Résumé
In agroforestry systems (AFS), quantifying the competition for light is a prerequisite toward understanding the impact of shade trees on the productivity of the under-crop. Models for homogeneous canopies and shade/full-sun approaches do not address the intra-plot heterogeneity, typical of AFS. For the first time, MAESTRA, a 3D light absorption model, was fully parameterized in a heterogeneous 2-canopy layers AFS. We quantified competition for photosynthetic photon flux density (Q) between shade trees (Erythrine poepiggiana) and coffee (Coffea arabica), with a spatial resolution from the plant to the plot (2.7 ha) and a temporal resolution from half-hour to one full year. The predicted transmittance through the 2-canopy layers was verified against field measurements. The goodness of fit (R-2 > 0.75, RRMSE < 26%) was comparable to the predictions from 10 other studies using 3D light models and mostly verified in one-layered systems (mean R-2 = 0.89 and mean RRMSE = 17%). Maps of absorbed Q showed that despite their low density in the plot (5.2 trees ha(-1)), the tall Erythrina trees reduced Q available for the coffee layer by 14% annually. Annual pruning of the oldest unproductive coffee resprouts maintained a large horizontal heterogeneity in coffee LAI, with direct impact on the Q absorption map. This management practice had a strong impact on seasonal variations of absorbed Q by the coffee canopy. We proposed also a simple approach to estimate Q absorbed yearly by the coffee plants in AFS of variable tree density, requiring only few measurements in the field. An extrapolation indicated that the amount of Q absorbed by the coffee canopy would display a negative exponential relationship (k = -0.34) when increasing shade tree density (from nil to 29 trees ha(-1)). The estimated k was similar to the shade tree extinction coefficient of diffuse radiation measured with a plant canopy analyzer. We showed that the presence of shade trees tends to reverse the diurnal time course of the fraction of Q(a) when compared to a plantation in the open. Overall, MAESTRA proved to successfully unlock the question of intra-plot heterogeneity for light absorption and to provide defensible light budgets as a continuous and mapped covariable, a crucial step for many field experimentations. (C) 2013 Elsevier B.V. All rights reserved.
Auteurs, date et publication :
Auteurs Fabien Charbonnier , Guerric le Maire , Erwin Dreyer , Fernando Casanoves , Mathias Christina , Jean Dauzat , Jan U. H. Eitel , Philippe Vaast , Lee A. Vierling , Olivier Roupsard
Publication : Agricultural and Forest Meteorology
Date : 2013
Volume : 181
Pages : 152-169
Catégorie(s)
#CIRAD #FORET CoffeeFluxRésumé
Synthetic aperture radar Tomography (TomoSAR) provides scene reflectivity estimation of vegetation along elevation coordinates. However, the more multi-baselines acquisition, the longer the time span of acquisition, which will result in serious temporal decorrelation in forested area. In this way, we expect to use as smaller number of baselines as possible to obtain high estimation accuracy in elevation direction. We thus investigate the performance of Polarimetric SAR tomography (Pol-TomoSAR) with small number of baselines in forested areas. The results show that compressive sensingbased Pol-TomoSAR has higher estimation accuracy in elevation direction than conventional Pol-TomoSAR with small number of baselines.
Auteurs, date et publication :
Auteurs Lei Liang , Chenghu Zhou , Xinwu Li , Xizhang Gao , Wenjin Wu
Publication : Chinese Journal of Electronics
Date : 2019
Volume : 28
Issue : 5
Pages : 1073-1079
Catégorie(s)
#CIRAD #FORET ParacouRésumé
The potential of interferometric synthetic aperture radar (InSAR) heights from TanDEM-X for vegetation canopy height and aboveground biomass (AGB) estimation has long been recognized. Penetration of X-band into the canopy affects these estimations. Thus, the canopy height and AGB retrieval from InSAR are typically biased and cannot be compared directly to estimates from other data sources. The objective of this letter was to apply a penetration depth model to compensate for height biases in TanDEM-X InSAR heights. The resulting canopy height estimates are subsequently converted to AGB estimates using regression models. The uncorrected InSAR heights of the forest canopy are biased due to the penetration of the signal into the canopy and differ substantially to light detection and ranging (LiDAR) canopy height estimates. The application of the penetration depth compensation results in unbiased forest canopy height estimates and AGB regression models that are comparable between InSAR and LiDAR. These results indicate that TanDEM-X InSAR and LiDAR technologies can be used to estimate AGB in complex tropical forests suggesting a synergistic use of these fundamentally different observation concepts.
