Relevant phenotypic descriptors of the resonance Norway spruce standing trees for the acoustical quality of wood for musical instruments

Identifying high-grade valuable wood resources by the visible individual traits of trees is a challenge for foresters and a requirement for sustainable resource management. The aim of this study was to identify the most relevant phenotypic descriptors of the acoustic quality of Norway spruce standing timber. Two highly valuable Norway spruce (Picea abies) stands located in the Romanian Carpathians were selected for this purpose. A total of 27 tree, bole, bark, and crown variables and nine variables related to wood structure were statistically checked against the velocities of stress waves measured on standing trees at breast height, and the derived parameters: the radiation, the impedance, and the moduli of elasticity in L and R directions. Principal component analysis was used for exploratory data analysis as well as mixed linear models were involved in explaining these acoustics. There were consistent variations in the measured acoustics from tree to tree, according to the age and social class. Wood acoustical parameters measured in the R direction are better predicted by tree phenotype than the acoustical parameters measured in the L direction. Bark thickness and branch width were the best predictors, while tree ring features were less predictive. At a given age, trees with high velocity had thinner and reddisher bark, thinner branches, and a narrower crown. Trees with high velocity anisotropy had narrower branches and wider sapwood. Furthermore, the phenotypic traits used had a poor explanatory power of the radiation ratio. In conclusion, spruce standing trees from the studied area bring forward certain outside features that enable us the multitrait identification of highly valuable wood for string instruments.