Cambial phenology and wood formation of Korean pine in response to climate change in Changbai Mountain, Northeast China

Korean pine (Pines koraiensis Sieb. et Zucc.) is a highly ecological and economic species due to its rarity, varied usage and favorable effect on the environment. To better understand the adaptation strategies of intra-annual radial growth of Korean pine to local environmental regimes, we continuously monitored the cambial activity and wood formation in northeastern China weekly from April to October across the two consecutive years of 2020 and 2021 using Trephor. The results indicated that the warmer spring in 2021 resulted in an earlier onset of cambial activity compared to that of 2020 (DOY 118 vs DOY129), but the cessation of wood formation was similar (DOY 250 vs DOY 248). In both years, similar thresholds were estimated using logistic regression, xylem growth was active when the daily mean air temperature was 11.5 degrees C. Sensitivity analysis revealed that 86% of xylem growth was attributed to the growth rate and 14% to its duration. The total number of xylem cells was positively correlated with air temperature, soil temperature and relative humidity, and negatively correlated with vapor pressure deficit and soil water content in both years. Temperature is the main factor limiting the growth of Korean pine. Our findings complement a description of cambial phenology and wood formation dy-namics of Korean pine at cellular levels and provide a better understanding of the climate-growth relationship, which will enable the improvement of climate-growth models used to predict climate change.