Forests play a crucial role by providing a wide range of goods and services, including industrial wood, fuel wood, and non-wood products such as animal fodder, essential oils, and food Planted forests contribute to conservation efforts, carbon sequestration, recreation activities like hunting and hiking, and help in erosion control and land rehabilitation For countries with low forest cover, establishing new forests through planting is essential to harness the numerous benefits that forests offer.
From 1990 to 2015, the global planted forest area expanded from 167.5 million hectares to 277.9 million hectares, with significant regional variations (Payn et al 2015) In Vietnam, the planted forest area rose dramatically from 0.58 million hectares in 1985 to 4.13 million hectares by 2016 (Ministry of Agriculture and Rural Development of Vietnam 2017) These plantations not only provide essential materials for pulp and paper production but also play a crucial role in environmental protection by reducing greenhouse gas emissions and alleviating rural poverty (Kim 2009) However, the decline in available wood resources and rising wood processing costs have heightened the focus on timber production from plantations Currently, timber from these plantations is often under-utilized and poorly managed, highlighting the need for effective and sustainable management practices to enhance timber quality and prevent resource depletion A promising approach to achieve sustainable utilization of wood resources is through research on wood properties.
Wood is a highly variable material due to its biological origin, exhibiting significant differences within a species This variability can be categorized into radial variation, which occurs from pith to bark, and axial variation along the stem While the diverse characteristics of wood complicate the prediction of its performance and processing efficiency, they also present opportunities for genetic enhancement and a wide range of applications Understanding the variability of wood within trees is essential for improving wood quality and optimizing processing and utilization methods.
Table 1.1 The area of natural and planted forest in Vietnam from 1985 to 2016
A re a (m il li on ha )
Melia azedarach L is a deciduous tree belonging to the family of Meliaceae It is native to the
The Himalaya region of Asia is home to the M azedarach species, which thrives in warm climates, poor soils, and seasonally dry conditions This tree typically reaches heights of 7 to 12 meters, but can exceptionally grow up to 45 meters Its leaves are long-petioled, measuring up to 50 cm, and are characterized by a dark green upper surface and a lighter green underside with serrate margins The small, fragrant flowers feature five pale purple or lilac petals and grow in clusters The fruit is a marble-sized drupe that matures to a light yellow, remaining on the tree throughout winter and gradually becoming wrinkled and nearly white.
M azedarach has the potential to aid in global warming prevention due to its significant carbon storage capabilities (Osei et al 2018) This species, alongside other fast-growing trees, is utilized for pulping materials because of its high productivity (Ministry of Agriculture and Rural Development of Vietnam 2014) Additionally, the use of M azedarach wood as a building material, such as for posts and beams in timber construction, is anticipated to enhance its value (Hasegawa et al 2015) Various researchers have explored the physical and mechanical properties of M azedarach wood, contributing to its understanding and potential applications.
Research has shown that M azedarach exhibits varied wood properties depending on its planting location, with studies from Japan (2006) highlighting its potential as a new timber source Additionally, Venson et al (2008) investigated the physical, mechanical, and biological characteristics of M azedarach in Mexico, concluding that with the right genotypes and clones, it can effectively serve as structural lumber.
In northern Vietnam, M azedarach is widely cultivated, primarily in short rotations of 5-6 years, to provide raw materials for the pulp and particleboard industries However, the decline in available wood resources and rising wood processing costs have heightened the demand for wood sourced from plantations.
M azedarach wood is known for its durability, termite and insect resistance, and ease of workability (Nghia 2007) However, there has been no research conducted on the within-tree variations of its wood properties in both radial and axial directions in Vietnam, despite the significance of this species and its versatile applications.
Rapid and nondestructive evaluation of wood properties is crucial for tree breeders and optimal timber utilization This evaluation method enhances quality control in the industry by minimizing property variation in raw materials and their by-products However, the inherent variability of wood characteristics poses challenges in accurately predicting performance, which complicates the application of nondestructive testing for wood quality assessment Research indicates that nondestructive techniques can effectively evaluate wood properties in small specimens, lumber, and even assess the quality of logs and standing trees One of the most reliable methods involves stress wave techniques, which analyze the relationship between wave propagation (velocity and attenuation) and the material's mechanical and physical properties, along with any irregularities in the wood Consequently, investigating the effectiveness of stress wave techniques for evaluating the wood properties of M azedarach in northern Vietnam is essential.
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
This article offers essential insights for wood industry professionals regarding the sustainable processing of M azedarach logs for timber It emphasizes the potential of employing rapid, nondestructive methods to accurately predict the dimensional stability and mechanical properties of M azedarach wood Additionally, the findings serve as a foundational basis for the machine grading of M azedarach timber in Vietnam.
Introduction
Wood is a versatile material with diverse applications, each requiring specific quality criteria, such as knot size, wood density, cell wall thickness, fiber length, and fiber content However, due to its biological origin, wood exhibits significant variability, making its properties inconsistent across different stands, trees, and even within individual growth rings This inherent variability complicates the accurate prediction of wood performance, posing challenges for efficient processing and utilization The primary sources of variation in wood properties must be carefully considered to optimize its use in various industries.
• Between-tree variations on similar sites;
• Between-site variations of the same genotype growing in different geographic regions
Radial variation is the most recognized and extensively researched form of within-tree variability in wood This variation is typically observed as a radial pattern in the characteristics of wood, distinguishing between core wood and outer wood, as well as juvenile and mature wood (Anoop et al 2014).
Within-tree variations in wood properties
A growth ring is a distinct layer of wood formed during a single growth period in plants, characterized by the contrast between light-colored earlywood and dark-colored latewood Earlywood, produced at the beginning of the growing season, consists of larger cells with thinner walls, while latewood, formed later in the season, features smaller cells with thicker walls This differentiation in cell structure is essential for understanding tree growth and development (Panshin and De Zeeuw 1980, Larson 1994, Missanjo 2017).
The growth rate has minimal impact on the wood properties of diffuse-porous species, as they maintain a consistent proportion of vessels throughout their annual rings, irrespective of growth speed Conversely, in ring-porous hardwoods, a higher growth rate significantly increases wood density, resulting in denser wood from faster growth Notably, the volume of vessel tissue in ring-porous hardwoods remains constant each year, leading to a smaller proportion of vessel tissue as the growth ring widens (Walker et al 1993).
