Search

Souvent dénigré et présenté comme une activité archaïque et incapable d’évolution, l’extractivisme pourrait n’être aujourd’hui qu’un témoignage désuet de l’un des nombreux cycles économiques vécus par le Brésil. Mais les mouvements politiques des seringueiros, aux revendications relayées par diverses institutions et par une opinion publique sensibilisée aux problèmes écologiques ont propulsé cette vieille activité au centre des débats sur la gestion de la forêt amazonienne. De 1990 à 1995, l’...

L'article constitue une approche originale de l'extractivisme. L'auteur à analyser les perspectives d'évolution du marché d'un produit d'origine extractiviste, l'huile essentielle de bois de rose. Il examine les concurrences auxquelles il doit faire face, mais aussi ses atouts face à des produits de synthèse ou issus d'une mise en culture. Ce faisant, il met l'accent sur la nécessité d'avoir recours aux approches complèmentaires des acteurs locaux, des scientifiques et des industriels pour une meilleure valorisation des produits issus de l'extractivisme. (résumé d'auteur)

Often decried and presented as an outdated activity incapable of progress, extractivism might today be nothing more than an obsolete testimony to one of the numerous economic cycles that Brazil has experienced. But the political movements of the seringueiros, whose demands are supported by various institutions, and a public opinion sensitive to ecological problems have placed this ancient activity in the centre of discussions concerning the management of the Amazonian forest. In the years 199...

Les études menées en différents points d’Amazonie centrale soulignent la persistance d’une composante extractiviste dans des systèmes de production essentiellement agricoles. L’extractivisme, par les revenus complémentaires qu’il engendre, conserve un intérêt pour les petits producteurs et s’insère parmi d’autres activités telles que l’agriculture, le petit élevage, la chasse, la pêche et la cueillette à des fins domestiques. Cette imbrication entre agriculture et collecte de produits foresti...

Frequëntemente denegrido e apresentado como uma atividade arcaica e incapaz de evoluir, o extrativismo poderia ser hoje apenas um testemunho ultrapassado de um dos numerosos ciclos econômicos que o Brasil viveu. Mas os movimentos politicos dos seringueiros, apoiados pelas reivindicações de diversas instituições e por uma opiniao pública sensibilizada pelos problemas ecológicos, impeliram esta velha atividade para o centro dos debates sobre o manejo da floresta amazônica. De 1990 a 1995 o Inst...

L’occupation de l’Amazonie s’est effectuée en plusieurs vagues de colonisation associées à la recherche des ressources naturelles de la forêt. L’exploitation de ces ressources, dont la nature a changé au cours du temps selon la demande des marchés de consommation et les progrès techniques, a durablement structuré le territoire et les rapports sociaux. L’histoire de l’Amazonie est indissociable de celle de l’extractivisme. Conquête et pillage Si le fleuve Amazone est reconnu de son cours supér...

Ces textes, réunis par Laure Emperaire, présentent les principaux résultats du programme de recherches interdisciplinaire « Extractivisme en Amazonie centrale. Viabilité et optimisation », mené en coopération par l’Orstom et l’Inpa. Catherine Aubertin, économiste, Orstom. Laboratoire des sciences sociales, centre Orstom, 32, avenue Henri-Varagnat, 93143 Bondy, France. Sylvia Bahri, botaniste, chercheur associé. Laboratoire de botanique tropicale, institut de botanique, 163, rue Auguste-Brouss...

L’extractivisme, une activité aux potentialités limitées La recherche de nouveaux modes de mise en valeur du milieu naturel qui limitent la déforestation a conduit à accorder un intérêt particulier à l’extractivisme. Depuis une dizaine d’années, cette activité fait l’objet de diverses recherches, tant sur sa viabilité écologique que sur son insertion socio-économique. Sur le plan écologique, on peut considérer que l’extractivisme préserve dans la majeure partie des cas la diversité biologique...

Depuis quelques années, le terme « extractivisme » est largement utilisé dans les discussions portant sur la mise en valeur et la conservation des forêts tropicales et particulièrement de la forêt amazonienne. Il désigne une pratique universelle dans l’espace et le temps, celle de l’exploitation à des fins commerciales des ressources naturelles. Popularisé par les luttes sociales des collecteurs de caoutchouc de l’Amazonie brésilienne, les seringueiros, il évoque plus particulièrement des mil...

Occupation - fortification, des siècles d’anonymat C’est à l’emplacement du fortin de São José do Rio Negro, construit en 1669, que s’élève l’actuelle ville de Manaus. Cette place militaire constituera le germe du village de Lugar da Barra, postérieurement nommé São José da Barra do Rio Negro et enfin Manaus, du nom d’une tribu indigène. Enclos dans la forêt, cet embryon de centre urbain se développe en tirant profit de sa position géographique privilégiée, à la confluence du rio Negro et du ...

