Abstract: Aims Intra-annual radial growth monitoring using the micro-coring method provides high-resolution and dynamic tree growth information, which is essential for understanding the trees’ responses to climate change. Methods In this study, we utilized the micro-coring method to monitor the seasonal growth dynamics of Pinus koraiensis and Ulmus japonica in the mixed broadleaf-Korean pine forest of Changbai Mountain. Important findings Our comparative analysis revealed the following: (1) The cell enlargement onset for U. japonica (day of the year (DOY) 116.0 ± 4.7) occurred earlier than for P. koraiensis (DOY 125 ± 2.64), with both species showing a similar trend of initial increase followed by a decrease in cell enlargement length. (2) The onset of the growth rate peak for P. koraiensis occurred earlier than for U. japonica, but the growth duration of U. japonica was longer than that of P. koraiensis. The average xylem growth rate of P. koraiensis was 3.4 μm·d–1, with a maximum rate of 9.4 μm·d–1, whereas for U. japonica, the respective rates were 11 and 23 μm·d–1. (3) Both species exhibited highly consistent response trends to environmental factors, although the response intensity of U. japonica to climatic factors was lower than that of P. koraiensis. The radial growth lengths of both species showed significant positive correlations with mean temperature, maximum temperature, minimum temperature, relative humidity, and soil temperature, and significant negative correlations with photosynthetically active radiation and vapor pressure deficit. No significant correlations were observed with soil moisture content and precipitation. The temperature is consistently the primary climatic factor influencing the radial growth of P. koraiensis and U. japonica during the year, with soil temperature being the most critical climatic factor.

Key words: radial growth, Pinus koraiensis, Ulmus japonica, climatic response, xylem