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) : The American Negro Academy The American Negro Academy
Résumé : (Funding) Digitized with funding from the Digital Library of the Caribbean grant awarded by TICFIA.
(Creation/Production Credits) Digitization performed at the U.S. Embassy in Haiti from material held at other institutions
South Carolina
Georgia
Haiti

Droits : All rights reserved by the source institution.

North America -- Trinidad and Tobago -- Queen's Park Savannah -- Trinidad -- Saint George -- Port of Spain
Caribbean

Droits : Copyright, 2005 Erich Kesse. Made available under a Creative Commons license - by-nc-sa (attribution required, non-commercial, share-alike)

Éditeur(s) : Elsevier France-editions Scientifiques Medicales Elsevier
Résumé : The essential characteristics of the vegetation dynamics of tropical Africa remain only partially known. This study assesses the succession of vegetation-types over Central Africa during the last two glacial/interglacial cycles. Analysis of core KZai 02, which contains pollen from the Zaire River watershed (latitudes 9°N-13°S), allows the investigation of long-term patterns of plant ecosystem development and their climatic causes. Core KZai 02 (18.20 m long) was recovered from 6°24.20′S/9°54.10′E in the uppermost axial edifice of the Zaire deep sea fan. The chronology of this sedimentary archive was established using nannofossils and correlations of pollen and total organic carbon signals with the nearby core GeoB1008. The pollen record indicates that: (i) glacials (MIS 6, 4, 2) are marked by the development of afromontane (Podocarpus) forest at high altitudes when central basin lowlands were occupied by Cyperaceae marshes and savannah; (ii) during interglacials (MIS 1, 5) lowland forests were developed, marked by the successive expansion of pioneer, warm-temperate, rain forests, and mangrove indicating sea-level rise; (iii) glacial-interglacial transitions (MIS 6/5, 2/1) display similar vegetation dynamics. The strong evidence of afromontane forest and the opening of the vegetation during glacials suggest a reduced latitudinal distribution of rainfall by the strengthening of the trade wind system. West African monsoon systems were enhanced during interglacials, allowing the progressive development of lowland forests. The development of rain and pioneer forests during glacial Heinrich stadials suggests an enhancement of water availability in tropical Africa associated with these high latitude events. However, no augmentation of wind activity, described by previous studies, is evidenced by our pollen record. Similar vegetation successions during glacial/interglacial transitions suggest the diachronous and stepped intervention of CO2 (emphasizing the influence of temperature on plant ecosystems) and water availability.
Geobios (0016-6995) (Elsevier France-editions Scientifiques Medicales Elsevier), 2014-07 , Vol. 47 , N. 4 , P. 183-198

Droits : 2014 Elsevier Masson SAS. All rights reserved.
http://archimer.ifremer.fr/doc/00199/31031/29436.pdf
DOI:10.1016/j.geobios.2014.06.002
http://archimer.ifremer.fr/doc/00199/31031/

Éditeur(s) : HAL CCSD Elsevier
Résumé : URL de l'article : http://www.sciencedirect.com/science/article/B6WPN-4XY3KDK-2/2/fd8508af63d82e29b4f9829c65194e26
The impact of climatic changes that occurred during the last glacial maximum and the Holocene on vegetation changes in the Amazon Basin and the Guiana Shield are still widely debated. The aim of our study was to investigate whether major changes in vegetation (i.e. transitions between rainforests and C4 savannas) occurred in northern French Guiana during the Holocene. We measured variations in the δ13C of soil organic matter at eight sites now occupied by forest or savannah. The forest sites were selected to cover two regions (forest refugia and peneplains) which are thought to have experienced different intensities of disturbance during the latest Pleistocene and the Holocene. We found that none of the forest sites underwent major disturbances during the Holocene, i.e. they were not replaced by C4 savannahs or C4 forest savannahs for long periods. Our results thus suggest that tropical rainforests in northern French Guiana were resilient to drier climatic conditions during the Holocene. Nevertheless, geographical and vertical variations in the 13C of SOM were compatible with minor changes in vegetation, variations in soil processes or in soil physical properties.
ISSN: 0033-5894

halshs-00551758
https://halshs.archives-ouvertes.fr/halshs-00551758
DOI : 10.1016/j.yqres.2009.11.007

Éditeur(s) : HAL CCSD Public Library of Science
Résumé : International audience
Domestication can influence many functional traits in plants, from overall life-history and growth form to wood density and cell wall ultrastructure. Such changes can increase fitness of the domesticate in agricultural environments but may negatively affect survival in the wild. We studied effects of domestication on stem biomechanics in manioc by comparing domesticated and ancestral wild taxa from two different regions of greater Amazonia. We compared mechanical properties, tissue organisation and wood characteristics including microfibril angles in both wild and domesticated plants, each growing in two different habitats (forest or savannah) and varying in growth form (shrub or liana). Wild taxa grew as shrubs in open savannah but as lianas in overgrown and forested habitats. Growth form plasticity was retained in domesticated manioc. However, stems of the domesticate showed brittle failure. Wild plants differed in mechanical architecture between shrub and liana phenotypes, a difference that diminished between shrubs and lianas of the domesticate. Stems of wild plants were generally stiffer, failed at higher bending stresses and were less prone to brittle fracture compared with shrub and liana phenotypes of the domesticate. Biomechanical differences between stems of wild and domesticated plants were mainly due to changes in wood density and cellulose microfibril angle rather than changes in secondary growth or tissue geometry. Domestication did not significantly modify "large-scale" trait development or growth form plasticity, since both wild and domesticated manioc can develop as shrubs or lianas. However, "finer-scale" developmental traits crucial to mechanical stability and thus ecological success of the plant were significantly modified. This profoundly influenced the likelihood of brittle failure, particularly in long climbing stems, thereby also influencing the survival of the domesticate in natural situations vulnerable to mechanical perturbation. We discuss the different selective pressures that could explain evolutionary modifications of stem biomechanical properties under domestication in manioc.
PLoS ONE

