Résumé
To recover verticality after disturbance, angiosperm trees produce ‘tension wood' allowing them to bend actively. The driving force of the tension has been shown to take place in the G-layer, a specific unlignified layer of the cell wall observed in most temperate species. However, in tropical rain forests, the G-layer is often absent and the mechanism generating the forces to reorient trees remains unclear. A study was carried out on tilted seedlings, saplings and adult Simarouba amara Aubl. trees—a species known to not produce a G-layer. Microscopic observations were done on sections of normal and tension wood after staining or observed under UV light to assess the presence/absence of lignin. We showed that S. amara produces a cell-wall layer with all of the characteristics typical of G-layers, but that this G-layer can be observed only as a temporary stage of the cell-wall development because it is masked by a late lignification. Being thin and lignified, tension wood fibres cannot be distinguished from normal wood fibres in the mature wood of adult trees. These observations indicate that the mechanism generating the high tensile stress in tension wood is likely to be the same as that in species with a typical G-layer and also in species where the G-layer cannot be observed in mature cells.
Auteurs, date et publication :
Auteurs Jean-Romain Roussel , Bruno Clair , Chung-Jui Tsai
Publication : Tree Physiology
Date : 2015
Volume : 35
Issue : 12
Pages : 1366–1377
Catégorie(s)
#CIRAD #FORET ParacouRésumé
Vegetation phenology is the study of the timing of seasonal events that are considered to be the result of adaptive responses to climate variations on short and long time scales. In the field of remote sensing of vegetation phenology, phenological metrics are derived from time series of optical data. For that purpose, considerable effort has been specifically focused on developing noise reduction and cloud-contaminated data removal techniques to improve the quality of remotely-sensed time series. Comparative studies between time series composed of satellite data acquired under clear and cloudy conditions and from radiometric data obtained with high accuracy from ground-based measurements constitute a direct and effective way to assess the operational use and limitations of remote sensing for predicting the main plant phenological events. In the present paper, we sought to explicitly evaluate the potential use of MODerate resolution Imaging Spectroradiometer (MODIS) remote sensing data for monitoring the seasonal dynamics of different types of vegetation cover that are representative of the major terrestrial biomes, including temperate deciduous forests, evergreen forests, African savannah, and crops. After cloud screening and filtering, we compared the temporal patterns and phenological metrics derived from in situ NDVI time series and from MODIS daily and 16-composite products. We also evaluated the effects of residual noise and the influence of data gaps in MODIS NDVI time series on the identification of the most relevant metrics for vegetation phenology monitoring. The results show that the inflexion points of a model fitted to a MODIS NDVI time series allow accurate estimates of the onset of greenness in the spring and the onset of yellowing in the autumn in deciduous forests (RMSE≤one week). Phenological metrics identical to those provided with the MODIS Global Vegetation Phenology product (MDC12Q2) are less robust to data gaps, and they can be subject to large biases of approximately two weeks or more during the autumn phenological transitions. In the evergreen forests, in situ NDVI time series describe the phenology with high fidelity despite small temporal changes in the canopy foliage. However, MODIS is unable to provide consistent phenological patterns. In crops and savannah, MODIS NDVI time series reproduce the general temporal patterns of phenology, but significant discrepancies appear between MODIS and ground-based NDVI time series during very localized periods of time depending on the weather conditions and spatial heterogeneity within the MODIS pixel. In the rainforest, the temporal pattern exhibited by a MODIS 16-day composite NDVI time series is more likely due to a pattern of noise in the NDVI data structure according to both rainy and dry seasons rather than to phenological changes. More investigations are needed, but in all cases, this result leads us to conclude that MODIS time series in tropical rainforests should be interpreted with great caution.
