Scots Pine Trees' Sap Wood Density in Trans-Volga Forests of the Mari El Republic

The relevance of the study is due to the need to improve the accuracy of assessing the quality of the Russia's forests resource potential and the efficiency of its use. That can only be done via an in-depth study of the tree coenopopulations' structure regarding their economically valuable traits, one of which is the basic density of wood. The purpose of the study is to assess the patterns of individual and group variability in the basic sapwood density of Scots pine trees in forest stands of different ages, origins, density and growing conditions located in the Mari El Republic, which will allow to select and subsequently reproduce the most economically promising individuals. The studies were conducted on 13 sample plots in pure, even-aged forest stands. To estimate the value of the basic density of sapwood, which was 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 were used in processing the empirical material. Results. It was 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 virtually independent of growing conditions, density and origin of tree stands, rank position of individuals in coenopopulations, width of the annual wood growth and the proportion of the late summer layer in it, and is mainly linked to the age of the trees (R2 = 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, and thus targeted selection based on this parameter will not subsequently affect the productivity of plantations.