Relationship between wood anatomical, physical and mechanical properties

Relationship between wood anatomical, physical and mechanical properties

Wood is one ofthe most important renewable raw materials, which has been used by human beings sin ce early years. W orld demand for wood is increasing at a rate of approximately 70 million m3 per year, due in part to the increasing world population (Ars en eau and Chiu 2003 ). Canada’ s challenge to meet the increasing demand for fi ber is also being impeded by a decreasing share in world markets due to new international competitors, mostly from the Southern Hemisphere. The driving force behind these newcomers in the wood fiber market is technology. They possess the scientific expertise to achieve high growth rates and yields from tree species adapted to their conditions as well as the processing technology to use low quality fiber in wood products manufacturing. This trend will continue to gain in prominence over the next century. Fast growing high yield plantations represent only 7% of the world’s total forest are a but already provide 30% oftimber supply (F AO 201 0). By 2020, the global roundwood supply from plantations should increase to 44% (F AO 2001 ). Se veral countries have chosen this path, are increasingly competing with Canadian products, and are already ahead of Canadian companies since they have developed and implemented the technology to produce low cost fiber from fast growing high-yield plantations.

Poplars are one of the most widespread and fastest-growing tree species in North America. The genus Populus contains over 25 species of deciduous trees including black cottonwood (Populus trichocarpa), eastern cottonwood (Populus deltoides), lombardy poplar (Populus nigra), and aspen, which are frequentlythe dominant broadleaved tree species in many forested regions. Poplars have a substantial breadth of distribution across geographie and climatic ecoregions, and are notable for their vigorous growth (Dickmann et al. 2001). Populus includes morphologically diverse species of deciduous, relatively short-lived, and fast-growing trees.

Hybrid pop lars are pro geny from crosses between trees of two or more species within the genus Populus. Hybrid poplars are genetically predisposed to grow faster and have wider adaptability than either parent species. Hybrid crosses also create heterosis (hybrid vigor) in which the progeny have increased performance of traits beyond what is capable by either parent. Hybridization can also increase developmental homeostasis, resulting in greater phenotypic stability in varied environments (Stettler et al. 1996). On good sites, hybrid poplars grow faster than any other northern temperate region tree. They can produce 21 to 25 rn trees with 20 to 25 cm diameter in 6 to 8 years (Zhao 2006). The hybrid poplar leaves can be four times larger than leaves of either parent at the same age and on the same site. They are easily propagated from stem cuttings, but because of quick re-sprouting, replanting after harvesting may be unnecessary, especially for short harvest cycles (Nesom 2002).

The majority of hybrid poplar breeding in Canada utilizes three native species: Populus deltoides (eastern cottonwood), Populus balsamifera (balsam poplar) and Populus trichocarpa (western black cottonwood) and two non-native species: Populus maximowiczii (Asian black poplar) and Populus nigra (European black poplar) (Demchik et al. 2002). Selected parents are usually inter-mated and superior progeny are selected for the next generation of mating. Selected trees can be vegetative propagated (cloned) and commercially released during any generation of the breeding process.

In Canada, hybrid poplar plantations are of particular interest because short rotation forestry can contribute to a stronger, more stable and renewable supply offiber. It can also help relieve the pressure on natural forests. In the past, small industrial plantations of hybrid poplar were established in Canada, from Québec to British Columbia. Nurseries of Québec ‘s Ministère des Ressources naturelles produced more than 1.5 million hybrid poplars in 2002, including hybrids of P. deltoides, P . balsamifera, P. nigra, P. trichocarpa, and P. maximowiczii. However, plantation sites Heritability estimates are important to assess the potential genetic gain of the preferred wood properties. Since heritability values and genetic correlations depend on the specifie test environment and population oftrees (Falconer and Mackay 1996), they should be evaluated in contrasting environments and in different populations. However, it is important for the tree breeders to know the major causes that can affect wood variability and consequences on the genetic parameters. Therefore, the selection phase is generally carried out at young ages to reduce the length of the breeding cycles. Final products are strongly affected by variability of many factors within tree, such as cambial age, growth rate and heartwood formation (Zobel and van Buijtenen 1989). However, from a tree breeding perspective, this provides many opportunities for improvement. In general, it has been reported that wood properties are under strong genetic control (Zobel and Jett 1995).

