Éditeur(s) : HAL CCSD Public Library of Science
Résumé : International audience
While the fire coral Millepora platyphylla is an important component of Indo-Pacific reefs,where it thrives in a wide range of environments, the ecological and biological processesdriving its distribution and population structure are not well understood. Here, we quantifiedthis species' population structure in five habitats with contrasting hydrodynamic regimes inMoorea, French Polynesia; two in the fore reef: mid and upper slopes, and three in thelagoon: back, fringing and patch reefs. A total of 3651 colonies of fire corals were mappedand measured over 45,000 m2 of surveyed reef. Due to the species' sensitivity to fragmentationin response to strong water movement, hydrodynamic conditions (e.g. waves, pass andlagoonal circulation) corresponded to marked differences in colony size distributions, morphologyand recruitment dynamics among habitats. The size structure varied among reefhabitats with higher proportions of larger colonies in calm nearshore reefs (fringing andpatch reefs), while populations were dominated by smaller colonies in the exposed forereefs. The highest densities of fire corals were recorded in fore reef habitats (0.12±0.20 n.m-2) where the proportion of recruits and juveniles was higher at mid slope populations(49.3%) than on the upper slope near where waves break (29.0%). In the latter habitat, mostcolonies grew as vertical sheets on encrusting bases making them more vulnerable to colonyfragmentation, whereas fire corals were encrusting or massive in all other habitats. Thelowest densities of M. platyphylla occurred in lagoonal habitats (0.02±0.04 n.m-2) characterizedby a combination of low water movement and other physical and biological stressors.This study reports the first evidence of population structure of fire corals
ISSN: 1932-6203

hal-01561659
https://hal-univ-perp.archives-ouvertes.fr/hal-01561659
https://hal-univ-perp.archives-ouvertes.fr/hal-01561659/document
https://hal-univ-perp.archives-ouvertes.fr/hal-01561659/file/millepora%20platyphylla.pdf
DOI : 10.1371/journal.pone.0173513

Éditeur(s) : Université des Antilles Études caribéennes
Résumé : L’incendie de forêt reste incontestablement un des facteurs de dégradation les plus dévastateurs dans le bassin méditerranéen, lequel est caractérisé par une végétation très inflammable et des conditions climatiques chaudes et sèches. Le Maroc, pays du pourtour méditerranéen, n’est pas épargné par ce fléau, avec 3000 ha de forêts qui partent annuellement en fumée ; cette situation est aggravée par les difficultés de régénération et de restauration des espaces, marqués par une vulnérabilité naturelle telle que celle de la Mâamora. Pour répondre à cela, la conception d’un plan d’aménagement anti-feux visant à conférer à la forêt de la Mâamora une immunité élevée contre les incendies, nécessite non seulement une connaissance approfondie du milieu, mais aussi une analyse appropriée du phénomène « incendie ». La présente étude qui se penche sur le diagnostic et l’analyse des incendies survenus en Mâamora, a permis de constater que les zones d’interface homme-forêt (routes, douars, etc.) n’ont pas d’influence sur l’occurrence des incendies. Il ressort également que l’activité pastorale, pratiquée d’une certaine façon, pourrait jouer un rôle important dans la diminution des risques d’incendie. En outre l’étude révèle que la charge du combustible représente le facteur prépondérant qui régit à la fois l’éclosion des incendies et leur propagation, cette charge étant étroitement liée à la qualité de la station (sol et pluviométrie).
Forest fires are the main disturbance and the degradation factor most devastating that can affect forested areas, especially in the Mediterranean basin when species are highly flammable and climate conditions are marginal. Morocco as a Mediterranean country is not spared from this phenomenon, thus 3000 ha of forest are burned every year, and this situation is aggravated by the low rate of regeneration and restoration of the unbalanced ecosystems such as the Mâamora. To mitigate this situation, the establishment of an effective management plan for forest fire prevention requires not only an intimate knowledge of environment but also a perfect analysis of fire phenomenon. Therefore in this study, we focused our diagnosis on the analysis of old fires occurred in the past in Mâamora forest. The study highlighted that human-forest interface areas (roads, villages) have no influence on fires occurrence. Besides it was shown that grazing practiced in a well-balanced way, could play a key role in reducing fire hazards. In addition the study reveals that fuel load of is the major factor that governs both fire ignition and fire spread of, this load is closely related to site quality (soil and rainfall)
Maroc

Droits : info:eu-repo/semantics/openAccess
urn:doi:10.4000/etudescaribeennes.10978
http://journals.openedition.org/etudescaribeennes/10978

