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-01189214
https://hal.archives-ouvertes.fr/hal-01189214
PRODINRA : 16123

Éditeur(s) : HAL CCSD European Geosciences Union
Résumé : International audience
The production of aboveground soft tissue represents an important share of total net primary production in tropical rain forests. Here we draw from a large number of published and unpublished datasets (n = 81 sites) to assess the determinants of litterfall variation across South American tropical forests. We show that across old-growth tropical rainforests, litterfall averages 8.61±1.91Mgha−1 yr−1 (mean±standard deviation, in dry mass units). Secondary forests have a lower annual litterfall than old-growth tropical forests with a mean of 8.01±3.41Mgha−1 yr−1. Annual litterfall shows no significant variation with total annual rainfall, either globally or within forest types. It does not vary consistently with soil type, except in the poorest soils (white sand soils), where litterfall is significantly lower than in other soil types (5.42±1.91Mgha−1 yr−1). We also study the determinants of litterfall seasonality, and find that it does not depend on annual rainfall or on soil type. However, litterfall seasonality is significantly positively correlated with rainfall seasonality. Finally, we assess how much carbon is stored in reproductive organs relative to photosynthetic organs. Mean leaf fall is 5.74±1.83Mgha−1 yr−1 (71% of total litterfall). Mean allocation into reproductive organs is 0.69±0.40Mgha−1 yr−1 (9% of total litterfall). The investment into reproductive organs divided by leaf litterfall increases with soil fertility, suggesting that on poor soils, the allocation to photosynthetic organs is prioritized over that to reproduction. Finally, we discuss the ecological and biogeochemical implications of these results.
ISSN: 1726-4170

hal-00594514
https://hal.archives-ouvertes.fr/hal-00594514

Résumé : En 2013, Le Groupe d'experts Intergouvernemental sur l'Evolution du Climat (GIEC) publie son cinquième rapport concernant les changements climatiques. Il y est souligné que le réchauffement climatique est sans équivoque, et que de nouvelles émissions de gaz à effet de serre impliqueront une poursuite du réchauffement et des changements affectant toutes les composantes du système climatique. En région tropicale, une hausse de la température, ainsi qu'une intensification des événements de sécheresse et de pluviométrie extrêmes sont à prévoir. C'est dans ce contexte que s'inscrit ce travail, dont le but est d'étudier la réponse de la forêt tropicale à ces changements climatiques prédits en Guyane Française. Pour ce faire, j'ai utilisé les données du dispositif de suivi forestier de Paracou pour construire un modèle de dynamique individuel basé sur les traits fonctionnels des arbres. Un modèle de mortalité a d'abord été réalisé puis couplé à un modèle de croissance.Le modèle couplé ainsi construit permet de modéliser la croissance et la mortalité des arbres sur un pas de temps de 2 ans tout en tenant compte de leur ontogénie et de leurs traits fonctionnels. Ce modèle a d'abord été appliqué aux essences commerciales de Guyane Française en forêt naturelle et exploitée en y ajoutant un indice de stress hydrique. Ceci permet de montrer que le stress hydrique fait baisser la croissance et augmenter la mortalité, tandis que l'exploitation a l'effet inverse. Malgré le signal commun, différentes réponses sont observées selon les espèces. Le modèle a ensuite été appliqué à la communauté en forêt naturelle pour identifier les drivers climatiques et les processus impactés. Il ressort que la croissance est impactée par le stress hydrique et la température, et que la mortalité est impactée par le stress hydrique et la pluviométrie totale.Ces résultats ont enfin permis de construire un modèle complet de dynamique forestière climat dépendant, et de simuler l'évolution d'une communauté pendant un siècle selon différents scénarios correspondant aux prédictions du GIEC. Les simulations mettent en évidence une très forte diminution de la croissance, ainsi qu'une plus faible diminution de la mortalité. Ceci entraine une diminution notable de la surface terrière, du diamètre quadratique et de la biomasse fraiche. Une analyse de sensibilité montre que ces changements sont principalement dus à l'augmentation sévère des températures prédites pour le siècle à venir. Des pistes de réflexion sur les enjeux de modélisation et les échelles considérées sont proposées en discussion de ce travail.
In 2013 the intergovernmental panel on climate change (ipcc) publishes its fifth report. This report underlines that an increase of temperature and a strengthening of drought and extreme rainfall are expected in tropical regions. This work was made in this context of climate changes, and aimed to study the response of the rainforest to predicted climate changes. To do this, i used the data from the study site of Paracou French Guiana to build an individual based dynamics model based on the functional traits of trees. This model was first applied to species with a commercial interest in French Guiana, in natural and logged forest and adding a water stress index as predictor. Water stress decreases growth and increases mortality, while logging had the opposite effect. The model was then applied to the community in natural forest for identifying potential climate drivers and impacted processes. Growth is impacted by the water stress and temperature and mortality is imp acted by the water stress and the total rainfall. These results allowed us to build a climate dependent model of forest dynamics and to run simulations of the evolution of a community under different scenarios for the next century. Simulations showed a decrease of growth and a small decrease of mortality. This resulted in a substantial decrease of basal area, squared diameter and fresh biomass.

