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International audience; The Milo River in Guinea is one of the tributaries of Upper Niger. Its basin has a semi-arid climate with alternating dry and wet seasons in a biogeographic context of savannah. The West African monsoon brings rain between June and September with a long dry period affecting river levels and vegetation. The rainfall and flow of the Milo River have declined of about 20 % since the 1970s. Trees that concentrate mainly along river margins are likely to be affected by this change in climate and water resource. Little data is available on the age, growth rate and origin of water used by riparian trees in Guinea. These data are nevertheless essential for measuring the impact of environmental changes on the functioning and sustainability of riparian forests. A dendrochronological and dendroisotopic study was carried out on trees bordering the Milo River in order to test the effectiveness of these techniques for obtaining such data. A difficulty with the use of dendrochronology in tropical environments is that few species form annual rings. Of thirteen tree species studied half form more or less distinct ring boundaries but three species showed clearly visible ring boundaries. These species are Pericopsis laxiflora, Tamarindus indica and Tectona grandis. This study shows that it is possible to estimate the age (15 to 102 years) and radial growth rates (0.26 to 1.39 cm/year) for species with discernible rings. However, the poor anatomical definition of ring boundaries on most of the other species, especially towards the pith, highlights all the difficulty of conducting a long-term, robust, dendroclimatic study in the semi-arid African context. A dendroisotopic test analysis (delta 13C, delta 18O) on a single tree of Pericopsis laxiflora, Tamarindus indica and Tectona grandis shows that this riparian species is able to regulate its water acquisition during hydrological variations. This is marked by a physical trace in the rings related to the use of the more perennial alluvial water during the dry period.; La rivière Milo, en Guinée, est l'un des affluents du haut-Niger. Son bassin connaît un climat de type semi-aride à saisons contrastées dans un contexte biogéographique de savane. La mousson d'Afrique de l'Ouest apporte ses pluies entre juin et septembre ; d'octobre à mai, une longue période sèche affecte le niveau des rivières et la végétation. Depuis les années 1970, la pluviométrie et le débit de la rivière Milo subissent une baisse d'environ 20 %. La végétation arborée, qui se concentre principalement le long du cours d'eau, est susceptible d'être touchée par cette évolution du climat et de la ressource en eau. Peu de données sont disponibles concernant l'âge, la vitesse de croissance et l'origine de l'eau utilisée par les arbres riverains du Milo. Ces données sont pourtant indispensables pour estimer l'impact des changements environnementaux sur le fonctionnement et la pérennité de la ripisylve. Une étude dendrochronologique et dendro-isotopique exploratoire a été réalisée sur des arbres riverains du Milo afin de tester ces techniques dans l'acquisition de telles données. Une difficulté liée à l'utilisation de la dendrochronologie en milieu tropical vient du fait que peu d'espèces ligneuses forment des cernes annuels. Sur treize espèces d'arbres étudiées, près de la moitié ont des limites de cernes peu distinctes, mais trois espèces ont des limites de cernes bien visibles. Il s'agit de Pericopsis laxiflora, Tamarindus indica et Tectona grandis. Cette étude montre qu'il est possible d'estimer l'âge (15 à 102 ans) et la vitesse de croissance radiale (0,26 à 1,39 cm/an) pour les espèces présentant des cernes discernables. Toutefois la mauvaise définition anatomique des limites de cernes sur la plupart des autres espèces, notamment vers le cœur, compromet la réalisation d'une étude dendroclimatique robuste en contexte semi-aride africain. Un essai d'analyse dendro-isotopique (delta13C, delta18O) réalisé sur un individu de Pericopsis laxiflora, de Tamarindus indica et de Tectona grandis montre comment l'arbre riverain peut réguler sa consommation hydrique en fonction des conditions hydriques locales et faire appel à l'eau de la nappe alluviale pendant la période sèche.

