Study on within tree variation in wood properties of melia azedarach planted in northern vietnam

Therefore, a better understanding of the wood variability within tree is of value to both wood quality improvement and efficient wood processing and utilization... The overall objective

Study on Within-tree Variation in Wood Properties of

Melia azedarach Planted in Northern Vietnam

Duong Van Doan

2018

Study on Within-tree Variation in Wood Properties of Melia azedarach

Planted in Northern Vietnam

By

Duong Van Doan

Laboratory of Wood Science, Division of Sustainable Bioresources Science, Department of Agro-environmental Sciences, Faculty of Agriculture, Graduate School of Bioresource and Bioenvironmental Sciences, Kyushu University, Japan

Supervisor

Professor Junji Matsumura

Advisory Committee Members

Associate Professor Shinya Koga Associate Professor Noboru Fujimoto

2018

Table of Contents

Table of Contents i

Abbreviations v

CHAPTER 1 1

Introduction 1

CHAPTER 2 8

Literature Review 8

2.1 Introduction 9

2.2 Within-tree variations in wood properties 9

2.2.1 Growth ring width 9

2.2.2 Wood density and specific gravity 11

2.2.3 Fiber length 14

2.2.4 Microfibril angle 15

2.2.5 Shrinkage properties 17

2.2.6 Mechanical properties 18

2.3 Nondestructive wood evaluation 20

2.4 Conclusion of literature review 21

CHAPTER 3 22

Variation in Intrinsic Wood Properties 22

3.1 Abstract 23

3.2 Introduction 24

3.3 Materials and methods 25

3.3.1 Study site and sampling 25

3.3.2 Wood specimen preparation 26

3.3.3 Growth ring width 26

3.3.4 Wood specific gravity 29

3.3.5 Fiber length and microfibril angle 29

3.3.6 Determination of fiber length increment (FLI) 31

3.3.7 Statistical analysis 31

3.4 Results and discussion 33

3.4.1 Growth ring width 33

3.4.2 Wood specific gravity 37

3.4.3 Microfibril angle 41

3.4.4 Fiber length 41

3.4.5 Stabilizing point of fiber length increment 46

3.4.6 Implications for wood utilization of M azedarach in northern Vietnam 46

3.5 Conclusions 48

CHAPTER 4 49

Transverse Shrinkage Variations within Tree Stems 49

4.1 Abstract 50

4.2 Introduction 51

4.3 Material and methods 53

iii

4.3.2 Dynamic modulus of elasticity of log (DMOElog) 54

4.3.3 Basic density and transverse shrinkage 56

4.3.4 Data analysis 57

4.3.5 Grade yield 57

4.4 Results and discussion 60

4.4.1 Basic density and transverse shrinkage 60

4.4.2 Relationships between transverse shrinkage and basic density 68

4.4.3 Prediction of transverse shrinkage 71

4.4.4 Grade yield of shrinkage properties 74

4.5 Conclusions 76

CHAPTER 5 77

Within-stem Variations in Mechanical Properties 77

5.1 Abstract 78

5.2 Introduction 79

5.3 Material and methods 80

5.3.1 Sampling 80

5.3.2 Wood density and dynamic modulus of elasticity (Ed) 81

5.3.3 MOR and MOE 82

5.3.4 Data analysis 82

5.3.5 Grade yield 84

5.4 Results and discussion 84

5.4.1 Wood density and mechanical properties 84

5.4.2 Correlation of wood density with mechanical properties 90

5.4.3 Correlation between moduli of elasticity 94

5.4.4 Prediction of bending strength 96

5.4.5 Grade yield of mechanical properties 96

5.5 Conclusions 100

CHAPTER 6 102

General Discussion and Conclusions 102

6.1 General discussion 103

6.2 Conclusions 109

References 111

Acknowledgements 126

• MFA: Mircofibril angle (o)

• VL: Acoustic wave velocity (m/s)

• WD: Wood density in air-dry condition (g/cm3)

• αR: Radial shrinkage (%)

• αT: Tangential shrinkage (%)

• αT/αR: Tangential/radial shrinkage ratio

• ρ: Green density of log (kg/m3)

CHAPTER 1

Introduction

2

All forests fulfil a range of roles and provide a variety of goods and services The roles fulfilled

by planted forests are diverse and the goods and services produced include the production of industrial wood, fuel wood, non-wood forest goods (eg animal fodder, apiculture, essential oils, tan bark, cork, latex, and food) and conservation, carbon sequestration, recreation (eg hunting, fishing, and hiking), erosion control, and rehabilitation of degraded lands, including landscape and amenity enhancement For countries with a low forest cover, the only way to obtain the multiple benefits from forests, is creating new forests, mainly through planting

