Effect of green density values on pinus radiata stiffness estimation using a stress-wave technique

Use of acoustic tools for assessing stiffness of green wood in standing trees relies on the assumption of a constant value for wood density. This study examined the variability in the green density of the outerwood (outer 5 rings) of 13-year-old Pinus radiata D.Don trees and determined the error introduced by using a constant value. Assuming a constant green density introduced a small (~3%) error in the calculated modulus of elasticity (i.e. density 'as measured' x acoustic velocity²). Acoustic velocity was the dominant term in the equation. Green density of the fresh core samples showed little variation (coefficient of variation = 2.8%) and was more strongly determined by the sample's moisture saturation than the amount of wood material (basic density). Modulus of elasticity was inversely related to diameter at 1.3 m (R² = 0.20). Basic density and fresh moisture content were inversely related (R² = 0.82). Basic density and fresh moisture content both influenced the acoustic velocity (R² ~ 0.07), but their effects were weak and opposite. The effect on the acoustic velocity of fresh moisture content at a level between 110% and 230% was less than found previously at lower fresh moisture contents.