Plusieurs dépérissements du début du XXe siècle ont montré que le Douglas français était vulnérable à la sécheresse. La question de savoir si les forêts de Douglas peuvent s'adapter au nouveau climat plus chaud et plus sec est une préoccupation majeure en France. Nous avons estimé la variation de la résistance à la cavitation d'un ensemble de provenances de Washington, de l'Oregon et de Californie dans deux expériences de jardins communs situées dans le sud de la France. Nous avons étudié les relations entre la résistance à la cavitation, la microdensité du xylème et l'anatomie du tronc et des branches. Nous avons constaté que la pression de sélection climatique dans la zone naturelle a façonné l'adaptation locale pour la résistance à la cavitation, la microdensité et l'anatomie des ponctuations du xylème. Les provenances de Californie intérieure tendent à être plus résistantes à la cavitation, avec une plus grande densité de bois d'été et des ponctuation plus sûres que les provenances de Californie côtière, puis de Washington et d'Oregon. Cependant, nous avons également constaté des variations importantes à l'intérieur d'une même région qui ne pouvaient pas être expliquées par les données climatiques disponibles. Nous avons trouvé différentes relations structure-fonctions, selon le niveau d'observation (arbre ou provenance) et la partie de l'arbre (tronc ou branche). Par exemple, au niveau individuel, les arbres les plus résistants à la cavitation ont des branches plus denses avec une ouverture de ponctuation plus petite, tandis qu'au niveau de la provenance, les arbres les plus résistants à la cavitation ont du bois moins dense dans le tronc et les branches, et des ponctuations plus sûrs. Dans l'ensemble, nous concluons qu'il existe un potentiel d'adaptation évolutive pour la résistance à la sécheresse du Douglas, disponible à différents niveaux, individuel et de provenance. Cependant, dans un contexte d'amélioration des arbres, le réseau complexe de relations entre la résistance à la cavitation, la microdensité et les traits anatomiques doit être soigneusement examiné afin d'éviter une éventuelle réponse corrélative défavorable à la sélection. / Several turn-of-the-20th-century diebacks have shown that French Douglas-fir was vulnerable to drought. Whether the Douglas-fir forests can adapt to the new warmer and dryer climate is a key concern in France. We estimated variation of resistance to cavitation traits of a set of Washington, Oregon and Californian provenances in two common garden experiments located in the south of France. We studied the relationships between resistance to cavitation, xylem microdensity and pit anatomy in the trunk and branches. We found that climatic selection pressure in the natural area has shaped local adaptation for resistance to cavitation, microdensity and pit's anatomy. Inland California provenances tend to be significantly more cavitation resistant, with a denser latewood and safer pits than coastal Californian, then Washington and Oregon provenances. However, we also found significant within region variation that could not be explained by the available climatic data. We found different structure-functions relationships, according to the observation level (tree or provenance) and the tree part (trunk or branch). For example, at the individual level, the most cavitation-resistant trees have branches with denser latewood and smaller pit aperture, while at the provenance level, the most cavitation resistant provenances have less dense wood in both trunk and branches, and safer pits. Overall, we conclude that there is a potential for evolutionary adaptation for resistance to drought in Douglas-fir, available at different levels, individual and provenance. However, in a tree improvement context, the complex network of relationships among the resistance to cavitation, the microdensity and the anatomy traits should be carefully monitored in order to avoid possible unfavourable correlative response to selection.

