Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
Orogenic wedges locally present chaotic tectonostratigraphic units that contain exotic blocks of various size, origin, age and lithology, embedded in a sedimentary matrix. The occurrence of ophiolitic blocks, sometimes huge, in such “mélanges” raises questions on (i) the mechanisms responsible for the incorporation of oceanic basement rocks into an accretionary wedge and (ii) the mechanisms allowing exhumation and redeposition of these exotic elements in “mélanges” during wedge growth.To address these questions, we present the results of a series of analogue experiments performed to characterize the processes and parameters responsible for accretion, exhumation and tectonosedimentary reworking of oceanic basement lithospheric fragments in an accretionary wedge.The experimental setup is designed to simulate the interaction between tectonics, erosion and sedimentation. Different configurations are applied to study the impact of various parameters, such as irregular oceanic floor due to structural inheritance, or the presence of layers with contrasted rheology that can affect deformation partitioning in the wedge (frontal accretion vs basal accretion) influencing its growth. Image correlation technique allows extracting instantaneous velocity field, and tracking of passive particles. By retrieving the particle paths determined from models, the pressure-temperature path of mélange units or elementary blocks can be discussed. The experimental results are then compared with observations from ophiolite-bearing mélanges in Taiwan (Lichi and Kenting mélanges) and Raman spectroscopy of carbonaceous material (RSCM) Thermometry data on rocks from the northern Apennines (Casanova mélange). A geological scenario is proposed following basic observations. The tectonic evolution of the retroside of doubly vergent accretionary wedges is mainly controlled by backthrusting and backfolding. The retro wedge is characterized by steep slopes that are prone to gravitational instabilities. It triggers submarine landslides inducing huge mass transfers. This erosion combined with backthrusting could favour exhumation of the ophiolitic fragments formerly accreted at the base of the wedge along the rough seafloor-sediments interface. Such an exhumed material can be reworked and deposited as debris- flows in proximal basins located at the foot of the retrowedge slope forming a tectono-sedimentary mélange. These syntectonic basins are continuously deformed and involved in prograding backthrusting-induced deformation.
ISSN: 0264-3707

hal-01395127
https://hal.archives-ouvertes.fr/hal-01395127
DOI : 10.1016/j.jog.2016.05.008

Éditeur(s) : HAL CCSD MDPI
Résumé : International audience
Canopy height is a key variable in tropical forest functioning and for regional carbon inventories. We investigate the spatial structure of the canopy height of a tropical forest, its relationship with environmental physical covariates, and the implication for tropical forest height variation mapping. Making use of high-resolution maps of LiDAR-derived Digital Canopy Model (DCM) and environmental covariates from a Digital Elevation Model (DEM) acquired over 30,000 ha of tropical forest in French Guiana, we first show that forest canopy height is spatially correlated up to 2500 m. Forest canopy height is significantly associated with environmental variables, but the degree of correlation varies strongly with pixel resolution. On the whole, bottomland forests generally have lower canopy heights than hillslope or hilltop forests. However, this global picture is very noisy at local scale likely because of the endogenous gap-phase forest dynamic processes. Forest canopy height has been predictively mapped across a pixel resolution going from 6 m to 384 m mimicking a low resolution case of 3 points·km −2. Results of canopy height mapping indicated that the error for spatial model with environment effects decrease from 8.7 m to 0.91 m, depending of the pixel resolution. Results suggest that, outside the calibration plots, the contribution of environment in shaping the global canopy height distribution is quite limited. This prevents accurate canopy height mapping based only on environmental information, and suggests that precise canopy height maps, for local management purposes, can only be obtained with direct LiDAR monitoring.
ISSN: 2072-4292

hal-01590726
https://hal-univ-guyane.archives-ouvertes.fr/hal-01590726
https://hal-univ-guyane.archives-ouvertes.fr/hal-01590726/document
https://hal-univ-guyane.archives-ouvertes.fr/hal-01590726/file/remotesensing-08-00747.pdf
DOI : 10.3390/rs8090747

