Prevost-Boure, N. C., Ngao, J., Berveiller, D., Bonal, D., Damesin, C., Dufrene, E., et al. (2009). Root exclusion through trenching does not affect the isotopic composition of soil CO2 efflux. Plant Soil, 319(1-2), 1–13.
Abstract: Disentangling the autotrophic and heterotrophic components of soil CO2 efflux is critical to understanding the role of soil system in terrestrial carbon (C) cycling. In this study, we combined a stable C-isotope natural abundance approach with the trenched plot method to determine if root exclusion significantly affected the isotopic composition (delta C-13) of soil CO2 efflux (R-S). This study was performed in different forest ecosystems: a tropical rainforest and two temperate broadleaved forests, where trenched plots had previously been installed. At each site, R-S and its delta C-13 (delta C-13(Rs)) tended to be lower in trenched plots than in control plots. Contrary to R-S, delta C-13(Rs) differences were not significant. This observation is consistent with the small differences in delta C-13 measured on organic matter from root, litter and soil. The lack of an effect on delta C-13(Rs) by root exclusion could be from the small difference in delta C-13 between autotrophic and heterotrophic soil respirations, but further investigations are needed because of potential artefacts associated with the root exclusion technique.
Keywords: Stable carbon isotopes; Natural abundance; Soil respiration; Trenched plot; Rainforest; Temperate forest
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Levionnois, S., Coste, S., Nicolini, E., Stahl, C., Morel, H., & Heuret, P. (2020). Scaling of petiole anatomies, mechanics and vasculatures with leaf size in the widespread Neotropical pioneer tree species Cecropia obtusa Trécul (Urticaceae). Tree Physiol., 40(2), 245–258.
Abstract: Although the leaf economic spectrum has deepened our understanding of leaf trait variability, little is known about how leaf traits scale with leaf area. This uncertainty has resulted in the assumption that leaf traits should vary by keeping the same pace of variation with increases in leaf area across the leaf size range. We evaluated the scaling of morphological, tissue-surface and vascular traits with overall leaf area, and the functional significance of such scaling. We examined 1,271 leaves for morphological traits, and 124 leaves for anatomical and hydraulic traits, from 38 trees of Cecropia obtusa Trécul (Urticaceae) in French Guiana. Cecropia is a Neotropical genus of pioneer trees that can exhibit large laminas (0.4 m2 for C. obtusa), with leaf size ranging by two orders of magnitude. We measured (i) tissue fractions within petioles and their second moment of area, (ii) theoretical xylem hydraulic efficiency of petioles and (iii) the extent of leaf vessel widening within the hydraulic path. We found that different scaling of morphological trait variability allows for optimisation of lamina display among larger leaves, especially the positive allometric relationship between lamina area and petiole cross-sectional area. Increasing the fraction of pith is a key factor that increases the geometrical effect of supportive tissues on mechanical rigidity and thereby increases carbon-use efficiency. We found that increasing xylem hydraulic efficiency with vessel size results in lower leaf lamina area: xylem ratios, which also results in potential carbon savings for large leaves. We found that the vessel widening is consistent with hydraulic optimisation models. Leaf size variability modifies scaling of leaf traits in this large-leaved species. © The Author(s) 2020. Published by Oxford University Press. All rights reserved. For permissions, please email: journals.permission@oup.com.
Keywords: allometry; leaf size; petiole anatomy; scaling; theoretical hydraulic conductivity; vessel widening; xylem
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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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Djenontin Tindo, S., Amusant, N., Dangou, J., Wotto, D. V., Avlessi, F., Dahouénon-Ahoussi, E., et al. (2012). Screening of Repellent, Termiticidal and Preventive activities on Wood, of Azadirachta indica and Carapa procera (Meliaceae) seeds oils. ISCA J. Biological Sci., 1(3), 25–29.
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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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De Weirdt, M., Verbeeck, H., Maignan, F., Peylin, P., Poulter, B., Bonal, D., et al. (2012). Seasonal leaf dynamics for tropical evergreen forests in a process-based global ecosystem model. Geoscientific Model Dev., 5(5), 1091–1108.
