Éditeur(s) : HAL CCSD Springer Verlag
Résumé : International audience
Variation of dead wood decay rates among tropical trees remains one source of uncertainty in global models of the carbon cycle. Taking advantage of a broad forest plot network surveyed for tree mortality over a 23-year period, we measured the remaining fraction of boles from 367 dead trees from 26 neotropical species widely varying in wood density (0.23–1.24 g cm-3) and tree circumference at death time (31.5–272.0 cm). We modeled decay rates within a Bayesian framework assuming a first order differential equation to model the decomposition process and tested for the effects of forest management (selective logging vs. unexploited), of mode of death (standing vs. downed) and of topographical levels (bottomlands vs. hillsides vs. hilltops) on wood decay rates. The general decay model predicts the observed remaining fraction of dead wood (R2 = 60%) with only two biological predictors: tree circumference at death time and wood specific density. Neither selective logging nor local topography had a differential effect on wood decay rates. Including the mode of death into the model revealed thatstanding dead trees decomposed faster than downed dead trees, but the gain of model accuracy remains rather marginal. Overall, these results suggest that the release of carbon from tropical dead trees to the atmosphere can be simply estimated using tree circumference at death time and wood density.
ISSN: 0029-8549

hal-01094187
https://hal-agroparistech.archives-ouvertes.fr/hal-01094187
DOI : 10.1007/s00442-010-1602-8

Éditeur(s) : HAL CCSD Nordic Ecological Society
Résumé : Niche differentiation and ecological filtering are primary ecological processes that shape community assembly, but their relative importance remains poorly understood. Analyses of the distributions of functional traits can provide insight into the community structure generated by these processes. We predicted the trait distributions expected under the ecological processes of niche differentiation and environmental filtering, then tested these predictions with a dataset of 4672 trees located in nine 1-ha plots of tropical rain forest in French Guiana. Five traits related to leaf function (foliar N concentration, chlorophyll content, toughness, tissue density and specific leaf area), and three traits related to stem function (trunk sapwood density, branch sapwood density, and trunk bark thickness), as well as laminar surface area, were measured on every individual tree. There was far more evidence for environmental filtering than for niche differentiation in these forests. Furthermore, we contrasted results from species-mean and individual-level trait values. Analyses that took within-species trait variation into account were far more sensitive indicators of niche differentiation and ecological filtering. Species-mean analyses, by contrast, may underestimate the effects of ecological processes on community assembly. Environmental filtering appeared somewhat more intense on leaf traits than on stem traits, whereas niche differentiation affected neither strongly. By accounting for within-species trait variation, we were able to more properly consider the ecological interactions among individual trees and between individual trees and their environment. In so doing, our results suggest that the ecological processes of niche differentiation and environmental filtering may be more pervasive than previously believed.
ISSN: 0030-1299

hal-01032397
https://hal.archives-ouvertes.fr/hal-01032397
DOI : 10.1111/j.1600-0706.2010.19110.x

Éditeur(s) : HAL CCSD Wiley
Résumé : International audience
1. Estimating forest above-ground biomass (AGB), or carbon (AGC), in tropical forests has become a majorconcern for scientists and stakeholders. However, AGB assessment procedures are not fully standardized andeven more importantly the uncertainty associated with AGB estimates is seldom assessed.2. Here, we present an R package designed to compute both AGB/AGC estimate and its associated uncertaintyfrom forest plot datasets, using a Bayesian inference procedure. The package builds upon previous work onpantropical and regional biomass allometric equations and published datasets by default but it can alsointegrate unpublished or complementary datasets in many steps.3. BIOMASS performs a number of standard tasks on input forest tree inventories: i) tree speciesidentification, if available, is automatically corrected; ii) wood density is estimated from tree species identity;iii) if height data are available, a local height-diameter allometry may be built; else height is inferred frompantropical or regional models; iv) finally, AGB/AGC are estimated by propagating the errors associated withall the calculation steps up to the final estimate. R code is given in the paper and in the appendix forillustration purpose.4. The BIOMASS package should contribute to improved standards for AGB calculation for tropical foreststands, and will encourage users to report the uncertainties associated with stand-level AGB/AGC estimatesin future studies.
ISSN: 2041-210X

hal-01558180
https://hal.archives-ouvertes.fr/hal-01558180
DOI : 10.1111/2041-210X.12753