Global planted forest area increased from 1990 to 2015 from 167.5 million ha to 277.9 million

ha with the increase varying by region and climate domain (Payn et al 2015) Together with global trend, Vietnam’s planted forest area increased considerably from 1985 with 0.58 million ha to 2016 with 4.13 million ha (Table 1.1) (Ministry of Agriculture and Rural Development of Vietnam 2017) Large areas of plantation do not only supply material for pulp and paper production but also play an important role in the protection of environment by reducing greenhouse gas and helping to reduce poverty in rural areas (Kim 2009) Besides, with the decrease in the available wood resources and the increase in wood processing costs have led to a significant interest in timber production from plantation For timber plantation, the current wood is under-utilised and poorly managed Therefore, there is a need for effective and sustainable utilization of the plantation forests in order to prevent further decline of timber sources and improve quality of timber products One of the ways of sustainably utilizing wood resources is to study on wood properties

Wood is a highly variable material due to its biological origin (Zobel and Van Buijtenen 1989) For a given species, the within-tree variation is further partitioned into variation from pith to bark (radial variation) and variation with position along the stem (axial variation) The large variability of

wood characteristics makes it difficult to precisely predict its performance and therefore to efficiently process and utilize the material On the other hand, the variability means that this material has potential for genetic improvement and diverse end uses (Zobel and Van Buijtenen 1989, Koga and Zang 2004) Therefore, a better understanding of the wood variability within tree is of value to both wood quality

improvement and efficient wood processing and utilization

Melia azedarach L is a deciduous tree belonging to the family of Meliaceae It is native to the

Himalaya region of Asia (EL-Juhany 2011) The species is well adapted to warm climates, poor soils and seasonally dry conditions (Harrison et al 2003) The fully-grown tree has a rounded crown, and

commonly measures 7 to 12 m tall However in exceptional circumstances, M azedarach can attain a

height of 45 m The leaves are up to 50 cm long, alternate, long-petioled, two or three times compound (odd-pinnate); the leaflets are dark green above and lighter green below, with serrate margins The flowers are small and fragrant, with five pale purple or lilac petals, growing in clusters The fruit is a drupe, marble-sized, light yellow at maturity, hanging on the tree all winter, and gradually becoming wrinkled and almost white (Rahman et al 2014)

M azedarach could contribute to the prevention of global warming due to their high ability to

stock carbon (Osei et al 2018) Together with other fast growing species, M azedarach trees are used

as pulping materials due to their high productivity(Ministry of Agriculture and Rural Development

of Vietnam 2014) Using wood of M azedarach as a building material (eg posts and beams in timber

construction) to increase their value is expected (Hasegawa et al 2015) There are some researchers

investigated the physical and mechanical properties of the M azedarach wood Matsumura et al (2006) reported the variation in wood properties of M azedarach planted in Japan and suggested the possibility of using it as new timber materials Venson et al (2008) experimented with the physical, mechanical, and biological properties of M azedarach planted in Mexico They demonstrated that M

azedarach can be used as structural lumber if the appropriate genotypes and clones were collected In

Vietnam, M azedarach is planted popularly in most of the provinces in northern Most of the M

azedarach were planted in short rotation around 5-6 years with the purpose to supply raw material for

pulp and particleboard industries Currently the decrease in the available wood resources and the increase in wood processing costs have led to a significant interest in wood from plantation Hence,

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quite durable, resistant to termites and insects, and easy to work (Nghia 2007) However, until now

no effort has been made to investigate the within-tree variations including radial and axial directions

in wood properties of M azedarach planted in Vietnam, despite the importance of this species and the

multiuse of its wood

Rapid and nondestructive evaluation of wood properties has great importance to tree breeders

as well as to several other considerations in optimal timber utilization Nondestructive evaluation is

an important tool for the characterization of wood and can be used in industry to improve quality control process through reducing the property variation of the raw material and its by-products (Oliveira et al 2005) However, the properties of wood vary considerably because it is a natural material The large variability of wood characteristics makes it difficult to precisely predict its performance This is one of the most important challenges to apply nondestructive testing method in wood quality evaluation A number of studies suggested that nondestructive technique may be used

to assess wood properties in small wood specimens, lumber and determine the quality of logs and standing trees (Wang et al 2001, Carter et al 2005, Ishiguri et al 2006, Ishiguri et al 2008) One of the most widespread and accurate nondestructive techniques used to study timber is based on stress waves These techniques are based on the observed relations between the propagation of a wave through a piece (velocity and attenuation) with some of the properties of the material (mechanical and physical properties), as well as some characteristics or singularities of the piece as decays, holes or other irregularities (Ross and Pellerin 1994, Montero et al 2015) Therefore, it is necessary to

investigate the usefulness of a stress wave technique for evaluation wood properties of M azedarach

planted in northern Vietnam

The overall objective of this study was to investigate within-tree variations in fulfilment wood properties including information on wood structure as well as physical and mechanical properties of

M azedarach planted at two different sites in northern Vietnam The specific objectives were:

• To determine and estimate the within-tree variations in intrinsic wood properties such as growth ring width, wood density, fiber length, and microfibril angle

• To determine and estimate the within-tree variations in radial and tangential shrinkages

• To investigate the usefulness of a stress wave technique for prediction wood dimensional stability

• To determine and estimate the within-tree variations in mechanical properties

• To investigate the usefulness of a stress wave technique for prediction wood strength and stiffness

