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Stahl, C., Burban, B., Goret, J. Y., & Bonal, D. (2011). Seasonal variations in stem CO(2) efflux in the Neotropical rainforest of French Guiana. Ann. For. Sci., 68(4), 771–782.
Abstract: Introduction Stem CO(2) efflux (E (s)) is a significant component of total ecosystem respiration, but there is only scant information on seasonal variations in E (s) in tropical rainforests and on the main factors explaining these variations. Methods We conducted a comprehensive 18-month study in French Guiana to try to better understand which environmental factors contribute to seasonal variations in E (s) in two habitats differing in soil water conditions. Results In both habitats, large seasonal variations in E (s) were observed for most trees. The main variations occurred during climatic transition periods and were consistent with seasonal variations in soil and total ecosystem respiration. Discussion Seasonal variations in atmospheric conditions, including air temperature, did not explain seasonal variations in E (s). In contrast, seasonal variations in surface soil water content clearly induced seasonal variations in E (s) in each habitat. Both soil drought and flooded conditions induced a decrease in E (s). Conclusion Our results emphasize the need to integrate the influence of soil water content on E (s) into global models that simulate the response of forest ecosystem fluxes to climate changes.
Keywords: Tropical rainforest; Stem CO(2) efflux; Soil water content; Terra Firme forest; Seasonally flooded forest
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Aguilos, M., Hérault, B., Burban, B., Wagner, F., & Bonal, D. (2018). What drives long-term variations in carbon flux and balance in a tropical rainforest in French Guiana? Agricultural and Forest Meteorology, 253–254, 114–123.
Abstract: A thorough understanding of how tropical forests respond to climate is important to improve ecosystem process models and to reduce uncertainties in current and future global carbon balance calculations. The Amazon rainforest, a major contributor to the global carbon cycle, is subject to strong intra- and interannual variations in climate conditions. Understanding their effect on carbon fluxes between the ecosystem and the atmosphere and on the resulting carbon balance is still incomplete. We examined the long-term (over a 12-year period; 2004–2015) variations in gross primary productivity (GPP), ecosystem respiration (RE) and net ecosystem exchange (NEE) in a tropical rainforest in French Guiana and identified key climatic drivers influencing the changes. The study period was characterized by strong differences in climatic conditions among years, particularly differences in the intensity of the dry and wet seasons, as well as differences in annual carbon fluxes and balance. Annual average GPP varied from 3384.9?g?C?m-2?yr?1 (95% CI [3320.7, 3445.9]) to 4061.2?g?C?m-2?yr?1 (95% CI [3980.1, 4145.0]). RE varied even more than GPP, with a difference of 933.1?C?m-2?yr?1 between the minimum (3020.6?g?C?m-2?yr?1; 95% CI [2889.4, 3051.3]) and maximum (3953.7?g?C?m-2?yr?1; 95% CI [3887.6, 4019.6]) values. Although NEE showed large interannual variability (nine-fold), from ?65.6?g?C?m-2?yr?1 (95% CI [?4.4, ?126.0]) to ?590.5?g?C?m-2 yr?1 (95% CI [?532.3, ?651.6]), the forest remained a carbon sink over the 12-year period. A combination of global radiation (Rg), relative extractable water (REW) and soil temperature (Ts) explained 51% of the daily variations for GPP, 30% for RE and 39% for NEE. Global radiation was always the best predictor of these variations, but soil water content and temperature did also influence carbon fluxes and balance. Seasonally, Rg was the major controlling factor for GPP, RE and NEE during the wet season. During the dry season, variations in carbon fluxes and balance were poorly explained by climate factors. Yet, REW was the key driver of variations in NEE during the dry season. This study highlights that, over the long-term, carbon fluxes and balance in such tropical rainforest ecosystems are largely controlled by both radiation and water limitation. Even though variations in Rg have a greater impact on these fluxes, water limitation during seasonal droughts is enough to reduce ecosystem productivity, respiration and carbon uptake. The reduced precipitation expected in tropical rainforest areas under future climatic conditions will therefore strongly influence carbon fluxes and carbon uptake. This study also highlights the importance for land surface or dynamic global vegetation models to consider the main drivers of carbon fluxes and balance separately for dry and wet seasons.