Éditeur(s) : HAL CCSD Cambridge University Press (CUP)
Résumé : The natural 15N abundance method for estimating symbiotic biological N2-fixation was tested on legume trees from two rain forests on contrasting soils (oxisols and spodosols) in French Guiana. When possible, the significance of N2-fixing species in the plant community was evaluated in terms of density, biomass and contribution of N2-fixation to the building up of the total nitrogen mass in the leaves. Of the two sites, the rain forest on spodosols was the less favourable for application of the [delta]15N method: the available soil nitrogen was isotopically similar to fixed-N2. Hence, the results showed that a reliable estimate of N2-fixation could not be obtained. A substantial contribution of fixed-N2 to the nitrogen nutrition of legumes was found on oxisols, with an average value of 54 % Ndfa (Nitrogen derived from the atmosphere). The contribution of the N2-fixing legumes to the biomass of the stand was estimated to be 2 t ha[minus sign]1 for the leaf biomass and 136 t ha[minus sign]1 for the total above-ground plant biomass. With 7.5 % of trees in the stand able to fix N2 (462 out of 6156), N2-fixation was estimated to be 7 kg ha[minus sign]1 y[minus sign]1. These results are the first use of the [delta]15N method to estimate nitrogen input by N2-fixing legumes to a natural rain forest. The inter-site variability observed in the [delta]15N of the non-fixing plants suggested different nitrogen-cycling processes in the two soils. The [delta]15N of the non-N2-fixing plants could be related to the soil nitrogen availability and be used as an indicator of efficient or non-efficient nitrogen-cycling rain forests. The spatial variability of the [delta]15N in the plant-available soil nitrogen pool and the nitrogen balance in tropical rain forests are discussed.
ISSN: 0266-4674

hal-01032201
https://hal.archives-ouvertes.fr/hal-01032201
DOI : 10.1017/S0266467499000644

Éditeur(s) : HAL CCSD Botanical Society of America
Résumé : Premise of the study : Wood density correlates with mechanical and physiological strategies of trees and is important for estimating global carbon stocks. Nonetheless, the relationship between branch and trunk xylem density has been poorly explored in neotropical trees. Here, we examine this relationship in trees from French Guiana and its variation among different families and sites, to improve the understanding of wood density in neotropical forests. Methods : Trunk and branch xylem densities were measured for 1909 trees in seven sites across French Guiana. A major-axis fit was performed to explore their general allometric relationship and its variation among different families and sites. Key results : Trunk xylem and branch xylem densities were significantly positively correlated, and their relationship explained 47% of the total variance. Trunk xylem was on average 9% denser than branch xylem. Family-level differences and interactions between family and site accounted for more than 40% of the total variance, whereas differences among sites explained little variation. Conclusions : Variation in xylem density within individual trees can be substantial, and the relationship between branch xylem and trunk xylem densities varies considerably among families and sites. As such, whole-tree biomass estimates based on non-destructive branch sampling should correct for both taxonomic and environmental factors. Furthermore, detailed estimates of the vertical distribution of wood density within individual trees are needed to determine the extent to which relying solely upon measures of trunk wood density may cause carbon stocks in tropical forests to be overestimated.
ISSN: 0002-9122

hal-01032401
https://hal.archives-ouvertes.fr/hal-01032401
DOI : 10.3732/ajb.1000034