Auteurs, date et publication :
Auteurs G. Hmimina , E. Dufrêne , J.-Y. Pontailler , N. Delpierre , M. Aubinet , B. Caquet , A. de Grandcourt , B. Burban , C. Flechard , A. Granier , P. Gross , B. Heinesch , B. Longdoz , C. Moureaux , J.-M. Ourcival , S. Rambal , L. Saint André , K. Soudani
Publication : Remote Sensing of Environment
Date : 2013
Volume : 132
Pages : 145–158
Catégorie(s)
#CIRAD #CNRS #FORET Paracou #FORET PuechabonAuteurs, date et publication :
Auteurs N. Baghdadi , G. le Maire , J. Bailly , K. Ose , Y. Nouvellon , M. Zribi , C. Lemos , R. Hakamada
Publication : IEEE Journal of Selected Topics in Applied Earth Observations and Remote Sensing
Date : 2025
Volume : 99
Pages : 1610
Catégorie(s)
#CIRAD #FORET Itatinga #INRAERésumé
The association of N-2-fixing species (NFS) could be an attractive option for achieving a sustainable increase of Eucalyptus plantations (EP) productivity through a positive balance between facilitative effects and competition between species. A randomised block design was replicated at four sites (Cenibra, USP, Suzano and IP) in Southern Brazil and at one site in Congo. The development of mono-specific stands of Acacia mangium (100A) and Eucalyptus grandis or urophylla x grandis (100E), was compared with N fertilisation treatment (100E + N) and with mixed-species plantations in a 1:1 ratio (50A:50E), and in an additive series with varying densities of acacia for the same density of eucalypt (25A:100E, 50A:100E, 100A:100E). The objectives were to assess the effect of mixtures on tree growth and stand production, and the behaviour of the two species in contrasting soil and climatic conditions. Tree growth was monitored over stand rotation and the biomass of aboveground tree components estimated at mid-rotation and at harvesting age. Eucalyptus height was 13% higher in Brazil than in Congo. Favourable ecological conditions in Congo and Cenibra led to 50% higher Acacia tree height than at the other sites. A depressive effect of Eucalyptus neighbour trees on Acacia height and circumference growth, lower in Congo than in Brazil, was observed in the mixtures from age 1-2 years onwards. Depressive effects of acacia on eucalypt height and circumference growth were low in USP, Suzano and IP, high in Cenibra, and not observed in Congo, in 50A:50E and 25A:100E. A positive though insignificant response to N fertilisation was only found in USP and Congo. Complementarity for light and soil resource capture between Eucalyptus and Acacia trees resulted in mean annual increments in total stand stemwood biomass (MAI) that were 7-15%, 6-12%, and 40% higher in the additive series than for 100E in Cenibra, LISP and Congo, respectively at mid-rotation. Whilst lasting complementarity and facilitation in Congo led to 17-34% higher MAI in mixtures than for 100E at harvesting age, MAIs were not significantly higher in mixtures than for 100E in Brazil. Mixed-species plantations of Eucalyptus and A. mangium might enhance aboveground stand production on poor nutrient soils in warm and humid tropical climates with low water limitations. (c) 2012 Elsevier B.V. All rights reserved.
Auteurs, date et publication :
Auteurs J.-P. Bouillet , J.-P. Laclau , J.-L. de Moraes Goncalves , M. Voigtlaender , J.-L. Gava , F.-P. Leite , R. Hakamada , L. Mareschal , A. Mabiala , F. Tardy , J. Levillain , P. Deleporte , D. Epron , Y. Nouvellon
Publication : Forest Ecology and Management
Date : 2013
Volume : 301
Pages : 89-101
Catégorie(s)
#CIRAD #FORET Itatinga #INRAERésumé
Dès son introduction à Madagascar, Eucalyptus robusta a été retenu comme espèce de reboisement pour sa remarquable capacité d'adaptation. L'extension de sa plantation par les populations rurales a abouti à la création d'un massif de près de 140 000 hectares autour d'Antananarivo. Son bois est devenu la principale source d'énergie utilisée par les ménages urbains et ruraux malgaches. Mais aujourd'hui, la production durable de cette ressource est gravement menacée. Le marché déficitaire et la pauvreté des populations rurales amènent les propriétaires forestiers à exploiter leurs taillis avec des rotations de plus en plus courtes, parfois inférieures à 2 ans. Cette surexploitation induit un gaspillage des éléments minéraux qui ne sont pas compensés par des apports extérieurs de nutriments. La production de charbon de bois se poursuit à partir de meules traditionnelles dont le rendement pondéral n'est que de 10 % environ. Le doublement de ce rendement par des méthodes simples permettrait pourtant de diminuer les superficies de forêt exploitées chaque année. À 6 ans, l'accroissement moyen annuel en volume commercial bois fort sur écorce des taillis anciens est de 18,8 m 3 /ha/an. Les meilleures provenances importées récemment permettent de doubler le volume moyen individuel des arbres à 9 ans. Des vergers à graines ont été plantés avec plusieurs provenances de