Résumé
textlessptextgreatertextlessptextgreatertextlessstrongtextgreaterAbstract.textless/strongtextgreater The fixation of carbon in tropical forests mainly occurs through the production of wood and leaves, both being the principal components of net primary production. Currently field and satellite observations are independently used to describe the forest carbon cycle, but the link between satellite-derived forest phenology and field-derived forest productivity remains opaque. We used a unique combination of a MODIS enhanced vegetation index (EVI) dataset, a wood production model based on climate data and direct litterfall observations at an intra-annual timescale in order to question the synchronism of leaf and wood production in tropical forests. Even though leaf and wood biomass fluxes had the same range (respectively 2.4 ± 1.4 and 2.2 ± 0.4 Mg C hatextlesssuptextgreater−1textless/suptextgreater yrtextlesssuptextgreater−1textless/suptextgreater), they occurred separately in time. EVI increased with leaf renewal at the beginning of the dry season, when solar irradiance was at its maximum. At this time, wood production stopped. At the onset of the rainy season, when new leaves were fully mature and water available again, wood production quickly increased to reach its maximum in less than a month, reflecting a change in carbon allocation from short-lived pools (leaves) to long-lived pools (wood). The time lag between peaks of EVI and wood production (109 days) revealed a substantial decoupling between the leaf renewal assumed to be driven by irradiance and the water-driven wood production. Our work is a first attempt to link EVI data, wood production and leaf phenology at a seasonal timescale in a tropical evergreen rainforest and pave the way to develop more sophisticated global carbon cycle models in tropical forests.textless/ptextgreatertextless/ptextgreater
Auteurs, date et publication :
Auteurs F. Wagner , V. Rossi , C. Stahl , D. Bonal , B. Hérault
Publication : Biogeosciences
Date : 2013
Volume : 10
Issue : 11
Pages : 7307–7321
Catégorie(s)
#CIRAD #FORET ParacouAuteurs, date et publication :
Auteurs L. Rowland , C. Stahl , D. Bonal , L. Siebicke , M. Williams , P. Meir
Publication : Ecosystems
Date : 2013
Volume : 16
Issue : 7
Pages : 1294–1309
Catégorie(s)
#CIRAD #FORET ParacouRésumé
textlessptextgreaterThe objective of this study was to examine the water relations and hydraulic architecture and vulnerability to cavitation in textlessemtextgreaterVirola surinamensis textless/emtextgreaterandtextlessemtextgreater V. micheliitextless/emtextgreater and to compare to similar measurements in textlessemtextgreaterEperua falcata. textless/emtextgreaterIn several previous reports textlessemtextgreaterVirolatextless/emtextgreater was seen to have a rather narrow range of xylem pressure potentials (textlessemtextgreaterΨtextless/emtextgreatertextlessemtextgreatertextlesssubtextgreaterxtextless/subtextgreatertextless/emtextgreater) near zero in the course of a wet-season day while having water fluxes quite close to textlessemtextgreaterEperuatextless/emtextgreater. We tested the hypothesis that the narrow range of textlessemtextgreaterΨtextless/emtextgreatertextlessemtextgreatertextlesssubtextgreaterxtextless/subtextgreatertextless/emtextgreater might be consistent with very high hydraulic conductivities of stems, roots and shoots and high vulnerability to cavitation in textlessemtextgreaterVirolatextless/emtextgreater compared to textlessemtextgreaterEperuatextless/emtextgreater. When this hypothesis proved false we concluded that the previous determinations of textlessemtextgreaterΨtextless/emtextgreatertextlessemtextgreatertextlesssubtextgreaterxtextless/subtextgreatertextless/emtextgreater might be wrong in textlessemtextgreaterVirolatextless/emtextgreater due to latex. We re-examined the determination of textlessemtextgreaterΨtextless/emtextgreatertextlessemtextgreatertextlesssubtextgreaterxtextless/subtextgreatertextless/emtextgreater in textlessemtextgreaterVirolatextless/emtextgreater by the pressure chamber technique and compared results to determination of textlessemtextgreaterΨtextless/emtextgreatertextlessemtextgreatertextlesssubtextgreaterleaftextless/subtextgreatertextless/emtextgreater by the thermocouple psychrometer technique and found that the likely range of textlessemtextgreaterΨtextless/emtextgreatertextlessemtextgreatertextlesssubtextgreaterxtextless/subtextgreatertextless/emtextgreater are more negative than previously reported. Problems concerning the determination of textlessemtextgreaterΨtextless/emtextgreatertextlessemtextgreatertextlesssubtextgreaterxtextless/subtextgreatertextless/emtextgreater in species with latex are discussed.textless/ptextgreater
Auteurs, date et publication :
Auteurs Têtè Sévérien Barigah , Gilbert Aussenac , Christopher Baraloto , Damien Bonal , Hervé Cochard , André Granier , Jean-Marc Guehl , Roland Huc , Mari A. Sobrado , Melvin T. Tyree