Keywords: Tropical rainforest; Nee; Gpp; Ecosystem respiration; Radiation; Drought
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Phillips, P. D., Thompson, I. S., Silva, J. N. M., van Gardingen, P. R., & Degen, B. (2004). Scaling up models of tree competition for tropical forest population genetics simulation. Ecol. Model., 180(2-3), 419–434.
Abstract: Understanding the effects of logging activity on genetic diversity is an important aspect of establishing the sustainability of selective logging management operations in tropical forests. Genetic variation is affected by selective logging directly, through the removal of and damage to trees within the population, and indirectly, through a change in the forest structure and environment in which the remaining population lives. Eco-Gene is a population genetics model applied to tropical forests over a scale of hundreds of hectares. SYMFOR is a modelling framework for individual-based spatially explicit ecological and management models applied to tropical forests over a scale of 0.25 4 ha. We have linked the models to enable simulations using processes involved in both models. To overcome problems of scale, the spatially explicit competition index calculated in SYMFOR simulations has been modelled such that it can be applied at scales representing much larger areas for which the data are not available, as required by Eco-Gene. The competition index is modelled as a distribution on a grid-square basis, and implemented in the linked Eco-Gene/SYMFOR system. Each tree within a grid-square is given a “relative competition” within the distribution, biased according to species. A competition index value is obtained for the tree by transforming the grid-square distribution to be relevant to the size of the tree, and extracting a value according to the tree's relative competition within the distribution. The distribution and each tree's relative competition within it change according to the effects of growth, mortality and logging activity. The model was calibrated using data from the Tapajos region of the Eastern Amazon forest. This paper describes the model, its calibration and validation and the implications of scaling up from an explicit representation to a modelled quantity. (C) 2004 Elsevier B.V. All rights reserved.
Keywords: tropical rain; forest; population genetics; model SYMFOR; eco-gene; scaling up; competition
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Dezerald, O., Céréghino, R., Corbara, B., Dejean, A., & Leroy, C. (2015). Temperature: Diet Interactions Affect Survival through Foraging Behavior in a Bromeliad-Dwelling Predator. Biotropica, 47(5), 569–578.
Abstract: Temperature, food quantity and quality play important roles in insect growth and survival, influencing population dynamics as well as interactions with other community members. However, the interaction between temperature and diet and its ecological consequences have been poorly documented. Toxorhynchites are well-known biocontrol agents for container-inhabiting mosquito larvae. We found that Toxorhynchites haemorrhoidalis larvae (Diptera: Culicidae) inhabiting water-filled rosettes of tank bromeliads catch and eat prey of both aquatic (mosquito larvae) and terrestrial origin (ants), using distinct predatory methods. They carried out frontal attacks on ants, but ambushed mosquito larvae. In choice tests, T. haemorrhoidalis favored terrestrial prey. Temperature had a significant effect on predator development and survival through its interaction with diet, but did not alter the preference for ants. T. haemorrhoidalis larvae emerged quickly when fed only mosquito larvae, whereas all individuals died before pupation when fed only ants. We conclude that behavioral factors (i.e., attraction to ants that disturb the surface of the water) overtake physiological factors (i.e., the adverse outcome of elevated temperature and an ant-based diet) in determining a predator's response to temperature:diet interactions. Finally, because T. haemorrhoidalis larvae preferentially feed on terrestrial insects in tank bromeliads, mosquito larvae may indirectly benefit from predation release. © 2015 Association for Tropical Biology and Conservation Inc.
Keywords: Toxorhynchites haemorrhoidalis; Biocontrol agent; Development; French Guiana; Selective feeding behavior; Tank bromeliad
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Odonne, G., Bourdy, G., Beauchene, J., Houel, E., Stien, D., Chevolot, L., et al. (2007). From Tonic-cups to Bitter-cups: Kwasi bita beker from Suriname Determination, past and present use of an ancient galenic artefact. J. Ethnopharmacol., 110(2), 318–322.