Abstract: The influence of seasonal phenology on canopy photosynthesis in tropical evergreen forests remains poorly understood, and its representation in global ecosystem models is highly simplified, typically with no seasonal variation of canopy leaf properties taken into account. Including seasonal variation in leaf age and photosynthetic capacity could improve the correspondence of global vegetation model outputs with the wet-dry season CO2 patterns measured at flux tower sites in these forests. We introduced a leaf litterfall dynamics scheme in the global terrestrial ecosystem model ORCHIDEE based on seasonal variations in net primary production (NPP), resulting in higher leaf turnover in periods of high productivity. The modifications in the leaf litterfall scheme induce seasonal variation in leaf age distribution and photosynthetic capacity. We evaluated the results of the modification against seasonal patterns of three long-term in-situ leaf litterfall datasets of evergreen tropical forests in Panama, French Guiana and Brazil. In addition, we evaluated the impact of the model improvements on simulated latent heat (LE) and gross primary productivity (GPP) fluxes for the flux tower sites Guyaflux (French Guiana) and TapajÃ3s (km 67, Brazil). The results show that the introduced seasonal leaf litterfall corresponds well with field inventory leaf litter data and times with its seasonality. Although the simulated litterfall improved substantially by the model modifications, the impact on the modelled fluxes remained limited. The seasonal pattern of GPP improved clearly for the Guyaflux site, but no significant improvement was obtained for the TapajÃ3s site. The seasonal pattern of the modelled latent heat fluxes was hardly changed and remained consistent with the observed fluxes. We conclude that we introduced a realistic and generic litterfall dynamics scheme, but that other processes need to be improved in the model to achieve better simulations of GPP seasonal patterns for tropical evergreen forests. © Author(s) 2012. CC Attribution 3.0 License.
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Verbeeck, H., Peylin, P., Bacour, C., Bonal, D., Steppe, K., & Ciais, P. (2011). Seasonal patterns of CO2 fluxes in Amazon forests: Fusion of eddy covariance data and the ORCHIDEE model. J. Geophys. Res.-Biogeosci., 116(2), G02018.
Abstract: [1] In some regions of the Amazon, global biogeophysical models have difficulties in reproducing measured seasonal patterns of net ecosystem exchange (NEE) of carbon dioxide. The global process-based biosphere model Organizing Carbon and Hydrology in Dynamic Ecosystems (ORCHIDEE) used in this study showed that a standard model parameterization produces seasonal NEE patterns that are opposite in phase to the eddy flux data of the tropical evergreen forest at the Tapajos km 67 site (Brazil), like many other global models. However, we optimized several key parameters of ORCHIDEE using eddy covariance data of the Tapajos km 67 site in order to identify the driving factors of the seasonal variations in CO2 flux in this tropical forest ecosystem. The validity of the retrieved parameter values was evaluated for two other flux tower sites in the Amazon. The different tested optimization scenarios showed that only a few parameters substantially improve the fit to NEE and latent heat data. Our results confirm that these forests have the ability to maintain high transpiration and photosynthesis during the dry season in association with a large soil depth (D-soil = 10 m) and a rooting system density that decreases almost linearly with depth (H-root = 0.1). Previous analyses of seasonal variations in eddy covariance fluxes indicated that higher GPP levels were reached in the dry season compared to the wet season. Our optimization analysis suggests that this pattern could be caused by a leaf flush at the start of the dry season increasing the photosynthetic capacity of the canopy. Nevertheless, the current model structure is not yet able to simulate such a leaf flush, and we therefore suggest improving the ORCHIDEE model by including a specific phenology module that is driven by light availability for the tropical evergreen plant functional types. In addition, our results highlight both the potential and the limitations of flux data to improve global terrestrial models. Several parameters were not identifiable, and the risk of overfitting of the model was illustrated. Nevertheless, we conclude that these models can be improved substantially by assimilating site level flux data over the tropics.
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Stahl, C., Burban, B., Bompy, F., Jolin, Z. B., Sermage, J., & Bonal, D. (2010). Seasonal variation in atmospheric relative humidity contributes to explaining seasonal variation in trunk circumference of tropical rain-forest trees in French Guiana. J. Trop. Ecol., 26, 393–405.
