Search

Introduction: Climate change will have a differential impact on mountain forest growth linked to elevation. Objective: To evaluate the interrelationships of growth ring components at altitudinal gradient limits of Pinus hartwegii Lindl. in three mountains of east-central Mexico. Materials and methods: We analyzed 295 tree samples from Cofre de Perote, Pico de Orizaba and Monte Tláloc corresponding to the period 1960-2017 with a total of 17 700 observations per variable (ring width and density [TRW, TRD], earlywood [EWW, EWD], latewood [LWW, LWD] and minimum and maximum density [MID, MAD]). Results and discussion: Growth parameters were higher at the lower limit (≈3 500 m). The correlation of TRW with EWW (r ≥ 0.95) and LWW (r ≥ 0.78) was significant (P < 0.05). TRD correlated with EWD (r ≥ 0.83) and MID (r ≥ 0.72), as well as EWD with MID (r ≥ 0.92) and LWD with MAD (r ≥ 0.92). At the upper limit (≈4 000 m), correlations of TRW, EWW and LWW with TRD, EWD and MID were negative (-0.3 ≥ r ≥ -0.8). This may be explained by lower temperatures and growth periods reducing the relative importance of latewood in ring width. Conclusions: The information provided contributes to understand the dynamics of P. h ar t we g ii xylogenesis in response to climate and possible implications for radial growth facing climate change.

In the long term, defoliation strongly decreases tree growth and survival. Insect outbreaks are a typical cause of severe defoliation. Eastern spruce budworm (Choristoneura fumiferana Clem.) outbreaks are one of the most significant disturbances of Picea and Abies boreal forests. Nevertheless, in boreal conifers, a 2-year defoliation has been shown to quickly improve tree water status, protect the foliage and decrease growth loss. It suggests that defoliation effects are time-dependent and could switch from favorable in the short term to unfavorable when defoliation duration exceeds 5–10 years. A better understanding of the effect of defoliation on stem radius variation during the needle flushing time-window could help to elucidate the relationships between water use and tree growth during an outbreak in the medium term. This study aims to assess the effects of eastern spruce budworm (Choristoneura fumiferana Clem.) defoliation and bud phenology on stem radius variation in black spruce [Picea mariana (Mill.) B.S.P.] and balsam fir [Abies balsamea (L.) Mill.] in a natural stand in Quebec, Canada. We monitored host and insect phenology, new shoot defoliation, seasonal stem radius variation and daytime radius phases (contraction and expansion) from 2016 to 2019. We found that defoliation significantly increased stem growth at the beginning of needle flushing. Needles flushing influenced the amplitude and duration of daily stem expansion and contraction, except the amplitude of stem contraction. Over the whole growing season, defoliation increased the duration of stem contraction, which in turn decreased the duration of stem expansion. However, the change (increase/decrease) of the duration of contraction/expansion reflects a reduced ability of the potential recovery from defoliation. Black spruce showed significantly larger 24-h cycles of stem amplitude compared to balsam fir. However, both species showed similar physiological adjustments during mild stress, preventing water loss from stem storage zones to support the remaining needles’ transpiration. Finally, conifers react to defoliation during a 4-year period, modulating stem radius variation phases according to the severity of the defoliation.

International audience; Context: Douglas-fir, a fast growing conifer from western North America, recently suffered diebacks following drought in France. We investigated the link between native-source climate and provenance drought resistance in a common garden in France. We compared the adaptive potential of provenances from different parts of the natural area. Methods: We collected branches from a 25-year-old provenance trial replicated in two test sites in southern France. We estimated provenance variation of cavitation resistance traits, survival and circumference. We compared Washington-Oregon provenances to coastal and interior Californian provenances. Results: In the common gardens, the hydraulic traits were significantly variable between provenances, with a strong site x provenance interaction, and significantly related to the climate of the natural area and survival. The relationships were different between variables and test-sites. The two test-sites and their particular climatic selective pressure revealed different geographical adaptive structures in the natural area. Conclusions: Douglas-fir evolutionary adaptation to drought results from natural selection to summer climate and shapes populations for cavitation resistance. In the dryer site only, the Interior California provenances seem more drought resistant. The strong within-provenance variations suggest that there is also a certain withinprovenance adaptation potential to drought at the cost of variable mortality rates.