Éditeur(s) : HAL CCSD Ecological Society of America
Résumé : Tropical plant diversity is extraordinarily high at both local and regional scales. Many studies have demonstrated that natural enemies maintain local diversity via negative density dependence, but we know little about how natural enemies influence beta-diversity across habitats and/or regions. One way herbivores could influence plant beta-diversity is by driving allocation trade-offs that promote habitat specialization across resource gradients. We therefore predicted that increasing resource availability should be accompanied by increasing herbivory rates and decreasing plant allocation to defense. Second, relative abundances within plant lineages are predicted to reflect patterns of habitat specialization and allocation trade-offs. A phylogenetic context is vital not only to compare homologous plant traits (including defense strategies) across habitat types, but also to connect evolutionary trade-offs to patterns of species diversification in each phylogenetic lineage. We tested these predictions for trees in white-sand, clay terra firme, and seasonally flooded forests in Peru and French Guiana that represent the range of soil fertility, forest structure, and floristic compositions found throughout the Amazon region. We established 74 0.5-ha plots in these habitats and sampled all trees. Within 12 representative plots we marked newly expanding leaves of 394 saplings representing 68 species, including the most abundant species in each plot in addition to species from five focal lineages: Swartzia and Inga (Fabaceae), Protieae (Burseracaeae), Bombacoideae (Malvaceae), and Micropholis (Sapotaceae). We measured total leaf production rates for each sapling and calculated relative herbivory impact as the ratio between herbivory rate and leaf production rate. Herbivory rates averaged 2.1% per month, did not correlate with leaf production rate, and were similar across habitats. Relative herbivore impacts exceeded leaf production rates for most species. Leaf production rate averaged 2.8%, was significantly higher in seasonally flooded forests than the other two habitats, and exhibited significant correlations with specific leaf area. Species with high herbivory rates exhibited significantly lower relative abundances in terra firme forests. Overall, focal species within lineages present contrasting patterns regarding their herbivory rates and leaf production rate within habitats. These results highlight why a lineage-based approach is necessary when attempting to connect hypotheses regarding evolutionary trade-offs to community assembly patterns.
ISSN: 0012-9658

hal-01032418
https://hal.archives-ouvertes.fr/hal-01032418

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
The study of decay resistance in wood is of interest for wood end-users but also for the global carbon balance since wood biodegradation is a key driver of forest ecosystem functioning through its impacts on carbon and nutrient cycling. We studied the density and wood extractive contents in order to understand decay resistance against soil microflora after 90 days exposure of sapwood and heartwood from three Neotropical wood species known for their decay resistance: Bocoa prouacensis, Vouacapoua americana, Inga alba. Decay resistance was correlated with density more than wood extractive content. The results highlighted different decay resistance strategies. In B. prouacensis, both sapwood and heartwood were highly resistant due to the high density and high content of antifungal wood extractives. In V. americana heartwood, decay resistance was due to the high synergistic-acting wood extractive content. Conversely, with the least dense wood species I. alba, we found that decay resistance was due to the antifungal wood extractives synthesized early in the sapwood. In conclusion, we showed that the three wood species with the same level of heartwood decay resistance performance had different decay resistance strategies according to the anatomic and defensive wood traits.
ISSN: 0964-8305

hal-01321162
https://hal.archives-ouvertes.fr/hal-01321162
https://hal.archives-ouvertes.fr/hal-01321162/document
https://hal.archives-ouvertes.fr/hal-01321162/file/Art_Amusant_al_Diversity_decay_resistance_strategies_Int.Biodet.Biodegr._2014.pdf
DOI : 10.1016/j.ibiod.2014.06.012