Ring width variation with age significantly influences wood properties, typically showing a decreasing trend in plantation trees as they mature due to competition among stands However, this pattern can be affected by various soil and climatic conditions, as noted in studies by Zobel and Sprague (1998), Matsumura et al (2006), Adamopoulos et al (2010), and Kiaei et al (2016).
In 2006, it was observed that the growth ring width of M azedarach in Japan decreases from the pith to the periphery In ring-porous hardwoods, the growth rate, indicated by ring width, shows a positive correlation with wood density This relationship is due to the earlywood zone remaining relatively constant annually, resulting in wider rings that predominantly consist of denser latewood with fewer vessels.
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 in trees is influenced by various factors, including environmental conditions and resource competition Research indicates a strong correlation between ring width and growth conditions, highlighting its role as a record of tree vitality in response to climate changes At the edges of their geographical distribution, tree growth is primarily constrained by temperature, with tree-ring data serving as an indicator of local temperature variations Furthermore, studies show that trees planted with wider spacing exhibit greater growth rates due to reduced competition for nutrients, water, and sunlight, resulting in wider growth rings.
2.2.2 Wood density and specific gravity
Specific gravity is the most crucial physical property of wood, as it is closely linked to various mechanical and physical characteristics Although specific gravity and wood density are often used interchangeably in general discussions, they have distinct definitions that refer to the same attribute (Bowyer et al 2007) To accurately assess wood density, it is essential to account for its moisture content In physics, density is defined as mass per unit volume; however, with wood, fluctuations in moisture content influence both mass and volume, necessitating precise specification.
Wood density is a critical property that directly influences mechanical resistance, wear, and overall technological quality It serves as a primary criterion for evaluating the potential value of timber species, significantly affecting the strength and stiffness of solid lumber Additionally, wood density impacts the physical yields of fiber used in composite products, pulp, and paper production.
Higher wood density is increasingly valued for its critical role in wood technology and its significance in estimating forest biomass and carbon storage The carbon stored in trees is influenced by both biomass and the carbon content of wood and other tissues Consequently, wood density and stem volume are key factors that govern carbon storage at the tree level.
Within-tree variation in wood density is particularly intricate in hardwoods, exhibiting a wide range of patterns throughout the stem Studies by Knapic et al highlight the complexity of wood density variation in the radial direction of hardwood trees.
A study in 2011 indicated a trend of decreasing density with cambial age in Quercus faginea, a pattern also observed in other Quercus species, including Q garryana (Lei et al., 1996) and Q suber (Knapic et al.).
In certain Meliaceae species, such as Melia azedarach and Toona ciliata, wood density exhibits a linear increase from the pith to the bark.
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
A study conducted in 2005 revealed that Cedrela odorata exhibits low wood density at the pith, which increases sharply outward to a peak before gradually declining towards the outer edge in a radial direction In contrast, the wood density of Acacia melanoxylon, planted in New, shows minimal variation with height in the axial direction.
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 typically exhibits lower density compared to outerwood, primarily due to its composition, which consists mainly of earlywood This results in a thinner S2 layer, leading to higher lignin content and lower cellulose content in corewood than in outerwood The transition from corewood to outerwood varies by species and the specific properties being analyzed, occurring between growth rings from the pith.
The average basic density of trees in a stand is significantly influenced by environmental factors, while genetic control accounts for the differences observed between individual trees, regardless of their location When a wood property is primarily influenced by the environment, it demonstrates considerable variation with environmental changes Conversely, wood properties under strong genetic control may remain consistent across various environments or vary independently of environmental conditions.
Both environmental and genetic factors play crucial roles in population dynamics While the environment influences the average basic density of a population, genetic control accounts for the variations between individual trees within that population Consequently, introducing a species to a new area can yield unpredictable outcomes, making it essential to initially cultivate the species on a small scale before committing to large-scale planting This cautious approach is vital, as the results of such introductions can often lead to unforeseen challenges and disappointments.
Nondestructive wood evaluation
Nondestructive evaluation (NDE) has become essential in the forest products industry, particularly for structural product grading, leading to engineered materials with clearly defined performance standards There is a growing interest in innovative, cost-effective NDE technologies aimed at assessing wood quality Among these, stress wave propagation techniques have gained significant attention over the past few decades, with research exploring the use of vibration modes in evaluating the quality of standing trees, logs, and small-dimension wood specimens.
Research indicates that the modulus of elasticity of lumber can be effectively predicted using the stress wave velocity of trees, logs, or small specimens (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) Notably, Wang et al (2001) established a strong correlation between the dynamic modulus of elasticity measured by the stress wave method and the modulus of elasticity of small, clear specimens derived from Tsuga heterophylla and Picea sitchensis through destructive testing Additionally, Ishiguri et al (2008) found a significant positive relationship between the stress wave velocity of trees and the static bending modulus of elasticity in Larix kaemferi.
Recent studies indicate that nondestructive methods can effectively evaluate the dimensional stability of structural lumber Research by Yamashita et al (2009a, 2009b) demonstrated a strong correlation between longitudinal-transversal shrinkage and the modulus of elasticity in Cryptomeria japonica logs, assessed through tapping while in their green state.
In 2006, research highlighted the effectiveness of acoustic analysis as a pre-sorting criterion for identifying warp-prone Pinus ponderosa boards before kiln-drying, revealing a significant correlation between the boards' acoustic properties and grade loss due to excessive warping Furthermore, studies by Dundar et al (2013, 2016) demonstrated that ultrasonic measurements taken in green conditions can effectively predict transverse shrinkage in both softwood and hardwood species.
Conclusion of literature review
Hardwoods possess a more intricate structure than softwoods, featuring a diverse array of cell types arranged in various patterns, which contributes to their unique appearance and grain The differences in wood properties within the same species arise from genetic variations and ecological conditions, such as altitude, precipitation, temperature, soil quality, water availability, and nutrient levels These factors significantly influence tree growth and development, with genetic structure being the primary determinant of wood properties, while ecological conditions directly or indirectly impact tree fertility, form, and height.
