Search

In tropical forest, landscape fragmentation and the consequent degradation of disturbed forests increase the incidence of light and dry hot winds, causing a disturbance on natural regeneration. Under these conditions, lianas (woody vines) development is stimulated instead of other species, which are more suited to mature forest and under less influence of the edge effect. For this, lianas colonization is an important variable for assessing the disturbance level of a forest. In this context, it becomes important to understand the nature of the competitive relationships between hyper-abundant lianas and ring growth of the host trees. Here, we selected trees with occupation or absence of lianas from two tropical species – Pinus caribaea var. hondurensis (Caribbean pine) and Tectona grandis (teak) – localized in a semideciduous forest fragment in southeastern Brazil, aiming to compare growth, climatic response, anatomy (vessels and intra-annual density fluctuations), wood density and carbon, by tree-ring analysis. The results showed that the lianas caused a change in tree-ring anatomy of host trees in last 10 years, mainly. We observed that trees occupied by lianas had a decrease the radial growth and carbon in the two species, an increase of the vessels size in teak and a decrease of the IADF frequency in Caribbean pine. In teak, the climate-tree relationship indicated that trees with lianas had lower response to rainfall and higher response to temperature in the summer (rainy and hottest period); in Caribbean pine, we observed that trees with lianas had a 2-month delay in the radial growth response to rainfall in the dry season. In the teak group, we observed that host trees had higher wood density values than liana-free tree in the outer rings, and the opposite was showed for pine. These findings show that tree-ring growth of host trees are a strong bioindicator of forest disturbance caused by aggressive colonization of lianas. We believe that these methods are applicable to future studies relating to the effects of habitat fragmentation and forest degradation on biodiversity and ecosystem services, particularly in the context of global climate change. (Resume d'auteur)

Average wood density of 38-year-old Cariniana legalis (Mart.) Kuntze, a Brazilian native forest species, was found to increase with faster growth and lower stocking, while decreasing from pith to bark. A complete randomised block design was planted with five blocks. Ten trees were harvested in each of three spacing treatments. We hypothesised that the stand stemwood production would not significantly differ depending on tree spacing. However, tree growth would be higher in the wider spacing and wood density would be higher in the narrower spacing. The diameter growth of trees was higher at 3 m × 2.5 m than at 3 m × 2 m and 3 m × 1.5 m. Nevertheless, this higher individual tree growth at 3 m × 2.5 m did not compensate for the greater tree stock density at 3 m × 1.5 m with stand stemwood production at 38 years of 530 m3 ha−1 and 649 m3 ha−1, respectively. These results suggest that C. legalis, which can produce up to 17 m3 ha−1 y−1 of medium- to high-density timber – about 800 kg m−3 – is a promising native species for forest plantations in Brazil.Keywords: Brazilian native wood, management of tropical timber, X -ray densitometry

Climatic conditions stimulates the cambial activity of plants, and cause significant changes in trunk diameter growth and wood characteristics. The objective of this study was to evaluate the influence of climate variables in the diameter growth rate of the stem and the wood density of Eucalyptus grandis trees in different classes of the basal area. A total of 25 Eucalyptus trees at 22 months of age were selected according to the basal area distribution. Dendrometer bands were installed at the height of 1.30 meters (DBH) to monitor the diameter growth every 14 days, for 26 months. After measuring growth, the trees were felled and wood discs were removed at the DBH level to determine the radial density profile through x-ray microdensitometry and then re-scale the average values every 14 days. Climatic variables for the monitoring period were obtained and grouped every 14 days. The effect of the climate variables was determined by maximum and minimum growth periods in assessing trunk growth. These growth periods were related with precipitation, average temperature and relative air humidity. The re-scaled wood density values, calculated using the radial growth of the tree trunks measured accurately with steel dendrometers, enabled the determination of the relationship of small changes in wood density and the effect of the climatic variations and growth rate of eucalyptus tree trunks. A high sensitivity of the wood density to variation in precipitation levels was found. RESUMO Os estímulos provocados na atividade cambial das plantas pelas condições climáticas promovem significativas alterações no incremento em diâmetro do tronco e nas características do lenho. O objetivo deste trabalho foi avaliar a influência das variáveis climáticas na taxa de crescimento em diâmetro do tronco e na densidade do lenho de árvores de Eucalypttis grandis em diferentes classes de área basal. Foram selecionadas 25 árvores de eucalipto, de acordo com a distribuição de área basal, com 22 meses de idade onde foram instaladas faixas dendrométricas a 1,30 metros (DAP) para o monitoramento do incremento em diâmetro do tronco a cada 14 dias, em um período de 26 meses. Após o período de medição do incremento, as árvores foram derrubadas e retirados discos de lenho no DAP para a determinação dos perfis radiais de densidade aparente por microdensitometria de raios x e posterior re-escala dos valores médios a cada 14 dias. Variáveis climáticas referentes ao período de monitoramento foram obtidas e agrupadas a cada 14 dias. Na avaliação do incremento do tronco o efeito das variáveis climáticas foi determinado pela ocorrência de períodos de máximo e mínimo crescimento, estando relacionados com a precipitação, temperatura média e umidade relativa do ar. A re-escala dos valores de densidade do lenho, aplicando-se o crescimento radial do tronco das árvores mensurado com precisão com dendrômetros de aço, permitiu determinar a relação das pequenas mudanças de densidade do lenho e o efeito das variações climáticas e da taxa de incremento do tronco das árvores de eucalipto, constatando-se uma alta sensibilidade da densidade do lenho em relação a variação dos níveis de precipitação.

1. Estimating forest above-ground biomass (AGB), or carbon (AGC), in tropical forests has become a major concern for scientists and stakeholders. However, AGB assessment procedures are not fully standardized and even more importantly the uncertainty associated with AGB estimates is seldom assessed. 2. Here, we present an R package designed to compute both AGB/AGC estimate and its associated uncertainty from forest plot datasets, using a Bayesian inference procedure. The package builds upon previous work on pantropical and regional biomass allometric equations and published datasets by default but it can also integrate unpublished or complementary datasets in many steps. 3. BIOMASS performs a number of standard tasks on input forest tree inventories: i) tree species identification, if available, is automatically corrected; ii) wood density is estimated from tree species identity; iii) if height data are available, a local height-diameter allometry may be built; else height is inferred from pantropical or regional models; iv) finally, AGB/AGC are estimated by propagating the errors associated with all the calculation steps up to the final estimate. R code is given in the paper and in the appendix for illustration purpose. 4. The BIOMASS package should contribute to improved standards for AGB calculation for tropical forest stands, and will encourage users to report the uncertainties associated with stand-level AGB/AGC estimates in future studies.