Les formes d’exploitation de l’andiroba, qu’il s’agisse de Carapa guianensis ou de C. procera, sont variées. Ces Méliacées amazoniennes sont exploitées en forêt mais également dans des jardins-vergers pour leurs graines oléagineuses, qui fournissent une huile médicinale aux nombreuses propriétés dont celle d’être insectifuge. De préparation artisanale, l’huile est fréquemment commercialisée sur les marchés locaux en petits flacons. Elle a aussi constitué un produit d’exportation pour la savon...

National audience; Cette conférence présentera une dimension méconnue de la biodiversité, très souvent abordée sous le seul angle de la diversité entre espèces ou de la diversité des écosystèmes. La diversité génétique présente au sein des espèces forestières souvent distribuée sur de grands espaces constitue une source majeure d’adaptation des forêts d’aujourd’hui aux changements climatiques annoncés. Seront successivement abordées les questions suivantes : -Comment mesurer la diversité génétique des espèces forestières pour leur capacité d’adaptation à des milieux changeants ? - Quelle information sur la diversité génétique et son évolution à court et à long terme nous est apportée par une analyse de l’ADN ? - Quelles sont les différentes facettes d’une gestion durable des ressources génétiques forestières ? Des illustrations pour plusieurs espèces forestières tempérées serviront de supports à cette présentation.

Élaborer des tarifs génériques, valables pour toutes les essences de la ressource forestière, est une véritable gageure compte tenu de la masse de données nécessaire pour ajuster les modèles. Si l’information est largement disponible pour certaines essences, d’autres sont peu (ou pas) renseignées. D’où l’idée de constituer des groupes d’essences de même architecture et structure interne, qui permettent de mutualiser l’information et proposer un modèle par groupe sinon par essence. Une opération structurante.

Wood specific gravity (WSG) is a strong predictor of tree performance across environmental gradients. Yet it remains unclear how anatomical elements linked to different wood functions contribute to variation in WSG in branches and roots across tropical forests. [br/][br/]We examined WSG and wood anatomy in white sand, clay terra firme and seasonally flooded forests in French Guiana, spanning broad environmental gradients found throughout Amazonia. We measured 15 traits relating to branches and small woody roots in 113 species representing the 15 most abundant species in each habitat and representative species from seven monophyletic lineages occurring in all habitats. [br/][br/]Fiber traits appear to be major determinants of WSG, independent of vessel traits, in branches and roots. Fiber traits and branch and root WSG increased from seasonally flooded species to clay terra firme species and lastly to white sand species. Branch and root wood traits were strongly phylogenetically constrained. Lineages differed in wood design, but exhibited similar variation in wood structure across habitats. [br/][br/]We conclude that tropical trees can invest differently in support and transport to respond to environmental conditions. Wind disturbance and drought stress represent significant filters driving tree distribution of Amazonian forests; hence we suggest that biophysical explanations should receive more attention.

Analyses of tree diversity and community composition in tropical rain forests are usually based either on general herbarium data or on a restricted number of botanical plots. Despite their high taxonomic accuracy, both types of data are difficult to extrapolate to landscape scales. Meanwhile, forestry surveys provide quantitative occurrence data on large areas, and are thus increasingly used for landscape-scale analyses of tree diversity. However, the reliability of these approaches has been challenged because of the ambiguity of the common (vernacular) names used by foresters and the complexity of tree taxonomy in those hyper-diverse communities. We developed and tested a novel approach to evaluate taxonomic reliability of forestry surveys and to propagate the resulting uncertainty in the estimates of several diversity indicators (alpha and beta entropy, Fisher-alpha and Sørensen similarity). Our approach is based on Monte-Carlo processes that simulate communities by taking into account the expected accuracy and reliability of common names. We tested this method in French Guiana, on 9 one-hectare plots (4279 trees – DBH ⩾ 10 cm) for which both common names and standardized taxonomic determinations were available. We then applied our method of community simulation on large forestry inventories (560 ha) at the landscape scale and compared the diversity indices obtained for 10 sites with those computed from precise botanical determination situated at the same localities. We found that taxonomic reliability of forestry inventories varied from 22% (species level) to 83% (family level) in this Amazonian region. Indices computed directly with raw forestry data resulted in incorrect values, except for Gini–Simpson beta-diversity. On the contrary, our correction method provides more accurate diversity estimates, highly correlated with botanical measurements, for almost all diversity indices at both regional and local scales. We obtained a robust ranking of sites consistent with those shown by botanical inventories. These results show that (i) forestry inventories represent a significant part of taxonomic information, (ii) the relative diversity of regional sites can be successfully ranked using forestry inventory data using our method and (iii) forestry inventories can valuably contribute to the detection of large-scale diversity patterns when biases are well-controlled and corrected. The tools we developed as R-functions are available in supplementary material and can be adapted with local parameters to be used for forest management and conservation issues in other regional contexts.