Éditeur(s) : HAL CCSD Public Library of Science
Résumé : International audience
Little is known of how linkage patterns between species change along environmental gradients. The small, spatially discrete food webs inhabiting tank-bromeliads provide an excellent opportunity to analyse patterns of community diversity and food-web topology (connectance, linkage density, nestedness) in relation to key environmental variables (habitat size, detrital resource, incident radiation) and predators: prey ratios. We sampled 365 bromeliads in a wide range of understorey environments in French Guiana and used gut contents of invertebrates to draw the corresponding 365 connectance webs. At the bromeliad scale, habitat size (water volume) determined the number of species that constitute food-web nodes, the proportion of predators, and food-web topology. The number of species as well as the proportion of predators within bromeliads declined from open to forested habitats, where the volume of water collected by bromeliads was generally lower because of rainfall interception by the canopy. A core group of microorganisms and generalist detritivores remained relatively constant across environments. This suggests that (i) a highly-connected core ensures food-web stability and key ecosystem functions across environments, and (ii) larger deviations in food-web structures can be expected following disturbance if detritivores share traits that determine responses to environmental changes. While linkage density and nestedness were lower in bromeliads in the forest than in open areas, experiments are needed to confirm a trend for lower food-web stability in the understorey of primary forests.
PLoS ONE

hal-00913931
https://hal.archives-ouvertes.fr/hal-00913931
https://hal.archives-ouvertes.fr/hal-00913931/document
DOI : 10.1371/journal.pone.0071735
OATAO : 10204

Éditeur(s) : HAL CCSD Wiley
Résumé : Tropical forests contain an important proportion of the carbon stored in terrestrial vegetation, but estimated aboveground biomass (AGB) in tropical forests varies two-fold, with little consensus on the relative importance of climate, soil and forest structure in explaining spatial patterns. Here, we present analyses from a plot network designed to examine differences among contrasting forest habitats (terra firme, seasonally flooded, and white-sand forests) that span the gradient of climate and soil conditions of the Amazon basin. We installed 0.5-ha plots in 74 sites representing the three lowland forest habitats in both Loreto, Peru and French Guiana, and we integrated data describing climate, soil physical and chemical characteristics and stand variables, including local measures of wood specific gravity (WSG). We use a hierarchical model to separate the contributions of stand variables from climate and soil variables in explaining spatial variation in AGB. AGB differed among both habitats and regions, varying from 78 Mg ha−1 in white-sand forest in Peru to 605 Mg ha−1 in terra firme clay forest of French Guiana. Stand variables including tree size and basal area, and to a lesser extent WSG, were strong predictors of spatial variation in AGB. In contrast, soil and climate variables explained little overall variation in AGB, though they did co-vary to a limited extent with stand parameters that explained AGB. Our results suggest that positive feedbacks in forest structure and turnover control AGB in Amazonian forests, with richer soils (Peruvian terra firme and all seasonally flooded habitats) supporting smaller trees with lower wood density and moderate soils (French Guianan terra firme) supporting many larger trees with high wood density. The weak direct relationships we observed between soil and climate variables and AGB suggest that the most appropriate approaches to landscape scale modeling of AGB in the Amazon would be based on remote sensing methods to map stand structure.
ISSN: 1354-1013

hal-01374829
https://hal.archives-ouvertes.fr/hal-01374829
DOI : 10.1111/j.1365-2486.2011.02432.x
PRODINRA : 183370

Éditeur(s) : HAL CCSD Elsevier
Résumé : Guadua sarcocarpa and Guadua weberbaueri (Poaceae: Bambuseae) have a negative influence on tree regeneration and recruitment in bamboo-dominated forests of southwestern Amazonia. The lack of advanced regeneration and sparse canopy in this forest type present a considerable challenge for developing sustainable timber management plans. We conducted field studies in the Porto Dias Agroextractive Settlement Project in Acre, Brazil to assess influences of logging in bamboo-dominated forest sites. Taxonomic composition, stand structure, aboveground biomass, commercial timber volume, and commercial tree seedling and bamboo culm density were compared between five logged vs. unlogged sites in different landholdings, using modified 0.5 ha Gentry plots. No differences in taxonomic composition, aboveground biomass, adult and juvenile stem density, or woody seedling and bamboo culm density were detected between paired logged and unlogged sites. Commercial timber volume, however, was reduced by almost two-thirds in logged plots, suggesting that long-term timber management goals in this forest type are compromised since so few future crop trees remained onsite. Our findings indicate that in order to maximize local management objectives, community forest managers must approach logging in bamboo-dominated forests with caution. We suggest an integration of non-timber forest product extraction with low harvest intensity and low-impact logging, tending of natural regeneration, and diversification of commercial species.
ISSN: 0378-1127

hal-01204213
https://hal.archives-ouvertes.fr/hal-01204213
DOI : 10.1016/j.foreco.2013.12.022
PRODINRA : 263103