Background: Mountain forest soils (≥2,500 m a.s.l.[1]), where elevation is crucial in the ecosystem dynamic, have a great capacity to capture and preserve carbon for a long time. The aim of this research was to determine the role of elevation combined with soil, climate, and vegetation variables on soil organic carbon (SOC) stocks distribution under P. hartwegii in the Nevado de Toluca Volcano, a protected area in Mexico. Topsoil samples (0-15 cm depth) collected every 100 m in elevation (3,400-4,000 m) were chemically and physically examined in statistical analysis together with vegetation structure and climate variables. Derived from field forest conditions, elevation plots were additional analyzed as logged (3,400-3,800 m) vs no-logged (3,900-4,000 m). Results: SOC stocks followed a significant linear trend (r2= 0.70; p= 0.02) along the elevation gradient, being highest at 4,000 m (173.1 ± 5.2 Mg C ha-1) and lowest at 3,700 m (146.8 Mg C ha-1). Multiple regression analyses showed that SOM, BD, and mean annual temperature (MAT) were the main abiotic drivers of SOC stocks variability (94.5 %) along the elevation gradient. Meanwhile, from the logistic multiple regression, higher tree shrubs and herbs density, in addition to lower tree height and grass cover at lower elevations, indicate a significant effect of logging on soil traits and vegetation structure, depending on the elevation plot. Conclusions: This research evaluated the SOC stocks and the potential effect of current warming over mountain soils, using the elevation as a proxy for both environmental and human drivers of SOC stocks in mountain forest ecosystems. Higher SOM and grass cover, larger-diameter trees together with low temperatures and logging restrictions in the high elevation range suggest a slower decomposition rate and SOC long-term stability. Despite the fact that we do not know about the intensity and cutting cycle, nor the size of the clearings derived from the trees removed, results from this research show how logging could exacerbate these effects and diminish SOC stocks, as well as the capacity of mountain soils to mitigate the effects of climate change.

Tree death is not always preceded by a visible decline in vigor (canopy dieback) or a progressive loss in crown volume. Identifying early-warning signals of incipient decline can help to implement the necessary measures to prevent tree death. The aim of this work is to understand what functional alterations preceded the massive drought-induced death of adult Pinus canariensis trees in an arid stand, located in the Canary Islands. To this aim, we analyzed interannual variations in earlywood and latewood width, wood density and anatomy, and carbon isotope composition, and the relationships among these variables, in dead and living trees from 1980 to 2013. Dead trees grew less since the 1990′s, produced fewer parenchyma rays and resin canals, and exhibited a trend of decreasing latewood density and a marked shift in carbon isotope discrimination over the last 34 years that were reversed in living trees. Higher wood density in living trees resulted from thicker tracheid cell walls rather than narrower lumens. The intrinsic water use efficiency shifted from higher to lower values in dead trees after the 2000s. These results suggest a carbon limitation to maintain hydraulic safety under xylem tension, as well as to maintain storage and defense capacity, which can render trees more vulnerable to severe drought episodes. A long-term trend of decreasing tree-ring density and a reduced intrinsic water use efficiency in the short-term can be early-warning signals of carbon limitation and tree decline in drought-stressed P. canariensis. The analysis of these variables can be used to assess tree decline risks in similarly vulnerable conifer populations inhabiting drought-prone regions.

