the seasonal evolution of sea-ice physical properties on ice-ocean biogeochemical exchanges were investigated in landfast ice at Barrow (Alaska) from January through June 2009. Three stages of brine dynamics across the annual cycle have been identified based on brine salinity, brine volume fraction and porous medium Rayleigh number [less ▲]

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See detailCurrent net ecosystem exchange of CO2 in a young mixed forest: any heritage from the previous ecosystem?
Violette, Aurélie ULg; Heinesch, Bernard ULg; Erpicum, Michel ULg et al

Poster (2013)

For 15 years, networks of flux towers have been developed to determine accurate carbon balance with the eddy-covariance method and determine if forests are sink or source of carbon. However, for ... [more ▼]

For 15 years, networks of flux towers have been developed to determine accurate carbon balance with the eddy-covariance method and determine if forests are sink or source of carbon. However, for prediction of the evolution of carbon cycle and climate, major uncertainties remain on the ecosystem respiration (Reco, which includes the respiration of above ground part of trees, roots respiration and mineralization of the soil organic matter), the gross primary productivity (GPP) and their difference, the net ecosystem exchange (NEE) of forests. These uncertainties are consequences of spatial and inter-annual variability, driven by previous and current climatic conditions, as well as by the particular history of the site (management, diseases, etc.). In this study we focus on the carbon cycle in two mixed forests in the Belgian Ardennes. The first site, Vielsalm, is a mature stand mostly composed of beeches (Fagus sylvatica) and douglas fir (Pseudotsuga menziesii) from 80 to 100 years old. The second site, La Robinette, was covered before 1995 with spruces. After an important windfall and a clear cutting, the site was replanted, between 1995 and 2000, with spruces (Piceas abies) and deciduous species (mostly Betula pendula, Aulnus glutinosa and Salix aurita). The challenge here is to highlight how initial conditions can influence the current behavior of the carbon cycle in a growing stand compared to a mature one, where initial conditions are supposed to be forgotten. A modeling approach suits particularly well for sensitivity tests and estimation of the temporal lag between an event and the ecosystem response. We use the forest ecosystem model ASPECTS (Rasse et al., Ecological Modelling 141, 35-52, 2001). This model predicts long-term forest growth by calculating, over time, hourly NEE. It was developed and already validated on the Vielsalm forest. Modelling results are confronted to eddy-covariance data on both sites from 2006 to 2011. The main difference between both sites seems to rely on soil respiration, which is probably partly a heritage of the previous ecosystem at the young forest site. [less ▲]

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See detailInitiation of methane turbulent flux measurements over a grazed grassland in Belgium
Dumortier, Pierre ULg; Aubinet, Marc ULg; Chopin, Henri ULg et al

in Geophysical Research Abstracts (2013), 15

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See detailEvaluation of the potential of MODIS satellite data to predict vegetation phenology in different biomes: An investigation using ground-based NDVI measurements
Hmimina, G.; Dufrêne, Eric; Pontailler, J.-Y. et al

in Remote Sensing of Environment (2013), (132), 145-158

Vegetation phenology is the st udy of the timing of seasonal events that are considered to be the result of adaptive responses to climate variations on short and long time scales. In the field of remote ... [more ▼]