International audience; Phenotypic traits and their associated trade-offs have been shown to have globally consistent effects on individual plant physiological functions1, 2, 3, but how these effects scale up to influence competition, a key driver of community assembly in terrestrial vegetation, has remained unclear4. Here we use growth data from more than 3 million trees in over 140,000 plots across the world to show how three key functional traits-wood density, specific leaf area and maximum height-consistently influence competitive interactions. Fast maximum growth of a species was correlated negatively with its wood density in all biomes, and positively with its specific leaf area in most biomes. Low wood density was also correlated with a low ability to tolerate competition and a low competitive effect on neighbours, while high specific leaf area was correlated with a low competitive effect. Thus, traits generate trade-offs between performance with competition versus performance without competition, a fundamental ingredient in the classical hypothesis that the coexistence of plant species is enabled via differentiation in their successional strategies5. Competition within species was stronger than between species, but an increase in trait dissimilarity between species had little influence in weakening competition. No benefit of dissimilarity was detected for specific leaf area or wood density, and only a weak benefit for maximum height. Our trait-based approach to modelling competition makes generalization possible across the forest ecosystems of the world and their highly diverse species composition.

In the context of sustainable development which has seen the introduction of the biocides directive BPD 98/8/CE in the EU, innovative wood preservation practices such as Heat Treatment (HT) become relevant. Wood HT, also termed wood thermal modification, is a physical modification technology by which wood is heated at around 200 °C in an inert atmosphere. The main purpose of the treatment is to improve the biological durability and dimensional stability of wood. Current studies on thermally modified wood (TMW) quality are focusing on treated material, on treatment conditions or on species effect on the end-product characteristics. Relatively little is known about the effect of intrinsic wood properties on its thermal modification. As wood properties vary especially under the influence of human activities through sylviculture, this thesis studied the effect of European oak and silver fir wood density and chemical composition on their thermal modification kinetic. An X rays computed tomography (CT) and densitometer were used to characterize wood samples. Boards were heat-treated by conduction under vacuum using a pilot furnace, whereas sawdust samples underwent thermo-gravimetric analysis under nitrogen. The analysis allowed finding intra- and interspecific variations, especially within growth rings and along radial direction (from pith to bark). Forest management impacted heat modification kinetic of the studied samples, especially in silver fir where fast grown wood was more sensitive to treatment. The finding will be used as additional information to the wood industry which will account for homogeneity of loadings destined to heat treatment, Dans le contexte du développement durable qui a vu l’introduction de la directive produits biocides BPD 98/8/CE, l’étude des méthodes innovantes de préservation du bois comme le traitement thermique revêt une importance prépondérante. Le traitement thermique du bois permet d’améliorer ses propriétés de résistance biologique, de stabilité dimensionnelle ainsi que son aspect esthétique, sans ajout de produit chimique. Les études actuelles sur la problématique de la qualité du bois traité thermiquement se focalisent sur les caractéristiques finales du bois déjà traité, l’influence des conditions de traitement ou encore l’effet essence. Les propriétés intrinsèques du bois avant le traitement ne sont pas encore prises en compte. Les propriétés du bois telles que la densité ou la composition chimique étant variables principalement sous l’effet de l’activité humaine comme la sylviculture, l’objectif de cette thèse était d’évaluer l’impact de cette variabilité chez le chêne sessile (Quercus petraea Liebll.) et le sapin (Abies alba Mill) sur leur modification par voie thermique. Un scanner et un micro-densitomètre à rayons X ont été utilisés pour caractériser la variation de la densité des échantillons de planches et des cernes de croissance provenant des arbres étudiés. Des traitements thermiques ont été réalisés dans un four pilote à conduction sous vide de type macro-thermobalance et un analyseur thermogravimétrique (ATG). Des analyses chimiques ont été également réalisées. Les résultats montrent qu’en prenant la perte de masse due à la dégradation thermique du bois comme réponse, les types de tissus du bois et la composition chimique influencent sa thermo-dégradation. Que ce soit chez Quercus petraea ou chez Abies alba, le bois de printemps était plus sensible au traitement thermique que son voisin de bois d’été. De plus, les portions radiales du tronc, du bois juvénile à l’aubier en passant par le bois mature, se dégradaient suivant des cinétiques différentes. En conclusion, la variation de la microstructure et la composition chimique de ces bois influencent leur cinétique globale de thermo-dégradation. La sylviculture impacte cette différence intraspécifique de cinétique de dégradation à l’échelle intra- et interarbre. En effet, dans le cas du sapin pectiné, une gestion très dynamique des forêts dans le but de stimuler la croissance rapide des arbres qui produisent de gros bois contenant des cernes très larges, est source de variation dans la structure anatomique et la composition chimique à l’intérieur des arbres en comparaison aux petits bois à croissance lente plus homogènes. Toutes ces analyses ont pour objectif final de comprendre le lien entre les propriétés initiales du bois et les modifications thermiques intervenant au cours du traitement afin d’apporter une information utile aux industriels lors du choix des pièces de bois destinées au traitement thermique en vue d’une amélioration de la qualité du bois traité thermiquement

Few studies have investigated the influence of environmental conditions on the within-tree variation in Eucalyptus wood traits. The genotype and environment effects and their interactions influence the wood properties. Their evaluations are crucial to estimate the genotype values and to select with efficiency. Thus, the aim of this study was to better understand the effect of ground slope and wind speed on the spatial variation of basic density (ρ), stiffness (MOE) and microfibril angle (MFA) of Eucalyptus wood. Wood discs cut along the trunk were sampled from one-hundred fifty 6-year-old Eucalyptus grandis × E. urophylla hybrids growing in three contrasting growing conditions influenced by ground slope and wind regime. Near infrared (NIR) calibrations previously developed for ρ, MOE and MFA were used to predict in our discs. 2-D plots presenting the spatial variation of predicted wood traits were compared. The higher the ground slope, the greater the magnitude of radial variation in ρ, principally in the medium zone of the trunk. The spatial variation of wood stiffness seems to be sensitive to two environmental conditions. The MFA radial decreases were more pronounced where the wind speed was higher. At the base and top of the trees, however, there was no significant effect of growing conditions on the radial variation of the wood properties considered here.

Classifying species into functional groups is a way to understand the functioning of species-rich ecosystems, or to model the dynamics of such ecosystems. Many statistical techniques have been defined to classify species into groups, and a question is whether different techniques bring consistent classifications. In a tropical rain forest in French Guiana, five species classifications have been defined by different authors for the purpose of forest growth modelling but using different data sets and different statistical techniques. The correspondence between the five classifications was measured using four indices that are generalizations of existing indices to compare two classifications. A multiple correspondence analysis was used to identify associations between groups of different classifications. In a second step, two-table multivariate analyses were used to characterize the relationships between species classifications and eight species traits (consisting of seven populational traits and one functional trait). We evidenced a consensus on the potential size of trees: species were similarly clustered by the five classifications along this trait that is correlated to turnover rate. More surprisingly, no consensus was found for growth rate, nor wood density, traits that are correlated with light requirement.

