Response of early and late wood growth of main coniferous species to multiple factors in spruce fir coniferous mixed forest

To analyze the impact and contribution rate differences of factors such as climate, site conditions, stand competition, and stand structure on the radial growth of early and late wood and tree-ring width in coniferous species, aiming to understand the response patterns of tree radial growth to multiple factors. This will provide a scientific basis for the study of growth dynamics and refined management of coniferous mixed forests in the Changbai mountain region.

Based on tree-ring cores and remeasurement data of Picea jezoensis, Abies nephrolepis, and Pinus koraiensis from fixed plots in Jingouling forest farm, a logistic function was selected as the base model. Stepwise multiple regression and variance inflation factor (VIF) analysis were applied to screen significant variables. The retained variables were incorporated into the base model using re-parameterization, and simultaneous equations models for earlywood, latewood, and total radial growth of each species were developed via seemingly unrelated regression (SUR). Model validation was conducted using independent test datasets. Hierarchical partitioning analysis was employed to quantify the contribution rates of climatic, competition, site, and stand structural factors to radial growth.

The basal area increment (BAI) of all three species followed an asymptotic trend with increasing cambial age. The simultaneous equations models exhibited high predictive accuracy (coefficients of determination [R²] = 0.813-0.917). Key climatic drivers included temperature and moisture during the pre-growing season, July, and winter, which positively influenced radial growth. In contrast, species diversity indices and stand competition factors predominantly exerted negative effects. Site factors (elevation, slope aspect, and gradient) showed positive correlations with growth. The difference in contribution rate indicates that different tree species and wood types are subject to different types of main controlling factors.

This study clarifies the specific response patterns of earlywood and latewood radial growth to various factors in three tree species, which helps provide guidance for formulating more precise management strategies for the coniferous mixed forests in Changbai Mountain.