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Clair, B., Ghislain, B., Prunier, J., Lehnebach, R., Beauchene, J., & Alméras, T. (2019). Mechanical contribution of secondary phloem to postural control in trees: the bark side of the force. New Phytol, 221(1), 209–217.
Abstract: Summary To grow straight, plants need a motor system that controls posture by generating forces to offset gravity. This motor function in trees was long thought to be only controlled by internal forces induced in wood. Here we provide evidence that bark is involved in the generation of mechanical stresses in several tree species. Saplings of nine tropical species were grown tilted and staked in a shadehouse and the change in curvature of the stem was measured after releasing from the pole and after removing the bark. This first experiment evidenced the contribution of bark in the up-righting movement of tree stems. Combined mechanical measurements of released strains on adult trees and microstructural observations in both transverse and longitudinal/tangential plane enabled us to identify the mechanism responsible for the development of asymmetric mechanical stress in the bark of stems of these species. This mechanism does not result from cell wall maturation like in wood, or from the direct action of turgor pressure like in unlignified organs, but is the consequence of the interaction between wood radial pressure and a smartly organized trellis structure in the inner bark.
Keywords: bark; Malvaceae; maturation stress; secondary phloem; tree biomechanics
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Flores, O., Rossi, V., & Mortier, F. (2009). Autocorrelation offsets zero-inflation in models of tropical saplings density. Ecol. Model., 220(15), 1797–1809.
Abstract: Modelling the local density of tropical saplings can provide insights into the ecological processes that drive species regeneration and thereby help predict population recovery after disturbance. Yet, few studies have addressed the challenging issues in autocorrelation and zero-inflation of local density. This paper presents Hierarchical Bayesian Modelling (HBM) of sapling density that includes these two features. Special attention is devoted to variable selection, model estimation and comparison. We developed a Zero-Inflated Poisson (ZIP) model with a latent correlated spatial structure and compared it with non-spatial ZIP and Poisson models that were either autocorrelated (Spatial Generalized Linear Mixed, SGLM) or not (generalized linear models, GLM). In our spatial models, local density autocorrelation was modeled by a Conditional Auto-Regressive (CAR) process. 13 explicative variables described ecological conditions with respect to topography, disturbance, stand structure and intraspecific processes. Models were applied to six tropical tree species with differing biological attributes: Oxandra asbeckii, Eperua falcata, Eperua grandiflora, Dicorynia guianensis, Qualea rosea, and Tachigali melinonii. We built species-specific models using a simple method of variable selection based on a latent binary indicator. Our spatial models showed a close correlation between observed and estimated densities with site spatial structure being correctly reproduced. By contrast, the non-spatial models showed poor fits. Variable selection highlighted species-specific requirements and susceptibility to local conditions. Model comparison overall showed that the SGLM was the most accurate explanatory and predictive model. Surprisingly, zero-inflated models performed less well. Although the SZIP model was relevant with respect to data distribution, and more flexible with respect to response curves, its model complexity caused marked variability in parameter estimates. In the SUM, the spatial process alone accounted for zero-inflation in the data. A refinement of the hypotheses employed at the process level could compensate for distribution flaws at the data level. This study emphasized the importance of the HBM framework in improving the modelling of density-environment relationships. (C) 2008 Elsevier B.V. All rights reserved.
Keywords: Hierarchical Bayesian Modelling; Conditional Auto-Regressive model; Variable selection; Zero-Inflated Poisson; Posterior predictive; Paracou; French Guiana
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Santiago, L. S., De Guzman, M. E., Baraloto, C., Vogenberg, J. E., Brodie, M., Hérault, B., et al. (2018). Coordination and trade-offs among hydraulic safety, efficiency and drought avoidance traits in Amazonian rainforest canopy tree species. New Phytol., 218(3), 1015–1024.