Mechanical properties of mature wood have relatively high heritability (Zobel and Jett 1995), which indicates that the variability in these properties is under relatively strong genetic control and not much affected by the environment. However, there has been relatively little research on genetic variation in mechanical properties of juvenile wood, their correlations with tree growth and their impact on end-uses products (Zobel and Sprague 1998). According to Hemândez et al. (1998), genetic variation in mechanical properties is significant in juvenile wood ofhybrid poplar clones. The same conclusion was reached for families of Eucalyptus grandis (Santos et al. 2003), clones of Cryptomeria japonica (Fujisawa et al. 1994) and provenance of Tectona grandis Linn F. (Bhat and Priya 2004). Strength and stiffness are important mechanical properties that determine suitability ofwood for specifie uses. Wood density is usually a good predictor of mechanical properties (Panshin and deZeeuw 1980). However, these properties can be influenced by other factors including the variability among species, among trees within species and environmental conditions that affect the tree growth (Tsoumis 1991).

This thesis is concemed with the characterization of hybrid poplar wood characteristics and properties, and their utilization in forest industries. This thesis presents estimates for genetic parameters such as genotypic correlations, heritability and genetic gain between properties that are related to wood anatomy, dimensional stability and application for wood industries.

GENERAL INFORMATION ON POPLAR SPECIES 

Poplar biology
The genus Populus belongs to the family Salicaceae widely known as pop lars. The number of species in the genus Populus varies among classifications from 22 to 85 (Eckenwalder 1996). Eckenwalder (1996), recognized 29 species subdivided into six sections based on relative morphological similarity and crossability Abaso, Turanga, Leucoides, Aigeiros, Tacamahaca and Populus (Table 1.1; Cagelli and Lefèvre 1995; Eckenwalder 1996). Only 5 among these species are indigenous to Canada: P . trichocarpa (black cottonwood), P . balsamifera (balsam poplar), P . angustifolia (narrowleaf cottonwood), P. deltoides (eastern cottonwood and plains cottonwood) and P . tremuloides (trembling aspen) (Farrar 1995)

Poplar morphology
Populus are deciduous tree species generally grown in the boreal, temperate, and subtropical zones of the northem hemisphere (Eckenwalder 1996; Dickmann 2001; Cronk 2005). They have tall and straight single trunks, with bark that tends to remain thin and smooth until more advanced ages than in other tree species (Eckenwalder 1996; Dickmann 2001). They rarely live longer than 100 to 200 years and can reach large sizes. Black cottonwood (Populus trichocarpa) can exceed 60 rn in height and reach up to 3 rn in diameter (DeBell 1990). Leaves are altemate and simple, with pinnato-palmate venation, and petioles are often transversally flattened distally (Eckenwalder 1996). The occurrence of hermaphroditic trees has been reported in multiple poplar species (Rottenberg 2000; Rowland et al. 2002; Cronk 2005; Slavov et al. 2009). Both male and female flowers are grouped in pendent catkins that burst between February and May. After pollination, female flowers develop into capsules that release 2 to 50 light seeds with cottony hairs promoting wind dispersion over greater distance (Schreiner 1974; Boes and Strauss 1994; Eckenwalder 1996). However, many hybrid pop lars never produce flowers and therefore to be sterile.

Poplar hybridization
Hybridization is done by crossing two different genera or species to create new individuals with varying degrees of the progenitors’ characteristics (Marques et al. 2007; 2014). Hybridization between species has traditionallybeen examined for its role in finalizing the speciation process through reinforcement of reproductive barriers (Howard 1993). Hybrid poplars are the results ofnatural and manmade crosses among different poplar species. Interspecies hybridization is one of the common features among many members ofthe genus Populus in the northem hemisphere (Bames 1961 ; Eckenwalder 1996; Stettler et al. 1996; Whitham et al. 1996). Several species of the genus Populus, particularly the species of the sections Tacamahaca and Aigeiros,which are represented in North America, are broadly sympatric and known to hybridize extensively (Brayshaw 1965; Eckenwalder 1984a, 1984b; Rood et al. 1986; Greenaway et al. 1991; Floate 2004 ).