Abstract: In the main markets of Paramaribo (Suriname), many stands offer what is locally called “Bitter-cups”, or “Kwasi bita beker”, small footed-cups, roughly carved from a whitish wood. The use of these cups is strictly medicinal and it seems to be restricted to Suriname, as they are not found in neighbouring countries (Guyana, French Guiana). The aim of this study was to identify the botanical origin of Bitter-cups still in use in the Saramaka traditional medicine (as information from field people was controversial), and document the ethnopharmacology of this original galenical artefact. Microscopic and high performance liquid chromatography (HPLC) analyses were carried out on Bitter-cup, and anatomical criteria (marginal parenchyma band, size of intervessel and vessel-ray pits, rays width and rays composition, vessels clustering, frequency and size of parenchyma pits) together with HPLC profiles of the macerates showed that the wood cup was similar to Quassia amara L. (Simaroubaceae) wood. Ethnopharmacological investigation indicates that the use of these cups is simply due to the pharmacological properties attributed to “bitters”, and is strongly linked to tradition and cultural attitudes. This study also emphasizes the long lasting use of these cups, now restricted to Suriname only, with almost no variation over one century. (c) 2006 Elsevier Ireland Ltd. All rights reserved.
Keywords: Tonic-cup; Bitter-cup; Quassia amara; Suriname; traditional remedy
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Boisse, P., Aimene, Y., Dogui, A., Dridi, S., Gatouillat, S., Hamila, N., et al. (2010). Hypoelastic, hyperelastic, discrete and semi-discrete approaches for textile composite reinforcement forming. International Journal of Material Forming, 3(Supplement 2), 1229–1240.
Abstract: The clear multi-scale structure of composite textile reinforcements leads to develop continuous and discrete approaches for their forming simulations. In this paper two continuous modelling respectively based on a hypoelastic and hyperelastic constitutive model are presented. A discrete approach is also considered in which each yarn is modelled by shell finite elements and where the contact with friction and possible sliding between the yarns are taken into account. Finally the semi-discrete approach is presented in which the shell finite element interpolation involves continuity of the displacement field but where the internal virtual work is obtained as the sum of tension, in-plane shear and bending ones of all the woven unit cells within the element. The advantages and drawbacks of the different approaches are discussed.
Keywords: Textile composites Forming simulations Continuous/discrete approaches Hyperelasticity Hypoelasticity Semi-discrete finite element
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Ruelle, J., Yoshida, M., Clair, B., & Thibaut, B. (2007). Peculiar tension wood structure in Laetia procera (Poepp.) Eichl. (Flacourtiaceae). Trees-Struct. Funct., 21(3), 345–355.
Abstract: Tension wood of Laetia procera (Poepp.) Eichl. (Flacourtiaceae), a neo-tropical forest species, shows a peculiar secondary wall structure, with an alternance of thick and thin layers, while opposite wood of this species has a typical secondary wall structure (S1 + S2 + S3). Samples for the study of microstructural properties were collected upon the estimation of growth stresses in the living tree, in order to analyze the correlation of the former with the latter. Investigation using optical microscopy, scanning electron microscopy and UV microspectrophotometry allowed the description of the anatomy, ultra-structure and chemistry of this peculiar polylaminate secondary wall. In the thick layers, cellulose microfibril angle is very low (i.e., microfibril orientation is close to fibre axis) and cellulose microfibrils are well organized and parallel to each other. In the thin layers, microfibrils (only observable in the inner layer) are less organized and are oriented with a large angle relative to the axis of the cell. Thick layers are lightly lignified although thin layers show a higher content of lignin, close to that of opposite wood secondary wall. The more the wood was under tensile stress, the less the secondary wall was lignified, and lower the syringyl on guaiacyl lignin units' ratio was. The innermost layer of the secondary wall looks like a typical S3 layer with large microfibril angle and lignin occurrence. The interest of this kind of structure for the understanding of stress generation is discussed.
