Éditeur(s) : HAL CCSD Elsevier Masson
Résumé : 14 pages
International audience
Central Africa hosts the world's second largest tropical forest after the Amazonian basin. However, as compared to its Amazonian counterpart, the Central Africa forests receive much less rain (∼1500 mm/year in mean spread over two rainy seasons in March-May and September-November, and two dry seasons). They also experience a slower deforestation rate, so that the main threat for the next decades might come from climate variations. Nonetheless, their response to the annual cycle of solar radiation and rainfall/clouds is still poorly known. Analysing high resolution remote sensing data of Enhanced Vegetation Index, rainfall, cloudiness, and solar radiation for a target region located between 0 and 5°N and 12–19°E, we explore the climatic drivers of the forests greenness mean annual cycle. Three main points emerge; first, the diurnal cycle is a key-scale for understanding the mean annual cycles of rainfall and incoming solar radiation at surface, then how climate shapes the greenness mean annual evolution; second, neither the two dry seasons nor the two rainy seasons resemble each other in terms of cloud cover, solar radiation and rainfall, and their links with greenness levels; third, whereas the first rainy season (March-May) appears optimal for greenness especially because of favorable light conditions, water availability is the main controlling factor during the main dry season and at the start of the first vegetative season (February). Regarding the little dry season (mid-June-mid-August) and the second rainy season (September-October), light availability might be the main limiting factor. These findings pave the way for further studies of the climate interannual variability and change impacts on the Central Africa forests, taking into account time-scale interactions.
ISSN: 0168-1923

hal-01309565
https://hal.archives-ouvertes.fr/hal-01309565
DOI : 10.1016/j.agrformet.2016.04.005

Résumé : Cette these etudie les effets de la conversion de la foret tropicale en parcelles agricoles, sur les emissions de n2o par les sols. Ce travail est realise a l’echelle du cycle cultural sur le dispositif experimental de combi (littoral guyanais), a l’aide de mesures in situ et de simulations (modele noe) des flux de n2o. La foret tropicale a ete comparee a des parcelles de foret converties en terres agricoles par la methode ‘chop-and-mulch’. La methode de deforestation ‘chop-and-mulch’ associe coupe mecanique de la vegetation, broyage puis enfouissement des residus forestiers dans le sol. Les terres agricoles etaient soient des parcelles de prairie non paturee soient des parcelles cultivees (maïs fertilise/soja) conduites en semis conventionnel (semis apres travail du sol, sans plante de couverture) ou en semis direct (sans travail du sol, avec plantes de couverture).Les principaux resultats de cette etude sont : le sol de la foret tropicale de combi est un faible emetteur de n2o ; la conversion par la methode ‘chop-and-mulch’ de cette foret en prairie ne conduit pas a une augmentation significative des emissions de n2o entre le 19eme et le 31eme mois suivant la conversion ; la conversion de la foret en parcelles cultivees induit une augmentation significative des emissions de n2o due a la fertilisation et a la modification des parametres edaphiques (densite apparente, temperature, humidite volumique) ; la technique sans travail du sol n’engendre pas de flux de n2o significativement plus eleves que la technique avec travail du sol ; l’introduction du phenomene d’hysterese hydrique dans le modele noe presente un reel potentiel pour l’estimation des emissions de n2o in situ.
This study investigates the effects of the conversion of tropical forest to cultivation on soil n2o emissions. The study was carried out over a complete crop cycle at the experimental site combi (french guianese coast). Nitrous oxide fluxes were obtained in the field and by conducting simulations with the noe model. Undisturbed tropical rainforest was compared to rainforest that had been converted to agricultural land using the ‘chop-and-mulch’ method. The ‘chop-and-mulch’ method is a fire-free method used for vegetation clearing combining the mechanical felling of trees with the mulching of small vegetation. Agricultural land included either mowed grassland or soybean/fertilised maize crop rotation. For croplands the two cultivation practices employed were: conventional seeding (using an offset disc harrow, without cover plants) or direct seeding (no till, with cover plants).The main results of this study are: rainforest soil at combi produced low n2o emissions; rainforest converted to mowed grassland using the 'chop-and-mulch’ method did not lead to a significant increase in n2o emissions between the 19th and 31st months after conversion; the conversion of rainforest to croplands induced a significant increase in soil n2o emissions due to the application of fertiliser and the modification of soil parameters (bulk density, temperature, volumetric moisture); n2o emissions from agricultural practices with no-till were no higher than those produced by conventional agricultural practices using an offset disc harrow; and, the introduction of an hydric hysteresis into the noe model constitutes a promising improvement to estimate in situ n2o emissions.