Annual radial growth and latewood formation increase during the period 1966–2015 in Larix cajanderi Mayr. and Pinus sylvestris L. along a latitudinal gradient on Siberian permafrost. Warmer temperatures and precipitation at the onset of the growth season favor growth in both species. A vast area of Siberian boreal forest is covered by continuous permafrost, where tree radial growth is strongly limited by low temperatures. Understanding how climate controls Siberian conifer growth is critical in order to predict their response to ongoing climate change. To explore variations in the radial growth and earlywood/latewood formation of Pinus sylvestris L. and Larix cajanderi Mayr. trees along a climate gradient within the continuous permafrost zone in Central Yakutia (Russia), a region experiencing accelerated warming. We evaluated spatiotemporal differences in tree-ring and latewood width among sites by using generalized additive mixed models. Pearson’s correlations were used to analyze the effect of local climate (temperature, precipitation) and drought (SPEI) on the formation of earlywood and latewood. Both conifers showed increased radial growth in recent decades. Radial growth was controlled by temperature and precipitation in both species along the gradient, with earlier precipitation events being critical for the formation of wide rings. Although temperature is considered as the main limiting factor triggering tree growth in the continuous permafrost zone, our results showed that water availability also plays a key role in radial tree growth even in the coldest sites.

International audience; Key messagePeriodic bending of young poplars increase the wood production whatever their hydric status; especially in the most highly stressed zones; improving the mechanical behaviour of the stem.AbstractThe ability of trees to acclimate the building of their structures to windy conditions under various hydric conditions is essential in the context of the predicted climate changes. In this study, we investigated the biomechanical responses of young poplar trees to periodic controlled bending stimulations that mimic the mechanical effect of trees growing under windy conditions. This treatment was conducted for 5months in well-watered conditions or under hydric stress. Results demonstrate the high impact of thigmomorphogenesis on growth processes, even under the water shortage. While axial growth was reduced by mechanical stimulations and hydric stress, radial growth was strongly increased by the periodic stem bending. The secondary growth was preferentially increased in the direction of highest longitudinal strains leading to the ovalisation of the cross-section. This ovalisation yielded 16%, regardless the hydric condition and generated a huge increase of the bending rigidity of the trees (+212%). Further, we observed a differential growth between the side growing under tension and the side growing under compression. A Finite Element model was built to investigate the mechanical benefits of the anisotropic cross-section shapes. This FE model enlightened the modulation of the spatial stress distribution that lead to a reduction of the stress in the weakest zones of the trunk; suggesting an improvement of the mechanical safety margin of wood. Thigmomorphogenesis acclimation appears as a complex and costly, but necessary process for the long-term mechanical support of the trees, even under hydric stress conditions.

[Notes_IRSTEA]revue en libre accès ; lien vers le texte intégral donné dans la notice [Departement_IRSTEA]Territoires [ADD1_IRSTEA]Dynamique et fonctionnement des écosystèmes; International audience; The link between phenotypic plasticity and heterosis is a broad fundamental question, with stakes in breeding. We report a case-study evaluating temporal series of wood ring traits of hybrid larch (Larix decidua x L. kaempferi and reciprocal) in relation to soil water availability. Growth rings record the tree plastic responses to past environmental conditions, and we used random regressions to estimate the reaction norms of ring width and wood density with respect to water availability. We investigated the role of phenotypic plasticity on the construction of hybrid larch heterosis and on the expression of its quantitative genetic parameters. The data came from an intra-/interspecific diallel mating design between both parental species. Progenies were grown in two environmentally contrasted sites, in France. Ring width plasticity with respect to water availability was confirmed, as all three taxa produced narrower rings under the lowest water availability. Hybrid larch appeared to be the most plastic taxon as its superiority over its parental species increased with increasing water availability. Despite the low heritabilities of the investigated traits, we found that the expression of a reliable negative correlation between them was conditional to the water availability environment. Finally, by means of a complementary simulation, we demonstrated that random regression can be applied to model the reaction norms of non-repeated records of phenotypic plasticity bound by a family structure. Random regression is a powerful tool for the modeling of reaction norms in various contexts, especially perennial species.

