Assessing corewood acoustic velocity and modulus of elasticity with two impact based instruments in 11-year-old trees from a clonal-spacing experiment of Pinus radiata D. Don

Outermost wood and whole stem modulus of elasticity (E) was measured acoustically from trees within an 11-year-old Pinus radiata experiment, which included six clones grown at two contrasting stand densities (833 and 2500 stems ha−1). This study examines the effect of bark removal on whole stem E as measured by resonance (Eres) in the lower log (0–2 m) and how branch removal influences Eres in the upper log (2 m to 70% tree height). An additional objective was to develop relationships between E of the outer part of the wood made on standing trees, using time of flight (Etof), and whole stem E measured using resonance (Eres).Both branch and bark removal significantly influenced Eres, increasing values by an average of 8.3% and 5.4%, respectively. The influence of bark on Eres was relatively constant across the E range examined, ranging from 8.0% at low values of Eres (2.6 GPa) to 8.6% at high values of Eres (5.5 GPa), with bark. In contrast, increases in Eres induced by branch removal ranged from 24% at low values of Eres (3.4 GPa) to 0% at high values of Eres (6.5 GPa).There were strong positive linear relationships between Etof and Eres, both when bark was present (r2 = 0.94) and removed (r2 = 0.92), from the whole stem. Values of Eres measured with and without bark, were respectively on average 38% and 33%, lower than Etof (with bark). Although stand density and tree diameter did not significantly influence these equations the relationship between Etof and Eres logs with bark attached was significantly influenced by clone (P < 0.05). The percentage of stems correctly reallocated by time of flight back to whole log modulus of elasticity classes (high, medium and low), was significant (P < 0.0001) and high, averaging 80% across the three classes. These results highlight the utility of Etof measurements on standing trees in predicting whole stem Eres, and also suggest that it is important to account for the effect of bark and branches when measuring whole stem E using acoustic methods.