http://www.theses.fr/2013AGUY0610/document

Éditeur(s) : HAL CCSD
Résumé : Couche G ou couche tertiaire : quel nom pour la couche interne des fibres du bois de tension ?. 11es Journées du Réseau Français des Parois
11es Journées du Réseau Français des Parois
Orléans, France

hal-01603178
https://hal.archives-ouvertes.fr/hal-01603178
PRODINRA : 398652

Éditeur(s) : HAL CCSD Wiley
Résumé :  
A digital land cover map of South America has been produced using remotely sensed satellite data acquired between 1995 and the year 2000. The mapping scale is defined by the 1 km spatial resolution of the map grid-cell. In order to realize the product, different sources of satellite data were used, each source providing either a particular parameter of land cover characteristic required by the legend, or mapping a particular land cover class. The map legend is designed both to fit requirements for regional climate modelling and for studies on land cover change. The legend is also compatible with a wider, global, land cover mapping exercise, which seeks to characterize the world's land surface for the year 2000. As a first step, the humid forest domain has been validated using a sample of high-resolution satellite images. The map demonstrates both the major incursions of agriculture into the remaining forest domains and the extensive areas of agriculture, which now dominate South America's grasslands.
ISSN: 1354-1013

hal-01032088
https://hal.archives-ouvertes.fr/hal-01032088
DOI : 10.1111/j.1529-8817.2003.00774.x

Éditeur(s) : IEEE
Résumé : Two approaches of ocean color data merging were tested and compared in the North and Equatorial Atlantic Basin: the weighted averaging and the objective analysis. The datasets used were the daily level-3 binned data of chlorophyll-a from the Sea-viewing Wide Field-of-view Sensor (SeaWiFS) and Moderate Resolution Imaging Spectroradiometer on the Aqua satellite over the year 2003, which is the first common full year of operation. Since they represent input for both approaches, matchups between the satellite and the in situ data from the SeaWiFS Bio-optical Archive and Storage System and the Atlantic Meridional Transect were first studied to compute a spatial map of the root mean-square error and of the bias. Because of the log distribution of the chlorophyll fields, each approach was applied to untransformed and log-transformed values. The application of the weighted averaging to log-transformed values does not show significant differences in comparison to its application to untransformed values. This is not the case, however, for the objective analysis that gives better results when applied to logtransformed values. Both approaches give combined chlorophyll data of equivalent quality, although the objective analysis could be improved with a better statistical characterization of noise and signal covariance. The main advantage of the objective analysis is its ability to interpolate in space (and time) by taking into account the characteristic scales of chlorophyll-a. As a result, the spatial coverage of the combined data is at least twice as large in the case of objective analysis than weighted averaging. OCR NOT CONTROLLED
IEEE (0196-2892) (IEEE), 2006-11 , Vol. 44 , N. 11 , P. 3436-3451

Droits : 2006 IEEE
http://archimer.ifremer.fr/doc/2006/publication-3631.pdf
DOI:10.1109/TGRS.2006.878441
http://archimer.ifremer.fr/doc/00000/3631/

Éditeur(s) : HAL CCSD Springer Verlag/EDP Sciences
Résumé : International audience
Context : Functional - structural models (FSM) of tree growth have great potential in forestry, but their development, calibration and validation are hampered by the difficulty of collecting experimental data at organ scale for adult trees. Due to their simple architecture and morphological properties, " model plants " such as Cecropia sciadophylla are of great interest to validate new models and methodologies, since exhaustive descriptions of their plant structure and mass partitioning can be gathered. * Aims : Our objective was to develop a model-based approach to analysing the influence of environmental conditions on the dynamics of trophic competition within C. sciadophylla trees. * Methods : We defined an integrated environmental factor that includes meteorological medium-frequency variations and a relative index representing the local site conditions for each plant. This index is estimated based on model inversion of the GreenLab FSM using data from 11 trees for model calibration and 7 trees for model evaluation. * Results : The resulting model explained the dynamics of biomass allocation to different organs during the plant growth, according to the environmental pressure they experienced. * Perspectives : By linking the integrated environmental factor to a competition index, an extension of the model to the population level could be considered.
ISSN: 1286-4560

hal-00780347
https://hal-ecp.archives-ouvertes.fr/hal-00780347
https://hal-ecp.archives-ouvertes.fr/hal-00780347/document
https://hal-ecp.archives-ouvertes.fr/hal-00780347/file/Letort2011AFS.pdf
DOI : 10.1007/s13595-011-0131-x