http://www.theses.fr/2014AGUY0802/document

Résumé : Les mécanismes à l’origine du maintien de la forte diversité locale des arbres des forêts tropicales humides constituent encore une énigme pour les scientifiques. Cette thèse a pour but d’étudier et de comprendre certains facteurs biotiques et abiotiques qui influencent l’assemblage des communautés des forêts tropicales humides d’Amazonie. A l’aide d’une approche empirique conduite dans les forêts tropicales de Guyane française et du Loreto au Pérou, de nombreuses expériences de terrain ont été mises en place dans le but d’apporter des éléments de réponse sur les mécanismes impliqués dans le maintien de la diversité des communautés d’arbres et d’insectes des forêts amazoniennes. Dans un premier temps, cette thèse permet de souligner l’importance des pressions biotiques exercées sur les communautés d’arbres. En effet, les communautés d’insectes peuvent influencer la composition des communautés d’arbres le long d’un gradient environnemental conduisant à des compromis entre la défense et la croissance. Ces compromis ou tradeoff permettent de maintenir la coexistence des espèces de forêts tropicales humides en favorisant la spécialisation des arbres à leur habitat (Chapitre 1, Annexe 3). Cependant, de nombreux facteurs peuvent engendrer des variations dans les compromis d’allocation exhibés par les plantes, ce qui peut compliquer la validité de ces résultats. Dans ce sens, nous avons souligné l’influence du rôle de la cascade trophique et l’existence chez certaines espèces d’arbres de stratégies d’évitement des insectes (Chapitre 2). Dans un second temps, nous avons montré que les filtres environnementaux et les distances géographiques favorisent un fort turnover de la composition des arthropodes des forêts tropicales (chapitre 3, Annexe 2). Les résultats de cette étude ont des implications fondamentales sur les mécanismes qui expliquent la structuration des communautés d’insectes herbivores. Nous avons souligné l’importance de l’interaction des communautés des insectes herbivores et de leurs plantes associées. De plus, des prédictions sont présentées sur le degré de spécialisation des insectes à leur plante-hôte (Annexe 3), notamment sur les implications possibles dans les compromis d’allocation chez les plantes. Finalement, des perspectives de recherche sont proposées en vue de poursuivre ces travaux de recherche, et notamment des extensions de mes expériences vers d’autres régions tropicales et tempérées et l’intégration de la phylogénie pour comprendre des mécanismes de coévolution entre communautés d’arbres et insectes. Nous proposons également une intégration des résultats de cette thèse dans les stratégies locales et régionales de conservation des forêts tropicales du bassin amazonien.
The mechanisms underlying the maintenance of local diversity of trees in tropical rainforests remain under debate. This dissertation aims to study and understand some biotic and abiotic factors that may influence both tree and insect community assembly in lowland tropical forests of Amazonia. I used an empirical approach to study communities of trees and insects in tropical forests of French Guiana and Peru, to address the extent to which insect herbivores contribute to the turnover of tree species across strong environmental gradients. In Chapter 1, I studied how herbivorous insect communities can influence the composition of tree communities along an environmental gradient by reinforcing tradeoffs between defense and growth that promote habitat specialization (Chapter 1, Appendix 3). The complicated variation in the patterns of growth and defense from this study led me to pursue further observations of an alternative plant defense strategy of time-avoidance of herbivores, which I examined in detail in Chapter 2. I found evidence for coordinated leaf production in some tree species that was consistent with the satiation of herbivores, suggesting that multiple interactions between plants and their herbivores may be responsible for patterns of habitat specialization in trees. In the second part of the dissertation, I examined insect herbivore communities in detail to test for turnover in species composition across geographic and environmental gradients. In Chapter 3, I present evidence for substantial beta-diversity in arthropod communities throughout lowland Amazonian forests. In the discussion I propose research perspectives to complete this research, including the extension of observations to compare tropical and temperate regions and the integration of molecular phylogenetics information to study coevolution of plant lineages and their insect herbivores. I conclude with suggestions for the integration of the results of this thesis in local and regional strategies for the preservation and conservation of tropical forests in the Amazon basin.