Highlights:• The climate-radial growth relationship of fir is studied along altitudinal gradients.• Summer drought of current and previous years is the main factor limiting fir growth.• Spring drought of the previous year is correlated with higher growth.• The climate-growth relationship varies among fir stands but not among trees.• The recent climate change has not altered the fir growth response to climate.Abstract:Tree ring widths provide very useful information to assess factors controlling tree radial growth and to estimate future growth trajectories under climate change. Radial growth variability has already been largely studied among tree populations that experience different environmental conditions and was most recently analyzed among individuals within populations. In the present study we assessed, over the 1960–2011 period, the growth response of silver fir (Abies alba Mill.) individuals originating from ten populations located along two altitudinal gradients (1000–1600 m a.s.l.) in the south east of France. Tree ring increments were estimated from wood cores collected from 129 adult trees. Results showed that (i) 30% of the growth variance among individuals was explained by competition; (ii) the climates of both the current and previous years were correlated with growth. Most of the climatic variables affecting growth were consistent with those identified in previous studies and with the known physiology of the species: negative effects of summer drought of the current and past years as well as a positive effect of the spring temperature of the current year. However in our study, fir growth was also enhanced by previous year spring droughts. The growth responses to precipitation, temperature, and, relative humidity of the current and previous years varied between sites and/or altitudinal levels, reflecting population acclimation by plasticity or genetic adaptation to local conditions. By contrast, only summer rainfall induced variable responses between individual trees, result attributed to the edaphic micro local heterogeneity. The recent climate change did not significantly alter the fir growth response to climate.

Tree resilience to drought was higher in drier sites and lower for suppressed trees grown in higher density stands, highlighting the role of acclimation and selection in tree responses to drought. Ongoing climate change will drive more frequent drought events in the future, with potential impacts on tree community structure and functioning. Growth responses of tree communities may depend on their past water status and on competition pressure. We investigated the effects of site water status, population density, and tree social status on tree growth resistance and resilience following the severe drought of 1976 in even-aged stands of sessile oak (Quercus petraea). We used retrospective growth data collected in permanent plots experiencing contrasted climatic and stand density conditions. We used boosted regression trees to calibrate a tree growth model over 1960–1975, which was then used to provide a baseline of expected tree growth following 1976. Growth dynamics during and after 1976 was examined using the ratio between observed and expected growths over 1976–1983. Tree radial growth was on average 0.6 times its expected values in 1976 and was still 0.63 times its expected value in 1977. Despite experiencing higher summer soil water deficit in 1976, trees growing in drier sites exhibited remarkably faster growth recovery than those in moister sites. Suppressed trees grown in higher density stands recovered their normal growth rate slower than dominant trees. Forest growth is evidenced to be more vulnerable to drought in moister than in drier sites. Competitive pressures also alter tree capacity to recover from a severe drought, accelerating suppression of smaller trees in high-density stands. These results highlight the role of acclimation and selection processes in tree community responses to present and future climates.

Evaluate the efficiency of Populus alba clone Villafranca in the uptake and translocation of Zn from contaminated soils. The effects of 48 days of zinc treatment (Zn t ) on the growth and the photosynthetic activities of P. alba L. clone Villafranca were studied using ZnSO4 (375 ppm per unit of soil dry weight) added in sand and peat moss substrate at the beginning of the treatment (T 0) and again after 30 days (T 1) in order to reach a target Zn concentration of 375 ppm at T 0 and 750 ppm at T 1 per unit of soil dry weight. Zn uptake in the different organs was analyzed after 30 (T 1) and 48 days (T 2) from the beginning of treatment, showing the following order: root ≫ leaves ≥ woody cutting = stem. The leaf area increased by 12 % in comparison to control plants at the end of second treatment (48 days). Cutting radial growth showed a high synchronicity in the growth rate fluctuation among control and Zn t plants, but a higher increase in radial diameter of Zn t cutting was observed starting from day 38 (after 8 days of second Zn t ) reaching after 48 days 38 % higher than control plants. Although our data of leaf Zn concentration were in the range usually reported as toxic for plants, Villafranca clone in Zn t substrate were unaffected in terms of net CO2 assimilation and stomatal conductance to water vapor.