Auteurs, date et publication :
Auteurs M. Schlund , S. Erasmi , K. Scipal
Publication : IEEE Geoscience and Remote Sensing Letters
Date : 2020
Volume : 17
Issue : 3
Pages : 367-371
Catégorie(s)
#CIRAD #FORET ParacouAuteurs, date et publication :
Auteurs Isabelle Pierrejean , Theophile Mehinto , Jacques Beauchene
Publication : Pro Ligno
Date : 2025
Volume : 13
Issue : 1
Pages : 3–17
Catégorie(s)
#CIRAD #FORET ParacouAuteurs, date et publication :
Auteurs A. Hamadi , L. Villard , P. Borderies , C. Albinet , T. Koleck , T. Le Toan
Publication : IEEE Geoscience and Remote Sensing Letters
Date : 2017
Volume : 14
Issue : 11
Pages : 1918–1922
Catégorie(s)
#CIRAD #FORET ParacouRésumé
The article “Conceptualization, modeling and environmental impact assessment of a natural rubber techno-ecological system with nutrient, water and energy integration” by Martinez-Hernandez E and Hernandez JE (2018, 185: 707–722) is based on a compilation of published information processed through a model linking natural rubber making to latex yield in rubber tree fields. Its main conclusion is that recycling processing wastewater could increase the yield by 62%. However, the statement that nitrogen input can significantly increase latex yield is based on a wrong quotation of the only cited reference. Moreover, the outputs of the model were not validated by actual data. The published literature actually shows that possible increase of latex yield by fertilization or irrigation would be much lower than 62%, and this invalidates the model. Its conclusions can then not be considered scientifically established.
Auteurs, date et publication :
Auteurs Philippe Thaler
Publication : Journal of Cleaner Production
Date : 2019
Volume : 210
Pages : 1063-1064
Catégorie(s)
#CIRAD #FORET RubberfluxRésumé
The objective of this study is to assess and compare different above-ground biomass (AGB) estimation models for tropical forest using P-band SAR tomography. In this paper, we investigate (1) comparative performance of back-projection and Capon beamforming tomographic estimators to analyze the vertical structure of tropical forest 2) impact of terrain slope correction on tomogram reflectivity and AGB estimates 3) correlation of tomogram reflectivity at 30m to forest AGB using different models 4) possibility of using tomographic retrieved height to improve the AGB estimation. The performance of these models is evaluated using dataset acquired during TropiSAR 2009 by ONERA over the Paracou site.
Auteurs, date et publication :
Auteurs N. Ramachandran , S. Tebaldini , M. M. d'Alessandro , S. Saatchi , O. Dikshit
Date : 2019
Pages : 1-5
Catégorie(s)
#CIRAD #FORET ParacouRésumé
Two-level data sets consist of higher level (say population) traits computed from lower level (say individual) observations. Cluster analysis for two-level data sets aims at classifying populations using individual observations. Most existing techniques to classify populations in two-level data sets actually operate on population traits (e.g. the k-means algorithm), thus disregarding the within-population individual variability. In this study, the k-means algorithm was compared with a recently developed classification method that accounts for within-population variability. Populations were tree species in a tropical rain forest in French Guiana, and individual observations were tree diameters and diameter growth rates. Tree species were classified according to either their diameter and growth rate, or to their asymptotic diameter distribution as predicted by an Usher matrix population model. In both cases, the k-means algorithm and the two-level classification method defined species clusters that were significantly related according to the Rand index. Nevertheless, clusters showed increasing differences between the two methods as the within-population individual variability increased. Whereas the k-means algorithm produced equally-sized spherical clusters, the two-level classification method adapted the size and shape of clusters to the individual within-population variability. Taking account of individual variability to classify populations in ecology may thus be important, albeit rarely done.