http://www.theses.fr/2013AGUY0582/document

Éditeur(s) : HAL CCSD Elsevier
Résumé :  
Previous studies in lowland tropical rainforests of French Guiana showed that, among non-N2-fixing trees, two groups of late successional species contrasting in their leaf 15N natural abundance coexist, suggesting two different main ways of nitrogen acquisition. Two abundant late-successional species typically co-occurring in rainforests in French Guiana, namely Eperua falcata and Dicorynia guianensis, were chosen as representative of each group. Stable isotope techniques and measurements of potentials of microbial N transformation were performed to assess to what extent leaf 15N natural abundance of these species could be related to (i) d15N signatures of soil mineral N sources and (ii) the capacity of soil to express nitrification and denitrification (both processes being directly involved in the balance between NH4 + and NO3 - ). Soil d15N-NH4 + was roughly similar to leaf d15N of D. guianensis (around 3.5%), suggesting a preferential use of NH4 +, whereas in E. falcata, leaf d15N values were closer to root d15N-NO3 _ values (0.2 and _2.0%, respectively), suggesting a preferential use of NO3 _. These differences in N source utilization were not accompanied by differences in availability in soil NO3 _ or in intensity of microbial functions responsible for soil N mineral evolution. However, (i) under both tree species, these functions showed clear spatial partitioning, with denitrification occurring potentially in soil and nitrification in the litter layer, and (ii) E. falcata fine roots colonized the litter layer much more strongly than D. guianensis fine roots. This strongly suggests that (i) the contrasted leaf d15N values found in the two late-successional species reveal distinct N acquisition strategies and (ii) the ability of roots to predominantly exploit the litter layer (E. falcata) or the soil (D. guianensis) may constitute an important explanation of the observed differences. A complementarity between tree species, based on mineral N resource partitioning (itself resulting from a spatially structured location of the microbial functions responsible for the balance between NH4 + and NO3 - ), can thus be supposed.
ISSN: 0038-0717

hal-01032035
https://hal.archives-ouvertes.fr/hal-01032035
DOI : 10.1016/j.soilbio.2007.09.011

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

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

Éditeur(s) : HAL CCSD
Résumé : International audience
The aboveground biomass density (AGBD) or aboveground carbon density is mapped for the rainforest of the Basse-Terre Island (Guadeloupe, French West Indies). This mapping is the first devoted to the rainforest of the Lesser Antilles.Mapping AGBD needs the successive realization of two steps. At first, AGBD was estimated in studied forest plots where trees were individually measured; secondly these local estimations were extended through multiple regression including remote sensing LiDAR measurements.Due to the structural specificity of the Caribbean-islands forests, applying general allometry relationship overestimates tree above-ground biomass. Yet we take advantage of pantropical database (Chave et al. 2014) by adopting a suitable statistical procedure: bayesian mixed decision rule.Despite the reduced canopy height, generally less than 35 m, Caribbean lowland rainforests have a high biomass, in every respect comparable to that of continental lowland forests. Such peculiarity is achieved through increased tree density that compensate for lower canopy height.
CAS
Deshaies, Guadeloupe

hal-01514241
https://hal.archives-ouvertes.fr/hal-01514241

Éditeur(s) : HAL CCSD Springer Verlag/EDP Sciences
Résumé :  
On 10 trees from 10 species of French Guyana tropical rainforest in a clear active process of restoring verticality growth strains were measured in situ in order to determine the occurrence of tension wood within samples. Wood specimens were cut in the vicinity of the growth strains measurements in order to measure some mechanical and physical properties. As suspected, tensile growth strains was very much higher in tension wood zone, because longitudinal modulus of elasticity was slightly higher. Longitudinal shrinkage was also much higher in tension wood than in opposite wood.
ISSN: 1286-4560

hal-01032110
https://hal.archives-ouvertes.fr/hal-01032110
DOI : 10.1051/forest:2007027