Abstract: Large seasonal variation in the rate of change in girth of tropical rain-forest tree species has been described, but its origin is still under debate. We tested whether this variation might be related to variation in atmospheric relative humidity through its influence on bark water content and thickness. Variation in trunk circumference of 182 adult trees was measured about twice a month in an undisturbed tropical rain forest over 18 mo using dendrometers. Furthermore, a laboratory experiment was conducted to test the direct influence of relative air humidity on bark water content and thickness. in the field, most trees displayed highly positive rates of change in girth at the onset of the wet season, while a quarter of the trees displayed negative changes during long dry seasons, whatever their total annual growth. This variation was correlated with environmental conditions, particularly with atmospheric relative humidity. Trees with high bark water content and thickness displayed a stronger decrease in girth during the dry season. in the chamber experiment, desiccation induced a decrease in the diameter of the trunk sections in tandem with a decrease in bark water content. As a result, seasonal variation in the rate of change in girth of tropical rain-forest trees reflects variation in trunk biophysical properties, through the influence of relative humidity on bark properties. but not directly variation in secondary growth.
Keywords: bark; drought; secondary growth; seasonality; tropical rain forest; water
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Lormée, H., Berzins, R., Rocheteau, V., De Coster, F., Denis, T., & Richard-Hanssen, C. (2021). Seasonal Variation in the Home Ranges of Black Curassow, Crax alector, in French Guiana. Tropical Conservation Science, 14(1), 1–10.
Abstract: Cracidae is the most threatened avian family in the Neotropics, mainly because of habitat destruction, heavy hunting pressure and poaching. In French Guiana, Black Curassows are heavily hunted, although basic knowledge of the ecological and demographical traits of the species remains limited. Such a gap prevents any attempt to assess the impact of hunting and to help stakeholders to develop proposals ensuring hunting sustainability. The spatial relationship between animals and their habitat is important for conservation management, being related to population densities through complex patterns. Here, we report on a radio-tracking study of Black Curassows in tropical primary rainforest, in Nouragues National Reserve, French Guiana. The aims of the study were to estimate home range size and its variation across seasons, and to quantify movement patterns of the birds. We captured and fitted VHF tags to four adults, and tracked them for 10 to 21.5 months. Daily movements were recorded, and home ranges estimated using the Kernel Density method, for two consecutive wet seasons and one dry season. Using 95% and 50% Kernel densities, the average annual home range and core area were 96.3± 32.6 ha (SE) and 22.8 ± 2.8 ha respectively. Home ranges appeared spatially stable over the two years, and overlapped between neighbouring groups. During the dry season, Black Curassows did not migrate but tended to enlarge their home range, with greater daily movements and higher home range overlap. Although additional data are still needed, our results can help to improve the knowledge and management of this poorly studied species
Keywords: spatial ecology, Cracids, tracking, Kernel method, Home range, movement pattern
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Morel, H., Mangenet, T., Beauchene, J., Ruelle, J., Nicolini, E., Heuret, P., et al. (2015). Seasonal variations in phenological traits: leaf shedding and cambial activity in Parkia nitida Miq. and Parkia velutina Benoist (Fabaceae) in tropical rainforest. Trees – Structure and Function, 29(4), 973–984.
Abstract: Key message: In French Guiana, the leaf and cambium phenologies should not be considered only as exogenous-driven processes, as the dry season, but also as endogenous-driven, as tree development stage. Abstract: Studies of the periodicity of wood formation provide essential data on tree age and on factors that control tree growth. The aim of this work was to investigate cambial phenology and its relation with leaf phenology and climatic seasonality in two briefly deciduous tropical rainforest species belonging to the genus Parkia. Wood microcores were collected every 15 days from April 2009 to February 2012 from five trees of each species. The microcores were stained with cresyl violet acetate to facilitate counting the number of cells in the cambial zone, in the radial enlargement zone and wall-thickening zone. At the same time, we observed leaf shedding pattern in the crown of the same trees. In both species, cambial activity was significantly reduced during the leafless period. In P. nitida, these two concomitant events were observed during the dry season whereas in P. velutina they can occur anytime in the year with no apparent link with seasonality. In conclusion, the period of reduced cambial activity in some tropical rainforest trees may be independent of rainfall seasonality and not necessarily follow an annual cycle. It appears that leaf phenology is a good proxy to estimate cambial activity. © 2015, Springer-Verlag Berlin Heidelberg.
Keywords: Cambial activity; Climate; French Guiana; Leaf shedding pattern; Tropical rainforest
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