Abstract: Predicting responses of tropical forests to climate change-type drought is challenging because of high species diversity. Detailed characterization of tropical tree hydraulic physiology is necessary to evaluate community drought vulnerability and improve model parameterization. Here, we measured xylem hydraulic conductivity (hydraulic efficiency), xylem vulnerability curves (hydraulic safety), sapwood pressure–volume curves (drought avoidance) and wood density on emergent branches of 14 common species of Eastern Amazonian canopy trees in Paracou, French Guiana across species with the densest and lightest wood in the plot. Our objectives were to evaluate relationships among hydraulic traits to identify strategies and test the ability of easy-to-measure traits as proxies for hard-to-measure hydraulic traits. Xylem efficiency was related to capacitance, sapwood water content and turgor loss point, and other drought avoidance traits, but not to xylem safety (P50). Wood density was correlated (r = −0.57 to −0.97) with sapwood pressure–volume traits, forming an axis of hydraulic strategy variation. In contrast to drier sites where hydraulic safety plays a greater role, tropical trees in this humid tropical site varied along an axis with low wood density, high xylem efficiency and high capacitance at one end of the spectrum, and high wood density and low turgor loss point at the other.
Keywords: Amazonian forest; cavitation; drought; hydraulic conductivity; sapwood capacitance; turgor loss point; wood density; xylem; cavitation; climate change; drought; forest canopy; forest ecosystem; hydraulic conductivity; rainforest; species diversity; tree; tropical forest; vulnerability; wood; Amazonia; French Guiana; Paracou
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Lamarre, G. P. A., Molto, Q., Fine, P. V. A., & Baraloto, C. (2012). A comparison of two common flight interception traps to survey tropical arthropods. ZooKeys, 216, 43–55.
Abstract: 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.
Keywords: Flight interception trap; French Guiana; Malaise trap; Performance; Sampling strategies; Tropical forest; Windowpane trap
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Lamarre, G. P. A., Mendoza, I., Fine, P. V. A., & Baraloto, C. (2014). Leaf synchrony and insect herbivory among tropical tree habitat specialists. Plant Ecol., 215(2), 209–220.
Abstract: Growth defense tradeoff theory predicts that plants in low-resource habitats invest more energy in defense mechanisms against natural enemies than growth, whereas plants in high-resource habitats can afford higher leaf loss rates. A less-studied defense against herbivores involves the synchrony of leaf production, which can be an effective defense strategy if leaf biomass production exceeds the capacity of consumption by insects. The aim of this study was to determine whether leaf synchrony varied across habitats with different available resources and whether insects were able to track young leaf production among tree habitat specialists in a tropical forest of French Guiana. We predicted that high-resource habitats would exhibit more synchrony in leaf production due to the low cost and investment to replace leaf tissue. We also expected closer patterns of leaf synchrony and herbivory within related species, assuming that they shared herbivores. We simultaneously monitored leaf production and herbivory rates of five pairs of tree species, each composed of a specialist of terra firme or white-sand forests within the same lineage. Our prediction was not supported by the strong interaction of habitat and lineage for leaf synchrony within individuals of the same species; although habitat specialists differed in leaf synchrony within four of five lineages, the direction of the effect was variable. All species showed short time lags for the correlation between leaf production and herbivory, suggesting that insects are tightly tracking leaf production, especially for the most synchronous species. Leaf synchrony may provide an important escape defense against herbivores, and its expression appears to be constrained by both evolutionary history and environmental factors. © 2014 Springer Science+Business Media Dordrecht.
Keywords: Escape; French Guiana; Herbivorous insects; Phenology; Resource availability; Time lag
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Roy, M., Vasco-Palacios, A., Geml, J., Buyck, B., Delgat, L., Giachini, A., et al. (2017). The (re)discovery of ectomycorrhizal symbioses in Neotropical ecosystems sketched in Florianópolis. New Phytologist, 214(3), 920–923.
Keywords: barcoding; biodiversity; ectomycorrhizal fungi; ectomycorrhizal roots; ectomycorrhizal symbioses; fruitbodies; Neotropical ecosystems
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Seymour, R. S., White, C. R., & Gibernau, M. (2009). Endothermy of dynastine scarab beetles (Cyclocephala colasi) associated with pollination biology of a thermogenic arum lily (Philodendron solimoesense). J. Exp. Biol., 212(18), 2960–2968.