International audience; In the subalpine forest ecosystems of the French Alps, European larch trees (Larix decidua Mill.) are periodically affected by outbreaks of a defoliating insect, the larch budmoth (Zeiraphera griseana (Hubner, 1799); LBM). To assess the long-term dynamics of LBM populations, we propose a spatiotemporal analysis of a long outbreak chronology reconstruction for the entire French Alps covering the period 1414-2009. This chronology was obtained by analyzing tree ring width (TRW) chronologies collected from 44 larch populations. The evidence of a latitudinal gradient in LBM is an original result that we have related to the "travelling waves" and "epicenter" theory. Wavelet analyses revealed a strong explicit continuous signal for periodicities of 4, 8, and 16 years throughout the entire 1500-2003 time series, except for a loss of power from 1690 to 1790 and since the early 1980s. We hypothesize that these abrupt changes could reflect a physiological response of LBM to past climatic variations. The spatial and temporal variability of LBM outbreaks and the propagation phenomenon in the French Alps highlighted by this study raises questions regarding its future dynamics in response to the expected climate change.; Dans les écosystèmes forestiers subalpins des Alpes françaises, le mélèze (Larix decidua Mill.) subit périodiquement les épidémies d’un insecte défoliateur, la tordeuse du mélèze (Zeiraphera griseana (Hübner, 1799); LBM). Afin de mieux comprendre les dynamiques à long terme des populations de tordeuse, nous proposons dans cet article une analyse spatio-temporelle d’une très longue reconstruction des épidémies pour la période 1414–2009 sur l’ensemble des Alpes françaises. Cette chronologie a pu être reconstruite à partir des cernes de croissance de 44 populations de mélèze. Les résultats ont permis de mettre en évidence le rôle d’un gradient latitudinal que nous avons attribué au phénomène théorique des « épicentres » et « vagues de dissémination ». D’autre part, les analyses temporelles, réalisées à l’aide de la méthode des ondelettes, ont révélé l’existence d’un fort signal continu pour des fréquences périodiques de 4, 8 et 16 ans sur l’ensemble de la chronologie à l’exception d’une perte d’énergie entre 1690 et 1790 et depuis le début des années 1980. Ces changements pourraient refléter une réponse physiologique de la tordeuse à des variations climatiques passées. La variabilité temporelle et spatiale des épidémies de tordeuse ainsi que le mode de propagation à travers les Alpes françaises nous ont conduits à nous interroger sur les dynamiques futures de l’insecte et de son hôte en réponse au réchauffement climatique rapide dans les écosystèmes de haute élévation.

Until recently, the roles of plant MADS-box genes have mainly been characterized during inflorescence and flower differentiation. In order to precise the roles of AGAMOUS-LIKE 12, one of the few MADS-box genes preferentially expressed in roots, we placed its cDNA under the control of the double 35S CaMV promoter to produce transgenic walnut tree and Arabidopsis plants. In Juglans sp., transgenic somatic embryos showed significantly higher germination rates but abnormal development of their shoot apex prevented their conversion into plants. In addition, a wide range of developmental abnormalities corresponding to ectopic root-like structures affected the transgenic lines suggesting partial reorientations of the embryonic program toward root differentiation. In Arabidopsis, AtAGL12 overexpression lead to the production of faster growing plants presenting dramatically wider and shorter root phenotypes linked to increased meristematic cell numbers within the root apex. In the upper part of the roots, abnormal cell divisions patterns within the pericycle layer generated large ectopic cell masses that did not prevent plants to grow. Taken together, our results confirm in both species that AGL12 positively regulates root meristem cell division and promotes overall root vascular tissue formation. Genetic engineering of AGL12 expression levels could be useful to modulate root architecture and development.

