Résumé
Soil CO2 flux (Fs) can be measured either manually or automatically. While manual measurements are well suited to capture the spatial variability of Fs, automated measurements are able to capture its temporal variability at fine time scales. The manual method is the most commonly used method to estimate annual carbon budgets. However, such estimates can be biased depending on the measurement frequency, the time at which measurements are made, and the method used to interpolate Fs between two measurements. In this study, we investigated the effects of within-day measurement frequency and of the time of measurement on the estimation of daily Fs. We also investigated the effects on cumulative Fs estimates of weekly and fortnightly sampling frequencies over several months and of the interpolation method used to cumulate Fs. We based our analyses on two complete datasets of automated measurements (one 12-month and one 4-month) recorded in two contrasting ecosystems (a tropical eucalypt plantation and a temperate poplar plantation). Low-frequency time step within a day (every 360 min for the eucalypt and every 180 min for the poplar plantations) was sufficient to capture mean daily Fs accurately. Furthermore, in the tropical site, measurements averaged over any 6h period provided good estimates of the daily flux. By contrast, biases were observed in the temperate site. With one measurement per week, linear interpolation methods provided accurate cumulative fluxes at both sites. However, all interpolation methods failed to produce robust estimates of cumulative Fs in the temperate plantation with one measurement every two weeks. Automated measurements will help to select the best time slot for manual measurements or to correct manual measurements from the apparent deviation between measurements collected during the sampling period and the 24 h-mean CO2 flux. It will also be useful to elaborate empirical equations used to cumulate Fs obtained manually. Combining manual and automated methods will enhance the accuracy of annual soil carbon budgets in forest plantations. (Résumé d'auteur)
Auteurs, date et publication :
Auteurs Cécilia Gana , Yann Nouvellon , Nicolas Marron , Jose Luiz Stape , Daniel Epron
Publication : Journal of Plant Nutrition and Soil Science
Date : 2025
Volume : 181
Issue : 1
Pages : 12-20
Catégorie(s)
#CIRAD #FORET AgroTCR #FORET Itatinga #FORET RubberfluxRésumé
Finding suitable models of canopy reflectance in forward simulation mode is a prerequisite for their use in inverse mode to characterize canopy variables of interest, such as leaf area index (LAI) or chlorophyll content. In this study, the accuracy of the three-dimensional reflectance model DART (Discrete Anisotropic Radiative Transfer) was assessed for canopies of different genotypes of Eucalyptus, having distinct biophysical and biochemical characteristics, to improve the knowledge on how these characteristics are influencing the reflectance signal as measured by passive orbital sensors. The first step was to test the model suitability to simulate reflectance images in the visible and near infrared. We parameterized DART model using extensive measurements from Eucalyptus plantations including 16 contrasted genotypes. Forest inventories were conducted and leaf, bark, and forest floor optical properties were measured. Simulation accuracy was evaluated by comparing the mean top of canopy (TOC) bidirectional reflectance of DART with TOC reflectance extracted from a Pleiades very high resolution satellite image. Results showed a good performance of DART with mean reflectance absolute error lower than 2%. Intergenotype reflectance variability was correctly simulated, but the model did not succeed at catching the slight spatial variation for a given genotype, excepted when large gaps appeared due to tree mortality. The second step consisted of sensitivity analysis to explore which biochemical or biophysical characteristics influenced more the canopy reflectance between genotypes. Perspectives for using DART model in inversion mode in these ecosystems were discussed. (Résumé d'auteur)
Auteurs, date et publication :
Auteurs Julianne de Castro Oliveira , Jean Baptiste Feret , Flávio Jorge Ponzoni , Yann Nouvellon , Jean-Philippe Gastellu Etchegorry , Otávio Camargo Campoe , Jose Luiz Stape , Luiz Carlos Estraviz Rodriguez , Guerric Le Maire
