Résumé
High-density Airborne Laser Scanning was used to derive the Canopy Height Model (CHM) of an experimental forest site in the neotropics (Paracou, French Guiana). Individual tree heights were computed by manually segmenting tree crowns on the CHM and then extracting the local maximum canopy height. Three hundred and ninety-six (396) height estimates were matched from dominant or emergent trees with the corresponding ground records of stem diameters sampled in two plots with different mean canopy heights (28.1 m vs. 31.3 m). Tree slenderness was found to be positively and very significantly correlated with mean canopy height at the plot level. The same correlation was observed at the species population level for the three species adequately sampled. It can therefore be concluded that stratification by canopy height is to be recommended when deriving allometric relationships in order to avoid bias in Above Ground Biomass estimations. (Résumé d'auteur)
Auteurs, date et publication :
Auteurs Grégoire Vincent , F. Caron , Damien Sabatier , Lilian Blanc
Publication : Bois et Forêts des Tropiques
Date : 2025
Catégorie(s)
#CIRAD #FORET ParacouRésumé
Key message Forest disturbance affects the within-population distribution of genetic diversity, but not its overall levels, in a tropical pioneer tree species. In particular, clumps of related saplings with impoverished diversity are found in canopy gaps but not under forest cover. Context Forest disturbances can have long-term consequences on the genetic structure of tree populations, because they can alter the demographic properties of the regeneration process and favour some subpopulations/genotypes, both by stochastic processes and by selection. Intermediate disturbances tend to favour species diversity, at least in highly diverse communities, but their effect on intra-specific diversity is unknown. Aims In this study, we have looked at the genetic consequences of forest disturbance in a stand of the long-lived Neotropical pioneer species, Jacaranda copaia. Methods The study site was experimentally logged in 1984, and the canopy gaps generated by the logging were mapped. Seedlings of J. copaia colonised the gaps, as expected, at a higher density than in the surrounding forest. In 2006, we exhaustively sampled all saplings and adult trees available in a 25-ha area. The samples were genotyped at nine microsatellite loci, and the distribution of genetic diversity was inspected by analyses of spatial autocorrelation, automated Bayesian assignment and comparisons of diversity between cohorts by bootstrap (RaBoT). Results Spatial autocorrelation was found to extend farther in post-disturbance saplings than in the undisturbed population (100 m and beyond versus less than 50 m), and divergent clumps (F ST = 0.05) of related genotypes were found; genetic diversity was found to be impoverished in each clump relative to the global population at about half of the loci. Conclusion Overall, our results suggest that forest disturbance has changed the patterns of distribution of genetic diversity, with potential consequences on long-term population viability.
Auteurs, date et publication :
Auteurs Thomas Leclerc , Ruppert Vimal , Valérie Troispoux , Sophie Périgon , Ivan Scotti
Publication : Annals of Forest Science
Date : 2015
Volume : 72
Issue : 5
Pages : 509–516
Catégorie(s)
#CIRAD #FORET ParacouAuteurs, date et publication :
Auteurs Stephan Hättenschwiler , Sylvain Coq , Sandra Barantal , Ira Tanya Handa
Publication : New Phytologist
Date : 2011
Volume : 189
Issue : 4
Pages : 950–965
Catégorie(s)
#CIRAD #FORET ParacouRésumé
Scalable indicators are promising to assess ecosystem services. In a large (660 ha) coffee agroforestry farm, we calibrated the relationship between the Normalized Difference Vegetation Index (NDVI), calculated on a High Resolution (HR) satellite image and ground-truth LAI, providing a 2-layer (shade trees and coffee) LAI calibration with LAI 2000 and a new technique based on the cumulative distribution of LAI along transects. The effective and apparent clumping of coffee leaves were computed (0.76 and 0.89, respectively). We also calibrated the relationship between the derived HR-LAI farm map and NDVI from the Moderate Resolution Imaging Spectroradiometer (MODIS) in order to re-construct LAI time-series (2001-2011). Coffee LAI, as derived from MODIS after substracting the contribution of shade tree LAI varied seasonally between 2.4 and 4.4 m(2) m(-2), with a maximum by the end of wet season (peak of harvest), steep decline during the drier-cooler season, minimum after annual coffee pruning, recovery during the next rainy season and pause during the grain filling period. MODIS also detected significant inter-annual variations in LAI originating from annual pruning, or plot renovation followed by a progressive LAI recovery during up to 4 years. We related the coffee-LAI time-series with farm registries to examine the impacts of management on LAI and on selected ecosystem services, namely yield and hydrological services. Nitrogen fertilization was adjusted annually by the farmer and appeared as the best yield predictor (R-2 = 0.53). Combining N-fertilization with LAI from 6 significant months of the year, the prediction was improved (R-2 = 0.74), confirming LAI as an important co-predictor of yield. We ended up with a yield prediction model including also the percentage of pruned resprouts (R-2 = 0.79), with potential uses for regional yield mapping or reconstruction of historical yield time-series. The impacts of varying LAI (from nil to double actual values) on hydrological services were simulated. LAI affected the partitioning between green water (evapotranspiration) and blue water (infiltration, aquifer recharge, streamflow), thus the water provisioning. We discussed how LAI was influenced by natural factors (phenology, interaction between vegetative and reproductive components, climate) and by management (pruning, renovation).We confirmed LAI as a powerful scalable indicator for several key ecosystem services. (C) 2014 Elsevier B.V. All rights reserved.