International audience; Characterizing drought resistance of forest trees is an important aim in the worldwide context of increasing forest decline and dieback. Furthermore, wood demand is increasing all around the world, urging the need for the domestication of native species and the selection of the most resistant individuals. While near-infrared spectroscopy is now recognized as an efficient tool to predict wood physical and chemical properties involves in wood quality, its ability to predict wood hydraulic function remains anecdotic, although it has recently gained interest. In this study, we tested near-infrared spectroscopy as a high-throughput method for quantifying both resistance to cavitation and basic wood density in the South American conifer Austrocedrus chilensis. Models were obtained in two laboratories using the same sample set. To assess resistance to cavitation, vulnerability curves were obtained using the air-injection method. Basic wood density was measured in the same samples as used for resistance to cavitation. Partial least squares regression models with cross-validation were used to establish relationships between the NIRS spectra and wood traits. The accuracy of the models strongly depended on the traits being used for calibration. Models obtained in both laboratories were similar, demonstrating the genericity of the approach whatever equipment used. Promising results were obtained for two cavitation parameters (water potential at 12% and 50% of hydraulic conductivity loss) and basic wood density. Prediction errors for these traits were low. In contrast to studies at the interspecific level, basic wood density and resistance to cavitation were negatively correlated at the intraspecific level in the studied species, but our calibration models shown than basic wood density cannot be used as a good predictor of functional traits. The NIRS has high potential to be put into practice as a rapid, reliable, and non-destructive method to determine, resistance to xylem cavitation, a trait involved in drought resistance.

Key message[br/] Despite variable dynamics of genetic diversification at the different altitudinal levels, strong gene flow tends to standardize larch genetic diversity: the larch forest distributed along the altitudinal gradient can be regarded as a single population.[br/] [br/] Context[br/] While in forest tree species many studies focus on the structure of the genetic diversity at the natural range and at the forest stand levels, few studies have worked at intermediate levels like the landscape level.[br/] [br/] Aims[br/] We tried to determine to what degree altitude variation can affect the genetic diversity and the local structure of the genetic diversity of European larch (Larix decidua Miller) at the landscape level.[br/] [br/] Methods[br/] Using microsatellite markers, we determined the between- and within-plot genetic structure and the spatial genetic structure (SGS) of four altitudinal plots distributed between 1,350 and 2,300 m a.s.l. in a European larch forest located in the French Alps.[br/] [br/] Results[br/] A homogenous neutral genetic structure was detected along this gradient. The intensity of the SGS was found to be stronger at 2,300 m and decreased at the 2,000-m plot. It was low or non-existent at the 1,700- and 1,350-m altitudinal levels.[br/] [br/] Conclusion[br/] Our results suggest that the genetic structure observed at the landscape level in this European larch forest was only slightly affected by climatic variation, human activities, or historical events. However, the variation of intensity of the SGS within the altitudinal plots indicates the existence of variable genetic dynamics, despite the globally uniform genetic structure along the altitudinal gradient.

International audience; The correlation between tree ring width and density and short-term climate fluctuations may be a useful tool for predicting response of wood formation process to long-term climate change. This study examined these correlations for different radiata pine genotypes and aimed at detecting potential genotype by climate interactions. Four data sets comprising ring width and density of half- and full-sib radiata pine families were used. Correlations with climate variables were examined, after the extraction of the effect of cambial age. Cambial age explained the highest proportion of the ring to ring variation in all variables. Calendar year and year by family interaction explained a smaller but significant proportion of the variation. Rainfall had a positive correlation with ring width and, depending on test site, either a negative or positive correlation with ring density. Correlations between temperature during growing season and ring density were generally negative. Climate variables that influence ring width and wood density can be identified from ring profiles, after removing the cambial age effect. Families can be selected that consistently show desirable response to climate features expected to become prevalent as a result of climate change.

International audience; Genetic variability of modulus of elasticity (MOE) was investigated in three genetic trials, including two progeny (16 years old) and one clonal (19 years old) trials of hybrid larch (Larix x eurolepis Henry). MOE was directly assessed on standing trees using the Rigidimeter, a bending device, and related to other traits including height, BH diameter and wood density. Mean MOE ranged from 5,183 to 9,228 MPa among families in the progeny trials and from 4,591 to 11,486 MPa in the clonal trial. Among traits studied, MOE was one of the most variable traits. It was strongly and positively related to wood density at both the individual and genotype mean levels. Interestingly too, wood stiffness did not seem, or only weakly, unfavourably linked to stem diameter at the phenotypical level, but it was negatively or not correlated to diameter at the genetic level. As well, MOE showed a high GxE stability over the two progeny trial sites. Narrow-sense heritabilities for MOE were moderate (around 0.36). In all three trials, they were lower than those for wood density or total height, and of the same level as for diameter. Improvement of wood stiffness of hybrid larch using the Rigidimeter seems possible and promising genetic gains are expected. Impacts of selection for growth traits on MOE are also discussed.