In North America, hybrid poplars occur naturally wherever compatible species come into close proximity. For example, hybridization between P. balsamifera and P. trichocarpa occurs in Southeastern Alaska and the Cook Inlet region. Rood et al. (1986) reported tri hybridization among P. deltoides, P. balsamifera, and P. angustifolia, in Southern Alberta. In addition, natural hybrids occur between P. deltoides and P. balsamifera in Eastern Canada (Rood et al. 1986; Floate 2004; Hamzeh et al. 2007). However, most hybrid pop lars result from artificial hybridization and subsequent planting. An unknown number of hybrids also form between native species and introduced clones, cultivars, and species (Eckenwalder 1996).

Poplar distribution and culture
Poplar species have wide native ranges, often spanning more than 20 degrees of latitude and a great diversity of climates and soils (Eckenwalder 1996; Dickmann 200 1 ). It grows in various habitats, ranging from hot and arid, desert-like sites in central Asia and northern and central Africa to alpine or boreal forests in Europe and North America.

Poplar culture spread across the world at the beginning of last century. In 1947, the International Poplar Commission (IPC) was founded under the patronization of the F AO of the United Nations. The work of the Commission has led to important agreements on nomenclature, registration of clones, and varietal control (Zsuffa et al. 1996). There has been an increase in poplar culture over recent decades as it can provide wood products for fiber, fuels and chemicals while at the same time contributing to a more favourable carbon balance (Klass 1998). In North America, about 50 to 80 clones are currently being used in poplar culture (Dickmann et al. 2001 ).

Poplar culture in Canada
Poplar is an important species in North America. A significant amount ofresearch on fast growing tree plantations has been carried out in Canada. In Ontario and Manitoba, research was initiated in the 1920s and 1930s (Dickmann and Stuart 1983, Ménétrier 2008). The poplar culture began by Carl Heimburger in Ontario in 1930s, by selecting and breeding poplars for wood production. In Quebec, intensive and large sc ale efforts be gan in the late 1960s (Ménétrier 2008). In the 1970s, programs of poplar hybridization became common in Ontario, Quebec, Saskatchewan and British Columbia, whereas, this was initiated in the 1990s in Alberta through private companies and joint efforts with various govemment agencies across Canada (Poplar Council of Canada 2012). Presently, hybrid poplar crops are almost exclusively on existing farmland or newly cleared agricultural class lands in private ownership, using agronomie methods (Table 1.2). The cultivation approach of short rotation intensive culture (SRIC) for hybrid poplar plantation in Canada are for the purpose of supplying pulp fiber and for engineered wood products, such as OSB, L VL.

The hybrid poplar industry in North America developed around the biomass industry during the oil crises of 1973 and 1979. Then, pulp and paper companies became interested in this species to compensate for fluctuations in the wood fiber and chip markets (Stanton et al. 2002). Hybrid poplar can advantageously replace natural poplar (Populus spp.) since its mechanical properties are similarto those of cottonwood (Populus deltoides Marsh.), but are slightly lower than those of large-tooth aspen (Populus grandidentata Michx.) and trembling aspen (Populus tremuloides Michx.) (Hemândez et al. 1998). In Canada, 27 559 ha ofhybrid poplars were planted in 2011 (Table 1.2) (Poplar Council of Canada, 2012; Derbowka et al. 2012).

