Éditeur(s) : HAL CCSD
Résumé : International audience
BackgroundTree above ground biomass (AGB) is currently estimated by tree-level allometrical models that take into account, tree volume estimated from proxy variables of tree size (DBH) and species average wood specific gravity (WSG). These methods are common and realistic from a practical point of view. However, they do not take into account deviance from fixed allometrical trajectories and species or tree level WSG variations. Here, we present Xtrawood software that allows computation of tree AGB according to structure and WSG variations.MethodXtrawood reconstructs tree structure and integrates WSG variations by merging tree structure and WSG data measured at different position in trees, leading to the computation of global AGB and visualization of WSG variation along tree structure. Tree structure is measured according to stem dimensions (length, diameter) and positions within tree, and encoded in Multiscale Tree Graph format (MTG). WSG data is made of radial WSG profiles (1 measure each 0,5 cm from pith to bark) sampled at different heights within whole tree. Xtrawood output are illustrated using a dataset collected on an Amazonian forest ‘biomass dominant species’, Dicorynia guianensis Amsh., also known to exhibit substantial WSG gradients along both radial and vertical axis. 9 trees ranging from 15 to 60 cm DBH were measured by climbers. Each tree was felled and samples were collected at different positions (3 in trunk, 1 to 5 in crown) to record WSG radial profiles.ResultsXtrawood allows computation of tree volume, but also visualization of WSG variations in tree as well as inference of WSG radial profiles at different heights. Output variables are decomposed according to different tree scale and locations (axis, trunk/crown) and easy to extract. Xtrawood results will be compared to those of standard estimation method and can be used to identify positions in trees where WSG value leads to the better estimate of tree AGB.Conclusion/perspectiveXtrawood produces AGB estimate with data from intensive measurements practices. The sampling protocol, used here, remains destructive and time-consuming because Xtrawood is not directly dedicated to forest managers, but to help calibration of realistic sampling strategies. Moreover, Xtrawood offers a way to understand relationships between tree development, WSG variations within tree structure and biomass accumulation in the context of natural forests or plantations. A software demo is available at coffee break.
53rd Annual Meeting of the Association for Tropical Biology and Conservation (ATBC 2016)
Montpellier, France

Droits : http://creativecommons.org/licenses/by/
hal-01349613
https://hal.archives-ouvertes.fr/hal-01349613

Éditeur(s) : HAL CCSD Cambridge University Press (CUP)
Résumé :  
Although the potential contribution to tropical tree species coexistence of niche differentiation along light gradients has receivedmuch attention, the degree to which species perform differentially along soil resource gradients remains unclear. To examine differential growth response to soil resources, we grew seedlings of nine tropical tree species at 6.0% of full sun for 12mo in a factorial design of two soil types (clay and white sand), two phosphate fertilization treatments (control and addition of 100mgP kg−1) and two watering treatments (field capacity and water limitation to one-third field capacity). Species differedmarkedly in biomass growth rate, but this hierarchy was almost completely conserved across all eight treatments. All species grew more slowly in sand than clay soils, and no species grew faster with phosphate additions. Only Eperua grandiflora and E. falcata showed significant growth increases in the absence of water limitation. Faster-growing species were characterized by high specific leaf area, high leaf allocation and high net assimilation rate but not lower root allocation. Slower-growing species exhibited greater plasticity in net assimilation rate, suggesting that tolerance of edaphic stress in these species is related more to stomatal control than to whole-plant carbon allocation. Although relative growth rate for biomass was correlatedwith both its physiological and morphological components, interspecific differences were best explained by differences in net assimilation rate across six of the eight treatments. A suite of traits including high assimilation and high specific leaf area maintains rapid growth rate of faster-growing species across awide gradient of soil resources, but the lack of plasticity they exhibit may compromise their survival in the poorest soil environments.
ISSN: 0266-4674

hal-01032086
https://hal.archives-ouvertes.fr/hal-01032086
DOI : 10.1017/S0266467406003439

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-01190909
https://hal.archives-ouvertes.fr/hal-01190909
PRODINRA : 73005

Éditeur(s) : HAL CCSD Wiley
Résumé : International audience
We assessed the extent of recent environmental changes on leaf morphological (stomatal density, stomatal surface, leaf mass per unit area) and physiological traits (carbon isotope composition, δ(13)C(leaf) , and discrimination, Δ(13)C(leaf) , oxygen isotope composition, δ(18)O(leaf) ) of two tropical rainforest species (Dicorynia guianensis; Humiria balsamifera) that are abundant in the Guiana shield (Northern Amazonia). Leaf samples were collected in different international herbariums to cover a 200 year time-period (1790-2004) and the whole Guiana shield. Using models describing carbon and oxygen isotope fractionations during photosynthesis, different scenarios of change in intercellular CO(2) concentrations inside the leaf (C(i)), stomatal conductance (g), and photosynthesis (A) were tested in order to understand leaf physiological response to increasing air CO(2) concentrations (C(a)). Our results confirmed that both species displayed physiological response to changing C(a) . For both species, we observed a decrease of about 1.7‰ in δ(13)C(leaf) since 1950, without significant change in Δ(13)C(leaf) and leaf morphological traits. Furthermore, there was no clear change in δ(18)O(leaf) for Humiria over this period. Our simulation approach revealed that an increase in A, rather than a decrease in g, explained the observed trends for these tropical rainforest species, allowing them to maintain a constant ratio of C(i)/C(a) .
ISSN: 0140-7791

halsde-00675165
https://hal.archives-ouvertes.fr/halsde-00675165
DOI : 10.1111/j.1365-3040.2011.02333.x
PUBMED : 21486302

