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Mirabel, A., Hérault, B., & Marcon, E. (2020). Diverging taxonomic and functional trajectories following disturbance in a Neotropical forest. Science of The Total Environment, 720, 137397.
Abstract: In the current global change context, it is urgent to anticipate the fate of tropical forests. This means understanding tree community response to disturbance and the underlying processes. In that respect, we aim here to clarify taxonomic and functional post-disturbance trajectories, and determine the scope of the Intermediate Disturbance Hypothesis (IDH) that remains debated in tropical forests. We analyzed community trajectories following a disturbance gradient from 10 to 60% of above-ground biomass loss in a Neotropical forest over 30 years. We considered trajectories along time of community taxonomic and functional trajectories in terms of richness, evenness, composition, and redundancy. We based on the annual botanical inventories of 75 ha of a Neotropical forest and on large trait datasets comprising seven leaf, stem, and life-history traits. We identified a decoupling between taxonomic composition, differing among communities, and functional composition, similar among communities and convergent in the functional space. The taxonomic diversity followed humped-shaped trajectories along time after disturbance depending on the initial disturbance intensity, which validated the IDH (Intermediate Disturbance Hypothesis). The functional diversity trajectories, however, were homogeneous among plots and dismissed the IDH. We explained this decoupling by the variations in community functional redundancy that mitigated the functional impact of disturbance. Although consistent, the recovery of community composition, diversity, and redundancy remained divergent from the initial state after 30 years. These results acknowledged the need of decades-long cycles without disturbance to ensure community complete recovery.
Keywords: Community ecology; Disturbance trajectories; Intermediate disturbance hypothesis; Mid-term resilience; Neotropical forests; Taxonomic and functional biodiversity
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Mirabel, A., Marcon, E., & Hérault, B. (2021). 30 Years of postdisturbance recruitment in a Neotropical forest. Ecology and Evolution, 11(21), 14448–14458.
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Molina, L., Broquet, G., Imbach, P., Chevallier, F., Poulter, B., Bonal, D., et al. (2015). On the ability of a global atmospheric inversion to constrain variations of CO2 fluxes over Amazonia. Atmospheric Chemistry and Physics, 15(14), 8423–8438.
Abstract: The exchanges of carbon, water and energy between the atmosphere and the Amazon basin have global implications for the current and future climate. Here, the global atmospheric inversion system of the Monitoring of Atmospheric Composition and Climate (MACC) service is used to study the seasonal and interannual variations of biogenic CO<inf>2</inf> fluxes in Amazonia during the period 2002-2010. The system assimilated surface measurements of atmospheric CO<inf>2</inf> mole fractions made at more than 100 sites over the globe into an atmospheric transport model. The present study adds measurements from four surface stations located in tropical South America, a region poorly covered by CO<inf>2</inf> observations. The estimates of net ecosystem exchange (NEE) optimized by the inversion are compared to an independent estimate of NEE upscaled from eddy-covariance flux measurements in Amazonia. They are also qualitatively evaluated against reports on the seasonal and interannual variations of the land sink in South America from the scientific literature. We attempt at assessing the impact on NEE of the strong droughts in 2005 and 2010 (due to severe and longer-than-usual dry seasons) and the extreme rainfall conditions registered in 2009. The spatial variations of the seasonal and interannual variability of optimized NEE are also investigated. While the inversion supports the assumption of strong spatial heterogeneity of these variations, the results reveal critical limitations of the coarse-resolution transport model, the surface observation network in South America during the recent years and the present knowledge of modelling uncertainties in South America that prevent our inversion from capturing the seasonal patterns of fluxes across Amazonia. However, some patterns from the inversion seem consistent with the anomaly of moisture conditions in 2009. © Author(s) 2015.
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Molto, Q., Herault, B., Boreux, J. - J., Daullet, M., Rousteau, A., & Rossi, V. (2014). Predicting tree heights for biomass estimates in tropical forests -A test from French Guiana. Biogeosciences, 11(12), 3121–3130.
Abstract: The recent development of REDD+ mechanisms requires reliable estimation of carbon stocks, especially in tropical forests that are particularly threatened by global changes. Even though tree height is a crucial variable for computing aboveground forest biomass (AGB), it is rarely measured in large-scale forest censuses because it requires extra effort. Therefore, tree height has to be predicted with height models. The height and diameter of all trees over 10 cm in diameter were measured in 33 half-hectare plots and 9 one-hectare plots throughout northern French Guiana, an area with substantial climate and environmental gradients. We compared four different model shapes and found that the Michaelis-Menten shape was most appropriate for the tree biomass prediction. Model parameter values were significantly different from one forest plot to another, and this leads to large errors in biomass estimates. Variables from the forest stand structure explained a sufficient part of plot-to-plot variations of the height model parameters to improve the quality of the AGB predictions. In the forest stands dominated by small trees, the trees were found to have rapid height growth for small diameters. In forest stands dominated by larger trees, the trees were found to have the greatest heights for large diameters. The aboveground biomass estimation uncertainty of the forest plots was reduced by the use of the forest structure-based height model. It demonstrated the feasibility and the importance of height modeling in tropical forests for carbon mapping. When the tree heights are not measured in an inventory, they can be predicted with a height-diameter model and incorporating forest structure descriptors may improve the predictions. © Author(s) 2014. CC Attribution 3.0 License.
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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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Mony, R., Dejean, A., Bilong, C. F. B., Kenne, M., & Rouland-Lefèvre, C. (2013). Melissotarsus ants are likely able to digest plant polysaccharides. C. R. Biol., 336(10), 500–504.
