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Feldpausch, T. R., Phillips, O. L., Brienen, R. J. W., Gloor, E., Lloyd, J., Lopez-Gonzalez, G., et al. (2016). Amazon forest response to repeated droughts. Global Biogeochemical Cycles, 30(7), 964–982.
Abstract: The Amazon Basin has experienced more variable climate over the last decade, with a severe and widespread drought in 2005 causing large basin-wide losses of biomass. A drought of similar climatological magnitude occurred again in 2010; however, there has been no basin-wide ground-based evaluation of effects on vegetation. We examine to what extent the 2010 drought affected forest dynamics using ground-based observations of mortality and growth from an extensive forest plot network. We find that during the 2010 drought interval, forests did not gain biomass (net change: −0.43 Mg ha−1, confidence interval (CI): −1.11, 0.19, n = 97), regardless of whether forests experienced precipitation deficit anomalies. This contrasted with a long-term biomass sink during the baseline pre-2010 drought period (1998 to pre-2010) of 1.33 Mg ha−1 yr−1 (CI: 0.90, 1.74, p < 0.01). The resulting net impact of the 2010 drought (i.e., reversal of the baseline net sink) was −1.95 Mg ha−1 yr−1 (CI:−2.77, −1.18; p < 0.001). This net biomass impact was driven by an increase in biomass mortality (1.45 Mg ha−1 yr−1 CI: 0.66, 2.25, p < 0.001) and a decline in biomass productivity (−0.50 Mg ha−1 yr−1, CI:−0.78, −0.31; p < 0.001). Surprisingly, the magnitude of the losses through tree mortality was unrelated to estimated local precipitation anomalies and was independent of estimated local pre-2010 drought history. Thus, there was no evidence that pre-2010 droughts compounded the effects of the 2010 drought. We detected a systematic basin-wide impact of the 2010 drought on tree growth rates across Amazonia, which was related to the strength of the moisture deficit. This impact differed from the drought event in 2005 which did not affect productivity. Based on these ground data, live biomass in trees and corresponding estimates of live biomass in lianas and roots, we estimate that intact forests in Amazonia were carbon neutral in 2010 (−0.07 Pg C yr−1 CI:−0.42, 0.23), consistent with results from an independent analysis of airborne estimates of land-atmospheric fluxes during 2010. Relative to the long-term mean, the 2010 drought resulted in a reduction in biomass carbon uptake of 1.1 Pg C, compared to 1.6 Pg C for the 2005 event. ©2016. American Geophysical Union. All Rights Reserved.
Keywords: carbon; forest productivity; precipitation; tree mortality; vegetation dynamics; water deficit
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Imbert, D. (2018). Hurricane disturbance and forest dynamics in east Caribbean mangroves. Ecosphere, 9(7), e02231.
Abstract: Despite low plant diversity and structural simplicity, mangroves offer various ecosystem services to local human communities, including sheltering coastal social-ecological systems from high-energy storm damage. The expected increasing intensity of hurricanes due to climate change raises questions concerning the capacity of mangroves to resist and recover from such disturbances. Herein, this study contributes to a better understanding of (1) the relation between storm intensity and damage to mangrove vegetation, (2) the contributions of species-specific as well as stand-specific components of mangrove vegetation to ecosystem resistance, and (3) the recovery of pre-hurricane forest structure through time. The first two issues have been addressed using a stand-level approach implemented at two east Caribbean mangrove sites in response to three storm events. The third was addressed through a 23-yr survey of forest recovery following the passage of a high-energy storm across one of the two study sites. Generally, hurricane damage was primarily controlled by wind velocity, followed by the hydro-geomorphic context of mangrove forests and species-specific composition, respectively. The relationship between damage to trees and wind velocity evidenced a sigmoidal trend, with a maximum slope at a wind velocity averaging 130 and 180 km/h for higher vs. lower canopy stands, respectively. The red mangrove, Rhizophora mangle, was significantly less resistant to hurricane damage than was the black mangrove, Avicennia germinans. Unlike the fringe and scrub stands, inner, tall-canopy stands fully recovered by the end of the study (23 yr). These stands were more resilient because of their growth performances. Finally, the time for east Caribbean mangroves to recover from high-energy storms seems to fall within the range of the average return time of such disturbances. This may prevent such ecosystems from ever reaching a steady state.
Keywords: Caribbean; forest recovery; high-energy storms; mangrove; resilience; resistance; Special Feature: High-Energy Storms
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Gibson, J. C., Larabee, F. J., Touchard, A., Orivel, J., & Suarez, A. V. (2018). Mandible strike kinematics of the trap-jaw ant genus Anochetus Mayr (Hymenoptera: Formicidae). Journal of Zoology, 306(2), 119–128.