Wood is a multifunctional tissue involved in sap conduction, storage of water and reserves as well as mechanical support. Tree during its development experiments various constraints due to its environment and its growing size. In response to these constraints, wood functional performances are adjusted by variations of property values, which are dependent on the xylogenesis product. However, wood properties may be modified by the deposition of chemical extractives during heartwood formation. Thus heartwood properties are the result of xylogenesis, heartwood formation and their interactions. This work gave rise to the term 'wood profile', designating all variations of wood properties at different scales and in an ontogenetic dimension, resulting from both processes described above. The diversity of shade tolerance (heliophilic to sciaphilic) strategies species suggests a diversity of wood profile expressions. The description of these different expressions could be a way to better understand plant strategies. Understanding and characterizing wood profile and variations in heartwood quantity in tree, is an economical issue since the Guyanese timber industry has been identified as a promising sector. The analysis of the diversity of wood profile—using a bottom-up approach, from the individual level to the interspecific level—proves to discriminate shade tolerance strategies efficiently. Wood specific gravity variation is especially relevant. However, its relevance is based on (1) combinations of both radial and vertical variations and (2) integration of heartwood that may impact range and direction of the gradient and shape of the profile as well. Effect of heartwood formation on wood specific gravity variations is suggestive of shade tolerance strategy as well as quality and/or quantity of chemical extractives. Relevant characterization of shade tolerance strategies by wood profile is the result of the integration of diverse processes and properties. To the view of growth allocation shift (from trunk to crown) observed in Dicorynia guianensis and of previous studies on tree growth, a potential link between wood profile diversity and growth allocation strategies may exist.; Le bois est un tissu plurifonctionnel permettant la conduction de la sève brute, le stockage de l’eau et des sucres ainsi que le soutien mécanique de la plante. L’arbre au cours de son développement expérimente différentes contraintes liées à son environnement et à sa taille croissante. En réponse à ces contraintes, les performances fonctionnelles du bois sont ajustées par des variations de valeurs de propriétés, elles-mêmes dépendantes du produit de la xylogénèse. Cependant les extrais chimiques déposés lors du processus de duraminisation, entraine la modification des propriétés du bois. Les propriétés du duramen sont le fruit de la xylognénése et de la duraminisation ainsi que de leurs interactions. Ce travail de thèse a donné naissance au terme ‘profil ligneux’, désignant l’ensemble des variations des propriétés du bois à différentes échelles et dans une dimension ontogénique résultant des deux processus cités précédemment. La diversité de tempéraments vis-à-vis de la lumière (héliophilie à sciaphilie) des essences tropicales suggère une diversité d’expressions du profil ligneux.La description de ces différentes expressions serait gage d’une meilleure compréhension du tempérament.Comprendre et caractériser le profil ligneux et la variation de la quantité de bois de coeur dans l’arbre, représentent également un enjeu économique puisque l’industrie du bois Guyanaise a été identifiée comme une filière d’avenir. L’analyse de la diversité du profil ligneux—par une approche ascendante, de l’échelle individuelle à l’échelle interspécifique—a prouvé son efficacité dans la discrimination du degré d’affinité à la lumière. La variation de densité est particuliérment pertinente. Néanmoins, sa pertinence réside dans (1) la combinaison du gradient radial et vertical et (2) la prise en compte du duramen qui modifie parfois, l’amplitude et la direction du gradient ainsi que la forme du profil. L’effet de la duraminisation sur la variation de densité devient alors évocateur du tempérament de l’espèce au même titre que la qualité et/ou la quantité d’extraits chimiques mis en jeu. La pertinence du profil ligneux dans la caractérisation du tempérament écologique est due à son aspect intégrateur de divers processus et propriétés. En regard du changement de l’allocation de croissance (i.e. du tronc vers la couronne) observé chez Dicorynia guianensis et de travaux précédents sur la croissance des arbres, un lien potentiel entre la diversité du profil ligneux et la stratégie d’allocation de la croissance pourrait exister.

National audience

International audience

Etude de la densité en poissons et du débit d'eau sur l'expression des gènes hépatiques et musculaires chez le saumon atlantique

International audience; AbstractKey messageA retrospective architectural analysis performed on planted teaks in Togo showed that the variation of wood radial properties were linked with tree ontogeny, and that these relationships depended on thinning practices and provenance.ContextVariability in growth, flowering and forking in individual trees according to origin and/or thinning practices may affect wood structure and consequently impact wood physical properties. We tested this hypothesis in teak.AimsWe sought evidence of: (1) origin effects (Togolese versus Tanzanian teak) on growth, flowering, cambial growth and wood properties; (2) thinning effects on these variables and (3) relationships between tree ontogeny and radial variations of wood properties.MethodsA retrospective architectural analysis was used to draw stem growth and near infrared spectroscopy to assess radial variations of wood properties.ResultsFlowering reflects tree vigour and began at an earlier age in Togolese than in Tanzanian provenances. No differences were detected in regards to growth ring surface area, basic density and modulus of elasticity. Both systematic and selective thinnings improved growth without impacting the two latter properties. Stabilization of the growth ring area observed at 4 years old was associated with a decline in stem annual extension with a 1-year time lag.ConclusionsArchitectural analyses showed that radial growth was linked with tree ontogeny. This method can be extended to subsequent developmental stages, i.e. to older trees with economic interest, and used to determine architectural traits that are useful in tree selection.

The increasing number of model types that are used to predict tree biomass from diameter, height and wood density has brought questioning about the biological relevance of complex allometries (i.e. non-power models). Statistical issues such as collinearity among predictors and unreliable coefficient estimates have also been associated with complex allometric models. Using a data set of 225 trees from central Africa, we assessed the relevance of simple allometry (i.e. power model) versus complex allometry to predict tree biomass. A complex allometric model of biomass was developed based on a model of resource partition between dbh and height growths. Although being a good model for biomass prediction, the power model was outperformed by the complex allometric model. A careful examination showed that the power model could be segmented into two pieces of power models. Using tree diameter and height as separated predictors improved the biomass prediction, irrespective of the collinearity between these two predictors. A critical value of 25% for the PRSE statistic used to assess the reliability of coefficient estimates corresponded to a significance level of 10 - 5 – 10 - 4 and was thus unreasonably low. We conclude that growth theories should be developed to explain allometric models, but that the arbitration between these models should ultimately rely on observed data, not on theories.