The branch autonomy principle, which states that the growth of individual branches can be predicted from their morphology and position in the forest canopy irrespective of the characteristics of the tree, has been used to simplify models of branch growth in trees. However, observed changes in allocation priority within trees towards branches growing in light-favoured conditions, referred to as ‘Milton’s Law of resource availability and allocation’, have raised questions about the applicability of the branch autonomy principle. We present models linking knot ontogeny to the secondary growth of the main stem in black spruce (Picea mariana (Mill.) B.S.P.), which were used to assess the patterns of assimilate allocation over time, both within and between trees. Data describing the annual radial growth of 445 stem rings and the three-dimensional shape of 5377 knots were extracted from optical scans and X-ray computed tomography images taken along the stems of 10 trees. Total knot to stem area increment ratios (KSR) were calculated for each year of growth, and statistical models were developed to describe the annual development of knot diameter and curvature as a function of stem radial increment, total tree height, stem diameter, and the position of knots along an annual growth unit. KSR varied as a function of tree age and of the height to diameter ratio of the stem, a variable indicative of the competitive status of the tree. Simulations of the development of an individual knot showed that an increase in the stem radial growth rate was associated with an increase in the initial growth of the knot, but also with a shorter lifespan. Our results provide support for ‘Milton’s Law’, since they indicate that allocation priority is given to locations where the potential return is the highest. The developed models provided realistic simulations of knot morphology within trees, which could be integrated into a functional-structural model of tree growth and above-ground resource partitioning.

International audience; Abstract Key message With a retrospective growth analysis over 20 years, we showed that silviculture (in particular thinning) ofCedrus atlantica(Manetti) could to some extent mitigate the effects of drought episodes. Severe reductions of density resulted in faster recovery of radial growth after severe drought episodes. Context Climate change is expected to increase the frequency and the intensity of drought in southern Europe. Silviculture could help in mitigating the effects of water deficit on forests. Aim The aim of this study is to assess the effect of thinning intensity on the climate-growth relationship of different crown classes in Cedrus atlantica (Manetti). Material and methods A 20-year annual survey was conducted on plots managed under contrasted thinning regimes in a site of the southern French Alps. Using a linear mixed modeling approach, we evaluated the modulation of the growth response to annual climate by thinning (climate × thinning interaction effect) during the experiment. The effect of thinning on the growth sensitivity to annual climate and the effect of thinning on the growth response to pointer years were also quantified. Results The highest intensity of thinning significantly changed the climate-growth relationship of the two most dominant crown classes. Heavy thinning reduced the impact of negative pointer years during a period of 4–5 years and improved the post-drought recovery for a decade. Heavily thinned plots and dominant crown classes had significantly higher relative growth sensitivities to annual climate over the studied period. Conclusions Forest management has the potential to reduce the effect of water deficit on the growth of Atlas cedar stands. We provide keystones for future silvicultural guidelines, in the context of a larger introduction of C. atlantica in the French territory.

International audience; The radial growth of mature cork oaks (Quercus suber L.) was studied during a 9-year production cycle using monthly dendrometer measurements and cork ring widths. The mean tree radial increase was 5.1 mm yr$^{-1}$ and the cork increment accounting for 3.8 mm yr$^{-1}$. The radial growth curves for cork, wood and stem were very similar, showing a decreasing trend along the production cycle. Cork increment was always the largest fraction of tree growth (on average 74%) and showed less inter-annual variations as compared to wood. Tree radial growth presented a clear within-the-year seasonal pattern, extending from March to October, with a maximum in June-July. The overall pattern of monthly growth distribution was similar among the years of the production cycle, but some inter-annual variations occurred with 1-2 month shifts or monthly growth rate decreases, related to climatic factors. Early spring growth was enhanced by winter rain, autumn growth by high summer rain and June increments by high temperatures during this month.; Influence du climat sur la variabilité saisonnière de la croissance radiale du chêne-liège au cours d'un cycle de production de liège. La croissance radiale de chênes-liège (Quercus suber L.) adultes en pleine production a été suivie pendant un cycle de production de 9 ans par des mesures mensuelles de dendromètres et par la mesure des cernes du liège. L'accroissement annuel des arbres a été de 5,1 mm an$^{-1}$, dont 3,8 mm an$^{-1}$ de liège. Les courbes de croissance du liège, du bois et de la tige ont montré une même tendance à la diminution de la croissance au cours du cycle. Le liège, qui correspond à la fraction majeure de l'accroissement de l'arbre (en moyenne 74 %), a montré une variation interannuelle de croissance moindre que le bois. La croissance soumise à une variation saisonnière marquée, s'étend de mars à octobre, avec un maximum en juin-juillet. La distribution de la croissance a été similaire toutes les années, parfois avec des déphasages de 1 à 2 mois ou avec une diminution de l'accroissement résultant de variations interannuelles de précipitation ou de température. La croissance au début du printemps a été favorisée par les pluies d'hiver, la croissance en automne par les pluies d'été et les accroissements en juin par une température moyenne plus élevée pendant ce mois.