Éditeur(s) : HAL CCSD
Résumé : absent
Actes du BRG

hal-01031523
https://hal.archives-ouvertes.fr/hal-01031523

Éditeur(s) : HAL CCSD INRA/EDP Sciences
Résumé : absent
ISSN: 0003-4312

hal-01032368
https://hal.archives-ouvertes.fr/hal-01032368

Éditeur(s) : HAL CCSD Springer Verlag
Résumé : The suitability of the natural 15N abundance and of total N concentration of leaves as indicators of the type of plant N nutrition in a rain forest of French Guiana were tested. Leaf samples from primary legume species, non-legumes (pioneer species) and from the non-N2-fixing species Dicorynia guianensis were analyzed. Both '15N and total leaf N varied widely (m1 r '15N (‰) r 7 and 1 r leaf N(%) r 3.2) suggesting possible distinctions between diazotrophic and non-fixing plants. The '15N also revealed two statistically distinct groups of non-N2-fixing species ('15N = 5.14 - 0.3 vs '15Nv=v1.65 - 0.17) related to the different ecological behaviors of these species in the successional processes. We conclude that the '15N signature of plant leaves combined with their total N concentration may be relevant indicators for identifying functional groups within the community of non-N2-fixing species, as well as for detecting diazotrophy. Despite the variability in the '15N of the non-N2-fixing species, N2-fixing groups can still be identified, provided that plants are simultaneously classified taxonomically, by their leaf '15N and total N concentration and by the presence or absence of nodules. The variability in the '15N of the non-fixing species is discussed.
ISSN: 0029-8549

hal-01031454
https://hal.archives-ouvertes.fr/hal-01031454
DOI : 10.1007/s004420050846

Éditeur(s) : HAL CCSD
Résumé : Le régime de reproduction de Dicorynia guianensis (caesalpiniaceae), arbre de la forêt guyanaise a été étudié à l'aide des marqueurs enzymatiques. Le matériel végétal a été collecté en 1993 et 1995, sur le dispositif sylvicole de Paracou. Le taux d'allofécondation moyen de la population est élevé, tm = 0,85, stable d'une année à l'autre malgré une variation importante du taux de floraison. Le taux individuel varie entre les arbres mais aucune corrélation n'a pu être établie avec des facteurs spatiaux, densité de floraison ou distance aux plus proches voisins. L'hétérogénéité des nuages polliniques est sensible au niveau des agrégats et des arbres individuels, échelle spatiale où se déploie l'activité des insectes pollinisateurs. Nous n'avons en évidence aucune corrélation spatiale entre compositions des nuages polliniques individuels. Des distances de migration du pollen de 190 mètres ont été mise en évidence grâce aux allèles rares. Aucune différence significative du régime de reproduction de D. guianensis n'a été trouvée entre parcelles traitées et parcelles témoin du dispositif.
Colloque BRG/USTL. Méthodologie de gestion et de conservation des ressources génétiques
Lille, France