The results should provide basic information to wood industry experts on the potential use and sustainable use of the species when processing logs for timber The results should also suggest the potential of using rapid and nondestructive method to predict the dimensional stability and mechanical

properties of M azedarach wood Finally, the results should provide foundation for machine grading

of M azedarach timber in Vietnam

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CHAPTER 2

Literature Review

2.1 Introduction

Wood has a variety of uses Each has a particular set of requirements regarding its quality and has to contend with a variable wood resource even after selection The criteria that a particular industry apply must be assessable (knot size, wood density, cell wall thickness, fiber length, and fiber content) and related to the wood resource (Walker et al 1993) However, wood is a highly variable material due to its biological origin Its properties vary from stand to stand, tree to tree, around the circumference, across the radius, along the height, and even within small sampling unit like growth ring (Sharma et al 2014) The large variability of wood characteristics makes it difficult to precisely predict its performance and therefore to efficiently process and utilize the material The principal sources of variation in wood properties relate to:

• Within-ring variations;

• Within-tree variations;

• Between-tree variations on similar sites;

• Between-site variations of the same genotype growing in different geographic regions

In these variations, variation along radial direction is the best known and most studied tree variability in wood, which is generally reflected as radial pattern of change in wood characteristics

within-of core wood and outer wood, juvenile and mature wood (Anoop et al 2014)

2.2 Within-tree variations in wood properties

2.2.1 Growth ring width

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Growth ring is a layer of wood formed in plant during a single period of growth Growth rings are often identified by the colour contrast between the light-coloured earlywood and the dark-coloured latewood Earlywood is part of the wood in a growth ring of a tree that is produced earlier in the growing season The cells of early wood are larger and have thinner walls than those produced later

in the growing season On the other hand, latewood is part of the wood in a growth ring of a tree that

is produced later in the growing season The cells of latewood are smaller and have thicker cell walls than those produced earlier in the season (Panshin and De Zeeuw 1980, Larson 1994, Missanjo 2017)

Growth rate has little effect on the wood properties of diffuse-porous species These have approximately the same proportion of vessels across the annual ring, regardless of the growth rate On the other hand, growth rate has a noticeable influence of the density of ring-porous hardwoods, which usually produce denser wood when fast grown The volume of vessel tissue produced each year in a ring-porous hardwood remains constant regardless of the total growth during the growing season and therefore the wider the growth ring the smaller the proportion of vessel tissue (Walker et al 1993)

Ring width variation with age is a potential source of wood property variation Ring width in plantation trees usually follows a general pattern of decrease as age increases as a result of stand competition while deviations might occur due to soil and climatic conditions (Zobel and Sprague 1998, Matsumura et al 2006, Adamopoulos et al 2010, Kiaei et al 2016) For example, Matsumura et al

(2006) reported the growth ring width of M azedarach planted in Japan decreased from pith towards

periphery In ring-porous hardwoods, growth rate, which is expressed by ring width, is positively correlated to wood density and is attributed to the fact that earlywood zone is nearly constant from year to year and the wider rings therefore contain denser latewood with fewer vessels (Panshin and

De Zeeuw 1980, Adamopoulos et al 2010) Nevertheless, other works failed to find any relationship between ring width and wood density (Van Eck and Woessner 1964, Taylor and Wooten 1973, Taylor

1977) A possible reason could be that the earlywood-latewood proportion, the percentage of cell wall material and the tissue proportions differ between the annual rings (Zang and Zhong 1992)

Ring width is highly variable as it is controlled by a variety of factors such as environmental fluctuations and competition for resources of nutrients or sunlight A number of studies found significant relationship between ring width and growth conditions (Woodcock 1989, Oleksyn and Fritts 1991, Larocque 1997) Variations in ring width can provide a detailed record of tree growth and vitality in response to climatic changes At the latitudinal and altitudinal edges of their distribution, the growth of tree species is believed to be chiefly limited by the temperature regime, with tree-ring records from these distribution sites generally providing a proxy of the temperature changes in an area (Buntgen et al 2005, Frank and Esper 2005, Zhuang et al 2017) In addition, Zhu et al (2000) reported

a wider growth ring width in wider planting spacing There is acceleration of growth for widely spaced trees than crowded trees, because widely spaced trees do not compete for growth elements such as nutrients, water, and sunlight Hence, they tend to have wider growth ring

2.2.2 Wood density and specific gravity

The specific gravity of wood is its single most important physical property Most mechanical and physical properties of wood are closely correlated to specific gravity and wood density In general discussions, the terms specific gravity and wood density are often used interchangeably These terms have distinct definitions though they refer to the same characteristic (Bowyer et al 2007) The density

of wood can be considered once its moisture content has been defined In physics the density of a material is defined as the mass per unit volume The situation is not so simple with wood because changes in moisture content affect both its mass and volume Therefore, it is necessary to specify the

12

Wood density is one of the most important properties because it correlates with most physical characteristics, namely mechanical resistance and wear Wood density is therefore a fundamental criterion to define the wood technological quality and one of the first to be studied when assessing the potential value of a timber species It is considered a vital wood property for imparting strength and stiffness to solid lumber as well as affecting the physical yields of fiber for composite products and pulp and paper (Zobel and Van Buijtenen 1989, Niklas and Spatz 2010, Shmulsky and Jones 2011)