Éditeur(s) : HAL CCSD Wiley
Résumé :  
The complex structure of tree bark reflects its many functions, which include structural support as well as defence against fire, pests and pathogens. Thick bark, however, might limit respiration by the living tissues of the trunk. Nevertheless, little research has addressed community-level variation in bark thickness, and to the best of our knowledge, no one has tested multiple hypotheses to explain variation in bark thickness. We conducted an extensive survey of bark thickness within and among species of trees in the tropical rain forests of French Guiana. Trunk bark thickness increased by 1.2 mm per 10 cm increase in stem diameter, and varied widely at all taxonomic levels. Mean trunk bark thickness was 4.5 mm (range: 0.5-29 mm), which was less that found in two Amazonian rain forests in previous studies. This survey of bark thickness should be of use for forest management since tree survival through fire is strongly predicted by bark thickness. We combined the survey data with multiple datasets to test several functional hypotheses proposed to explain variation in bark thickness. We found bark to provide an average of 10% of the flexural rigidity of tree stems, which was substantially less than that found in the only other study of bark stiffness. Bark thickness was uncorrelated with species' association with fire-prone habitats, suggesting that the influence of fire on bark thickness does not extend into moist Forests. There was also little evidence that bark thickness is affected by its function as a defence against herbivory. Nor was there evidence that thick bark limits trunk respiration. A re-analysis of previously collected anatomical data indicated that variation in rhytidome (non-conducting outer bark) thickness explains much of the variation in overall bark thickness. As rhytidome is primarily involved in protecting the living tissues of the trunk, we suggest that bark thickness is driven mostly by its defensive function. Functional explanations for the variation in bark thickness were not clear-cut. Nevertheless, this study provides a foundation for further investigation of the functional bases of bark in tropical trees.
ISSN: 0269-8463

hal-01032124
https://hal.archives-ouvertes.fr/hal-01032124
DOI : 10.1111/j.1365-2435.2010.01736.x

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 Elsevier
Résumé : International audience
Because territoriality is energetically costly, territorial animals frequently respond less aggressively toneighbours than to strangers, a reaction known as the "dear enemy phenomenon" (DEP). The contrary,the "nasty neighbour effect" (NNE), occurs mainly for group-living species defending resource-basedterritories. We studied the relationships between supercolonies of the pest fire ant Solenopsis saevissimaand eight ant species able to live in the vicinity of its nests plus Eciton burchellii, an army ant predatorof other ants. The workers from all of the eight ant species behaved submissively when confrontedwith S. saevissima (dominant) individuals, whereas the contrary was never true. Yet, S. saevissima weresubmissive towards E. burchellii workers. Both DEP and NNE were observed for the eight ant species, withsubmissive behaviours less frequent in the case of DEP. To distinguish what is due to chemical cues fromwhat can be attributed to behaviour, we extracted cuticular compounds from all of the nine ant speciescompared and transferred them onto a number of S. saevissima workers that were then confronted withuntreated conspecifics. The cuticular compounds from three species, particularly E. burchellii, triggeredgreater aggressiveness by S. saevissima workers, while those from the other species did not.
ISSN: 0376-6357

hal-00913344
https://hal.archives-ouvertes.fr/hal-00913344
https://hal.archives-ouvertes.fr/hal-00913344/document
https://hal.archives-ouvertes.fr/hal-00913344/file/roux_10206.pdf
DOI : 10.1016/j.beproc.2013.04.014

Éditeur(s) : HAL CCSD
Résumé : More than 15% of Amazon forest has been converted to pastures these last decades. Some authors argued the world’s permanent pastures (30 % of total land) could potentially offset up to 4% of the global GHG emissions, having a carbon (C) storage potential equal to 0.5 Mg C.ha-1.yr-1(Schulze et al 2009). Accordingly, pastures are good candidates to increase soil uptake C in soil while ensuring a basic food production. Here we would like to assess the effects of tropical forest conversion to cattle pasture in the French Amazonia (French Guiana), by following the long-term dynamics of soil C stocks of permanent tropical pastures (Brachiaria humidicola) after deforestation from 1970. A soil inventory campaign was performed to analyse soil C and N stocks (to 1 m depth) along a pasture chronosequence of 6 months to 36 years old pastures and 4 native forest sites (total 24 sites). The annual C sequestration potential demonstrated by the chronosequence, was compared with eddy covariance flux measurements on 2 pastures and one native forest. Our study shows that old (≥ 24 years) tropical pastures resettle the recurrent C storage observed in native forest. These pastures stored between 1.8 ± 0.5 and 5.3 ± 2.1 tC ha-1 yr-1 compared with 2.6 ± 0.5 tC ha-1 yr-1 for the nearby native forest. Our finding show that old tropical pastures accumulate carbon in soil organic matter, particularly in the deep soil layers (0.2-1 m) and without loss of soil fertility. It suggests that such pastures can be exploited by farmers in the long term with appropriate practices (no fire and no overgrazing, but a mixture of grasses and legumes and a grazing rotation plan). Clearly, efforts to curb deforestation are a priority in order to preserve forest biodiversity and C stocks. But it seems now that, in a climate-smart agriculture way, the current challenge is to manage these deforested areas to maintain the productivity of agricultural ecosystems and in the same time their capacity to mitigate GES.
Building tomorrow’s research agenda and bridging the science-policy gap
Montpellier, France

hal-01204231
https://hal.archives-ouvertes.fr/hal-01204231
PRODINRA : 324147