Abstract: Cyclocephala colasi beetles are facultative endotherms that spend most of their adult lives inside the inflorescences of Philodendron solimoesense, where ambient temperature (T-a) averages about 28 degrees C due to floral thermogenesis. Measurements of respiration within a range of T-a showed that active beetles became spontaneously endothermic at T-a below 28 degrees C but were rarely endothermic above it. There was no evidence of endothermy within the inflorescences, indicating that activities in the floral chamber can occur without the high energy expense of endothermy. Bouts of endothermy occurred at lower T-a in respirometer chambers mainly in the evening, when the insects normally fly from one inflorescence to another, and during the night, when they normally eat and mate within the inflorescence. Patterns of endothermy in individual episodes were studied in non-flying beetles with respirometry and infrared thermal imaging. Heat was generated in the thorax by oscillatory waves of respiration that were coupled with thoracic temperature (T-th) increases. Stationary beetles could regulate T-th at about 33 degrees C independently of T-a between 16 and 29 degrees C. At T-a=20 degrees C, this represents a 116-fold increase in metabolic rate over resting, ectothermic values. Endothermy was clearly a requirement for flight, and beetles departing inflorescences warmed to about 30 degrees C before take-off. During flight, T-th was dependent on T-a, decreasing from 37 to 28 degrees C at T-a of 37 to 20 degrees C, respectively. The lowest T-a at which flight could occur was about 20 degrees C. Thermal conductance of stationary, endothermic beetles increased at higher metabolic rates, probably because of increased ventilatory heat loss.
Keywords: beetle; endothermy; pollination biology; Cyclocephala; Philodendron
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Gourlet-Fleury, S., Comu, G., Jesel, S., Dessard, H., Jourget, J. G., Blanc, L., et al. (2005). Using models to predict recovery and assess tree species vulnerability in logged tropical forests: A case study from French Guiana. For. Ecol. Manage., 209(1-2), 69–86.
Abstract: A major challenge for forest managers is to define the optimal cutting cycle to ensure that the resource is sustained in the long term. Matrix models of forest dynamics allow time-projection of diameter-class distributions and thus assessment of the time needed, after logging, to recover a given part of the exploitable stock. They are easy to build and they only require, as input variables, the diameter structure of the population(s) under scope. However, such models are based on a coarse description of tree population dynamics and must be used with caution. In particular, as trees are only described from a diameter threshold (usually 10 cm dbh), recruitment of a new tree cannot be linked with the preceding generation since too much time elapsed between seed dispersal and the installation of a 10-cm recruit. This causes predictions of matrix models to be highly questionable in the long term when ingrowth to larger dbh classes greatly depends on the way recruitment has been modelled. We used a case study from French Guiana to test whether or not a simple matrix model is reliable enough to help forest managers choose between management alternatives. We focused on the major timber species Dicorynia guianensis Amshoff (Caesalpiniaceae) harvested under a selective cutting regime. We compared predictions of D. guianensis stock recovery in the short and long term provided by two models: StoMat, a non-regulated matrix model, and SELVA, a single-tree distance dependent model explicitly simulating the entire species life cycle. Both models were independently calibrated on data from Paracou permanent sample plots. We showed that: (i) the short-term recovery of the exploitable stock predicted by StoMat is reliable for a large range of disturbance conditions; (ii) recruitment implementation in StoMat does not influence projections until the third felling cycle; (iii) for shared initial stand conditions SELVA and StoMat give consistent mid- and long-term predictions: the simple recruitment model used into StoMat could efficiently summarise the regeneration processes of the species under low felling intensity. Our results indicate that the current felling regime used in French Guiana may not be sustainable on a long-term basis. In any case, no more than 60% of the initial stock would be recovered after logging. We conclude that simple models can provide as reliable predictions as more complicated ones. They may be sufficient to assess the recovery of a species' exploitable stock even in the long term, or at least assess the (un)sustainability of particular harvesting regimes. (c) 2005 Elsevier B.V. All rights reserved.
Keywords: matrix model; individual-based spatially explicit model; regeneration; recruitment; long-term population dynamics
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Petitjean, C., Hénault, C., Perrin, A. - S., Pontet, C., Metay, A., Bernoux, M., et al. (2015). Soil N2O emissions in French Guiana after the conversion of tropical forest to agriculture with the chop-and-mulch method. Agriculture, Ecosystems and Environment, 208, 64–74.