International audience; Picea sitchensis is an ecological and economical component of North America north temperate rain forest. In Haida Gwaii which is one of the most productive forest land of British Columbia archipelago (Canada), it is an important and a valuable commercial species. The present study aims at precising deer browsing consequences on growth regeneration of Picea sitchensis. Using ring-width series, an empirical model is built which describes browsing impact on radial growth and removal of these pressure. Taking into account deer pressure and browsing upper limit when building predictive height growth models proves valuable for comparing growth pattern of different species under browsing pressure and deducing changes in forest dynamics.; Influence de l'arrêt de l'abroutissement sur la croissance radiale de Picea sitchensis.Picea sitchensis est un composant majeur tant au niveau écologique qu'au niveau économique des forêts pluviales et tempérées de l'Amérique du Nord. Sur l'archipel Haida Gwaii, qui est recouvert par une forêt des plus productive de Colombie Britannique (Canada), c'est une essence à forte valeur commerciale. La présente étude vise à préciser les conséquences de l'abroutissement par le cerf à queue noire sur la croissance des individus au cours de la régénération. Sur la base de séries d'épaisseurs de cernes, un modèle empirique de croissance radiale est construit. Il décrit l'effet de l'abroutissement et de la suppression de celui-ci lorsque les individus parviennent à dépasser la limite supérieure d'abroutissement. La prise en compte de l'impact du cerf sur la croissance radiale et de la limite supérieure d'abroutissement dans l'élaboration des modèles prédictifs de croissance en hauteur s'avère intéressante pour comparer les modèles de croissance de différentes espèces abrouties et en déduire des conséquences sur la dynamique forestière.

International audience; Global change—particularly climate change, forest management, and atmospheric deposition—has significantly altered forest growing conditions in Europe. The influences of these changes on beech growth (Fagus sylvatica L.) were investigated for the past 80 years in Belgium, using non-linear mixed effects models on ring-width chronologies of 149 mature and dominant beech trees (87–186 years old). The effects of the developmental stage (i.e., increasing tree size) were filtered out in order to focus on time-dependent growth changes. Beech radial growth was divided into a low-frequency signal (=growth rate), mainly influenced by forest management and atmospheric deposition, and into a high-frequency variability (≈mean sensitivity), mainly influenced by climate change. Between 1930 and 2008, major long-term and time-dependent changes were highlighted. The beech growth rate has decreased by about 38% since the 1950–1960s, and growth variability has increased by about 45% since the 1970–1980s. Our results indicate that (1) before the 1980s, beech growth rate was not predominantly impacted by climate change but rather by soil alteration (i.e., soil compaction and/or nitrogen deposition); and (2) since the 1980s, climate change induced more frequent and intense yearly growth reductions that amplified the growth rate decrease. The highlighted changes were similar in the two ecoregions of Belgium, although more pronounced in the lowlands than in the uplands.