Auteurs, date et publication :
Auteurs Simon Taugourdeau , Guerric le Maire , Jacques Avelino , Jeffrey R. Jones , Luis G. Ramirez , Manuel Jara Quesada , Fabien Charbonnier , Federico Gomez-Delgado , Jean-Michel Harmand , Bruno Rapidel , Philippe Vaast , Olivier Roupsard
Publication : Agriculture Ecosystems & Environment
Date : 2014
Volume : 192
Pages : 19-37
Catégorie(s)
#CIRAD #FORET CoffeeFluxAuteurs, date et publication :
Auteurs G. Le Maire , C. Marsden , W. Verhoef , F. J. Ponzoni , D. Lo Seen , A. Bégué , J. L. Stape , Y. Nouvellon
Publication : Remote Sensing of Environment
Date : 2025
Volume : 115
Pages : 586-599
Catégorie(s)
#CIRAD #FORET Itatinga #INRAERésumé
Abundant Neotropical canopy-tree species are more resistant to drought-induced branch embolism than what is currently admitted. Large hydraulic safety margins protect them from hydraulic failure under actual drought conditions.
Auteurs, date et publication :
Auteurs Camille Ziegler , Sabrina Coste , Clément Stahl , Sylvain Delzon , Sébastien Levionnois , Jocelyn Cazal , Hervé Cochard , Adriane Esquivel-Muelbert , Jean-Yves Goret , Patrick Heuret , Gaëlle Jaouen , Louis S. Santiago , Damien Bonal
Publication : Annals of Forest Science
Date : 2019
Volume : 76
Issue : 4
Pages : 115
Catégorie(s)
#ANR-Citation #CIRAD #FORET ParacouRésumé
The sequence of key water potential thresholds from the onset of water stress to mortality, and the timing of stomatal closure with regard to leaf xylem embolism formation are essential to characterizing plant adaptive strategies to drought. This constitutes a critical knowledge gap for tropical rainforest species, which may be less vulnerable to drought than previously thought. We recorded key leaf and stem water potential thresholds, leaf hydraulic safety margins (HSMleaf), leaf stomatal safety margins (SSMleaf) and estimated native embolism levels during a normal-intensity dry season across 18 neotropical rainforest tree species. We also solved a sequence of key water potential thresholds. Additionally, we provide a cross-biome analysis of SSMleaf encompassing 97 species from four major biomes based on a literature survey. In the studied rainforest species, leaf turgor loss point, used as a surrogate for stomatal closure, typically occurred before the onset of leaf xylem embolism. Most species exhibited positive HSMleaf and SSMleaf, with contrasting values across species and nearly absent embolism levels during the dry season irrespective of the experienced midday leaf water potentials. Our results point out that leaf xylem embolism is not routine for Neotropical rainforest tree species. Based on our proposal of the water potential sequence for tropical rainforest trees, we argue that leaf xylem embolism is a rare event for these species. This was supported by the literature survey, indicating that across biomes, most woody species have rather large SSMleaf and that leaves of tropical rainforest trees are not necessarily more vulnerable than in other biomes. However, we found evidence that some tropical rainforest species may be more vulnerable than others to ongoing climate change. Our data provide an opportunity to parametrize tree-based or land-surface models for tropical rainforests. Read the free Plain Language Summary for this article on the Journal blog.
Auteurs, date et publication :
Auteurs Camille Ziegler , Sébastien Levionnois , Damien Bonal , Patrick Heuret , Clément Stahl , Sabrina Coste
Publication : Functional Ecology
Date : 2025
Volume : 37
Issue : 6
Pages : 1717–1731
Catégorie(s)
#CIRAD #FORET ParacouRésumé
Assessing the spatial variability of soil organic carbon (SOC) is crucial for SOC monitoring and comparing management options. Topsoil (0–5 cm) SOC concentrations were surveyed in a coffee agroforestry watershed (0.9 km2) on Andisols in Costa Rica with uniform farm management. We encountered high values and large spatial variations of SOC, from 48.1 to 172 g kg− 1 in the dry combustion set (SOCref; n = 72) used for calibrating the visible-near-infrared reflectance spectroscopy (VNIRS) samples (SOCVNIRS; 350–2500 nm; n = 520). VNIRS using partial least squares regression was effective in predicting SOC (R2 = 0.85; a root mean square error (RMSE) = 12.3 g kg− 1) and proved an effective proxy measurement. We assessed several topographic, vegetation and andic soil property variables, of which only the latter (metal–humus complexes and allophanes) displayed strong correlations with SOCref concentrations. We compared Random Forest and three geostatistical approaches for the interpolation of SOC in unsampled locations. Ordinary kriging with SOCref yielded an RMSE of 28.0 g kg− 1. Random Forest was successful in incorporating many weakly and non-linearly correlated covariates with SOC (RMSE = 14.7 g kg− 1), provided Alp (the sodium pyrophosphate extractable aluminum), the best predictor of SOC (r = 0.85) but also the most costly variable to acquire. Co-kriging with Alp also showed high reduction in RMSE (16.0 g kg− 1). Co-kriging with SOCVNIRS only showed marginal reduction in RMSE to 24.2 g kg− 1 due to the presence of a high nugget effect. Local variability of SOC in this volcanic agroforestry watershed was dominated by andic properties whereas topographic or vegetation variables had very little impact. Estimation of SOC variability is recommended using inexpensive proxy measurements like VNIRS (RMSE = 12.3 g kg− 1) rather than spatial interpolation techniques.
