Auteurs, date et publication :
Auteurs Florian Schnabel , Elias de Melo Virginio Filho , Su Xu , Ian D. Fisk , Olivier Roupsard , Jeremy Haggar
Publication : Agroforestry Systems
Date : 2017
Catégorie(s)
#CIRAD #FORET CoffeeFluxRésumé
Despite advances in Earth observation and modeling, estimating tropical biomass remains a challenge. Recent work suggests that integrating satellite measurements of canopy height within ecosystem models is a promising approach to infer biomass. We tested the feasibility of this approach to retrieve aboveground biomass (AGB) at three tropical forest sites by assimilating remotely sensed canopy height derived from a texture analysis algorithm applied to the high-resolution Pleiades imager in the Organizing Carbon and Hydrology in Dynamic Ecosystems Canopy (ORCHIDEE-CAN) ecosystem model. While mean AGB could be estimated within 10% of AGB derived from census data in average across sites, canopy height derived from Pleiades product was spatially too smooth, thus unable to accurately resolve large height (and biomass) variations within the site considered. The error budget was evaluated in details, and systematic errors related to the ORCHIDEE-CAN structure contribute as a secondary source of error and could be overcome by using improved allometric equations.
Auteurs, date et publication :
Auteurs E. Joetzjer , M. Pillet , P. Ciais , N. Barbier , J. Chave , M. Schlund , F. Maignan , J. Barichivich , S. Luyssaert , B. Herault , F. von Poncet , B. Poulter
Publication : GEOPHYSICAL RESEARCH LETTERS
Date : 2017
Volume : 44
Issue : 13
Pages : 6823-6832
Catégorie(s)
#ANR-Citation #CIRAD #CNRS #FORET NouraguesRésumé
Very high spatial resolution (VHSR) optical satellite imagery has shown good potential to provide non-saturating proxies of tropical forest aboveground biomass (AGB) from the analysis of canopy texture, for instance through the Fourier Transform Textural Ordination method. Empirical case studies however showed that the relationship between Fourier texture features and forest AGB varies across forest types and regions of the world, limiting model transferability. A better understanding of the biophysical mechanisms on which canopy texture – forest AGB relation relies is a prerequisite to move toward broad scale applications. Here we simulated VHSR optical canopy scenes in identical sun-sensor geometry for 279 1-ha tropical forest inventory plots distributed across the tropics. Our aim was to assess the respective merits and complementarity of two types of texture analysis techniques (i.e. Fourier and lacunarity) on a set of forests with contrasted structure and geographical origin, and develop a general texture-based approach for tropical forest AGB mapping. Across forests, Fourier texture captured a gradient of stands mean crown size reflecting well the progressive changes in stand structure throughout forest aggradation phase (e.g. Pearson's r=−0.42 with basal area) while lacunarity texture captured a gradient of canopy openness (, i.e. Pearson's r=−0.57 with stand gap fraction). Both types of texture indices were highly complementary for predicting forest AGB at the global level (so-called FL-model). The residual error of the FL-model was structured across sites and could be partially captured with a bioclimatic proxy, further improving the performance of the global model (so-called FLE-model) and reducing site-level biases. The FLE model was tested on a set of real Pleiades images covering a mosaic of high-biomass forests in the Congo basin (mean AGB over 49 field plots: 359±98Mgha−1), leading to a significant relationship (R2=0.47 on validation data) with reasonable error levels (textless25% rRMSE). The increasing availability of VHSR optical sensors (such as from constellations of small satellite platforms) raises the possibility of routine repeated imaging of the world's tropical forests and suggests that texture-based analyses could become an essential tool in international efforts to monitor carbon emissions from deforestation and forest degradations (REDD+).
Auteurs, date et publication :
Auteurs P. Ploton , N. Barbier , P. Couteron , C.M. Antin , N. Ayyappan , N. Balachandran , N. Barathan , J.-F. Bastin , G. Chuyong , G. Dauby , V. Droissart , J.-P. Gastellu-Etchegorry , N.G. Kamdem , D. Kenfack , M. Libalah , G. Mofack , S.T. Momo , S. Pargal , P. Petronelli , C. Proisy
Publication : Remote Sensing of Environment
Date : 2017
Volume : 200
Pages : 140–153
Catégorie(s)
#CIRAD #FORET ParacouAuteurs, date et publication :
Auteurs Paulin Bazié , Catherine Ky-Dembele , Christophe Jourdan , Olivier Roupsard , Gérard Zombré , Jules Bayala
Publication : Agroforestry Systems
Date : 2017
Catégorie(s)
#CIRAD #FORET CoffeeFluxAuteurs, date et publication :
Auteurs Laëtitia Bréchet , Valérie Le Dantec , Stéphane Ponton , Jean-Yves Goret , Emma Sayer , Damien Bonal , Vincent Freycon , Jacques Roy , Daniel Epron
Publication : Ecosystems
Date : 2017
Volume : 20
Issue : 6
Pages : 1190–1204
Catégorie(s)
#CIRAD #FORET ParacouRésumé
© 2017 The Author(s). Heterotrophic microorganisms are commonly thought to be stoichiometrically homeostatic but their stoichiometric plasticity has rarely been examined, particularly in terrestrial ecosystems. Using a fertilization experiment in a tropical rainforest, we evaluated how variable substrate stoichiometry may influence the stoichiometry of microbial communities in the leaf litter layer and in the underlying soil. C:N:P ratios of the microbial biomass were higher in the organic litter layer than in the underlying mineral soil. Regardless of higher ratios for litter microbial communities, C, N, and P fertilization effects on microbial stoichiometry were strong in both litter and soil, without any fundamental difference in plasticity between these two communities. Overall, N:P ratios were more constrained than C:nutrient ratios for both litter and soil microbial communities, suggesting that stoichiometric plasticity arises because of a decoupling between C and nutrients. Contrary to the simplifying premise of strict homeostasis in microbial decomposers, we conclude that both litter and soil communities can adapt their C:N:P stoichiometry in response to the stoichiometric imbalance of available resources.
