Résumé
Wood density (WD) is a central trait driving life-history variations among tree species. Density, however, is a property of wood that depends, in angiosperms, on three cell types, namely vessels, fibers and parenchyma. These wood cells are mainly involved in water transport, mechanical support and storage, respectively. Therefore, wood anatomical traits may provide a more mechanistic understanding of life-history variations than WD. Yet, studies formally comparing wood anatomical traits among ecological guilds or life stages of tropical trees have been scarce. This study examined the variation of wood functional traits between ecological guilds (i.e., light-demanding and shade-tolerant species) and life stages (i.e., sapling and adult wood), as well as the possible trade-offs between wood traits. Nineteen tree species with contrasting shade-tolerance were selected in a lowland tropical forest from eastern Amazonia. WD, fiber wall thickness, vessel lumen area, as well as fractions of fibers, vessels and parenchyma cells (i.e., axial, radial and total) were measured in sapling (up to 2.5 cm from the pith) and adult wood (> 5 cm to the bark). Overall, light-demanding and shade-tolerant species had different wood traits at the sapling, but not at the adult stage. Shifts in wood anatomical traits from sapling to adult wood were more common in light-demanding species than in shade-tolerants. Furthermore, at the sapling stage, wood allocation reflects a trade-off between growth and defense, with light-demanding species having traits that favor growth (i.e., low WD and fiber wall thickness, and wider conduits), while shade-tolerants had traits that maximize defense (i.e., high WD, fiber wall thickness, and parenchyma fractions). These findings represent valuable insights into wood allocation patterns among ecological guilds and life stages, and therefore, may expand our knowledge of trees life-history strategies.
Auteurs, date et publication :
Auteurs Andrés González-Melo
Publication : Trees
Date : 2025
Volume : 36
Issue : 4
Pages : 1337–1347
Catégorie(s)
#CIRAD #FORET ParacouRésumé
Increasing or decreasing wood density (WD) from pith to bark is commonly observed in tropical tree species. The different types of WD radial variations, long been considered to depict the diversity of growth and mechanical strategies among forest guilds (heliophilic vs. shade-tolerant), were never analyzed in the light of heartwood (HW) formation. Yet, the additional mass of chemical extractives associated to HW formation increases WD and might affect both WD radial gradient (i.e., the slope of the relation between WD and radial distance) and pattern (i.e., linear or nonlinear variation). We studied 16 legumes species from French Guiana representing a wide diversity of growth strategies and positions on the shade-tolerance continuum. Using WD measurements and available HW extractives content values, we computed WD corrected by the extractive content and analyzed the effect of HW on WD radial gradients and patterns. We also related WD variations to demographic variables, such as sapling growth and mortality rates. Regardless of the position along the shade-tolerance continuum, correcting WD gradients reveals only increasing gradients. We determined three types of corrected WD patterns: (1) the upward curvilinear pattern is a specific feature of heliophilic species, whereas (2) the linear and (3) the downward curvilinear patterns are observed in both mid- and late-successional species. In addition, we found that saplings growth and mortality rates are better correlated with the corrected WD at stem center than with the uncorrected value: taking into account the effect of HW extractives on WD radial variations provides unbiased interpretation of biomass accumulation and tree mechanical strategies. Rather than a specific feature of heliophilic species, the increasing WD gradient is a shared strategy regardless of the shade tolerance habit. Finally, our study stresses to consider the occurrence of HW when using WD.