Éditeur(s) : HAL CCSD North Carolina State University
Résumé : Few studies have been conducted about relation between cellulose parameters and biomechanical properties of wood in tropical angiosperms species. For this purpose, on 13 trees from 3 species of French Guyana tropical rainforest in a clear active process of restoring verticality, i) growth strains were measured in situ in order to determine the occurrence of tension wood within samples and ii) cellulose structural parameters were estimated on all the samples using X-ray diffraction method. Crystallite size was estimated from the full-width at half-maximum of the Miller index (002) arc diffraction and angle T was measured following Cave's method. Relationships between these parameters and growth stresses were good and the variations between normal and tension wood were significant, i.e. a lower angle T and a larger crystallite size in tension wood. In order to have a good estimation of the microfibril angle in the main layer of the secondary wall for each species, an experimental calibration was done between angle T and microfibril angle observed with scanning electron microscopy.
ISSN: 19302126

hal-01031799
https://hal.archives-ouvertes.fr/hal-01031799
https://hal.archives-ouvertes.fr/hal-01031799/document
https://hal.archives-ouvertes.fr/hal-01031799/file/42-575-1-PB.pdf

Éditeur(s) : HAL CCSD American Association for the Advancement of Science
Résumé : International audience
Most eukaryotic organisms are arthropods. Yet, their diversity in rich terrestrial ecosystems is still unknown. Here we produce tangible estimates of the total species richness of arthropods in a tropical rainforest. Using a comprehensive range of structured protocols, we sampled the phylogenetic breadth of arthropod taxa from the soil to the forest canopy in the San Lorenzo forest, Panama. We collected 6144 arthropod species from 0.48 hectare and extrapolated total species richness to larger areas on the basis of competing models. The whole 6000-hectare forest reserve most likely sustains 25,000 arthropod species. Notably, just 1 hectare of rainforest yields >60% of the arthropod biodiversity held in the wider landscape. Models based on plant diversity fitted the accumulated species richness of both herbivore and nonherbivore taxa exceptionally well. This lends credence to global estimates of arthropod biodiversity developed from plant models.
ISSN: 0036-8075

hal-00817285
https://hal.archives-ouvertes.fr/hal-00817285
https://hal.archives-ouvertes.fr/hal-00817285/document
https://hal.archives-ouvertes.fr/hal-00817285/file/1226727Revisedtext.pdf
DOI : 10.1126/science.1226727

Éditeur(s) : HAL CCSD Wiley
Résumé : International audience
Mycoheterotrophic orchids have adapted to shaded forest understory by shifting to achlorophylly and receiving carbon from their mycorrhizal fungi. In temperate forests, they associate in a highly specific way with fungi forming ectomycorrhizas on nearby trees, and exploiting tree photosynthates. However, many rainforests lack ectomycorrhizal fungi, and there is evidence that some tropical Asiatic species associate with saprotrophic fungi. To investigate this in different geographic and phylogenetic contexts, we identified the mycorrhizal fungi supporting two tropical mycoheterotrophic orchids from Mascarene (Indian Ocean) and Caribbean islands. We tested their possible carbon sources by measuring natural nitrogen (15N) and carbon (13C) abundances. Saprotrophic basidiomycetes were found: Gastrodia similis associates with a wood-decaying Resinicium (Hymenochaetales); Wullschlaegelia aphylla associates with both litter-decaying Gymnopus and Mycena species, whose rhizomorphs link orchid roots to leaf litter. The 15N and 13C abundances make plausible food chains from dead wood to G. similis and from dead leaves to W. aphylla. We propose that temperature and moisture in rainforests, but not in most temperate forests, may favour sufficient saprotrophic activity to support development of mycoheterotrophs. By enlarging the spectrum of mycorrhizal fungi and the level of specificity in mycoheterotrophic orchids, this study provides new insights on orchid and mycorrhizal biology in the tropics. New Phytologist (2009)doi: 10.1111/j.1469-8137.2009.02987.x
ISSN: 0028-646X

hal-01199356
http://hal.univ-reunion.fr/hal-01199356
DOI : 10.1111/j.1469-8137.2009.02987.x

