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See detailUse of the daily differencing approach to evaluate uncertainties affecting eddy covariance measurements
Laffineur, Quentin ULg; Aubinet, Marc ULg

Poster (2008)

The eddy covariance technique is recognised to be the most adapted micrometeorological method to study the exchange processes between terrestrial ecosystems and the atmosphere. Like all other methods, it ... [more ▼]

The eddy covariance technique is recognised to be the most adapted micrometeorological method to study the exchange processes between terrestrial ecosystems and the atmosphere. Like all other methods, it is submitted to systematic and random measurement errors. A thorough analysis of these errors is necessary in order to set the limits of validity of the method and to quantify the uncertainty that affects net carbon exchange computed with this method. In this presentation, we’ll concentrate on the random errors using the dailydifferencing approach (DDA) developed by Hollinger and Richardson (2005). The interest of this approach is that it requests only single tower measurements and is thus applicable to all flux tower sites. In this approach, uncertainties are estimated by comparing flux values taken at two successive days at the same hour and under similar meteorological conditions. The analysis may be applied to sensible heat, latent heat and CO2 flux densities. It was applied here to the eddy-covariance data from the Vielsalm mixed forest site (10 years of data) and from the Lonzée agricultural site (4 years of data). Both sites are situated in Belgium and are part of the Carboeurope IP network. The study is developed in the frame of the European IMECC project. The absolute and relative random error was quantified for both sites. Their daily evolution and their dependencies on different climate conditions (magnitude of the flux, PPFD, Rnet, wind velocity, wind direction, clarity index) were analysed. For both sites, the absolute random error increases linearly with the absolute value of flux. This is the principal factor controlling the random error. More particularly the response of the random error to wind velocity was analysed. For the CO2 flux, the absolute random error decreases with increasing wind speed. This effect is more important for the agricultural site than for the forest site. The behaviour of the relative random error with wind speed is more contrasted: it generally decreases with increasing wind speed at low velocities but, for some directions may increase with wind speed at high velocities. In addition, the random error was found very dependent on wind direction at the forest site probably as a result of site heterogeneity. [less ▲]

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See detailDescription of cropland CO2 exchange : a comparison of empirical and physiologically based estimates of Reco, GPP and NEE
Tenhunen, J.; Li, Y.-L.; Dinh, N. Q. et al

in CarboEurope-IP meeting 2008 (2008)

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See detailMesure des flux de CO2 et bilan carboné de grandes cultures : Etat de la question et méthodologie
Moureaux, Christine ULg; Bodson, Bernard ULg; Aubinet, Marc ULg

in Biotechnologie, Agronomie, Société et Environnement = Biotechnology, Agronomy, Society and Environment [=BASE] (2008), 12(3), 303-315

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See detailExtrapolating the gross primary productivity from leaf to canopy scale in a winter wheat crop
Hoyaux, Julien; Moureaux, Christine ULg; Tourneur, Denis et al

in Agricultural and Forest Meteorology (2008), 148(4), 668-679

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See detailEddy Covariance Co2 Flux Measurements In Nocturnal Conditions: An Analysis Of The Problem
Aubinet, Marc ULg

in Ecological Applications (2008), 18(6),

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See detailNos grandes cultures captent aussi le CO2
Bodson, Bernard ULg; Moureaux, Christine ULg; Aubinet, Marc ULg

in Nouvelles du Printemps (Les) (2007), (2ème trimestre 2007), 30-31

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See detailLinking flux network measurements to continental scale simulations: Ecosystem carbon dioxide exchange capacity under non-water-stressed conditions
Owen, Katherine; Tenhunen, John; Reichstein, Markus et al

in Global Change Biology (2007), 13

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See detailDeterminants of terrestrial ecosystem carbon balance inferred from European eddy covariance flux sites
Reichstein, Markus; Papale, Dario; Valentini, Riccardo et al

in Geophysical Research Letters (2007), 34(1),

Pioneering work in the last century has resulted in a widely accepted paradigm that primary production is strongly positively related to temperature and water availability such that the northern ... [more ▼]