Keywords: tension wood; tropical rainforest species; UV microspectrophotometry; scanning electron microscopy; cellulose microfibril angle
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Ruelle, J., Beauchene, J., Thibaut, A., & Thibaut, B. (2007). Comparison of physical and mechanical properties of tension and opposite wood from ten tropical rainforest trees from different species. Ann. For. Sci., 64(5), 503–510.
Abstract: On 10 trees from 10 species of French Guyana tropical rainforest in a clear active process of restoring verticality growth strains were measured in situ in order to determine the occurrence of tension wood within samples. Wood specimens were cut in the vicinity of the growth strains measurements in order to measure some mechanical and physical properties. As suspected, tensile growth strains was very much higher in tension wood zone, because longitudinal modulus of elasticity was slightly higher. Longitudinal shrinkage was also much higher in tension wood than in opposite wood.
Keywords: tension wood; opposite wood; tropical rainforest; physical and mechanical properties
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Ruelle, J., Clair, B., Beauchene, J., Prevost, M. F., & Fournier, M. (2006). Tension wood and opposite wood in 21 tropical rain forest species 2. Comparison of some anatomical and ultrastructural criteria. IAWA J., 27(4), 341–376.
Abstract: The anatomy of tension wood and opposite wood was compared in 21 tropical rain forest trees from 21 species belonging to 18 families from French Guyana. Wood specimens were taken from the upper and lower sides of naturally tilted trees. Measurement of the growth stress level ensured that the two samples were taken from wood tissues in a different mechanical state: highly tensile-stressed wood on the upper side, called tension wood and normally tensile-stressed wood on the lower side, called opposite wood. Quantitative parameters relating to fibres and vessels were measured on transverse sections of both tension and opposite wood to check if certain criteria can easily discriminate the two kinds of wood. We observed a decrease in the frequency of vessels in the tension wood in all the trees studied. Other criteria concerning shape and surface area of the vessels, fibre diameter or cell wall thickness did not reveal any general trend. At the ultrastructural level, we observed that the microfibril angle in the tension wood sample was lower than in opposite wood in all the trees except one (Licania membranacea).
Keywords: tension wood; opposite wood; tropical rain forest; vessels; wood anatomy; wood fibre
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Niamke, F. B., Amusant, N., Charpentier, J. P., Chaix, G., Baissac, Y., Boutahar, N., et al. (2011). Relationships between biochemical attributes (non-structural carbohydrates and phenolics) and natural durability against fungi in dry teak wood (Tectona grandis L. f.). Ann. For. Sci., 68(1), 201–211.
Abstract: Introduction Non-structural carbohydrates and phenolic compounds are implicated in the natural durability of wood. In order to find the chemical traits of natural durability in teak wood, the radial distribution of phenolics compounds and non-structural carbohydrates were studied in trees ranked by contrasting natural durability class against Antrodia sp. Methods Non-structural carbohydrates were analyzed by spectrophotometry after enzymatic assays and phenolics compounds using HPLC. Results High concentrations of starch, sucrose, glucose, and fructose were found in the sapwood, whereas only trace amounts were found in the heartwood. In the sapwood, low concentrations of H1 (a hydroxycinnamic acid derivative) were specifically detected. Tectoquinone was also detected in the sapwood but its content increased dramatically in the heartwood. 2-(Hydroxymethyl) anthraquinone and P1, an unidentified compound, were only detected in the heartwood and at high concentrations (>3 mg equivalent 5-methoxyflavone g(-1) dry weight. Lower concentrations of 1,4-naphthoquinone, anthraquinone-2-carboxylic acid, and lapachol were also only detected in the heartwood. H1 and tectoquinone present in the sapwood could be considered as phenolic precursors of the synthesis of heartwood toxic phenolics in the heartwood. Conclusion Correlations between natural durability and chemical composition of heartwood (quinone derivatives, P1, and non-structural carbohydrates) suggest that P1, 2-(hydroxymethyl) anthraquinone and tectoquinone could be natural durability traits. Heartwood extractives,
Keywords: Tectona grandis; Teak heartwood; Phenolic compound; Non-structural carbohydrate; Natural durability
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