Three studies were conducted to characterize and present early-seral competition between Douglas-fir seedlings and the surrounding vegetation communities during Pacific Northwest forest establishment. The first experiment served as the foundation for this dissertation and was designed to quantify tradeoffs associated with delaying forest establishment activities by introducing a fallow year in order to provide longer-term management of competing vegetation. A range of six operationally relevant treatments were applied over two growing seasons that included in the first (1) a no-action control, (2) a spring release only, (3) a fall site preparation without sulfometuron methyl followed by a spring release, as well as (4) a fall site preparation with sulfometuron methyl and a spring release. In the second year, there was (5) a fall site preparation without sulfometuron methyl followed by a spring release and also in the second year (6) a fall site preparation with sulfometuron methyl and a spring release. Treatments 5 and 6 were left fallow without planting during the first year. These treatments were applied in two replicated experiments within the Oregon Coast Range. After adjusting for initial seedling size, year-3 results indicated that plantation establishment and competition control immediately after harvest (i.e. no fallow period) enabled seedlings to be physically larger than those planted after a one year delay. At the Boot study site, limiting vegetation below 20% for the first growing season improved year-3 Douglas-fir seedling stem volume over 273 cm³. Delaying establishment activities one year and reducing competing vegetation below 11% enabled seedling volume after two years to be statistically the same as three year old seedlings in the no-action control, a volume range of between 148 to 166 cm³. Delaying forest establishment at Jackson Mast improved seedling survivorship over 88% when a spring heat event reduced survivorship of trees planted a year earlier to less than 69%. The combined effect of applying a fall site preparation and spring release was necessary to reduce competitive cover below 10% in the year following treatment and provided longer-lasting control of woody/semi-woody plants. Less intense control measures (i.e. no-action control and treatment 2) were not able to restrain woody/semi-woody plant cover which grew to nearly 40% at Boot and over 24% at Jackson Mast in three years. No treatment regime provided multi-year control of herbaceous species. Including sulfometuron methyl in the fall site preparation tank-mix did not have a negative effect on seedling growth or provide significant reductions in plant community abundance in the year following application when compared to similar regimes that did not include the chemical. Delaying establishment lengthened the amount of time associated with forest regeneration except on a site that accentuated a spring heat event. In the second study, horizontal distance and azimuth readings provided by a ground-based laser were used to stem map seedling locations and experimental unit features at Boot. These data were used to create a relative Cartesian coordinate system that defined spatially explicit polygons enabling, for the first time, the ability to collect positional data on competing forest vegetation within an entire experimental unit. Deemed "vixels" or vegetation pixels, these polygons were assessed for measures of total cover and cover of the top three most abundance species during the initial three years of establishment. An alternate validity check of research protocols was provided when total cover resulting from this vixel technique was compared to a more traditional survey of four randomly located subplots. The resulting linear regression equation had an adjusted R² of 0.90 between these two techniques of assessing total cover. When compared within a treatment and year, total cover differed by less than 12 percentage points between the two techniques. Analysis of year-3 woody/semi-woody plant cover produced by the techniques led to identical treatment differences. Two treatments resulted in woody/semi-woody cover of approximately 1500 ft² by the vixel method and nearly 40% cover by the subplot method while the remaining four treatments were grouped below 600 ft² or 20% cover, respectively. With continued refinement, these techniques could visually present forest development through all phases and provide long-term information used to bolster growth and yield models, measures of site productivity, as well as community ecology research. The third study evaluated the season-long gas exchange and biomass partitioning of four weedy plant species capable of rapidly colonizing Pacific Northwest regenerating forests. Cirsium arvense, Cirsium vulgare, Rubus ursinus and Senecio sylvaticus were studied at two sites. A greenhouse was used to introduce two levels of irrigation (well-watered and droughty). These species were also studied while growing among a larger vegetation community at a field site. Irrigation treatments had little impact on gas exchange rates. Species achieved maximum photosynthetic rates of 30, 20, 15 and 25 μmol CO₂ m⁻² s⁻¹ (respectively) prior to mid-July coinciding with an active phase of vegetative growth. As the season progressed, photosynthetic rates declined in spite of well-watered conditions while transpiration rates remained relatively consistent even when soil water decreased below 0.25 m³ H₂O/m³ soil. Water use efficiency was high until late-July for all study species, after which time it decreased below 5 μmol CO₂ · mmol H₂O⁻¹. Multi-leaf gas exchange measurements as well as biomass data provided a holistic view of plantlevel mechanisms used to shunt activity toward developing tissues. Herbaceous species had assimilation rates that differed vertically (within each species) by as much as 10 to 20 μmol CO₂ m⁻² s⁻¹ from July to September as lower leaves senesced in favor of those higher on study plants. Specific leaf area was greatest in June for all species then declined indicating species placed little effort into sacrificial early season leaves when compared to those higher on the plant that could continue to support flowering or vegetative growth. The study of seasonal gas exchange in the presence of declining water availability has helped to describe competitive mechanisms at work during forest regeneration as well as provide physiologic support for the application of vegetation management regimes. / Graduation date: 2013

No description available.

