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 Oxford University Press (OUP)
Résumé : International audience
Background and Aims: In rain forests, sapling survival is highly dependent on the regulation of trunk slenderness (height/diameter ratio): shade-intolerant species have to grow in height as fast as possible to reach the canopy but also have to withstand mechanical loadings (wind and their own weight) to avoid buckling. Recent studies suggest that mechanosensing is essential to control tree dimensions and stability-related morphogenesis. Differences in species slenderness have been observed among rainforest trees; the present study thus investigates whether species with different slenderness and growth habits exhibit differences in mechanosensitivity. Methods: Recent studies have led to a model of mechanosensing (sum-of-strains model) that predicts a quantitative relationship between the applied sum of longitudinal strains and the plant's responses in the case of a single bending. Saplings of five different neotropical species (Eperua falcata, E. grandiflora, Tachigali melinonii, Symphonia globulifera and Bauhinia guianensis) were subjected to a regimen of controlled mechanical loading phases (bending) alternating with still phases over a period of 2 months. Mechanical loading was controlled in terms of strains and the five species were subjected to the same range of sum of strains. The application of the sum-of-strain model led to a dose-response curve for each species. Dose-response curves were then compared between tested species. Key Results: The model of mechanosensing (sum-of-strain model) applied in the case of multiple bending as long as the bending frequency was low. A comparison of dose-response curves for each species demonstrated differences in the stimulus threshold, suggesting two groups of responses among the species. Interestingly, the liana species B. guianensis exhibited a higher threshold than other Leguminosae species tested. Conclusions: This study provides a conceptual framework to study variability in plant mechanosensing and demonstrated interspecific variability in mechanosensing.
ISSN: 0305-7364

halsde-00454145
https://hal.archives-ouvertes.fr/halsde-00454145
DOI : 10.1093/aob/mcp286

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
Résumé : International audience
We examined fine-scale heterogeneity of environmental conditions in a primary rain forest in French Guiana to describe variation in microhabitats that plants may experience during establishment. We characterized both the range as well as the spatial structuring of 11 environmental factors important for seedling establishment in six hexagonal sampling grids, one each in gap and understory sites at three points representing the predominant geomorphic units in this primary forest. Each grid contained 37 sampling points separated by 31 cm-20 m. Monte-Carlo tests of semivariograms against complete spatial randomness indicated that for many variables in all six sampling grids, spatial dependence did not exceed 1 m. A principal component analysis of all sampling points revealed a lack of spatial microhabitat structure, rather than homogeneous patches associated with canopy structure or geomorphology. Our results suggest that ample fine-scale spatial heterogeneity exists to support the coexistence of plant species with differential abiotic requirements for regeneration.
Botropica

halsde-00520179
https://hal.archives-ouvertes.fr/halsde-00520179
DOI : 10.1111/j.1744-7429.2009.00620.x

Éditeur(s) : HAL CCSD Wiley
Résumé :  
The forests in Cat Tien National Park, appear as a mosaic of different communities, distinct from each other with respect to their floristic and structural parameters. The objectives of this study are (1) to characterize the different formations occurring in the lowland part and (2) to identify the main successional trends in the area. Understanding forest succession is important for silviculture and restoration of forests and land rehabilitation, as adequate information on the ecological role of local species in the functioning of the forests is not available in Vietnam. Five plots (1 ha each) were established in the lowland part of Cat Tien National Park, where all the trees ≥ 10 cm d.b.h. (diameter at breast height) were located, measured and identified. A systematic sampling was made to assess the regeneration. Three plots (A, C and D) can be considered as secondary forests on the basis of their structural parameters. Plots A and C are dominated by Lagerstrmia calyculata and plot D by Dipterocarpus alatus. The other two plots can be regarded as mature forests. Plot B corresponds to a semideciduous formation dominated by Lagerstrmia calyculata and Fabaceae species, and plot E to an evergreen one dominated by dipterocarp species. The floristic composition of plots A and C will change in the future because dominant canopy species are rare or absent in regeneration. A correspondence analysis performed on the number of trees per species shows two kinds of successional trends: one from A to B on shallow and drier soils, and another from C to E on deeper and wetter soils.
ISSN: 0305-0270

hal-01032094
https://hal.archives-ouvertes.fr/hal-01032094
DOI : 10.1046/j.1365-2699.2000.00347.x

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-01189178
https://hal.archives-ouvertes.fr/hal-01189178
PRODINRA : 12114