Poplar culture in Quebec
The poplar-breeding program has been started smce 1969 in Quebec (Riemenschneider et al. 2001). The hybrid poplar genetic improvement program led by the Direction de la recherche forestière, ministère des Ressources naturelles du Québec, aims at developing high yielding and disease resistant hybrid varieties that can grow well within the range of bioclimatic conditions found in Que bec (Périnet et al. 2012). Selection criteria are vigour, hardiness potential, stem taper, wood quality, and degree of resistance to diseases and insects. A list of about 40 recommended clones exists, and all of these clones originated from hybrids of poplar species from the Tacamahace and Aigeiros sections (Périnet 2007). The species used include Populus balsamifera L., Populus deltoides Bartr. Ex Marsh., Populus maximowiczii A. Henry, Populus trichocarpa Torr. & A. Gray, and Populus nigra L. (Périnet et al. 2008). Generally, fast-growing hybrid poplar plantations are considered as a potential alternative for producing high yields in temperate region for intensive production (Messier et al. 2003, Bilodeau-Gauthier et al. 2011 ). Accordingto Messier et al. (2003),the  anticipated yields were 14m3/ ha.yr on average sites, and 20m3 / ha.yr on the best sites of southem Québec in 2003. On the other hand, in the boreal region, the yields were 12 m3 / ha.yr on the best sites and 10 m3 / ha.yr on average sites (Messier et al.2003). Attractive potential yields motivate the Quebec’s forest industries to plant hybrid poplar for fiber production. As a result, approximately 10 000 to 12 000 ha of fast-growing poplar plantations are managed by industrials, whereas only 1 000 ha have been planted by small private landowners in the province of Que bec (Derbowka et al. 20 12; F ortier et  al. 20 12). Today, approximately 1 500 ha of land are planted annually with hybrid pop lars in Quebec (Périnet et al. 2012) with 1.5 million to 2.0 million plants produced by govemment nurseries (F ortier et al. 20 11).

WOOD QUALITY AND WOOD PROPERTIES 

Wood quality
Wood quality is currently receiving considerable attention from the whole forest industries, because wood quality measures the success of forest growing practices. There are many definitions of wood quality (Keith 1985), but the definition proposed by Mitchell (1961) is widely cited, « Wood quality is the resultant of physical and chemical characteristics possessed by a tree or a part of a tree that enable it to meet the property requirements for different end products ». Another wood quality defination in broad sense is, « All wood characteristics that affect the value recovery chain and the serviceability of end products ».

Wood quality can be influenced by several traits, such as wood density, earlywood to latewood ratio, and presence of knots, decay, spiral grain etc. Besicles, traits like wood density, fiber length, fiber coarseness, microfibril angle and cell wall chemistry may be a valuable tool when selecting superior donal material (Mansfield and Weinseisen 2007). Moreover, wood quality can become valuable for any end uses (Jozsa and Middleton 1994).

Properties influences wood qualities
Wood properties are a result of the combination of three characteristics: macroscopic morphology, wood anatomy and chemical composition (Pereira el al. 2003). The macroscopic morphology includes different types of wood tissue, such as reaction wood, growth rings, juvenile wood, and knots, whereas, the anatomical aspects include the types of cells and biometry and the proportions of each comparatively. The chemical composition of wood, the cell wall components and extraneous materials, also have a direct influence on the properties of wood.

Fi ber morphology, such as fiber length and coarseness, are attributes of importance to the pulp and paper industry. Fiber length, diameter and cell wall thickness have a direct influence on pulp and paper quality (Seth 1990a; Seth 1990b; Mansfield and Weinseisen 2007). Fiber length impacts inter-fiber bonding and tear strength is proportional to fiber length (Seth and Page 1988). Fiber wall thickness also plays an important role in determining wood quality for the pulp industry. Thin walled cells contribute to burst and tensile strength, whereas, thicker walled cells are favorable to tear strength, breaking length, bulk and absorbance properties, but are less conformable than thinner cell-walled fibers (Da Silva Perez and Fauchon 2003). Fiber wall thickness also has a direct influence on wood density and degree of shrinkage, and indirect influence on the mechanical properties of wood (Polge 1978; Holmberg et al. 1999).

Another anatomical factor that influences the wood quality is reaction wood and compression wood. Reaction wood is generally formed in the upper side of the leaning trees, which is termed as tension wood (Wardrop and Dadswell1948; Wardrop 1964).

