Dimensional and qualitative structure of Quercus robur L. trunks in stands of coppice origin of the Left-Bank Forest-Steppe of Ukraine

One of the important tasks of the production activity of forestry enterprises in Ukraine is to determine the structure of operational forests. In the current conditions, part of the regulatory framework, which was developed in previous years to address these issues, has partially lost relevance because of new standards adopted. The experimental data are presented by the results of measuring 256 model oak trees on 28 temporary sample plots in premature, mature and overmature oak stands of coppice origin of the Left-Bank Forest-Steppe. To obtain data on the distribution of industrial timber by quality and size classes, we used the algorithm of conditional bucking of model trees and implemented it in the Field-Map Stem Analyst. The volume of the merchantable part of the trunks was calculated in the bark and without the bark sequentially, from the base to the top of the trunk, according to the requirements for the appropriate quality class. The classification of logs by quality was carried out both according to the standards in force until 2019 (hereinafter - GOST) and according to the new ones, which came into force in 2019 (DSTU). The closest linear correlation is established for absolute values of volumes of qualitative categories of timber with volume of a trunk in bark. This dependence takes into account the impact on the yield of timber qualitative categories (not only diameter but also other biometric indicators of the trunk). Data on the dimensional structure of industrial timber were summarized according to a method based on the study of patterns of distribution of the volume by dimensional classes in relative terms. According to the results of the analysis, a close dependence of the relative indicators of trunk timber dimensional structure by DBH was revealed. On the basis of the developed mathematical models the tables of distribution of volume of industrial timber of merchantable oak trunks on dimensional classes of average diameter without bark are made. According to the research results the average yield of industrial timber for oak stands of coppice origin of the Left-Bank Forest-Steppe is 58.6% (according to GOST), although the experimental data have trunks with a high share of industrial timber (up to 74.3%). The increase in the average value of the share of industrial timber from 58.6% (according to GOST) to 68.0% (according to DSTU) was recorded mainly in trunks with a minimum length of the industrial part. The yield of industrial timber for such trunks increased due to the transition of the volume of some assortments classified according to GOST to technological fuelwood, to quality category D of industrial round timber according to the new DSTU. To verify the developed tables, the data on final felling of 2019–2020 in SE “Konotop Forestry” and SE “Krasnopillia Forestry” were used. The comparison shows that the nature of the distribution by dimensional classes is similar. According to the tables, as a rule, the share of round timber of larger diameter is slightly higher, but the difference is insignificant. The developed distribution tables make it possible to predict the yield of industrial timber for oak stands of coppice origin of the Left-Bank Forest-Steppe with sufficient accuracy according to the new European standards and to divide it into dimensional classes