Microdensity profiles of Douglas-fir's clones and weather data were used to study phenotypic plasticity (dendroplasticity). Within-ring microdensity was interpreted as the variation of tree response to drought constraints during selected growing seasons. An original norm of reaction was obtained by pairing evident points of abrupt changes in tree-ring microdensity profiles and in weather indices. The coefficients of the non-linear models adjusted to the reaction norms were analysed as dendroplasticity variables. Dendroplasticity variables were significantly different between geographical locations, years and clones. Heritability of the dendroplasticity variables ranged from low to high and was similar to heritability values of microdensity variables such as mean ring density (MRD). Coefficients of genetic variation of dendroplasticity variables were intermediate between those of wood density and growth variables. Dendroplasticity variables were phenotypically and genetically related to ring microdensity variables, more strongly to latewood variables. Dendroplasticity provides retrospective, synthetic and easy-to-interpret information about tree response to the variation of the balance between water availability and water demand during the growing season. The proposed model of dendroplasticity is described by a number of parameters that are linked to a biological meaning. Our results suggest that there is a potential for adaptation to drought in Douglas-fir, with two mechanisms involved: at individual level, short-term plastic response during the growing season and, at population level, long-term, between-generation, evolution process.

In this work, we present a fast and promising method to evaluate the natural durability of wood based on X-ray microdensitometry. Tested on beech and Scots pine wood samples, our findings show that this methodology and the traditional EN standards methodology based on mass loss are strongly correlated. X-ray methodology is less time consuming (we can detect the effectiveness of the attack within 5-6 weeks) and less expensive (very cheap plastic Petri dishes instead of the expensive glass Kolle flasks); moreover, the proposed method allows to thoroughly examine the phases and the kinetics of the fungal attack, and to investigate the spatial repartition of the attack within the samples due to the low thickness of the sample.

International audience; Wood can be seen as a record of cambial activity. Within a ring, density variation from earlywood to latewood is a consequence of the within growing season climate changes. We propose a method to synchronize the within-ring density profile with within-growing season climate variables. Thanks to this synchronization, we show that Douglas-fir cambium reaction to the variation of the withingrowing season minimum temperature is variable and quite strongly genetically controlled. Such variation has a direct consequence on wood density, and thus on wood quality.

International audience; Genetic parameters were estimated for wood and growth traits in two 19-yr-old clonal trials and a 40-yr-old full-sib progeny trial of Norway spruce [Picea abies (L.) Karst.]. In the clonal trials high (>0.4) broad-sense heritabilities were found for wood density traits, lignin content, number of internal cracks, growth traits, spiral grain and number of resin canals. Moderate (0.2-0.4) heritabilities were found for tracheid lumen diameter and cell wall thickness, microfibril angle and tracheid length, while low heritabilities (

Classical quantitative genetics and quantitative trait dissection analysis (QTL) approaches were used in order to investigate the genetic determinism of wood cellulose carbon isotope composition (δ 13 C, a time integrated estimate of water use efficiency) and of diameter growth and their relationship on adult trees (15 years) of a forest tree species (maritime pine). A half diallel experimental set-up was used to (1) estimate heritabilities for δ 13 C and ring width and (2) to decompose the phenotypic δ 13 C/growth correlation into its genetic and environmental components. Considerable variation was found for δ 13 C (range of over 3%‰) and for ring width (range of over 5 mm) and significant heritabilities (narrow sense 0.17/0.19 for δ 13 C and ring width, respectively, 100% additivity). The significant phenotypic correlation between δ 13 C and ring width was not determined by the genetic component, but was attributable to environmental components. Using a genetic linkage map of a full-sib family, four significant and four suggestive QTLs were detected for δ 13 C, the first for δ 13 C in a forest tree species, as far as known to the authors. Two significant and four suggestive QTLs were found for ring width. No co-location of QTLs was found between δ 13 C and growth.

