Éditeur(s) : HAL CCSD
Résumé :  
absent
33. European Geosciences Union General Assembly
Vienne, Austria

hal-01032070
https://hal.archives-ouvertes.fr/hal-01032070

Éditeur(s) : HAL CCSD Elsevier
Résumé : Vegetation phenology is the study 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, phenological metrics are derived from time 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 from radiometric data obtained with high accuracy from ground-based measurements 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 influence 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 inflexion 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 <= one week). Phenological metrics identical to those provided with the MODIS Global Vegetation Phenology product (MDC12Q2) are less robust to data gaps, and they can be subject to large biases of approximately two weeks 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 is more 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. (C) 2013 Elsevier Inc. All rights reserved.
ISSN: 0034-4257

hal-01032407
https://hal.archives-ouvertes.fr/hal-01032407
DOI : 10.1016/j.rse.2013.01.010

Éditeur(s) : HAL CCSD
Résumé : absent
7. Journées d'Ecologie Fonctionnelle
Super Besse, France

hal-01032031
https://hal.archives-ouvertes.fr/hal-01032031

Éditeur(s) : HAL CCSD Elsevier
Résumé : absent
ISSN: 0034-4257

hal-01019844
https://hal.archives-ouvertes.fr/hal-01019844
DOI : 10.1016/j.rse.2012.03.012

Éditeur(s) : HAL CCSD
Résumé :  
absent
Séminaire du "Dipartimento di Scienze Ambientali"
Naples, Italy

hal-01032045
https://hal.archives-ouvertes.fr/hal-01032045

Éditeur(s) : HAL CCSD
Résumé : absent
Xèmes Journées d'Ecologie fonctionnelle
La Grande Motte, France

hal-01032384
https://hal.archives-ouvertes.fr/hal-01032384

Éditeur(s) : HAL CCSD
Résumé : Carbon isotopic signature has been measured at the different stages of the soil CO2 efflux production in trenched and control plots to improve the knowledge about the physical and biochemical processes of the soil respiration. All the measurements of _13C have been performed using a mass-spectrometer.We have compared the isotopic signatures of the CO2 going out of the soil, the CO2 of the soil atmosphere, the organic carbon in the material that could be considered as the main soil respiration sources (live and dead roots, soil organic matter, aerial litter) and the CO2 produced by these sources in incubation jars. The aims of this study were to evaluate the possibilities to combine these different data sets to estimate the partitioning of soil respiration between its autotrophic and heterotrophic components, and to get more insight into potential fractionation during biochemical or diffusion processes. Measurements were conducted in a beech forest located at Hesse in the North East of France (site equipped with a flux tower and belonging to the CarboEurope network) and in a neotropical primary rainforest located at Paracou (French Guiana). Preliminary results show first a very tenuous difference between CO2 isotopic signatures of efflux coming from the trenched and control plots and, secondly, _13C significant divergences between bulk organic material and CO2 produced in the corresponding incubation jars. Our ability to use this kind of data for partitioning soil respiration into its main components will be discussed.
European Geosciences Union. General Assembly 2006
Vienne, Austria

hal-01032380
https://hal.archives-ouvertes.fr/hal-01032380

Éditeur(s) : HAL CCSD
Résumé :  
absent
Programme National coordonné ANR " ECCO "
Toulouse, France

hal-01032072
https://hal.archives-ouvertes.fr/hal-01032072

Éditeur(s) : HAL CCSD
Résumé : Carbon isotopic signature has been measured at the different stages of the soil CO2 efflux production in trenched and control plots to improve the knowledge about the physical and biochemical processes of the soil respiration. All the measurements of d13C have been performed using a mass-spectrometer. We have compared the isotopic signatures of the CO2 going out of the soil, the CO2 of the soil atmosphere, the organic carbon in the material that could be considered as the main soil respiration sources (live and dead roots, soil organic matter, aerial litter) and the CO2 produced by these sources in incubation jars. The aims of this study were to evaluate the possibilities to combine these different data sets to estimate the partitioning of soil respiration between its autotrophic and heterotrophic components, and to get more insight into potential fractionation during biochemical or diffusion processes. Measurements were conducted in a beech forest located at Hesse in the North East of France (site equipped with a flux tower and belonging to the CarboEurope network) and in a neotropical primary rainforest located at Paracou (French Guiana). Preliminary results show first a very tenuous difference between CO2 isotopic signatures of efflux coming from the trenched and control plots and, secondly, d13C significant divergences between bulk organic material and CO2 produced in the corresponding incubation jars. Our ability to use this kind of data for partitioning soil respiration into its main components will be discussed.
AGU Fall Meeting
San Francisco, United States

hal-01032042
https://hal.archives-ouvertes.fr/hal-01032042

Éditeur(s) : HAL CCSD Wiley
Résumé :  
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 (511605400N, 5215404400W). 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 gCm_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 gCm_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 gCm_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.
ISSN: 1354-1013

hal-01032067
https://hal.archives-ouvertes.fr/hal-01032067
DOI : 10.1111/j.1365-2486.2008.01610.x

Éditeur(s) : HAL CCSD
Résumé : Carbon isotopic signature has been measured at the different stages of the soil CO2 efflux production in trenched and control plots to improve the knowledge about the physical and biochemical processes of the soil respiration. All the measurements of _13C have been performed using a mass-spectrometer.We have compared the isotopic signatures of the CO2 going out of the soil, the CO2 of the soil atmosphere, the organic carbon in the material that could be considered as the main soil respiration sources (live and dead roots, soil organic matter, aerial litter) and the CO2 produced by these sources in incubation jars. The aims of this study were to evaluate the possibilities to combine these different data sets to estimate the partitioning of soil respiration between its autotrophic and heterotrophic components, and to get more insight into potential fractionation during biochemical or diffusion processes. Measurements were conducted in a beech forest located at Hesse in the North East of France (site equipped with a flux tower and belonging to the CarboEurope network) and in a neotropical primary rainforest located at Paracou (French Guiana). Preliminary results show first a very tenuous difference between CO2 isotopic signatures of efflux coming from the trenched and control plots and, secondly, _13C significant divergences between bulk organic material and CO2 produced in the corresponding incubation jars. Our ability to use this kind of data for partitioning soil respiration into its main components will be discussed.
Geophysical Research Abstracts

hal-01031785
https://hal.archives-ouvertes.fr/hal-01031785

Éditeur(s) : HAL CCSD
Résumé :  
absent
Réunion du projet Galiléo "Traçage isotopique du carbone dans les écosystèmes forestiers"
Napoli, Italy

hal-01032064
https://hal.archives-ouvertes.fr/hal-01032064