l'aire naturelle pour créer des variétés composites. Cependant, des fécondations préférentielles intra-provenances et des pollutions par le pollen extérieur affectent fortement la qualité des variétés produites. Pour l'extension du massif d'eucalyptus, les populations rurales continuent à utiliser des graines locales ou planter des sauvageons. Ces plantations en E. robusta devront continuer à produire du bois malgré les modifications biotiques et abiotiques déjà constatés à Madagascar. Face à ces changements, les technologies modernes peuvent aider la recherche forestière à proposer un système durable de production de bois énergie autour des grands centres urbains. Cela aurait pour effet de maintenir un revenu régulier participant à la survie des populations rurales. (Résumé d'auteur)
Auteurs, date et publication :
Auteurs D. Verhaegen , H. Randrianjafy , H. Rakotondraoelina , M.-C. Trendelenburg Rakotonirina , N. Andriamampianina , P. Montagne , A. Rasamindisa , G. Chaix , J.-P. Bouillet , J.-M. Bouvet
Publication : Bois et Forêts des Tropiques
Date : 2025
Issue : 320
Pages : 15-30
Catégorie(s)
#CIRAD #FORET Itatinga #INRAEAuteurs, date et publication :
Auteurs Bini D , Alcantara dos Santos C , Bouillet J P , De Morais Gonçalves J L , Bran Nogueira Cardoso E J
Publication : Applied soil ecology
Date : 2025
Volume : 63
Pages : 57-66
Catégorie(s)
#CIRAD #FORET Itatinga #INRAEAuteurs, date et publication :
Auteurs A. Bar-Hen , J. Chadø euf , H. Dessard , P. Monestiez
Publication : Statistics and Computing
Date : 2013
Volume : 23
Issue : 3
Pages : 297–309
Catégorie(s)
#CIRAD #FORET ParacouRésumé
Leaf mass per area (LMA) and leaf equivalent water thickness (EWT) are key leaf functional traits providing information for many applications including ecosystem functioning modeling and fire risk management. In this paper, we investigate two common conclusions generally made for LMA and EWT estimation based on leaf optical properties in the near-infrared (NIR) and shortwave infrared (SWIR) domains: (1) physically-based approaches estimate EWT accurately and LMA poorly, while (2) statistically-based and machine learning (ML) methods provide accurate estimates of both LMA and EWT. Using six experimental datasets including broadleaf species samples of >150 species collected over tropical, temperate and boreal ecosystems, we compared the performances of a physically-based method (PROSPECT model inversion) and a ML algorithm (support vector machine regression, SVM) to infer EWT and LMA based on leaf reflectance and transmittance. We assessed several merit functions to invert PROSPECT based on iterative optimization and investigated the spectral domain to be used for optimal estimation of LMA and EWT. We also tested several strategies to select the training samples used by the SVM, in order to investigate the generalization ability of the derived regression models. We evidenced that using spectral information from 1700 to 2400 nm leads to strong improvement in the estimation of EWT and LMA when performing a PROSPECT inversion, decreasing the LMA and EWT estimation errors by 55% and 33%, respectively. The comparison of various sampling strategies for the training set used with SVM suggests that regression models show limited generalization ability, particularly when the regression model is applied on data fully independent from the training set. Finally, our results demonstrate that, when using an appropriate spectral domain, the PROSPECT inversion outperforms SVM trained with experimental data for the estimation of EWT and LMA. Thus we recommend that estimation of LMA and EWT based on leaf optical properties should be physically-based using inversion of reflectance and transmittance measurements on the 1700 to 2400 nm spectral range.
Auteurs, date et publication :
Auteurs J. -B. Féret , G. le Maire , S. Jay , D. Berveiller , R. Bendoula , G. Hmimina , A. Cheraiet , J. C. Oliveira , F. J. Ponzoni , T. Solanki , F. de Boissieu , J. Chave , Y. Nouvellon , A. Porcar-Castell , C. Proisy , K. Soudani , J. -P. Gastellu-Etchegorry , M. -J. Lefèvre-Fonollosa
Publication : Remote Sensing of Environment
Date : 2019
Volume : 231
Pages : 110959
Catégorie(s)
#ANR-Citation #CIRAD #CNRS #FORET ItatingaAuteurs, date et publication :
Auteurs Quentin Molto , Vivien Rossi , Lilian Blanc , Robert Freckleton
Publication : Methods in Ecology and Evolution
Date : 2013
Volume : 4
Issue : 2
Pages : 175–183
Catégorie(s)
#CIRAD #FORET ParacouRésumé
entropart is a package for R designed to estimate diversity based on HCDT entropy or similarity-based entropy. It allows calculating species-neutral, phylogenetic and functional entropy and diversity, partitioning them and correcting them for estimation bias.
Auteurs, date et publication :
Auteurs Eric Marcon , Bruno Hérault
Publication : Journal of Statistical Software
Date : 2015
Volume : 67
Issue : 8
Pages : 1–26