Master; Dans un contexte de changement climatique nous nous sommes intéressés à la détermination de stratégies adaptatives d’espèces forestières, mises en place pour faire face à des épisodes de sécheresse plus intenses et plus long et à une diminution des précipitations. Pour cela, nous nous sommes intéressés à quatre espèces méditerranéennes : Quercus ilex L., Pinus halepensis Mill, Abies alba Mill et Fagus sylvatica L.. Nous avons récolté un maximum de données à partir de la littérature et de bases de données diverses, sur des traits physiologiques concernant la croissance, les propriétés hydrauliques, la photosynthèse et les caractéristiques foliaires. Une analyse de variance sur ces variables, suivie d’une analyse en composante principale, nous ont permis de comprendre que nos quatre espèces réagissent différemment même lorsqu’elles partagent le même milieu. D’une manière générale, nous avons remarqué que le Pin d’Alep se caractérise par des variables photosynthétiques, il réalise donc fortement la photosynthèse même lorsque le potentiel hydrique est fortement négatif, il est donc également résistant à l’embolie. A l’inverse, le Sapin pectiné et le Hêtre sont beaucoup plus vulnérables à la cavitation et ferment donc rapidement leurs stomates. En revanche, ils maintiennent une croissance forte. Le Chêne vert est le plus résistant à la cavitation et il a un transport hydraulique efficace. Cependant, nous avons pu mettre en évidence uniquement des groupes de variables caractéristiques du fonctionnement des espèces et il reste tout de même difficile de les appeler « stratégies ». Nous avons ensuite confronté ces tendances aux stratégies évoquées dans la littérature. Cette analyse réalisée mériterait d’être approfondie en multipliant le nombre de données et en éclaircissant certains points protocolaires de mesures.

Pourquoi aborder les volumes en commençant par le volume total de l'arbre, peu familier et difficile à appréhender ? Parce qu'il est total, justement : indispensable pour assurer la cohérence des estimations par compartiment (tige, branches, à telle ou telle découpe).Et parce qu'on en a besoin pour les nouveaux enjeux, ceux du carbone par exemple. La méthode est complexe mais le résultat est là : un modèle général, paramétré pour 28 essences avec aussi une formule simplifiée pour des estimations approchées rapides.

This two-part session focused on: 1) ecophysiological studies aiming at understanding the adaptive value of xylem and leaf function, including approaches linking xylem traits such as hydraulic capacitance and parameters of hydraulic vulnerability across climatic gradients; 2) genetic studies aimed at estimating the potential for genetic adaptation to climate change in experimental trials as well as in natural populations; 3) investigating how specific functional traits may be fixed or adaptive within a species and related to climatic distribution more broadly; and 4) dendroecological studies aiming at retrospectively investigating tree responses to climate change. Fifteen oral presentations based on reviews and recent studies of novel and applied research were included in the session related to drought responses and adaptation. These were studied within a number of disciplines: ecophysiology, dendroecology, remote sensing and genetics. Some studies were integrated at the genus level (multi-species studies of eucalypts), genetic level (clone and provenance studies of eucalypts, lodgepole pine and radiata pine) or bioclimatic/environmental level (multisite studies of lodgepole pine and eucalypts). Studies employed drought treatments (piñon pine, juniper, radiata pine, and eucalypts) and inter-annual variation of response to drought by direct and retrospective approaches (oak, eucalypts, Siberian pine and fir). In addition there was one multi-generation study on radiata pine, and age effects were indirectly represented by height gradients of Douglas fir. Physiological studies of response to drought were presented at different levels, including: hydraulic vulnerability of leaf and branch xylem with reference also to carbon depletion and starvation. Several studies discussed interspecific variation in functional drought adaptation by comparing seasonal and controlled (water-exclusion or water-deficit) conditions. There was evidence of common plasticity in seasonal adaptation to declining water potential between eucalyptus species from different climatic zones. Other studies suggested within-species variation for drought-resistance strategies (lodgepole pine). In addition, fast natural selection (micro evolution) was apparent in drought resistance in radiata pine. In ecosystems, genus, and species, evidence of variation in drought resistance strategies were related to different levels and components of hydraulic vulnerability from leaves to xylem, with variable relative weights. These levels also varied with environment: between growing season, between sites, and between fertilization treatments. Reliable proxies or methodological improvement for the measurement of some physiological traits including resistance to cavitation (hydraulic vulnerability or hydraulic capacitance) and stomatal regulation of water potential should be investigated to develop large-scale studies involving many species and replicates and for better comparison of results from independent studies.