Auteurs, date et publication :
Auteurs Nicolas Fanin , Nathalie Fromin , Sandra Barantal , Stephan Hättenschwiler
Publication : Scientific Reports
Date : 2017
Volume : 7
Issue : 1
Pages : 12498
Catégorie(s)
#CIRAD #FORET ParacouRésumé
Investigations of basic radial wood den- sity (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 longi- tudinal 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/cm 3 . 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-indivi- dually when both longitudinal and radial gradient are covered
Auteurs, date et publication :
Auteurs Hélène Morel , Romain Lehnebach , Jérémy Cigna , Julien Ruelle , Eric Nicolini , Jacques Beauchêne
Publication : Bois et Forêts des Tropiques
Date : 2025
Volume : 335
Pages : 59–69
Catégorie(s)
#CIRAD #FORET ParacouAuteurs, date et publication :
Auteurs J. - M. Floch , E. Marcon , F. Puech , V. Loonis , M. - P. de Bellefon
Date : 2025
Pages : 71–111
Catégorie(s)
#CIRAD #FORET ParacouRésumé
Although large amounts of potassium (K) are applied in tropical crops and planted forests, little is known about the interaction between K nutrition and water supply regimes on water resources in tropical regions. This interaction is a major issue because climate change is expected to increase the length of drought periods in many tropical regions and soil water availability in deep soil layers is likely to have a major influence on tree growth during dry periods in tropical planted forests. A process-based model (MAESPA) was parameterized in a throughfall exclusion experiment in Brazil to gain insight into the combined effects of K deficiency and rainfall reduction (37% throughfall exclusion) on the water used by the trees, soil water storage and water table fluctuations over the first 4.5 years after planting Eucalyptus grandis trees. A comparison of canopy transpiration in each plot with the values predicted for the same soil with the water content maintained at field capacity, made it possible to calculate a soil-driven tree water stress index for each treatment. Compared to K-fertilized trees with undisturbed rainfall (+K+W), canopy transpiration was 40% lower for K deficiency (−K+W), 20% lower for W deficit (+K−W) and 36% lower for combined K deficiency and W deficit (−K−W) on average. Water was withdrawn in deeper soil layers for −W than for +W, particularly over dry seasons. Under contrasted K availability, water withdrawal was more superficial for −K than for +K. Mean soil water content down to 18 m below surface (mbs) was 24% higher for −K+W than for +K+W from 2 years after planting (after canopy closure), while it was 24% lower for +K−W and 12% lower for −K−W than for +K+W. The soil-driven tree water stress index was 166% higher over the first 4.5 years after planting for −W than for +W, 76% lower for −K than for +K, and 14% lower for −K−W than for +K+W. Over the study period, deep seepage was higher by 371 mm yr−1 (+122%) for −K than for +K and lower by 200 mm yr−1 (−66%) for −W than for +W. Deep seepage was lower by 44% for −K−W than for +K+W. At the end of the study period, the model predicted a higher water table for −K (10 mbs for −K+W and 16 mbs for −K−W) than for +K (16 mbs for +K+W and 18 mbs for +K−W). Our study suggests that flexible fertilization regimes could contribute to adjusting the local trade-off between wood production and demand for soil water resources in planted forests.
Auteurs, date et publication :
Auteurs M. Christina , G. le Maire , Y. Nouvellon , R. Vezy , B. Bordon , P. Battie-Laclau , J.L.M. Gonçalves , J.S. Delgado-Rojas , J.-P. Bouillet , J.-P. Laclau
Publication : Forest Ecology and Management
Date : 2025
Catégorie(s)
#CIRAD #FORET Itatinga #FORET Rubberflux #INRAEAuteurs, date et publication :
Auteurs Elodie A. Courtois , Clément Stahl , Joke Van den Berge , Laëtitia Bréchet , Leandro Van Langenhove , Andreas Richter , Ifigenia Urbina , Jennifer L. Soong , Josep Peñuelas , Ivan A. Janssens
Publication : Ecosystems
Date : 2018
Pages : 1–14