In general, density and microfibril angle are the key determinant factors of wood quality (van Leeuw en 2011 ). The density of wood is defined as the mass per volume unit. Density is relatively easy to measure and a good predictor of other physical and mechanical properties (Zobel and van Buijtenen 1989). Wood density is most widely used factor to characterize wood quality (Zobel 1961; Yanchuk et al. 1983; Bamber and Burley 1983; Butterfiend 2003). According to Bamber and Burley (1983) « of all the wood properties, density is the most significant in determining end use as it has considerable influence on wood strength, machinability, conversion, acoustic properties, paper yield properties and probably many others ». Wood density is considered as a determinant factor of wood quality for two reas ons: first, suitability of wood to different end-uses purposes, and second, it is a relatively cheap and an easy parameterto measure (Walker and Woolons 1998). Wood density is well correlated to many other physical properties, including strength, stiffness and performance in many end-uses (Panshin and de Zeeuw 1980; Oliveira et al. 2005; Apiolaza 2009). This makes wood density an excellent trait to predict end-use characteristics of wood (Jozsa and Middleton 1995; Pot et al. 2002). Wood with thicker cell walls has ahigher density than the same volume of wood with thinner cell walls. Cell wall thickness is species related, but can vary significantly with different factors, such as, cambial age, earlywood and latewood fiber, and growth rings. Latewood cells that produce denser wood have much thicker walls than earlywood cells (Butterfield 2003). On the other hand, wood that has a relatively high fi ber to vessel ratio yields more dense wood than wood with a lower ratio (Savidge 2003).

HYBRID POPLAR WOOD PROPERTIES 

Anatomical properties
The literature addressing variations m anatomical properties of poplars is extensive. Panshin and de Zeeuw (1980) conducted a literature review on longitudinal and radial variations in wood anatomical properties. They found three patterns of radial variation in tracheid and fiber length: 1) a rapid increase followed by constant length from pith to bark; 2) a smooth and continuous increase from pith to bark; and 3) an increase from pith to bark up to a maximum, followed by a smooth decrease. A similar trend was reported for vessel element length and for fiber and vessel diameter, although the increase was moderate. Bendtsen et al. (1981), Bendtsen and Senft (1986) and Koubaa et al. (1998a) observed that fiber length in poplar wood increased from pith to bark and with tree age. In addition, clone type and height significantly affected average fiber length of Populus x euramericana (Koubaa et al. 1998a). Fiber wall thickness increased from pith to bark in sorne species and remains constant in others. According to Matyas and Peszlen (1997), wood properties vary greatly within and among poplar trees. However, the findings on variation in poplar wood properties are inconclusive and in sorne cases contradictory. More specifically, within-tree variation in anatomical properties in hybrid poplars has not been examined, except for a few studies on fiber length (Holt and Murphey 1978; Murphey et al. 1979; Yanchuk et al. 1984; Bendtsen and Senft 1986; Koubaa et al. 1998a; DeBell et al. 1998).

Information on fiber length is important for several applications. Strength of wood and wood products is related to fi ber length. Average fi ber length for 40 different poplar clones was reported as 0.86 mm, and significant differences were found between individual trees both within and among clones (Klasnja et al. 2003) (Table 1.5). Geyer et al. (2000) reported that fiber length of eleven four-year old poplar clones ranged from 0.76 mm to 0.87 mm and the average fiber length was 0.84 mm. Bendtsen et al. (1981) and Bendtsen and Senft (1986) reported higher fiber length ranging from 1.02 mm to 1.27 mm for poplar wood.

Physical properties
Wood density is considered as the most important wood property as it has a major impact on other wood properties and their end uses. Wood density of hybrid poplar in North America ranges from 0.30 to 0.39 (Balatinecz et al. 2001). This is consistent with the density of poplar wood documented in other studies (Y anchuk et al. 1983; Hemândez et al. 1998; Goyal et al. 1999; Klasnja et al. 2003). Beaudoin et al. (1992) reported significant differences in wood density among poplar clones according to the height at which samples were collected. In the longitudinal direction, density is usually higher at breast height (dbh), decreases until mid-height then increases upward (Beaudoin et al. 1992; De Boever et al. 2007). On the other hand, in the radial direction, density increases from the pith outwards (Yanchuk et al. 1983; Beaudoin et al. 1992; Hemindez et al. 1998).

ARIA TI ON OF THE PHYSICAL AND MECHANICAL PROPERTIES OF HYBRIDµ POPLAR CLONES

Hybrid poplar has received considerable attention for its high productivity compared to other Canadian hardwood and softwood species. It has been widely planted throughout North America due to its fast growth rate and easy hybridization. Hybrid poplar yield reaches up to 15 m3 /ha·yr, much higher than the 1.7 m3 /ha·yr current average yield in Canadian natural forests (Arseneau and Chui 2003). Perinet (1999) reported yields ranging from 8 to 12 m3 /ha·yr in Quebec. The maximum yield observed is 40 m3 /ha·year in Southem Que bec, with 2222 stems/ha (Fortier et al. 2010). Mean annual increment in hybrid poplar plantations at age 7 to 15 years has also been reported to be over 2.6 times higher than that of unmanaged natural stands at age 55 years in southem Ontario (Zsuffa 1973).