Bacterial-feeding nematodes constitute one of the primary grazers of soil bacteria. We investigated the effects of selective grazing of a representative nematode (Zeldia punctata, Cephalobidae) on nematode life history and population biology and on the soil microbial community. Firstly, we measured (i) the effect of five different bacterial strains on the nematode life cycle using petri dishes and (ii) the impact of bacterial inoculation on nematode population growth in a soil microcosm. Selection of the five bacterial strains was based on morphology, cell-wall characteristics and mucus production. Z. punctata development was strongly affected by the type of bacteria ingested, independent of experimental design. Bacterial cell-wall characteristics seemed to directly affect Z. punctata development since high nematode densities were only reached with gram-negative strains (Pseudomonas monteilii and Methylobacterium nodulans). In petri dishes, the filamentous organisms (Actinomyces sp.) and mucus-producing bacteria (Bradyrhizobium sp.) led to the least reproduction. Duration of the various nematode life phases (egg, juvenile, reproductive stage and non-reproductive stage) was significantly affected by the bacterial food source. Total life span varied from 12.5 days (Bradyrhizobium sp.) to 40 days (Pseudomonas monteilii). Secondly, we monitored the influence of Z. punctata on the indigenous soil microbial community in the presence or absence of a maize plantlet. Nematode inoculation led to an increase in bacterial activity (as measured by alkaline phosphatase activity) but did not significantly influence bacterial biomass. The genetic fingerprint (DGGE) of soil bacteria was more influenced by plant presence than by nematode inoculation. Nematode activity has important repercussions on N flux in the soil since inoculation of Z. punctata in the absence of plants resulted in a net increase of N mineralization (2 mg N per pot) while a decrease of mineral N (0.5 mg N per pot) was observed in the absence of the nematodes, due to bacterial immobilization. This study underscores the close relationship between selective bacterial grazing and nematode development. Nevertheless, the impact of nematode grazing on the overall soil microbial community seems to primarily affect microbial activity and relative dominance rather than microbial diversity.

International audience; Brazil's population is very unevenly distributed, due to rapid growth mainly benefiting coastal cities. Differentiated ethnic origins draw regions dominated by a particular skin color and disparities in levels of development are only partially corrected by large-scale pioneer fronts still progressing in the Amazon.; La population du Brésil est très inégalement répartie, en raison d'une croissance rapide qui a bénéficié principalement aux villes littorales. Des origines ethniques différenciées dessinent des ensembles où domine telle ou telle couleur de peau et ses fortes disparités de niveaux de développement ne sont qu'en partie corrigées par des fronts pionniers de grande ampleur qui progressent encore en Amazonie.

Climate changes result in hydrological cycle alterations, with impacts on distribution and quantity of rainfall affecting forest plantations in the tropics and subtropics. Trees minimize water stress effects by leaf osmotic adjustments which are dependent on K ions. Eucalyptus plantations were established in tropical and subtropical soils especially poor in K. Fertilization by substitution of K by Na is a potential alternative way, at lower cost and greater availability, that is especially suitable for smallholder plantations. For these reasons, we studied respective K and Na fertilization effects on growth and basic wood density of Eucalyptus grandis plantations with different objectives (domestic energy, timber). Significant differences in volume of trunk and wood density were observed on 8-year-old E. grandis trees fertilized with Na vs. K and the control. Trees with Na fertilization showed a significantly higher volume with Na vs. the control and a lower volume vs. K. Wood density and radial variability were significantly lower compared to trees with K and the control. In this paper we discuss the advantages of Na fertilization both to minimize the drought stress effect due to global climate change and to optimize economically the wood production of smallholder plantations. (Texte intégral)

Brazil's population is very unevenly distributed, due to rapid growth mainly benefiting coastal cities. Differentiated ethnic origins draw regions dominated by a particular skin color and disparities in levels of development are only partially corrected by large-scale pioneer fronts still progressing in the Amazon., La population du Brésil est très inégalement répartie, en raison d'une croissance rapide qui a bénéficié principalement aux villes littorales. Des origines ethniques différenciées dessinent des ensembles où domine telle ou telle couleur de peau et ses fortes disparités de niveaux de développement ne sont qu'en partie corrigées par des fronts pionniers de grande ampleur qui progressent encore en Amazonie.

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; 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.

Population Growth and Settlement Dynamics in Senegal, since the Indépendance. Senegal has a population of a little more than 8 million for a size of 196 722 km2, i.e. an average density of 41,3 inhabitants per km2. This population has been growing rapidly for several decades. It went up from 2,8 million inhabitants in 1960 to 5 million in 1976, and to more than 8 million in 1994, i.e. an annual rate of growth around 2,7 %. It is a young population - 47,2 % are 15 - as a result of a high and steady reproduction index - 6 children per woman on average in 1992. On the other hand, mortality is still high, 1,8 %, especially among young people. Disparities are important regarding both densities and population growth, from one area to another, and even more so when considered within « département », « arrondissement » or rural community. These disparities are an illustration of the recent moves among the population according to new spatial entities as a consequence of labour mobility. Urban areas are gaining more and more importance while rural areas are undergoing the severe consequences of the drought that occured in the seventies. Meanwhile, international migrations, and the importance of their impact on local economies should help highlight how density and popu- lation growth can be interpreted in some areas., Le Sénégal compte un peu plus de 8 millions d'habitants (estimation 1994) pour une superficie de 196 722 km2, soit une densité moyenne de 41,3 habitants au km2. Cette population est en croissance rapide depuis plusieurs décennies. Elle est passée de 2,8 millions d'habitants en 1960 à 5 millions en 1976 et à plus de 8 millions en 1994, soit un taux de croissance annuel moyen d'environ 2,7 %. C'est une population jeune, 47,2 % de jeunes de moins de 15 ans, du fait d'une fécondité élevée et stable, 6 enfants en moyenne par femme en 1992. En revanche la mortalité reste forte, 18 %o, notamment chez les plus jeunes. Les disparités sont grandes aussi bien en termes de densité que de croissance de population d'une région à l'autre. Elles le sont plus encore quand elles sont envisagées à l'échelle du département, de l'arrondissement ou de la communauté rurale. Elles illustrent le redéploiement de la population entre les différentes entités spatiales, conséquence de la mobilité de la force de travail. Les zones urbaines pèsent d'un poids de plus en plus important, contrairement aux régions rurales qui subissent de façon brutale les conséquences de la sécheresse des années 70-80. Cependant, les migrations internatio nales et l'importance de leur impact sur les économies locales doivent conduire à relativiser la signification des densités et de la croissance de la population dans certaines régions., Lericollais André, Roquet Dominique. Croissance de la population et dynamique du peuplement au Sénégal depuis l'indépendance. In: Espace, populations, sociétés, 1999-1. Les populations de l'Afrique subsaharienne. pp. 93-106.

