Developing a sampling strategy for measuring acoustic velocity in standing Pinus radiata using the treetap time of flight tool

Acoustic velocity, measured using time of Right tools, provides a non-destructive measure of wood stiffness in standing trees. In order to assess how best to assess a stand of trees to a given level of precision, acoustic velocity was measured across three sites in New South Wales, Australia. All sites had similar climatic conditions and had had the same silviculture but different establishment dates. Analysis of variance and regression analysis were used to determine the components of variation and relationships between acoustic velocity, diameter at breast height, and age. The variation within a stand was greatest between trees, followed by that between sides within trees, between plots, and within each side of a tree. There was a significant positive relationship between acoustic velocity squared and age, but little relationship between acoustic velocity squared and diameter at breast height. An optimal sampling strategy was developed that involved sampling four plots per stand, each plot containing 12 trees, and acoustic velocity measurements being taken four times on each of the two sides of the trees being sampled. With this strategy the mean acoustic velocity squared of a stand can be estimated to within at least ±10% of the mean.