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Molto, Q., Rossi, V., & Blanc, L. (2013). Error propagation in biomass estimation in tropical forests. Methods in Ecology and Evolution, 4(2), 175–183.
Abstract: Reliable above-ground biomass (AGB) estimates are required for studies of carbon fluxes and stocks. However, there is a huge lack of knowledge concerning the precision of AGB estimates and the sources of this uncertainty. At the tree level, the tree height is predicted using the tree diameter at breast height (DBH) and a height sub-model. The wood-specific gravity (WSG) is predicted with taxonomic information and a WSG sub-model. The tree mass is predicted using the predicted height, the predicted WSG and the biomass sub-model. Our models were inferred with Bayesian methods and the uncertainty propagated with a Monte Carlo scheme. The uncertainties in the predictions of tree height, tree WSG and tree mass were neglected sequentially to quantify their contributions to the uncertainty in AGB. The study was conducted in French Guiana where long-term research on forest ecosystems provided an outstanding data collection on tree height, tree dynamics, tree mass and species WSG. We found that the uncertainty in the AGB estimates was found to derive primarily from the biomass sub-model. The models used to predict the tree heights and WSG contributed negligible uncertainty to the final estimate. Considering our results, a poor knowledge of WSG and the height-diameter relationship does not increase the uncertainty in AGB estimates. However, it could lead to bias. Therefore, models and databases should be used with care. This study provides a methodological framework that can be broadly used by foresters and plant ecologist. It provides the accurate confidence intervals associated with forest AGB estimates made from inventory data. When estimating region-scale AGB values (through spatial interpolation, spatial modelling or satellite signal treatment), the uncertainty of the forest AGB value in the reference forest plots has to be taken in account. We believe that in the light of the Reducing Emissions from Deforestation and Degradation debate, our method is a crucial step in monitoring carbon stocks and their spatio-temporal evolution. © 2012 The Authors. Methods in Ecology and Evolution © 2012 British Ecological Society.
Keywords: Bayesian framework; Modelling; Redd; Uncertainty propagation
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Rodrigues, A. M. S., Theodoro, P. N. E. T., Eparvier, V., Basset, C., Silva, M. R. R., Beauchene, J., et al. (2010). Search for Antifungal Compounds from the Wood of Durable Tropical Trees. J. Nat. Prod., 73(10), 1706–1707.
Abstract: Research on antifungal compounds from the durable wood from French Guiana Amazonian forest trees highlights the correlation between the activity of their extracts against wood-rotting fungi and human pathogens. The fractionation of an ethyl acetate extract of Sextonia rubra wood led to the isolation of rubrenolide (1) and rubrynolide (2). The potential of compounds 1 and 2 is described through the evaluation of their activity against 16 pathogenic fungi and their cytotoxicity toward NIH-3T3 mammalian fibroblast cells.
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Falkowski, M., Jahn-Oyac, A., Ferrero, E., Issaly, J., Eparvier, V., Girod, R., et al. (2016). Assessment of A Simple Compound-Saving Method to Study Insecticidal Activity of Natural Extracts and Pure Compounds Against Mosquito Larvae. Journal of the American Mosquito Control Association, 32(4), 337–340.
Abstract: Research on natural insecticides has intensified with the spread of resistance to chemicals among insects, particularly disease vectors. To evaluate compounds, the World Health Organization (WHO) has published standardized procedures. However, those may be excessively compound-consuming when it comes to assessing the activity of natural extracts and pure compounds isolated in limited amount. As part of our work on the discovery of new mosquito larvicides from Amazonian plants, we developed a compound-saving assay in 5-ml glass tubes instead of WHO larval 100-ml cups. Comparing activity of synthetic and natural chemicals validated the glass tube assay. Raw data, lethal doses that kill 50% (LD50) and 90% (LD90) at 24 and 48 h, were highly correlated (0.68 < R2 < 0.96, P < 0.001, Pearson test) between cups and tubes. It was also established that 10 tubes (N = 50 larvae) provided the same level of sensitivity as 20 tubes (N = 100). This method proved suitable for rapid screening of natural extracts and molecules, identifying active compounds using 10 times less material than in the WHO protocol. © 2016 by The American Mosquito Control Association, Inc.
Keywords: Mosquitoes; natural insecticides; screening method
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Urbina, I., Grau, O., Sardans, J., Margalef, O., Peguero, G., Asensio, D., et al. (2021). High foliar K and P resorption efficiencies in old-growth tropical forests growing on nutrient-poor soils. Ecology and Evolution, 11(13), 8969–8982.