Éditeur(s) : HAL CCSD
Résumé : In the tropical rainforest of Amazonia, the factors driving the evolution of tree species remain poorly understood, and the relative influence of neutral and adaptive processes is continuously debated. In particular, local habitat patchiness draws much attention, as profound changes in the structure and composition of forest communities occur among micro-habitats. Thus, micro-environmental variations related to topography have frequently been invoked as drivers of adaptive radiation leading to sympatric speciation in Neotropical trees. On one hand, the hypothesis of local adaptation has never been investigated at the intra-specific level, i.e. within species currently undergoing population differentiation; on the other hand, many tree species are genetically structured over local scales due to neutral processes, mainly limited gene flow (caused by restricted pollen and seed dispersal). In this study, I used populations of a common tree species of the Guiana Shield - Eperua falcata (Fabaceae) - to study how neutral and adaptive processes shape the distribution of genetic diversity across forest landscapes characterized by local micro-habitat patchiness. I asked three main questions by combining both phenotypic (quantitative genetics) and molecular (population genetics) approaches: 1) How is the genetic diversity structured in forest landscapes of French Guiana? 2) Which evolutionary drivers are relevant to explain the structure of genetic diversity at local scale? 3) Does local adaptation contribute to structure genetic diversity within continuous populations?
En forêt tropicale humide Amazonienne, les facteurs gouvernant l'évolution des espèces d'arbres restent peu connus et continuellement débattus. En particulier, les micro-variations environnementales attirent beaucoup d'attention car elles induisent de profondes modifications de structure et composition des communautés. Les variations micro-environnementales associées à la topographie ont couramment été évoquées comme facteur de radiations adaptatives chez les espèces d'arbres. Cependant, l'hypothèse de l'adaptation locale n'a jamais été testée au niveau intra-spécifique chez les arbres de forêt amazonienne alors que l'on sait que la diversité génétique des arbres tropicaux est couramment structurée à faibles échelles spatiales par des processus neutres (en particulier du fait de restrictions de flux de gènes). Dans cette étude, j'ai étudié le processus de différentiation génétique d'une espèce d'arbre (Eperua falcata, Fabaceae) dans les paysages forestiers de Guyane française grâce à la combinaison d'une approche phénotypique (génétique quantitative) et d'une approche moléculaire (génétique des populations). Je me suis attachée à répondre à trois questions principales : 1) Comment se distribue la diversité génétique dans les paysages forestiers de Guyane française ? 2) Quelles forces évolutives sont impliquées dans le processus de différentiation génétique à faible échelle spatiale ? 3) Est-ce que le processus d'adaptation locale contribue à structurer la diversité génétique à faible échelle spatiale ?
https://tel.archives-ouvertes.fr/tel-00967318

NNT : 2013LORR0188
tel-00967318
https://tel.archives-ouvertes.fr/tel-00967318
https://tel.archives-ouvertes.fr/tel-00967318/document
https://tel.archives-ouvertes.fr/tel-00967318/file/THESE_Louise_Brousseau.pdf

Éditeur(s) : HAL CCSD Springer Verlag/EDP Sciences
Résumé : International audience
In the dense tropical rainforest understorey, saplings exhibit different growth strategies aiming at reaching light levels better fitting their ecology. Investing mainly in height growth, at the expense of their width, a lot are close to mechanical instability. Tachigali melinonii, a long living heliophilic tree species, is frequently observed to be extremely slender and supported by neighbours. Such observations suggest an active growth control through the perception of mechanical environment. * Mechanical environment or light availability, which one is the most influent on growth and slenderness (H/D)? To test this question, we recorded growth of control and staked saplings of two species with contrasting habits and ecology: T. melinonii, and Dicorynia guianensis, along a natural light gradient. * Dicorynia, the more stable, responded more clearly to the staking treatment, showing slenderness increase when light is available, whereas for Tachigali, only light availability governed growth. * For Tachigali, growth allocation is mainly governed by light availability and ontogeny, whereas Dicorynia is probably similar to the average tree strategy, using the thigmomorphogenetic physiological process to control its stability.
ISSN: 1286-4560

hal-00534019
https://hal.archives-ouvertes.fr/hal-00534019
DOI : 10.1051/forest/2009104