Abstract: Melissotarsus ants have an extremely specialized set of behaviours. Both workers and gynes tunnel galleries in their host tree bark. Workers walk with their mesothoracic legs pointing upwards and tend Diaspididae hemiptera for their flesh. The ants use their forelegs to plug the galleries with silk that they secrete themselves. We hypothesised that the ants' energetic needs for nearly constant gallery digging could be satisfied through the absorption of host tree tissues; so, using basic techniques, we examined the digestive capacities of workers from two species. We show that workers are able to degrade oligosaccharides and heterosides as well as, to a lesser degree, polysaccharides. This is one of the rare reports on ants able to digest plant polysaccharides other than starch. © 2013 Académie des sciences.
Keywords: Ant-plant interactions; Degradation of plant material; Enzymatic activity; Melissotarsus ants
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Moore, A. L., McCarthy, M. A., Parris, K. M., & Moore, J. L. (2014). The optimal number of surveys when detectability varies. PLoS ONE, 9(12), e115345.
Abstract: The survey of plant and animal populations is central to undertaking field ecology. However, detection is imperfect, so the absence of a species cannot be determined with certainty. Methods developed to account for imperfect detectability during surveys do not yet account for stochastic variation in detectability over time or space. When each survey entails a fixed cost that is not spent searching (e.g., time required to travel to the site), stochastic detection rates result in a trade-off between the number of surveys and the length of each survey when surveying a single site. We present a model that addresses this trade-off and use it to determine the number of surveys that: 1) maximizes the expected probability of detection over the entire survey period; and 2) is most likely to achieve a minimally-acceptable probability of detection. We illustrate the applicability of our approach using three practical examples (minimum survey effort protocols, number of frog surveys per season, and number of quadrats per site to detect a plant species) and test our model's predictions using data from experimental plant surveys. We find that when maximizing the expected probability of detection, the optimal survey design is most sensitive to the coefficient of variation in the rate of detection and the ratio of the search budget to the travel cost. When maximizing the likelihood of achieving a particular probability of detection, the optimal survey design is most sensitive to the required probability of detection, the expected number of detections if the budget were spent only on searching, and the expected number of detections that are missed due to travel costs. We find that accounting for stochasticity in detection rates is likely to be particularly important for designing surveys when detection rates are low. Our model provides a framework to do this. © 2014 Moore et al.
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Morel, H., Lehnebach, R., Cigna, J., Ruelle, J., Nicolini, É., & Beauchene, J. (2018). Basic wood density variations of Parkia velutina Benoist, a long-lived heliophilic Neotropical rainforest tree. Bois et Forets des Tropiques, 335, 59–69.
Abstract: Investigations of basic radial wood density (WD) in tropical trees revealed linear patterns and some curvilinear patterns. Studies usually disregard longitudinal variations, which are often considered to be similar to radial variations. This study aimed to show (1) a new radial curvilinear WD pattern, (2) differences in amplitude between radial and longitudinal gradients and (3) to partition WD variations according to different scales in Parkia velutina, an emergent tree found in Neotropical rain forests. We collected full discs from six felled trees and radial cores from 10 standing trees to check WD variability, plus one dominant axis per tree for analysis of height growth rates. This species showed very high growth rates indicative of heliophilic habits. WD varied from 0.194 to 0.642 g/cm3. Such amplitude is rarely observed within the same tree. Radial variation in WD was curvilinear, with an amplitude generally less than the longitudinal amplitude. Consequently, in mature trees, WD values in the crown were higher than those in the outer trunk. WD variations can be highly significant at different scales. The variance partitioning also revealed that the whole WD range of Parkia velutina is more accurately estimated intra-individually when both longitudinal and radial gradient are covered.
Keywords: Curvilinear pattern; French Guiana; Intra-tree; Tropical species
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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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Morel, H., Nicolini, E., Bossu, J., Blanc, L., & Beauchene, J. (2017). Qualité et usages du bois de cinq espèces forestières adaptées à la plantation à vocation de bois d’oeuvre et testées en Guyane française. Bois & Forêts des Tropiques, 334, 61–74.
Abstract: Des essais de plantations forestières ont été menés en Guyane française depuis le début des années 1960 sur plus de 138 espèces (70 espèces natives et 68 espèces exotiques). Une étude récente sur la productivité de ces espèces en plantation (projet ForesTreeCulture, 2013-2015) a mis en avant le fort potentieldeproductiondetroisespècesnatives ( Simarouba amara Aubl., Vochysia tomentosa (G. Mey.) DC., Bagassa guianensis ( Aubl.)) et d’une espèce d’Afrique de l’Ouest ( Tarrietia utilis Sprague) avec des volumes de bois produits supérieurs à 20 m3/ha/an. Cependant, les propriétés du bois de ces espèces commerciales ne sont connues qu’au travers d’arbres issus de forêt naturelle. Nous présentons les propriétés du bois de ces espèces en conditions de plantation – densité, retrait, élasticité, angle du fil, durabilité – et discutons de leurs potentiels et de leurs usages respectifs futurs. Une autre espèce, Cordia alliodora ((Ruiz et Pavon) Oken), a également été retenue bien qu’elle n’ait pas encore été plantée en Guyane française. Cette espèce, native de Guyane, est bien connue en Amérique latine pour son bois et son fort potentiel de croissance en milieu anthropisé.
Keywords: propriétés technologiques; qualité du bois; plantation; Guyane française
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