Éditeur(s) : HAL CCSD Oxford University Press (OUP)
Résumé : Publication Inra prise en compte dans l'analyse bibliométrique des publications scientifiques mondiales sur les Fruits, les Légumes et la Pomme de terre. Période 2000-2012. http://prodinra.inra.fr/record/256699
Background and Aims Plastic tree-shelters are increasingly used to protect tree seedlings against browsing animals and herbicide drifts. The biomass allocation in young seedlings of deciduous trees is highly disturbed by common plastic tree-shelters, resulting in poor root systems and reduced diameter growth of the trunk. The shelters have been improved by creating chimney-effect ventilation with holes drilled at the bottom, resulting in stimulated trunk diameter growth, but the root deficit has remained unchanged. An experiment was set up to elucidate the mechanisms behind the poor root growth of sheltered Prunus avium trees. Methods Tree seedlings were grown either in natural windy conditions or in tree-shelters. Mechanical wind stimuli were suppressed in ten unsheltered trees by staking. Mechanical stimuli (bending) of the stem were applied in ten sheltered trees using an original mechanical device. Key Results Sheltered trees suffered from poor root growth, but sheltered bent trees largely recovered, showing that mechano-sensing is an important mechanism governing C allocation and the shoot-root balance. The use of a few artificial mechanical stimuli increased the biomass allocation towards the roots, as did natural wind sway. It was demonstrated that there was an acclimation of plants to the imposed strain. Conclusions This study suggests that if mechanical stimuli are used to control plant growth, they should be applied at low frequency in order to be most effective. The impact on the functional equilibrium hypothesis that is used in many tree growth models is discussed. The consequence of the lack of mechanical stimuli should be incorporated in tree growth models when applied to environments protected from the wind (e.g. greenhouses, dense forests).
ISSN: 0305-7364

hal-01032056
https://hal.archives-ouvertes.fr/hal-01032056
DOI : 10.1093/aob/mcn054

Éditeur(s) : HAL CCSD Oxford University Press
Résumé : International audience
It was recently reported that the sizes of many mRNAs change when budding yeast cells exit mitosis and enter the meiotic differentiation pathway. These differences were attributed to length variations of their untranslated regions. The function of UTRs in protein translation is well established. However, the mechanism controlling the expression of distinct transcript isoforms during mitotic growth and meiotic development is unknown. In this study, we order developmentally regulated transcript isoforms according to their expression at specific stages during meiosis and gametogenesis, as compared to vegetative growth and starvation. We employ regulatory motif prediction, in vivo protein-DNA binding assays, genetic analyses and monitoring of epigenetic amino acid modification patterns to identify a novel role for Rpd3 and Ume6, two components of a histone deacetylase complex already known to repress early meiosis-specific genes in dividing cells, in mitotic repression of meiosis-specific transcript isoforms. Our findings classify developmental stage-specific early, middle and late meiotic transcript isoforms, and they point to a novel HDAC-dependent control mechanism for flexible transcript architecture during cell growth and differentiation. Since Rpd3 is highly conserved and ubiquitously expressed in many tissues, our results are likely relevant for development and disease in higher eukaryotes.
ISSN: 0305-1048

Droits : http://creativecommons.org/licenses/by/
hal-01122128
https://hal-univ-rennes1.archives-ouvertes.fr/hal-01122128
https://hal-univ-rennes1.archives-ouvertes.fr/hal-01122128/document
https://hal-univ-rennes1.archives-ouvertes.fr/hal-01122128/file/The%20conserved%20histone%20deacetylase.pdf
DOI : 10.1093/nar/gku1185

Éditeur(s) : HAL CCSD Wiley-Blackwell
Résumé : International audience
1. Our understanding of the contribution of interspecific interactions to functional diversity in nature lags behind our knowledge of spatial and temporal patterns. Although two-species mutualisms are found in all types of ecosystems, the study of their ecological influences on other community members has mostly been limited to third species, while their influence on entire communities remains largely unexplored. 2. We hypothesized that mutualistic interactions between two respective ant species and an epiphyte mediate the biological traits composition of entire invertebrate communities that use the same host plant, thereby affecting food webs and functional diversity at the community level. 3. Aechmea mertensii (Bromeliaceae) is both a phytotelm ('plant-held water') and an ant-garden epiphyte. We sampled 111 bromeliads (111 aquatic invertebrate communities) associated with either the ant Pachycondyla goeldii or Camponotus femoratus. The relationships between ants, bromeliads and invertebrate abundance data were examined using a redundancy analysis. Biological traits information for invertebrates was structured using a fuzzy-coding technique, and a co-inertia analysis between traits and abundance data was used to interpret functional differences in bromeliad ecosystems. 4. The vegetative traits of A. mertensii depended on seed dispersion by C. femoratus and P. goeldii along a gradient of local conditions. The ant partner selected sets of invertebrates with traits that were best adapted to the bromeliads' morphology, and so the composition of the biological traits of invertebrate phytotelm communities depends on the identity of the ant partner. Biological traits suggest a bottom-up control of community structure in C. fenaoratus-associated phytotelmata and a greater structuring role for predatory invertebrates in P. goeldii-associated plants. 5. This study presents new information showing that two-species mutualisms affect the functional diversity of a much wider range of organisms. Most biological systems form complex networks where nodes (e.g. species) are more or less closely linked to each other, either directly or indirectly, through intermediate nodes. Our observations provide community-level information about biological interactions and functional diversity, and perspectives for further observations intended to examine whether large-scale changes in interacting species/community structure over broad geographical and anthropogenic gradients affect ecosystem functions.
Functional Ecology

hal-01096909
https://hal-agroparistech.archives-ouvertes.fr/hal-01096909
DOI : 10.1111/j.1365-2435-2011.01863.x