Éditeur(s) : HAL CCSD
Résumé :   Diplôme : DEA
il s'agit d'un type de produit dont les métadonnées ne correspondent pas aux métadonnées attendues dans les autres types de produit : DISSERTATION
Tropical rainforests are complex ecosystems, rarely investigated from ground-level. The canopy, highest part of the cover, can on the other hand be studied by several remote sensing tools. The aim of this study is to assess in what way the canopy is related to the forest structure below and the forest dynamic. We looked for correlation between the canopy texture (crown size) observed from aerial photographs and various parameters of the forest (spatial and demographic structure, forest dynamic, floristic structure). We worked on the Paracou experimental device, in French Guiana, at two different scales. 1- At a local scale (6.5 ha ; scale of the photographs 1: 4 000), we demarcated six sub-plots with big crowns in the canopy and six with small crowns. 2- At a forest scale (approximately one hundred ha ; scale of the photograph 1: 25 000), we compared 2 forest plots: one with a rough canopy texture and one with a smooth canopy texture. We found that the size of the crowns in the canopy do not express the same characteristics of the fore according to the scale of study : at the local scale, difference in crown size means a difference in basal area but not in density, while at the forest scale it is the opposite. Several hypotheses related to the sylvigenetic cycle, the floristic structure or the nature of the substratum are suggested to explain these results.
Les forêts tropicales humides (FTH) sont des écosystèmes complexes difficiles à étudier depuis le sol. Leur canopée, partie supérieure du couvert, est en revanche abordable par divers outils de télédétection. Cette étude vise à déterminer en quoi la structure de la canopée est le reflet de la structure forestière sous-jacente et de la dynamique spatio-temporelle qui s'y exerce. Nous avons donc recherché des corrélations, entre la texture de canopée (taille des couronnes) vue sur des photographies aériennes, et différents paramètres de la forêt sous-jacente (structure spatiale et démographique, dynamique forestière, structure floristique). Ce travail a été abordé sur le dispositif expérimental forestier de Paracou, en Guyane Française, à 2 échelles différentes. 1- A l'échelle de la parcelle (6,5 ha ; photographies au 1: 4 000), nous avons délimité des placettes à grosses couronnes en canopée et des placettes à petites couronnes. 2- A l'échelle du massif forestier (une centaine d'ha ; photographies IGN au 1: 25 000) nous comparons une parcelle de texture de canopée, grossière et une parcelle de texture fine. Le résultat principal de notre étude est que la taille des couronnes en canopée ne reflète pas les mêmes caractéristiques du couvert selon l'échelle de l’étude : à l'échelle de la parcelle, des différences de taille de couronnes traduisent des différences de surface terrière mais pas de densité, tandis qu'à l'échelle du massif forestier c'est l'inverse. Plusieurs hypothèses, invoquant des différences dans le stade sylvigénétique, la composition floristique ou la nature du substrat des placettes ou parcelles comparées, sont proposées pour expliquer ces résultats.
https://hal.archives-ouvertes.fr/hal-01189180

hal-01189180
https://hal.archives-ouvertes.fr/hal-01189180
PRODINRA : 12184

Éditeur(s) : HAL CCSD Springer Verlag
Résumé :  
The high spatial variability of soil respiration in tropical rainforests is well evaluated, but influences of biotic factors are not clearly understood. This study underlines the influence of tree species characteristics on soil respiration across a 16-monospecific plot design in a tropical plantation of French Guiana. A large variability of soil CO2 fluxes was observed among plots (i.e. 2.8 to 6.8 μmol m−2 s −1 ) with the ranking being constant across seasons. There were no significant relationships between soil respiration and soil moisture or soil temperature, neither spatially, nor seasonally. The variability of soil respiration was mainly explained by quantitative factors such as leaf litterfall and basal area. Surprisingly, no significant relationship was observed between soil respiration and root biomass. However, the influence of substrate quality was revealed by a strong relationship between soil respiration and litterfall P (and litterfall N, to a lesser extent).
ISSN: 0032-079X

hal-01032069
https://hal.archives-ouvertes.fr/hal-01032069
DOI : 10.1007/s11104-008-9866-z