This report shows the work done in 2011 by Irstea, INRA, ONF and CNPF in the framework of a research programme dedicated to improved varieties testing. It includes six species (Douglas-fir, larch, Black and Scots pines, wild cherry, ash) and a transversal topic (remote detection). With regard to Douglas-fir, the four partners continued the establishment of a network of comparative trials including the 8 French seed orchards and a control from the natural range. With two new trials, the network is now composed of 17 experimental plots and 10 demonstration plots. On the whole, survival is satisfactory. Most of the improved varieties show a better initial growth than the control. Still, the Californian variety is characterised by a slow growth in every site. Moreover, all the orchards have been ranked for timing of bud flushing. Ranking the varieties for cold hardiness in autumn will be the next step. Research has begun in 2011 in that respect. In larch, INRA studied the interest of IR spectrométry for larch taxa identification. The results obtained in 2011 on needles are encouraging. Furthermore, Irstea analysed the performances of hybrids and pure species individuals in the progenies of four "hybrid" varieties. Simulated thinnings show that the stand will become richer in hybrids if the trees are selected for growth. However, the final percentage of hybrid will depend on the variety. On the other hand, hybrid percentage will remain the same if the preference is given to stem form. Concerning remote sensing, Irstea work has focused on image segmentation. Several experimental plots and orchards have been analysed.; Ce compte rendu d'activité présente les actions entreprises de mars 2011 à mars 2012 par Irstea, l'INRA, l'ONF et le CNPF dans le cadre de l'évaluation des variétés issues des vergers à graines de l'Etat. Elles concernent 6 espèces – Douglas, mélèzes, pins laricio et sylvestre, merisier, frêne – et un thème transversal qui consiste à identifier des techniques susceptibles de caractériser l'état physiologique des arbres de différentes espèces/provenances. Dans un premier temps, l'accent est mis sur les applications possibles de la télédétection. Pour ce qui concerne le Douglas, les quatre partenaires se sont mobilisés pour mettre en pace un réseau national de dispositifs destiné à évaluer les performances des 8 vergers de Douglas français. En 2011, le réseau s'est enrichi de deux nouveaux essais plantés au printemps dans le coeur de l'aire et en altitude. Il est à présent constitué de 17 dispositifs d'évaluation et 10 tests de démonstration. En outre, deux dispositifs comparant les variétés La Luzette et Californie, pures et en mélange, auront été installés. Dans l'ensemble, l'état des dispositifs est satisfaisant puisque 24 d'entre eux ont une mortalité inférieure à 20%. On déplore néanmoins la perte de deux tests. Des mesures de hauteur ont été prises régulièrement dans la majorité des sites. La variété californienne se caractérise par une faible vigueur initiale dans tous les milieux. Si l'on excepte Darrington, relativement peu vigoureuse, les autres variétés ont généralement une croissance supérieure au témoin de l'aire naturelle (seed zone Washington 403). Les notations de débourrement confirment la hiérarchie établie l'année précédente et, surtout, permettent de classer le verger Washington par rapport aux 7 autres vergers français. En définitive, 4 vergers de l'Etat apportent une amélioration sur ce caractère par rapport au témoin Washington 403 : Washington 2, La Luzette, Washington et, à un degré moindre, Darrington. Concernant la résistance au froid, l'enjeu est maintenant de classer les vergers pour l'aoûtement à l'automne. Une étude bibliographique a été faite dans cette perspective. En outre, Irstea a aménagé une serre de manière à conduire des essais en conditions semi-contrôlées. Des plants issus des vergers La Luzette et Californie ont été installés dans des caisses métalliques et seront soumis à trois ambiances climatiques en 2012. D'autre part, des mesures indirectes de densité du bois ont été prises par l'INRA dans deux tests de descendances du verger Darrington. En moyenne, les familles sont proches de la provenance Sauk River, originaire de la seed zone 403 (Etat du Washington) pour la densité du bois et la vigueur. Malgré des différences nettes entre moyennes familiales, une amélioration significative des performances du verger Darrington ne pourrait s'envisager que par une éclaircie vigoureuse, réduisant fortement la base génétique du verger qui est déjà limitée. Pour le mélèze, l'INRA a étudié le potentiel de la spectrométrie infra-rouge pour identifier les différents taxa de mélèze. Les travaux réalisés en 2011sur aiguilles sont encourageants. De plus, Irstea a analysé les performances des individus hybrides et d'espèces pures de quatre variétés "hybrides" implantées dans un dispositif du Limousin. Les simulations d’éclaircies montrent que la plantation s’enrichit en hybrides si on met l’accent sur la production de bois mais que le taux d’hybrides évolue peu si l’on privilégie la forme. En définitive, l'impact du taux d'hybrides dans les MFR dépend de deux facteurs : la stratégie du propriétaire (objectif vigueur ou forme) et la variété considérée (différentiel de croissance entre hybrides et espèces pures). En matière de télédétection, les travaux d'Irstea se sont concentrés sur la segmentation d’images afin de tirer le meilleur parti des photographies aériennes prises en 2009 au-dessus de plusieurs dispositifs expérimentaux et vergers à graines

The genetic and environmental control of microfibril angle (MFA) and its genetic correlations with other wood and growth traits are still not well established in Eucalyptus sp. To determine the narrow-sense heritability estimates (h 2) of MFA, wood density (D), Klason lignin (KL) content, syringyl to guaiacyl (S/G) ratio and growth traits, their variation from pith to cambium and their genetic correlations. Heritability and correlations were assessed in 340 control-pollinated progenies of 14-year-Eucalyptus urophylla S.T. Blake using near infrared spectroscopic models. Moderate to high heritability were found for MFA (h 2 = 0.43), D (h 2 = 0.61), S/G (h 2 = 0.71) and LK (h 2 = 0.76). The genetic control of D and MFA and the genetic and residual correlation between chemical and growth traits varied with age. The genetic correlation C × D was always strongly negative (r

International audience; Plant species (exotic invasive vs native non-invasive) colonization pattern and the relation with the soil nutrient availability and AM fungi abundance, was investigated. Soil samples were collected from two sites: one invaded by the exotic plant. Amaranthus viridis, and one uninvaded site for chemical and AM propagules density analyses. Additionally, we grew five Sahelian Acacia species in soil from the two sites, sterilized or not, to test the involvement of soil biota in the invasion process. While nutrient availability was significantly higher in soil samples from the invaded sites, a drastic reduction in AM fungal community density, was observed. Moreover, Acacia seedlings' growth was severely reduced in soils invaded by Amaranthus and this effect was similar to that of sterilized soil of both origins. The observed growth inhibition was accompanied by reduction of AM colonization and nodulation of the roots. Finally, the influence of soil chemistry and AM symbiosis on exotic plants' invasion processes is discussed. (C) 2011 Elsevier Ltd. All rights reserved.

1. Considerable debate surrounds the extent to which tropical forests can be managed for resource extraction while conserving biodiversity and ecosystem properties, which depend on functional composition. Here we evaluate the compatibility of these aims by examining the effects of logging on taxonomic and functional diversity and composition in a tropical forest. 2. Twenty years after selective logging, we inventoried 4140 stems regenerating in logging gaps and adjacent undisturbed areas, and we integrated a database of 13 functional traits describing leaf and wood economics of tropical trees. 3. We found no differences in taxonomic and functional richness among habitats, but logging gaps had significantly higher taxonomic and functional evenness. 4. Logging also effected striking, long-term changes in both species and functional composition. In particular, the xylem density of recruits in logging gaps was 6% less than in unlogged forests, leaves were 11% less tough and had 613% greater mineral nutrient concentrations. 5. Synthesis and applications. Our results suggest that managers of tropical forests should limit overall surface area converted to logging gaps by creating fewer, larger gaps during selective logging, to reduce impacts on the taxonomic and functional composition of the regenerating stand.