Abstract: High-speed power-amplification mechanisms are common throughout the animal kingdom. In ants, power-amplified trap-jaw mandibles have evolved independently at least four times, including once in the subfamily Ponerinae which contains the sister genera Odontomachus and Anochetus. In Odontomachus, mandible strikes have been relatively well described and can occur in <0.15 ms and reach speeds of over 60 m s−1. In contrast, the kinematics of mandible strikes have not been examined in Anochetus, whose species are smaller and morphologically distinct from Odontomachus. In this study, we describe the mandible strike kinematics of four species of Anochetus representative of the morphological, phylogenetic, and size diversity present within the genus. We also compare their strikes to two representative species of Odontomachus. We found that two species, Anochetus targionii and Anochetus paripungens, have mandible strikes that overall closely resemble those found in Odontomachus, reaching a mean maximum rotational velocity and acceleration of around 3.7 × 104 rad s−1 and 8.5 × 108 rad s−2, respectively. This performance is consistent with predictions based on body size scaling relationships described for Odontomachus. In contrast, Anochetus horridus and Anochetus emarginatus have slower strikes relative to the other species of Anochetus and Odontomachus, reaching mean maximum rotational velocity and acceleration of around 1.3 × 104 rad s−1 and 2 × 108 rad s−2, respectively. This variation in strike performance among species of Anochetus likely reflects differences in evolutionary history, physiology, and natural history among species. © 2018 The Zoological Society of London
Keywords: catapult mechanism; comparative biomechanics; Formicidae; functional morphology; kinematics; mandible strike; power amplification
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Mathieu, A., Letort, V., Cournède, P. H., Zhang, B. G., Heuret, P., & De Reffye, P. (2012). Oscillations in functional structural plant growth models. Mathematical Modelling of Natural Phenomena, 7(6), 47–66.
Abstract: The dynamic model of plant growth GreenLab describes plant architecture and functional growth at the level of individual organs. Structural development is controlled by formal grammars and empirical equations compute the amount of biomass produced by the plant, and its partitioning among the growing organs, such as leaves, stems and fruits. The number of organs initiated at each time step depends on the trophic state of the plant, which is evaluated by the ratio of biomass available in plant to the demand of all the organs. The control of the plant organogenesis by this variable induces oscillations in the simulated plant behaviour. The mathematical framework of the GreenLab model allows to compute the conditions for the generation of oscillations and the value of the period according to the set of parameters. Two case-studies are presented, corresponding to emergence of oscillations associated to fructification and branching. Similar alternating patterns are commonly reported by botanists. In this article, two examples were selected: alternate patterns of fruits in cucumber plants and alternate appearances of branches in Cecropia trees. The model was calibrated from experimental data collected on these plants. It shows that a simple feedback hypothesis of trophic control on plant structure allows the emergence of cyclic patterns corresponding to the observed ones. © EDP Sciences, 2012.
Keywords: Cecropia trees; Cucumber plant; Dynamic system of plant growth; Functional-structural plant models; GreenLab
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Letort, V., Heuret, P., Zalamea, P. - C., De Reffye, P., & Nicolini, E. (2012). Analysing the effects of local environment on the source-sink balance of Cecropia sciadophylla: A methodological approach based on model inversion. Ann. Forest Sci., 69(2), 167–180.
Abstract: Context Functional-structural models (FSM) of tree growth have great potential in forestry, but their development, calibration and validation are hampered by the difficulty of collecting experimental data at organ scale for adult trees. Due to their simple architecture and morphological properties, “model plants” such as Cecropia sciadophylla are of great interest to validate new models and methodologies, since exhaustive descriptions of their plant structure and mass partitioning can be gathered. Aims Our objective was to develop a model-based approach to analysing the influence of environmental conditions on the dynamics of trophic competition within C. sciadophylla trees. Methods We defined an integrated environmental factor that includes meteorological medium-frequency variations and a relative index representing the local site conditions for each plant. This index is estimated based on model inversion of the GreenLab FSM using data from 11 trees for model calibration and 7 trees for model evaluation. Results The resulting model explained the dynamics of biomass allocation to different organs during the plant growth, according to the environmental pressure they experienced. Perspectives By linking the integrated environmental factor to a competition index, an extension of the model to the population level could be considered. © INRA and Springer Science+Business Media B.V. 2011.
Keywords: Cecropia; Functional-structural model; Model inversion; Morphology; Trophic competition
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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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Alméras, T., Gronvold, A., van der Lee, A., Clair, B., & Montero, C. (2017). Contribution of cellulose to the moisture-dependent elastic behaviour of wood. Composites Science and Technology, 138, 151–160.
