Dynamic base-age invariant site index models based on generalized algebraic diference approach for mixed Scots pine (Pinus sylvestris L.) and Oriental beech (Fagus orientalis Lipsky) stands

Abstract

Data from stem analysis of 397 dominant trees (198 Scots pine and 199 Oriental beech) were used to evaluate dynamicbase-age invariant site index models derived from Bertalanfy Richards, Hossfeld, and Lundqvist Korf functions with the generalizedalgebraic diference approach (GADA) for mixed Scots pine (Pinus sylvestris L. ) and Oriental beech (Fagus orientalis Lipsky) stands.Tese functions were compared with respect to residuals of these models; specifcally, the evaluation criteria were bias (E), root meansquare error (RMSE), absolute mean error (AME), adjusted coefcient of determination (R2adj), and Akaike information criterion.Te best results were obtained with generalized algebraic diference equations derived from the base models of Bertalanfy Richardsfor Oriental beech and Hossfeld for Scots pine. Tese selected models accounted for 95% 96% of the total variance in height agerelationships in dominant trees with bias of 0.049841 and 0.00171, RMSE of 1.55624 and 1.353736, AME of 0.940128 and 0.884034,and AIC of 723.55 and 1250.78 for Scots pine and Oriental beech, respectively. Tese dynamic base-age invariant site index models forthe 2 tree species presented more efective and accurate polymorphic site index curves with multiple asymptotes than earlier site indexmodels for Oriental beech and Scots pine. Te important diferences of height growth trend between developed base-age invariant siteindex models in this study and earlier site curves were determined by graphical comparisons for site index predictions. Terefore, thenew dynamic base-age invariant site index models developed based on GADA methodology can be recommended for dominant heightprediction and forest site quality evaluations in the mixed stands of these 2 species.