Stand-level incremental growth model incorporating thinning effects for Pinus densiflora, Pinus koraiensis, and Larix kaempferi plantations in Korea

초록

Stand incremental growth models are essential tools for predicting stand dynamics and supporting forest management decisions. In this study, empirical models were developed to predict stand-level increments, providing a quantitative framework for understanding growth processes in major coniferous species in Korea. Long-term monitoring data were obtained from permanent plots, with 2-5 repeated measurements per plot across 135, 141, and 135 plots of Korean red pine (Pinus densiflora), Korean white pine (Pinus koraiensis), and Japanese larch (Larix kaempferi), respectively. Three types of linear mixed-effects models were constructed according to the available variable levels and intended applications, in which the increments of mean DBH (cm year-1), mean height (m year-1), stand basal area (m2 ha-1 year-1), and stand volume (m3 ha-1 year-1) were set as dependent variables. Independent variables included stand age, site index (SI), relative density (RD), and initial stand size (DBH, height, basal area, and volume), while the thinning variable (THIN) was defined by combining thinning intensity (TING) based on basal area removal and time after last thinning in years (Talty) to quantify the thinning effect. As a result, DBH and basal area increments declined with increasing stand age, whereas height and volume increments were less age-dependent and more influenced by structural factors such as SI and RD. Including the thinning variable significantly improved model performance, and simulation results produced biologically consistent relationships among predictors, with growth tending to increase with thinning intensity under the same stand conditions. The developed models provide scientific basis for predicting stand growth and evaluating thinning regimes in major coniferous plantations in Korea.

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