Pour satisfaire la consommation croissante de produits chocolatés, de nombreuses initiatives ont été lancées depuis une décennie afin d'augmenter la production de cacao. Ces initiatives continuent de promouvoir le modèle intensif en intrants préconisé depuis les années 1960, alors que ce modèle a atteint ses limites agronomiques, socio-économiques et environnementales. D'où la proposition de s'inspirer de l'agroforesterie pour faire évoluer le modèle actuel : introduire des arbres fruitiers et forestiers dans les cacaoyères contribue à l'intensification agroécologique de la cacaoculture, tout en apportant souplesse et résilience, nécessaires aux petits agriculteurs, qui produisent 95 % du cacao mondial.

Designing Trees for the Future

En zone tropicale humide, la valeur des systèmes agroforestiers pour les agriculteurs est souvent difficile à évaluer. À partir d'un inventaire floristique réalisé dans 14 cacao - yères agroforestières du Centre-Cameroun, l'article propose leur évaluation participative basée sur la méthode de distribution des cailloux mobilisée pour quantifier la valeur accordée par les agriculteurs à chaque espèce en fonction des usages attribués. Au total, 86 espèces ligneuses ont été inventoriées. Les cinq espèces les plus fréquentes ont été le safoutier, Dacryodes edulis, avec 18 % des arbres inventoriés, l'avocatier, Persea americana, avec 11 %, le fraké, Terminalia superba, avec 10 %, le figuier, Ficus mucoso, avec 5 %, et Albizia adianthifolia, avec 3 %. Vingt-deux espèces (26 %) n'ont eu aucun usage pour les agriculteurs qui ont défini sept usages différents pour les autres espèces inventoriées. Parmi ces espèces, la valeur d'usage la plus élevée a été attribuée au cacaoyer (20 %). Ensuite, par ordre décroissant, les cinq espèces qui ont eu les valeurs d'usage les plus élevées ont été l'ayous, Triplochyton scleroxylon, le sapelli, Entandrophragma cylindricum, le safoutier, Dacryodes edulis, le palmier à huile, Elaeis guineensis, et le manguier, Mangifera indica. Le profil d'usage des cacaoyères a montré qu'elles sont principalement pilotées par les agriculteurs pour la vente de produits ligneux et non ligneux, l'autoconsommation de produits non ligneux et de produits médicinaux. Les résultats indiquent que les innovations techniques visant à améliorer les systèmes agroforestiers cacaoyers doivent tenir compte de leur complexité et de leur plurifonctionnalité.

International audience; We propose and study a model for tree-grass interactions in the context of savannas which are subjected to fire pressure. Several theoretical models in the literature which have highlighted the impact of fire on tree-grass interactions did not explicitly deal with the indirect feedback of dry grass biomass onto tree dynamics through fire intensity and frequency. The novelty in our work is to consider a fairly generic modeling of fire impact on woody biomass by means of a family of increasing and bounded functions of grass biomass. The characteristic feature of this family of functions is that, it could include several forms: linear as well as non-linear ones (sigmoidal or not). Since the nonlinear shape brings more diverse results than the previous attempts using a linear function, it could be used to show that several vegetation equilibria exist with some of them showing tree-grass coexistence features.We show that the number of equilibria with both grass and trees depends on the choice of the fire impact function. We also established thresholds defining the stability domains of the equilibria and highlighted some bifurcation parameters to provide numerical simulations complying with the theoretical properties of the model.

Increasingly severe droughts are expected to negatively impact forest functioning in the future, especially in the Mediterranean region. Favoring mixed species stands has been advocated as a compromise between wood production and biodiversity conservation, but whether such management practices would allow forest ecosystems to acclimate to future climate conditions remains to be addressed. We tested whether the transpiration of Quercus cerris (Qc) and Quercus petraea (Qp) during droughts differ when they grow in pure or mixed forests. We measured sap flux density ( F D ) and leaf carbon isotope composition ( δ 13 C), as a proxy for intrinsic water use efficiency ( WUE int ), in pure and mixed Qc and/or Qp forest plots in Italy during the summer 2012. Qc and Qp showed a drop in F D of 41% and 52% respectively during the summer drought independently of the mixtures, but with different seasonal trends. Qp transpiration response to soil drought did not differ between pure and mixed plots. In contrast, Qc transpiration was reduced by 56% in mixed plots at the maximum of the drought and only by 31% in the pure plot. Furthermore, we observed higher WUE int for Qc in the mixed plot and no change for Qp, supporting the higher water stress intensity in the mixed plot for Qc. Our study illustrated the negative impact of Qp on Qc when these species compete for water resources. We suggest that managing for mixed stands in the Mediterranean region might, in some cases, increase the detrimental effect of drought on species functioning.