Éditeur(s) : HAL CCSD Wiley
Résumé : 1. Trade-offs among functional traits reveal major plant strategies that can give insight into species distributions and ecosystem processes. However, current identification of plant strategies lacks the integration of root structural traits together with leaf and stem traits. 2. We examined correlations among 14 traits representing leaf, stem and woody root tissues. Traits were measured on 1084 individuals representing 758 Neotropical tree species, across 13 sites representative of the environmental variation encompassed by three widespread habitats (seasonally flooded, clay terra firme and white-sand forests) at opposite ends of Amazonia (French Guiana and Peru). 3. Woody root traits were closely aligned with stem traits, but not with leaf traits. Altogether leaf, stem and woody root traits delineated two orthogonal axes of functional trade-offs: a first axis defined by leaf traits, corresponding to a leaf economics spectrum, and a second axis defined by covarying stem and woody root traits, corresponding to a wood economics spectrum. These axes remained consistent when accounting for species evolutionary history with phylogenetically independent contrasts. 4. Despite the strong species turnover across sites, the covariation among root and stem structural traits as well as their orthogonality to leaf traits were strongly consistent across habitats and regions. 5. We conclude that root structural traits mirrored stem traits rather than leaf traits in Neotropical trees. Leaf and wood traits define an integrated whole-plant strategy in lowland South American forests that may contribute to a more complete understanding of plant responses to global changes in both correlative and modelling approaches. We suggest further meta-analyses in expanded environmental and geographic zones to determine the generality of this pattern.
ISSN: 0269-8463

hal-01032415
https://hal.archives-ouvertes.fr/hal-01032415
DOI : 10.1111/j.1365-2435.2012.02020.x

Éditeur(s) : HAL CCSD Public Library of Science
Résumé : International audience
Local variation in the density of Anopheles mosquitoes and the risk of exposure to bites are essential to explain the spatial and temporal heterogeneities in the transmission of malaria. Vector distribution is driven by environmental factors. Based on variables derived from satellite imagery and meteorological observations, this study aimed to dynamically model and map the densities of Anopheles darlingi in the municipality of Saint-Georges de l’Oyapock (French Guiana). Longitudinal sampling sessions of An. darlingi densities were conducted between September 2012 and October 2014. Landscape and meteorological data were collected and processed to extract a panel of variables that were potentially related to An. darlingi ecology. Based on these data, a robust methodology was formed to estimate a statistical predictive model of the spatial-temporal variations in the densities of An. darlingi in Saint-Georges de l’Oyapock. The final cross-validated model integrated two landscape variables—dense forest surface and built surface—together with four meteorological variables related to rainfall, evapotranspiration, and the minimal and maximal temperatures. Extrapolation of the model allowed the generation of predictive weekly maps of An. darlingi densities at a resolution of 10-m. Our results supported the use of satellite imagery and meteorological data to predict malaria vector densities. Such fine-scale modeling approach might be a useful tool for health authorities to plan control strategies and social communication in a cost-effective, targeted, and timely manner.
ISSN: 1932-6203

hal-01383486
https://hal.archives-ouvertes.fr/hal-01383486
https://hal.archives-ouvertes.fr/hal-01383486/document
https://hal.archives-ouvertes.fr/hal-01383486/file/Adde_et_al_PlosONE_2016.pdf
DOI : 10.1371/journal.pone.0164685

