Résumé
The consequences of diversity on belowground processes are still poorly known in tropical forests. The distributions of very fine roots (diameter < 1 mm) and fine roots (diameter < 3 mm) were studied in a randomized block design close to the harvest age of fast-growing plantations. A replacement series was set up in Brazil with mono-specific Eucalyptus grandis (100E) and Acacia mangium (100A) stands and a mixture with the same stocking density and 50 % of each species (50A:50E). The total fine root (FR) biomass down to a depth of 2 m was about 27 % higher in 50A:50E than in 100A and 100E. Fine root over-yielding in 50A:50E resulted from a 72 % rise in E. grandis fine root biomass per tree relative to 100E, whereas A. mangium FR biomass per tree was 17 % lower than in 100A. Mixing A. mangium with E. grandis trees led to a drop in A. mangium FR biomass in the upper 50 cm of soil relative to 100A, partially balanced by a rise in deep soil layers. Our results highlight similarities in the effects of directional resources on leaf and FR distributions in the mixture, with A. mangium leaves below the E. grandis canopy and a low density of A. mangium fine roots in the resource-rich soil layers relative to monospecific stands. The vertical segregation of resource-absorbing organs did not lead to niche complementarity expected to increase the total biomass production.
Auteurs, date et publication :
Auteurs J.-P. Laclau , Y. Nouvellon , C. Reine , J.-L. de Moraes Goncalves , A.-V. Krushe , C. Jourdan , G. le Maire , J.-P. Bouillet
Publication : Oecologia
Date : 2013
Volume : 172
Issue : 3
Pages : 903-913
Catégorie(s)
#CIRAD #FORET Itatinga #INRAEAuteurs, date et publication :
Auteurs François Maillard , Valentin Leduc , Cyrille Bach , José Leonardo de Moraes Gonçalves , Fernando Dini Androte , Laurent Saint-André , Jean-Paul Laclau , Marc Buée , Agnès Robin
Publication : Microbial ecology
Date : 2025
Pages : 1-6
Catégorie(s)
#CIRAD #FORET Itatinga #INRAERésumé
The preparation of tropical wood surface sections for time‐of‐flight secondary ion mass spectrometry imaging is described, and the use of delayed extraction of secondary ions and its interest for the analysis of vegetal surface are shown. The method has been applied to the study by time‐of‐flight secondary ion mass spectrometry imaging with a resolution of less than one micron of a tropical wood species, Dicorynia guianensis, which is one of the most exploited wood in French Guiana for its durable heartwood. The heartwood of this species exhibits an economical importance, but its production is not controlled in forestry. Results show an increase of tryptamine from the transition zone and a concomitant decrease of inorganic ions and starch fragment ions. These experiments lead to a better understanding of the heartwood formation and the origin of the natural durability of D. guianensis.
Auteurs, date et publication :
Auteurs Quentin P. Vanbellingen , Tingting Fu , Claudia Bich , Nadine Amusant , Didier Stien , Serge Della-Negra , David Touboul , Alain Brunelle
Publication : Journal of Mass Spectrometry
Date : 2016
Volume : 51
Issue : 6
Pages : 412–423
Catégorie(s)
#CIRAD #FORET ParacouRésumé
Forests play a crucial role in the global carbon (C) cycle by storing and sequestering a substantial amount of C in the terrestrial biosphere. Due to temporal dynamics in climate and vegetation activity, there are significant regional variations in carbon dioxide (CO2) fluxes between the biosphere and atmosphere in forests that are affecting the global C cycle. Current forest CO2 flux dynamics are controlled by instantaneous climate, soil, and vegetation conditions, which carry legacy effects from disturbances and extreme climate events. Our level of understanding from the legacies of these processes on net CO2 fluxes is still limited due to their complexities and their long-term effects. Here, we combined remote sensing, climate, and eddy-covariance flux data to study net ecosystem CO2 exchange (NEE) at 185 forest sites globally. Instead of commonly used non-dynamic statistical methods, we employed a type of recurrent neural network (RNN), called Long Short-Term Memory network (LSTM) that captures information from the vegetation and climate's temporal dynamics. The resulting data-driven model integrates interannual and seasonal variations of climate and vegetation by using Landsat and climate data at each site. The presented LSTM algorithm was able to effectively describe the overall seasonal variability (Nash-Sutcliffe efficiency, NSE = 0.66) and across-site (NSE = 0.42) variations in NEE, while it had less success in predicting specific seasonal and interannual anomalies (NSE = 0.07). This analysis demonstrated that an LSTM approach with embedded climate and vegetation memory effects outperformed a non-dynamic statistical model (i.e. Random Forest) for estimating NEE. Additionally, it is shown that the vegetation mean seasonal cycle embeds most of the information content to realistically explain the spatial and seasonal variations in NEE. These findings show the relevance of capturing memory effects from both climate and vegetation in quantifying spatio-temporal variations in forest NEE.