Vegetation phenology is the st udy of the timing of seasonal events that are considered to be the result of adaptive responses to climate variations on short and long time scales. In the field of remote sensing of vegetation phenology, phenologicalmetrics are derived fromtime series of optical data. For that purpose, considerable effort has been specifically focused on developing noise reduction and cloud-contaminated data removal techniques to improve the quality of remotely-sensed time series. Comparative studies between time series composed of satellite data acquired under clear and cloudy conditions and fromradiometric data obtainedwith high accuracy fromground-basedmeasurements constitute a direct and effective way to assess the operational use and limitations of remote sensing for predicting the main plant phenological events. In the present paper, we sought to explicitly evaluate the potential use of MODerate resolution Imaging Spectroradiometer (MODIS) remote sensing data for monitoring the seasonal dynamics of different types of vegetation cover that are representative of the major terrestrial biomes, including temperate deciduous forests, evergreen forests, African savannah, and crops. After cloud screening and filtering, we compared the temporal patterns and phenological metrics derived from in situ NDVI time series and from MODIS daily and 16-composite products. We also evaluated the effects of residual noise and the in uence of data gaps in MODIS NDVI time series on the identification of the most relevant metrics for vegetation phenology monitoring. The results show that the in exion points of a model fitted to a MODIS NDVI time series allow accurate estimates of the onset of greenness in the spring and the onset of yellowing in the autumn in deciduous forests (RMSE<oneweek). Phenologicalmetrics identical to those providedwith theMODIS Global Vegetation Phenology product (MDC12Q2) are less robust to data gaps, and they can be subject to large biases of approximately twoweeks or more during the autumn phenological transitions. In the evergreen forests, in situ NDVI time series describe the phenology with high fidelity despite small temporal changes in the canopy foliage. However, MODIS is unable to provide consistent phenological patterns. In crops and savannah, MODIS NDVI time series reproduce the general temporal patterns of phenology, but significant discrepancies appear between MODIS and ground-based NDVI time series during very localized periods of time depending on the weather conditions and spatial heterogeneity within the MODIS pixel. In the rainforest, the temporal pattern exhibited by a MODIS 16-day composite NDVI time series ismore likely due to a pattern of noise in the NDVI data structure according to both rainy and dry seasons rather than to phenological changes. More investigations are needed, but in all cases, this result leads us to conclude that MODIS time series in tropical rainforests should be interpreted with great caution. [less ▲]

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See detailDiurnal CO2 flux responses in cultivated savanna in Benin (West Africa)
Ago, Expédit Evariste ULg; Agbossou, Euloge Kossi; Galle, Sylvie et al

Scientific conference (2012, February 08)

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See detailAbiotic and biotic control of methanol exchanges in a temperate mixed forest
Laffineur, Quentin ULg; Aubinet, Marc ULg; Schoon, N. et al

in Atmospheric Chemistry and Physics (2012), 12

Methanol exchanges over a mixed temperate forest in the Belgian Ardennes were measured for more than one vegetation season using disjunct eddy-covariance by a mass scanning technique and Proton Transfer ... [more ▼]

Methanol exchanges over a mixed temperate forest in the Belgian Ardennes were measured for more than one vegetation season using disjunct eddy-covariance by a mass scanning technique and Proton Transfer Reaction Mass Spectrometry (PTR-MS). Half-hourly methanol fluxes were measured in the range of −0.6 μgm−2 s−1 to 0.6 μgm−2 s−1, and net daily methanol fluxes were generally negative in summer and autumn and positive in spring. On average, the negative fluxes dominated (i.e. the site behaved as a net sink), in contrast to what had been found in previous studies. An original model describing the adsorption/desorption of methanol in water films present in the forest ecosystem and the methanol degradation process was developed. Its calibration, based on field measurements, predicted a mean methanol degradation rate of −0.0074 μgm−2 s−1 and a half lifetime for methanol in water films of 57.4 h. Biogenic emissions dominated the exchange only in spring, with a standard emission factor of 0.76 μgm−2 s−1. The great ability of the model to reproduce the long-term evolution, as well as the diurnal variation of the fluxes, suggests that the adsorption/desorption and degradation processes play an important role in the global methanol budget. This result underlines the need to conduct long-term measurements in order to accurately capture these processes and to better estimate methanol fluxes at the ecosystem scale. [less ▲]

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See detailGround-based Network of NDVI measurements for tracking temporal dynamics of canopy structure and vegetation phenology in different biomes
Soudani, K.; Hmimina, K.; Delpierre, N. et al

in Remote Sensing of Environment (2012), 123

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See detailChapter 3: Data Acquisition and Flux Calculations
Rebmann, Corinna; Kolle, Olaf; Heinesch, Bernard ULg et al

in Aubinet, Marc; Vesala, Timo; Papale, Dario (Eds.) Eddy Covariance: A Practical Guide to Measurement and Data Analysis (2012)

