Abstract Timber quality modeling is essential for value-oriented forest management since the traditional, volume-only yield models often ignore internal defects (notably knots) and overestimate usable wood. In this study, we developed an integrated framework to quantify knot-free and knotty core volumes in Korean pine (Pinus koraiensis) plantations in Northeast China. The framework couples a re-parameterized Kozak (For Chron 80: 507-515, 2004) taper equation with a bark factor model to convert outside- to inside-bark diameters and two height-dependent functions to describe sound- and loose-knot vertical distribution. Nonlinear mixed-effects models were employed with climatic, stand, competition, and tree predictors (e. g. , DBH DBH, CR CR, Hegyi Hegyi index, SI SI, CMD CMD) to partition each stem into knot-free and knotty core sections (sound- and loose-knot) based on the heights to crown base (HCB HCB) and lowest dead branch (HDB HDB), ensuring consistency with observed stem–crown structure. Model evaluation showed high accuracy for all three curves (RMSE RMSE 0. 70–1. 04 cm; MAE MAE 0. 72–0. 98 cm), supporting reliable prediction of stem profiles and internal knot distributions. We further identified the drivers of section yields at tree and stand scales: at the tree scale, climate, stand, competition, and tree attributes contributed comparably to knot-free yield; for the loose-knot (lowest-quality) section, climate (51%) and tree factors (37%) dominated. At the stand scale, knot-free proportion was accurately predicted using only basal area (BAS BAS), dominant height (H₃₎₌ H dom), and mean annual temperature (MAT MAT), with an RMSE RMSE of 0. 03. The framework delivers fast, reliable estimates of timber quantity and quality under varying stand and climate conditions, supporting higher-value management of Korean pine.
Zheng et al. (Sun,) studied this question.