Abstract: Resorption is the active withdrawal of nutrients before leaf abscission. This mechanism represents an important strategy to maintain efficient nutrient cycling; however, resorption is poorly characterized in old-growth tropical forests growing in nutrient-poor soils. We investigated nutrient resorption from leaves in 39 tree species in two tropical forests on the Guiana Shield, French Guiana, to investigate whether resorption efficiencies varied with soil nutrient, seasonality, and species traits. The stocks of P in leaves, litter, and soil were low at both sites, indicating potential P limitation of the forests. Accordingly, mean resorption efficiencies were higher for P (35.9%) and potassium (K; 44.6%) than for nitrogen (N; 10.3%). K resorption was higher in the wet (70.2%) than in the dry (41.7%) season. P resorption increased slightly with decreasing total soil P; and N and P resorptions were positively related to their foliar concentrations. We conclude that nutrient resorption is a key plant nutrition strategy in these old-growth tropical forests, that trees with high foliar nutrient concentration reabsorb more nutrient, and that nutrients resorption in leaves, except P, are quite decoupled from nutrients in the soil. Seasonality and biochemical limitation played a role in the resorption of nutrients in leaves, but species-specific requirements obscured general tendencies at stand and ecosystem level.
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Fanin, N., Hättenschwiler, S., Schimann, H., & Fromin, N. (2015). Interactive effects of C, N and P fertilization on soil microbial community structure and function in an Amazonian rain forest. Funct. Ecol., 29(1), 140–150.
Abstract: Resource control over abundance, structure and functional diversity of soil microbial communities is a key determinant of soil processes and related ecosystem functioning. Copiotrophic organisms tend to be found in environments which are rich in nutrients, particularly carbon, in contrast to oligotrophs, which survive in much lower carbon concentrations. We hypothesized that microbial biomass, activity and community structure in nutrient-poor soils of an Amazonian rain forest are limited by multiple elements in interaction. We tested this hypothesis with a fertilization experiment by adding C (as cellulose), N (as urea) and P (as phosphate) in all possible combinations to a total of 40 plots of an undisturbed tropical forest in French Guiana. After 2 years of fertilization, we measured a 47% higher biomass, a 21% increase in substrate-induced respiration rate and a 5-fold higher rate of decomposition of cellulose paper discs of soil microbial communities that grew in P-fertilized plots compared to plots without P fertilization. These responses were amplified with a simultaneous C fertilization suggesting P and C colimitation of soil micro-organisms at our study site. Moreover, P fertilization modified microbial community structure (PLFAs) to a more copiotrophic bacterial community indicated by a significant decrease in the Gram-positive : Gram-negative ratio. The Fungi : Bacteria ratio increased in N fertilized plots, suggesting that fungi are relatively more limited by N than bacteria. Changes in microbial community structure did not affect rates of general processes such as glucose mineralization and cellulose paper decomposition. In contrast, community level physiological profiles under P fertilization combined with either C or N fertilization or both differed strongly from all other treatments, indicating functionally different microbial communities. While P appears to be the most critical from the three major elements we manipulated, the strongest effects were observed in combination with either supplementary C or N addition in support of multiple element control on soil microbial functioning and community structure. We conclude that the soil microbial community in the studied tropical rain forest and the processes it drives is finely tuned by the relative availability in C, N and P. Any shifts in the relative abundance of these key elements may affect spatial and temporal heterogeneity in microbial community structure, their associated functions and the dynamics of C and nutrients in tropical ecosystems.
Keywords: Ecosystem functioning; Functional significance; Microbial community structure; Multiple resource limitation; Phospholipid fatty acids (PLFA); Phosphorus; Soil functioning; Tropical forest
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Marcon, E., Traissac, S., & Lang, G. (2013). A Statistical Test for Ripley’s Function Rejection of Poisson Null Hypothesis. ISRN Ecology, 2013(Article ID 753475), 9.
Abstract: Ripley’s K function is the classical tool to characterize the spatial structure of point patterns. It is widely used in vegetation studies. Testing its values against a null hypothesis usually relies on Monte-Carlo simulations since little is known about its distribution.
We introduce a statistical test against complete spatial randomness (CSR). The test returns the p-value to reject the null hypothesis of independence between point locations. It is more rigorous and faster than classical Monte-Carlo simulations. We show how to apply it to a tropical forest plot. The necessary R code is provided.
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Brosse, S., Baglan, A., Covain, R., Lalague, H., Le Bail, P. - Y., Vigouroux, R., et al. (2021). Aquarium trade and fish farms as a source of non-native freshwater fish introductions in French Guiana. Annales de Limnologie – International Journal of Limnology, 57(4).
Abstract: Rivers of French Guiana are still little invaded by non-native fish, but several fish introductions were recently recorded through the development of aquarium fish trade and fish farms. Here we report records of 11 non-native fish species. Among them, four (Cichla monoculus, Heros efasciatus, Mesonauta guyanae and Poecilia reticulata) are established and one of them (Heros efasciatus) is rapidly increasing its spatial range. Two species (Hyphessobrycon eques and Pterophyllum scalare) were not retrieved in recent records and are probably extinct from French Guiana. The establishment status of the five other species (Arapaima gigas, Colossoma macropomum, Cyprinus carpio, Oreochromis mossambicus and Osteoglossum bicirrhosum) is uncertain and only a few specimens were observed in the wild. Nevertheless, these species, intensively reared in nearby countries, belong to highly invasive species able to cause detrimental impacts on recipient ecosystems. Those first occurrences of invasive fish species in French Guiana should therefore act as an early warning for both researchers and environmental managers.