halsde-00917926
https://hal.archives-ouvertes.fr/halsde-00917926
https://hal.archives-ouvertes.fr/halsde-00917926/document
DOI : 10.1371/journal.pone.0074727

Éditeur(s) : HAL CCSD
Résumé : International audience
Background Mycobacterium ulcerans infection is the third most common mycobacterial disease in the world after tuberculosis and leprosy. To date, transmission pathways from its environmental reservoir to humans are still unknown. In South America, French Guiana has the highest reported number of M ulcerans infections across the continent. This empirical study aimed to characterise the epidemiology of M ulcerans infection in French Guiana between 1969 and 2013.MethodsData were collected prospectively mainly by two dermatologists at Cayenne Hospital’s dermatologydepartment between Jan 1, 1969, and Dec 31, 2013, for age, date of diagnosis, sex, residence, location of the lesion,type of lesion, associated symptoms, and diagnostic method (smear, culture, PCR, or histology) for all confirmed andsuspected cases of M ulcerans. We obtained population data from censuses. We calculated mean M ulcerans infectionincidences, presented as the number of cases per 100 000 person-years.Findings 245 patients with M ulcerans infections were reported at Cayenne Hospital’s dermatology department duringthe study period. M ulcerans infection incidence decreased over time, from 6·07 infections per 100 000 person-years(95% CI 4·46–7·67) in 1969–83 to 4·77 infections per 100 000 person-years (3·75–5·79) in 1984–98 and to3·49 infections per 100 000 person-years (2·83–4·16) in 1999–2013. The proportion of children with infections alsodeclined with time, from 42 (76%) of 55 patients in 1969–83 to 26 (31%) of 84 in 1984–98 and to 22 (21%) of 106 in1999–2013. Most cases occurred in coastal areas surrounded by marshy savannah (incidence of 21·08 per100 000 person-years in Sinnamary and 21·18 per 100 000 person-years in Mana). Lesions mainly affected limbs (lowerlimbs 161 [66%] patients; upper limbs 60 [24%] patients). We diagnosed no bone infections.Interpretation The decrease of M ulcerans infection incidence and the proportion of children with infections over a45 year period in this ultra-peripheral French territory might have been mostly driven by improving living conditions,prophylactic recommendations, and access to health care.
The Lancet Planetary Health

inserm-01545603
http://www.hal.inserm.fr/inserm-01545603
http://www.hal.inserm.fr/inserm-01545603/document
http://www.hal.inserm.fr/inserm-01545603/file/2017%2C%20Douine%20-%20Mycobacterium%20ulcerans%20infection%20%28Buruli%20ulcer%29.pdf
http://www.hal.inserm.fr/inserm-01545603/file/Comments.pdf

Éditeur(s) : HAL CCSD Wiley
Résumé : The intensification of the hydrological cycle, with an observed and modeled increase in drought incidence and severity, underscores the need to quantify drought effects on carbon cycling and the terrestrial sink. FLUXNET, a global network of eddy covariance towers, provides dense data streams of meteorological data, and through flux partitioning and gap filling algorithms, estimates of net ecosystem productivity (FNEP), gross ecosystem productivity (P), and ecosystem respiration (R). We analyzed the functional relationship of these three carbon fluxes relative to evaporative fraction (EF), an index of drought and site water status, using monthly data records from 238 micrometeorological tower sites distributed globally across 11 biomes. The analysis was based on relative anomalies of both EF and carbon fluxes and focused on drought episodes by biome and climatic season. Globally P was ≈50% more sensitive to a drought event than R. Network-wide drought-induced decreases in carbon flux averaged −16.6 and −9.3 g C m−2 month−1 for P and R, i.e., drought events induced a net decline in the terrestrial sink. However, in evergreen forests and wetlands drought was coincident with an increase in P or R during parts of the growing season. The most robust relationships between carbon flux and EF occurred during climatic spring for FNEP and in climatic summer for P and R. Upscaling flux sensitivities to a global map showed that spatial patterns for all three carbon fluxes were linked to the distribution of croplands. Agricultural areas exhibited the highest sensitivity whereas the tropical region had minimal sensitivity to drought. Combining gridded flux sensitivities with their uncertainties and the spatial grid of FLUXNET revealed that a more robust quantification of carbon flux response to drought requires additional towers in all biomes of Africa and Asia as well as in the cropland, shrubland, savannah, and wetland biomes globally.
ISSN: 1354-1013

hal-01032076
https://hal.archives-ouvertes.fr/hal-01032076
DOI : 10.1111/j.1365-2486.2009.01991.x