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 Wiley
Résumé : White-sand forests represent natural laboratories of evolution over their long history throughout Amazonia and the Guiana Shield and pose significant physiological challenges to the plants and animals they host. The study of diversification in plant lineages comprising species endemic to white-sand forest can therefore give insights into processes of evolution and community assembly in tropical forests. In this article, we synthesize recent studies of white-sand forests to integrate patterns of plant species distribution with processes of lineage diversification and community assembly in the white-sand flora. We contrast lineages that have radiated uniquely in these habitats (e.g., Pagamea, Rubiaceae), with cosmopolitan lineages comprising specialists to white-sand forests and other habitats that may have arisen via ecological speciation across habitat gradients (e.g., Protium, Burseraceae). In both cases, similar suites of functional traits have evolved, including investment in dense, long-lived tissues that are well-defended structurally and chemically. White-sand endemics, therefore, play an important role in biodiversity conservation because they represent unique combinations of functional and phylogenetic diversity. Furthermore, white-sand endemics may respond differently than other tropical forest plant species to contemporary global changes because they comprise resilient functional types that may better withstand increased drought, temperature, and invasions of exotic pests in these regions.
ISSN: 0006-3606

hal-01531635
https://hal.archives-ouvertes.fr/hal-01531635
DOI : 10.1111/btp.12301
PRODINRA : 353397

Éditeur(s) : HAL CCSD Wiley
Résumé :  
1. Relationships between tropical rain forest biomass and environmental factors have been determined at regional scales, e.g. the Amazon Basin, but the reasons for the high variability in forest biomass at local scales are poorly understood. Interactions between topography, soil properties, tree growth and mortality rates, and treefalls are a likely reason for this variability. 2. We used repeated measurements of permanent plots in lowland rain forest in French Guiana to evaluate these relationships. The plots sampled topographic gradients from hilltops to slopes to bottomlands, with accompanying variation in soil waterlogging along these gradients. Biomass was calculated for >175 tree species in the plots, along with biomass productivity and recruitment rates. Mortality was determined as standing dead and treefalls. 3. Treefall rates were twice as high in bottomlands as on hilltops, and tree recruitment rates, radial growth rates and the abundance of light-demanding tree species were also higher. 4. In the bottomlands, the mean wood density was 10% lower than on hilltops, the basal area 29% lower and the height:diameter ratio of trees was lower, collectively resulting in a total woody biomass that was 43% lower in bottomlands than on hilltops. 5. Biomass productivity was 9% lower in bottomlands than on hilltops, even though soil Olsen P concentrations were higher in bottomlands. 6. Synthesis. Along a topographic gradient from hilltops to bottomlands there were higher rates of treefall, which decreased the stand basal area and favoured lower allocation to height growth and recruitment of light-demanding species with low wood density. The resultant large variation in tree biomass along the gradient shows the importance of determining site characteristics and including these characteristics when scaling up biomass estimates from stand to local or regional scales.
ISSN: 0022-0477

hal-01032100
https://hal.archives-ouvertes.fr/hal-01032100

Éditeur(s) : HAL CCSD Wiley
Résumé : [b]1.[/b] Plant functional traits, in particular specific leaf area (SLA), wood density and seed mass, are often good predictors of individual tree growth rates within communities. Individuals and species with high SLA, low wood density and small seeds tend to have faster growth rates.[br/][br/][b]2.[/b] If community-level relationships between traits and growth have general predictive value, then similar relationships should also be observed in analyses that integrate across taxa, biogeographic regions and environments. Such global consistency would imply that traits could serve as valuable proxies for the complex suite of factors that determine growth rate, and, therefore, could underpin a new generation of robust dynamic vegetation models. Alternatively, growth rates may depend more strongly on the local environment or growth–trait relationships may vary along environmental gradients.[br/][br/][b]3.[/b] We tested these alternative hypotheses using data on 27 352 juvenile trees, representing 278 species from 27 sites on all forested continents, and extensive functional trait data, 38% of which were obtained at the same sites at which growth was assessed. Data on potential evapotranspiration (PET), which summarizes the joint ecological effects of temperature and precipitation, were obtained from a global data base.[br/][br/][b]4.[/b] We estimated size-standardized relative height growth rates (SGR) for all species, then related them to functional traits and PET using mixed-effect models for the fastest growing species and for all species together.[br/][br/][b]5.[/b] Both the mean and 95th percentile SGR were more strongly associated with functional traits than with PET. PET was unrelated to SGR at the global scale. SGR increased with increasing SLA and decreased with increasing wood density and seed mass, but these traits explained only 3.1% of the variation in SGR. SGR–trait relationships were consistently weak across families and biogeographic zones, and over a range of tree statures. Thus, the most widely studied functional traits in plant ecology were poor predictors of tree growth over large scales.[br/][br/][b]6.[/b] Synthesis. We conclude that these functional traits alone may be unsuitable for predicting growth of trees over broad scales. Determining the functional traits that predict vital rates under specific environmental conditions may generate more insight than a monolithic global relationship can offer.
ISSN: 0022-0477