Root length density (RLD) is a critical feature in determining crops potential to uptake water and nutrients, but it is difficult to be measured. No standard method is currently available for assessing RLD in the soil. In this study, an in situ method used for other crops for studying root length density and distribution was tested for sugarcane (Saccharum spp.). This method involved root intersection counting (RIC) on a Rhodic Eutrudox profile using grids with 0.05 x 0.05 m and modeling RLD from RIC. The results were compared to a conventional soil core-sampled method (COR) (volume 0.00043 m³). At four dates of the cropping season in three tillage treatments (plowing soil, minimum tillage and direct planting), with eight soil depths divided in 0.1 m soil layer (between 0-0.6 and 1.6-1.8 m) and three horizontal distances from the row (0-0.23, 0.23-0.46 and 0.46-0.69 m), COR and RIC methods presented similar RLD results. A positive relationship between COR and RIC was found (R² = 0.76). The RLD profiles considering the average of the three row distances per depth obtained using COR and RIC (mean of four dates and 12 replications) were close and did not differ at each depth of 0.1 m within a total depth of 0.6 m. Total RLD between 0 and 0.6 m was 7.300 and 7.100 m m-2 for COR and RIC respectively. For time consumption, the RIC method was tenfold less time-consuming than COR and RIC can be carried out in the field with no need to remove soil samples. The RLD distribution in depth and row distance (2-D variability) by RIC can be assessed in relation to the soil properties in the same soil profiles. The RIC method was suitable for studying these 2-D (depth and row distance in the soil profile) relationships between soil, tillage and root distribution in the field. A densidade de comprimento de raízes (DCR) é uma característica importante para determinar o potencial de absorção de água e nutrientes das plantas, mas é difícil de ser medida. Nenhum método padrão está atualmente disponível para avaliar a DCR no solo. Neste estudo, um método in situ usado em outras culturas para estudo da densidade de comprimento e distribuições das raízes foi testado para a cana-de-açúcar (Saccharum spp.). O método envolveu contagem de intersecções de raízes (CIR) no perfil de um Latossolo Vermelho eutroférrico, usando grade com quadrículas de 0.05 x 0.05 m, modelizando a DCR a partir da CIR. Os resultados foram comparados com o método do trado cilíndrico (TRA) (volume de 0.00043 m-3). Em quatro épocas durante o ciclo em três manejos do solo (plantio convencional, cultivo mínimo e plantio direto), em oito profundidades divididas a cada 0.1 m (entre 0 - 0.6 e 1.6 - 1.8 m) e três distâncias horizontais em relação à linha de plantio (0 - 0.23, 0.23 - 0.46 e 0.46 - 0.69 m), os métodos TRA e CIR apresentaram resultados de DCR similares. Encontrou-se positiva entre TRA e CIR (R² = 0,76). As DCRs nos perfis, considerando as médias das três distâncias da linha por profundidade, obtida utilizando-se de TRA e CIR (média de quatro datas e 12 repetições), foram próximas e não diferiram a cada 0.1 m de profundidade até 0.6 m de profundidade. A DCR total entre 0 e 0.6 m foi de 7.300 e 7.100 m m-2 para TRA e CIR, respectivamente. Para o tempo de realização, o método CIR foi 10 vezes mais rápido do que TRA e o método CIR pode ser realizado no campo, sem necessidade de remover amostras de solo. A distribuição da DCR em profundidade e distância da linha (variabilidade 2D) pelo método CIR pode ser avaliada em relação às propriedades do solo nos mesmos perfis do solo. O método CIR foi apropriado para estudos dessas relações 2D (profundidade e distância da linha no perfil do solo) entre solo, manejo e distribuição de raízes no campo.

Le contrôle génétique et l'environnemental de l'angle des microfibrilles (MFA), les corrélations génétiques du MFA avec d'autres caractères du bois et de croissance, et par conséquent les implications pour la sélection sont très peu documentés pour les Eucalyptus. Les objectifs de cette étude étaient d'établir la variation spatiale du MFA, de la densité du bois (p) et de sa rigidité (E); de déterminer les relations entre MFA et propriétés du bois et enfin d'estimer le contrôle génétique et environnemental des caractères du bois et de la croissance dans le cadre de tests clonaux et de test de descendances d'Eucalyptus au Brésil et au Congo. Méthodes classiques, résonance, diffraction des rayons-X et la spectroscopie proche infrarouge ont été combinées pour évaluer les propriétés du bois. La variation du MFA représente 44% de la variation du module spécifique (E/p) du bois. La densité du bois est le principal déterminant de la rigidité et de la résistance du bois alors que le MFA joue un rôle secondaire. Les estimations de l'héritabilité sont de modéré à élevées pour le MFA, p, E, la lignine de Klason (KL) et les caractères de croissance, selon la position spatiale et le dispositif expérimental. Le contrôle génétique du MFA, p et E et leurs corrélations génétiques avec KL et la circonférence à 1.3 mètre des arbres varient avec l'âge. Les résultats suggèrent que les arbres à forte croissance sont génétiquement plus aptes à produire du bois de faible densité et un MFA plus faible pour assurer la rigidité du bois nécessaire à leur développement. La plupart des propriétés du bois sont génétiquement corrélées négativement avec la croissance, bien que corrélations génétiques favorables entre propriétés du bois sont observés. Les corrélations génétiques et environnementales sont parfois de signes opposés selon les caractères considérés. Ceci peut s'expliquer par l'effet pléiotropique des gènes et/ou par le déséquilibre de liaison. Les conséquences de ces résultats sur les stratégies de sélection sont discutées selon l'usage final du bois d'Eucalyptus.

International audience; The main objective of Eucalyptus breeding programs for the pulp and paper industry is to produce varieties of trees with high levels of cellulose with the least possible amount of lignin. However, trees with these characteristics can be a major problem in the field, because of their fragility that makes them susceptible to breaking. The aim of this study was to investigate the clonal and environmental variation of the growth, wood density, and dynamic properties on large pieces of Eucalyptus wood by means of resonance technique. Here, we demonstrated that no other non-destructive technique is able to characterize the mechanical properties of wood so simply and rapidly at such low cost. The resonance technique provided a large, accurate data set of the key mechanical traits (such as the Young, the shear modulus and the loss tangent) of the wood even in lumber containing knots, small cracks and also slightly damaged areas. There were significant differences between clones and sites for height and circumference, and density of the trees. Using the dynamic elastic estimates, significant differences were detected between clones for all traits; however, no significant differences between sites were detected for dynamic modulus of elasticity. There were significant, classifications, or preliminary selections in breeding programs of Eucalyptus.; O objetivo principal dos programas de melhoramento genético de Eucalyptus para a indústria de celulose e papel é produzir variedades de árvores com níveis elevados de celulose e com a menor quantidade de lignina possível. No entanto, as árvores com estas características podem ser um grande problema em campo, devido à sua fragilidade que as torna suscetíveis à quebra. Este estudo foi realizado com o objetivo de investigar a variação do crescimento, da densidade da madeira e das propriedades dinâmicas por meio da técnica de ressonância em vigas de Eucalyptus em função dos clones e do ambiente. Os resultados mostram que nenhuma outra técnica não-destrutiva é capaz de caracterizar as propriedades mecânicas da madeira de forma tão simples, rápida e a baixo custo. A técnica de ressonância é capaz de estimar características mecânicas (como o módulo de elasticidade e de cisalhamento e o amortecimento interno) em grandes amostragens de madeira, mesmo com presença de nós, pequenas fissuras e também com áreas ligeiramente danificadas. Houve diferenças significativas entre os clones e os sítios para altura, circunferência e densidade da madeira das árvores. A partir das estimativas dinâmico-elásticas, foram detectadas diferenças significativas entre os clones para todas as características, no entanto, não houve diferenças significativas entre os sítios, para o módulo de elasticidade dinâmico. Houve efeito significativo da interação clone x site para a circunferência, altura, densidade e módulo de cisalhamento. Estes resultados podem ser úteis para a classificação ou a seleção preliminares em programas de melhoramento de Eucalyptus.