International audience; Wood is one of our most important natural resources and has been exploited for many hundreds of years as fuel, building material and a source of paper. Its composition is variable among and within species. The ability to monitor the intra-specific variability is a prerequisite to improve wood and end-products properties. This paper describes a study of the genetic control of a large set of wood properties, including growth, timber quality traits, wood chemical composition, kraft pulp production parameters and pulp properties, in a 12 $\times$ 12 half diallel of maritime pine (Pinus pinaster Ait.). While relatively high (h$^{2}_{\rm ns} > 0.3$) narrow-sense heritabilities were observed for density heterogeneity, lignin content, alpha-cellulose content and coarseness, no significant genetic effect was detected for hemi cellulose, water extractives, kraft pulp production parameters and pylodin. Slightly lower heritabilities ($0.15 < {\rm h}^{2}_{\rm ns} < 0.3$) were also obtained for wood density and fibre properties (length, width, curl, zero span). As a consequence and considering the phenotypic coefficient of variation obtained for these traits, improvement by selection of trees with outstanding wood quality is feasible. Nevertheless, it seems obvious that wood quality breeding can not be done without taking into account growth, and the only way to manage this constraint (negative correlation between growth and density) will be the constitution of elite "wood quality" populations in a already growth improved genetic population.; Déterminisme génétique des propriétés du bois impliquées dans la production papetière et la qualité du bois d'œuvre chez le Pin maritime (Pinus pinaster Ait.). Le bois, une des ressources naturelles les plus importantes, est exploité depuis des centaines d'années comme combustible, matériau de construction et source de papier. Sa composition est très variable, non seulement entre espèces mais aussi au niveau intra spécifique. La compréhension de cette variabilité intra spécifique est un pré-requis de l'amélioration des propriétés des produits à base de bois. L'objectif de l'étude présentée ici est la compréhension du déterminisme génétique de plusieurs caractères impliqués dans la composition chimique et les propriétés du bois (caractéristiques physiques, paramètres de production industrielle et propriétés de la pâte) grâce à l'étude d'un demi diallèle 12 $\times$ 12. Bien que des héritabilités au sens strict relativement élevées (h$^{2}_{\rm ns} >0,3$) aient été obtenues pour l'hétérogénéité de la densité, les contenus en lignine et en alpha-cellulose et la masse linéique, aucun effet génétique significatif n'a été mis en évidence pour le contenu en hémi-cellulose, les extractibles, les paramètres de production de pâtes kraft, et la densité estimée grâce au pilodyn. Des héritabilités plus faibles ($0.15 < {\rm h}^{2}_{\rm ns} < 0.3$) ont quant à elles été obtenues pour la densité du bois et les propriétés des fibres (longueur, largeur, courbure, rigidité). En conséquence, considérant les coefficients de variation phénotypiques obtenus pour ces caractères, des gains génétiques significatifs peuvent être attendus. Néanmoins, l'amélioration des propriétés du bois ne pourra pas se faire sans prendre en compte la croissance. Le seul moyen de gérer cette contrainte (induite par des corrélations négatives entre croissance et densité) sera la constitution de populations élites pour la qualité du bois au sein de bases génétiques déjà améliorées pour la croissance.