La variabilité des propriétés du bois ainsi que son hygroscopicité pourraient être un frein à son utilisation dans la construction, même s’il peut être considéré comme un matériau de choix dans le contexte environnemental et économique actuel. Il est donc primordial de mieux comprendre les origines physiques du comportement du bois pour être capable d’améliorer la prédiction de ses propriétés, et pouvoir ainsi le rendre plus compétitif par rapport aux autres matériaux de construction. Le comportement hygromécanique du bois, caractérisé par des variations dimensionnelles en présence de variations d’hygrométrie, est particulièrement difficile à prédire, du fait de sa microstructure multi-échelle et de ses interactions complexes avec l’eau.Dans ce contexte, la thèse vise à comprendre et enrichir les relations entre la microstructure du bois, ses propriétés de sorption et son comportement hygromécanique, en étudiant l’influence de l’hétérogénéité de l’accroissement annuel (cerne), constitué de bois initial et de bois final dont la structure et les propriétés présentent de nombreuses différences. Cette étude est menée sur du Douglas (Pseudotsuga menziesii (Mirb.) Franco), actuellement référencé comme un matériau de structure intéressant. Des outils de caractérisation avancés sont utilisés : la Résonance Magnétique Nucléaire (RMN) du proton pour caractériser les mécanismes de sorption ; la corrélation d’images volumiques (DVC) pour mesurer les champs de déformations à partir d’images 3D de microtomographie aux rayons X (µTRX), donnant aussi accès à la densité locale du bois.Après une introduction sur le matériau bois et un état de l’art sur son comportement hygromécanique, une caractérisation préliminaire de la microstructure (angle des microfibrilles, largeur de cerne, densité) et du comportement hygromécanique d’échantillons de bois initial et de bois final prélevés dans différents cernes est menée. Une forte anisotropie du bois initial est mise en évidence en opposition au comportement isotrope transverse du bois final. Les déformations suivant la direction des fibres présentent aussi de fortes non-linéarités peu discutées dans la littérature. Une discussion sur la variabilité des propriétés est par ailleurs engagée, ainsi que sur les relations structure-propriétés à l’échelle macroscopique.L’origine des différences de comportement hygromécanique entre le bois initial et le bois final est tout d’abord recherchée au niveau des mécanismes de sorption, au travers une étude de relaxométrie RMN du proton en 2D (cartes T1-T2). Deux types d’eau liée situés dans des environnements distincts sont mis en évidence et leur isotherme de sorption diffère dans les deux types de bois. Une hypothèse sur leur localisation dans la paroi cellulaire est proposée, puis une modélisation simplifiée 2D est effectuée pour évaluer leur impact respectif sur le comportement hygromécanique du bois initial et du bois final, en particulier dans la direction des fibres.Enfin, les champs de déformations locaux et globaux sont étudiés en analysant par DVC des images de µTRX de bois initial et de bois final soumis à différentes sollicitations hydriques. Le couplage entre ces deux matériaux est aussi étudié pour évaluer leurs interactions et comprendre le comportement du bois à l’échelle du cerne. Un protocole de DVC adapté aux images de bois est proposé. Les comportements hygromécaniques du bois initial, du bois final et du cerne sont comparés. A l’échelle locale, des hétérogénéités du champ de déformations sont mises en évidence et corrélées à la densité locale. Leur effet sur le comportement du cerne et sur la courbure des échantillons induite par le chargement hydrique est analysé. Une modélisation 3D par éléments finis, tenant compte des gradients locaux de propriétés, vient enfin compléter cette étude pour améliorer la compréhension des interactions mécaniques entre le bois initial et le bois final / Wood has highly variable properties and is also hygroscopic. These characteristics may restrict its use in construction even if it can be considered as a material of choice with the current environmental and economical concerns. Therefore, it is essential to better understand the physical origins of the behavior of wood in order to improve the prediction of its properties, and making it competitive with respect to other building materials. Dimensional changes of wood appear when it is subjected to relative humidity variations. This hygromechanical behavior is particularly difficult to predict because of the multiscale structure of wood and its complex interactions with water.In this context, the present work aims to understand and enrich relationships between microstructure, sorption properties and hygromechanical behavior of wood. More specifically, it is focused on the influence of the growth-ring heterogeneity, constituted of earlywood and latewood which have different structures and properties. The study is performed on Douglas fir (Pseudotsuga menziesii (Mirb.) Franco), which is a species of significant interest for structural applications. Advanced characterization tools are used: proton Nuclear Magnetic Resonance (NMR) to characterize sorption mechanisms; digital volume correlation (DVC) to measure deformation fields from X-Ray microtomography 3D images (XRµT), also providing local density of wood.At first wood properties and its hygromechanical behavior are described through a literature overview. Preliminary microstructural (microfibril angle, growth-ring width, density) and hygromechanical behavior characterizations of earlywood and latewood samples with different cambium age are performed. Earlywood reveals a strong anisotropic behavior compared to latewood which is isotropic in the transversal plane. Moreover, strains along the fiber direction nonlinearly evolve with moisture content. This phenomenon has been hardly reported and studied in the literature. Discussions on variability of properties and on relationships between structure and properties are also initiated.Sorption mechanisms are then studied by 2D NMR relaxometry (T1-T2 correlation spectra) in order to investigate differences between earlywood and latewood hygromechanical behaviors. Two types of bound water located in distinct environments are highlighted and their sorption isotherms are shown to be different in the two types of wood. A hypothesis on their location in the cell-wall is proposed and a simple 2D model is developed to evaluate their respective effect on the hygromechanical behavior of earlywood and latewood, especially in the fiber direction.Furthermore, local and global strains fields are studied using DVC from XRµT images of earlywood and latewood subjected to relative humidity variations. The coupling of these two materials is also investigated in order to evaluate their mechanical interactions and to understand the behavior at the growth-ring scale. A specific DVC procedure is developed for images of wood. The hygromechanical behaviors of earlywood, latewood and a growth-ring are compared. At the local scale, strains fields heterogeneities are highlighted and correlated to the local density. Their effect on the growth-ring behavior and the samples curvature is analyzed. A 3D finite elements model which takes into account local gradients of properties is finally developed to better understand earlywood-latewood mechanical interactions

