Éditeur(s) : HAL CCSD Editions Quae
Résumé :  
absent
De l'observation des écosystèmes forestiers à l'information sur la forêt
Paris, France

hal-01032065
https://hal.archives-ouvertes.fr/hal-01032065

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 Springer Verlag
Résumé : International audience
Disentangling the autotrophic and heterotrophic components of soil CO2 efflux is critical to understanding the role of soil system in terrestrial carbon (C) cycling. In this study, we combined a stable C-isotope natural abundance approach with the trenched plot method to determine if root exclusion significantly affected the isotopic composition (δ13C) of soil CO2 efflux (RS). This study was performed in different forest ecosystems: a tropical rainforest and two temperate broadleaved forests, where trenched plots had previously been installed. At each site, RS and its δ13C (δ13CRs) tended to be lower in trenched plots than in control plots. Contrary to RS, δ13CRs differences were not significant. This observation is consistent with the small differences in δ13C measured on organic matter from root, litter and soil. The lack of an effect on δ13CRs by root exclusion could be from the small difference in δ13C between autotrophic and heterotrophic soil respirations, but further investigations are needed because of potential artefacts associated with the root exclusion technique.
ISSN: 0032-079X

bioemco-00353850
https://hal-bioemco.ccsd.cnrs.fr/bioemco-00353850
DOI : 10.1007/s11104-008-9844-5

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 Springer Verlag
Résumé : International audience
Research has been conducted within the framework of the French Initiative for Coral Reefs (IFRECOR) to assess pesticide pollution levels in the coral reef trophic webs in French Polynesia. Unexpected widespread contamination by herbicides was found in algae, fishes and macro-invertebrates located at various levels of the reef trophic web. Concentrations in organisms investigated were for the majority below the lowest observable effect level and do not pose a dietary risk to native population who subsist on these fish. However, the widespread contamination may affect the reef ecosystem in the future as coral symbiotic algae, Symbidinium sp. (Dinophyta) are particularly sensitive to photosystem II herbicides, particularly the substituted urea and triazine derivatives.
ISSN: 0944-1344

hal-01145504
https://hal.archives-ouvertes.fr/hal-01145504
DOI : 10.1007/s11356-015-4395-9

Éditeur(s) : HAL CCSD Springer Verlag
Résumé : International audience
Ants figure prominently among the worst invasive species because of their enormous ecological and economic impacts. However, it remains to be investigated which species would be behaviourally dominant when confronted with another invasive ant species, should two species be introduced in the same area. In the future, many regions might have suitable environmental conditions for several invasive ant species, as predicted under climate change scenarios. Here, we explored interactions among several highly invasive ant species, which have been shown to have overlapping suitable areas. The aim of this study was to evaluate the performance in interference competition of seven of the world's worst invasive ant species (Anoplolepis gracilipes, Paratrechina longicornis, Myrmica rubra, Linepithema humile, Lasius neglectus, Wasmannia auropunctata and Pheidole megacephala). We conducted pairwise confrontations, testing the behaviour of each species against each of the six other species (in total 21 dyadic confrontations). We used single worker confrontations and group interactions of 10 versus 10 individuals to establish a dominance hierarchy among these invasive ant species. We discovered two different behavioural strategies among these invasive ants: three species displayed evasive or indifferent behaviour when individuals or groups were confronted (A. gracilipes, Pa. longicornis, M. rubra), while the four remaining species were highly aggressive during encounters and formed a linear dominance hierarchy. These findings contrast with the widespread view that invasive ants form a homogeneous group of species displaying the `invasive syndrome', which includes generally aggressive behaviour. The dominance hierarchy among the four aggressive species may be used to predict the outcome of future competitive interactions under some circumstances. Yet, the existence of several behavioural strategies renders such a prediction less straightforward.
ISSN: 1387-3547

hal-01444816
https://hal.archives-ouvertes.fr/hal-01444816
DOI : 10.1007/s10530-015-0892-5

Éditeur(s) : HAL CCSD Elsevier Masson
Résumé : International audience
ISSN: 0168-1923

hal-01086595
https://hal-agroparistech.archives-ouvertes.fr/hal-01086595
DOI : 10.1016/j.agrformet.2009.06.020

Éditeur(s) : HAL CCSD
Résumé : absent
Actes du BRG

hal-01031523
https://hal.archives-ouvertes.fr/hal-01031523