Fairly strong positive relationships between stiffness and density have often been reported. No stronger relationships have been found when using parameters of density profiles based on an earlywood-latewood boundary. In this study, we attempt to model the relationships among the stiffness of different samples and simple parameters derived from microdensity profiles, not established according to an earlywood-latewood boundary. Furthermore, we try to determine if there is a genetic variation for the relationship between stiffness and density. From the results, we find that the strongest relationship between a single density parameter and stiff- ness is r0.78, whereas it is r = 0.37 when involving a classical within-ring density parameter. At clone level, r 2 ranges from 0.88 to 0.95, while it is 0.51 for the bulked samples. The mathematical form of the models differ from one clone to another: there is a

Air entry in the plant water-transport system leads to vascular embolism that has a major impact on plant water relations by disrupting the water-transport capacity, impairing its functioning and even triggering the plant death. Forestry tree species should exhibit both high survival and fast growth rate. From this point of view, Eucalyptus is an interesting genus since it inhabits a wide diversity of climatic and environmental conditions and covers more than 20 million planted hectares worldwide. This genus presents solitary vessels, i.e. not directly connected to other vessels but surrounded by different imperforate tracheary elements and parenchyma that participate in a less known form in xylem safety and hydraulic efficiency.

Phenotypic selection generally reduces the variability of both the selected trait and other associated characteristics. Some species show a negative strong relationship between growth traits and wood density. In the present study, basic wood density was assessed in a group of 23 control trees and 25 Pinus ponderosa plus trees, selected for growth and form traits in the Argentine Patagonia region. Trees were sampled in four different sites from the environmental and silvicultural point of view. We aim to study if the phenotypic variation in wood density is somehow influenced by the selection for productivity and form. The average wood density of plus trees was 0.37 g cm(-3), ranging from 0.29 to 0.46 g cm(-3). These values were not significantly different to control trees and were similar to those previously found in P. ponderosa plantations growing in the region. Wood density of the improved population, represented by plus trees did not differ from that of base population from which plus trees were selected. Significant differences were found in wood basic density among sites and age-classes. The phenotypic variation of the increment of wood density from pith to bark and among trees was different from zero. Not significant association was found between wood basic density and growth and form traits, except for stem straightness. It would be possible to identify high wood density trees at half of the rotation age., La selección fenotípica generalmente reduce la variabilidad de los caracteres seleccionados y la de los caracteres asociados. Algunas especies muestran asociación negativa entre crecimiento y densidad de la madera. En este estudio, se evaluó la densidad básica de la madera en un grupo de 23 árboles control y 25 árboles plus de Pinus ponderosa seleccionados por criterios de crecimiento y forma en la región norpatagónica de Argentina. Las muestras provinieron de cuatro sitios con diferente clima y silvicultura. El objetivo fue determinar si la variación fenotípica de la densidad de la madera pudo haber sido afectada por la selección para productividad y forma. La densidad media de la madera de los arboles plus fue de 0,37 g cm-3, variando desde 0,29 hasta 0,46 g cm-3. Estos valores no fueron significativamente diferentes a los registrados en los árboles control y similares a los previamente registrados para P. ponderosa creciendo en la región. La densidad de la madera de la población de mejora (árboles plus) no difirió de la población base donde fue seleccionada. Diferencias significativas para la densidad de la madera se pudieron establecer entre sitios y clases de edad. El incremento de la densidad desde la médula hacia la corteza y la variación fenotípica entre árboles fue significativamente diferente de cero. La densidad no se encontró asociada a las características de crecimiento y forma, por las cuales los árboles plus fueron seleccionados, excepto con la rectitud de fuste. Sería posible identificar árboles de alta densidad básica cerca de la mitad del turno de rotación.

* INRA Orléans, Documentation, Ardon 45166 Olivet Diffusion du document : INRA Orléans, Documentation, Ardon 45166 Olivet; National audience

Among the ecosystem services provided by forests, wood provisioning takes a central position. Wood and derived products have played a critical role in the evolution of human kind and demand for raw material is increasing in a foreseeable future. Wood is used for energy production, construction and a wide variety of products for which different properties are required. Anatomical, chemical and physical properties of wood are determined through a complex process called xylogenesis controlled by internal and external signals and occurring during the life of the tree. In this chapter we describe i/how wood is formed and ii/the different factors controlling this developmental process with emphasis on the molecular machinery involved, iii/the functions of wood and iv/the biotechnology approaches developed to improve wood biomass production and properties genetically.