Auteurs, date et publication :
Auteurs S. Besnard , N. Carvalhais , M. A. Arain , A. Black , B. Brede , N. Buchmann , J. Q. Chen , Jgpw Clevers , L. P. Dutrieux , F. Gans , M. Herold , M. Jung , Y. Kosugi , A. Knohl , B. E. Law , E. Paul-Limoges , A. Lohila , L. Merbold , O. Roupsard , R. Valentini
Publication : Plos One
Date : 2019
Volume : 14
Issue : 2
Catégorie(s)
#CIRAD #FORET CoffeeFluxRésumé
Evapotranspiration and energy partitioning are complex to estimate because they result from the interaction of many different processes, especially in multi-species and multi-strata ecosystems. We used MAESPA model, a mechanistic, 3D model of coupled radiative transfer, photosynthesis, and balances of energy and water, to simulate the partitioning of energy and evapotranspiration in homogeneous tree plantations, as well as in heterogeneous multi-species, multi-strata agroforests with diverse spatial scales and management schemes. The MAESPA model was modified to add (1) calculation of foliage surface water evaporation at the voxel scale; (2) computation of an average within-canopy air temperature and vapour pressure; and (3) use of (1) and (2) in iterative calculations of soil and leaf temperatures to close ecosystem-level energy balances. We tested MAESPA model simulations on a simple monospecific Eucalyptus stand in Brazil, and also in two complex, heterogeneous Coffea agroforests in Costa Rica. MAESPA satisfactorily simulated the daily and seasonal dynamics of net radiation (RMSE = 29.6 and 28.4 W m−2; R2 = 0.99 and 0.99 for Eucalyptus and Coffea sites respectively) and its partitioning between latent-(RMSE = 68.1 and 37.2 W m−2; R2 = 0.87 and 0.85) and sensible-energy (RMSE = 54.6 and 45.8 W m−2; R2 = 0.57 and 0.88) over a one-year simulation at half-hourly time-step. After validation, we use the modified MAESPA to calculate partitioning of evapotranspiration and energy between plants and soil in the above-mentioned agro-ecosystems. In the Eucalyptus plantation, 95% of the outgoing energy was emitted as latent-heat, while the Coffea agroforestry system's partitioning between sensible and latent-heat fluxes was roughly equal. We conclude that MAESPA process-based model has an appropriate balance of detail, accuracy, and computational speed to be applicable to simple or complex forest ecosystems and at different scales for energy and evapotranspiration partitioning. (Résumé d'auteur)
Auteurs, date et publication :
Auteurs Rémy Vezy , Mathias Christina , Olivier Roupsard , Yann Nouvellon , Remko A. Duursma , Belinda E. Medlyn , Maxime Soma , Fabien Charbonnier , Céline Blitz-Frayret , Jose Luiz Stape , Jean-Paul Laclau , Elias de Melo Virginio Filho , Jean-Marc Bonnefond , Bruno Rapidel , Frédéric C. Do , Alain Rocheteau , Delphine Picart , Carlos Borgonovo , Denis Loustau , Guerric Le Maire
Publication : Agricultural and Forest Meteorology
Date : 2025
Volume : 253-254
Pages : 203-2017
Catégorie(s)
#CIRAD #FORET CoffeeFlux #FORET Itatinga #FORET RubberfluxRésumé
To grow straight, plants need a motor system that controls posture by generating forces to offset gravity. This motor function in trees was long thought to be only controlled by internal forces induced in wood. Here we provide evidence that bark is involved in the generation of mechanical stresses in several tree species. Saplings of nine tropical species were grown tilted and staked in a shadehouse and the change in curvature of the stem was measured after releasing from the pole and after removing the bark. This first experiment evidenced the contribution of bark in the up-righting movement of tree stems. Combined mechanical measurements of released strains on adult trees and microstructural observations in both transverse and longitudinal/tangential plane enabled us to identify the mechanism responsible for the development of asymmetric mechanical stress in the bark of stems of these species. This mechanism does not result from cell wall maturation like in wood, or from the direct action of turgor pressure like in unlignified organs, but is the consequence of the interaction between wood radial pressure and a smartly organized trellis structure in the inner bark.
Auteurs, date et publication :
Auteurs Bruno Clair , Barbara Ghislain , Jonathan Prunier , Romain Lehnebach , Jacques Beauchêne , Tancrède Alméras
Publication : New Phytologist
Date : 2025
Volume : 221
Issue : 1
Pages : 209-217
Catégorie(s)
#CIRAD #FORET ParacouRésumé
Recent studies have shown that the inner bark is implicated in the postural control of inclined tree stems through the interaction between wood radial growth and tangential expansion of a trellis f...