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Baraloto, C., Alverga, P., Quispe, S. B., Barnes, G., Chura, N. B., da Silva, I. B., et al. (2015). Effects of road infrastructure on forest value across a tri-national Amazonian frontier. Biological Conservation, 191, 674–681.
Abstract: Road construction demonstrably accelerates deforestation rates in tropical forests, but its consequences for forest degradation remain less clear. We estimated a series of forest value metrics including components of biodiversity, carbon stocks, and timber and non-timber forest product resources, along the recently paved Inter-Oceanic Highway (IOH) integrating Brazil and Peru along the Bolivian border. We installed 69 vegetation plots in intact terra firme forests representative of local community holdings near and far from the IOH, and we characterized 15 components of forest value for each plot.We observed strong geographic gradients in forest value components across the region, with increases from west to east in aboveground biomass and in the abundance of timber and non-timber forest product trees and regeneration. Plots in communities in Pando, Bolivia, where the IOH remains in part unpaved, had the highest aboveground biomass, standing timber volumes and Brazil nut tree density. In contrast, communities in Madre de Dios, Peru, where settlements and unpaved portions of the IOH have existed for decades, and in Acre, Brazil, where paving of the IOH has been underway for more than a decade, were more degraded. Seven of the fifteen forest value components we measured increased with increasing distance from the IOH, although the magnitude of these effects was weak. Landscape scale remote sensing analyses showed much stronger effects of road proximity on deforestation. We suggest that remote sensing techniques including canopy spectral signatures might be calibrated to characterize multiple components of forest value, so that we can estimate landscape scale impacts of infrastructure developments on both deforestation and forest degradation in tropical regions. © 2015 Elsevier B.V.
Keywords: Açai; Biodiversity; Brazil nut; Carbon stocks; Connectivity; Infrastructure; Livelihood; Ntfp; Redd; Road impact; Rubber; Timber; Tropical rainforest
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Christensen-Dalsgaard, K. K., Ennos, A. R., & Fournier, M. (2007). Changes in hydraulic conductivity, mechanical properties, and density reflecting the fall in strain along the lateral roots of two species of tropical trees. J. Exp. Bot., 58(15-16), 4095–4105.
Abstract: Roots have been described as having larger vessels and so greater hydraulic efficiency than the stem. Differences in the strength and stiffness of the tissue within the root system itself are thought to be an adaptation to the loading conditions experienced by the roots and to be related to differences in density. It is not known how potential mechanical adaptations may affect the hydraulic properties of the roots. The change in strength, stiffness, conductivity, density, sapwood area, and second moment of area distally along the lateral roots of two tropical tree species in which the strain is known to decrease rapidly was studied and the values were compared with those of the trunk. It was found that as the strain fell distally along the roots, so did the strength and stiffness of the tissue, whereas the conductivity increased exponentially. These changes appeared to be related to differences in density. In contrast to the distal-most roots, the tissue of the proximal roots had a lower conductivity and higher strength than that of the trunk. This suggests that mechanical requirements on the structure rather than the water potential gradient from roots to branches are responsible for the general pattern that roots have larger vessels than the stem. In spite of their increased transectional area, the buttressed proximal roots were subjected to higher levels of stress and had a lower total conductivity than the rest of the root system. © 2007 The Author(s).
Keywords: Buttress roots; Density; Hydraulic conductivity; Hydraulic-mechanical trade-offs; Modulus of elasticity; Tropical trees; Wood; Elastic moduli; Hydraulic conductivity; Wood; Buttress roots; Hydraulic-mechanical trade-offs; Tropical trees; Forestry; water; article; biomechanics; histology; legume; physiology; plant root; plant stem; tree; wood; Xylopia; Biomechanics; Fabaceae; Plant Roots; Plant Stems; Trees; Water; Wood; Xylopia; Conductivity; Elastic Strength; Forestry; Wood
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Amusant, N., Beauchene, J., Digeon, A., & Chaix, G. (2016). Essential oil yield in rosewood (Aniba rosaeodora Ducke): Initial application of rapid prediction by near infrared spectroscopy based on wood spectra. Journal of Near Infrared Spectroscopy, 24(6), 507–515.
Abstract: Rosewood (Aniba rosaeodora) essential oil is a valuable ingredient that has long been used in the perfume and cosmetic industries. The main rosewood timber quality parameters are its essential oil yield and quality. A hydrodistillation method has been developed for yield determination, but it is time consuming. Here we tested the applicability of near infrared (NIR) spectroscopy for determining essential oil yield directly from wood powder. Essential oil from 139 wood powders was extracted via hydrodistillation. The measurements were based on the ratio between the extracted essential oil mass and the oven-dried wood mass and were correlated with the wood powder NIR spectra. The calibration model statistical findings demonstrated that NIR could be a fast and feasible alternative method for selecting trees with a high essential oil yield potential. NIR-based predictions obtained in an independent validation set indicated a high correlation (r2e = 0.92) with laboratory essential oil yield measurements. This NIR model could help wood managers in selecting trees with a high essential oil yield potential and in developing sustainable rosewood management strategies. © IM Publications LLP 2016. All rights reserved.
Keywords: Aniba rosaeodora; Calibration; Essential oil yield; Nir; Pls; Rosewood
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