Éditeur(s) : HAL CCSD Wiley-Blackwell
Résumé : International audience
The spatio‐temporal dynamics of disease spread provide an area of acute scientific interest but substantial analytic challenges. Analytic approaches need to draw from current knowledge of disease systems yet be flexible enough to provide targeted inference without restrictive assumptions. We explore this balance in detail with respect to the observed pattern of spread of sugarcane yellow leaf virus, the causal agent of yellow leaf disease. This disease affects cultivated sugarcane plants and spreads via an aphid vector (Melanaphis sacchari). The system is of considerable economic interest, but presents several analytic complications. First, the plants begin as well separated individuals that grow into large plants with overlapping leaf canopies enabling increased vector access between neighbouring plants. The overlap between neighbouring plants first occurs within rows and then extends between rows, presenting another interesting spatial component to consider when modelling the propagation of infection. Second, the vector initially flies between plants but at some point sheds wings and shifts to walking between plants. We are particularly interested in how these two features of the system and their interrelation may impact the spatial spread of disease over time. In addition, we also explore the impact of potential immigration of infected vectors from outside of the study area. We treat our observed cane field as a spatial grid with regular spacing between rows and smaller spacing within rows. Our data consist of observed disease status of each of 1643 plants at each of six time points. We provide descriptive summaries of the temporal evolution of spatial pattern in infection, then propose hierarchical models to describe the pattern and capture the influence of the ecological and environmental factors listed above.
ISSN: 0143-9782

hal-00684235
https://hal.archives-ouvertes.fr/hal-00684235

Éditeur(s) : HAL CCSD European Geosciences Union
Résumé : International audience
Natural disturbances are the dominant form of forest regeneration and dynamics in unmanaged tropical forests. Monitoring the size distribution of treefall gaps is important to better understand and predict the carbon budget in response to land use and other global changes. In this study, we model the size frequency distribution of natural canopy gaps with a discrete power law distribution. We use a Bayesian framework to introduce and test, using Monte Carlo Markov chain and Kuo–Mallick algorithms, the effect of local physical environment on gap size distribution. We apply our methodological framework to an original light detecting and ranging dataset in which natural forest gaps were delineated over 30 000 ha of unmanaged forest. We highlight strong links between gap size distribution and environment, primarily hydrological conditions and topography, with large gaps being more frequent on floodplains and in wind-exposed areas. In the future, we plan to apply our methodological framework on a larger scale using satellite data. Additionally , although gap size distribution variation is clearly under environmental control, variation in gap size distribution in time should be tested against climate variability.
ISSN: 1726-4170

hal-01590729
https://hal-univ-guyane.archives-ouvertes.fr/hal-01590729
https://hal-univ-guyane.archives-ouvertes.fr/hal-01590729/document
https://hal-univ-guyane.archives-ouvertes.fr/hal-01590729/file/bg-14-353-2017.pdf
DOI : 10.5194/bg-14-353-2017

Éditeur(s) : HAL CCSD
Résumé : Tropical forests are predicted to harbor most of the insect diversity on earth, but few studies have been conducted to characterize insect communities in tropical forests. One major limitation is the lack of consensus on methods for insect collection. Deciding which insect trap to use is an important consideration for ecologists and entomologists, yet to date few study has presented a quantitative comparison of the results generated by standardized methods in tropical insect communities. Here, we investigate the relative performance of two flight interception traps, the windowpane trap, and the more widely used malaise trap, across a broad gradient of lowland forest types in French Guiana. The windowpane trap consistently collected significantly more Coleoptera and Blattaria than the malaise trap, which proved most effective for Diptera, Hymenoptera, and Hemiptera. Orthoptera and Lepidoptera were not well represented using either trap, suggesting the need for additional methods such as bait traps and light traps. Our results of contrasting trap performance among insect orders underscore the need for complementary trapping strategies using multiple methods for community surveys in tropical forests.
Zookeys

hal-01032428
https://hal.archives-ouvertes.fr/hal-01032428
DOI : 10.3897/zookeys.216.3332