Auteurs, date et publication :
Auteurs Romain Lehnebach , Léopold Doumerc , Bruno Clair , Tancrède Alméras
Publication : Botany
Date : 2019
Catégorie(s)
#CIRAD #FORET ParacouAuteurs, date et publication :
Auteurs M. Christina , Le Maire G , P. Battie-Laclau , Nouvellon Y , Bouillet J-P , Jourdan C , de Moraes Gonçalves J-L-M , J.-P. Laclau
Publication : Global Change Biology
Date : 2025
Volume : 21
Pages : 2022-2039
Catégorie(s)
#CIRAD #FORET Itatinga #INRAERésumé
Local tree density may vary in young Eucalyptus plantations under the effects of environmental conditions or inadequate management, and these variations need to be mapped over large areas as they have a significant impact on the final biomass harvested. High spatial resolution optical satellite images have the potential to provide crucial information on tree density at an affordable cost for forest management. Here, we test the capacity of this promising technique to map the local density of young and small Eucalyptus trees in a large plantation in Brazil. We use three Worldview panchromatic images acquired at a 50 cm resolution on different dates corresponding to trees aged 6, 9 and 13 months and define an overall accuracy index to evaluate the quality of the detection results. The best agreement between the local densities obtained by visual detection and by marked point process modeling was found at 9 months, with only small omission and commission errors and a stable 4% underestimation of the number of trees across the density gradient. We validated the capability of the MPP approach to detect trees aged 9 months by making a comparison with local densities recorded on 112 plots of similar to 590 m(2) and ranging between 1360 and 1700 trees per hectare. We obtained a good correlation (r(2) = 0.88) with a root mean square error of 31 trees/ha. We generalized detection by computing a consistent map over the whole plantation. Our results showed that local tree density was not uniformly distributed even in a well-controlled intensively-managed Eucalyptus plantation and therefore needed to be monitored and mapped. Use of the marked point process approach is then discussed with respect to stand characteristics (canopy closure), acquisition dates and recommendations for algorithm parameterization. (c) 2012 Elsevier B.V. All rights reserved.
Auteurs, date et publication :
Auteurs J. Zhou , C. Proisy , X. Descombes , G. Le Maire , Y. Nouvellon , J.-L. Stape , G. Viennois , J. Zerubia , P. Couteron
Publication : Forest Ecology and Management
Date : 2013
Volume : 301
Pages : 129-141
Catégorie(s)
#CIRAD #FORET Itatinga #INRAERésumé
Leaf area index estimates in dense evergreen tropical moist forest almost exclusively rest on indirect methods most of which being of limited accuracy or spatial resolution. In this study we examine the potential of full waveform Aerial Laser Scanning (ALS) to derive accurate spatially explicit estimates of Plant Area Index (PAI). A discrete representation of the forest canopy is introduced in the form of a 3D voxelized space. For each voxel (elementary volume, typically one cubic m) a first estimate of local transmittance of vegetation is computed as the ratio of the sum of energy exiting a voxel to the sum of energy entering the same voxel. A spatially hierarchical model is subsequently applied to refine estimates of individual voxel transmittance. Plant area density (PAD) profiles are then computed from the local transmittance values by applying Beer Lambert's turbid medium approximation. PAI values are obtained from vertical integration of PAD profiles. The model is shown to be robust to low sampling intensity and high occlusion rates. We further compared simulated values of gap fraction obtained by ray tracing for 5 angular sectors with in situ LAI2200 measurements taken at 135 positions in a 0.5ha forest plot located in the center of the scene. The overall patterns of simulated and measured values (average value per inclination and pattern of variation along a 70m transect line) were highly consistent. A slight but systematic discrepancy was observed along the inclination gradient, gap fractions derived from ray tracing in the voxelized scene being slightly lower than the measured values. This difference might be the consequence of multiple reflections which have been found to bias gap fractions estimates produced by LAI2200. PAI estimates derived from LAI2200 measurements (either simulated 6.8 or observed 5.9) are much lower than the PAI derived from vertical integration of local PAD (13.6). This large difference reflects the fact that distribution of foliage is strongly spatially structured and that this structural information is not properly accounted for in PAI estimates derived from mean gap fraction per elevation angle. After adjusting local transmittance to match mean LAI 2200 profiles the PAI at plot level was found to be 13.2m2·m−2. We conclude that Aerial Laser Scanning can produce accurate maps of Plant Area Index over large areas with unmatched efficacy, accuracy and ease. This should be of major relevance for many forest ecological studies.
Auteurs, date et publication :
Auteurs Grégoire Vincent , Cécile Antin , Marilyne Laurans , Julien Heurtebize , Sylvie Durrieu , Claudia Lavalley , Jean Dauzat
Publication : Remote Sensing of Environment
Date : 2017
Volume : 198
Pages : 254–266