Within a given species, wood variation can be divided into radial variation, which occurs from pith to bark, and axial variation, which occurs along the stem Radial variation is the most extensively studied aspect of within-tree variability, typically demonstrated by changes in wood characteristics between inner and outer wood This substantial variability complicates the accurate prediction of wood performance, hindering efficient processing and utilization However, this variability also presents opportunities for genetic improvement and a range of potential applications Therefore, it is essential to examine wood property variations in the context of specific species.
Abstract
A study on the intrinsic wood properties of 17–19-year-old Melia azedarach L trees in northern Vietnam revealed variations in growth ring width (GRW), specific gravity (SG), fiber length (FL), and microfibril angle (MFA) Discs were collected from five heights (0.3, 1.3, 3.3, 5.3, and 7.3 m) to assess these properties The average measurements were found to be 7.44 mm for GRW, 0.548 for SG, 1.07 mm for FL, and 14.65° for MFA Notably, significant differences (P < 0.05) were observed in SG, FL, and MFA among the trees and between the two sites, indicating the importance of longitudinal position in wood property variation.
Radial position significantly influences wood properties, with high significance levels observed (P < 0.001) across all measured attributes The total variations contributed by radial position are notable, with GRW at 52.58%, SG at 58.49%, FL at 77.83%, and MFA at 26.20% Notably, fiber length (FL) and specific gravity (SG) increase from the pith to the bark, while growth ring width (GRW) and microfibril angle (MFA) decrease in the same direction Fiber length increment (FLI) stabilizes between the 7th and 10th rings, which is crucial for log processing These findings establish a foundation for developing effective management strategies for structural timber production from M azedarach plantation trees in northern Vietnam.
Keywords: Melia azedarach, Growth ring width, Specific gravity, Fiber length, Microfibril angle
Introduction
Melia azedarach L is a deciduous tree belonging to the family of Meliaceae It is native to the
The M azedarach species, native to the Himalaya region of Asia, thrives in warm climates, poor soils, and seasonally dry conditions This tree typically reaches heights of 7 to 12 meters, but can grow up to 45 meters under exceptional circumstances Its leaves, which can measure up to 50 cm in length, are alternate, long-petioled, and odd-pinnate, featuring dark green leaflets on top and lighter green underneath with serrate edges The small, fragrant flowers have five pale purple or lilac petals and bloom in clusters The fruit, a marble-sized drupe, matures to a light yellow color, remains on the tree throughout winter, and gradually becomes wrinkled and nearly white.
M azedarach is primarily valued for its high-quality timber, which dries easily without cracking or warping, making it resistant to fungal infections This durable wood is commonly utilized in the production of agricultural tools, furniture, plywood, boxes, poles, and tool handles.
M azedarach, a versatile tree species, is utilized in cabinet making and construction, as well as serving multiple purposes such as providing green manure and insecticides It is commonly planted for fuel supply in regions like the Middle East and Assam, India, where it is cultivated on tea estates In Vietnam, M azedarach is typically grown in short rotations of 5 to 6 years to supply raw materials for the pulp and particleboard industries.
Understanding wood properties is crucial for enhancing the quality of wood products, as they exhibit significant variability across different dimensions, including stand, tree, circumference, radius, height, and even within growth rings Despite the potential for sustainable wood utilization, there is a lack of information regarding the wood properties of M azedarach in Vietnam This study aims to examine the variations in wood properties—such as growth ring width, specific gravity, fiber length, and microfibril angle—within individual trees, among different trees, and across various sites in northern Vietnam The findings will inform management strategies for the sustainable use of M azedarach wood resources in the region.
Materials and methods
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–
At 19 years old, the trees, planted at a density of 830 per hectare with a spacing of 4 m × 3 m, are derived from seeds sourced from nearby natural forests This species is expected to reach a rotational age of 15–20 years Thinning occurred at 3 and 6 years, removing 50% of the standing trees each time, with the thinned trees repurposed as poles and branches used for firewood In August 2016, six trees were harvested based on criteria such as straightness, normal branching, and absence of disease or pests The harvesting involved cutting the stems 15 cm above ground, with measurements taken for diameter at breast height (1.3 m) and total stem height prior to felling.
Cross-sectional discs, each 3 cm thick, were obtained from various heights (0.3, 1.3, 3.3, 5.3, and 7.3 m above ground) of each tree to analyze growth ring width (GRW) and specific gravity (SG) Additionally, a disc at 1.3 m height was collected for assessing fiber length (FL) and the microfibril angle of the S2 layer of the cell wall (MFA).
Pith-to-bark strips measuring 30 mm tangentially and 15 mm longitudinally were cut from the south side of the discs and air-dried These strips were then conditioned at a consistent temperature of 20°C and relative humidity of 60% until they reached a constant weight Subsequently, images of the strips were captured using a Canon MP-650 scanner connected to a computer, and GRW measurements were obtained through image analysis.
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
Province Tuyen Quang Son La
Table 3.2 Age, diameter at breast height, and total stem height of sampled Melia azedarach trees
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
After measuring the growth ring width (GRW) and observing distinct growth rings, the strips were cut into individual rings for specific measurements of specific gravity (SG) in air-dry conditions In cases where the rings were too small for individual measurement, two or more rings were combined SG, defined as the ratio of wood density to water density at 4 ºC (Zobel and Van Buijtenen 1989), was determined using an electronic densimeter MD-300S from Alfamirage Co Ltd, Japan, with each sample taking approximately 10 seconds to measure.
3.3.5 Fiber length and microfibril angle
Pith-to-bark strips measuring 20 mm in thickness and 10 mm in length were extracted from discs taken at a height of 1.3 m to analyze fiber length (FL) and microfibril angle (MFA) The outermost latewood from specific ring numbers (1, 2, 3, 5, 8, 10, 13, 15, and 17) was macerated using a 1:1 solution of 65% nitric acid and distilled water, supplemented with potassium chlorate, over a period of five days After rinsing the samples three times with distilled water, they were stained with safranin and mounted on glass slides for further examination.
30 fibers was measured by using a profile projector (V-12, Nikon) at a 50-fold magnification
Small blocks measuring 10 mm in each dimension were prepared from strips at ring numbers 1, 2, 5, 10, and 15 Radial sections with a thickness of 8 µm were cut using a microtome, macerated for 40 minutes with a specified solution, and then cleaned with distilled water The sections underwent dehydration in a series of ethanol solutions, starting with 10% ethanol and progressing through 30%, 60%, 80%, and 100% ethanol, with each step lasting 5 minutes After dehydration, the sections were placed on glass slides, immersed in a 3% iodine-potassium solution for 2-5 seconds, and treated with one or two drops of 60% HNO3 before covering with a coverslip The mean fiber area (MFA) of 25 fibers per small block was measured using a light microscope (Olympus DP70, Nikon) and Image J software version 1.50i.