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
This paper examines the thermal properties of cement composites reinforced with vegetable bagasse fibres (1.5% and 3% wrtc). Thermal properties have been correlated to macroscopic density and porosity in order to estimate thermal conductivity of fibres using a calculation inspired from the Maxwell-Eucken modelling. Experimental investigations reveal that adding retified bagasse fibres reduces composites thermal conductivity and yields a weaker specific heat in comparison with composites made with alkaline bagasse fibres. Moreover, the more the fibres, the lighter the specimen; lower its thermal conductivity and lower its specific heat. Thermal conductivity of alkaline fibres is lower than retified fibres one.
ISSN: 1359-835X

hal-00809831
https://hal.univ-antilles.fr/hal-00809831
DOI : 10.1016/j.compositesa.2010.01.002

Résumé : Les stocks des éléments dans les sols, et en particulier ceux du carbone, sont en constante évolution sous l’effet de facteurs naturels (climat, végétation, teneurs en argiles, etc.) et anthropiques (usages des sols, etc.). Notre objectif est donc, (i) de mieux comprendre les relations entre type de sol, système de culture et quantité de carbone stockée, (ii) d’étudier les conséquences des changements d’usage et de gestion des terres sur les formes de matière organique dans les sols et (iii) de préciser le rôle de la matière organique sur les propriétés physiques des sols.Des situations agro-pédologiques représentatives des trois grands modèles minéralogiques des sols tropicaux (Sols à allophanes (argiles non cristallisées), Sols à argiles 1/1 et Sols à argiles 2/1) et présentant des systèmes culturaux de différents niveaux d’intensification (monocultures intensives destinées à l’exportation, systèmes paysans faiblement intensifiés, etc.) ont ainsi été sélectionnées sur les sols de Martinique. Par ailleurs, afin de limiter les effets des usages antérieurs des parcelles, nous avons généralement choisi des situations culturales âgées au minimum de 3 ans.L’analyse des stocks de carbone des différentes parcelles fait apparaître des comportements différents : dans les sols à allophanes, il y a un effet de la minéralogie sur la stabilisation des matières organiques ; dans les sols à argiles cristallisées, il existe une corrélation entre la teneur en carbone (ou le stock organique) et la texture (ou teneur en éléments fins), aussi bien pour les situations non cultivées que pour les situations sous cultures. L’amplitude des variations (diminution) des stocks en carbone observées sous l’effet de différents modes de gestion des sols, dépend elle aussi de la texture : dans les sols sableux, la potentialité de séquestration du carbone est faible ou nulle, en revanche, les potentialités de stockage du carbone sont plus fortes dans les sols argileux.L’estimation des stocks totaux de carbone à l’échelle de la Martinique, pour un mètre de profondeur et pour une situation moyenne entre les cartes d’usage des terres de 1969/1970 et 1979/1980, s’élèvent à 11,859 Mt de C calculés pour 95,8% de la surface.La distribution de la matière organique du sol varie avec la texture du sol : dans les sols sableux, à faibles teneurs en matière organique, les matières organiques sont principalement associées aux fractions sableuses ; dans les sols argileux, plus riches en matières organiques, 50 à 60 % de la matière organique sont associées à la fraction argileuse. De même, la dynamique de la matière organique dépend également de la texture du sol : dans les sols sableux, les variations des stocks organiques sont essentiellement dues à la perte ou à l’accumulation en carbone de la fraction sableuse ; dans les sols argileux, la fraction argileuse participe de manière prépondérante aux variations des stocks organiques de ces sols lors de leur mise en culture ou en prairie ; les sols sablo-argileux ont un comportement intermédiaire entre ces deux pôles.La stabilité structurale varie avec la minéralogie. Les andosols (ou ALL) présentent un haut degré d’agrégation et de stabilité, du à la présence d’allophanes et à leur association particulière avec les composés organiques. Dans les sols à argiles cristallisées, la stabilité de l’agrégation est plus élevée dans les sols à argiles 1/1 (ou LAC) ; les valeurs les plus faibles sont généralement observées dans les parcelles sur sols à argiles 2/1 (ou HAC). En outre, la mise en culture se traduit généralement par une diminution de la stabilité de l’agrégation.L’intensification des cultures (labours fréquents, faibles restitutions de matière organique au sol, etc.) accentue la perte de la stabilité de l’agrégation provoquée par la mise en culture, en particulier dans les parcelles sur sols à argiles 2/1 (ou HAC).
Soils elements stocks, and particularly those of carbon, are in constant evolution under natural factors effect (climate, vegetation, clays content, etc) and anthropic factors effect (soils uses, etc). Our objective is thus, (i) to better understand the relations between soil, farming system and stored carbon quantity, (ii) to study the consequences of soils uses changes and of soils managements changes on organic matter shapes in soil and (iii) to specify organic matter role on soil properties physics.Representative agri-pedological situations of the three great mineralogical models of tropical soils (allophonic soils (not crystallized clays), 1:1 clay soils and 2:1 clay soils) and presenting agricultural systems of various levels of intensification (intensive monocultures intended for export, slightly intensified farming systems, etc) were thus selected in the soils of Martinique. In addition, to limit the effects of their former uses, we generally chose to the minimum 3 years old farming situations.The analysis of the various lands carbon stocks reveals different behaviors: in allophonic soils, a correlation exists between carbon content (or organic stock) and texture (or fine elements content), as well for not cultivated as for cultivated situations. Variations ranges (reduction) of carbon stocks observed under various management soils systems effect, also depends on texture: in sandy soils, carbon sequestration potentiality is low or null, on the other hand, carbon storage potentialities are higher in clay soils.The estimation of total carbon stocks on the scale of Martinique, for one meter of depth and for and average situation between the use soils charts of 1969/70 and 1979/80, rises to 11,859 Mt of C calculated for 95,8% of the surface.Soil organic matter distribution varies with soil texture: in sandy soils, with low contents of organic matter, organics matters are mainly associated with the sandy fractions; in clay soils, richer in organic matters, 50 to 60% of the organic matters are associated with the argillaceous fraction. In the same way, the organic matter dynamics also depends on soil texture: in sandy soils, organic stocks variations are primarily due to carbon loss or accumulation of the sandy fraction; in clay soils, the argillaceous fraction takes part in a dominating way in organic stocks variations of these soils at the time of their setting in culture or meadow; the sand-clay soils have an intermediate behavior between these two poles.Structural stability varies with mineralogy. Andosols (or ALL) present a high degree of aggregation and stability, due to the presence of allophones and their particular association with the organics compounds. In crystallized clay soils, aggregation stability is higher in 1:1 clay soils (or LAC); the lowest values are generally observed in the lands on 2:1 clay soils (or HAC). Moreover, culture setting generally results in aggregation stability reduction.Cultures intensification (frequent ploughings, low organic matter restitutions to the soil, etc) accentuates aggregation stability loss caused by culture setting, particularly in lands on 2:1 clay soils (or HAC).

