References of "Ibrom, A"
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See detailInterpreting canopy development and physiology using a European phenology camera network at flux sites
Wingate, L.; Ogée, J.; Cremonese, E. et al

in Biogeosciences (2015), 12(10), 5995-6015

Plant phenological development is orchestrated through subtle changes in photoperiod, temperature, soil moisture and nutrient availability. Presently, the exact timing of plant development stages and ... [more ▼]

Plant phenological development is orchestrated through subtle changes in photoperiod, temperature, soil moisture and nutrient availability. Presently, the exact timing of plant development stages and their response to climate and management practices are crudely represented in land surface models. As visual observations of phenology are laborious, there is a need to supplement long-term observations with automated techniques such as those provided by digital repeat photography at high temporal and spatial resolution. We present the first synthesis from a growing observational network of digital cameras installed on towers across Europe above deciduous and evergreen forests, grasslands and croplands, where vegetation and atmosphere CO2 fluxes are measured continuously. Using colour indices from digital images and using piecewise regression analysis of time series, we explored whether key changes in canopy phenology could be detected automatically across different land use types in the network. The piecewise regression approach could capture the start and end of the growing season, in addition to identifying striking changes in colour signals caused by flowering and management practices such as mowing. Exploring the dates of green-up and senescence of deciduous forests extracted by the piecewise regression approach against dates estimated from visual observations, we found that these phenological events could be detected adequately (RMSE < 8 and 11 days for leaf out and leaf fall, respectively). We also investigated whether the seasonal patterns of red, green and blue colour fractions derived from digital images could be modelled mechanistically using the PROSAIL model parameterised with information of seasonal changes in canopy leaf area and leaf chlorophyll and carotenoid concentrations. From a model sensitivity analysis we found that variations in colour fractions, and in particular the late spring `green hump' observed repeatedly in deciduous broadleaf canopies across the network, are essentially dominated by changes in the respective pigment concentrations. Using the model we were able to explain why this spring maximum in green signal is often observed out of phase with the maximum period of canopy photosynthesis in ecosystems across Europe. Coupling such quasi-continuous digital records of canopy colours with co-located CO2 flux measurements will improve our understanding of how changes in growing season length are likely to shape the capacity of European ecosystems to sequester CO2 in the future. [less ▲]

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See detailDetecting the critical periods that underpin interannual fluctuations in the carbon balance of European forests
Le Maire, G.; Delpierre, N.; Jung, M. et al

in Journal of Geophysical Research: Biogeosciences (2010), 115(4),

The interannual variability of CO<inf>2</inf> exchange by forest ecosystems in Europe was analyzed at site and regional scales by identifying critical periods that contributed to interannual flux ... [more ▼]

The interannual variability of CO<inf>2</inf> exchange by forest ecosystems in Europe was analyzed at site and regional scales by identifying critical periods that contributed to interannual flux anomalies. Critical periods were defined as periods in which monthly and annual flux anomalies were correlated. The analysis was first conducted at seven European forest flux tower sites with contrasting species and climatic conditions. Organizing Carbon and Hydrology in Dynamic Ecosystems (ORCHIDEE), a generic process-based model, represented fairly well most features of the critical period patterns and their climate drivers at the site scale. Simulations at the scale of European forests were performed with ORCHIDEE integrated at a 0.25° spatial resolution. The spatial and temporal distributions of critical periods for canopy photosynthesis, ecosystem respiration, and net ecosystem exchange (NEE) as well as their underlying climate drivers were analyzed. The interannual variability in gross primary productivity (GPP) was explained by critical periods during spring and summer months. In contrast, the interannual variability in total ecosystem respiration (TER) was explained by critical periods occurring throughout the year. A latitudinal contrast between southern and northern Europe was observed in the distributions of critical periods for GPP and TER. The critical periods were positively controlled by temperature in northern Europe and by soil water availability in southern Europe. More importantly, the latitudinal transition between temperature-driven and water-driven critical periods for GPP varied from early spring to late summer. Such a distinct seasonal regime of critical periods was less clearly defined for TER and NEE. Overall, the critical periods associated with NEE variations and their meteorological drivers followed those associated with GPP. Copyright © 2010 by the American Geophysical Union. [less ▲]

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See detailMethodology for data acquisition, storage and treatment
Aubinet, Marc ULg; Clément, R.; Elbers, J. A. et al

in Valentini, R. (Ed.) Fluxes of Carbon, Water and Energy of European Forests (2003)

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See detailSpruce forests (Norway and Sitka spruce, including Douglas fir): Carbon and water fluxes, Balances, Ecological and ecophysiological determinants
Bernhofer, C.; Aubinet, Marc ULg; Clément, R. et al

in Valentini, Riccardo (Ed.) Fluxes of Carbon, Water and Energy of European Forests (2003)

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See detailEnergy Balance Closure At Fluxnet Sites
Wilson, K.; Goldstein, A.; Falge, E. et al

in Agricultural and Forest Meteorology (2002), 113(1-4),

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See detailProductivity Overshadows Temperature In Determining Soil And Ecosystem Respiration Across European Forests
Janssens, Ia.; Lankreijer, H.; Matteucci, G. et al

in Global Change Biology (2001), 7(3),

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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 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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See detailEstimates of the annual net carbon and water exchange of forests: the EUROFLUX methodology.
Aubinet, Marc ULg; Grelle, A.; Ibrom, A. et al

in Advances in Ecological Research (1999), 30

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