Wood and Wood Density

The density of wood is determined by the relative proportions of its components: vesselsVessels, fibers, and parenchyma cellsParenchyma cells. Vessels are responsible for water transport in trees and are found in hardwoods (angiosperms), while tracheidsTracheids perform the same function in softwoods (gymnosperms). The thickness of cell walls and the presence of extractives, such as lignin and hemicelluloses, also influence wood density. Wood density (WD) and specific gravity (SGSG) are both measures of the density of wood, but they are not the same. WD is a measure of the mass of a wood sample per unit volume, while SG is a measure of the density of wood relative to the density of water. WD is always expressed with a unit, such as g cm−3 or kg m−3, while SG is a ratio and therefore dimensionless. Three main ways to calculate SG are described in this chapter. Destructive methods involve collecting wood samples from either living or dead trees and then determining their moisture content by drying in an oven. Non-destructive methods do not require collecting samples and the WD is determined independent of the sample's moisture content. Destructive methods include increment corerIncrement corer method and disk sampling method. Non-destructive methods include X-ray densitometry, Ultrasonic methods, Near infrared spectroscopy (NIRS), etc. The choice of method depends on the specific application. Destructive methods are more accurate, but they also require more time and effort. Non-destructive methods are less accurate, but they are more convenient and can be used on living trees. The tree species with the highest WD is Olea capensis L, with a WD of 1.49 g/cm3. The tree species with the lowest WD is Ochroma pyramidale with a WD of 0.16 g/cm3. The WD of all other tree species ranges between these two values.