Publication : IEEE Journal of Selected Topics in Applied Earth Observations and Remote Sensing
Date : 2025
Volume : 10
Issue : 11
Pages : 4844-4852
Catégorie(s)
#CIRAD #FORET Itatinga #INRAEAuteurs, date et publication :
Auteurs Odhran S. O'sullivan , Mary A. Heskel , Peter B. Reich , Mark G. Tjoelker , Lasantha K. Weerasinghe , Aurore Penillard , Lingling Zhu , John J. G. Egerton , Keith J. Bloomfield , Danielle Creek , Nur H. A. Bahar , Kevin L. Griffin , Vaughan Hurry , Patrick Meir , Matthew H. Turnbull , Owen K. Atkin
Publication : Global Change Biology
Date : 2017
Volume : 23
Issue : 1
Pages : 209–223
Catégorie(s)
#CIRAD #FORET ParacouRésumé
The influence of vegetation on slope stability is well understood at the slope level but scaling up to the catchment level is still a challenge, partially because of a lack of suitable data to validate models. We tested the physical landslide model, LAPSUS_LS, which models slope stability at the catchment scale. LAPSUS_LS combines a hydrological model with a Limit Equilibrium Method model, and calculates the factor of safety of individual cells based on their hydrological and geomorphological characteristics. We tested two types of vegetation on slope stability: (i) coffee monoculture (Coffea arabica) and (ii) a mixed plantation of coffee and deep rooting Erythrina (Erythrina poeppigiana) trees. Using soil and root data from Costa Rica, we performed simulations to test the response of LAPSUS_LS to root reinforcement, soil bulk density, transmissivity, internal friction angle and depth of shear plane. Furthermore, we modified the model to include biomass surcharge effect in the calculations. Results show that LAPSUS_LS was most sensitive to changes in additional cohesion from roots. When the depth of the shear plane was fixed at 1.0 m, slopes were not unstable. However, when the shear plane was fixed to 1.5 m, the mixed plantation of coffee and trees stabilized slopes, but the coffee monoculture was highly unstable, because root reinforcement was low at a depth of 1.5 m. Soil transmissivity had a limited impact on the results compared to bulk density and internal friction angle. Biomass surcharge did not have any significant effect on the simulations. In conclusion, LAPSUS_LS responded well to the soil and vegetation input data, and is a suitable candidate for modeling the stability of vegetated slopes at the catchment level.
Auteurs, date et publication :
Auteurs L.M.W. Rossi , B. Rapidel , O. Roupsard , M. Villatoro-sánchez , Z. Mao , J. Nespoulous , J. Perez , I. Prieto , C. Roumet , K. Metselaar , J.M. Schoorl , L. Claessens , A. Stokes
Publication : Ecological Engineering
Date : 2025
Volume : 109
Pages : 249-255
Catégorie(s)
#CIRAD #FORET CoffeeFluxRésumé
The soil microbial activity is a key parameter in numerous studies aiming to assess soil quality in agricultural plots. Basal Soil Respiration (BSR) has been extensively used as an indicator of this soil microbial activity. However, available methods to measure BSR remain time- and labor- consuming and must be performed in the laboratory which may lead to result distortion due to the needed soil pre-treatments. The SituResp® method was developed to assess BSR in a time- and cost-effective way. This method was adapted from a laboratory methodology, the MicroResp™ method, in order to be implemented in the field on fresh soil samples. It is based on the color change of a pH-sensitive gel in reaction to the CO2 concentration change in the headspace of a soil sample over the 24-h incubation. This study presents the calibration and validation of the SituResp® method in laboratory conditions, and a comparison in the field with the Solvita® tool, a comparable method used by agricultural scientists and advisors. The results of the calibration showed a high correlation between the air CO2 concentration and the absorbance variation of the gel at 570 nm (R2 = 0.95). The validation against the titration alkali-trap method, on 21 soil samples, showed a strong correlation between the two methods (R2 = 0.90). In the field test on 9 agricultural-plots, the SituResp® method yielded similar results to the Solvita® tool. The SituResp® method is therefore a reliable method for performing a cheap, rapid but efficient assessment of soil microbial activity in the field which could be included in soil quality monitoring.