Éditeur(s) : HAL CCSD Oxford University Press (OUP)
Résumé :  
The maintenance in the long run of a positive carbon balance under very low irradiance is a prerequisite for survival of tree seedlings below the canopy or in small gaps in a tropical rainforest. To provide a quantitative basis for this assumption, experiments were carried out to determine whether construction cost (CC) and payback time for leaves and support structures, as well as leaf life span (i) differ among species and (ii) display an irradiance-elicited plasticity. Experiments were also conducted to determine whether leaf life span correlates to CC and payback time and is close to the optimal longevity derived from an optimization model. Saplings from 13 tropical tree species were grown under three levels of irradiance. Specific-CC was computed, as well as CC scaled to leaf area at the metamer level. Photosynthesis was recorded over the leaf life span. Payback time was derived from CC and a simple photosynthesis model. Specific-CC displayed only little interspecific variability and irradiance-elicited plasticity, in contrast to CC scaled to leaf area. Leaf life span ranged from 4 months to >26 months among species, and was longest in seedlings grown under lowest irradiance. It was always much longer than payback time, even under the lowest irradiance. Leaves were shed when their photosynthesis had reached very low values, in contrast to what was predicted by an optimality model. The species ranking for the different traits was stable across irradiance treatments. The two pioneer species always displayed the smallest CC, leaf life span, and payback time. All species displayed a similar large irradiance-elicited plasticity.
ISSN: 0022-0957

hal-01032198
https://hal.archives-ouvertes.fr/hal-01032198
DOI : 10.1093/jxb/err092

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 : 1- We examined among- and within-species effects of seed mass for seedling establishment from seed to 5 years of age in a field experiment at Paracou, French Guiana. 2- Six seeds of each of eight species were weighed and planted into each of 120 plots (1 m2) throughout closed-canopy forest along 12 100-m transects in 1998. 3- We described the microhabitat of each planting site using principal components derived from measurements of light availability, soil moisture, carbon and nitrogen content, and soil phosphorus availability. Although both survival and relative growth rate (RGR) increased with increasing light availability, no other microhabitat variable significantly affected seedling performance. Nor did the magnitude of microhabitat effects on survival or RGR differ among species. 4- Larger-seeded species were more likely to survive from germination to 1 year as well as from 1 to 5 years of age. RGR for seedling height during the first year post-germination was not related to seed mass, but smaller-seeded species did grow slightly faster thereafter. Path analyses revealed that correlations between seed mass and performance were explained in part because larger seeds produced larger initial seedlings, which tended to survive better but grow more slowly. 5- We also analysed within-species effects of seed mass for the larger-seeded Eperua grandiflora and Vouacapoua americana (both Caesalpiniaceae). Larger seeds produced larger seedlings in both species, but larger seeds survived better only for Eperua. Larger seedlings grew more slowly in both species, but did not offset the early (Eperua) and later (Vouacapoua) positive direct effects of seed mass on RGR that may represent contrasting strategies for reserve deployment. 6- Our results demonstrate that seed size influences performance within and among species in part because of indirect effects of initial seedling size. However, we suggest that traits tightly correlated with seed mass at the species level, such as specific leaf area, leaf longevity and photosynthetic capacity, may also contribute to interspecific performance differences.
ISSN: 0022-0477

hal-01031089
https://hal.archives-ouvertes.fr/hal-01031089
DOI : 10.1111/j.1365-2745.2005.01041.x

Éditeur(s) : HAL CCSD Elsevier Masson
Résumé : International audience
The maintenance in the long run of a positive carbon balance under very low irradiance is a prerequisite for survival of tree seedlings below the canopy or in small gaps in a tropical rainforest. To provide a quantitative basis for this assumption, experiments were carried out to determine whether construction cost (CC) and payback time for leaves and support structures, as well as leaf life span (i) differ among species and (ii) display an irradiance-elicited plasticity. Experiments were also conducted to determine whether leaf life span correlates to CC and payback time and is close to the optimal longevity derived from an optimization model. Saplings from 13 tropical tree species were grown under three levels of irradiance. Specific-CC was computed, as well as CC scaled to leaf area at the metamer level. Photosynthesis was recorded over the leaf life span. Payback time was derived from CC and a simple photosynthesis model. Specific-CC displayed only little interspecific variability and irradiance-elicited plasticity, in contrast to CC scaled to leaf area. Leaf life span ranged from 4 months to >26 months among species, and was longest in seedlings grown under lowest irradiance. It was always much longer than payback time, even under the lowest irradiance. Leaves were shed when their photosynthesis had reached very low values, in contrast to what was predicted by an optimality model. The species ranking for the different traits was stable across irradiance treatments. The two pioneer species always displayed the smallest CC, leaf life span, and payback time. All species displayed a similar large irradiance-elicited plasticity.
ISSN: 1631-0691

hal-01095975
https://hal-agroparistech.archives-ouvertes.fr/hal-01095975
DOI : 10.1016/j.crvi.2011.01.007

Éditeur(s) : HAL CCSD Wiley
Résumé : International audience
ISSN: 0021-8901

hal-01093618
https://hal-agroparistech.archives-ouvertes.fr/hal-01093618
DOI : 10.1111/j.1365-2664.2010.01826.x