Éditeur(s) : HAL CCSD Springer Verlag
Résumé : International audience
Decomposition processes in tropical semi-evergreen forests are still poorly understood. The influence of soil properties and litter quality on decomposition rate was studied in two semi-evergreen forests of Guadeloupe, a forest plantation and a secondary forest, located on different soils. Leaf litter of four tree species was enclosed in litterbags for a 14-month period. Nonlinear correlations were calculated between mass loss and the concentration of major leaf components (soluble C, N, lignin, cellulose, tannins, total soluble phenols) in order to determine the best predictor of leaf litter decomposition. Soil physico-chemical properties and ratios between some of the above-mentioned litter quality parameters were also examined as mass loss predictors. In addition, non-linear correlations were calculated between mass loss and litter quality parameters, at successive periods. Litter quality was the main determinant of litter decomposition in the studied forests. Several litter quality parameters were correlated with leaf disappearance, varying according to stages of decomposition. Between 1 month and 2.5 months, the mass loss was correlated negatively with the initial phenol content and with initial lignin:N and (lignin+phenol):N ratios. From 2.5 to 5.5 months, the mass loss was correlated negatively with the initial phenol content and positively with the initial cellulose content. At later stages of decomposition (9-14 months), the mass loss was correlated negatively with the initial tannin content. Differences in soil characteristics and fauna did not seem to be enough to affect decomposition.
ISSN: 0178-2762

hal-00499535
https://hal.archives-ouvertes.fr/hal-00499535
https://hal.archives-ouvertes.fr/hal-00499535/document
https://hal.archives-ouvertes.fr/hal-00499535/file/Article_decomposition.pdf
DOI : 10.1007/s00374-002-0467-3

Éditeur(s) : HAL CCSD
Résumé : Cette étude se situe dans la perspective de l'analyse de l'évolution post-messinienne de la marge ouest-tyrrhénienne (programme Metyss). Les pentes accidentées des reliefs granitiques au dessus de la vallée du Cedrino sont couvertes de l'amont vers l'aval par des blocs chaotiques, des accumulations de poudingues et brèches polygéniques ou monogéniques qui sont irrégulièrement cimentées et, plus localement, par des séquences gravelo-sableuses granoclassées de crues torrentielles dessinant des structures en auge. Plus bas, d'autres séquences plutôt sablo-silteuses correspondent à des éventails de chenaux anastomosés de plaine alluviale. En transgression sur ces dépôts de piedmont ou plus ou moins directement sur un socle granitique ou encore schisteux, plusieurs faciès marins composés aussi de sables granitiques relativement bien triés sont observés en bordure d'un golfe. L'ensemble des dépôts ont livré une microfaune permettant de leur attribuer un âge Pliocène supérieur et parfois proche de la limite Pliocène-Pléistocène. Ils correspondent à des environnements bathymétriques variés (littoral côtier, pro-delta, plateforme ou haut de pente) qui se succèdent verticalement sur seulement quelques dizaines de mètres. Les successions observées ne correspondent pas à des séquences transgressives classiques: en plusieurs cas, la séquence débute par un dépôt relativement profond, puis montre des oscillations variables avec des tendances très littorales, avant l'émersion finale, ailleurs la séquence marine est réduite à un seul dépôt littoral. Ces séquences dont les termes sont variables dans l'espace impliquent une activité tectonique synsédimentaire qui est attestée par plusieurs accidents et par des éboulements de falaise. Enfin, tous ces dépôts marins et continentaux sont cachetés par un ensemble de coulées basaltiques d'âge pléistocène. Les accumulations détritiques marines évoquent des corps sableux de type " Gilbert delta ". Cette étude montre que de tels édifices n'existent pas tout au moins à l'échelle de cette zone périlittorale. En effet, la géométrie des corps sableux n'est pas orientée vers la mer, mais présente des directions variables dictées par les axes gravitaires de plus grande pente, puis par des basculements post-sédimentaires d'origine tectonique. Par ailleurs, des lambeaux résiduels d'une surface d'érosion renfermant des blocs, des galets ou des nummulites oxydées de l'Éocène, ou encore des microfaunes allant de l'Oligocène jusqu'au Miocène moyen pourraient correspondre à la surface d'érosion messinienne. Cette marge est-sarde est cependant atypique dans la mesure où les premiers témoins d'une transgression n'apparaissent qu'à partir du Pliocène supérieur.
13ème Congrès Français de Sédimentologie
Dijon, France