hal-01204226
https://hal.archives-ouvertes.fr/hal-01204226
DOI : 10.1111/1365-2745.12401
PRODINRA : 307144

Éditeur(s) : HAL CCSD Wiley
Résumé : 1. Considerable debate surrounds the extent to which tropical forests can be managed for resource extraction while conserving biodiversity and ecosystem properties, which depend on functional composition. Here we evaluate the compatibility of these aims by examining the effects of logging on taxonomic and functional diversity and composition in a tropical forest. 2. Twenty years after selective logging, we inventoried 4140 stems regenerating in logging gaps and adjacent undisturbed areas, and we integrated a database of 13 functional traits describing leaf and wood economics of tropical trees. 3. We found no differences in taxonomic and functional richness among habitats, but logging gaps had significantly higher taxonomic and functional evenness. 4. Logging also effected striking, long-term changes in both species and functional composition. In particular, the xylem density of recruits in logging gaps was 6% less than in unlogged forests, leaves were 11% less tough and had 613% greater mineral nutrient concentrations. 5. Synthesis and applications. Our results suggest that managers of tropical forests should limit overall surface area converted to logging gaps by creating fewer, larger gaps during selective logging, to reduce impacts on the taxonomic and functional composition of the regenerating stand.
ISSN: 0021-8901

hal-01032420
https://hal.archives-ouvertes.fr/hal-01032420
DOI : 10.1111/j.1365-2664.2012.02164.x

Éditeur(s) : HAL CCSD Montpellier : CIRAD
Résumé : This article presents the effects of logging on the dynamics of above-ground biomass from the results of the post-logging study within two forests: Cikel in Eastern Para, Brazil and Paracou in French Guiana. The main objective is to compare the impact of commercial logging on the regeneration of the above-ground biomass in these forests whose characteristics differ in terms of structure and growth. In both sites, the intensity of exploitation is a key factor in determining the loss of biomass and the time required for its regeneration. In Paracou, the regeneration of biomass lost during conventional logging of 10 trees per hectare takes 45 years and more than 100 years when operating with higher intensity (21 trees/ha). In Cikei the forest biomass regenerates after 49 years harvesting 6 trees/ha and that takes 87 years after removal of 8 trees/ha. This regeneration needs similar time on both sites but with lower logging intensity at Cikel, in which felled trees are larger with a greater biomass than those of Paracou. This post-logging study has established a direct correlation of the dynamics of the biomass with the initial structure of the forest, as well as with the parameters of forest dynamics: mortality, growth and recruitment. The accumulation of biomass by the tree growth of the two remaining stands is a key parameter for the net carbon storage, while the contribution of recruitment in Paracou becomes significant only after 10 years after felling. Therefore in view to improve the growth of residual trees, it is compulsory to apply adequate silvicultural treatments such as selective thinning or removal of vines. While the two forests are geographically close enough, their regenerative abilities differ and because of the significant difference in size of the trees, the forest could tolerate more intensive harvesting in French Guiana
ISSN: 0006-579X

