The optimal wood utilization requires fully information on wood properties. Forest resource managers and foresters, who wish to maximize forest values, need to understand not only the principles of tree growth, but also some of the macroscopic and microscopic features that determine wood quality. Wood quality characteristics can be inherent to particular species, but are also influenced by tree growing conditions. This connection to tree growth gives forest managers both an opportunity and an obligation to manage judiciously for value on every site be it only through choice of rotation length, species selection, and initial spacing and stocking control on some sites, to fertilization, thinning, and pruning on others (Jozsa and Middleton 1994). A comprehensive knowledge of the characteristics of any material is essential to its best utilization. This is especially true for wood because of its cellular nature and its complex cell wall structure, which makes its high variation (Kamala 2012). It is well known that wood property is closely to its structure. Hence, wood quality assessment involves the fulfillment consideration of wood structure as well as physical and mechanical properties.
M. azedarach, a deciduous tree belonging to the family of Meliaceae, is an important fast-growing plantation species in Vietnam. Together with other fast fast-growing species, M. azedarach trees are mainly used as pulping materials due to their high productivity. The decrease in the available wood resources and the increase in wood processing costs have led to a significant interest in wood from plantation. Using wood of M. azedarach as a timber material to increasing their value is expected in Vietnam. However, there is little information regarding to assess its variations within tree including radial and axial variations of M. azedarach in Vietnam. Therefore, this study was carried out to
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for determining management strategies appropriate for sustainable wood utilization of M. azedarach trees growing in northern Vietnam.
In Chapter 3, the variations in intrinsic wood properties were studied. The results indicate that there were significant within-tree variations in wood SG and GRW. Wood SG of M. azedarach increased from pith to bark and decreased from the stump to intermediate stem before slight increasing to the top. Mean GRW near the pith was large and decreased rapidly with cambial up to 5 and 6 years before being less or more stable to the bark. In vertical direction, mean GRW decreased with height level. 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 difference was observed on mean GRW between the sites.
The radial variation in MFA and FL was also studied in Chapter 3. The results indicate that there were statistically significant variations in MFA and FL from pith to bark. FL increased from pith to bark while MFA followed a declining from pith toward the periphery. The length of fibers in wood is essential for the optimization of timber utilization, quality, and value of final products (Shmulsky and Jones 2011). Mature wood with long FL, high SG, and low MFA is preferred for structural purposes (Shmulsky and Jones 2011, Uetimane and Ali 2011, Hein and Lima 2012). In the present study, FL increased from pith to bark and wood beyond ring number 7 from the pith consists of comparatively long fibers, high SG, and low MFA. Therefore, wood from ring number 7 to the bark could be used for structural purposes. This should be taken into account when processing logs of M.
azedarach trees in northern Vietnam.
Dimensional stability and warp are major concerns in wood processing (mainly drying) and utilization. This problem is believed to be caused by gradients of wood anisotropic shrinkage both in radial and tangential directions (Wang et al. 2008). Shrinkage is a physical property of wood that significantly affects its usability in products. Therefore, in Chapter 4 within-tree variations in radial and tangential shrinkages were assessed. Radial position had a significant effect on shrinkage and contributed the highest to the total variation in radial and tangential shrinkages. While αT and αR increased from pith to bark, αT/αR decresead from pith to outwards. The radial variation pattern of transverse shrinkage are maintained at the different height levels of the tree and similar between two sites. The most important factor affecting shrinkage is wood density, because wood shrinks by an amount that is proportional to the moisture lost from the cell wall (Yamashita et al. 2009b). There were strong positive relationships between transverse shrinkage and basic density. This implies that the selection for high wood density may lead to increase wood transverse shrinkage. The differential of radial-tangential shrinkage is one of the primary factors causing shape distortion during seasoning of lumber and during ultimate use (Dundar et al. 2016). In this study, in radial direction, the αT/αR
decreased significantly from 10 to 50% of the radial length from pith before approaching a constant value toward the outside. The difference in radial and tangential shrinkage is attributed to differences in wood density of earlywood and latewood. The shrinkage of latewood cells with thick cell wall is greater than that of earlywood with thin cell wall. 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, whereas tangential shrinkage is largely controlled by the changes in latewood (Walker et al. 1993).