International audience; The aim of this paper is to illustrate how some extreme events could affect forest ecosystems. Forest tree response can be analysed using dendroecological methods, as tree-ring widths are strongly controlled by climatic or biotic events. Years with such events induce similar tree responses and are called pointer years. They can result from extreme climatic events like frost, a heat wave, spring water logging, drought or insect damage... Forest tree species showed contrasting responses to climatic hazards, depending on their sensitivity to water shortage or temperature hardening, as illustrated from our dendrochronological database. For foresters, a drought or a pest disease is an extreme event if visible and durable symptoms are induced (leaf discolouration, leaf loss, perennial organs mortality, tree dieback and mortality). These symptoms here are shown, lagging one or several years behind a climatic or biotic event, from forest decline cases in progress since the 2003 drought or attributed to previous severe droughts or defoliations in France. Tree growth or vitality recovery is illustrated, and the functional interpretation of the long lasting memory of trees is discussed. A coupled approach linking dendrochronology and ecophysiology helps in discussing vulnerability of forest stands, and suggests management advices in order to mitigate extreme drought and cope with selective mortality.; Cet article illustre comment des événements extrêmes peuvent affecter les écosystèmes forestiers. La réponse des arbres peut être étudiée par des méthodes dendroécologiques, les largeurs de cernes étant étroitement contrôlées par les contraintes climatiques ou biotiques. Ces contraintes induisent des réponses similaires des arbres, lors d’années dites « années caractéristiques ». Elles traduisent les réponses de la croissance à un événement climatique ou biotique extrême : gel intense,canicule, excès d’eau printanier, sécheresse, ravageur. . . comme l’illustre notre base de données dendrochronologiques. Pour le forestier, une sécheresse ou un aléa biotique sont considérés comme extrêmes s’ils induisent des dysfonctionnements visibles et durables (coloration anormale du feuillage, perte foliaire, mortalité de branches, dépérissement, mortalités anormales). De tels impacts, souvent différés de quelques années après l’aléa, sont illustrés à partir d’études de dépérissements forestiers avérés depuis 2003, ou attribués à des sécheresses ou des défoliations plus anciennes en France. La récupération de la croissance ou la vitalité des arbres est illustrée et des éléments fonctionnels d’interprétation des effets différés sont discutés. Enfin, en couplant dendroécologie et écophysiologie, nous abordons la vulnérabilité des peuplements forestiers et suggérons des recommandations de gestion forestière permettant d’atténuer l’intensité des sécheresses extrêmes et d’anticiper les mortalités sélectives des espèces ou des individus les moins résistants.

Des plants de Populus tremula Michx. × Populus alba L. clone 717-1B4 ont été cultivés en système de culture hydroponique pour obtenir une activité cambiale dans un milieu nutritif variable. La croissance secondaire de la tige a été caractérisée par une mesure automatique de la croissance radiale et des observations histologiques. Les résultats montrent le premier enregistrement de l'activité cambiale en hydroponie chez le peuplier. En outre, nous démontrons que les carences nutritives peuvent être étudiées en privant progressivement les plants de solution nutritive. Le système se prête à la mesure de la conductance stomatique, de la croissance primaire de la tige, de la croissance foliaire et de la croissance radiale. Dans cette étude nous observons que les croissances primaire et secondaire sont touchées par les carences nutritives. Ce système de culture en hydroponie est exploitable pour l'élucidation de l'impact des facteurs environnementaux, physiologiques et moléculaires sur l'activité cambiale et la formation du bois., Populus tremula Michx. × Populus alba L. clone 717-1B4 plants were grown in a hydroponic system in an effort to detect cambial activity in a changing nutrient environment. The secondary growth of the stem was determined by automated measurement of radial growth, as well as by histological study. This is the first time poplar cambial activity has been recorded in a hydroponic system. Further, we demonstrate that nutrient limitations can be tested with progressive deprivation of liquid medium. The system lends itself to measurements of stomatal conductance, primary stem growth, leaf growth, and radial stem growth. In this study we found that primary and secondary growth were affected by nutrient solution limitations. This hydroponic system will be valuable in elucidating the impact of environmental, physiological, and molecular factors on cambial activity and wood formation.

The respective roles of carbon and water in radial growth were assessed using double girdling and water stress as experimental factors to induce variations of the carbon and water status of tissues of Juglans nigra x Juglans regia grown in France. The results show that structural radial growth (with its specific energy requirement) occurred mainly during the night-time, in relation with an improved water status, and consequently higher turgor pressure which allows tissue enlargement (cell division and/or expansion). Maximal respiration rate occurring at night, when transpiration was minimal, suggests no or very low involvement of dissolved CO2 originating from a distance, i.e. carried by the transpirational flux of xylem sap, in the total stem CO2 efflux rate. The observations point out the importance of current photoassimilate flux for active radial growth. Local stem reserves could only marginally contribute to radial growth, although sharp shortage in assimilate supply could induce, within a few days, significant mobilization of local parenchyma reserves which allowed growth resumption. However, the driving force of mobilization was apparently not organ-wide sugar deficiency, as mobilization was not associated with any significant drop of sugars at the organ level.