Auteurs, date et publication :
Auteurs Nicolas Picard , Avner Bar-Hen
Publication : Ecological Informatics
Date : 2013
Volume : 15
Pages : 1–7
Catégorie(s)
#CIRAD #FORET ParacouRésumé
Selection for drought-tolerant clones has become a major challenge in rubber breeding programs undertaken to ensure the sustainability of natural rubber production, as rubber plantations are expanding in drought-prone areas. Xylem vulnerability to cavitation is a trait related to drought-induced mortality. It can be rapidly evaluated without subjecting plant materials to drought stress, making it useful in large-scale screening for drought tolerance in the near future. We first compared the most widely used techniques for measuring vulnerability to cavitation (air pressurization and Cavitron) on this species, and the effect of sample conditions (size, age and sunlight exposure), in order to ensure reliable analysis. Secondly, ten rubber clones were compared for their xylem vulnerability to cavitation in branches and petioles, and for other traits related to drought response, including stomatal response and leaf shedding occurring during a simulated drought. We also tested the plasticity of vulnerability to cavitation on two clones grown in three locations with contrasting precipitation regimes. We found no clonal variability and a small phenotypic plasticity for xylem vulnerability to cavitation in branches. However, clonal differences in xylem vulnerability to cavitation were found in petioles, and clones also showed differences in stomatal response and in leaf shedding behavior in response to a simulated drought. Our study suggests a genetic canalization for vulnerability to cavitation in organs critical for survival, such as branches, whereas there are clonal differences for traits related to drought avoidance: vulnerability to cavitation of petioles, leaf shedding behavior and stomatal response. The insights gained in this study for screening rubber tree clones for drought tolerance is also discussed.
Auteurs, date et publication :
Auteurs Wanploy Jinagool , Ratchanee Rattanawong , Krissada Sangsing , Têtè Sévérien Barigah , Frederic Gay , Hervé Cochard , Poonpipope Kasemsap , Stéphane Herbette
Publication : The Journal of Plant Hydraulics
Date : 2025
Volume : 2
Pages : 14
Catégorie(s)
#CIRAD #FORET RubberfluxRésumé
textlessptextgreaterThe seasonal climate drivers of the carbon cycle in tropical forests remain poorly known, although these forests account for more carbon assimilation and storage than any other terrestrial ecosystem. Based on a unique combination of seasonal pan-tropical data sets from 89 experimental sites (68 include aboveground wood productivity measurements and 35 litter productivity measurements), their associated canopy photosynthetic capacity (enhanced vegetation index, EVI) and climate, we ask how carbon assimilation and aboveground allocation are related to climate seasonality in tropical forests and how they interact in the seasonal carbon cycle. We found that canopy photosynthetic capacity seasonality responds positively to precipitation when rainfall is textless 2000 mm yrtextlesssuptextgreater−1textless/suptextgreater (water-limited forests) and to radiation otherwise (light-limited forests). On the other hand, independent of climate limitations, wood productivity and litterfall are driven by seasonal variation in precipitation and evapotranspiration, respectively. Consequently, light-limited forests present an asynchronism between canopy photosynthetic capacity and wood productivity. First-order control by precipitation likely indicates a decrease in tropical forest productivity in a drier climate in water-limited forest, and in current light-limited forest with future rainfall textless 2000 mm yrtextlesssuptextgreater−1textless/suptextgreater.textless/ptextgreater
Auteurs, date et publication :
Auteurs Fabien H. Wagner , Bruno Hérault , Damien Bonal , Clément Stahl , Liana O. Anderson , Timothy R. Baker , Gabriel Sebastian Becker , Hans Beeckman , Danilo Boanerges Souza , Paulo Cesar Botosso , David M. J. S. Bowman , Achim Bräuning , Benjamin Brede , Foster Irving Brown , Jesus Julio Camarero , Plínio Barbosa Camargo , Fernanda C. G. Cardoso , Fabrício Alvim Carvalho , Wendeson Castro , Rubens Koloski Chagas
Publication : Biogeosciences
Date : 2016
Volume : 13
Issue : 8
Pages : 2537–2562