Trembling aspen (Populus tremuloides Michx.) is one of the most common tree species in the boreal and temperate forests of North America. It grows on many different sites and associates with a variety of tree species. In BC, aspen is frequent throughout all submontane and montane continental forested zones. Relationships between environmental factors and forest productivity have been the subjects of many studies. Most of these studies, using various topographic, soil, physical and chemical properties as independent variables, had limited success in accounting for the variation in SI over a large geographic area. The objectives of this study were (1) to quantify relationships between aspen SI and environmental factors at two spatial scales, and (2) to develop predictive SI models from easily measurable environmental factors.

Douglas-fir (Pseudotsuga menziesii) is an economically important softwood that is clonally propagated for reforestation purposes by somatic embryogenesis. The molecular basis of embryogenesis in conifers is largely unknown and this prevents progress in somatic embryogenesis protocols. In angiosperms, the LEAFY COTYLEDON1 (LEC1) gene, encoding the HAP3 subunit of the eukaryotic CCAAT box-binding factor, is important in embryo formation, and necessary for somatic embryogenesis. A candidate gene strategy was employed to isolate the Douglas-fir LEC1 homologue, PmLEC1, via the polymerase chain reaction (PCR) with degenerate primers based on the Arabidopsis conserved domain, and the full-length cDNA sequence was obtained by rapid amplification of cDNA ends-PCR (RACE-PCR). The putative protein sequence shared high sequence identity with Arabidopsis LEC1. Northern analysis and quantitative real-time PCR indicate that this is an embryo-specific gene, expressed with the highest abundance during early embryogenesis. Antibodies were raised against a synthetic 18-amino acid PmLEC1 peptide, and in contrast to mRNA expression, Western blotting shows that PmLEC1 protein expression persists until the seedling stage. To gain insight into modulation of PmLEC1 expression and its inducibility in mature tissues, stress and hormone treatments were performed on mature seed and the promoter sequence was isolated by genome walking. Sorbitol, mannitol and 2,4-epibrassinolide were found to significantly up-regulate PmLEC1 expression. The PmLEC1 promoter contains a 5’ UTR intron with numerous enhancer elements, and factors that bind to these elements mediate responses to auxin, UV light and developmental cues, osmotic stress, biotic stress, and tissue culture. Some of the regulatory elements are binding sites for seed-specific transcription factors that are well known from angiosperms, providing new evidence that AGL15, ABI3 and VP1 proteins have a direct role on LEC1 expression. In investigating the embryogenic capacity of PmLEC1, ectopic expression of PmLEC1 in the embryo lethal Arabidopsis lec1-1 null mutant complemented the mutation and permitted the production of viable, desiccation tolerant seeds. In addition, transgenic seedlings produced embryo-like structures from vegetative organs and expressed seed-specific genes. In wild type plants, ectopic expression of PmLEC1 resulted in a bushy phenotype but expression of seed-specific genes was not observed. Taken together, these results show that PmLEC1 is an embryo-specific gene with an essential role throughout embryogenesis, and PmLEC1 expression may be induced in mature seeds by stress and hormone treatments. Because mature seeds show only trace amounts of PmLEC1 transcripts and Douglas-fir somatic embryogenesis can only be induced from immature embryos, this information provides useful insight into initiation of embryogenesis from vegetative tissues. The identification of binding sites for transcription factors known from angiosperms in the promoter region of PmLEC1 has revealed the identity of several genes which are expected to play pivotal roles in conifer embryogenesis.