In general, higher wood density is desirable Besides its importance in wood technology, wood density has received increasingly higher attention due to its importance in estimating forest biomass and carbon storage in recent years (Henry et al 2010, Njana et al 2016) The amount of carbon stored in trees depends on the biomass as well as the carbon content of the wood and other tissues Therefore, wood density and stem volume alone may control carbon storage at the tree level (Zang et al 2012, Wassenberg et al 2015)

The within-tree variation in wood density is more complex with hardwoods All possible patterns of wood density variation appear in the stem of hardwoods In radial direction, Knapic et al

(2011) reported that there was a trend of decreasing density with cambial age in Quercus faginea This

is a common pattern in Quercus species such as Q garryana (Lei et al 1996), Q suber (Knapic et al

2008) In the contrast, wood density increases linearly from the pith to the bark in some species belong

to Meliaceae family such as Melia azedarach (Matsumura et al 2006), Toona ciliate (Nock et al 2009), and Swietenia macrophylla (Lin et al 2012) On the other hand, Wahyudi et al (2016) reported

a nearly constant basic density of Azadirachta excelsa from pith to bark Besides, Ofori and Brentuo (2005) showed that the wood density of Cedrela odorata was low at the pith, increased rapidly

outwards to a peak and declined steadily towards the periphery in the radial direction In axial direction,

the wood density was reported to vary very little with height in Acacia melanoxylon planted in New

Zealand (Nicholas and Brown 2002), while a significant increase of wood density with height was

found in Acacia melanoxylon planted in Portugal (Machado et al 2014)

Corewood is generally of lower density than the outerwood (Matsumura et al 2006, Ishiguri

et alt 2007, Nock et al 2009, Lin et al 2012) It consists largely of earlywood and has a correspondingly low density The S2 layer is quite thin and so it is not unexpected than the lignin content of corewood is greater and the cellulose content is less than that of outerwood The transition

to outerwood occurs between growth rings from the pith depending on the species and the property being examined (Walker et al 1993)

The environment exerts strong control over the average basic density of trees in a stand At the same time genetic control determines the variations between trees within a stand regardless of location When we say that a wood property is under environmental control we mean that it varies considerably with a change in the environment When a wood property is under strong genetic control,

it may vary without regard to the environment under which the tree is grown or its properties may stay constant despite the trees having been grown in differing environments (Zobel and Van Buijtenen 1989)

Both factors can be important at the same time The environment exerts strong control over the average basic density of the population while genetic control determines the tree-to-tree variations within the population occupying a particular environment For this reason, the consequences of introducing a species to a new region are generally difficult to predict and it is desirable to grow that species in a limited way before becoming committed to a major plantation programme The end results are often unforeseen and there have been numerous disappointments

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In addition, wood density data can be used to estimate its intra-species and inter-species variation and indicate variations available for selection in tree improvements Furthermore, knowledge of wood density profile is likely to improve the accuracy of estimate of stem biomass (Walker et al 1993)

2.2.3 Fiber length

The term fiber if often used in a general way to refer to all wood cells isolated in pulping processes However, in the context of wood morphology, the term fiber refers to a specific cell type Thus libriform wood fibers, or fiber tracheids as they are more properly called, are long, tapered, and usually thick-walled cells of hardwood xylem (Bowyer et al 2007)

In hardwood, the cells make up the anatomical organization are vessels, fibers, parenchyma cells, and ray parenchyma cells Fibers are the principal element that is responsible for the strength of the wood (Panshin and De Zeeuw 1980) Thus, cell wall thickness of the fibers and their fractional volume are known to influence wood density, a parameter generally associated with mechanical strength of hardwood species (Ocloo and Laing 2003, Salmen and Burget 2009)

Fiber length is particularly important for the pulp and paper industry since it determines to a large extent the physical and mechanical properties of paper and paperboard (Van Buijtenen et al

1962, Einspahr et al 1963, Zobel and Van Buijtenen 1989) Numerous publications on radial variation

in fiber length of ring-porous hardwoods reviewed by Dinwoodie (1961) who reported that fibers are shortest near the pith A common variation pattern is a rapid increase in fiber length during the first

years, followed by a more gradual increase until a maximum is reached This was shown in Robinia

pseudoacacia L and Castanea sativa Mill (Adamopoulos 2010) For Acacia magium (Honjo 2005)

and Acacia hybrids (Kim et al 2008), it has been reported as a pattern of a continuous increase in fiber length from the pith to bark The pattern of radial variation of fiber length differs across species with radial growth rate which is determined by internal (cambial age) and external factors, such as climatic factors (Nicholls 1986) Therefore, it is necessary to investigate variation in fiber length with

respect to a particular species including M azedarach

2.2.4 Microfibril angle

Microfibril angle (MFA) is perhaps the easiest ultrastructural variable to measure for wood cell walls, and certainly the only such variable that has been measured on a large scale The secondary cell walls of xylem cells typically have three layers, an outer S1 with transversely oriented microfibrils,

a thick S2 layer with axially oriented microfibrils, and an inner S3 layer also with transversely oriented microfibrils The S2 layer is generally much thicker than the other layers and may therefore dominate the physical and chemical properties of the cell wall (Donaldson 2008)