This study deals with rearing methods, growth and mortality performances, and problems encountered by the oyster farmers from Quiberon Bay (2800 ha of leases) : it relies on a survey achieved in july 2001, about 18 oyster farmers, and 2 diving campaigns (july and october 2001) on 2 years old oyster batches from the same farmers. The analysed enterprises vary in particular by the location and depth of their concession inside the bay, but also by their rearing scheme : a majority favours seedings with 18 month old oysters or more, according to prices and availability of oysters supplies. The duration until marketable size and mean mortalities seem to have increased since a preceding inquiry in 1986. The main constraint, affecting priorly the south border parks, expoded to the open sea, occurs from starfish (Asterias rubensin peculiar). Benthic red algae are also a nuisance to exploitation and eventually to oysters themselves, when they accumulate in thick layers. The main concern declared by the farmers is mortality rates, both at spat stage and commercial size. Difficulties have emerged from the variability in practices and bottom situations, but references have been acquired that may be used in ecosystem studies or long run monitoring of the area., L'étude porte sur les méthodes d'élevage, les performances de croissance-mortalité et les problèmes rencontrés par les éleveurs d'huîtres creuses de la baie de Quiberon (2800 ha concédés) : elle s'appuie sur une enquête réalisée en juillet 2001 auprès de 18 exploitants, et 2 campagnes de plongée (juillet et octobre 2001) sur des semis d'huîtres de 2 ans des mêmes concessionnaires. Les entreprises étudiées se différencient par leur outil de production et en particulier l'emplacement de la concession en baie de Quiberon, mais également part le schéma d'élevage : une majorité privilégie les semis d'huîtres de 18mois ou plus, en adaptant leurs approvisionnements aux disponibilités et prix du moment. Depuis une première enquête en 1986, la durée d'élevage semble s'être allongée et les mortalités accrues. La contrainte principale, qui affecte en particulier les concessions les plus au large est liée à l'augmentation apparente du nombre d'étoiles de mer (Asterias rubens majoritairement). Les algues benthiques (essentiellement des algues rouges) représentent une gêne à l'exploitation, mais pourraient aussi, là où elles s'accumulent en grande épaisseur, avoir un impact direct sur les huîtres. La première préoccupation des ostréiculteurs reste la mortalité des huîtres creuses en élevage, que ce soit au stade de naissain ou plus encore au stade terminal de l'élevage. Ces acquis demeurent limités par la variabilité tant des pratiques que des situations observées sur le terrain, mais constituent une base de référence pour une analyse du fonctionnement de l'écosystème ou un suivi à plus long terme.

International audience; Six different indoor rearing densities (250 to 500 animals per m$^2$) were tested. Three repeats were carried out for each density. The following were recorded: feed intake, weight and number of adult individuals (animals with a reflected peristome), non-adult weight at the end of the experiment, and mortality. A simplified calculation of gross margin is also presented. It was observed that, at low densities, the animals consumed more, were bigger and more of them became adults. However, the total amount of biomass produced is greater at higher densities. If the breeder merely fattens the snails, then the gross margin is maximal at a density of 250 animals per m$^2$. If the breeder fattens and cooks his own produce, then the gross margin is maximal at high densities. Compared to the mixed rearing method currently used, the performances observed in this indoor rearing experiment could be improved further (particularly in terms of the percentage of adult animals obtained).; Influence de la densité sur les performances zootechniques d'escargots Petit-Gris (Helix aspersa Müller) en élevage hors sol. L'effet de six densités d'engraissement (250 à 500 animaux par m$^2$) sur les performances d'élevage hors-sol est étudié. Trois répétitions pour chaque densité sont formées. On mesure la consommation alimentaire, le poids des individus bordés et leur nombre, le poids des individus non bordés en fin d'expérience et la mortalité. Un calcul simplifié de marge brute est aussi présenté. On constate que pour les faibles densités, les animaux consomment plus, sont plus gros et qu'il y a plus d'individus bordés. Cependant, si l'on s'intéresse à la biomasse totale produite, les fortes densités fournissent de meilleurs résultats. La marge brute est maximale pour une densité de 250 individus par m$^2$ si l'éleveur est engraisseur seulement. Si l'éleveur transforme lui-même sa production, la marge brute est maximale pour les fortes densités. En comparaison avec l'élevage mixte actuellement pratiqué, les performances observées dans cet essai d'élevage hors-sol, en particulier le pourcentage d'animaux bordés obtenu, peuvent être encore largement améliorées.

Dans le but d'optimiser l'utilisation de la méthode d'isolement "in vitro" des trypanosomes sanguicoles par le "kit for in vitro isolation" (KIVI), une étude a été réalisée sur 14 KIVI positifs obtenus à partir de malades du foyer de Campo au Cameroun. Une estimation de la densité parasitaire par comptage régulier a été effectuée du jour où les KIVI ont été déclarés positifs à celui où les trypanosomes ont complètement disparu du milieu. Après application des analyses statistiques, nous avons pu observer que les trypanosomes se multiplient activement dans le KIVI et atteignent leur pic optimal de croissance après 26 jours plus or minus 1 (risque 5%) en moyenne. Il existe une corrélation linéaire significative (p=0.03) entre la quantité de parasites présents dans le KIVI le jour de son ensemencement et le jour où les parasites dans ce KIVI atteignent leur pic optimal de croissance. Ainsi, le nombre maximal de jours mis par les trypanosomes pour atteinde le pic optimal de croissance est significativement d'autant plus bas que la densité parasitaire de départ est élevée. Après ensemencement, un KIVI a besoin d'être surveillé pendant 40 jours avant d'être déclaré négatif. La durée pendant laquelle un KIVI positif conserve les trypanosomes dépasse 50 jours mais elle est variable selon les souches. La recherhce nécessite de grandes quantités de trypanosomes que le KIVI ne peut fournir. Il faut donc passer par une culture de masse sur le milieu de Cunnigham. Les repiquages effectués sur ce milieu avant J22 aboutissent à des densités élevées de trypanosomes (1200 x 10(exp 6) parasites/ml). Tous les repiquages effectués après J34 donnent des densités parasitaires faibles (200x10exp6 parasites/ml), insuffisantes pour la recherche. Il ressort de cette étude que le KIVI est un outil très utile pour l'isolement des trypanosomes sur le terrain... (D'après résumé d'auteur)