Fig 3.1 Tree ring in cross section obtained from Melia azedarach (at 3.3 m height, Tree
3.3.6 Determination of fiber length increment (FLI )
The length variations of wood fibers were estimated using a logarithmic relationship based on the annual rings from the pith The Fiber Length Index (FLI) was calculated following the methodology outlined by Honjo et al (2005), with the FLI determined annually from ring to ring using a specific formula.
Where: FLI is the fiber length increment; ΔFL is the change in fiber length; and ΔRN is the change in ring number The FLI was then expressed as a percentage
An analysis of variance (ANOVA) was conducted on wood properties, including growth rate (GRW), specific gravity (SG), fiber length (FL), and microfibril angle (MFA), to evaluate the significance of factors such as site, tree, height level, and radial position In this study, trees were treated as random effects while other sources of variation were considered fixed effects Additionally, variance components for these sources of variation were estimated The statistical analysis was performed using R software version 3.2.3.
Table 3.3 Model used in the analysis of variance
11 Residuals a Source of variations excluded in fiber length and microfibril angle analysis, since wood specimens were collected at 1.3 m stem height only
Results and discussion
The average growth ring width (GRW) of M azedarach was 7.44 mm, with individual tree measurements ranging from 6.53 to 8.64 mm Variations in GRW were minimally influenced by site and tree-to-tree differences, accounting for only 0.28% and 1.58% of the total variation, respectively In contrast, radial variation in GRW was highly significant, contributing 52.58% to the total variation GRW was largest near the pith and decreased rapidly with cambial age up to 5 to 6 years, stabilizing thereafter, although some trees exhibited fluctuations Longitudinal variation in GRW was also significant but contributed only 2.67% to total variation, with mean GRW decreasing from 8.70 mm at lower heights to 6.34 mm at higher levels.
The current study aligns with previous research on M azedarach, particularly the findings of Matsumura et al (2006), which highlighted the wood properties and growth ring width (GRW) variation in 17-year-old trees in Japan It was observed that GRW near the pith was substantial up to 3 meters in height and stabilized beyond the fourth ring, regardless of stem height GRW variability is influenced by various factors, including environmental changes (Zobel and Van Buijtenen, 1989) and plant spacing Specifically, widely spaced trees exhibit accelerated growth due to reduced competition for essential resources such as nutrients, water, and sunlight, resulting in broader GRW (Zhu et al., 2000) However, in this study, consistent plant spacing across two sites resulted in no significant difference in mean GRW (P > 0.05) between the locations.
Table 3.4 Mean values per site and tree for selected wood properties of Melia azedarach
Category Growth ring width (mm)
2 7.15 ± 0.32 a 0.559 ± 0.004 a 1.12 ± 0.01 a 13.17 ± 0.14 b Mean 7.44 ± 0.24 0.548 ± 0.003 1.07 ± 0.01 14.65 ± 0.12 Mean values are followed by standard errors a,b,c,d Means with different superscript within a column significantly differ (P < 0.05)
Table 3.5 Variance components for growth ring width and specific gravity of Melia azedarach
Growth ring width Specific gravity
Residuals 250 11.34 9.33 df degrees of freedom, Var variance (%)
Fig 3.2 Variation of growth ring width in the radial and vertical directions of Melia azedarach in two sites
G row th ri ng w idt h (m m )
G row th ri ng w idt h (m m )
The study on wood specific gravity (SG) of M azedarach reveals significant influences from site, tree-to-tree variations, stem height position, and radial position, with radial position accounting for the highest contribution (58.49%) to total variation Wood SG values ranged from 0.523 to 0.572, aligning with previous literature that reported values between 0.5 and 0.65, while some studies noted lower SG values of 0.49 and 0.404–0.413 These discrepancies may stem from factors such as tree age and geographic variations, including latitude, temperature, and precipitation Additionally, differences in altitude, mean annual rainfall, and soil types between study sites may have affected wood SG variation Future research is necessary to explore the genetic impacts on wood SG variation for M azedarach in northern Vietnam.
The wood density of M azedarach consistently increased from the pith to the bark across all stem height levels, aligning with previous studies (Matsumura et al 2006; Nock et al 2009; El-Juhany 2011) This trend is also observed in other Meliaceae species, such as Toona ciliata and Swietenia macrophylla In contrast, Wahyudi et al (2016) found that Azadirachta excelsa exhibited a nearly constant basic density from pith to bark, while Ofori and Brentuo (2005) reported that Cedrela odorata displayed low density at the pith, peaking before gradually declining towards the outer layers.
38 previous reports, radial variation of wood SG depends on species For M azedarach planted in northern Vietnam, this study showed that wood SG increases gradually from pith toward outside
Significant differences (P < 0.05) in specific gravity (SG) were observed across various height levels, showing a general decline from 0.3 to 3.3 m, followed by a slight increase towards the top (Fig 3.3) These findings align with Kim et al (2008), who noted that SG was highest at the stump and exhibited a similar decreasing and then increasing trend in Acacia mangium and Acacia auriculiformis in northern Vietnam Additionally, as illustrated in Fig 3.4, Matsumura et al (2006) confirmed the presence of low and high SG zones within the stem, with higher SG found in the outer regions and lower SG in the inner areas.
Fig 3.3 Variation of specific gravity in the radial and vertical directions of Melia azedarach in two sites
Spe ci fi c gr avi ty
Spe ci fi c gr avi ty
The tree stem maps illustrate variations in growth ring width and specific gravity, with each graph representing an individual tree from distinct sites The use of light and dark colors effectively indicates low and high specific gravity levels, respectively.
The analysis of the Microfibril Angle (MFA) in the S2 layer of the cell wall of M azedarach wood fibers, as shown in Tables 3.4 and 3.6, reveals significant differences (P < 0.001) in MFA across various sites, among individual trees, and along the radial direction Notably, radial position emerged as the most influential factor, accounting for 26.20% of the total variation observed The mean MFA exhibited a declining trend from the pith to the bark, as illustrated in Fig 3.5 These phenotypic trends align with earlier findings in M azedarach (Matsumura et al 2006) and similar species.