hal-01032427
https://hal.archives-ouvertes.fr/hal-01032427

Éditeur(s) : HAL CCSD Public Library of Science
Résumé : We examined tree-soil habitat associations in lowland forest communities at Paracou, French Guiana. We analyzed a large dataset assembling six permanent plots totaling 37.5 ha, in which extensive LIDAR-derived topographical data and soil chemical and physical data have been integrated with precise botanical determinations. Map of relative elevation from the nearest stream summarized both soil fertility and hydromorphic characteristics, with seasonally inundated bottomlands having higher soil phosphate content and base saturation, and plateaus having higher soil carbon, nitrogen and aluminum contents. We employed a statistical test of correlations between tree species density and environmental maps, by generating Monte Carlo simulations of random raster images that preserve autocorrelation of the original maps. Nearly three fourths of the 94 taxa with at least one stem per ha showed a significant correlation between tree density and relative elevation, revealing contrasted species-habitat associations in term of abundance, with seasonally inundated bottomlands (24.5% of species) and well-drained plateaus (48.9% of species). We also observed species preferences for environments with or without steep slopes (13.8% and 10.6%, respectively). We observed that closely-related species were frequently associated with different soil habitats in this region (70% of the 14 genera with congeneric species that have a significant association test) suggesting species-habitat associations have arisen multiple times in this tree community. We also tested if species with similar habitat preferences shared functional strategies. We found that seasonally inundated forest specialists tended to have smaller stature (maximum diameter) than species found on plateaus. Our results underline the importance of tree-soil habitat associations in structuring diverse communities at fine spatial scales and suggest that additional studies are needed to disentangle community assembly mechanisms related to dispersal limitation, biotic interactions and environmental filtering from species-habitat associations. Moreover, they provide a framework to generalize across tropical forest sites.
ISSN: 1932-6203

hal-01260289
https://hal.archives-ouvertes.fr/hal-01260289
PRODINRA : 342930
DOI : 10.1371/journal.pone.0141488

Éditeur(s) : HAL CCSD Public Library of Science
Résumé : International audience
Challenging evaluation of tropical forest biodiversity requires the reporting of taxonomic diversity but also the systematic characterization of wood properties in order to discover new promising species for timber industry. Among wood properties, the dimensional stability is regarded as a major technological characteristic to validate whether a wood species is adapted to commercial uses. Cell structure and organization are known to influence the drying shrinkage making wood density and microfibrils angle markers of choice to predict wood dimensional stability. On the contrary the role of wood extractive content remains unclear. This work focuses on the fast-growing tropical species Bagassa guianensis and we report herein a correlation between heartwood drying shrinkage and extractive content. Chemical extractions and shrinkage experiments were performed on separate wood twin samples to better evaluate correctly how secondary metabolites influence the wood shrinkage behaviour. Extractive content were qualitatively and quantitatively analysed using HPLC and NMR spectroscopy. We found that B guianensis heartwood has a homogeneous low shrinkage along its radius that could not be explained only by its basic density. In fact the low drying shrinkage is correlated to the high extractive content and a corrected model to improve the prediction of wood dimensional stability is presented. Additionally NMR experiments conducted on sapwood and heartwood extracts demonstrate that secondary metabolites biosynthesis occurs in sapwood thus revealing B. guianensis as a Juglans-Type heartwood formation. This work demonstrates that B. guianensis, a fast-growing species associated with high durability and high dimensional stability, is a good candidate for lumber production and commercial purposes.
ISSN: 1932-6203

hal-01392725
https://hal.archives-ouvertes.fr/hal-01392725
https://hal.archives-ouvertes.fr/hal-01392725/document
https://hal.archives-ouvertes.fr/hal-01392725/file/2016_BossuBeaucheneEstevezDuplaisClair_PlosOne_WoodDimentionalStabilityAndSecondaryMetabolites.pdf
DOI : 10.1371/journal.pone.0150777.s005