National audience; Global climate change is a challenge for the conservation of natural resources. Shifts in rainfall patterns and increasing temperature may push several forest tree species over the limits of their adaptation capacity.

Les chiroptères sont reconnus comme de potentiels régulateurs des populations d’insectes. Ce sont aussi les mammifères européens pour lesquels les enjeux de conservation sont les plus importants. Ils trouvent dans les forêts des habitats favorables qui sont cependant menacés par les changements climatiques et la fragmentation. Il convient donc de mieux comprendre lesrelations entre les communautés de chiroptères, leurs habitats et leurs proies en forêt. L'objectif de cette thèse est de quantifier les effets, à différentes échelles spatiales, desprincipales composantes de l’habitat forestier sur l’activité, la richesse spécifique, la diversité fonctionnelle et la composition des communautés de chiroptères européens. Les résultats reposent sur des données collectées grâce à des protocoles expérimentaux en Aquitaine et dans les six pays du réseau de placettes forestières organisé par le projet FunDivEurope. De la parcelle au continent, l'accroissement de la diversité des essences forestières, de la proportion de feuillus et du bois mort, en augmentant les ressources en proies et en gîtes, ont des effets positifs sur les communautés de chiroptères. Ces effets, non stationnaires, se renforcent vers le nord avec la rigueur du climat. Nous confirmons également que les chiroptères forestiers, par leur réponse numérique et fonctionnelle aux densités de proie, peuvent limiter la démographie d’un insecte défoliateur. Des mesures de gestion, visant le renforcement des structures-clés des habitats forestiers, sont proposées pour favoriser la conservation des communautés de chiroptères et leur capacité de régulation des insectes ravageurs., Insectivorous bats are increasingly recognized as potential regulators of pest insect populations.They also represent the group of European mammals with the most unfavorable conservation status. Forests are key habitats for many bat species but are currently under threat from climate change and fragmentation. It is therefore urgent to better understand the relationships between the bats, their prey and their habitats in forests. Our main objective was to quantify the effects, at multiple spatial scales, of the main attributes of forest habitats on the activity, species richness, functional diversity and composition of European bat communities. They were studied using manipulative experiments in Aquitaine plantation forests and automatic recordings in the network of exploratory plots set up in six European countries by the FunDivEurope project. From the plot to the continent scale, increasing tree diversity, amount of broad leaved trees and dead wood, had positive effects on bat communities through an increase in prey and roost resources. However these effects were not stationary, being stronger at higher latitudes, probably due to lower habitat carrying capacity in relation to harsher climatic conditions. In addition we experimentally demonstrated that the numerical and functional responses of bats to prey density could result in effective regulation of pine processionary moth populations. Forest management strategies aim at enhancing key habitat structures, are eventually proposed in order to improve the conservation of bats and to increase the service of pest regulation they can provide.

International audience

National audience

International audience; Aim: Successional and soil filtering processes are key drivers of the assembly of tropical tree communities, yet little is known about how they interact. Herein, we determine whether successional pathways depend on soil type, how the soil filtering effect varies during forest succession and whether succession is accompanied by changes in trait composition.Location: South-western Central African Republic.Methods: We used inventory data on 90 dominant tree species (72% of the stems ≥ 30 cm d.b.h.) in 15,420 plots (each 0.5 ha) distributed over an 8300-km2 mosaic of primary and secondary forests on contrasting clay and sandy soils. We gathered data on six traits: dispersal mode, nitrogen fixation, deciduousness, leaf area, wood density and maximum diameter. After validation with historical information, we used a successional index based on pioneer proportion to assess variations in trait composition, and in α- and β-diversity, in forest succession, and within and between soil types.Results: Taxonomic and functional dissimilarities between clay and sandy soils decreased continuously during forest succession. Within soil types, early-successional communities had a low taxonomic but relatively high functional α-diversity. At the landscape scale, β-diversity was higher among earlier successional stages, except in rich soils where taxonomic β-diversity was high throughout the succession. Mean values for all traits, except leaf area, showed marked variations during forest succession in both soil types.Main conclusions: The effect of soil type on community composition declines during succession, suggesting that the relative importance of neutral processes is higher in mature forests. Successional pathways were fairly similar in both soil types: disturbances reduced taxonomic diversity locally and enhanced β-diversity between sites, probably because the disturbances varied in type. We also demonstrated how easy-to-collect traits help improve predictions of ecological patterns and deepen our understanding of species assembly processes.