In conifers, MFA varies from pith to bark, with the highest angles occurring in the first five growth rings from the pith at the base of the tree (Donaldson 1992, Cave and Walker 1994, Zhang et

al 2007) In hardwoods, there are generally fewer information on within-tree variation in MFA, most

of the information being for Eucalyptus trees MFA declines from pith to bark but, unlike conifers, the angles are much lower near the pith Pith to bark variation in Populus clones showed MFA values

ranging from 28˚ (pith) to 8˚ (bark) in 11-year-old trees at breast height (Fang et al 2006) In

Eucalyptus nitens, MFA decreases with height, reaching a minimum at 30-50% of stem height before

increasing again towards the crown (Evans et al 2000, Donaldson 2008)

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In addition, there are differences in variation in MFA among trees both in softwoods and hardwoods In softwoods, the differences among trees are generally more apparent in the juvenile wood The tendency of MFA to show less among-tree variation in the mature wood (15+ years) than

in the juvenile wood (Cown et al 1999) In hardwoods, the most notable difference is that among-tree

variation at the pith is only slightly greater than at the bark in 15-year-old Eucalyptus nitens (Evans

et al 2000, Donaldson 2008) Significant variation in MFA among provenances has been observed in

a number studies For example, Vainio et al (2002) have shown significant variation in MFA between

provenances in Picea sitchensis or Yamashita et al (2000) reported that MFA values varied widely among cultivars in Cryptomeria japonica

The MFA has two major effects on wood properties First, the stiffness of the cell wall increases enormously (five-fold) from pith to cambium as the MFA decreases from 40° to 10° Secondly, longitudinal shrinkage increases with MFA but in a highly non-linear manner and is responsible for some degrade on drying, especially crook (Walker and Butterfield 1995) The importance of MFA, as it relates to wood mechanical properties, is established for hardwoods Evans and Ilic (2001) investigated the relationship between MFA and mechanical traits indicating that MFA

would be the prime determinant of wood stiffness in Eucalyptus delegatensis Yang and Evans (2003) reported that MFA alone accounted for 87% of the variation in modulus of elasticity in Eucalyptus

globulus, Eucalyptus nitens, Eucalyptus regnans MFA is also known to have a large and direct effect

on shrinkages Because crystalline cellulose is strong, stiff, and does not absorb moisture, the wood shrinks very little in the direction that is parallel to cellulose microfibrils Therefore, transverse shrinkage increases and longitudinal shrinkage decreases with the decrease of MFA Yamashita et al (2009a, 2009b) reported that MFA was one of the most important indicators of both longitudinal and

transverse shrinkages in Cryptomeria japonica

2.2.5 Shrinkage properties

Wood only shrinks when water is lost from the cell walls and it shrinks by an amount that is proportional to the moisture lost below fiber saturation point The amount of shrinkage depends on the basic density of the wood As drying progress from green wood condition, it is inevitable that the moisture content at the center of the piece will be above the fiber saturation point while the fibers at and near the surface will be well below the fiber saturation point There will be a moisture gradient within the wood and the drying system will not be in equilibrium In this situation the surface fibers will have started to shrink and the overall volume of the piece will be reduced even though the average moisture content is above fiber saturation This accounts for the shrinkage of the wood at mean moisture contents a little above the fiber saturation point (Walker et al 1993, Bowyer et al 2007)

The shrinkage of wood is different in the three principal directions: longitudinal, radial, and tangential Typical oven-dry shrinkage values for medium density woods would be:

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as much as it would wish In the radial direction, both the earlywood and latewood shrink independently and the total shrinkage corresponds roughly to the weighted mean shrinkage of the two components (Pentoney 1953, Walker et al 1993)

The patterns of within-tree variations in wood shrinkage can differ widely among genera and species They can also differ among sites, genotypes, and tree ages For example, Ofori and Brentuo (2005) and Kord et al (2010) reported that transverse shrinkage increased from pith to outwards in

Cedrela odorata and Populus euramericana, respectively On the other hand, Anoop et al (2014)

reported that along the radial positions, there was no significant difference of transverse shrinkage in

Swietenia macrophylla Shanavas and Kumar (2006) showed that the trend for transverse shrinkages

decreased from pith towards periphery in Acacia mangium The effects of seed source and growth

condition on transverse shrinkage have been investigated in other hardwood species Montes et al

(2007) found there was significant genetic variation in wood shrinkage of Calycophyllum spruceanum

while Yang et al (2002) reported that site had a highly significant effect on shrinkage properties in