Éditeur(s) : HAL CCSD
Résumé : The genus Cecropia includes pioneer trees that colonize canopy gaps and cleared areas. It is widely distributed from Mexico to Northern Argentina. Cecropia trees have architecture, which corresponds to the Rauh’s architectural model. In recent studies we have found that C. obtusa/ and C. sciadophylla, in French Guiana, have a strong annual periodicity for growth, branching and flowering processes, with annual emission of 35 nodes for C. obtusa and 25 for C. sciadophylla. Those species show different life histories since C. sciadophylla has longer life expectancy. In addition, C. sciadophylla is found more frequently in forest gaps, although in French Guiana mixed populations are found. The aim of this work was to compare developmental strategies of both species in three different field stations in French Guiana and to determine how these two species coexist during its first years of life. We studied a 20-year old population of /C. sciadophylla/ at Saint Elie’s Road, a 10-year old population of /C. obtusa/ at Paracou’s field station, and a 7-year old mixed population at Counami’s Road. /C. sciadophylla /emits 25 nodes per year in both studied populations, while/ C. obtusa /emits 35 nodes in the monospecific population and 30 nodes in the mixed population. In the monocaule stage, the lower number of nodes emitted by /C. sciadophylla/ compared to /C. obtusa /is compensated with a higher internodal length, which allows finding individuals with similar ages and lengths, but different number of nodes. The branching and flowering processes start on average three years before in /C. obtusa/, however for 12-year old individuals we observed a dominancy of C. sciadophylla over C. obtusa. In the mixed population it is likely that the different life histories would decrease competition effects allowing coexistence of both species during the first stages of life
Botany 2008
Vancouver, Canada

hal-01190209
https://hal.archives-ouvertes.fr/hal-01190209
PRODINRA : 182910

Éditeur(s) : HAL CCSD Elsevier
Résumé :  
Tree species-rich tropical rainforests are characterized by a highly variable quality of leaf litter input to the soil at small spatial scales. This diverse plant litter is a major source of energy and nutrients for soil microorganisms, particularly in rainforests developed on old and nutrient-impoverished soils. Here we tested the hypothesis that the variability in leaf litter quality produced by a highly diverse tree community determines the spatial variability of the microbial respiration process in the underlying soil. We analyzed a total of 225 litter-soil pairs from an undisturbed Amazonian rainforest in French Guiana using a hierarchical sampling design. The microbial respiration process was assessed using substrateinduced respiration (SIR) and compared to a wide range of quality parameters of the associated litter layer (litter nutrients, carbon forms, stoichiometry, litter mass and pH). The results show that the variability of both litter quality and SIR rates was more important at large than at small scales. SIR rates varied between 1.1 and 4.0 mg g_1 h_1 and were significantly correlated with litter layer quality (up to 50% of the variability explained by the best mixed linear model). Total litter P content was the individual most important factor explaining the observed spatial variation in soil SIR, with higher rates associated to high litter P. SIR rates also correlated positively with total litter N content and with increasing proportions of labile C compounds. However, contrary to our expectation, SIR rates were not related to litter stoichiometry. These data suggest that in the studied Amazonian rainforest, tree canopy composition is an important driver of the microbial respiration process via leaf litter fall, resulting in potentially strong plant-soil feedbacks. .
ISSN: 0038-0717

hal-01032139
https://hal.archives-ouvertes.fr/hal-01032139
DOI : 10.1016/j.soilbio.2011.01.018

Éditeur(s) : HAL CCSD
Résumé : In a recent study based on a retrospective reconstruction of growth, we showed for Cecropia sciadophylla that branching and flowering processes, as well as alternation of long and short nodes were regularly spaced by ~23 nodes. We also found that this strong periodicity was related to an annual cycle of growth. Adult trees are successful individuals that have reached the canopy and our previous results were found in adult trees, suggesting that variability in the number of nodes produced per year is underestimated, because the degree of variation decreases with age. Here, we hypothesized that growth periodicity could be related to rainfall and we focus on two C. sciadophylla populations with contrasting precipitation seasonality. During 19 months and for 69 saplings, we measured growth at regular monthly intervals to test the intra-annual variability in the number of nodes produced per month and per year. We also characterized the intra-annual fluctuations in the number of present leaves in the main axis and internode lengths among months. We found that node elongation and number of present leaves in the main axis vary among months in the population subjected to a strong seasonal precipitation. In contrast, the population subjected to a non-seasonal precipitation showed smaller variation in node elongation and no variation in the number of leaves presented in the main axis among months. Regardless the population of origin, we also found that ~23 was the number of nodes produced per year and that the time required to produce a new node was ~15 days at any month of the year. The strong stability in the average number of nodes produced per month and per year among populations, suggests a genetically controlled trait. In spite of a strong genetic determination on the number of nodes produced per year, several environmental factors, including rainfall, could be the cause of the observed variation in elongation and number of present leaves in the main axis.INRAUM2
Botany 2010
Rhode Island, United States