Abstract: Wood has a hierarchical structure involving several levels of organisation. The stiffness of wood relies on its capacity to transfer mechanical stress to its stiffest element at the lowest scale, namely crystalline cellulose. This study aims at quantifying to what extend crystalline cellulose contributes to wood stiffness depending on its moisture content. The crystal strains of cellulose were measured using X-ray diffraction on wet and dry specimens of spruce, based on a previously published methodology. The comparison between crystal strain and macroscopic strain shows that, during elastic loading, cellulose strain is lower than macroscopic strain. The means ratio of crystal/macroscopic strain amounts 0.85 for dry specimens and 0.64 for wet specimens. This strain ratio cannot be explained just by the projection effect due to the difference in orientation between cellulose microfibrils and cell wall, but results from deformation mechanisms in series with cellulose. Analysis shows that this series contribution represents a non-negligible contribution to wood compliance and is strongly moisture-dependent. This contribution amounts 9% for dry specimens and 33% for wet specimens, corresponding to a 4-fold increase in compliance for the series contribution. The origin of these strains is ascribed to mechanisms involving bending or shear strain at different scales, due to the fact that reinforcing element are neither perfectly straight nor infinitely long. © 2016
Keywords: Cellulose; Crystal strain; Micromechanics; Wood; X-ray diffraction
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Ruelle, J., Yamamoto, H., & Thibaut, B. (2007). Growth Stresses and Cellulose Structural Parameters in Tension and Normal Wood from Three Tropical Rainforest Angiosperm Species. BioResources, 2(2), 235–251.
Abstract: Few studies have been conducted about relation between cellulose parameters and biomechanical properties of wood in tropical angiosperms species. For this purpose, on 13 trees from 3 species of French Guyana tropical rainforest in a clear active process of restoring verticality, i) growth strains were measured in situ in order to determine the occurrence of tension wood within samples and ii) cellulose structural parameters were estimated on all the samples using X-ray diffraction method. Crystallite size was estimated from the full-width at half-maximum of the Miller index (002) arc diffraction and angle T was measured following Cave's method. Relationships between these parameters and growth stresses were good and the variations between normal and tension wood were significant, i. e. a lower angle T and a larger crystallite size in tension wood. In order to have a good estimation of the microfibril angle in the main layer of the secondary wall for each species, an experimental calibration was done between angle T and microfibril angle observed with scanning electron microscopy.
Keywords: Cellulose; Microfibril angle; Crystallite size; Tension wood; Tropical rainforest; Growth stresses
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Lang, G., & Marcon, E. (2013). Testing randomness of spatial point patterns with the Ripley statistic. ESAIM PS, 17, 767–788.
Abstract: Aggregation patterns are often visually detected in sets of location data. These clusters may be the result of interesting dynamics or the effect of pure randomness. We build an asymptotically Gaussian test for the hypothesis of randomness corresponding to a homogeneous Poisson point process. We first compute the exact first and second moment of the Ripley K-statistic under the homogeneous Poisson point process model. Then we prove the asymptotic normality of a vector of such statistics for different scales and compute its covariance matrix. From these results, we derive a test statistic that is chi-square distributed. By a Monte-Carlo study, we check that the test is numerically tractable even for large data sets and also correct when only a hundred of points are observed
Keywords: Central limit theorem, goodness-of-fit test, Höffding decomposition, null, point pattern, Poisson process, null
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Cottet, K., Fromentin, Y., Kritsanida, M., Grougnet, R., Odonne, G., Duplais, C., et al. (2015). Isolation of Guttiferones from Renewable Parts of Symphonia globulifera by Centrifugal Partition Chromatography. Planta Medica, 81(17), 1604–1608.
Abstract: The aim of this study was to investigate the species Symphonia globulifera, a source of polycyclic polyprenylated acyl phloroglucinols such as guttiferone A, which is known to exhibit a variety of biological activities including noticeable antileishmanial properties. Our goal was the identification and the quantification of guttiferone A in different renewable parts of S. globulifera and its preparative isolation. To the best of our knowledge, there is no data concerning its mechanism of action. Consequently, it is particularly interesting to isolate it in gram quantities in order to establish structure activity relationship studies. After performing high-performance liquid chromatography profiles detecting the presence of guttiferone A and proceeding to its quantification, a centrifugal partition chromatography methodology using a two-phase solvent system of cyclohexane/ethyl acetate/methanol/water (20 : 1 : 20 : 1, v/v/v/v) was applied to each extract. In conclusion, a centrifugal partition chromatography system has been developed to ensure a fast, reliable, and scalable way to isolate, with a high level of purity, guttiferone A from five renewable parts of S. globulifera. Moreover, this methodology can be extended to the isolation of other polycyclic polyprenylated acyl phloroglucinols such as guttiferones B, C, and D. © Georg Thieme Verlag KG Stuttgart.
Keywords: centrifugal partition chromatography; Clusiaceae; countercurrent chromatography guttiferones; PPAPs; Symphonia globulifera
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