Wood density is an important physical property that can be easily measured and is closely related to many other wood properties. Furthermore, wood density is a good indicator of the usability and applicability of wood in the wood processing, construction and energy industries. Because it is strongly dependent on moisture content and porosity, there are various definitions of wood density in the literature, among which the density measured on the basis of dry matter and volume is the most commonly used. The aim of this paper is to present different methods for wood density determination and the importance of collecting such data for the development of the forest-based bioeconomy. In practice, there are several direct and indirect methods of density measurement; in addition to the most basic volumetric approach, the density of wood can be measured by penetrometer, resistograph, high frequency densitometry, X-rays, near infrared spectroscopy and microwaves. Wood will continue to grow in importance, as it is one of the key raw materials for the transition to a sustainable bioeconomy. The accurate and timely determination of wood density allows for the appropriate distribution and direction of flows of this raw material between individual conventional and new sectors (areas of use) and thus its more efficient and sustainable use.
The research study examined the effect of tree properties (crown social class, diameter at breast height (DBH), and tree height) on bark thickness (BT) and sapwood moisture content (SMC) in Norway spruce (Picea abies (L.) H. Karst.). Both examined variables were shown to be positively affected by DBH and tree height. The relationship between DBH and SMC varied among crown social classes, while the relationship between DBH and BT was relatively constant across crown social classes. Crown social class had a relatively small effect on BT and SMC, having a more pronounced effect on SMC than on BT. The relationship between tree height and BT did not vary across crown social classes, while the relationship between SMC and tree height was found to change slightly across crown social classes. Measurements of BT and SMC in the field are affordable, fast, and easy to use. Both variables could potentially be used to improve predictions of bark beetle attacks, as they reflect the physiological state of an individual tree.