Éditeur(s) : HAL CCSD Springer Verlag
Résumé : Functional aspects of biodiversity were investigated in a lowland tropical rainforest in French Guyana (5°2'N, annual precipitation 2200 mm). We assessed leaf '15N as a presumptive indicator of symbiotic N2 fixation, and leaf and wood cellulose '13C as an indicator of leaf intrinsic water-use efficiency (CO2 assimilation rate/leaf conductance for water vapour) in dominant trees of 21 species selected for their representativeness in the forest cover, their ecological strategy (pioneers or late successional stage species, shade tolerance) or their potential ability for N2 fixation. Similar measurements were made in trees of native species growing in a nearby plantation after severe perturbation (clear cutting, mechanical soil disturbance). Bulk soil '15N was spatially quite uniform in the forest (range 3-5‰), whereas average leaf '15N ranged from m0.3‰ to 3.5‰ in the different species. Three species only, Diplotropis purpurea, Recordoxylon speciosum (Fabaceae), and Sclerolobium melinonii (Caesalpiniaceae), had root bacterial nodules, which was also associated with leaf N concentrations higher than 20 mg gm1. Although nodulated trees displayed significantly lower leaf '15N values than non-nodulated trees, leaf '15N did not prove a straightforward indicator of symbiotic fixation, since there was a clear overlap of '15N values for nodulated and non-nodulated species at the lower end of the '15N range. Perturbation did not markedly affect the difference '15Nsoil m '15Nleaf, and thus the isotopic data provide no evidence of an alteration in the different N acquisition patterns. Extremely large interspecific differences in sunlit leaf '13C were observed in the forest (average values from m31.4 to m26.7‰), corresponding to intrinsic water-use efficiencies (ratio CO2 assimilation rate/leaf conductance for water vapour) varying over a threefold range. Wood cellulose '13C was positively related to total leaf '13C, the former values being 2-3‰ higher than the latter ones. Leaf '13C was not related to leaf '15N at either intraspecific or interspecific levels. '13C of sunlit leaves was highest in shade hemitolerant emergent species and was lower in heliophilic, but also in shade-tolerant species. For a given species, leaf '13C did not differ between the pristine forest and the disturbed plantation conditions. Our results are not in accord with the concept of existence of functional types of species characterized by common suites of traits underlying niche differentiation; rather, they support the hypothesis that each trait leads to a separate grouping of species.
ISSN: 0029-8549

hal-01032378
https://hal.archives-ouvertes.fr/hal-01032378
DOI : 10.1007/s004420050593

Éditeur(s) : HAL CCSD Springer Verlag/EDP Sciences
Résumé : We characterised the among species variability in leaf gas exchange and morphological traits under controlled conditions of seedlings of 22 tropical rainforest canopy species to understand the origin of the variability in leaf carbon isotope discrimination (Delta) among species with different growth and dynamic characteristics (successional gradient). Our results first suggest that these species pursue a consistent strategy in terms of (Delta) throughout their ontogeny (juveniles grown here versus canopy adult trees from the natural forest). Second, leaf (Delta) was negatively correlated with WUE and N, and positively correlated with gs, but among species differences in (Delta) were mainly explained by differences in WUE. Finally, species belonging to different successional groups display distinct leaf functional and morphological traits. We confirmed that fast growing early successional species maximise carbon assimilation with high stomatal conductance. In contrast, fast and slow growing late successional species are both characterised by low carbon assimilation values, but by distinct stomatal conductance and leaf morphological features. Along the successional gradient, these differences result in much lower (Delta) for the intermediate species (i.e. fast growing late successional) as compared to the two other groups.
ISSN: 1286-4560

hal-01032038
https://hal.archives-ouvertes.fr/hal-01032038
DOI : 10.1051/forest:2006101

Éditeur(s) : HAL CCSD Wiley
Résumé : The extent of gene dispersal is a fundamental factor of the population and evolutionary dynamics of tropical tree species, but directly monitoring seed and pollen movement is a difficult task. However, indirect estimates of historical gene dispersal can be obtained from the fine-scale spatial genetic structure of populations at drift-dispersal equilibrium. Using an approach that is based on the slope of the regression of pairwise kinship coefficients on spatial distance and estimates of the effective population density, we compare indirect gene dispersal estimates of sympatric populations of 10 tropical tree species. We re-analysed 26 data sets consisting of mapped allozyme, SSR (simple sequence repeat), RAPD (random amplified polymorphic DNA) or AFLP (amplified fragment length polymorphism) genotypes from two rainforest sites in French Guiana. Gene dispersal estimates were obtained for at least one marker in each species, although the estimation procedure failed under insufficient marker polymorphism, limited sample size, or inappropriate sampling area. Estimates generally suffered low precision and were affected by assumptions regarding the effective population density. Averaging estimates over data sets, the extent of gene dispersal ranged from 150 m to 1200 m according to species. Smaller gene dispersal estimates were obtained in species with heavy diaspores, which are presumably not well dispersed, and in populations with high local adult density. We suggest that limited seed dispersal could indirectly limit effective pollen dispersal by creating higher local tree densities, thereby increasing the positive correlation between pollen and seed dispersal distances. We discuss the potential and limitations of our indirect estimation procedure and suggest guidelines for future studies
ISSN: 0962-1083