hal-00657312
https://hal-brgm.archives-ouvertes.fr/hal-00657312

Éditeur(s) : HAL CCSD Wiley
Résumé : International audience
1. The Before-After Control-Impact Paired Series (BACIPS) design distinguishes natural spatial and temporalvariability from variation induced by an environmental impact (or intervention) of interest. BACIPS is a powerfultool to derive inferences about interventions when classic experimental approaches (e.g. which rely on spatialreplicates and random assignment of treatments) are not feasible or desirable. Previously applied BACIPSdesigns generally assume that effects are sudden, constant and long-lived: that is, that systems exhibit ‘stepchanges’in response to interventions. However, complex ecological interactions or gradual interventions maycreate delayed and/or progressive responses, potentially impeding the reliability of classic (step-change) analyses.2. We propose a novel approach, the Progressive-Change BACIPS, which generalizes and expands the scope ofBACIPS analyses.We evaluate the relative performance of this approach using both simulated and real data thatexhibit step-change, linear, asymptotic and sigmoid responses following an intervention.We quantify the statisticalpower and accuracy of the Progressive-Change BACIPS under varying initial population densities, intensityof spatial sampling, effect sizes and number of sampling dates After the intervention.3. We show that Progressive-Change BACIPS identified the correct model among the set of candidate modelsunder most conditions and led to accurate estimates of the parameters that were used to generate the simulateddata. When data were sparse, and the dynamics complex, simpler (more parsimonious) models were favouredover the more complex models that actually generated the simulated data. Application of the Progressive-Change BACIPS to existing data sets from the literature led to strong support for specific models (over alternatives)and led to more specific inferences than possible under the classic BACIPS approach.4. The Progressive-Change BACIPS proposed here is more flexible than the original BACIPS formulationbecause the data are used to inform the form of the final model, rather than having the form of the modelimposed on the data. This leads to better estimates of the effects of environmental impacts and the time-scalesover which they operate. As a result, the Progressive-Change BACIPS should be applicable to a wide range ofstudies and should help improve investigation of time-dependent effects. R code to perform Progressive-ChangeBACIPS analysis is provided.
ISSN: 2041-210X

hal-01416668
https://hal-univ-perp.archives-ouvertes.fr/hal-01416668
DOI : 10.1111/2041-210X.12655

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
New investigations in the Neogene Boudinar basin (Morocco) provide new information about the Messinian Salinity Crisis (MSC) and Zanclean reflooding in the southern part of the Alboran realm (westernmost Mediterranean). Based on a new field, sedimentological and palaeontological analyses, the age and the geometry of both the Messinian erosional surface (MES) and the overlying deposits have been determined. The MES is of late Messinian age and was emplaced in subaerial settings. In the Boudinar basin, a maximum of 200 m of Miocene sediments was eroded, including late Messinian gypsum blocks. The original geometry of the MES is preserved only when it is overlain by late Messinian continental deposits, conglomeratic alluvial fans or lacustrine marly sediments. These sediments are interpreted as indicators of the sea-level fall during the MSC. Elsewhere in the basin, the contact between late Messinian and early Pliocene deposits is a low-angle dipping, smooth surface that corresponds to the early Pliocene transgression surface that subsequently re-shaped the regressive MES. The early Pliocene deposits are characterized by: (i) their onlap onto either the basement of the Rif chain or the late Miocene deposits; (ii) lagoonal deposits at the base to offshore marls and sands at the top (earliest Pliocene; 5.33–5.04 Ma interval; foraminifer zone PL1); (iii) marine recovery occurring in the 5.32–5.26 Ma interval; and (iv) the change from lagoonal to offshore environments occurring within deposits tens of metres thick. This information indicates that at least the end of the reflooding period was progressive, not catastrophic as previously thought.
ISSN: 0037-0738

hal-01306672
https://hal.archives-ouvertes.fr/hal-01306672
DOI : 10.1016/j.sedgeo.2015.12.014

Éditeur(s) : HAL CCSD Royal Meteorological Society
Résumé : Assessing the impact/adaptation of human activities on/to climate change is a key issue, especially in the tropics that concentrate major anthropogenic dynamics such as deforestation and nearly two-thirds of the planetary rainfall. However, this task is often made tough because human activities such as agricultural dynamics are usually analysed at local or regional scale whereas climate related studies are led at large to global scales due to a lack of reliable data, especially in the tropics. In this article we argue that the increased spatial resolution of remote sensing-based rainfall estimates enables assessing the spatiotemporal variability of rainfall regimes at regional and local scales, thus allowing fine analysis of the interactions with human activities. We processed Tropical Rainfall Measuring Mission (TRMM) 3B42 daily rainfall estimates over the state of Mato Grosso (southern Brazilian Amazon) for the 1998-2012 study period in order to compute rainfall metrics such as annual rainfall and duration, onset and end dates of the rainy season based on the Anomalous Accumulation methodology (at a 0.25◦ spatial resolution). We then crossed these metrics with agricultural maps (produced at a 250m spatial resolution) and proved that the adoption of intensive agricultural practices such as double cropping systems is partly the result of a strategy to adapt practices to local climatic conditions. Finally, we discuss how such results raise important issues regarding the sustainability of the agricultural development model in the Southern Amazon.
International Journal of Climatology

halshs-00910825
https://halshs.archives-ouvertes.fr/halshs-00910825
DOI : 10.1002/joc.3863