http://www.theses.fr/2012AGUY0513/document

Éditeur(s) : HAL CCSD Springer Verlag
Résumé : International audience
Trophobiotic associations between Caternaultiella rugosa (Heteroptera; Plataspidae) and two ant species, Camponotus brutus (Formicidae) and Myrmicaria opaciventris (Myrmicinae), were recorded at the base of the trunks of Bridelia micrantha (Euphorbiaceae). The bug colonies were generally sheltered in pavilions built by the ants, but during periods of proliferation, part of the colonies developed outside the pavilions. We examined the protective activity of the two associated ant species against an encyrtid parasitoid wasp that parasitized egg masses of the bug. Egg masses situated outside the pavilions were significantly less parasitized on trees occupied by either ant species than on experimental trees where ants were excluded by a sticky barrier. Egg masses were significantly less parasitized on trees occupied by C. brutus than on those occupied by M. opaciventris, both inside and outside the pavilions. Moreover, they were less parasitized inside than outside the pavilions when protected by C. brutus. Inside the pavilions, parental care of the egg masses and first-instar nymphs was abandoned to the ants. In contrast, outside the pavilions, the females of C. rugosa guarded egg masses and clusters of first-instar nymphs. Furthermore, adults and last-instar nymphs grouped around and above first-instar nymphs, forming a protective shield. These groups formed and disintegrated daily, according to the attending ant's rhythm of activity
ISSN: 0029-8549

hal-01202757
https://hal.archives-ouvertes.fr/hal-01202757
DOI : 10.1007/s004420000479