The variations of stem diameter as they can be accurately measured by Linear Variable Differential Transformer (LVDT) reflect the addition of four components: irreversible radial growth, reversible living-cell dehydration/rehydration, thermal expansion and contraction, and expansion of dead conducting elements due to the increase and relaxation of internal tensions. The correct interpretation of LVDT signals, with respect to the practical applications, should make an exact distinction between these four components. This paper describes a set of two experiments with potted hybrid walnut trees. Double girdling, water stress, and duration of the day versus night periods were used in the phytotron as experimental factors to induce variations of the carbon and water status of plant tissues. The latter were assessed, respectively, by water potential and transpiration, and by local stem respiration and carbohydrate content. The results are interpreted in terms of carbon or water limitation effects on stem diameter variations where radial growth and tissue elasticity could be distinguished. Moreover, they suggest no or very low involvement of CO2 originating from a distance, i.e. carried by the transpirational flux of xylem sap, in the total stem CO2 efflux rate.

International audience; The main objective of this study was to describe trends in genetic parameters for wood density and radial growth through cambial age in a radiata pine progeny test established in the south of Chile. Wood samples from 31 half-sib families of radiata pine were obtained and submitted to an X-ray densitometry procedure. The analyzed traits were total ring width (TRW), ring area (RA), and average ring density (ARD). Statistical analyses were conducted to estimate the heritability of individual traits at the ring level and the ring-to-ring genetic correlation between ARD and radial growth. The pattern of change of genetic parameters with cambial age is especially affected between rings 6 to 10, which can be related with the transition from juvenile wood to adult wood. The genetic control of ring density was strong at cambial ages 2 and 3 and dropped to zero within the transition zone (rings 6 and 8). After ring 10, the genetic control of ARD varied from low to moderate. From cambial ages 3 to 9, the genetic correlation between ring density and radial growth was positive. From rings 5 to 9, the phenotypic correlation was also positive but low. At rings 8 and 9, the relationship between radial growth and density changed and strong within-plot competition effects possibly affected the phenotypic correlation between ring density and radial growth. After ring 9, the genetic correlation was negative but weak. The phenotypic correlation between ring density and radial growth increased its negative magnitude towards cambial age 14, which may have been the result of local micro site influences, such as competition for light and nutrients.; Contrôle génétique de la densité et de la croissance radiale en fonction de l'âge cambial dans un test de familles de pin radiata. L'objectif de cette analyse est d'évaluer le contrôle génétique de la densité du cerne en fonction de l'âge cambial, et d'estimer les corrélations génétiques entre croissance radiale et densité du bois, en fonction également de l'âge cambial, chez le pin radiata au Chili. Des échantillons de bois provenant de 31 familles de demi-frères de pin radiata installées dans un test de descendances maternelles installé au Chili ont été récoltés et soumis à une procédure d'analyse microdensitométrique aux rayons X. Les caractères analysés sont la largeur de cerne (TRW), la surface du cerne (RA) et la densité moyenne du cerne (ARD). Des analyses statistiques ont permis d'estimer l'héritabilité de ces caractères au niveau du cerne, ainsi que les corrélations génétiques entre caractères de croissance radiale et densité du cerne en fonction de l'âge cambial. La tendance générale de l'évolution des paramètres génétiques change particulièrement au niveau des cernes 6 à 10 depuis la moelle, ce qui reflète peut-être le passage du bois juvénile au bois adulte. Le contrôle génétique de la densité du cerne est élevé aux âges cambiaux 2 et 3, et tombe à 0 au niveau des cernes 6 à 8. Après le cerne 10, le contrôle génétique de la densité du cerne devient faible à modéré. De l'âge cambial 3 à l'âge cambial 9, la corrélation génétique entre la densité du cerne et la croissance radiale est positive. Entre les cernes 5 et 9, la corrélation phénotypique entre les mêmes caractères est également positive, mais faible. Au niveau des cernes 8 et 9, la relation entre la densité et la croissance radiale change et la corrélation phénotypique entre la densité du cerne et la croissance radiale est alors probablement affectée par de forts effets compétition à l'intérieur des placeaux. Après le cerne 9, la corrélation génétique devient négative mais reste faible. Par contre, la corrélation phénotypique négative entre densité du cerne et croissance radiale devient plus intense jusqu'à culminer à l'âge cambial 14. L'ampleur de cette corrélation phénotypique est peut-être dominée par des effets microsite du type compétition pour la lumière et pour les éléments minéraux.