Éditeur(s) : HAL CCSD European Geosciences Union
Résumé : International audience
During the GWADASEIS cruise (Lesser Antilles volcanic arc, February-March 2009) a very high resolution (VHR) seismic-reflection survey was performed in order to constrain Late Quaternary to Present faulting. The profiles we obtained evidence frequent "ponding" of reworked sediments in the deepest areas, similar to the deposition of Mediterranean "homogenites". These bodies are acoustically transparent (few ms t.w.t. thick) and are often deposited on the hanging walls of dominantly normal faults, at the base of scarps. Their thickness appears sufficient to compensate (i.e. bury) co-seismic scarps between successive earthquakes, resulting in a flat and horizontal sea floor through time. In a selected area (offshore Montserrat and Nevis islands), piston coring (4 to 7 m long) was dedicated to a sedimentological analysis of the most recent of these particular layers. It corresponds to non-stratified homogenous calcareous silty sand (reworked calcareous plankton and minor volcanoclastics). This layer can be up to 2 m thick, and overlies finegrained hemipelagites. The upper centimeters of the latter represent the normal RedOx water/sediment interface. 210Pb and 137Cs activities lack in the massive sands, while a normal profile of unsupported 210Pb decrease is observed in the hemipelagite below, together with a 137Cs peak correspond- ing to the Atmospheric Nuclear Experiments (1962). The RedOx level was thus capped by a recent instantaneous major sedimentary event considered as post-1970 AD; candidate seismic events to explain this sedimentary deposits are either the 16 March 1985 earthquake or the 8 October 1974 one (Mw=6.3 and Mw=7.4, respectively). This leads to consider that the syntectonic sedimentation in this area is not continuous but results from accumulation of thick homogenites deposited after the earthquakes (as observed in the following weeks after Haiti January 2010 event, McHugh et al., 2011). The existence of such deposits suggests that, in the area of study, vertical throw likely results from cumulated effects of separated earthquakes rather than from aseismic creep. Examination of VHR profiles shows that all major co-seismic offsets are recorded in the fault growth sequence and that co-seismic offsets can be precisely estimated. By using a sedimentation rate deduced from 210Pb decrease curve (0.5 mm yr−1) and taking into account minor reworking events detected in cores, we show that the Redonda system may have been responsible for five >M6 events during the last 34 000 yr. The approach presented in this work differs from fault activity analyses using displaced sets of isochronous surfaces and postulating co-seismic offsets. Combining VHR seismic imagery and coring we can decipher co-seismic vs. slow continuous displacement, and thus actually estimate the amplitude and the time distribution of major co-seismic offsets.
ISSN: 1561-8633

insu-00844581
https://hal-insu.archives-ouvertes.fr/insu-00844581
https://hal-insu.archives-ouvertes.fr/insu-00844581/document
https://hal-insu.archives-ouvertes.fr/insu-00844581/file/nhess-12-1755-2012.pdf
DOI : 10.5194/nhess-12-1755-2012

Éditeur(s) : HAL CCSD European Geosciences Union
Résumé : International audience
The seasonal climate drivers of the carbon cycle in tropical forests remain poorly known, although these forests account for more carbon assimilation and storage than any other terrestrial ecosystem. Based on a unique combination of seasonal pan-tropical data sets from 89 experimental sites (68 include aboveground wood productivity measurements and 35 litter productivity measurements), their associated canopy photosynthetic capacity (enhanced vegetation index, EVI) and climate, we ask how carbon assimilation and aboveground allocation are related to climate seasonality in tropical forests and how they interact in the seasonal carbon cycle. We found that canopy photosynthetic capacity seasonality responds positively to precipitation when rainfall is < 2000 mm yr(-1) (water-limited forests) and to radiation otherwise (light-limited forests). On the other hand, independent of climate limitations, wood productivity and litterfall are driven by seasonal variation in precipitation and evapotranspiration, respectively. Consequently, light-limited forests present an asynchronism between canopy photosynthetic capacity and wood productivity. First-order control by precipitation likely indicates a decrease in tropical forest productivity in a drier climate in water-limited forest, and in current light-limited forest with future rainfall < 2000 mm yr(-1).
ISSN: 1726-4170

hal-01557759
https://hal.univ-lorraine.fr/hal-01557759
https://hal.univ-lorraine.fr/hal-01557759/document
https://hal.univ-lorraine.fr/hal-01557759/file/bg-13-2537-2016.pdf
DOI : 10.5194/bg-13-2537-2016