Abstract: In French Guiana, the population growth will result in an increase in demand for agricultural products and thus, will lead to an increase in the amount of tropical forests converted into cropland or pasture. Impacts of different agricultural systems on greenhouse gas (GHG) fluxes have not been studied in French Guiana. In this context, the fire-free chop-and-mulch method was used to convert a tropical forest site to agriculture. This study focused on soil nitrous oxide (N<inf>2</inf>O) emissions and we compared four land uses: (1) the undisturbed tropical forest, (2) recently converted grassland and recently converted croplands (fertilized soybean/maize rotation) with either (3) disk tillage or (4) no tillage.N<inf>2</inf>O measurements were obtained through the chamber technique and conducted over a 1-year period (measurements began 19 months after the forest was cleared). N<inf>2</inf>O fluxes were related to soil parameters measured at each sampling date: nitrate and ammonium contents, gravimetric water content (GWC) and temperature. Through the entire period, the mean (± standard error) and median N<inf>2</inf>O fluxes were 3.8 ± 0.5 and 2.7 gNha-1day-1, respectively for undisturbed tropical forest and 2.4 ± 0.9 and 0.8gNha-1day-1, respectively for grassland (mowed Brachiaria ruziziensis). For croplands, no significant difference was found for N<inf>2</inf>O emissions between both agricultural practices. The mean (± standard error) and median N<inf>2</inf>O fluxes were 8.5 ± 1.2 and 4.0 gNha-1day-1, respectively for disk tillage plots and 8.5 ± 1.3 and 3.6gNha-1day-1, respectively for no tillage plots. Nitrogen inputs (due to the application of fertilizer or due to the mineralization of crop residues) led to higher N<inf>2</inf>O fluxes, resulting in significantly higher mean N<inf>2</inf>O emissions from croplands compared to the forest, when only considering land use effect on N<inf>2</inf>O fluxes in a statistical model. The soil nitrate content, GWC and temperature had a significant positive effect on N<inf>2</inf>O fluxes. Taking into account these soil parameters in another statistical model, N<inf>2</inf>O emissions from croplands were not higher than the natural N<inf>2</inf>O emissions from tropical forest soils. Our results suggest that, if more forest will have to be converted in the course of the expected population growth in French Guiana, it could have low impact on the soil N<inf>2</inf>O fluxes (similar to natural fluxes from forest) with the improving of farming techniques (for example modification of the splitting of N-fertilizer) in the cropping plots. © 2015 Elsevier B.V.
Keywords: Chop-and-mulch method; Fire-free deforestation; French Guiana; Land use change; Soil N<inf>2</inf>O emissions
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Chang, S. - S., Quignard, F., Alméras, T., & Clair, B. (2015). Mesoporosity changes from cambium to mature tension wood: A new step toward the understanding of maturation stress generation in trees. New Phytologist, 205(3), 1277–1287.
Abstract: In order to progress in the understanding of mechanical stress generation, the mesoporosity of the cell wall and its changes during maturation of poplar (Populus deltoides × P. nigra) tension wood (TW) and opposite wood (OW) were measured by nitrogen adsorption-desorption. Variations in the thickness of the gelatinous layer (G-layer) were also measured to clarify whether the mesoporosity change simultaneously with the deposition of the G-layer in TW. Results show that mesoporous structures of TW and OW were very similar in early development stages before the deposition of G-layers. With the formation of the S2 layer in OW and the G-layer in TW, the mesopore volume decreased steeply before lignification. However, in TW only, the decrease in mesopore volume occurred together with the pore shape change and a progressive increase in pore size. The different patterns observed in TW revealed that pores from G-layers appear with a different shape compared to those of the compound middle lamella, and their size increases during the maturation process until stabilising in mature wood. This observation strongly supports the hypothesis of the swelling of the G-layer matrix during maturation as the origin of maturation stress in poplar tension wood.
Keywords: Cell wall maturation; Maturation stress; Mesoporosity; Poplar (Populus deltoides × P. nigra); Tension wood
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