hal-01191343
https://hal.archives-ouvertes.fr/hal-01191343
PRODINRA : 178581

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
Résumé : Biogenic volatile organic compound (BVOCs) emissions play an important role in regional air quality and global atmospheric chemistry. In addition, these natural VOC emissions serve important biological functions including attracting and repelling pollinators and herbivores. Some biological organisms use ambient air as a communication medium and the oxidation of these compounds brings about the concentration gradients sensed by insects and other organisms. Isoprene is the predominant BVOC emitted by vegetation and tropical forests are the dominant global source. This compound is very reactive in the atmosphere and contributes to the reactions that control tropospheric oxidant concentrations and thus the concentrations and lifetimes of longer-lived species. This paper presents a study on the seasonal variations in isoprene and some other significant BVOCs such as µ-pinene, µ-pinene, limonene, e-µ ocimene and longifolene, measured at the Guyaflux Tower located in a wet tropical forest in Paracou French Guiana (5o16´54´´N, 52o54´44´´W), during the year of 2011, using the Relaxed Eddy Accumulation technique at approximately 20 meters high above the canopy. The results show a lower concentration of isoprene during the month of February and March which correspond to the wet season with an average of 0,545 µg/m3 and 0,341 µg/m3, respectively followed by a slight increase in middle April (still wet season) and a higher concentration later in mid-June. The same behavior was observed for µ-pinene with higher concentrations for the same periods as isoprene however with a smaller increase. All the other compounds had concentrations below 1 µg/m3during the whole year: The monoterpene, e-µ ocimene, was observed and is known as a stress compound but the vegetation at the site did not face any known severe stress condition such as excessive drought or flooding. Concerning the fluxes, the results showed that just a small amount of BVOCs were deposited by wet or dry process and the majority of them were released in the atmosphere. Isoprene was by far the biogenic volatile organic compound with the highest concentration and flux, followed by alpha-pinene. The lowest concentration and flux rate for all the studied compounds was observed during the months of March and late July and beginning of August indicating a lower production of those BVOCs by vegetation during those periods. Previous limited studies in Amazonia and the Congo suggested that a higher concentration and flux rate of isoprene and µ-pinene should be expected during the dry season with lower emissions during the wet season, which is in relative agreement with what was observed at this tropical forest site in French Guiana. The exceptions were observed in April and June which correspond to a long wet period in which the concentration of isoprene and µ-pinene increased more than it was expected for this time of the year. The observations will be compared to output from the global chemistry transport model CAM-chem, which includes the MEGAN biogenic emissions model.
10th EGU General Assembly
vienne, Austria

hal-01204214
https://hal.archives-ouvertes.fr/hal-01204214
PRODINRA : 276525

Éditeur(s) : HAL CCSD Springer Verlag/EDP Sciences
Résumé : International audience
Background : This study examines the radial trend in wood stiffness of tropical rainforest trees. The objective was to determine if the type of growing environment (exposed plantation or dense primary forest) would have an effect on this radial trend. Methods : The axial elastic modulus of wood samples, representing a pith to bark cross-section, of six trees from several French Guianese species (two of Eperua falcata, one of Eperua grandiflora, two of Carapa procera and one of Symphonia gloubulifera) was measured using a dynamic "forced vibration" method. Results : Primary forest trees were observed to have a decrease in wood stiffness from pith to bark, whereas plantation trees, from the same genus or species, displayed a corresponding increase in wood stiffness. Juvenile wood stiffness appears to vary depending on the environment in which the tree had grown. Conclusion : We suggest that the growth strategy of primary forest trees is to produce wood resistant to selfbuckling so that the height of the canopy may be obtained with the maximum of efficiency. In contrast, the growth strategy of the trees growing in an exposed plantation is to produce low-stiffness wood, important to provide flexibility in wind. Further experiments to study the behaviour of more species, with more individuals per species, growing across a range of physical environments, are required.
ISSN: 1286-4560

hal-00644335
https://hal.archives-ouvertes.fr/hal-00644335
https://hal.archives-ouvertes.fr/hal-00644335/document
https://hal.archives-ouvertes.fr/hal-00644335/file/McLean_al.pdf
DOI : 10.1007/s13595-011-0085-z