Pioneering work in the last century has resulted in a widely accepted paradigm that primary production is strongly positively related to temperature and water availability such that the northern hemispheric forest carbon sink may increase under conditions of global warming. However, the terrestrial carbon sink at the ecosystem level (i.e. net ecosystem productivity, NEP) depends on the net balance between gross primary productivity (GPP) and ecosystem respiration ( TER). Through an analysis of European eddy covariance flux data sets, we find that the common climate relationships for primary production do not hold for NEP. This is explained by the fact that decreases in GPP are largely compensated by parallel decreases in TER when climatic factors become more limiting. Moreover, we found overall that water availability was a significant modulator of NEP, while the multivariate effect of mean annual temperature is small and not significant. These results indicate that climate- and particularly temperature-based projections of net carbon balance may be misleading. Future research should focus on interactions between the water and carbon cycles and the effects of disturbances on the carbon balance of terrestrial ecosystems. [less ▲]

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See detailCO2 balance of boreal, temperate, and tropical forests derived from a global database
Luyssaert, S.; Inglima, I.; Jung, M. et al

in Global Change Biology (2007), 13(12), 2509-2537

Terrestrial ecosystems sequester 2.1 Pg of atmospheric carbon annually. A large amount of the terrestrial sink is realized by forests. However, considerable uncertainties remain regarding the fate of this ... [more ▼]

Terrestrial ecosystems sequester 2.1 Pg of atmospheric carbon annually. A large amount of the terrestrial sink is realized by forests. However, considerable uncertainties remain regarding the fate of this carbon over both short and long timescales. Relevant data to address these uncertainties are being collected at many sites around the world, but syntheses of these data are still sparse. To facilitate future synthesis activities, we have assembled a comprehensive global database for forest ecosystems, which includes carbon budget variables (fluxes and stocks), ecosystem traits (e.g. leaf area index, age), as well as ancillary site information such as management regime, climate, and soil characteristics. This publicly available database can be used to quantify global, regional or biome-specific carbon budgets; to re-examine established relationships; to test emerging hypotheses about ecosystem functioning [e.g. a constant net ecosystem production (NEP) to gross primary production (GPP) ratio]; and as benchmarks for model evaluations. In this paper, we present the first analysis of this database. We discuss the climatic influences on GPP, net primary production (NPP) and NEP and present the CO2 balances for boreal, temperate, and tropical forest biomes based on micrometeorological, ecophysiological, and biometric flux and inventory estimates. Globally, GPP of forests benefited from higher temperatures and precipitation whereas NPP saturated above either a threshold of 1500 mm precipitation or a mean annual temperature of 10 degrees C. The global pattern in NEP was insensitive to climate and is hypothesized to be mainly determined by nonclimatic conditions such as successional stage, management, site history, and site disturbance. In all biomes, closing the CO2 balance required the introduction of substantial biome-specific closure terms. Nonclosure was taken as an indication that respiratory processes, advection, and non-CO2 carbon fluxes are not presently being adequately accounted for. [less ▲]

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See detailResponse of autotrophic and heterotrophic respiration to biotic and abiotic factors over a cropland
Suleau, Marie ULg; Debacq, Alain ULg; Moureaux, Christine ULg et al

in Final conference of the programme "The role of soils in the terrestrial carbon balance", European Science Foundation (2007)

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See detailTowards a carbon balance at the Lonzée crop site
Moureaux, Christine ULg; Debacq, Alain ULg; Suleau, Marie ULg et al

Conference (2007)

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See detailEvidence For Soil Water Control On Carbon And Water Dynamics In European Forests During The Extremely Dry Year: 2003
Granier, A.; Reichstein, M.; Breda, N. et al

in Agricultural and Forest Meteorology (2007), 143(1-2),

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See detailSome Methodological Questions Concerning Advection Measurements: A Case Study
Heinesch, Bernard ULg; Aubinet, Marc ULg; Yernaux, Michel ULg

in Boundary-Layer Meteorology (2007), 122(2),

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See detailReduction Of Ecosystem Productivity And Respiration During The European Summer 2003 Climate Anomaly: A Joint Flux Tower, Remote Sensing And Modelling Analysis
Reichstein, M.; Ciais, P.; Papale, D. et al

in Global Change Biology (2007), 13(3),

Detailed reference viewed: 36 (5 ULg)