The shape of the trunk of Scots pine in the stands of the Ukrainian Polissia

Due to the transition of Ukraine in 2019 new regulatory documents on standardisation regarding classification round timber by quality classes, it became necessary develop standards for evaluating volumes accordance with requirements. The purpose study was a mathematical model forming stem Scots pine trees two groups diameters. is based use empirical material collected different years researchers Department forest taxation and management National University Life Environmental Sciences Ukraine, which 583 trees. Kozak as basic modelling pine. A mixed effect calibrated characterise variability tree shape Parameters role random effects were selected their coefficients variation using bootstrap process. Data grouped into diameters analysing residues models Akaike information criterion (AIC). By dividing data array thickness degrees developing creator each separately, decrease indicator (AIC) achieved level AIC=7433.02 group (8-28 cm) AIC=13154.67 (32-76 cm), increased accuracy developed models. Enabling parameters A. equations allowed more accurately describing obtained give clear fairly accurate prediction determination along entire length. can serve basis improving traction estimating volume process forestry production predicting yield roundwood classes