Résumé
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
Catégorie(s)
#ANR-Citation #CIRAD #CNRS #FORET NouraguesRésumé
1.”What controls the distribution and abundance of organisms”? This question, at the heart of the dynamics of ecological communities, would have been familiar to the earliest ecologists. Having lain effectively abandoned for many years, community dynamics today is a vibrant research topic of great conceptual interest with practical import for conservation, ecological management, ecosystem services and the responses of ecological communities to climate change. 2.We describe how modern coexistence theory can be applied to predict community dynamics through the use of demography. We explore the challenges that limit the deployment of this demographic framework, and the tools from phylogenetic and functional ecology that have been used to surmount them. 3.Finding existing tools not altogether sufficient, we propose the use of ‘hard' functional traits and physiological tolerances of environmental conditions and low resource availability to extend the demographic framework so that the dynamics of a broader range of ecological communities can be accurately predicted. 4.We illustrate these new approaches with two case studies. Given the urgent need to accurately forecast the dynamics of ecological communities, we hope that many ecologists will adopt these tools.
Auteurs, date et publication :
Auteurs C. E. Timothy Paine , Anna Deasey , A. Bradley Duthie
Publication : Functional Ecology
Date : 2018
Catégorie(s)
#CIRAD #FORET ParacouRésumé
© 2018, INRA and Springer-Verlag France SAS, part of Springer Nature. Key message: The natural durability ofDicorynia guianensis Amsh's Heartwood is conferred by the high content of antioxidant phenolic compounds, especially tannins and flavonoids combined with the presence of fungistatic alkaloids. The content of phenolic compounds increases according to the natural durability classes, from durable wood (class 2) to moderately durable wood (class 3) and correlated to the antioxidant capacity. Context: The heartwood of Dicorynia guianensis Amsh is resistant to white rot fungi decay, but the mechanism of this natural durability is not fully elucidated. Aims: Biochemical studies were carried out in order to better understand the role of extractives in natural durability of D. guianensis. Methods: The powders from durable and moderately durable heartwood were extracted with methanol, ethanol, and hot water. The quantity of total phenols, tannins, and flavonoids as well as antioxidant activity, evaluated by 2,2′-azino-bis-(3-ethylbenzothiazoline-6-sulfonic acid) were determined using colorimetric methods. Antifungal activity was assessed by using two white rot fungi. The bioactive fractions and compounds were obtained using bio-guided fractionation, HPLC isolation, MS and RMN spectroscopic analyses. Results: Durable woods contain higher amounts of heartwood extract and antioxidant activity. Antioxidant activity was highly correlated with the content of phenolics. The purification of the most antioxidant fraction FII affords the characterization of (+)-catechin (−)-epicatechin, neoastilbin, astilbin, and isoastilbin. Alkaloid fraction FIII exhibits dose-dependent fungistatic activity against Pycnoporus sanguineus Linnaeus and Trametes versicolor Quelet. Conclusion: Phenolic antioxidants and fungistatic alkaloids positively impact the natural durability of D. guianensis.
Auteurs, date et publication :
Auteurs Jean Baptiste Say Anouhe , Florence Bobelé Niamké , Milcard Faustin , David Virieux , Jean Luc Pirat , Augustin Amissa Adima , Seraphin Kati-Coulibaly , Nadine Amusant
Publication : Annals of Forest Science
Date : 2018
Volume : 75
Issue : 1
Pages : 15