Éditeur(s) : HAL CCSD Ecoscience
Résumé : International audience
Hymenoptera pollinators and figs (ripe or unripe) of Ficus vallis-choudae are protected from the predatory activity of myrmicine ants (Atopomyrmex mocquerisi; Crematogaster clariventris; Cremato gaster sp.) by other ants (Camponotus acvapimensis and Camponotus brutus; Formicinae) who attack neither unripe figs nor the pollinator. On trees occupied by Atopomyrmex and Crematogaster, and on trees invaded by columns of workers after recruitment by scouts, the predatory activity begins when the fig wasps emerge. Then, the ants attack unripe figs (asynchronization in ripeness), destroying whole figs of certain trees. The male function of the trees through pollen dispersal by fig wasps is, therefore, severely reduced, while the female function (seed dispersal) is affected only on unripe figs before fig wasp emergence. We recorded 13 ant species on the 73 Ficus vallis-choudae of the Batchenga savanna (Cameroon) studied, but only the five previously cited species were able to occupy an entire fig tree. The three Myrmicinae which have a status of dominant (large colony size; strong territoriality vis-à-vis other dominant species; can tolerate non-dominant species) tended scale insects. Both Camponotus species (and the eight other ant species) are non-dominant (small colony size), but are able to occupy a whole tree under certain conditions (here, when they tend the tettigometrid Hilda undata) and to be territorial. Their status corresponds, therefore, to that of sub-dominant. Tests of aggressiveness showed that each ant species is aggressive towards alien conspecifics. C. brutus individuals were tolerated on fig trees occupied by Atopomyrmex mocquerisi or by Crematogaster clariventris, while workers of both latter species, who do not tolerate one another, were not tolerated on fig trees occupied by C. brutus. In this situation, the cost-benefit for the trees depends on the ant species that occupies their foliage; C. brutus, when tending tettigometrids, is advantageous. There is, therefore, an indirect influence of the tettigometrids on the production of fig pollinating wasps and seeds. Chez Ficus vallis-choudae, les figues, matures ou non, et leurs hyménoptères pollinisateurs sont protégés de l'activité prédatice de la part de trois espèces de fourmis Myrmicinae (Atopomyrmex mocquerisi; Crematogaster clariventris; Crematogaster sp.) par d'autres fourmis (Camponotus acvapimensis et Camponotus brutus; Formicinae) qui, elles, ne s'attaquent ni aux figues non matures, ni aux pollinisateurs. L'action prédatrice des Atopomyrmex et des Crematogaster débute à l'émergence des pollinisateurs et sétend sur des figuiers qu'elles n'occupent pas grâce à la formation de colonnes recrutées par des ouvrières éclaireuses. Ensuite, elles attaquent les figues moins mûres (asynchronie dans la maturation), toutes les figues d'un arbre pouvant être détruites. La fonction mâle de l'arbre est donc sévèrement réduite via la prédation des pollinisateurs. La fonction femelle est moins affectée, les figues, au moment de l'émergence des pollinisateurs ayant des graines matures. Nous avons recensé 13 espèces de fourmis sur les 73 Ficus vallis-choudae étudiés dans la savane de Batchenga (Cameroun), mais uniquement les cinq espèces citées ci-haut peuvent occuper un figuier entier. Les trois Myrmicinae sont des « dominantes » (grosses colonies; forte territorialité contre les autres dominantes; peuvent tolérer des « non-dominantes » ) qui exploitent des cochenilles. Les deux Camponotus (ainsi que les huit autres espèces) appartiennent au lot des « non-dominantes » (petites colonies), mais dans certaines situations (ici, lorsqu'elles exploitent le Tettigometridae Hilda undata) elles peuvent aussi occuper un arbre entier et en défendre l'accès. On les qualifie alors de « sub-dominantes » . Des tests d'agressivité ont permis de montrer que chaque espèce est agressive vis-à-vis d'ouvrières étrangères conspécifiques, que les ouvrières de Camponotus brutus sont tolérées sur les figuiers occupés par Atopomyr ex mocquerisi ou par Crematogaster clariventris, alors que les ouvrières de ces deux espèces, qui ne se tolèrent pas entre elles, ne sont pas tolérées sur les figuiers occupés par Camponotus brutus. Dans ces conditions, le rapport coût/bénéfice pour l'arbre dépend de l'espèce de fourmi qui l'occupe, Camponotus brutus étant l'espèce avantageuse, grâce à l'exploitation des tettigomètres. En conséquence, il y a une influence indirecte du tettitogomètre sur la production d'insectes pollinasiteurs et de graines.
ISSN: 1195-6860

hal-01214443
https://hal.archives-ouvertes.fr/hal-01214443
DOI : 10.2307/42902390

Éditeur(s) : Gauthier-Villars
Résumé : The mangroves of Senegal are limited to the inlet of the Casamance - a river with very low discharge - and to the Sine-Saloum. The mineralogical and geochemical analysis of sediments (derived from 30 deep bore-holes) shows the thickness of the mangrove substrate, which overlies the continental terminal formation. Kaolinite and smectite account for over 90% of the clay fraction. The former is derived from the continental terminal whereas the latter is of marine origin. The chemical composition of the mangrove sediments is remarkably stable and clays play an overwhelming role in the preservation of organic matter and pyrite. Since 1968, a drought in Senegal has caused an important increase in the salinity levels of streams and water-tables; a considerable modification of vegetation zones in the Casamance, especially manifest in the extension of bare flats locally known as "tannes" at the expense of mangroves and marked changes in the morphology and geochemistry of mangrove soils. Compared to most mangrove areas in the humid tropics, mangroves in Senegal are characterized by a very fragile equilibrium.
Oceanologica Acta, Special issue (0399-1784) (Gauthier-Villars), 1982

Droits : info:eu-repo/semantics/openAccess
http://archimer.ifremer.fr/doc/00246/35744/34252.pdf
http://archimer.ifremer.fr/doc/00246/35744/