Hybrid poplars are hybridizations of two or more spectes within the genus Populus, which, as one of the fastest growing temperate trees, has considerable commercial value (Zsuff et al. 1996). Hybrid pop lars have been genetically improved through selection and crossbreeding to improve growth rate, trunk form, adaptability, and disease resistance (Hemandez et al. 1998; Riemenschneider et al. 2001; Zhang et al. 2003; Pliura et al. 2007).

For many years the selection criteria were mainly good tree and growth characteristics, resistance to pest and disease, adaptability, and low levels of growth stress. Despite the need to include wood properties in breeding programs, basic wood properties were not seriously considered so far. Since timber is the final objective of genetic tree improvement program, studies on wood properties of clones appear to be of far greater interest (Nocetti 2008). This increase has revealed a need for the selection and improvement of planting materials, to be used in the production of high quality timber. Thus, wood properties ofhybrid poplar clones and their end-use potential have been taken into account in breeding programs (Zhang et al. 2003).

Clonal variation 

The analysis of variance  indicated significant clonai variation in the physical and  mechanical properties of hybrid poplar clones wood. The significant differences observed among clones for the studied properties are an indication of a clonai effect on wood properties. As indicated by the variance component results, the clone is either low or high, ranging from 2.7% to 50.4%, depending on the examined property .

With respect to physical properties, clonai variation accounted for 42.3% of the total variance in wood density . The high clonai variation in wood density is in good agreement with previous works (Yanchuk et al. 1983; Beaudoin et al. 1992; Zhang et al. 2003; Pliuraet al. 2005; 2007). Clone DxN-4813 showed the highest wood density (380 kg/m3), whereas clone DxN-3586 showed the lowest (327 kg/m3). Similar results were obtained with samples taken at greater heights within the same trees in a wood machining experiment (Hemandez et al. 20 11).

On the other hand, the clonai variation accounted for only 2.7% of the total variance in volumetrie shrinkage. This result is in good agreement with previous reports (Nepveu et al. 1978; Koubaa et al. 1998b; Pliura et al. 2005). Clone DxN-4813 showed the highest volumetrie shrinkage . The clonai variation accounted for 16%, 4%, and 10% of the total variance in longitudinal, radial, and tangential shrinkages, respectively. Overall means for longitudinal, radial, and tangential shrinkages were 0.43%, 2.6%, and 5%, respectively . These values are slightly lower than those reported in previous studies (Alden 1995; Koubaa et al. 1998b; Pliura et al. 2005). These lower shrinkage values indicate higher dimensional stability ofthese clones.

GENERAL CONCLUSIONS 

Hybrid poplar plantations is of particular interest because short rotation forestry can contribute to a stronger, more stable and renewable supply of fi ber. These hybrids are valued for both lumber and pulpwood production. Therefore, the use of fastgrowing trees such as the species of the Populus genus and their clones in conjunction with intensive silvicultural practices has been postulated as a mean to meet the increasing demand for wood products. Besicles, forest products companies are interested in hybrid poplar clones for manufacturing a variety of products, such as pulp and paper, panels, veneers, and solid wood products. Thus, this thesis is concemed with the assessment of hybrid poplar wood properties, and their utilization by the forest industry. Fast growth tree species are known to lead to a significant loss of wood quality, namely in wood density and mechanical properties. Therefore, along with growth rate, health and adaptability, wood quality should be included into selection criteria ofhybrid poplar breeding programs. This research was undertaken to improve the understanding of the wood quality variation in hybrid poplar clones grown in Southem Quebec, for optimum use of this wood for fiber based and timber-based products manufacturing.