hal-01032382
https://hal.archives-ouvertes.fr/hal-01032382

Éditeur(s) : HAL CCSD
Résumé : The functioning of ecosystems is based on the functional diversity, which is the complementto the species diversity. In the tropical rain forest, the saplings grow in the dense and stratifiedunderstorey. This thesis deals with the diversity of realisation of the support function by thesaplings in this context. The hypotheses are that the race through higher and so brighter levelsconstrains the mechanical security of the saplings with necessary biomass saving and need ofreorientation (gravitropism) and acclimation (mecanoperception and response) processes andthat diversity is thus structured by the species light-demand and affinity for the risk. Using awide sample of 16 species, at the Paracou station, relevant functional traits - risk of not-selfsupportingand gravitropic performance - are defined through adapted modellings whichcombine trunk shape, biomass distribution and wood properties. The traits values varybetween species and also with ontogeny and saplings environment. These variations are dueto elementary traits (shape, biomass, wood) with strong geometrical effects. The less selfsupportingspecies (low mechanical security) have the highest gravitropic performances andare also the most light-demanders. A species, Tachigali melinonii, distinguishes itself bystrong slendernesses and a frequent not-self-supporting habit letting suppose a strongadaptability to its mechanical environment. An experiment (growth response to staking),however, did not provide the expected results whereas the species with lower risks, Dicoryniaguianensis, reacted more.
Le fonctionnement des écosystèmes repose sur la diversité fonctionnelle, complément de ladiversité spécifique. En forêt tropicale humide, les jeunes arbres croissent en sous-bois denseet stratifié. Cette thèse porte sur la diversité de réalisation de la fonction biomécanique desoutien. Les hypothèses sont que la "course" vers les strates plus éclairées contraint lasécurité mécanique des jeunes arbres, avec de nécessaires économies de matière et recours àdes processus de réparation (gravitropisme) et d'acclimatation (mécanoperception et réponse),et que la diversité est donc structurée par le besoin en lumière et l'affinité pour le risque desespèces. Avec un échantillon de 16 espèces sur le dispositif de Paracou, des traits fonctionnelspertinents - risque de non-autoportance et performance gravitropique - sont définis au traversde modélisations adaptées qui combinent forme des troncs, répartition des masses etpropriétés du bois. Ces traits varient entre espèces mais aussi avec le développement etl'environnement des arbres. Ces variations sont dues aux variations des traits élémentaires(forme, masses, bois) avec de forts effets géométriques. Les espèces les moins autoportantes(faible sécurité) ont les plus fortes performances gravitropiques. Ce sont aussi les plusdemandeuses de lumière. Une espèce Tachigali melinonii se distingue par de fortsélancements et une fréquente non-autoportance laissant supposer une adaptabilité forte àl'environnement mécanique. Une expérimentation (réponse de croissance au tuteurage) n'acependant pas abouti aux résultats supposés puisque c'est au contraire l'espèce à faible risque,Dicorynia guianensis, qui s'est montrée plus réactive.
https://tel.archives-ouvertes.fr/tel-00272100

tel-00272100
https://tel.archives-ouvertes.fr/tel-00272100
https://tel.archives-ouvertes.fr/tel-00272100/document
https://tel.archives-ouvertes.fr/tel-00272100/file/TheseJaouen.pdf

Éditeur(s) : HAL CCSD Springer Verlag
Résumé : We conducted a rigorous test of tropical tree seedling microhabitat differentiation by examining microhabitat associations, survival and growth of established seedlings of ten tropical tree species representing a four-factor gradient in seed size. Eight microhabitat variables describing soil and light conditions were measured directly adjacent to each of 588 seedlings within twelve 10×100 m belt transects at Paracou, French Guiana, and at 264 reference points along the transects. From these measurements, we defined three principal components describing soil richness, soil softness and canopy openness. Six of ten species (in 9 of 30 total cases) were distributed non-randomly with respect to microhabitat along at least one principal component. However, few species demonstrated clear microhabitat specialization. All shifts in distribution relative to reference points were in the same direction (richer, softer soil). Furthermore, of 135 pairwise comparisons among the species, only 7 were significantly different. More than three-fourths of all seedlings (75.3%) survived over the 2-year monitoring period, but survival rates varied widely among species. In no case was the probability of survival influenced by any microhabitat parameter. Relative height growth rates for the seedlings over 2 years varied from -0.031 cm cm-1 year-1 (Dicorynia guianensis, Caesalpiniaceae) to 0.088 cm cm-1 year-1 (Virola michelii, Myristicaceae). In only 4 of 30 cases was height growth significantly associated with one of the three principal components. Because the conditions in this study were designed to maximize the chance of finding microhabitat differentiation among a group of species differing greatly in life history traits, the lack of microhabitat specialization it uncovered suggests that microhabitat partitioning among tropical tree species at the established seedling stage is unlikely to contribute greatly to coexistence among these species.
ISSN: 0029-8549

hal-01031928
https://hal.archives-ouvertes.fr/hal-01031928
DOI : 10.1007/s00442-004-1691-3

Éditeur(s) : HAL CCSD
Résumé :  
En Guyane française où les sols sont généralement acides et pauvres en éléments minéraux, la forêt est caractérisée par sa plurispécificité. Une approche de type écologique a montré, dans les racines des principales espèces forestières, la dominance d'endomycorhizes à structure intracellulaire particulière : des hyphes de type Paris, spiralé. Leur rôle dans l'acquisition du phosphore a été étudié expérimentalement chez deux Césalpiniacées. Les semis d'Angélique, Dicorynia guianensis Amshoff, sont très dépendants, pour leur croissance et leur teneur en phosphore, des mycorhizes à mycélium spiralé ; ce type de mycélium représente plus de 90 % de la colonisation fongique. Par contre, les semis de Wapa (Eperua falcata Aublet) forment également des mycorhizes mais ces dernières améliorent le statut phosphaté et sont sans effet sur la croissance de cette espèce. Ces résultats contribuent à la compréhension du rôle des symbioses endomycorhiziennes dans le processus de régénération naturelle et ouvrent des perspectives de recherche quant à leur intervention éventuelle dans le maintien de la diversité forestière.
Revue Forestière Française

hal-01032197
https://hal.archives-ouvertes.fr/hal-01032197