The effects of a deep-burrowing earthworm species, #Martiodrilus carimagnuensis$, on soil fertility and plant growth were assessed in two grasslands in the Eastern Plains of Colombia. This species aestivates deep in the soil during the dry season. Fibre glass netting was used to prevent colonisation of the top soil at the onset of the humid season. Effects of earthworm absence on soil properties and plant biomass were analysed with principal component analysis. Experimental manipulation succeeded in preventing #M. carimaguensis$ activity in the top soil. The larger part of the variance in our data (29.35%) was explained by the effect of pasture type and age on soil structure and organic matter. A lesser part (10.81%) was due to the effect of legumes on soil physical properties. The effect of earthworm absence on soil properties and plant growth explained 16.50% of the total variance. #M. carimaguensis$ biomass was associated with low soil compaction, high C contents, low Al saturation, high herbaceous biomass and low weed biomass. These results support the general knowledge of how earthworms can affect soil fertility and plant growth. (Résumé d'auteur)

La densite moyenne, les largeurs et densites du bois initial et final ont ete mesurees par microdensitometrie sur des barrettes de bois. Les barrettes ont ete prelevees sur deux rayons et echantillonnees a plusieurs hauteurs sur 82 arbres repartis en parcelles et regions (24 200 cernes mesures). Des modeles a effets mixtes sont construits avec l'âge depuis la moelle et la largeur de cerne de maniere a evaluer les effets des facteurs region, placette, arbre et position dans l'arbre sur les composantes densitometriques des arbres. La contribution de chaque effet teste est ensuite estimee par rapport a la variation totale des composantes de la densite. Dans un troisieme temps, le modele mixte de densite moyenne etabli a 1,30 m est teste sur un nouvel echantillonnage. Enfin, ce modele est utilise pour simuler l'influence de pratiques sylvicoles contrastees sur la densite du bois, la simulation prenant en compte les variabilites inter-arbre pour la densite et la croissance radiale des arbres.

A mechanistic model of xylem production based on physiological and anatomical assumptions is proposed. It focuses on tracheids and on the main phases of cell development: cell division, enlargement and wall thickening. For each phase, the most limiting environmental factors are assessed and their effect is modeled with a weekly time step. Combined with simple process-based stand growth and yield models, which take the mean monthly climatic data into account, the xylem production model provides simulations of infra-annual density profiles along stem radius. Simulations are performed for two sites in northeastern France, using past climatic data. The outputs are qualitatively discussed and visually compared with the observed microdensitometric profiles of Pinus sylvestris and Picea abies in these two sites. These models provide a basis for integrating timber quality features into process-based models. They also point to new sources of data that could be used to validate process-based models, and suggest some biological assumptions to understand the infra-annual variability of wood basic density.

Compte rendu des résultats obtenus dans le cadre du projet et entre décembre 94 et novembre 95, dans les études suivantes : mesures de biomasse chez les jeunes feuilles et les régimes en croissance, densité du stipe, dynamique de répartition des biomasses dans les différents organes aériens (feuilles, régimes, stipe), évolution de la masse surfacique (matière sèche par unité de surface de foliole) au cours de la journée

Ar experiment concerning a clonal test of E. urophylla*grandis was carried out in Congo and presented the following results. The study of variation along the stem showed that basic density decreased sharply from the base to 1.3 m and then increased as the sampling height increased. Consequently, the best prediction of the mean tree basic density was obtained with disks taken at 25 or 50% of the commercial height. A different result was obtained for the mean tree bark percentage which was correctly predicted with 3 samples. Genetic analysis indicated a higher heritability for basic density and low genetic correlations with volume, confirming results obtained from breeding populations of E. urophylla*grandis. Results relating to the method of sampling and selection strategy are discussed in this paper.

Dans le cadre d'un essai fertilisation sur sols pauvres dans les savanes côtières congolaises, les auteurs étudient les relations entre croissance individuelle et densité basale du bois de quatre clones d'Eucalyptus hybrides. Quoi qu'il en soit, la fertilisation ne peut qu'améliorer la productivité de ces plantations à but papetier

Les fentes et les déformations dues à la libération des contraintes de croissance limitent l'utilisation des Eucalyptus sous forme de bois d'oeuvre. Suivant la direction longitudinale des fibres, ces contraintes résultent du blocage des déformations de maturation dans l'arbre en croissance. Leur intensité dépend donc du module d'élasticité longitudinal du bois vert et de la déformation longitudinale de maturation mesurable à la surface des arbres sur pied. L'étude des variations de ces deux paramètres montre que : Les déformations de maturation dépendent du génotype, et diminuent au delà d'un seuil d'âge correspondant à un stade de perte de vitalité. Le module d'élasticité et la densité varient avec l'état de juvénilité primaire et secondaire du bois. Un modèle de distribution des contraintes de croissance est alors développé; il prend en compte les variations radiales du module d'élasticité longitudinale et généralise les formulations usuelles qui présupposent que la qualité du bois est homogène sur la section. Une validation du modèle est entreprise à travers des essais de sciage en quartiers de billons d'Eucalyptus. Les déformations modèlisées à partir des distributions de contraintes.

Dans un élevage Intensif en claires expérimentales de palourdes japonaises semées à la taille de 28 mm et aux densités de 100, 200 et 300/m2, différentes rations alimentaires de la diatomée Skeletonema costatum. cultivée à partir d'eau salée souterraine, ont été testées de mars à novembre 1988. Pour la densité 100/m2, le taux de croissance n'est pas significativement différent avec des concentrations de pigment dans l'eau injectée comprises entre 31 et 126 µg.l(1) de Chia. Toutefois celui-ci est 1,5 fois supérieur à celui observé dans la claire témoin. Avec 1.8 kg.m-2 la biomasse finale représente 2 fois la charge récoltée dans la claire extensive. Après analyse, la densité de 300/m2 semble être le meilleur compromis pour l'élevage intensif même si la taille finale maximale de palourde est obtenue avec la densité de 100/m2. En effet. avec 84 % de recapture, 4 kg/m2 de biomasse et 16 % de rendement d'assimilation, la production récoltée est 5 fols supérieure au témoin et 10 fois plus forte que les biomasses extensives produites dans les marais atlantiques. Cependant, les essais de réduction des quantités d'eau de mer. des volumes de phytoplancton et l'hétérogénité de croissance des palourdes devront être étudiés avant de pouvoir envisager le transfert de cette technique aux aquaculteurs.