Abstract: Abstract Aims Our purpose is to explore the radial variation patterns and their influencing factors under different tree species and different environmental conditions, and to lay a foundation for quantifying and evaluating forest carbon sinks and their carbon fixation processes. Methods We used dendrometers to continuously monitor the dynamic changes in trunk radials of Fraxinus mandshurica and Larix gmelinii for three years, and to analyze the intra-annual and inter-annual variability, as well as the effects of environmental factors on stem radial variation. Important findings Intra-annual stem radial variation in both Fraxinus mandshurica and Larix gmelinii conformed to the Gompertz model, but were not fully synchronized on seasonal scales, and the annual cumulative radial increment and annual mean daily rate of change in the fracture area of the two species were significantly different between species. During the three years from 2020 to 2022, the stem radial variation of Fraxinus mandshurica started earlier than that of Larix gmelinii, and the annual cumulative radial increment of Fraxinus mandshurica reached 25% (DOY₂₅) 3 to 17 days earlier than that of Larix gmelinii, and the peak growth season length (L_PGS) of Fraxinus mandshurica in 2021 was 28 days longer than that of Larix gmelinii, while the radial variation termination time of the two species was consistent. The daily rate of radial variation for both tree species showed a unimodal trend of increasing and then decreasing, reaching the peak in early summer (147-157 days). Important time nodes (DOY₂₅, DOY₅₀, DOY₇₅) and L_PGS of radial variation of the two tree species are affected by interannual environmental factors. The daily stem radial variation of the two tree species during the growing season showed different trends depending on weather conditions, with a sinusoidal function type of fluctuation on sunny days. Daily amplitudes of Fraxinus mandshurica and Larix gmelinii at the peak period of stem radial growth was significantly negatively correlated with volumetric soil water content (P < 0.001) and significantly positively correlated with photosynthetically active radiation (P < 0.05). The amount of daily stem radial variation was negatively correlated with VPD for both species during the peak period of stem radial growth. This shows that stem radial seasonal dynamics are influenced by the characteristics of tree species, while the daily variation pattern is influenced by environmental factors such as volumetric soil water content, light conditions, etc. Moisture conditions are an important factor influencing the radial growth of Fraxinus mandshurica and Larix gmelinii.

Key words: radial variation, Fraxinus mandshurica, Larix gmelinii, plantation