A number of studies suggest that nondestructive techniques may be used to assess the
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2009, Dundar et al. 2016). If the lumber was sorted by shrinkage properties and appropriate drying schedules were applied to each group, it is expected that the drying yield would increase and the cost and energy consumption would decrease. In this study, we found that stress wave velocity was a significant predictor of transverse shrinkage and therefore has a good potential to be used as a field method to evaluate the dimensional stability of wood. The better prediction of the transverse shrinkage of M. azedarach can be achieved when both stress wave velocity and green wood density of log are used as predicting parameters through calculation of dynamic modulus of elasticity of log in green condition. This result suggests that it might be possible to sort lumber with large transverse shrinkage by stress wave method for M. azedarach planted in northern Vietnam.
Wood quality assessment involves the consideration of wood density and mechanical properties (Anoop et al. 2014). 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 (Walker et al.
1993). Modulus of elasticity (MOE) and modulus of rupture (MOR) are important properties for the use of wood as structural material. MOE is an indication of stiffness of board or structural member, while MOR is an indication of strength (Johnson and Gartner 2006, Missanjo 2017). Therefore, the determination of mechanical properties (MOR and MOE) together with WD is important to understand their relationships. Therefore, in Chapter 5 WD and mechanical properties of M.
azedarach were studied. Within tree, the mechanical variation with height was very small and without statistical significant. In radial direction, MOR and MOE increased from pith to bark and radial position is the most important and highly significant source of variation in mechanical properties. WD had a strong positive linear relationship with mechanical properties. This suggests that improving WD would have a positive impact on mechanical properties of M. azedarach.
Nondestructive techniques are widely used in several fields of technology to estimate the properties of materials. Stress-wave-based nondestructive evaluation techniques have been investigated extensively during the past few decades and have shown promise for predicting the mechanical properties of wood materials. Several wood and wood-based materials, including small, clear wood specimens, lumber, veneer, and wood-based composites, have been investigated (Kaiserlik and Pellerin 1977, Ross and Pellerin 1988, Wang et al. 2001). Considerable savings in material and processing costs could be realized if nondestructive wood-sorting technology, based on anticipated final product quality, can be achieved. In this study, we found that MOR had a strong linear relationship with Ed. This indicates that Ed is a good indicator to predicting the strength of wood if the density of measured element is known. In addition, the correlation coefficient between Ed measured by acoustic method and MOE measured by destructive test was very high. This result indicates that the stress wave method used in this study provides relatively accurate information for determining the stiffness of M. azedarach.
Structural grading is the process by which timber is sorted into groups – or stress grades – with ideally, similar structural properties in each group. The grading of timber should be viewed as part of a marketing strategy, designed to ensure that the timber buyers obtain the quality of timber appropriate for their needs and timber sellers receive an optimal price for their products (Walker et al. 1993). In Vietnam, timber is mostly sold and used without proper grading. Thus, it is basically sold and used on the basic of dimension size. Without grading, timber is sold at low prices. This mean that the forestry and wood industry as well as the country is on loss as a business entity. Grading would enable maximization of the timber value (Missanjo 2017). In Chapter 5 grade yield for the specimens were checked using the grading standard of mechanical properties of timbers from Southeast Asia and
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be allocated in grade III. This research has established the first step in assigning allowable mechanical properties for M. azedarach grown in Vietnam. Besides, wood of M. azedarach planted in northern Vietnam can be allocated into grade II for tangential shrinkage property and grade III for radial shrinkage property using grading standard of physical properties of timbers from Southeast Asia and Pacific regions. These results should provide useful information to assess the wood quality of this species and for wood processors in wood drying and furniture industry as well as for the sustainable wood utilization of the M. azedarach trees planted in northern Vietnam.
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, sunlight, 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, and it directly controls the internal processes relevant to the composition of wood, and indirectly, it controls the form and growth of tree. Ecological conditions of site directly or indirectly affect on the availability, development and fertility, body form and height of tree types, herbal type variety, stand closure, and availability rates of plants (Usta et al. 2014).
Results obtained from this study show that M. azedarach planted in site 2 had higher SG, longer FL, lower MFA, higher transverse shrinkage (αT and αR) and higher mechanical properties (MOR, MOE, and Ed). The significant differences in all selected wood properties in this study excluded in GRW between site 1 and site 2 may be contributed by the differences in altitude, mean annual rainfall, and soil types between two sites (Table 3.1). However, further experiments will be needed to determine genetic effect on variation in wood properties for M. azedarach planted in northern Vietnam.