Éditeur(s) : HAL CCSD Wiley-Blackwell Wiley
Résumé : A new record from the heart of the Moroccan Middle Atlas cedar forests spans the last 18 000 years and provides valuable insight into our understanding of the natural vegetation and environmental changes. The approach is based on the study of pollen content, geochemical elements and grain size analysis. The pollen data indicate that the vegetation was dominated by herbaceous plants until 9000 BP. Such open landscape allowed greater soil erosion and an input of chemical elements from the watershed. After 9000 BP, tree cover, mainly oak, increased slightly and was accompanied by a higher taxonomic diversity. However, several steppe elements remain well represented in the area until 5000 BP, which suggests that the climate was rather dry during the first part of the Holocene. After 6000 BP, the climate became more favourable to expansion of the forest ecosystems, including Cedrus atlantica, thereby reducing erosion. A strong reduction of the tree pollen percentages is recorded after 2000 BP, which may be related to increasing human activities during the Roman period. These forest changes are concomitant with an increase of lead and copper concentrations in the record, probably related to Roman metalworking activities.
ISSN: 0267-8179

hal-01122848
https://hal.archives-ouvertes.fr/hal-01122848
DOI : 10.1002/jqs.2708

Éditeur(s) : HAL CCSD
Résumé :   Diplôme : Master Recherche
il s'agit d'un type de produit dont les métadonnées ne correspondent pas aux métadonnées attendues dans les autres types de produit : DISSERTATION
Notre étude porte sur la caractérisation à l'échelle de l'hectare de la variabilité spatiale (1) du fonctionnement microbien du sol et (2) de sa stabilité (i.e. de sa réponse à un stress). Elle a été menée sur une forêt tropicale humide (forêt primaire) proche de Kourou en Guyane (site de Paracou). Les indicateurs fonctionnels utilisés sont les potentiels d'activités respiratoires (RP) et dénitrifiantes (OP). La variabilité spatiale du fonctionnement microbien du sol a fait l'objet d'un nombre important d'études mais très peu d'entre elles ont concerné ce type d'écosystème. Un autre aspect novateur réside dans la recherche de la variabilité spatiale de la stabilité du fonctionnement. A notre connaissance, il s'agit de la première étude de ce type en milieu tropical comme en milieu tempéré. Les principales conclusions sont les suivantes : (1) à l'échelle 10m (grille principale) les coefficients de variation (CV) des potentiels de fonction sont similaires pour les 2 processus et élevés (RP : 53% ; OP : 54%) au regard des valeurs de la littérature sur des milieux tempérés, mais RP et OP présentent des variabilités spatiales différentes à des échelles inférieures ; (2) l'utilisation d'un indice de densité locale (ID) des arbres n'a pas permis de mettre en évidence une corrélation entre les répartitions spatiales de la végétation et du fonctionnement microbien du sol. De même, aucun déterminisme clair de l'intensitè des potentiels microbiens n'a pu être dégagé par la prise en compte de la variabilité des caractéristiques physico-chimiques du sol; (3) un stress thermique génère à très court terme (résistance) un accroissement de la spatialisation du potentiel de respiration. A plus long terme, la variabilité inter-échantillons s'atténue pour retrouver ses valeurs initiales et, (4) l'activité originelle (avant stress) n'est pas corrélée avec la résistance et est négativement corrélée aux valeurs observées 15 et 30 jours après le stress. Outre son intérêt intrinsèque, cette étude vise à se doter de données de « cadrage » sur la forêt primaire (non perturbée) qui nous permettront d'accéder à de meilleures évaluations et compréhensions des mécanismes impliqués dans la réponse des écosystèmes tropicaux à l'anthropisation lors de projets en cours. Un exemple de ce type d'application est brièvement décrit.
https://hal.archives-ouvertes.fr/hal-01189259

hal-01189259
https://hal.archives-ouvertes.fr/hal-01189259
PRODINRA : 20250

Éditeur(s) : HAL CCSD Muséum national d'histoire naturelle
Résumé :  
La mise en place d'une gestion des milieux, compatible avec l'existence du futur parc national progresse en Guyane. Elle nécessite à la fois une présence sur le terrain plus importante, mais aussi une approche plus systémique du milieu. Dans ce contexte, l'utilisation de moyens modernes de cartographie (systèmes d'information géographiques, image satellitales) ont leur place. L'intégration de données multisources (cartographies, photos aériennes, etc) dans un système d'information géographique est l'occasion d'établir une première représentation de l'emprise humaine sur le milieu naturel. Nous présentons ici les premiers résultats d'un travail relatif à la cartographie de la végétation et de l'occupation du sol à différentes échelles de la région de Saül (Guyane). Ce travail s'intègre dans les travaux scientifiques et techniques liés à la préparation de la mise en place du futur parc national de la Guyane.
ISSN: 0183-5173

hal-01032115
https://hal.archives-ouvertes.fr/hal-01032115

Éditeur(s) : Gauthier-Villars
Résumé : The continental shelf is very narrow and steep to the north, and broader to the South. This shelf is structuraly influenced by the Andes. This area is mainly covered with terrigenous deposits, i.e. muds and sands which are recent on the internal shelf and relict on the external shelf. The sediments, supplied by rivers, reflect the intense erosion of the Andean backland. This erosion can only be reduced in situ by the vegetation cover. Clays are the main component of the fine fraction reaching the sea. Three different clay assemblages are observed: 1) an Andean (illite-chlorite) assemblage, reflecting the proximity of the cordillera; 2) a mid-American assemblage (smectite), which supplies the North Pacific Margin through the Choco counter-current; 3) an Equatorial assemblage (smectites) which is brought to the South by the Colombian current.
Oceanologica Acta (0399-1784) (Gauthier-Villars), 1995 , Vol. 18 , N. 1 , P. 1-18