Auteurs, date et publication :
Auteurs Rintaro Kinoshita , Olivier Roupsard , Tiphaine Chevallier , Alain Albrecht , Simon Taugourdeau , Zia Ahmed , Harold M. van Es
Publication : Geoderma
Date : 2025
Volume : 262
Pages : 254-265
Catégorie(s)
#CIRAD #FORET CoffeeFluxRésumé
The rubber tree (Hevea brasiliensis) is an important economic crop, particularly in Thailand. As the plantations extend to new and drier areas, information on physiological parameters such as water use efficiency (WUE) is required to help breeding for adapted genotypes. Carbon isotope composition of bulk leaf (δ¹³C) can be used as an indicator of intrinsic water use efficiency (WUEi) of plants. A prerequisite step is to analyse the genetic variability of δ¹³C. We compared the carbon isotope composition of bulk rubber tree leaf (δ¹³C) in rainy and dry seasons in a collection of 49 wild genotypes of rubber in Northern Thailand. There were large δ¹³C variations among the genotypes at all seasons. δ¹³C ranged between -33.3‰ to -30.0‰ in rainy season and -33.1‰ to -29.9‰ in dry season. δ¹³C was rather stable with a good correlation between rainy and dry season. In rainy season, there was a positive significant correlation between δ¹³C, leaf mass per area (LMA) and leaf nitrogen per area (NA). The average δ¹³C was significantly different between two genetic clusters previously identified in this population. The large genetic variability of δ¹³C in wild rubber population is promising for breeding genotypes using less water.
Auteurs, date et publication :
Auteurs N. Kampanon , P. Kamensap , P. Thaler , B. Kositsup , Ratchanee Rattanawong , Daniel Epron
Publication : Journal of Rubber Research
Date : 2025
Volume : 20
Issue : 1
Pages : 58-70
Catégorie(s)
#CIRAD #FORET RubberfluxRésumé
Costa Rica is located on the Central American Isthmus, which receives moisture inputs directly from the Caribbean Sea and the Eastern Pacific Ocean. This location includes unique mountainous and lowland microclimates, but only limited knowledge exists about the impact of relief and regional atmospheric circulation patterns on precipitation origin, transport, and isotopic composition. Therefore, the main scope of this project is to identify the key drivers controlling stable isotope variations in daily-scale precipitation of Costa Rica. The monitoring sites comprise three strategic locations across Costa Rica: Heredia (Central Valley), Turrialba (Caribbean slope), and Caño Seco (South Pacific slope). Sporadic dry season rain is mostly related to isolated enriched events ranging from −5.8‰ to −0.9‰ δ18O. By mid-May, the Intertropical Convergence Zone reaches Costa Rica resulting in a notable depletion in isotope ratios (up to −18.5‰ δ18O). HYSPLIT air mass back trajectories indicate the strong influence on the origin and transport of precipitation of three main moisture transport mechanisms, the Caribbean Low Level Jet, the Colombian Low Level Jet, and localized convection events. Multiple linear regression models constructed based on Random Forests of surface meteorological information and atmospheric sounding profiles suggest that lifted condensation level and surface relative humidity are the main factors controlling isotopic variations. These findings diverge from the recognized ‘amount effect’ in monthly composite samples across the tropics. Understanding of stable isotope dynamics in tropical precipitation can be used to a) enhance groundwater modeling efforts in ungauged basins where scarcity of long-term monitoring data drastically limit current and future water resources management, b) improve the re-construction of paleoclimatic records in the Central American land bridge, c) calibrate and validate regional circulation models.
Auteurs, date et publication :
Auteurs R. Sánchez-Murillo , C. Birkel , K. Welsh , G. Esquivel-Hernández , J. Corrales-Salazar , J. Boll , E. Brooks , O. Roupsard , O. Sáenz-Rosales , I. Katchan , R. Arce-Mesén , C. Soulsby , L. J. Araguás-Araguás
Publication : Quaternary Science Reviews
Date : 2025
Volume : 131, Part B
Pages : 250-261