Table des matières

GENERAL INTRODUCTION 
CHAPTER I LITERA TURE REVIEW 
1.1 General Information on poplar species
1.1.1 Poplar biology
1.1.2 Poplar morphology
1.1.3 Poplar hybridization
1. 1.4 Pop lar dis tri bu ti on and culture
1.1.4 .1 Pop lar culture in Canada
1.1.4.2 Poplar culture in Que bec
1.2 Wood quality and wood properties
1.2.1 Wood quality
1.2.2 Properties influences wood qualities
1.3 Hybrid poplar wood properties
1.3.1 Anatomical properties
1.3.2 Physical properties
1.3.3 Mechanical properties
1. 4 Relationship between wood anatomical, physical and mechanical properties
1.4.1 Growth effect on wood properties
1.4.2 Relationship between wood properties and anatomical properties
1.4.3 Relationship between wood properties and physical properties
1.4.4 Relationship between wood properties and mechanical properties
1.5 Genetic control of wood properties
1. 5.1 Genotypic and phenotypic variation
1. 5. 2 Heritability
1.5.3 Genetic gain
1. 6 Potential USES ofhybrid poplars in wood products manufacturing
1.6.1 Anatomical properties and potential applications in paper manufacture
1.6.2 Physico-mechanical properties: potential application in solid wood products
1. 7 Research Objectives and hypotheses
CHAPTER II MATERIALS AND METHODS
2.1 Materials
2.1.1 Study area
2.1.2 Sample collection
2. 2 Methods
2. 2.1 Anatomical properties
2.2.1.1 Image analysis for fiber morphological property measurements
2.2.1.2 Fi ber length and width
2.2.2 Physical properties
2.2.2.1 Density with X-ray densitometer
2.2.2.2 Moisture content
2.2.2.3 Basic density
2.2.2.4 Shrinkage and swelling properties
2.2. 3 Mechanical properties
2.2.3.1 Static bending test
2.2.3.2 Compression test
2.3 Statistical Analysis
CHAPTER III ANATOMICAL PROPERTIES OF SELECTED HYBRID POPLAR CLONES GROWN IN SOUTHERN QUE BEC 
3.1 Abstract
3.2 Résumé
3.3 Introduction
3.4 Materials and Methods
3.4.1 Study area
3.4.2 Sample collection and preparation
3.4.3 Statistical analysis
3.5 Results and Discussion
3.5.1 Within- and among-site variation
3.5.2 Clonai variation in fiber anatomical properties
3. 5. 3 Within-tree variation
3.6 Conclusions
3. 7 Acknowledgements
CHAPTERIV   ARIA TION IN WOOD DENSITY AND RADIAL GROWTH WITH CAMBIAL AGE IN HYBRID POPLAR CLONES 
4.1 Abstract
4.2 Résumé
4. 3 Introduction
4.4 Materials and Methods
4.4.1 Study area
4.4.2 Sample collection and preparation
4.4. 3 Statistical analysis
4. 5 Results and Discussion
4. 5.1 Analysis ofvariance
4. 5.2 Radial variation in ring density components
4. 5.3 Age trend of heritability in ring density components
4. 6 Conclusions
4. 7 Acknowledgements
CHAPTER V  ARIA TION OF THE PHYSICAL AND MECHANICAL PROPER TIES OF HYBRID POPLAR CLONES
5.1 Abstract
5.2 Résumé
5.3 Introduction
5.4 Material and Methods
5.4.1 Sample collection and preparation
5.4.2 Statistical analysis
5. 5 Results and Discussion
5.5.1 Site variation
5.5.2 Clonai variation
5.5.3 Genetic parameters of wood properties
5.5.4 Practical implications
5.6 Conclusions
5. 7 Acknowledgements
CHAPTER VI PHENOTYPIC AND GENOTYPIC CORRELATIONS FOR WOOD PROPERTIES OF HYBRID POPLAR CLONES OF SOUTHERN QUEBEC 
6.1 Abstract
6. 2 Résumé
6.3 Introduction
6.4 Materials and Methods
6.4.1 Plant material
6.4.2 Sampling and measurement
6.4.3 Statistical analysis
6. 5 Results and discussion
6. 5.1 General descriptive statistics
6.5.2 Phenotypic correlations between wood properties
6.5.3 Genotypic correlations between wood properties
6.6 Conclusions
6.7 Acknowledgments
CHAPTER VII GENERAL CONCLUSIONS

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