Comparative studies of the macro- and microstructures of stump-root wood and stemwood

Abstract It is found that the existing problem of wood resources can be partially solved by attracting additional reserves, in particular, stump-root wood (SRW). In order to apply SRW in woodworking and to fill the scientific base with indicators of the macro- and microstructures of the stump-root systems of individual species, studies were carried out on the main characteristics that are decisive for using composite materials in the industrial production. Based on the study results, it was found that there are differences in the internal structure between SRW and stemwood (SW). It was found that in all species, the width of annual rings in the SRW was greater than that in the SW, in particular, in pine (Pinus sylvestris L.) – by 84.62%; in spruce (Picea abies Karst.) – by 73.68%; in fir (Abies alba) – by 93.75%; in aspen (Populus tremula L.) – by 35.71% and in birch (Betula pendula Roth.) – by 105.00%. It has been found that the content of late wood in the SRW of coniferous tree species is less than that in the SW, on average by 20–25%, and the number of annual rings per 1 cm in the SRW is 40–52% less than in the SW. Differences in the microscopic structure between SRW and SW are revealed, which consist in the difference in the size of tracheids in softwoods and of vessels and fibres of libriform in hardwoods. It was found that the transverse dimensions of early tracheids in the SRW were larger than in the SW, in particular, in the radial direction by 19–33% and in the tangential direction by no more than 15%, and the interval of dimensions in the radial direction was 1.5–2.5. It was found that the early tracheids of root wood had thinner walls (by 19–28%) and a larger internal cavity (by 15–25%) compared to similar elements of SW. It was revealed that the diameters of vessels and fibres of libriform in SRW are greater than in SW, in particular, in aspen (Populus tremula L.) – by 20.41% for vessels and by 12.95% for libriform fibres and in birch (Betula pendula Roth.) – by 20.69% for vessels and by 18.41% for libriform fibres. The practical significance of the studies lies in the fact that the obtained characteristics of the structural components of the SRW can be used to predict the strength indicators of composite materials.