(Ishiguri et al 2012, Todoroki et al 2015) High MFA in rings close to the pith ensure flexibility and protect the young shoots from wind damage (Walker and Butterfield 1995)
The findings on fruit length (FL) of M azedarach, as presented in Tables 3.4 and 3.6, indicate an average FL of 1.07 mm, with variations ranging from 0.98 to 1.15 mm across different trees Significant sources of variation in FL include site, tree-to-tree differences within sites, and radial position, with radial position accounting for the largest share at 77.83% of the total variation Notably, FL at breast height increases from the pith to the bark, a trend attributed to the growth in length associated with cambial age, as outlined by Matsumura et al (2006).
The length of fibers in the present study is in agreement to those in literature for M azedarach Abdul (2007) reported a 0.78–1.3 mm length for M azedarach fibers, while Richter and Dallwitz
(2000) reported an average FL of 0.8–1.65 mm Contrary, El-Juhany (2011) reported a lower average
FL of 0.742–0.792 mm for eight-year-old M azedarach The significant variation between trees in
Research indicates that while some studies show consistent fiber length (FL) across trees (Leal et al 2006), others have noted slight variations (Gartner et al 1997) This tree-to-tree variation in FL may stem from the unique genetic potential of individual trees to produce either longer or shorter fibers compared to their neighbors (El-Juhany 2011).
Table 3.6 Variance components for fiber length and microfibril angle of Melia azedarach
Residuals 1566 13.12 720 45.86 df degrees of freedom, Var variance (%)
Fig 3.5 Radial variation of MFA for two different sites of Melia azedarach
M ic rof ibr il a ngl e ( o )
Fig 3.6 Radial variation of fiber length for two different sites of Melia azedarach y 1 = 0.2196ln(x 1 ) + 0.6309
3.4.5 Stabilizing point of fiber length increment
The logarithmic regression analysis of fiber length (FL) for site 1 and site 2 revealed specific functions: y₁ = 0.2196ln(x₁) + 0.6309 and y₂ = 0.1784ln(x₂) + 0.8039, where y represents fiber length and x denotes ring number The fiber length index (FLI) was estimated and plotted, demonstrating that FLI began to stabilize between the 7th and 10th rings for both sites This stabilization indicates that the wood produced beyond the 7th ring contains relatively long fibers.
3.4.6 Implications for wood utilization of M azedarach in northern Vietnam
The length of wood fibers is crucial for maximizing timber quality and value, with mature wood exhibiting long fiber length (FL), high specific gravity (SG), and low microfibril angle (MFA) being ideal for structural applications In this study, FL was found to increase from the pith to the bark, particularly beyond ring number 7, indicating that wood from this area is suitable for structural uses Additionally, M azedarach trees from Son La (site 2) demonstrated superior SG, longer FL, and lower MFA compared to those from Tuyen Quang (site 1), suggesting that site 2 and similar environments are preferable for M azedarach plantations in northern Vietnam Further research is necessary to explore the impact of seed sources and mechanical properties for sustainable wood utilization of M azedarach in the region.
Fig 3.7 Fiber length increment with cambial age of Melia azedarach in Vietnam (Bars mean standard error)
Fi be r l engt h inc re m ent (% )
Conclusions
The study revealed significant within-tree variation in wood properties, with longitudinal position affecting growth ring width (GRW) and wood specific gravity (SG) Specifically, mean GRW decreased with increasing stem height, while wood SG showed a decline from the stump to the intermediate stem, followed by a slight increase towards the top Radial position was highly significant for all wood properties, contributing the most to total variation; fiber length (FL) and wood SG increased from the pith to the bark, whereas GRW and microfibril angle (MFA) decreased in the same direction Notably, fiber length index (FLI) stabilized beyond ring number 7 from the pith, which is crucial for processing logs of M azedarach trees in northern Vietnam.
Abstract
This study quantified variations within tree stems in tangential shrinkage (αT), radial shrinkage
(αR), and tangential/radial shrinkage ratio (αT/αR) of Melia azedarach grown in two different sites in northern Vietnam The overall values of αT, αR, and αT/αR were 7.05%, 4.38%, and 1.64, respectively
The variation in αT and αR increased progressively from the pith to the bark, exhibiting a consistent trend across both study sites In the radial direction, αT/αR significantly decreased from 10% to 50% of the radial length from the pith, stabilizing toward the outer regions Transverse shrinkage variation with height was minimal and statistically insignificant A strong positive correlation was observed between transverse shrinkage and basic density (BD), indicating that selecting for higher wood density may enhance transverse shrinkage Furthermore, αT and αR demonstrated significant positive linear relationships with both acoustic wave velocity (VL) and dynamic modulus of elasticity of logs (DMOElog), suggesting the potential for sorting lumber with high transverse shrinkage using stress wave methods for M azedarach in northern Vietnam.
Keywords: Melia azedarach, Transverse shrinkage, Nondestructive evaluation, Radial position
Introduction
Wood is a highly variable material due to its biological origins, exhibiting significant differences both radially from pith to bark and axially along the stem This variability complicates the prediction of wood performance, impacting its processing and utilization However, it also presents opportunities for genetic improvement and diverse applications Understanding wood variability within a tree is essential for enhancing wood quality and optimizing processing methods.
Dimensional stability and warping are critical issues in the drying, processing, and use of wood, primarily due to the anisotropic shrinkage that occurs in both radial and tangential directions (Wang et al 2008) The shrinkage of wood, which varies by species, significantly impacts its usability in products; lower shrinkage values can be advantageous for certain types When dried from a green to an oven-dry state, hardwood can experience tangential shrinkage ranging from 6% to 12%, while radial shrinkage is approximately half of that in the tangential direction This differential shrinkage is a key factor contributing to shape distortion during lumber seasoning and its subsequent use (Dundar et al 2016).
Wood density is the primary factor influencing shrinkage, as the amount of shrinkage correlates with the moisture lost from the cell wall (Skaar 1988) Understanding the relationship between transverse shrinkage and wood density is crucial for effective lumber management.
