Ukrainian Journal of Forest and Wood Science

The experience in describing the shape of a tree trunk is generalized. The relevance of the study is due to the need to take into account the individual characteristics of the trunks in the accuracy of the forecast of diameters according to the mathematical model of the generatrix. Thus, the purpose of the research is to identify the dependence of the taper of the trunks on the ranks they occupy in the stands. Based on experimental data (Girs, 1981) collected in artificial stands of Polissia, the dependences of the change in the shape of silver birch trunks (Betula pendula Roth.) were analyzed. To analyze the taper, the trunks of model trees were divided into eight zones by relative heights. The taper of each zone was defined as the tangent of the inclination angle of the line connecting two consecutive points on the trunk. The dataset was checked for the presence of atypical trees, which were excluded from further research. Model trees were ranked according to the average diameters of the sample plots, natural degrees of thickness (Tyurin, 1938) and generalized series of the distribution of the number of trees in birch stands of Ukraine (Girs, 1981). Statistical and graphical analysis of the dynamics of the change of the tangent of the angle of inclination of the approximating line by zones and ranks has been performed. The difference in the nature of taper in the upper part of trunks of different ranks is revealed. Using the t-test, the hypothesis of differences in taper in groups of trunks with ranks ≤ 60 % and > 60 % at a relative height of 0.5h – 0.85h was confirmed at the 5 % level of significance. Thus, trunks of higher ranks turned out to have greater taper, in contrast to trees with a rank of ≤ 60 %, which are characterized by smaller taper. The established difference in shape can be explained by the height of the beginning and the length of the crown in trees of different ranks. The obtained results can be used to improve the accuracy of mathematical models of generatrixes by calibrating their parameters according to the respective ranks of the trunks.

tree trunk formation, zonal approximation, tree ranks, crown height, t-test