Droits : info:eu-repo/semantics/openAccess
http://archimer.ifremer.fr/doc/00097/20862/18480.pdf
http://archimer.ifremer.fr/doc/00097/20862/

Éditeur(s) : Université des Antilles Études caribéennes
Résumé : The tropical coast of Queensland, Australia is experiencing rapid population and tourism growth. Heavy development pressure is being placed on the biophysical environment, which includes the largest sand island in the world (World Heritage listed), Fraser Island. Despite the existence of State planning legislation oriented towards environmental sustainability, it is apparent that little, if any, regard is being paid to the long-term effects of resort and canal-estate development on the underlying biophysical environment of the coast and islands. While the remarkable surface features of the tropical coastal environment such as the surf beaches, the unique dune lakes, and the coastal vegetation, as well as the prolific wildlife, are used as selling points for new settlement and above all tourism, little is known or apparently of major concern with respect to the long term environmental impact of coastal development. While the crowding effect of large numbers of visitors and their impact on the natural environment - through significant degradation, site hardening or lack of proper on-site management – has been identified as a particular problem in certain areas, there is little knowledge of impacts on the underlying coastal geomorphology. In particular, developmental choices are often made in ignorance of, or disregard of, the widespread existence of tropical acid sulfate soils in that coastal environment. Reactive soils such as these can, and do, greatly affect the biophysical outcomes of a development if they are exposed. This paper documents such impacts in the form of a case study of the acid sulfate soil problem in relation to the development of tourist resorts, and suggests that part of the solution is for the State Government to insist on enforceable standards relating to their development for tourism in the coastal zone. These would reduce the use by many resort owners of fancy golf course developments as an environmental cover up to make it look as if they put a lot of effort into protecting the environment….
La côte tropicale du Queensland est confrontée à un accroissement rapide de la population. Les fortes pressions anthropiques pèsent sur le milieu biophysique, qui comprend notamment a plus grande île de sable du monde, un site classé Patrimoine de l’Humanité, Port Hinchinbrook et Fraser Island. Malgré l’existence d’une législation nationale orientée vers la préservation de l’environnement, il est manifeste que peu d’attention est accordée aux effets à long terme des sites touristiques et du développement de l’urbanisation sur ces franges côtières sensibles. L’aspect massif des flux de visiteurs et leurs impacts sur le milieu naturel a été identifié comme un sujet d’inquiétude particulier dans certaines régions. La connaissance des impacts sur la géomorphologie côtière souterraine est très réduite et les choix de développement sont souvent faits dans l’ignorance ou au mépris de la présence répandue de terrains de sulfate d’acide dans ce milieu côtier. Des sols réactifs comme ceux-là peuvent affecter, et affectent, grandement les résultats géophysiques d’un développement lorsqu’ils sont connus. Des études de cas sur le problème des sols de sulfate d’acide suggèrent qu’une partie de la solution pour le gouvernement de l’Etat du Queensland est d’imposer des normes obligatoires pour le développement du tourisme dans la zone côtière.
Australie
Queensland

Droits : info:eu-repo/semantics/openAccess
urn:doi:10.4000/etudescaribeennes.1272
http://journals.openedition.org/etudescaribeennes/1272

Éditeur(s) : HAL CCSD Botanical Society of America
Résumé :  
International audience
The different hypotheses about buttress function and formation mainly involve mechanical theory. Forces were applied to two trees of Sloanea spp., a tropical genus that develops typical thin buttresses, and the three-dimensional strains were measured at different parts of the trunk base. Risks of failure were greater on the buttress sides, where shear and tangential stresses are greater, not on the ridges, in spite of high longitudinal (parallel to the grain) stresses. A simple beam model, computed from the second moment of area of digitized cross sections, is consistent with longitudinal strain variations but cannot predict accurately variations with height. Patterns of longitudinal strain variation along ridges are very different in the two individuals, owing to a pronounced lateral curvature in one specimen. The constant stress hypothesis is discussed based on these results. Without chronological data during the development of the tree, it cannot be proved that buttress formation is activated by stress or strain.
ISSN: 0002-9122

hal-01032155
https://hal.archives-ouvertes.fr/hal-01032155
https://hal.archives-ouvertes.fr/hal-01032155/document
https://hal.archives-ouvertes.fr/hal-01032155/file/Biomechanics_buttressed_trees_Clair_al_2003.pdf
DOI : 10.3732/ajb.90.9.1349