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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 detailMultiple quality tests for analysing CO2 fluxes in a beech temperate forest
Longdoz, Bernard ULg; Gross, P.; Granier, A.

in Biogeosciences (2008), 5(3), 719-729

Eddy covariance (EC) measurements are widely used to estimate the amount of carbon sequestrated by terrestrial biomes. The decision to exclude an EC flux from a database (bad quality records, turbulence ... [more ▼]

Eddy covariance (EC) measurements are widely used to estimate the amount of carbon sequestrated by terrestrial biomes. The decision to exclude an EC flux from a database (bad quality records, turbulence regime not adequate, footprint problem,...) becomes an important step in the CO2 flux determination procedure. In this paper an innovative combination of existing assessment tests is used to give a relatively complete evaluation of the net ecosystem exchange measurements. For the 2005 full-leaf season at the Hesse site, the percentage of rejected half-hours is relatively high (59.7%) especially during night-time (68.9%). This result strengthens the importance of the data gap filling method. The data rejection does not lead to a real improvement of the accuracy of the relationship between the CO2 fluxes and the climatic factors especially during the nights. The spatial heterogeneity of the soil respiration (on a site with relatively homogenous vegetation pattern) seems large enough to mask an increase of the goodness of the fit of the ecosystem respiration measurements with a dependence on soil temperature and water content when the tests are used to reject EC data. However, the data rejected present some common characteristics. Their removal lead to an increase in the total amount of CO2 respired (24%) and photosynthesised (16%) during the 2005 full-leaf season. Consequently the application of our combination of multiple quality tests is able improve the inter-annual analysis. The systematic application on the large database like the CarboEurope and FLUXNET appears to be necessary. [less ▲]

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See detailImpact of severe dry season on net ecosystem exchange in the Neotropical rainforest of French Guiana
Bonal, D.; Bosc, A.; Ponton, S. et al

in Global Change Biology (2008), 14(8), 1917-1933

The lack of information on the ways seasonal drought modifies the CO2 exchange between Neotropical rainforest ecosystems and the atmosphere and the resulting carbon balance hinders our ability to ... [more ▼]

The lack of information on the ways seasonal drought modifies the CO2 exchange between Neotropical rainforest ecosystems and the atmosphere and the resulting carbon balance hinders our ability to precisely predict how these ecosystems will respond as global environmental changes force them to face increasingly contrasting conditions in the future. To address this issue, seasonal variations in daily net ecosystem productivity (NEPd) and two main components of this productivity, daily total ecosystem respiration (REd) and daily gross ecosystem productivity (GEPd), were estimated over 2 years at a flux tower site in French Guiana, South America (5°16′54″N, 52°54′44″W). We compared seasonal variations between wet and dry periods and between dry periods of contrasting levels of intensity (i.e. mild vs. severe) during equivalent 93-day periods. During the wet periods, the ecosystem was almost in balance with the atmosphere (storage of 9.0 g Cm-2). Seasonal dry periods, regardless of their severity, are associated with higher incident radiation and lower REd combined with reduced soil respiration associated with low soil water availability. During the mild dry period, as is normally the case in this region, the amount of carbon stored in the ecosystem was 32.7 g Cm-2. Severe drought conditions resulted in even lower REd, whereas the photosynthetic activity was only moderately reduced and no change in canopy structure was observed. Thus, the severe dry period was characterized by greater carbon storage (64.6 g C m-2), emphasizing that environmental conditions, such as during a severe drought, modify the CO2 exchange between Neotropical rainforest ecosystems and the atmosphere and potentially the resulting carbon balance. © 2008 The Authors Journal compilation © 2008 Blackwell Publishing. [less ▲]

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See detailTen years of fluxes and stand growth in a young beech forest at Hesse, North-eastern France
Granier, A.; Bréda, N.; Longdoz, Bernard ULg et al

in Annals of Forest Science (2008), 64(7),

• Water and carbon fluxes, as measured by eddy covariance, climate, soil water content, leaf area index, tree biomass, biomass increment (BI), litter fall and mortality were monitored for 10 successive ... [more ▼]

• Water and carbon fluxes, as measured by eddy covariance, climate, soil water content, leaf area index, tree biomass, biomass increment (BI), litter fall and mortality were monitored for 10 successive years in a young beech stand in Hesse forest (north-eastern France) under contrasting climatic and management conditions. • Large year-to-year variability of net carbon fluxes (NEE) and to a lesser extent, of tree growth was observed. The variability in NEE (coefficient of variation, CV = 44%) was related to both gross primary production (GPP) and to variations in total ecosystem respiration (TER), each term showing similar and lower interannual variability (CV = 14%) than NEE. Variation in the annual GPP was related to: (i) the water deficit duration and intensity cumulated over the growing season, and (ii) the growing season length, i.e. the period of carbon uptake by the stand. Two thinnings occurring during the observation period did not provoke a reduction in either GPP, water fluxes, or in tree growth. Interannual variation of TER could not be explained by any annual climatic variables, or LAI, and only water deficit duration showed a poor correlation. Annual biomass increment was well correlated to water shortage duration and was significantly influenced by drought in the previous year. • The relationship between annual NEE and biomass increment (BI) was poor: in some years, the annual carbon uptake was much higher and in others much lower than tree growth. However this relationship was much stronger and linear (r2 = 0.93) on a weekly to monthly time-scale from budburst to the date of radial growth cessation, indicating a strong link between net carbon uptake and tree growth, while carbon losses by respiration occurring after this date upset this relationship. • Despite the lack of correlation between annual data, the NEE and BI cumulated over the 10 years of observations were very close. • On the annual time-scale, net primary productivity calculated from eddy fluxes and from biological measurements showed a good correlation. © 2008 INRA EDP Sciences. [less ▲]

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See detailCarbon balance gradient in European forests: should we doubt 'surprising' results? A reply to Piovesan & Adams
Jarvis, P. G.; Dolman, A. J.; Schulze, E. D. et al

in Journal of Vegetation Science (2001), 12(1), 145-150

This paper responds to the Forum contribution by Piovesan & Adams (2000) who criticized the results obtained by the EUROFLUX network on carbon fluxes of several European forests. The major point of ... [more ▼]

This paper responds to the Forum contribution by Piovesan & Adams (2000) who criticized the results obtained by the EUROFLUX network on carbon fluxes of several European forests. The major point of criticism was that the data provided by EUROFLUX are inconsistent with current scientific understanding. It is argued that understanding the terrestrial global carbon cycle requires more than simply restating what was known previously, and that Piovesan & Adams have not been able to show any major conflicts between our findings and ecosystem or atmospheric-transport theories. [less ▲]

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See detailGap Filling Strategies For Long Term Energy Flux Data Sets
Falge, E.; Baldocchi, D.; Olson, R. et al

in Agricultural and Forest Meteorology (2001), 107(1),

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See detailGap Filling Strategies For Defensible Annual Sums Of Net Ecosystem Exchange
Falge, E.; Baldocchi, D.; Olson, R. et al

in Agricultural and Forest Meteorology (2001), 107(1),

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See detailRespiration As The Main Determinant Of Carbon Balance In European Forests
Valentini, R.; Matteucci, G.; Dolman, Aj. et al

in Nature (2000), 404(6780),

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