International audience; Trees are one of the main components of forest ecosystems; they modify resource levels (light, nutrients, water) that affect understory vegetation composition and diversity. Tree species diversity is used as a biodiversity indicator in various European and French monitoring schemes for sustainable forest management. Moreover, tree species basal area has been found to better indicate floristic biodiversity than tree species richness or diversity. Herein we empirically check this finding by analyzing data from mountain spruce-fir forests in France with Bayesian statistical models. We insist on the magnitude of the relationship and its variation in geographical and ecological space. Our results indicate that both tree species abundance (based on cover or basal area) and tree species richness and dominance are good indicators of some parts of understory vascular plant species richness. The effect of dendrometric indicators on floristic biodiversity varied among ecological groups and along ecological gradients such as aspect, soil acidity, region and altitude. As a result, plots with north-facing and south-facing slopes exhibited opposite relationships of species richness with tree species abundance, and so did plots located on acidic and basic sites. We discuss these results in light of other empirical results relating positive interactions between species and abiotic stress. Our study supports evaluating biodiversity indicators to determine when they actually have non-negligible relationships with biodiversity, i.e. for which ecological groups and in which ecological contexts.

International audience; Climate models predict significant rainfall reduction in Amazonia, reducing water availability for trees. We present how functional traits modulate the tree growth response to climate. We used data from 3 years of bimestrial growth measurements for 204 trees of 53 species in the forest of Paracou, French Guiana. We integrated climate variables from an eddy covariance tower and functional trait values describing life history, leaf, and stem economics. Our results indicated that the measured functional traits are to some extent linked to the response of trees to climate but they are poor predictors of the tree climate-induced growth variation. Tree growth was affected by water availability for most of the species with different species growth strategies in drought conditions. These strategies were linked to some functional traits, especially maximum height and wood density. These results suggest that (i) trees seem adapted to the dry season at Paracou but they show different growth responses to drought, (ii) drought response is linked to growth strategy and is partly explained by functional traits, and (iii) the limited part of the variation of tree growth explained by functional traits may be a strong limiting factor for the prediction of tree growth response to climate.

The development of a given species in a natural forest depends on a multitude of factors. Insects are one of the factors that have an important impact. We would like to present initial observations about the behaviour of longicorns of the Onciderini tribe and their impact on the development of Dicorynia guianensis.A study of the development of D. guianensis was conducted in French Guiana (5°18'N, 5°48'W), at the Paracou silvicultural facility. We studied plots where the Dicorynia inventory was extended to trees 1 m tall or over. In order to describe the impact of longicorn activity on a Dicorynia stand in which spatial distribution is aggregative (Kokou 1992), we chose trees (156 observed trees) in a control plot (plot 11, area: 17 500 m2). Height, trunk basal diameter and DBH were measured on each tree. A precise morphological description was established for each tree. It was during morphological description that the signs of longicorn attacks were sought. In all the species of the genus Oncideres, the female girdles the tree by removing the bark and some of the wood using its mandibles. It then digs deep into the wood above the cut and lays its eggs. The branch then breaks and falls to the ground (Hequet 1996). All that is left on the tree is a stump with characteristic signs of insect activity (Figure 1a). When such signs were seen on a plant, the type of structure (trunk, branch) was noted.

Afin de pallier le manque de simulateurs adaptés à la sylviculture locale et intense du hêtre (détourage d'arbres d'avenir), nous avons construit un modèle d'arbre à partir d'hypothèses écophysiologiques. Ce modèle linéaire relie la croissance de la tige à la taille du houppier. Le rapport de proportionnalité est nommé rendement du houppier. Ce paramètre macroscopique peut être obtenu comme combinaison de quelques paramètres écophysiologiques élémentaires (rendement photosynthétique, coefficient d'allocation à la tige, coefficients de respiration etc.). La simplicité du modèle permet d'analyser les variations du rendement du houppier dans un essai sylvicole. On montre à cette occasion que : - l'éclaircie entraîne un effet direct d'augmentation du rendement du houppier ; - la refermeture du couvert et les fluctuations climatiques entraînent d'importantes différences de rendement entre périodes successives ; - pour montrer un effet de l'âge, la structure mathématique du modèle doit être améliorée, notamment par une description plus fidèle de la respiration d'entretien et de la géométrie des cernes annuels, In order to design a simulator of local, intensive silviculture to the benefit of future crop trees in Common Beech, an individual-tree growth model was built using ecophysiological assumptions. This linear model links stem growth and crown size. The proportionality factor is named crown efficiency. This macroscopic parameter may be obtained as a combination of several elementary ecophysiological parameters (photosynthetic efficiency, allocation coefficient to stem, respiration coefficients etc.). The simple structure of the model allows the analysis of crown efficiency variations in a thinning trial. We show that: - thinning directly increase crown efficiency; - canopy closure and climatic fluctuations lead to large differences of crown efficiency between successive periods; - in order to show an effect of age, the mathematical structure of the model should be improved, e.g. by a better account of maintenance respiration and geometry of the annual ring.