Eucalyptus globulus Labill

2.2.6 Mechanical properties

Mechanical properties are usually the most important characteristics of wood products for structural applications (Bowyer et al 2007) Strength and stiffness of timber are primary considerations in the construction industry, for pallets and containers Strength is defined in terms of the ability of a material to sustain a load The magnitude of the load that can be sustained varies with the shape and size of the sample being tested, which is inconvenient Therefore, strength is defined in terms of stress, that is the load or force per unit area The specific strength or stiffness of a material is the value of that property divided by its density (Walker et al 1993)

As regards the within-tree variation, the radial variation is the most important for all wood properties, thereby showing the important of cambial age for the wood characteristics (Zobel and Van Buijitenen 1989) In the radial direction, the variation followed the common trend of increase from pith to bark that is linked to the tree age and the transition from juvenile to mature wood (softwood) and from corewood to outerwood (hardwood) (Fuwape and Fabiyi 2003, Izekor et al 2010, Anoop et

al 2014, Missanjo and Matsumura 2016) In axial direction, the variation of mechanical properties

with height was very small and without statistical significant found in Acacia melanoxylon R Br

(Machado et al 2014)

Wood density is a useful index for predicting the strength properties of clearwood, because it

is a direct measure of the amount of cell wall material in a given volume Even with small clearwood specimens there is a large natural variability in strength It reflects differences in wood density within tree, between trees in a particular stand, and between trees from contrasting locations and growing under different management systems (Walker et al 1993) The effects of wood density on variations

in the mechanical properties of plantation trees were examined by many researchers The positive linear relationships between wood density and mechanical properties were found on hardwood species

such as Eucalyptus tereticornis (Sharma et al 2005), Tectona grandis (Izekor et al 2010), and Acacia

melanoxylon (Igartua et al 2015) However, the relationships between wood density and mechanical

properties are highly dependent on species (Rozenberg et al 1999, Yang and Evans 2003) Low density correlations with mechanical properties were some cases attributed to the influence of MFA (Cave and Waker 1994, Evans and Ilic 2001) The reasoning is that wood density increases while MFA decreases with age, thereby impacting the mechanical tests and resulting in poor correlations when density alone is considered The grain can also affect the correlation between wood density and mechanical properties (Green et al 1999, Machado et al 2014)

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2.3 Nondestructive wood evaluation

In the forest products industry, nondestructive evaluation has been developed and is used in structural product grading programs that result in engineered material with well-defined performance Currently, there is a strong interest in developing and using new, cost-effective nondestructive evaluation technology to evaluate wood quality One nondestructive technique, which uses stress wave propagation characteristic, has reveived considerable attention during the past few decades The applicability of vibration modes on wood materials for assessing wood quality has been investigated for standing tree, log, and small-dimension wood specimens

Numerous publications reported that the modulus of elasticity of lumber can be predicted by stress wave velocity of a tree, log or small specimen (Nanami et al 1993, Ross et al 1997, Ikeda and Arima 2000, Wang et al 2001, Carter et al 2005, Ishiguri et al 2006, Ishiguri et al 2008) For example, Wang et al (2001) found a strong relationship between dynamic modulus of elasticity of wood in trees measured by stress wave method and modulus of elasticity of small, clear specimens obtained

from these trees measured by destructive method in Tsuga heterophylla and Picea sitchensis Ishiguri

et al (2008) reported a positive significant correlation between the stress wave velocity of trees and

modulus of elasticity in static bending of lumber in Larix kaemferi

A number of studies also suggested that nondestructive techniques may be used to assess the dimensional stability of structural lumber Yamashita et al (2009a, 2009b) showed that there were close relationships between longitudinal-transversal shrinkage and modulus of elasticity of logs

measured by tapping the logs in the green condition in Cryptomeria japonica Wang and Simpson

(2006) found the potential of acoustic analysis as presorting criteria to identify warp-prone boards

before kiln-drying in Pinus ponderosa The results showed a statistically significant correlation

between acoustic properties of the boards and the grade loss because of exceeding warp limits In addition, Dundar et al (2013, 2016) indicated that ultrasonic measurement in green condition has a good potential for predicting the transverse shrinkages both in softwood and hardwood species

2.4 Conclusion of literature review

Hardwoods have a more complex overall structure than softwood, because they contain more cell types arranged in a greater variety of patterns The proportion, structure, and distribution of the cell types combine to give these wood a more varied appearance and grain The variations in the wood properties of the same species are due to different genotypes and ecological conditions of sites such

as altitude, precipitation, temperature, soil, water, and nutrients These two factors affect both the growth and development of trees Genetic structure is the main source of change of wood’s properties, while ecological conditions of site directly or indirectly affect on the development and fertility, body form and height of tree

For a given species, the within-tree variation is further partitioned into variation from pith to bark (radial variation) and variation with position along the stem (axial variation) Variation along radial direction is the best known and most studied within tree variability in wood, which is generally reflected as radial pattern of change in wood characteristics of inner and outer wood The large variability of wood characteristics makes it difficult to precisely predict its performance and therefore

to efficiently process and utilize the material On the other hand, the variability means that this material has potential for genetic improvement and diverse end uses Because the differences between species, therefore, it is necessary to discuss variations in wood properties with respect to a particular species