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See detailChapter 5: Night time Flux correction
Aubinet, Marc ULg; Feigenwinter, Christian; Heinesch, Bernard ULg et al

in Aubinet, Marc; Vesala, Timo; Papale, Dario (Eds.) Eddy Covariance: A Practical Guide to Measurement and Data Analysis (2012)

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See detailCO2 exchange above a cultivated savanna in sudanian region in northern part of Benin (West Africa)
Ago, Expédit Evariste ULg; Agbossou, Euloge; Galle, Sylvie et al

Poster (2011, October)

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See detailClear link between drought stress, photosynthesis and biogenic volatile organic compounds in Fagus sylvatica L.
Šimpraga, M.; Verbeeck, H.; Demarcke, M. et al

in Atmospheric Environment (2011), 45(30), 5254-5259

Direct plant stress sensing is the key for a quantitative understanding of drought stress effects on biogenic volatile organic compound (BVOC) emissions. A given level of drought stress might have a ... [more ▼]

Direct plant stress sensing is the key for a quantitative understanding of drought stress effects on biogenic volatile organic compound (BVOC) emissions. A given level of drought stress might have a fundamentally different effect on the BVOC emissions of different plants. For the first time, we continuously quantified the level of drought stress in a young potted beech (Fagus sylvatica L.) with a linear variable displacement transducer (LVDT) installed at stem level in combination with simultaneous measurements of BVOC emissions and photosynthesis rates at leaf level. This continuous set of measurements allowed us to examine how beech alters its pattern of photosynthesis and carbon allocation to BVOC emissions (mainly monoterpenes, MTs) and radial stem growth during the development of drought stress. We observed an increasing-decreasing trend in the MT emissions as well as in the fraction of assimilated carbon re-emitted back into the atmosphere (ranging between 0.14 and 0.01%). We were able to link these dynamics to pronounced changes in radial stem growth, which served as a direct plant stress indicator. Interestingly, we detected a sudden burst in emission of a non-identified, non-MT BVOC species when drought stress was acute (i.e. pronounced negative stem growth). This burst might have been caused by a certain stress-related green leaf volatile, which disappeared immediately upon re-watering and thus the alleviation of drought stress. These results highlight that direct plant stress sensing creates opportunities to understand the overall complexity of stress-related BVOC emissions. [less ▲]

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See detailComparing monoterpenoid emissions and net photosynthesis of beech (Fagus sylvatica L.) in controlled and natural conditions
Šimpraga; Verbeeck, H.; Demarcke, M. et al

in Atmospheric Environment (2011), 45(17), 2922-2928

Although biogenic volatile organic compounds (BVOCs) only represent a very limited fraction of the plant's carbon (C) budget, they play an important role in atmospheric chemistry for example as a ... [more ▼]

Although biogenic volatile organic compounds (BVOCs) only represent a very limited fraction of the plant's carbon (C) budget, they play an important role in atmospheric chemistry for example as a precursor of tropospheric ozone. We performed a study comparing BVOC emissions of European beech (Fagus sylvatica L.) in controlled and natural environmental conditions. A young and adult beech tree was exposed to short-term temperature variations in growth room conditions and in an experimental forest, respectively. This study attempts to clarify how short-term temperature variations between days influenced the ratio between monoterpenoid (MT) emissions and net photosynthesis (Pn). Within a temperature range of 17-27 °C and 13-23 °C, the MT/Pn carbon ratio increased 10-30 fold for the growth room and forest, respectively. An exponential increasing trend between MT/Pn C ratio and air temperature was observed in both conditions. Beech trees re-emitted a low fraction of the assimilated C back into the atmosphere as MT: 0.01-0.12% and 0.01-0.30% with a temperature rise from 17 to 27 °C and 13-23 °C in growth room and forest conditions, respectively. However, the data showed that the MT/Pn C ratio of young and adult beech trees responded significantly to changes in temperature. [less ▲]

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