References of "Heinesch, Bernard"
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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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See detailO2/Ar and CH4 measurements in sea ice : clues for the key status of sea ice in the climate system
Zhou, Jiayun; Tison, Jean-Louis; Eicken, Hajo et al

in Geophysical Research Abstracts (2011, April 08), 13

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See detailIsoprene and monoterpene emissions from a mixed temperate forest
Laffineur, Quentin ULg; Heinesch, Bernard ULg; Amelynck, Crist et al

Poster (2011, April 07)

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See detailMeasurement and modeling of methanol deposition/emission in a mixed forest
Laffineur, Quentin ULg; Heinesch, Bernard ULg; Amelynck, Crist et al

in Geophysical Research Abstracts (2011, April 07), 13

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See detailTemporal evolution of biogeochemical properties of landfast sea ice at Barrow (Alaska)
Zhou, Jiayun ULg; Tison, Jean-Louis; Eicken, Hajo et al

Poster (2011, March)

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See detailA multidisciplinary approach to understanding the sea ice system: implications on gas. Gordon Research Seminars
Zhou, Jiayun ULg; Tison, Jean-Louis; Eicken, Hajo et al

Conference (2011, March)

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See detailFINAL REPORT PHASE II "Impact of Phenology and Environmental Conditions on BVOC Emissions from Forest Ecosystems" "IMPECVOC"
Dewulf, Jo; Joó, Eva; Van Langenhove, Herman et al

Report (2011)

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See detailEffect of seasonality and short-term light and temperature history on monoterpene emissions from European beech (Fagus sylvatica L.)
Demarcke, M.; Amelynck, Crist; Schoon, N. et al

in Hansel, Armin; Dunkl, Jürgen (Eds.) 5th International PTR-MS Conference on Proton Transfer Reaction Mass Spectrometry and its Applications (2011, January)

Branch enclosure measurements of monoterpene emision rates have been performed at different positions in the canopy of a European beech tree in natural environmental conditions. Strong and position ... [more ▼]

Branch enclosure measurements of monoterpene emision rates have been performed at different positions in the canopy of a European beech tree in natural environmental conditions. Strong and position-dependent standard emission rate variations were observed in the course of the growth season. By using the obtained dataset and a modified vesrion of the MEGAN algorithm, the response of the emissions to short-term light and temperature history was investigated [less ▲]

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See detailWhat can we learn from year-round BVOC disjunct eddycovariance measurements? A case example from a temperate forest
Laffineur, Quentin ULg; Heinesch, Bernard ULg; Schoon, N. et al

in Hansel, Armin; Dunkl, Jürgen (Eds.) 5th International PTR-MS Conference on Proton Transfer Reaction Mass Spectrometry and its Applications (2011, January)

Long term ecosystem-scale biogenic volatile organic compounds (BVOC) flux measurements by disjunct eddy-covariance are needed to determine and characterize the BVOC emissions/depositions from episodic ... [more ▼]

Long term ecosystem-scale biogenic volatile organic compounds (BVOC) flux measurements by disjunct eddy-covariance are needed to determine and characterize the BVOC emissions/depositions from episodic events (budburst, stress) as well as the continuous emission/deposition during vegetation growth and its seasonal evolution in interaction with climate and environment. If the data coverage is sufficient, this technique has the potential to provide a dataset covering the whole spectrum of meteorological and phenological conditions encountered by the studied ecosystem ending in a statistically more robust dataset than what can be provided by other BVOC measurement techniques. In addition, long term measurements allow in Oxygenated VOCs (OVOCs) depositions to be estimated in a realistic manner with is not the case with the enclosure technique. Here we present a year-round campaign of disjunct eddy-covariance BVOC fluxes above a mixed temperate forest performed in the frame of the IMPECVOC (Impact of Phenology and Environmental Conditions on BVOC Emissions from Forest Ecosystems) project. We will analyse the three main BVOC species (isoprene/monoterpenes and methanol) in order to illustrate the interest of long-term flux measurements by investigating the main driving variables and the underlying mechanisms of emission/deposition, how de novo carbon allocation to the isoprene/monoterpenes skeleton structure is altered through the time. For methanol, we will show the importance of deposition on a long-term basis and use an empirical model to discriminate the physical and physiological components of the exchange. [less ▲]

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