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CHAPTER 3

Variation in Intrinsic Wood Properties

A part of this chapter was published as: Doan Van Duong, Edward Missanjo, Junji Matsumura (2017) Variation in intrinsic

wood properties of Melia azedarach L planted in northern Vietnam J Wood Sci 63(6):560-567

3.1 Abstract

Variation in intrinsic wood properties [growth ring width (GRW), specific gravity (SG), fiber

length (FL), and microfibril angle (MFA)] of 17–19-year-old Melia azedarach L trees grown in two

sites in northern Vietnam were investigated for effective utilization of the wood Five discs were

collected at 0.3, 1.3, 3.3, 5.3, and 7.3 m heights above the ground The estimated mean GRW, SG, FL,

and MFA were 7.44 mm, 0.548, 1.07 mm, and 14.65o, respectively There were significant (P < 0.05)

differences among trees and between sites in SG, FL and MFA Longitudinal position significantly (P

< 0.05) influenced GRW and SG Radial position was highly (P < 0.001) significant to all the wood

properties and contributed highest (GRW: 52.58%, SG: 58.49%, FL: 77.83%, and MFA: 26.20%) of

the total variations FL and SG increased from pith to bark, while GRW and MFA decreased from

pith to bark Fiber length increment (FLI) tends to stabilize between 7th and 10th rings This should

be taken into account when processing logs The results of this study, therefore, provide a basis for

determining management strategies appropriate to structural timber production of M azedarach

plantation trees in northern Vietnam

Keywords: Melia azedarach, Growth ring width, Specific gravity, Fiber length, Microfibril angle

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3.2 Introduction

Melia azedarach L is a deciduous tree belonging to the family of Meliaceae It is native to the

Himalaya region of Asia (EL-Juhany 2011) The species is well adapted to warm climates, poor soils, and seasonally dry conditions (Harrison et al 2003) The fully grown tree has a rounded crown, and

commonly measures 7–12-m tall However in exceptional circumstances, M azedarach can attain a

height of 45 m The leaves are up to 50-cm-long, alternate, long-petioled, two or three times compound (odd-pinnate); the leaflets are dark green above and lighter green below, with serrate margins The flowers are small and fragrant, with five pale purple or lilac petals, growing in clusters The fruit is a drupe, marble-sized, light yellow at maturity, hanging on the tree all winter, and gradually becoming wrinkled and almost white (Rahman et al 2014)

The main utility of M azedarach is its high-quality-timber Seasoning is relatively simple in

that planks dry without cracking or warping and are resistant to fungal infection The wood is used to manufacture agricultural implements, furniture, plywood, boxes, poles, and tool handles (EL-Juhany

2011) It is also used in cabinet making as well as in construction (Nghia 2007) Besides, M azedarach

is a multi-purpose tree species Its leaves can be used as green manure and insecticides It is often planted for fuel supply in Middle East and in Assam (India), where it is grown on tea estates for fuel

(EL-Juhany 2011) In Vietnam, most of the M azedarach were planted in short rotation around 5–6

years with the purpose to supply raw material for pulp and particleboard industries

Wood property knowledge is of great importance in the quality improvement of various wood products (Kamala et al 2013) An examination of literature reveals that wood properties are highly variable They vary from stand to stand, tree-to-tree, around the circumference, across the radius, along the height, and even within small sampling unit like growth ring (Sharma et al 2014) Although

these variations provide great potential for sustainable utilization of wood, there is no information

about wood properties of M azedarach grown in Vietnam Thus, no effort has been made to investigate the variation in wood properties of M azedarach in Vietnam, despite the importance of

this species and the multiuse of its wood Therefore, this study was carried out to investigate variations

in wood properties (growth ring width, specific gravity, fiber length, and microfibril angle) within

tree, between trees, and between sites of M azedarach trees grown in northern Vietnam Information

gained provide basis for determining management strategies appropriate for sustainable wood

utilization of M azedarach trees growing in northern Vietnam

3.3 Materials and methods

3.3.1 Study site and sampling

Samples were collected from two M azedarach state-owned plantations in Vietnam The

location and detailed information of the two sites are given in Table 3.1 The trees were around 17–

19 years old (ring count at 15 cm above the ground) The trees were planted at a density of 830 trees per hectare at spacing of 4 m × 3 m from seedlings produced by seeds from natural forests located near each site The anticipated rotational age of this species is approximately 15–20 years Thinning was carried out at the ages of 3 and 6 (removing 50% of standing trees each time) The thinned trees were used as poles while the branches were used as firewood In August 2016, six trees (three from each plantation) were harvested The trees were chosen based on straightness, normal branching, and

no signs of any diseases or pest symptoms The trees were felled through cutting their stems at 15 cm above the ground Diameter at breast height (1.3 m above the ground) as well as the total stem height for each tree were measured just before felling (Table 3.2)

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3.3.2 Wood specimen preparation

Cross-sectional discs of 3 cm thickness from each tree were cut at different heights (0.3, 1.3, 3.3, 5.3, and 7.3 m height above the ground) to examine growth ring width (GRW) and specific gravity (SG) A 3-cm-thick disc was also collected from each tree at the height of 1.3 m for measurement of fiber length (FL) and microfibril angle of S2 layer of cell wall (MFA)