Research indicates that optimizing shrinkage properties can enhance drying yield while reducing costs and energy consumption Additionally, studies have proposed the use of acoustic wave techniques to evaluate the dimensional stability of structural lumber.
Research by Yamashita et al (2009a, 2009b) established significant correlations between longitudinal and transversal shrinkage and the dynamic modulus of elasticity of green Sugi (Cryptomeria japonica) logs Wang and Simpson (2006) demonstrated the effectiveness of acoustic analysis as a presorting method to identify warp-prone Ponderosa pine (Pinus ponderosa) boards prior to kiln-drying, revealing a statistically significant relationship between the acoustic properties and grade loss due to warp Furthermore, Dundar et al (2013, 2016) highlighted the potential of ultrasonic measurements in green conditions for accurately predicting transverse shrinkage in both softwood and hardwood species.
Melia azedarach, a deciduous tree belonging to the family of Meliaceae, is native to the
The M azedarach species, native to the Himalaya region of Asia, thrives in warm climates and poor soils, making it well-suited for subtropical and tropical environments worldwide In Vietnam, it is widely cultivated across northern provinces With the decline in natural wood resources and rising processing costs, there is growing interest in plantation-sourced wood The furniture industry has recently recognized M azedarach for its fine grains, durability, termite and insect resistance, and ease of workability However, there is a lack of information on its dimensional stability, particularly concerning variations in transverse shrinkage within the tree, including radial and axial differences.
This study aimed to examine the within-tree variation in transverse shrinkage properties of M azedarach in northern Vietnam, focusing on three specific objectives: (1) analyzing the radial and axial patterns of wood transverse shrinkage from pith to bark at various stem heights, (2) exploring the correlation between transverse shrinkage and basic density (BD), and (3) identifying nondestructive parameters to predict transverse shrinkage for sorting high-quality lumber Additionally, the research evaluated the physical properties of M azedarach timber to assess its quality for grading purposes.
Material and methods
In this study, sample trees were collected from state-owned plantations in Tuyen Quang (Northeast) and Son La (Northwest) in northern Vietnam Six trees, approximately 17–19 years old, were selected based on criteria such as straight trunks, normal branching, and absence of diseases or pests These trees were planted at a density of 830 trees per hectare, with a spacing of 4 m × 3 m, using seedlings sourced from nearby natural forests The trees were felled at 15 cm above ground level, and 50-cm-long logs were extracted from various heights (0.3, 1.3, 3.3, 5.3, and 7.3 m) Prior to felling, the north and south sides of each tree were marked, and the sample trees were consistent with those used in previous studies.
4.3.2 Dynamic modulus of elasticity of log (DMOE log )
The Dynamic Modulus of Elasticity (DMOElog) was assessed using the stress wave method on green logs A Fakopp microsecond timer, manufactured in Hungary, was utilized to measure the acoustic wave propagation time through the log's axis This device features two electrodes—transducer and receiver—positioned centrally from the pith to the bark on each side of the log An acoustic signal is generated by striking the starting transducer with a hammer Each log underwent five repeated measurements, with the average value taken as the experimental result The velocity of acoustic wave propagation is calculated as the log length divided by the propagation time Additionally, the green density of the logs was measured as green weight per green volume, allowing for the determination of DMOElog in the direction parallel to the grain through a straightforward relationship.
DMOElog – dynamic modulus of elasticity of log (GPa), ρ – green density of log (kg/m 3 ),
Fig 4.1 Method of measuring dynamic modulus of elasticity of log (DMOElog) and cutting specimens from each tree
4.3.3 Basic density and transverse shrinkage
In the conducted experiment, 3 cm thick discs were prepared to evaluate transverse shrinkage and bulk density (BD) Measurements of tangential shrinkage (αT), radial shrinkage (αR), and BD were carried out following the Japanese Industrial Standards (JIS 2000) at various radial and height positions Specimens measuring 30 × 30 × 5 mm (Tangential × Radial × Longitudinal) were extracted at an interval of 10.
The study involved 180 small clear wood specimens, measured at various heights (0.3, 1.3, 3.3, 5.3, and 7.3 meters) from the ground, specifically focusing on 50% and 90% of the radial length from the pith on both the North and South sides To minimize drying stress on shrinkage, the samples were conditioned at a constant temperature of 20 °C and relative humidity of 60% before being oven-dried at 60 °C for one night and 103 °C for two nights to determine their oven-dry weight and dimensions Each specimen had centerlines drawn parallel to the radial and tangential directions for accurate length measurement The dimensions in both radial and tangential directions were measured in green and oven-dried conditions using a Mitutoyo digital micrometer CD-S20C, with a minimum scale of 0.01 mm The tangential/radial shrinkage ratio (αT/αR) was calculated by dividing αT by αR, while the basic density (BD) was determined as the oven-dry weight per green volume Shrinkage was calculated accordingly.
𝑙 , ×100 where: l g: length of centerline which was measured at green condition (mm), l o: length of centerline which was measured at oven-dry condition (mm), α: shrinkage from green to oven-dry (%)
The analysis of variance (ANOVA) was conducted on wood shrinkage properties (α T, α R, and α T /α R) to evaluate the significance of factors such as site, tree, height level, and radial position, with trees treated as random effects and other variations as fixed effects Variance components for these sources were estimated, and differences between radial and height positions within the stem were assessed using the Tukey-Kramer HSD test All statistical analyses were performed using R software version 3.2.3.
The grade yield of the specimens was evaluated according to the grading standards for the physical properties of timbers from Southeast Asia and the Pacific, as established by the Forestry and Forest Products Research Institute (FFPRI) in Japan (1975).
Table 4.1 Model used in the analysis of variance
Shrinkage from green to oven dry Tangential (%) Radial (%)
Table 4.2 Grading standard of physical properties of timber from Southeast Asia and Pacific regions by Forestry and Forest Products Research Institute (1975)
Results and discussion
4.4.1 Basic density and transverse shrinkage
Table 4.3 presents the statistics for bulk density (BD) and transverse shrinkage from green to oven-dry conditions for M azedarach trees in northern Vietnam, with average values of 0.43 g/cm³ for BD, 7.05% for tangential shrinkage (αT), 4.38% for radial shrinkage (αR), and a ratio of 1.64 for αT/αR across six trees at various stem heights For comparative analysis, Table 4.4 includes equivalent properties reported by Botero (1956), Coronel (1989), Pramana (1998), and Venson et al (2008) for M azedarach trees cultivated in different countries.