Auteurs, date et publication :
Auteurs Alexis Thoumazeau , Frédéric Gay , Pascal Alonso , Nopmanee Suvannang , Audjima Phongjinda , Phantip Panklang , Tiphaine Chevallier , Cécile Bessou , Alain Brauman
Publication : Applied Soil Ecology
Date : 2025
Volume : 121
Pages : 223-230
Catégorie(s)
#CIRAD #FORET Itatinga #FORET RubberfluxAuteurs, date et publication :
Auteurs Talie Musavi , Mirco Migliavacca , Markus Reichstein , Jens Kattge , Christian Wirth , T. Andrew Black , Ivan Janssens , Alexander Knohl , Denis Loustau , Olivier Roupsard , Andrej Varlagin , Serge Rambal , Alessandro Cescatti , Damiano Gianelle , Hiroaki Kondo , Rijan Tamrakar , Miguel D. Mahecha
Publication : Nature Ecology & Evolution
Date : 2017
Volume : 1
Issue : 2
Pages : 0048
Catégorie(s)
#CIRAD #CNRS #FORET CoffeeFlux #FORET PuechabonRésumé
Upscaling instantaneous evapotranspiration retrieved at any specific time-of-day (ETi) to daily evapotranspiration (ETd) is a key challenge in mapping regional ET using polar orbiting sensors. Various studies have unanimously cited the shortwave incoming radiation (RS) to be the most robust reference variable explaining the ratio between ETd and ETi. This study aims to contribute in ETi upscaling for global studies using the ratio between daily and instantaneous incoming shortwave radiation (RSd / RSi) as a factor for converting ETi to ETd.
Auteurs, date et publication :
Auteurs Loise Wandera , Kaniska Mallick , Gerard Kiely , Olivier Roupsard , Matthias Peichl , Vincenzo Magliulo
Publication : Hydrology and Earth System Sciences
Date : 2017
Volume : 21
Issue : 1
Pages : 197-215
Catégorie(s)
#CIRAD #FORET CoffeeFluxRésumé
Modern measures of diversity satisfy reasonable axioms, are parameterized to produce diversity profiles, can be expressed as an effective number of species to simplify their interpretation, and come with estimators that allow one to apply them to real-world data. We introduce the generalized Simpson's entropy as a measure of diversity and investigate its properties. We show that it has many useful features and can be used as a measure of biodiversity. Moreover, unlike most commonly used diversity indices, it has unbiased estimators, which allow for sound estimation of the diversity of poorly sampled, rich communities.
Auteurs, date et publication :
Auteurs Michael Grabchak , Eric Marcon , Gabriel Lang , Zhiyi Zhang , Stefan J. Green
Publication : Plos One
Date : 2017
Volume : 12
Issue : 3
Pages : e0173305
Catégorie(s)
#CIRAD #FORET ParacouRésumé
Although vegetation is increasingly used to mitigate landslide risks, how vegetation affects the temporal variability of slope stability is poorly understood, especially in earthquake-prone regions. We combined 3-year long soil moisture monitoring, measurements of soil physical properties and plant functional traits, and numerical modeling to compare slope stability under paired land uses with and without trees in tropical, subtropical, and temperate landslide- and earthquake-prone regions. Trees improved stability for 5–12 months per year from drawdown of soil moisture and resulted in less interannual variability in the duration of high-stability periods compared to slopes without trees. Our meta-analysis of published data also showed that slopes with woody vegetation were more stable and less sensitive to climate and soil factors than slopes with herbaceous vegetation. However, estimates of earthquake magnitude necessary to destabilize slopes at our sites suggest that large additional stabilization from trees is necessary for meaningful protection against external triggers.
Auteurs, date et publication :
Auteurs John H. Kim , Thierry Fourcaud , Christophe Jourdan , Jean-Luc Maeght , Zhun Mao , James Metayer , Louise Meylan , Alain Pierret , Bruno Rapidel , Olivier Roupsard , Anneke de Rouw , Mario Villatoro Sanchez , Yan Wang , Alexia Stokes
Publication : Geophysical Research Letters
Date : 2017
Volume : 44
Issue : 10
Pages : 4897-4907
Catégorie(s)
#CIRAD #FORET CoffeeFluxAuteurs, date et publication :
Auteurs Lucy Rowland , Joana Zaragoza-Castells , Keith J. Bloomfield , Matthew H. Turnbull , Damien Bonal , Benoit Burban , Norma Salinas , Eric Cosio , Daniel J. Metcalfe , Andrew Ford , Oliver L. Phillips , Owen K. Atkin , Patrick Meir
Publication : New Phytologist
Date : 2017
Volume : 214
Issue : 3
Pages : 1064–1077