Abstract <p>The relevance of the study is determined by the need to improve the accuracy of assessing the quality of Russia’s forest resource potential and the efficiency of its utilization, which can be achieved only through an in-depth study of the structure of tree coenopopulations with respect to economically valuable traits, one of which is the basic wood density. The goal is to assess the patterns of individual and group variability in the basic sapwood density of Scotch pine trees in forest stands of different ages, origins, density, and growing conditions located in the Mari El Republic, which will make it possible to select and subsequently reproduce the most economically promising individuals. The studies are conducted on 13 sample plots in pure, even-aged forest stands. To estimate the value of the basic density of sapwood, which is carried out by stereometric and hydrostatic methods, we used 50 mm long cores, manually extracted with a Pressler borer from 1072 trees at a height of 1.3 m from the base of the trunk. Standard methods of mathematical statistics are used in processing the empirical material. It is found that the value of the estimated parameter varies in trees from 291 to 660 kg m^–3, overlapping with the limits established by domestic researchers. It is practically independent of growing conditions, density and origin of tree stands, rank position of individuals in coenopopulations, and width of the annual wood growth and the proportion of the late summer layer in it, and it is mainly linked to the age of the trees (<i>R</i>² = 0.9). It has been proven that the ecological requirements for environmental conditions are different for trees with different wood density, which is reflected in the nature of their radial annual growth dynamics. A scale has been developed for assessing the economic value of trees in coenopopulations of different ages based on the density of their sapwood. Natural selection of trees based on wood density in coenopopulations that reaches its maximum at the age of 100–110 years does not occur, so targeted selection based on this parameter will not subsequently affect the productivity of plantations.</p>