hal-01031603
https://hal.archives-ouvertes.fr/hal-01031603
DOI : 10.1111/j.1365-294X.2005.02785.x

Éditeur(s) : HAL CCSD Springer Verlag/EDP Sciences
Résumé : International audience
Context and aim : This study aimed to examine the effect of the tension wood G‐layer on the viscoelastic properties of wood. Methods : Tension wood and opposite wood samples were obtained from six French Guianese tropical rainforest species (Sextonia rubra, Ocotea guyanensis, Inga alba, Tachigali melinoni, Iyranthera sagotiana and Virola michelii); the tension wood of the former three of these species had a Glayer, whilst the tension wood from the latter three had no Glayer. Tensile dynamic mechanical analysis (DMA) was performed on green never dried wood samples in the longitudinal direction with samples submerged in a water bath at a temperature (30°C) and frequency (1 Hz) representative of the conditions experienced by wood within a living tree. Then, DMA was repeated with samples conditioned to an air-dried state. Finally, samples were oven-dried to measure longitudinal shrinkage. Results : Tension wood did not always have a higher longitudinal storage (elastic) modulus than opposite wood from the same tree regardless of the presence or absence of a G‐layer. For the species containing a G‐layer, tension wood had a higher damping coefficient and experienced a greater longitudinal shrinkage upon drying than opposite wood from the same species. No difference was found in damping coefficients between tension wood and opposite wood for the species that had no G‐layer. Conclusion : It is proposed that the different molecular composition of the G-layer matrix has an influence on the viscoelasticity of wood, even if a biomechanical gain is not yet clear. This study shows that rheological properties and longitudinal shrinkage can be used to detect the presence of a G‐layer in tension wood.
ISSN: 1286-4560

hal-00677460
https://hal.archives-ouvertes.fr/hal-00677460
https://hal.archives-ouvertes.fr/hal-00677460/document
https://hal.archives-ouvertes.fr/hal-00677460/file/Clair2.pdf
DOI : 10.1007/s13595-011-0164-1

Éditeur(s) : HAL CCSD Oxford University Press (OUP)
Résumé : International audience
Gravitropism is necessary for plants to control the orientation of their axes while they grow in height. In woody plants, stem re-orientations are costly because they are achieved through diameter growth. The functional diversity of gravitropism was studied to check if the mechanisms involved and their efficiency may contribute to the differentiation of height growth strategies between forest tree species at the seedling stage. Seedlings of eight tropical species were grown tilted in a greenhouse, and their up-righting movement and diameter growth were measured during three months. Morphological, anatomical and biomechanical traits were measured at the end of the survey. Curvature analysis was used to analyse the up-righting response along the stems. Variations in stem curvature depend on diameter growth, size effects, the increase in self-weight, and the efficiency of the gravitropic reaction. A biomechanical model was used to separate these contributions. Results showed that (1) gravitropic movements were based on a common mechanism associated to similar dynamic patterns, (2) clear differences in efficiency (defined as the change in curvature achieved during an elementary diameter increment for a given stem diameter) existed between species, (3) the equilibrium angle of the stem and the anatomical characters associated to the efficiency of the reaction also differed between species, (4) the differences in gravitropic reaction were related to the light requirements: heliophilic species, compared to more shade-tolerant species, had a larger efficiency and an equilibrium angle closer to vertical. This suggests that traits determining the gravitropic reaction are related to the strategy of light interception and may contribute to the differentiation of ecological strategies promoting the maintenance of biodiversity in tropical rain forests.
ISSN: 0022-0957

hal-00797023
https://hal.archives-ouvertes.fr/hal-00797023
https://hal.archives-ouvertes.fr/hal-00797023/document
https://hal.archives-ouvertes.fr/hal-00797023/file/Functional_diversity_gravitropic_Almeras_al.pdf