Determining the effectiveness of using acoustic velocity as an indirect measurement of branchiness in standing longleaf pine

Branches reduce stem quality, and the level of the effect is determined by the geometry, size, and number, of associated knots. Quantifying branchiness is difficult, as visual estimates are subjective, and mechanical measurements are impractical. Acoustic velocity (AV) is a relatively novel measurement capturing the speed stress travels through wood. AV is correlated with wood stiffness and is affected by internal characteristics like knots. This project tested AV as an indirect branchiness metric by measuring AV, height, diameter, and counting branches classified by diameter on 255 standing 8 year old longleaf pine (Pinus palustris). AV was highly correlated with height (r = 0.76, p < 0.0001) and slenderness (r = 0.52, p < 0.0001). AV was moderately correlated with large living branches (diameter > 2.54 cm) (r = -0.27, p < 0.0001), but not correlated with total branches. Height, slenderness, and the count of large living branches (diameter > 2.54 cm) were included in the selected model for AV. Inclusion of dead or small (diameter < 2.54 cm) branches reduced model power. The best model captured 11% of the variation in AV, of which branches explained 5%. We conclude that AV does not appropriately quantify individual tree branchiness, but may be suitable for comparing populations such as families or provenances.

Automated summary

Branches reduce stem quality, and the effect is determined by geometry, size, and number of knots. Quantifying branchiness is difficult. Acoustic velocity (AV) is correlated with wood stiffness and affected by knots. This study tested AV as a metric for branchiness by measuring AV, height, diameter, and counting branches on longleaf pine trees. AV was correlated with height and slenderness. AV was moderately correlated with large living branches, but not total branches. AV may be suitable for comparing populations, but not individual tree branchiness.