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
We present new, full geomagnetic field vector results from three Neolithic ovens discovered at the archaeological site of Portonovo (Marche, Italy). The discovered structures are a rare example of very well preserved underground ovens from the Early Neolithic period. Standard thermal demagnetization procedures were used to isolate the direction of the Characteristic Remanent Magnetization acquired by the baked clay during the ovens' last firing. The corresponding archaeointensities were determined by the multi-specimen procedure (MSP-DSC) and show a clear intensity low during the Neolithic period. Both directional and intensity results are of high quality, offering the first contribution of full geomagnetic field vector data for this period in Italy. The new data are compared with other contemporaneous data from Europe and with global geomagnetic field models. Independent archaeomagnetic dating of the three ovens was also performed by means of the SCHA.DIF.14k model. The obtained results are in excellent agreement with available radiocarbon dates and confirm that all ovens belong to the Neolithic. These new data importantly enrich our knowledge of the geomagnetic field during the Neolithic period that is poorly documented by data, not only in Italy but also in the whole of Europe and show that archaeomagnetic dating can provide precise results even for prehistoric periods.
ISSN: 0012-821X

hal-01357276
https://hal.archives-ouvertes.fr/hal-01357276
DOI : 10.1016/j.epsl.2016.05.003

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
ISSN: 0378-8741

hal-01087030
https://hal-agroparistech.archives-ouvertes.fr/hal-01087030
DOI : 10.1016/j.jep.2009.07.037

Éditeur(s) : HAL CCSD Éditions de la Maison des sciences de l'homme
Résumé : International audience
For over a century, the complementary nature of fishing and farming activities in the floodplain of the Rufiji River (Tanzania) has formed the basis of the economy in its villages. Starting in the 1970s, the fishery evolved from a seasonal activity practiced on foot during flooding and using traditional traps to year-round dugout canoe operated lake fisheries using nets.The paper analyses the drivers of this change. After having rejected the simplistic technocratic hypothesis that technical innovation equals progress, the paper examines the relevance of the productivity of the different fishing techniques in the light of the evolution of the role of fisheries in the village economy. During the change-over period, the national and international economy deprives the villages of their main habitual sources of cash income. In the absence of any alternative, fisheries imposed themselves as the unique source of cash income, a function they can only fulfil if practiced year-round and this can only be achieved using canoes and nets. However, the perception of the causes of these changes in the villages is differentiated. For those who initiated the change-over, and who are now of an advanced age, the main driver of the transition to nets was the empowerment of the youth versus the elders. Such an interpretation resonates well with the economic determinants. However, it requires considering the modernisation process as a contextualised multi-sided expression of market globalisation.
Depuis plus d’un siècle, l’économie des villages de la plaine inondable du Rufiji (Tanzanie) est fondée sur la complémentarité des activités agricoles et des activités halieutiques. À partir de la fin des années 1970, les pêches traditionnelles à la nasse, pratiquées à pied saisonnièrement lors de la crue annuelle, sont supplantées par les pêches embarquées (pirogues monoxyles) au filet dans les lacs, pratiquées elles toute l’année. L’article s’interroge sur les déterminants de cette substitution.Après avoir rejeté l’hypothèse techniciste vulgaire qui voudrait que l’innovation technique soit synonyme de progrès, la pertinence du critère de productivité des différentes techniques de pêche est examinée à la lumière de l’évolution de la place des activités halieutiques dans l’économie villageoise. Il apparaît qu’à partir de cette époque, l’évolution économique nationale et internationale prive les villageois de leurs principales ressources monétaires habituelles. En l’absence de toute alternative, la pêche s’impose alors comme unique source de revenu monétaire, une fonction qu’elle ne peut remplir qu’à condition d’être pratiquée tout au long de l’année, ce que seules les techniques au filet permettent. Cependant, les représentations villageoises des causes de la généralisation de la pêche au filet sont différentes. Pour ceux d’entre eux, aujourd’hui très âgés, qui furent les pionniers de cette innovation, c’est le souci d’émancipation des cadets vis-à-vis des aînés qui aurait été le moteur de l’adoption de techniques de pêche au filet. Ce point de vue entre en résonance avec les déterminations économiques à condition de considérer le processus de modernisation comme manifestation multiforme contextualisée de la mondialisation marchande.
ISSN: 0248-6016

hal-01344410
https://hal.univ-antilles.fr/hal-01344410
https://hal.univ-antilles.fr/hal-01344410/document
https://hal.univ-antilles.fr/hal-01344410/file/Pauletal2015Version_Def.pdf