Radial variation is a key aspect of within-tree variability in wood, significantly influencing shrinkage characteristics Research indicates that radial position markedly affects shrinkage (P < 0.001), accounting for 42.38% of total variation in αT and 45.54% in αR As illustrated in Fig 4.2, both αT and αR increase from the pith to the bark, while the ratio αT/αR decreases outward This consistent radial shrinkage pattern persists across different tree heights and sites, suggesting minimal significant variation (P × L and P × S: no significant) The contrasting trends of αR and αT/αR may arise from greater within-tree variation in αR compared to αT These findings align with previous studies on Cedrela odorata and Populus euramericana, which also reported increased transverse shrinkage from pith to bark However, variations exist among hardwood species; for instance, Swietenia macrophylla showed no significant radial differences, while Acacia mangium exhibited a decrease in αT and αR towards the periphery, contrary to Acacia auriculiformis and Grevillea robusta, which had higher values at the outer positions This study confirms that in M azedarach from northern Vietnam, αT and αR increase radially, indicating that transverse shrinkage trends can vary by species due to differences in wood density, microfibril angle, and anatomical structures The subsequent section will explore the relationship between transverse shrinkage and wood density to assess its impact on αT and αR.
Table 4.3 Variation in basic density (BD), tangential shrinkage (αT), radial shrinkage (αR), and tangential/radial shrinkage ratio (αT/αR) within stem and between sites of Melia azedarach
Mean 180 0.43 ± 0.01 7.05 ± 0.06 4.38 ± 0.06 1.64 ± 0.02 n number of wood specimen
Mean values are followed by standard errors a,b,c Means with different superscript within a column significantly differ (P < 0.05)
Table 4.4 Shrinkage parameter of Melia azedarach planted in northern
Vietnam compared with corresponding data of Melia azedarach planted from other provenances
Shrinkage from green to oven dry α T (%) α R (%) α T /α R This study (17-19) 6.73 – 7.37 4.10 – 4.67 1.68 – 1.60
Age of tree was given in parentheses; a Pramana (1998); b Venson et al (2008); c Botero (1956); d Coronel (1989)
Table 4.5 Variance components for tangential shrinkage (α T ), radial shrinkage (α R ), and tangential/radial shrinkage ratio (α T /α R ) of Melia azedarach
% Site (S) 1 0.001 15.39 0.001 13.93 0.017 3.17 Tree/Site (T/S) 4 0.326 2.21 0.358 2.12 0.044 5.26 Height level (L) 4 0.163 3.64 0.712 1.20 0.092 4.43
Residuals 90 19.02 12.80 24.71 df degrees of freedom, Var variance (%)
Fig 4.2 Radial variation in tangential shrinkage (α T ), radial shrinkage (α R ), and tangential/radial shrinkage ratio (αT/αR) for two different sites of Melia azedarach (Bars mean standard deviation)
Microfibril angle (MFA) significantly influences wood shrinkage, with a direct relationship established by Barber and Meylan (1964) MFA, defined as the angle between microfibril orientation and the wood's longitudinal axis, affects shrinkage patterns; as MFA decreases, transverse shrinkage increases while longitudinal shrinkage decreases Duong et al (2017) observed that MFA in M azedarach decreases from the pith (16°) to the bark (12°), which correlates with increased transverse shrinkage in outer wood compared to inner wood Additionally, the earlywood-latewood ratio, characterized by larger vessels and thinner fiber walls in earlywood compared to latewood, may further contribute to shrinkage variability in ring-porous species Future research is necessary to explore the variations in cell morphology and earlywood-latewood proportions from pith to bark in M azedarach wood.
Cutting logs into thin discs enhances the understanding of drying stresses by allowing comparisons of drying strains between tangential and radial directions (Fu et al 2016) The shrinkage ratio is a crucial parameter for characterizing wood drying performance, as the disparity between tangential and radial shrinkage significantly influences internal stresses during the drying process (Dahlblom et al 1999) For M azedarach, tangential shrinkage is typically 1.5 to 2.5 times greater than radial shrinkage (Table 4.4) This study reveals that the αT/αR ratio decreases significantly from 10% to 50% of the radial length from the pith before stabilizing towards the outer regions, with a ratio of 1.76 near the pith compared to 1.59 and 1.56 in the middle and outer parts, respectively (Table 4.3) The variation in radial and tangential shrinkage is linked to the differences in wood density between earlywood and latewood, where latewood cells exhibit greater shrinkage due to their higher density In the radial direction, earlywood and latewood shrink independently, resulting in total shrinkage that approximates the weighted mean of both components, while tangential shrinkage is primarily influenced by latewood changes.
Anagnost et al (2005) proposed that the microfibril angle (MFA) in the radial walls of Acer saccharum and Prunus serotina species is comparable, while it is significantly larger in Drimys winteri species compared to the tangential walls This difference is attributed to the presence of bordered pits in the radial walls, which cause the microfibrils to deviate around them.
ANOVA results revealed that height level was not a significant source of variation, while site was a significant factor (P < 0.05) affecting α T, α R, and α T /α R Notably, α T and α R values were higher in site 2 compared to site 1 Variations in wood properties among the same species can be attributed to different genotypes and growth conditions Although the impact of these factors on transverse shrinkage in M azedarach has not been previously reported, similar studies in other hardwood species have shown that seed source and growth conditions significantly influence transverse shrinkage, as demonstrated by Montes et al (2007), who identified substantial genetic variation in wood shrinkage.
Calycophyllum spruceanum exhibits significant variations in shrinkage properties influenced by site conditions, as highlighted by Yang et al (2002) in their study of Eucalyptus globulus Labill The differences in transverse shrinkage observed between two sites in this research may stem from varying growth conditions, including altitude, mean annual rainfall, and soil types Future investigations should focus on the impact of seed source factors on wood shrinkage in M azedarach, as previous studies have shown differing transverse shrinkage results for this species across various countries These discrepancies are likely linked to the specific forest sites examined in each study, indicating that variations in transverse shrinkage can affect drying stress and overall wood quality.