Auteurs, date et publication :
Auteurs Romain Lehnebach , Julie Bossu , Stéphanie Va , Hélène Morel , Nadine Amusant , Eric Nicolini , Jacques Beauchêne
Publication : Forests
Date : 2019
Volume : 10
Issue : 2
Pages : 80
Catégorie(s)
#CIRAD #FORET ParacouAuteurs, date et publication :
Auteurs Malia Chevolot , Eliane Louisanna , Wassim Azri , Nathalie Leblanc-Fournier , Patricia Roeckel-Drevet , Caroline Scotti-Saintagne , Ivan Scotti
Publication : Tree Genetics & Genomes
Date : 2011
Volume : 7
Issue : 3
Pages : 655–661
Catégorie(s)
#CIRAD #FORET ParacouRésumé
Classifiers trained on airborne hyperspectral imagery are proficient in identifying tree species in hyperdiverse tropical rainforests. However, spectral fluctuations, influenced by intrinsic and environmental factors, such as the heterogeneity of individual crown properties and atmospheric conditions, pose challenges for large-scale mapping. This study proposes an approach to assess the instability of airborne imaging spectroscopy reflectance in response to environmental variability. Through repeated overflights of two tropical forest sites in French Guiana, we explore factors that affect the spectral similarity between dates and acquisitions. By decomposing acquisitions into subsets and analyzing different sources of variability, we analyze the stability of reflectance and various vegetation indices with respect to specific sources of variability. Factors such as the variability of the viewing and sun angles or the variability of the atmospheric state shed light on the impact of sources of spectral instability, informing processing strategies. Our experiments conclude that the environmental factors that affect the canopy reflectance the most vary according to the considered spectral domain. In the short wave infrared (SWIR) domain, solar angle variation is the main source of variability, followed by atmospheric and viewing angles. In the visible and near infrared (VNIR) domain, atmospheric variability dominates, followed by solar angle and viewing angle variabilities. Despite efforts to address these variabilities, significant spectral instability persists, highlighting the need for more robust representations and improved correction methods for reliable species-specific signatures.
Auteurs, date et publication :
Auteurs Colin Prieur , Antony Laybros , Giovanni Frati , Daniel Schläpfer , Jocelyn Chanussot , Grégoire Vincent
Publication : IEEE Journal of Selected Topics in Applied Earth Observations and Remote Sensing
Date : 2025
Volume : 17
Pages : 18751-18768
Catégorie(s)
#CIRAD #CNRS #FORET Nouragues #FORET ParacouAuteurs, date et publication :
Auteurs M. Tella , E. Doelsch , P. Letourmy , S. Chataing , F. Cuoq , M. N. Bravin , H. Saint Macary
Publication : Waste Management
Date : 2025
Volume : 33
Issue : 1
Pages : 184-92
Catégorie(s)
#CIRAD #INRAE #PRO #PRO QualiAgroAuteurs, date et publication :
Auteurs M. Voigtlaender , J. P. Laclau , J. L. M. Gonçalves , M. C. Piccolo , M. Z. Moreira , Y. Nouvellon , J. Ranger , J. P. Bouillet
Publication : Plant and Soil
Date : 2025
Volume : 352
Pages : 99-111
Catégorie(s)
#CIRAD #FORET Itatinga #INRAERésumé
1. Understanding species differences in plant functional traits has been critical in developing a mechanistic understanding of terrestrial ecological processes. Greater attention is now being placed on understanding the extent, causes and consequences of intraspecific trait variation (ITV).
Auteurs, date et publication :
Auteurs Adam R. Martin , Bruno Rapidel , Olivier Roupsard , Karel Van den Meersche , Elias de Melo Virginio Filho , Mirna Barrios , Marney E. Isaac , Kasey Barton
Publication : Functional Ecology
Date : 2025
Volume : 31
Issue : 3
Pages : 604-612
Catégorie(s)
#CIRAD #FORET CoffeeFluxRésumé
Hypotheses on the existence of a universal “Root Economics Spectrum” (RES) have received arguably the least attention of all trait spectra, despite the key role root trait variation plays in resource acquisition potential. There is growing interest in quantifying intraspecific trait variation (ITV) in plants, but there are few studies evaluating (i) the existence of an intraspecific RES within a plant species, or (ii) how a RES may be coordinated with other trait spectra within species, such as a leaf economics spectrum (LES). Using Coffea arabica (Rubiaceae) as a model species, we measured seven morphological and chemical traits of intact lateral roots, which were paired with information on four key LES traits. Field collections were completed across four nested levels of biological organization. The intraspecific trait coefficient of variation (cv) ranged from 25 to 87% with root diameter and specific root tip density showing the lowest and highest cv, respectively. Between 27 and 68% of root ITV was explained by site identity alone for five of the seven traits measured. A single principal component explained 56.2% of root trait covariation, with plants falling along a RES from resource acquiring to conserving traits. Multiple factor analysis revealed significant orthogonal relationships between root and leaf spectra. RES traits were strongly orthogonal with respect to LES traits, suggesting these traits vary independently from one another in response to environmental cues. This study provides among the first evidence that plants from the same species differentiate from one another along an intraspecific RES. We find that in one of the world’s most widely cultivated crops, an intraspecific RES is orthogonal to an intraspecific LES, indicating that above and belowground responses of plants to managed (or natural) environmental gradients are likely to occur independently from one another.