Since 1984, the diameter increment of nearly 50 000 trees ⩾10 cm DBH has been monitored every year in 12 long-term experimental 6.25 ha plots of the Paracou experimental station, French Guiana. In order to study and compare forest dynamics in disturbed and undisturbed stands, contrasted silvicultural treatments were performed between 1986 and 1988 in these plots. Taking advantage of this experimental design and of this large database, a forest dynamics modelling project was started in 1992. This paper aims at presenting the growth component of the single-tree, distance-dependent model that was developed within the framework of this project. This individual diameter growth model was built according to the ‘potential × modifier’ paradigm: it links tree annual diameter increment to variables describing tree size and instantaneous competition as well as the recent past evolution of the competition. Species information was also taken into account and resulted: (i) in the classification of tree species into 15 functional groups that are homogeneous for diameter growth; and (ii) in a definite improvement of model efficiency. Attempts to further reduce the residual variance through the use of soil and topographical information remained unsuccessful.

International audience; This paper summarises the main characteristics of a new functional-structural ecophysiological model EMILION elaborated for pine species. It is based on the integration of the functioning of the tree aerial organs, shoots, buds and cones. It is founded on the modelling of carbon- and water- related processes at the organ level, and on the links that exist between the organs. The main processes described by EMILION are light distribution and interception, photosynthesis, respiration, stomatal conductance, transpiration, water transfer, phenology, and intra-annual growth. It uses an object-oriented approach. It has been parameterised and applied to adult Maritime pine (Pinus pinaster Ait.). The model simulates the distribution in the tree of carbon and water fluxes at a short time step. The principal inputs are stand and tree structure, and meteorological data. EMILION allows one to study the interaction of processes at the organ and tree level. An example application is presented, in which EMILION was used to simulate the carbon budget of existing branches, according to their age and location within the crown. This study was used to test one hypothesis of branch death, that death is a consequence of an imbalance between branch assimilate production and use. Our results show that the old branches of Pinus pinaster are autonomous for the carbon, but the ability of these branches to supply assimilates to rest of the tree appears very low. We conclude that this small carbon availability in the oldest branches is a cause of their limited development.; Principes du modèle structure-fonction Emilion et application à l'analyse de l'autonomie carbonée des branches dans le houppier. Un nouveau modèle écophysiologique EMILION de type structure-fonction est présenté. Ce modèle élaboré pour les espèces du genre Pinus, est basé sur l'intégration des connaissances relatives au fonctionnement des organes formant l'arbre, il est actuellement adapté au cas du Pin maritime (Pinus pinaster Ait.) adulte. Il s'appuie sur la modélisation des processus carbonés et hydriques à l'échelle de l'organe et sur les relations qu'établissent entre eux les organes qui sont liés. Différents types d'organes aériens sont distingués, les rameaux, les bourgeons et les cônes. Les principaux processus intégrés dans le fonctionnement des organes sont la distribution et l'interception du rayonnement, la photosynthèse, la respiration, la conductance stomatique, la transpiration, les transferts hydriques xylémiens, la phénologie et la croissance intra annuelle. Dans le modèle, chaque organe est représenté par un objet, et un arbre ou une branche par un objet Structure. Le modèle simule les flux de carbone et d'eau au sein de l'arbre à un pas de temps demi-horaire. EMILION permet d'étudier l'interaction des différents processus au sein des organes et au sein de l'arbre. Les entrées du modèle sont la structure du peuplement et de l'arbre modélisé, ainsi que les conditions climatiques. Une utilisation du modèle est présentée. EMILION est utilisé pour simuler, en fonction de leur âge et de leur position dans l'arbre, le bilan de carbone de branches réelles, afin d'analyser les hypothèses expliquant la mort des branches âgées, basées sur un déséquilibre entre production et consommation d'assimilats. Nos résultats montrent que les vieilles branches sont autonomes vis-à-vis du carbone, mais que la quantité d'assimilats quelles sont en mesure de fournir au reste de l'arbre devient relativement faible. Finalement nous supposons que cette faible disponibilité des assimilats, au sein des vieilles branches en peuplement, participe à la limitation de leur développement.