Éditeur(s) : HAL CCSD
Résumé : In this paper we introduce k-laminar graphs a new class of graphs which extends the idea of Asteroidal triple free graphs. Indeed a graph is k-laminar if it admits a diametral path that is k-dominating. This bio-inspired class of graphs was motivated by a biological application dealing with sequence similarity networks of reads (called hereafter read networks for short). We briefly develop the context of the biological application in which this graph class appeared and then we consider the relationships of this new graph class among known graph classes and then we study its recognition problem. For the recognition of k-laminar graphs, we develop polynomial algorithms when k is fixed. For k=1, our algorithm improves a Deogun and Krastch's algorithm (1999). We finish by an NP-completeness result when k is unbounded.
https://hal.inria.fr/hal-01282715

hal-01282715
https://hal.inria.fr/hal-01282715
ARXIV : 1603.01179

Éditeur(s) : HAL CCSD European Geosciences Union
Résumé : International audience
Natural disturbances are the dominant form of forest regeneration and dynamics in unmanaged tropical forests. Monitoring the size distribution of treefall gaps is important to better understand and predict the carbon budget in response to land use and other global changes. In this study, we model the size frequency distribution of natural canopy gaps with a discrete power law distribution. We use a Bayesian framework to introduce and test, using Monte Carlo Markov chain and Kuo–Mallick algorithms, the effect of local physical environment on gap size distribution. We apply our methodological framework to an original light detecting and ranging dataset in which natural forest gaps were delineated over 30 000 ha of unmanaged forest. We highlight strong links between gap size distribution and environment, primarily hydrological conditions and topography, with large gaps being more frequent on floodplains and in wind-exposed areas. In the future, we plan to apply our methodological framework on a larger scale using satellite data. Additionally , although gap size distribution variation is clearly under environmental control, variation in gap size distribution in time should be tested against climate variability.
ISSN: 1726-4170

hal-01590729
https://hal-univ-guyane.archives-ouvertes.fr/hal-01590729
https://hal-univ-guyane.archives-ouvertes.fr/hal-01590729/document
https://hal-univ-guyane.archives-ouvertes.fr/hal-01590729/file/bg-14-353-2017.pdf
DOI : 10.5194/bg-14-353-2017

Éditeur(s) : HAL CCSD Société nationale de protection de la nature
Résumé : International audience
The island of Moorea in French Polynesia is representative of a relatively well preserved small tropical oceanic island but both its terrestrial and marine ecosystems are currently under strong anthropogenic pressures. The terrestrial ecosystems are facing an increasing urbanization, and the destruction and modification of their natural habitats by cultivation and forestry plantations, accidental or intentional fires, and particularly by the invasion of alien plant and animal species. Coastal areas and reef ecosystems are threatened by shoreline artificialization, sedimentation due to soil erosion, increasing uses of marine and lagoon resources and frequency of coral bleaching events. A significant erosion of terrestrial and marine biodiversity is observed on the island since the last decades. In the context of the Land Management Plan (PGA) and Marine Area Management Plan (PGEM) recently set up in the island by local authorities, scientific surveys and inventories were made in 2006 in order to assess the status of terrestrial biodiversity (vascular plants) and marine biodiversity (reef fishes) and compare areas with different anthropogenic pressures. Studies conducted on the flora and the vegetation at low and middle elevation along altitudinal transects show that the plant invasion process is related to climatic and topographic factors, and species autoecology. The marine study aims to compare the protected areas with control areas in order to test the effectiveness of protection measures and to propose a streamlined monitoring protocol. A methodological study in both terrestrial and marine ecosystems was conducted in order to propose biodiversity indicators which are crucial for decision making in conservation and sustainable development of island biodiversity. We used Geographic Information System (GIS) as a fast and intuitive tool for mapping indicators and their variability. This methodological approach developed on the island of Moorea could be used as a model for other tropical islands
Moorea est une petite île océanique tropicale de la Polynésie française relativement bien préservée, mais dont les écosystèmes terrestres et marins sont actuellement soumis à de fortes pressions anthropiques. Le milieu terrestre est confronté à une urbanisation croissante, à la destruction ou à la modification des habitats naturels pour l’extension des cultures ou des plantations forestières, aux incendies volontaires ou accidentels, et particulièrement à l’invasion d’espèces végétales et animales introduites. Les zones côtières et les récifs coralliens sont menacés par de multiples perturbations telles que l’artificialisation des lignes de rivage, l’apport de sédiments dus à l’érosion des sols, l’augmentation des usages des ressources marines et lagonaires et de la fréquence des phénomènes de blanchissement du corail. Une érosion sensible de la biodiversité terrestre et marine de l’île est observée depuis les dernières décennies. Dans le cadre du Plan Général d’Aménagement (PGA) et du Plan de Gestion de l’Espace Maritime (PGEM) mis en place par les autorités locales, des inventaires scientifiques ont été réalisés en 2006 dans le but d’évaluer l’état de la biodiversité terrestre (plantes vasculaires) et marine (poissons récifaux) et de comparer des zones soumises à différentes perturbations. Les études réalisées sur la flore et la végétation de basse et moyenne altitude le long de transects altitudinaux montrent des processus d’invasion végétale différents en relation avec les facteurs climatiques, topographiques et autoécologiques des espèces. Les études en milieu marin visent à comparer des aires protégées à des aires témoins afin de suivre l’efficacité des mesures de gestion. La réflexion méthodologique menée parallèlement sur les deux écosystèmes a pour but d’illustrer différents indices de biodiversité nécessaires à la prise de décision en matière de conservation ou de développement durable de la biodiversité insulaire et de réaliser un état de référence pour établir un diagnostic sur l’état de la biodiversité. La représentation cartographique des indices à l’aide d’un SIG, illustrée dans cette étude avec la richesse spécifique terrestre et marine, permet une lecture intuitive et rapide de la variabilité de cet indice dont la restitution est basée sur une standardisation du nombre d’espèces. Cette approche méthodologique développée sur l’île de Moorea pourrait servir de modèle pour d’autres îles tropicales
EISSN: 2429-6422