Trees compete for various resources such as sunlight, water, and nutrients, which can be expressed as numerical terms, called competition indices (CI). Competition between individual trees is correlated with their growth and mortality. Therefore, CIs are used as independent variables to develop, improve and modify growth and yield models. This study was conducted to test the effect of neighborhood competition on tree diameter growth among Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco), western hemlock (Tsuga heterophylla (Raf.) Sarg) and red alder (Alnus rubra Bong.), in the Pacific Northwest Coast Range, USA. After testing seven distance-independent CIs and three distance-dependent CIs, only the distance-independent CIs were found to significantly affect the diameter growth model. Among them, CIs with basal area and diameter information were the most impactful. As a result, a simple CI was very effective in a model that accounts for the basal area information of different tree species.

A trait based approach was used to assess impacts of overstory density and thinning on understory vegetation components related to wildlife habitat. The relationship between overstory basal area and understory vegetation for species grouped by traits, such as production of flowers, fleshy-fruit and palatable leaves, was characterized in thinned and unthinned stands at seven Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) forests in western Oregon six years following harvests. The ranges of overstory densities within thinned and unthinned stands represent gradients of resource availability and thinning disturbance. Lower overstory densities and thinnings were associated with improved ecosystem functions, specifically the provision of wildlife habitat, as evident by higher cover of flowering and fleshy-fruit and palatable leaf producing species. Greater cover of drought, fire and heat tolerant species in low density stands and after thinnings suggested that these ecosystem functions are more likely to be maintained under climate change conditions, indicating higher resilience. The response of specific functions and response types reflect the traits characteristic for each species group and the impact of these traits on sensitivity to resource availability and disturbances. Thus, the correlation between grouping criteria and the main gradients created by management activities can provide an indication of the expected vegetation response, and therefore the impact of management practices on resilience. / Graduation date: 2012

No description available.

The wall thickness of pulp fibers plays a major role in the paper industry, but it is currently not possible to measure this property without manual laboratory work. In 2007, researcher Ho Fan Jang patented a technique to automatically measure fiber wall thickness, combining the unique optical properties of pulp fibers with image analysis. In short, the method creates images through the use of an optical system resulting in color values which demonstrate the retardation of a particular wave length instead of the intensity. A device based on this patent has since been developed by Eurocon Analyzer. This thesis investigates the software aspects of this technique, using sample images generated by the Eurocon Analyzer prototype. The software developed in this thesis has been subdivided into three groups for independent consideration. First being the problem of solving wall thickness for colors in the images. Secondly, the image analysis process of identifying fibers and good points for measuring them. Lastly, it is investigated how statistical analysis can be applied to improve results and derive other useful properties such as fiber coarseness. With the use of this technique there are several problems which need to be overcome. One such problem is that it may be difficult to disambiguate the colors produced by fibers of different thickness. This complication may be reduced by using image analysis and statistical analysis. Another challenge can be that theoretical values often differ greatly from the observed values which makes the computational aspect of the method problematic. The results of this thesis show that the effects of these problems can be greatly reduced and that the method offers promising results. The results clearly distinguish between and show the expected characteristics of different pulp samples, but more qualitative reference measurements are needed in order to draw conclusions on the correctness of the results.