68 incidence of drying defects such as cracks or deformations might differ among lumber sawn from different sites
4.4.2 Relationships between transverse shrinkage and basic density
Linear regression analysis assessed the correlation between transverse shrinkage and bulk density (BD), with results detailed in Table 4.6 and Figure 4.3 A significant positive linear correlation was found between BD and both α T and α R at a confidence level of 0.001 for individual and combined sites, with correlation coefficients of 0.72 and 0.82, respectively Additionally, a negative correlation was observed between the ratio α T /α R and BD (r = -0.53, P < 0.001), indicating an inverse relationship compared to α T and α R.
Wood density is widely acknowledged to reflect shrinkage property Istikowati et al (2014) found strong positive correlations of BD with αT (r = 0.83), and αR (r = 0.83) in Artocarpus elasticus,
Neolitse latifolia and Alphitonia excelsa have been studied by Pliura et al (2005), Wu et al (2006), Kord et al (2010), and Sadegh et al (2012), who found significant positive correlations between wood density (BD) and both α T and α R in various species such as Poplar hybrid crosses, Eucalypt species, Populus euramericana, and Tamarix aphylia These findings indicate that selecting for high wood density in M azedarach planted in northern Vietnam may result in increased wood transverse shrinkage.
Table 4.6 Relationship between transverse shrinkage and basic density (BD) for each site and combined sites of Melia azedarach
180 12.63 1.56 0.72 *** 13.31 - 1.41 0.82 *** - 2.43 2.69 - 0.53 *** n number of wood specimen α T tangential shrinkage, α R radial shrinkage, α T /α R tangential/radial shrinkage ratio r correlation coefficient; *** P < 0.001
Fig 4.3 Relationships between transverse shrinkage (αT, αR, and αT/αR) and basic density
(BD) for combined sites of Melia azedarach (Triple asterisk: P < 0.001) y = 12.63x + 1.56 r = 0.72 ***
The results of linear regression analysis for the transverse shrinkage (α T , α R , and α T /α R ) and
The analysis of V L and DMOElog in green condition, as shown in Table 4.7 and Fig 4.4, reveals a positive correlation between αT and αR with V L, with respective r values of 0.47 and 0.45 This suggests that acoustic wave measurements in green condition can serve as an effective nondestructive method for predicting the transverse shrinkage of M azedarach cultivated in northern Vietnam Previous studies by Dundar et al (2013, 2016) have also indicated that ultrasonic velocity is a strong predictor of transverse shrinkage, demonstrating significant correlations across both softwood (Picea sitchensis and Tsuga heterophylla) and hardwood species (Quercus petrea).
Lieblein and Castanea sativa Mill.), respectively
The correlation coefficients between DMOElog and transverse shrinkage were stronger than those between V L and transverse shrinkage, with values of 0.62 for αT and 0.59 for αR When combining acoustic wave velocity (V L) and green density (ρ) to predict shrinkage, the coefficients of determination significantly increased, with V L explaining 21.8% for αT and 19.9% for αR alone, which rose to 39.1% for αT and 34.3% for αR when both parameters were utilized This indicates that using both V L and ρ enhances the prediction of transverse shrinkage through DMOElog calculations in green conditions Additionally, αT/αR showed a negative correlation with both V L and DMOElog, though not significantly Previous studies have confirmed the significant relationship between DMOElog in green conditions and transverse shrinkage, suggesting that measuring the modulus of elasticity in Cryptomeria japonica could help sort lumber with high transverse shrinkage Moreover, it has been noted that the prediction of transverse shrinkage improves when both ultrasonic velocity and specific gravity are considered for species like Quercus petrea and Castanea sativa.
Table 4.7 The coefficients of correlation (r) and coefficients of determination
(R 2 ) between transverse shrinkage (α T , α R , and α T /α R ) and acoustic wave velocity (V L), dynamic modulus of elasticity of log (DMOElog) for the combined sites
Fig 4.4 Relationships between transverse shrinkage (α T , α R , and α T /α R ) and acoustic wave velocity (V L); transverse shrinkage and dynamic modulus of elasticity of log (DMOElog) for combined sites of
Melia azedarach exhibits relationships at 10%, 50%, and 90% of the radial position from the pith, represented by long dash dot, round dot, and long dash lines, respectively The thick solid lines indicate the relationship for combined samples taken from three different positions, along with their corresponding coefficients of determination (R²).
4.4.4 Grade yield of shrinkage properties
The grade yield analysis for α T and α R, based on the FFPRI grading standards for physical properties of timbers from Southeast Asia and the Pacific regions, reveals that site 1 recorded the highest yield for grade II at 68%, with grade I and III yielding 28% and 4%, respectively Similarly, site 2 showed a predominant yield for grade II at 78%, followed by grade III.
The study found that M azedarach wood planted in northern Vietnam predominantly falls into grade II for tangential shrinkage and grade III for radial shrinkage, based on Southeast Asian grading standards Notably, there was no grade yield of αT in grades IV and V at both sites, while the highest frequency of αR specimens was observed in grade III, with frequencies of 62% and 59% for site 1 and site 2, respectively These findings are crucial for assessing the wood quality of this species and will aid wood processors in the drying and furniture industries, promoting sustainable utilization of M azedarach trees in the region.
The allocation of specimen grades based on tangential shrinkage (αT) and radial shrinkage (αR) for both sites is illustrated in Fig 4.5, adhering to the grading standards for the physical properties of timbers from Southeast Asia and Pacific regions as established by FFPRI.
Conclusions
This study found that radial position significantly affects shrinkage variations in M azedarach, with αT and αR increasing from pith to bark The αT/αR ratio decreased from 10% to 50% of the radial length before stabilizing outward Transverse shrinkage variation with height was minimal and not statistically significant A strong correlation between bulk density (BD) and transverse shrinkage indicates that BD is a reliable predictor of dimensional stability Both αT and αR positively correlated with longitudinal velocity (V L) and dynamic modulus of elasticity (DMOElog), with optimal shrinkage predictions achieved when combining V L and density (ρ) in DMOElog calculations Acoustic wave measurements in green conditions show promise for predicting transverse shrinkage in M azedarach in northern Vietnam Consequently, this research supports the use of stress wave methods for sorting lumbers with high drying shrinkage and classifies M azedarach wood into grade II for tangential and grade III for radial shrinkage according to Southeast Asian and Pacific timber grading standards.