This study analyses the possibility of assessing standing-tree wood density by microdrilling during tending forestry work carried out on Norway spruce stands. The research material comes from 4 experimental plots and consists of 270 trees (78 trees = control variant, 85 trees = moderate variant, and 107 trees = strong variant). The research objectives were to: (1) highlight wood density particularities, (2) identify wood resistance to microdrilling particularities, and (3) assess standing-tree wood density by microdrilling. For the control variant, average density recorded values of 0.357 ± 0.021 and 0.386 ± 0.027 g·cm⁻³; in the moderate variant, values were between 0.359 ± 0.029 and 0.393 ± 0.027 g·cm⁻³; and the strong variant was characterized by the limits of 0.364 ± 0.020 and 0.397 ± 0.027 g·cm⁻³. Average microdrilling resistance values were between 16.6 ± 2.6 and 22.5 ± 3.0% for the control variant; the moderate variant was characterized by the limits of 18.3 ± 3.1 and 23.4 ± 3.3%; and the strong variant recorded value of 19.7 ± 2.6 and 20.5 ± 2.6 (1.5)%. The linear regression results showed that microdrilling resistance increased as wood density increased. Additionally, generalized linear models showed that, when using covariates of microdrill resistance and tree diameter at breast height, there was a significant influence on the dependent variable, wood density, for all considered work variants. These results suggest that it is possible to consistently estimate both quality and resistance in Norway spruce standing trees using microdrilling. Our findings suggest that wood density and microdrilling resistance are dependent on biometric and qualitative characteristics, as well as the amount of tending forestry work conducted on Norway spruce stands.

This study analyses the influence of a planting scheme on physical properties of Norway spruce wood. The research material consisted of 326 Norway spruce trees (Picea abies (L.) H. Karst) selected from an experimental plot with four planting variants (2500, 3330, 5000, and 7510 trees·ha⁻¹). The research aspects were: (1) wood density (measured by volumetric method and using microdrilling resistance as proxy), (2) microdrilling resistance, and (3) sound speed. There was a decrease in wood density values (from 0.3376 to 0.3367 g·cm⁻³) and in microdrilling resistance values (from 15.136% to 14.292%) as the number of trees·ha⁻¹ used for plantation increased from 2500 to 5000. The planting variant with 7510 trees·ha⁻¹ had the largest value (0.3445 g·cm⁻³ for wood density and 15.531% for microdrilling resistance). Sound speed decreased from 1032.8 to 989.8 m·s⁻¹ as the number of trees·ha⁻¹ increased from 2500 to 7510. These results show a relationship between DBH values and studied physical properties. This relationship is more evident for variants with low planting density (e.g., 2500, 3330 trees·ha⁻¹) than that of dense planting variants (e.g., 7510 trees·ha⁻¹). The explanation may be that the growth of trees in dense plantings is slower; in less dense planting variants, the increase in wood is greater, and as a result, wood volumetric density dependence on the DBH value is greater.