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.

International audience; The past history of a 300-year-old Quercus petraea stand (the "Futaie des Clos", 8 ha) located 20 km from the town of Le Mans in the Forest of Bercé in the western part of France (Sarthe) was analysed by a dendroecological approach. According to the number of healthy trees alive (> 400), the stand age (> 300 years), and the dimensions of the trees (dia: 92 cm; height: 45.2 m), this plot constitutes one of the most remarkable oak grove in France. High competition pressure between trees appeared to be the most important factor to explain the high-quality timber (high straight stems without wood defaults, narrow regular rings). After an initial 90-year period of decrease, this stand shows a 1 mm*year-1 growth increment from the 1810s to the present. The growth increase of 40-50% occurring for over than 20 years can be interpreted as a response to the increase of harvesting intensity. The influence of climate was evaluated by comparing earlywood, latewood and total ring indices with monthly climatic data collected at Le Mans over the period 1921-2001. Extreme growth years coincided with wet or dry springs (May-June) (± 40% of rainfall in relation to normal conditions) often associated with warm or fresh July. The climatic models accounted for between 18 and 26% of the variability of ring widths, and suggested that earlywood formation depended mainly on previous autumn hydric balance and winter temperature whereas the growth of the latewood band was maximum in early spring (positive effect of May hydric balance). The ecophysiological interpretations of the climatic correlations are discussed.; Dendroclimatologie du chêne sessile (Quercus petraea Mill.) en forêt de Bercé ("Futais des Clos", Sarthe, France). Une étude dendroécologique a été entreprise afin d'analyser l'évolution de la croissance radiale d'un peuplement âgé de chêne sessile (Quercus petraea Mill.) (la Futaie des Clos) localisé dans la forêt de Bercé à 20 km du Mans (Sarthe - France). En raison du nombre d'arbres présents (plus de 400 sur les 8 ha), de leur âge (> 300 ans en 2001) et de leur dimension (diamètre et hauteur moyens : 92 cm et 45,2 m), ce peuplement constitue une des plus remarquables chênaie sessiliflore de France. La sylviculture peu intensive pratiquée dans le peuplement explique en grande partie la très grande qualité des arbres (tronc très droit sans défaut, cernes fins réguliers). Après une période de décroissance de 90 ans, la largeur moyenne des cernes est d'environ 1 mm par an depuis 1810. L'augmentation de croissance observée depuis une vingtaine d'années (1980-2001) peut être interprétée comme l'expression de l'augmentation de l'intensité des éclaircies (diminution de la compétition entre les arbres). L'effet du climat a été analysé en comparant les variations du bois initial, du bois final et du cerne complet aux données climatiques du Mans sur la période 1921-2001. Les années de croissance extrêmes (années " caractéristiques ") coïncident avec des printemps pluvieux ou secs (mai-juin) (± 40 % de pluies par rapport aux conditions normales) souvent associés avec un mois de juillet frais ou très chaud. Les modèles climatiques expliquent entre 18 et 26 % de la variabilité des largeurs des cernes et suggèrent que la formation du bois initial dépend essentiellement du bilan hydrique de l'automne précédent et des températures hivernales alors que le bois final est fortement influencé par le bilan hydrique du printemps (rôle essentiel du mois de mai). Les interprétations écophysiologiques des corrélations climatiques sont discutées.

International audience; Improved wood production is a major aim for walnut forests and especially for hybrid walnut (Juglans nigra x Juglans regia). This paper presents the first report describing the structure and function of a CDKA gene potentially involved in radial growth and wood production in walnut. We report the isolation of the full sequence of a CDKA gene by the use of degenerate primers and RACE approaches. We also describe the expression of the CDKA gene during radial growth. The analysis of intron sizes and positions as well as Southern-blot analysis suggest the presence of multiple copies (more than 2) of the CDKA gene in the hybrid walnut genome. Two different promoter sequences were cloned by the use of two different second-intron-specific primers.