1for correspondence) Summary The effects of poplar varietal mixture on infection levels caused by Melampsora larici-populina and on plant growth were studied during two consecutive growing seasons. The varietal mixture consisted of an intimate mixture of three poplar clones, Populus x interamericana ‘Boelare’, ‘Rap’ and Populus candicans ‘NNT’, expressing different race-specific resistances. Infection levels of M. larici-populina were assessed in monoclonal and polyclonal plots. Plant heights were determined at the end of each growing season. Infection levels in the growing season of the first year were not significantly different between monoclonal and polyclonal plots at the end of the epidemic. During the second growing season, a naturally occurring complex pathotype, able to infect clones ‘Boelare’ and ‘Rap’, invaded some plots prematurely and changed the composition of pathogen population. During this season, four infection assessments were conducted. Infection reduction in polyclonal plots compared with monoclonal plots was observed on ‘Boelare’ and P. candicans plants. Nevertheless, no significant difference was observed for growth between monoclonal and polyclonal plots. Biological factors which may be involved in the reduction of infection levels in polyclonal plots are dilution of susceptible individuals, physical barriers caused by resistant plants and cross-protection. A high auto-infection ratio may have partly hidden the positive effects of the clonal mixture.

Les techniques de levee de dormance des faines (Fagus sylvatica) ont ete grandement ameliorees au cours des vingt dernieres annees. Un progres majeur a resulte de l'introduction d'une technique de pretraitement apres rehydratation des semences a un niveau de teneur en eau (TE) controle (28-30 %). De plus, ceci a ouvert la voie a la conservation a long terme des faines dans un etat non-dormant. Notre etude visait a : i) optimiser les conditions du pretraitement : TE des faines variant entre 28 et 34 % et durees variant entre X et X+6 (ou X represente le nombre de semaines permettant la germination de 10 % des faines viables, en condition de stratification dans un milieu humide a 3 °C) ; ii) suivre pendant trois annees de conservation l'evolution de la faculte germinative des faines ainsi pretraitees. Des tests de germination ont ete effectues juste apres le pretraitement, apres pretraitement et sechage a TE 8 %, et apres pretraitement, sechage et conservation. Le meilleur maintien de la faculte germinative est obtenu a la suite d'un pretraitement a TE 30 % pendant X+2 semaines. Le sechage occasionne une baisse de faculte germinative lorsque le pretraitement a ete effectue a TE 34 % et pour la duree la plus longue (X+6). Lorsque le pretraitement est applique apres conservation, les meilleurs resultats sont obtenus a TE 32 %.

International audience; Nutrient fluxes were determined in a chronosequence of Douglas-fir stands in the Beaujolais Mounts (France). Annual and seasonal variations occurred during the 3 years of investigation; fluxes were generally highest in autumn-winter. Atmospheric inputs were among the mean values from a monitoring network of forest ecosystems in France. Nutrient outputs from the soil profile were higher than average and occurred mainly during vegetation dormancy. Mean input-output budgets were negative for N, S, K, Ca and Mg, characterising an imbalance of the site chemistry dynamics. The P budget was positive. Most of the nutrient output from the ecosystem occurred as losses in the drainage water. These losses were related to excess nitrification and consecutive cation mobilisation throughout the soil profile. Surface water, however, had a neutral pH and very low nitrate and aluminium contents, which may have been buffered by the subsoil. Budgets differed between stands and tended to be more negative in the youngest stand. Part of this behaviour was related to stand age and part to the former land use of plots. Theoretical budgets were calculated for forest rotation lengths of 20, 40 and 60 years; it was concluded that shorter rotations would increase nutrient losses. The trend of a decrease in budget deficits with stand age suggests that the effect of vegetation change will be reduced at the next rotation but the impact of stand development may remain. Predicted nutrient budgets for a second 60 year Douglas-fir rotation suggested that available Ca in the soil would be depleted and that this depletion would be even more drastic if whole tree harvesting were adopted. In conclusion, Douglas-fir stands introduced changes in soil function that may impoverish the soil if present trends remain the same over the next forest rotations. The maintenance of sustainability will require nutrient input by fertilisation.

We have developed an efficient transformation system for the tropical actinorhizal tree #Allocasuarina verticillata$ using #Agrobacterium tumefaciens$ mediated gene transfer. Mature zygotic embryos were inoculated with the disarmed strain C58C1 carrying, in the binary vector BIN19, the nptll gene, providing kanamycin resistance as a selectable marker, and the reporter gene beta-glucuronidase containing an intron. The transformed embryos were cultivated on nutrient medium supplemented with 0,5 microM NAA, 2,5 microM BA, 100 mg/l kanamycin and 250 mg/l cefotaxime. After 2 months, a 21% transformation frequency was obtained. Within 6-9 months, transgenic plants were recovered from 70% of the transformed calli. The presence of the trangenes was demonstrated by PCR analysis and by the expression of the beta-glucuronidase; integration of the T-DNA was confirmed by Southern hybridization. More than 100 transgenic plants from a total of 23 independent events have been successfully established in soil. The possibility to obtain nitrogen-fixing nodules after inoculation of transgenic #A. verticillata$ plants by the actinomycetal strain of Frankia Allo2 was established. (Résumé d'auteur)