Auteurs, date et publication :
Auteurs Marney E. Isaac , Adam R. Martin , Elias de Melo Virginio Filho , Bruno Rapidel , Olivier Roupsard , Karel Van den Meersche
Publication : Frontiers in Plant Science
Date : 2017
Volume : 8
Catégorie(s)
#CIRAD #FORET CoffeeFluxRésumé
Warmer and drier climates over Amazonia have been predicted for the next century with expected changes in regional water and carbon cycles. We examined the impact of interannual and seasonal variations in climate conditions on ecosystem-level evapotranspiration (ET) and water use efficiency (WUE) to determine key climatic drivers and anticipate the response of these ecosystems to climate change. We used daily climate and eddyflux data recorded at the Guyaflux site in French Guiana from 2004 to 2014. ET and WUE exhibited weak interannual variability. The main climatic driver of ET and WUE was global radiation (Rg), but relative extractable water (REW) and soil temperature (Ts) did also contribute. At the seasonal scale, ET and WUE showed a modal pattern driven by Rg, with maximum values for ET in July and August and for WUE at the beginning of the year. By removing radiation effects during water depleted periods, we showed that soil water stress strongly reduced ET. In contrast, drought conditions enhanced radiation-normalized WUE in almost all the years, suggesting that the lack of soil water had a more severe effect on ecosystem evapotranspiration than on photosynthesis. Our results are of major concern for tropical ecosystem modeling because they suggest that under future climate conditions, tropical forest ecosystems will be able to simultaneously adjust CO2 and H2O fluxes. Yet, for tropical forests under future conditions, the direction of change in WUE at the ecosystem scale is hard to predict, since the impact of radiation on WUE is counterbalanced by adjustments to soil water limitations. Developing mechanistic models that fully integrate the processes associated with CO2 and H2O flux control should help researchers understand and simulate future functional adjustments in these ecosystems.
Auteurs, date et publication :
Auteurs Maricar Aguilos , Clément Stahl , Benoit Burban , Bruno Hérault , Elodie Courtois , Sabrina Coste , Fabien Wagner , Camille Ziegler , Kentaro Takagi , Damien Bonal
Publication : Forests
Date : 2019
Volume : 10
Issue : 1
Pages : 14
Catégorie(s)
#ANR-Citation #CIRAD #FORET ParacouRésumé
A new processing technique, i.e., ground cancellation, which removes the ground signal from a pair of interferometric synthetic aperture radar (SAR) images, is used to emphasize the response from above-ground targets. This technique is of particular interest when studying forest canopies using low-frequency signals able to reach the underlying ground, in which case the portion of the signal coming from the ground interferes with the recovery of information about the vegetation. We demonstrate that the power in ground-canceled P-band HV SAR data gives significantly higher correlations with above-ground biomass (AGB) than the interferometric images considered separately. In addition, a significant increase in the sensitivity of backscatter to AGB is observed. Ground-canceled power may then be modeled or regressed to estimate AGB; these possibilities are not discussed here as they will be the topic of forthcoming publications. The effectiveness of this technique is proven through simulations and analysis of real data gathered on tropical forests. The stability of the technique is analyzed under the digital terrain model and baseline control errors, and compensation strategies for these errors are presented.
Auteurs, date et publication :
Auteurs M. Mariotti d’Alessandro , S. Tebaldini , S. Quegan , M. J. Soja , L. M. H. Ulander , K. Scipal
Publication : IEEE Transactions on Geoscience and Remote Sensing
Date : 2020
Volume : 58
Issue : 9
Pages : 6410-6419