Auteurs, 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 CoffeeFluxAuteurs, date et publication :
Auteurs Julie Bossu , Romain Lehnebach , Stephane Corn , Arnaud Regazzi , Jacques Beauchêne , Bruno Clair
Publication : Trees
Date : 2018
Pages : 1–13
Catégorie(s)
#CIRAD #FORET ParacouRésumé
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
Catégorie(s)
#CIRAD #FORET ParacouRésumé
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.
Auteurs, date et publication :
Auteurs Nicolas Fanin , Stephan Hättenschwiler , Heidy Schimann , Nathalie Fromin , Joseph K. Bailey
Publication : Functional Ecology
Date : 2015
Volume : 29
Issue : 1
Pages : 140–150