The study aims to investigate the effects of climatic factors and interspecific competition on the radial growth of Pinus koraiensis, and to provide scientific support for predicting forest productivity and carbon sink potential under future climate change, as well as the conservation and sustainable management of regional forest resources.

Pinus koraiensis trees from two national nature reserves (Xiaobeihu and Xilinhe) in the mountainous eastern Heilongjiang Province were selected as research materials. Dendrochronological techniques were adopted to acquire radial growth data. Combined with meteorological datasets and neighborhood competition indices, correlation analysis and linear mixed-effects models (LMM) were applied to quantify the independent impacts of climate and competition on the radial growth of Pinus koraiensis. Variance decomposition was further performed to calculate their relative contributions, so as to explore the effects of climatic conditions and neighborhood competition on radial growth as well as corresponding regional disparities.

1) The radial growth of Pinus koraiensis in the Xiaobeihu study area showed significantly positive correlations with temperatures of the previous winter and current spring. Linear mixed-effects model (LMM) outputs indicated that the diameter at breast height (DBH) of competing trees achieved the optimal fitting performance with cumulative radial growth over the past 20 years; 2) Radial growth of Pinus koraiensis in the Xilinhe study area was primarily controlled by March temperature of the current year. LMM results revealed that DBH of neighboring competitive trees had the best fitting effect with cumulative growth over the recent 10 years; 3) The contribution proportions of climatic factors and inter-tree competition differed along the latitudinal gradient. With increasing latitude, the relative contribution rate of climate rose from 39% to 88%, while that of competition decreased from 61% to 11%.

This study indicates that the dominant factor regulating radial growth of Pinus koraiensis shifts from biotic competition to climatic limitation along mountainous eastern Heilongjiang. Thinning can alleviate competitive pressure in low-latitude forest stands, while high-latitude forests should be alert to growth stress induced by spring warming.