hal-01306285
https://hal-univ-perp.archives-ouvertes.fr/hal-01306285

Éditeur(s) : HAL CCSD
Résumé : Les populations envahissantes sont généralement confrontées à un monde hétérogène où les conditions abiotiques, la distribution et la disponibilité en ressource et les densités d’espèces natives varient à la fois dans le temps et dans l’espace. Une telle hétérogénéité environmentale peut jouer un rôle décisif dans le succès d’établissement et sur la vitesse d’expansion d’une invasion. Des capacités de dispersion dans le temps et dans l’espace sont attendues pour permettre aux populations envahissantes de faire face à ces contraintes. Les Hyménoptères spécialistes des graines du genre Megastigmus (Torymidae) sont des modèles invasifs intéressants parce-qu’ils exploitent des populations d’arbres qui sont réparties en patchs discontinus dans le paysage et qui montrent des variations inter-annuelles synchronisées et de forte amplitude dans la production de graines (masting). Nous nous sommes intéressés à l’invasion récente des forêts de cèdre de l’Atlas du sud-est de la France par M. schimitscheki, qui montre de fortes propensions à : (i) la dispersion passive par le vent (dispersion spatiale), et (ii) la diapause prolongée, une forme de dormance larvaire pouvant durer de 3 à 5 années consécutives (dispersion temporelle). Dans un premier temps, nous montrons que, malgré une distribution très fragmentée de son hôte obligatoire à l’échelle du paysage, M. schimitscheki a pu envahir la quasi-totalité des cédraies de la région PACA par des évènements de dispersion à longue distance depuis sa zone d’introduction, à la faveur d’un vent régional dominant (le Mistral). Dans un second temps, nous montrons que, à l’échelle d’une population, la diapause prolongée peut constituer un refuge temporel démographique et génétique pour des cohortes soumises aux variations extrêmes de disponibilité en ressources, qui résultent du masting de leur hôte obligatoire.
Colloque de lancement du GdR ‘Invasions Biologiques’
Rennes, France

hal-01601706
https://hal.archives-ouvertes.fr/hal-01601706
PRODINRA : 404855

Éditeur(s) : HAL CCSD Elsevier
Résumé :  
absent
Ecology and management of a neotropical rainforest: lessons drawn from Paracou, a long-term experimental research site in French Guiana

ISBN : 2-84299-455-8
hal-01189534
https://hal.archives-ouvertes.fr/hal-01189534
PRODINRA : 45867

Éditeur(s) : HAL CCSD Wiley
Résumé : 1- We examined among- and within-species effects of seed mass for seedling establishment from seed to 5 years of age in a field experiment at Paracou, French Guiana. 2- Six seeds of each of eight species were weighed and planted into each of 120 plots (1 m2) throughout closed-canopy forest along 12 100-m transects in 1998. 3- We described the microhabitat of each planting site using principal components derived from measurements of light availability, soil moisture, carbon and nitrogen content, and soil phosphorus availability. Although both survival and relative growth rate (RGR) increased with increasing light availability, no other microhabitat variable significantly affected seedling performance. Nor did the magnitude of microhabitat effects on survival or RGR differ among species. 4- Larger-seeded species were more likely to survive from germination to 1 year as well as from 1 to 5 years of age. RGR for seedling height during the first year post-germination was not related to seed mass, but smaller-seeded species did grow slightly faster thereafter. Path analyses revealed that correlations between seed mass and performance were explained in part because larger seeds produced larger initial seedlings, which tended to survive better but grow more slowly. 5- We also analysed within-species effects of seed mass for the larger-seeded Eperua grandiflora and Vouacapoua americana (both Caesalpiniaceae). Larger seeds produced larger seedlings in both species, but larger seeds survived better only for Eperua. Larger seedlings grew more slowly in both species, but did not offset the early (Eperua) and later (Vouacapoua) positive direct effects of seed mass on RGR that may represent contrasting strategies for reserve deployment. 6- Our results demonstrate that seed size influences performance within and among species in part because of indirect effects of initial seedling size. However, we suggest that traits tightly correlated with seed mass at the species level, such as specific leaf area, leaf longevity and photosynthetic capacity, may also contribute to interspecific performance differences.
ISSN: 0022-0477

hal-01031089
https://hal.archives-ouvertes.fr/hal-01031089
DOI : 10.1111/j.1365-2745.2005.01041.x