Publication : Journal of Plant Hydraulics
Date : 2014
Volume : 1
Pages : 002
Catégorie(s)
#CIRAD #FORET ParacouRésumé
The Geoscience Laser Altimeter System (GLAS) has provided a useful dataset for estimating forest heights in many areas of the globe. Most of the studies on GLAS waveforms have focused on natural forests and only a few were conducted over forest plantations. This work set out to estimate the stand-scale dominant height and aboveground biomass of intensively managed Eucalyptus plantations in Brazil using the most commonly used models developed for natural forests. These forest plantations are valuable case studies, with large and numerous stands that are very uniform, in which field measurements are precise compared to natural forests. The height of planted Eucalyptus forest stands estimated from waveforms acquired by GLAS were compared with in situ measurements in order to determine the model that produced the best forest height estimates. For our slightly sloping study site (slope < 7 degrees), the direct method defined as the difference between the signal begin and the ground peak provided forest height estimates with an accuracy of 2.2 m. The use of statistical models based on waveform metrics and digital elevation models provided slightly better results (1.89 m accuracy) in comparison with the direct method and the most relevant metrics proved to be the trailing edge extent and the waveform extent. Moreover, a power law model was used to fit in situ aboveground biomass to in situ forest height. The results using this model with GLAS-derived heights showed an accuracy for biomass of 16.1 Mg/ha.
Auteurs, date et publication :
Auteurs N. Baghdadi , G. le Maire , I. Fayad , J.-S. Bailly , Y. Nouvellon , C. Lemos , R. Hakamada
Publication : IEEE Geoscience and Remote Sensing Letters
Date : 2014
Volume : 7
Issue : 1
Pages : 290-299
Catégorie(s)
#CIRAD #FORET Itatinga #INRAEAuteurs, date et publication :
Auteurs A. Hamadi , C. Albinet , P. Borderies , T. Koleck , L. Villard , D. Ho Tong Minh , T. Le Toan
Publication : IEEE Transactions on Geoscience and Remote Sensing
Date : 2014
Volume : 52
Issue : 8
Pages : 4539–4547
Catégorie(s)
#CIRAD #FORET ParacouAuteurs, date et publication :
Auteurs Grégoire Vincent , Daniel Sabatier , Ervan Rutishauser
Publication : Oecologia
Date : 2014
Volume : 175
Issue : 2
Pages : 439–443
Catégorie(s)
#CIRAD #FORET ParacouAuteurs, date et publication :
Auteurs Dinh Ho Tong Minh , Stefano Tebaldini , Fabio Rocca , Thuy Le Toan , Pierre Borderies , Thierry Koleck , Clement Albinet , Alia Hamadi , Ludovic Villard
Publication : IEEE Geoscience and Remote Sensing Letters
Date : 2014
Volume : 11
Issue : 8
Pages : 1438–1442
Catégorie(s)
#CIRAD #FORET ParacouRésumé
Differential growth response to light level is widely accepted as a potential mechanism for maintaining tree species richness in tropical forests. The position of tree species in the hierarchy of the canopy is considered an important indicator of species light capture and growth strategy. Paradoxically, the relative importance of species identity and competition for light in determining individual tree growth is poorly documented at the adult stage. In this study, we used a hierarchical Bayesian model to quantify the overall importance of species identity, light and belowground competition as determinants of tree growth in French Guiana tropical forest. Light competitive status is assessed by a crown exposure score and below ground competition is estimated from local crowding. We examined species sensitivity to both types of competition in relation to adult stature. Our results are based on annual diameter increments of more than 13,510 stems from 282 species monitored over 10years. Mean annual growth rate was 0.11cmy−1 with species identity explaining 35% of the individual variation in growth rate. Crown exposure and local crowding explained 3.5% and 2.4% of the variation in growth rate, respectively. Predicted changes in growth rate as crown exposure (resp. local crowding) index changed from lower to upper interquartile level was 0.03cmy−1 (resp. 0.02cmy−1). Species sensitivity to crown exposure and to local crowding were positively correlated (i) with predicted growth rate at high-light standardized conditions and (ii) with adult stature. This vertical niche partitioning is invoked to explain the limited contribution made by level of light competition for predicting individual tropical tree growth as the community-level response is dominated by the abundance of small-statured species with low sensitivity to light level. Light appears to drive the stem growth rate of tropical trees through species differentiation more than through individual tree growth limitation. This vertical stratification complements the previously reported regeneration niche and together these provide evidence for light niche partitioning in the three-dimensional space of tropical forests.