3.3.3 Growth ring width

Pith-to-bark strips [Radius × 30 (Tangential) × 15 (Longitudinal) mm] from the south side were cut from the discs and air-dried Thus, the strips were conditioned in a room at a constant temperature (20 oC) and relative humidity (60%) to constant weight With the same strips, images were taken using a Canon MP-650 scanner attached to a computer GRW were measured using Image

J software version 1.50i (Image-J) GRW of each tree was expressed as a mean value of all rings in that tree

Table 3.1 General characteristics of the study sites

Description

Site 1 Northeast

Site 2 Northwest

DBH (cm)

H (m)

DBH diameter at breast height (at 1.3 m above the ground), H tree height

a Measured by ring counting at the 15 cm above the ground

3.3.4 Wood specific gravity

Due to distinct growth rings (Fig 3.1), after measuring the GRW, the same strips were then cut into individual rings for measurement of SG in air-dry Two or more rings were combined in some positions where the rings were too small to be measured SG, which is the ratio of the density of a wood to that of water at 4 ºC (Zobel and Van Buijtenen 1989), was measured by an electronic densimeter MD-300S (Alfamirage Co.Ltd, Japan) Measurement time per sample was about 10 s

3.3.5 Fiber length and microfibril angle

Pith-to-bark strips [Radius × 20 (T) × 10 (L) mm] were cut from discs cut at 1.3 m for measuring FL and MFA The outermost latewoods at ring number 1, 2, 3, 5, 8, 10, 13, 15, and 17 from pith of strips were cut and macerated by dipping in 1:1 solution of 65% nitric acid (HNO3) and distilled water (H2O) plus potassium chlorate (KClO3) (3 g/100 ml solution) for 5 days The pieces were rinsed three times with distilled water, stained with safranin, and then mounted on a glass slide The FL of

30 fibers was measured by using a profile projector (V-12, Nikon) at a 50-fold magnification

Small blocks [10 (R) × 10 (T) × 10 (L) mm] at ring number 1, 2, 5, 10, and 15 were also prepared from the strips Radial sections of 8 µm thickness were cut by microtome, macerated (using the solution described above) for 40 min, and cleaned in distilled water The sections were dehydrated

in 10% ethanol, and subsequently in an ethanol series of 30, 60, 80, and 100% ethanol for 5 min each The sections were then placed on a slide glass and immersed in a 3% solution of iodine-potassium for 2-5 s One or two drops of 60% HNO3 were added and a coverslip was placed over the wetted specimen MFA of 25 fibers per small block was measured by light microscope (Olympus DP70, Nikon) and Image J software version 1.50i (Image-J)

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Fig 3.1 Tree ring in cross section obtained from Melia azedarach (at 3.3 m height, Tree

No.1, site 1)

3.3.6 Determination of fiber length increment (FLI)

Variations in length of wood fibers were approximated by a logarithmic relationship to the annual ring from the pith The FLI was calculated using the procedure described by Honjo et al (2005) The FLI annually (from ring to ring) was determined using the following formula:

as fixed effects Variance components for the sources of variation were also estimated Statistical analysis was performed using R software version 3.2.3 (R-software)

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Table 3.3 Model used in the analysis of variance

No Source of variation

a Source of variations excluded in fiber length and microfibril

angle analysis, since wood specimens were collected at 1.3 m stem height only

3.4 Results and discussion

3.4.1 Growth ring width

The GRW of M azedarach was on average 7.44 mm, with an average range between trees

from 6.53 to 8.64 mm (Table 3.4) Site and tree-to-tree within a site were not a source of variations of GRW, explaining only 0.28 and 1.58% of the total variation, respectively (Table 3.5) The radial

variation of GRW was highly (P < 0.001) significant and contributed the highest (52.58%) of the total

variation Mean GRW near the pith was large and decreased rapidly with cambial age up to 5 and 6 years before being less or more stable to the bark However, there were some fluctuations and spikes

in some trees (Fig 3.2) The longitudinal variation of GRW was highly significant (P < 0.05) but

contributed little (2.67%) to the total variation (Table 3.5) Mean GRW decreased with height level ranged from 8.70 to 6.34 mm

The findings of the present study are in agreement to those in literature for this species

Matsumura et al (2006) reported wood properties and their variation in the stem of 17-year-old M

azedarach plantation trees grown in Japan It was found that GRW near the pith up to 3-m height

above the ground was large and became stable beyond the fourth ring regardless of stem height GRW

is highly variable as it is controlled by a variety of factors such as environmental fluctuations (Zobel and Van Buijtenen 1989) Besides, plant spacing is also a factor that can influence GRW There is acceleration of growth for widely spaced trees than crowded trees, because widely spaced trees do not compete for growth elements such as nutrients, water, and sunlight, hence, they tend to have wider GRW (Zhu et al 2000) In the present study, plant spacing was the same for two sites, hence, no

significant (P > 0.05) difference was observed on mean GRW between the sites