Éditeur(s) : HAL CCSD
Résumé : Le projet terre-mer METYSS a pour objectif de comprendre les effets immédiats et différés de la Crise de Salinité Messinienne (CSM) ainsi que les relations tectonique et sédimentation sur la marge est-sarde. Cette marge résulte de l'ouverture de la Mer Tyrrhénienne à partir du Tortonien et jusqu'au Messinien (c. 9 à 5 Ma). Des bassins profonds existaient déjà au Messinien dans le domaine tyrrhénien, comme l'atteste l'identification, à partir des données sismiques, d'épaisses séries évaporitiques messiniennes (Gaullier et al., 2009). Le principal canyon creusé dans la marge est connecté en amont avec le golfe d'Orosei, où affleurent à terre les seuls dépôts pliocènes connus. Dans la région d'Orosei, ces dépôts correspondraient donc potentiellement au remplissage de la partie amont des incisions liées à la CSM, lors de la remise en eau de la Méditerranée, comme c'est le cas en de nombreux endroits du pourtour méditerranéen (Clauzon, 1982). Les investigations de terrain MeTySar-2010 montrent que le principal fleuve actuel, le Cedrino, suit le cours d'une paléovallée qui incise le soubassement granitique et ses altérites. Ces dépôts ont été érodés (au Messinien ?) puis remaniés lors d'une transgression marine. Les microfaunes, présentes dans les faciès marins fins, indiquent un âge Pliocène supérieur (Giresse et al., ce congrès). Cette série marine présente des pendages de l'ordre de 20 à 30 ° qui s'organisent selon une direction NNE-SSW, subparallèle aux structures tectoniques majeures associées au rifting de la marge est-sarde. Le basculement des séries pliocènes est scellé par un ensemble de coulées volcaniques dont les plus anciennes sont datées du Quaternaire ancien. La cartographie et la caractérisation des dépôts mettent en évidence un paléo-relief orienté NNE-SSW qui contrôle la répartition des unités sédimentaires. Ces résultats suggèrent que l'activité tectonique post-messinienne participe au contrôle de l'architecture et de la paléogéographie des séries pliocènes dans ce secteur. Aucune trace de dépôts marins du Pliocène Inférieur, ni de Gilbert deltas s.s. n'a été relevée à terre. La transgression observée au Pliocène supérieur sur cette bordure du bassin implique 1) une position haute de la marge au Pliocène inférieur, et 2) une forte subsidence de ce secteur de la marge au Pliocène moyen. Cette subsidence serait la conséquence de l'activité tectonique post-rift, par ailleurs mise en évidence en mer grâce à deux campagnes récentes (METYSS 1 et 3, Gaullier et al., ce congrès).
13ème Congrès Français de Sédimentologie
Dijon, France

hal-00657307
https://hal-brgm.archives-ouvertes.fr/hal-00657307

Éditeur(s) : HAL CCSD Botanical Society of America
Résumé :  
To investigate the existence of coordinated sets of seedling traits adapted to contrasting establishment conditions, we examined evolutionary convergence in seedling traits for 299 French Guianan woody plant species and the stress response in a shadehouse of species representing seed size gradients within five major cotyledon morphology types. The French Guianan woody plant community has larger seeds than other tropical forest communities and the largest proportion of hypogeal cotyledon type (59.2%) reported for tropical forests. Yet the community includes many species with intermediate size seeds that produce seedlings with different cotyledonal morphologies. A split-plot factorial design with two light levels (0.8% and 16.1% PAR) and four damage treatments (control, seed damage, leaf damage, stem damage) was used in the shadehouse experiment. Although larger-seeded species had higher survival and slower growth, these patterns were better explained by cotyledon type than by seed mass. Even larger-seeded species with foliar cotyledons grew faster than species with reserve-type cotyledons, and survival after stem grazing was five times higher in seedlings with hypogeal cotyledons than with epigeal cotyledons. Thus, to predict seedling performance using seed size, seedling morphology must also be considered.
ISSN: 0002-9122

hal-01032177
https://hal.archives-ouvertes.fr/hal-01032177
DOI : 10.3732/ajb.94.6.901