Auteurs, date et publication :
Auteurs Marilyne Laurans , Bruno Hérault , Ghislain Vieilledent , Grégoire Vincent
Publication : Forest Ecology and Management
Date : 2014
Volume : 329
Pages : 79–88
Catégorie(s)
#CIRAD #FORET ParacouRésumé
Cronbach's alpha is an estimate of the reliability of a test score if the items are essentially tau-equivalent. Several authors have derived results that provide al-ternative interpretations of alpha. These interpretations are also valid if essential tau-equivalency does not hold. For example, alpha is the mean of all split-half reliabilities if the test is split into two halves that are equal in size. This note presents several con-nections between Cronbach's alpha and the Spearman-Brown formula. The results provide new interpretations of Cronbach's alpha, the stepped down alpha, and stan-dardized alpha, that are also valid in the case that essential tau-equivalency or parallel equivalency do not hold. The main result is that the stepped down alpha is a weighted average of the alphas of all subtests of a specific size, where the weights are the de-nominators of the subtest alphas. Thus, the stepped down alpha can be interpreted as an average subtest alpha. Furthermore, we may calculate the stepped down alpha without using the Spearman-Brown formula.
Auteurs, date et publication :
Auteurs Renato Cordeiro de Amorim
Publication : Journal of Classification
Date : 2025
Volume : 32
Issue : March
Pages : 46–62
Catégorie(s)
#CIRAD #FORET ParacouRésumé
Understanding how plants are constructed—i.e., how key size dimensions and the amount of mass invested in different tissues varies among individuals—is essential for modeling plant growth, carbon stocks, and energy fluxes in the terrestrial biosphere. Allocation patterns can differ through ontogeny, but also among coexisting species and among species adapted to different environments. While a variety of models dealing with biomass allocation exist, we lack a synthetic understanding of the underlying processes. This is partly due to the lack of suitable data sets for validating and parameterizing models. To that end, we present the Biomass And Allometry Database (BAAD) for woody plants. The
BAAD contains 259 634 measurements collected in 176 different studies, from 21 084 individuals across 678 species. Most of these data come from existing publications. However, raw data were rarely made public at the time of publication. Thus, the BAAD contains data from different studies, transformed into standard units and variable names. The transformations were achieved using a common workflow for all raw data files. Other features that distinguish the BAAD are: (i) measurements were for individual plants rather than stand averages; (ii) individuals spanning a range of sizes were measured; (iii) plants from 0.01– 100 m in height were included; and (iv) biomass was estimated directly, i.e., not indirectly via allometric equations (except in very large trees where biomass was estimated from detailed sub-sampling). We included both wild and artificially grown plants. The data set contains the following size metrics: total leaf area; area of stem cross-section including sapwood, heartwood, and bark; height of plant and crown base, crown area, and surface area; and the dry mass of leaf, stem, branches, sapwood, heartwood, bark, coarse roots, and fine root tissues. We also report other properties of individuals (age, leaf size, leaf mass per area, wood density, nitrogen content of leaves and wood), as well as information about the growing environment (location, light, experimental treatment, vegetation type) where available. It is our hope that making these data available will improve our ability to understand plant growth, ecosystem dynamics, and carbon cycling in the world’s vegetation
Auteurs, date et publication :
Auteurs D.-S. Falster , R.-A. DUURSMA , MASAE I-I , D.-R. BARNECHE , R.-G. FITZJOHN , A. VA ˚ RHAMMAR , M. AIBA , M. ANDO , N.-I. ANTEN , M.-J. ASPINWALL , J.-L. BALTZER , C. BARALOTO , M. BATTAGLIA , J.-J. BATTLES , B. BOND-LAMBERTY , M. VAN BREUGEL , J. CAMAC , Y. CLAVEAU , L. COLL , M. DANNOURA
Publication : Ecology
Date : 2025
Volume : 96
Issue : 5
Pages : 1445