Abstract: Accurately obtaining the age of regenerated individuals is the precondition for understanding regeneration status, quantifying regeneration age structure, and dividing regeneration stages, which is important for foresters to formulate reasonable forest management plan. However, two commonly used methods for age estimation of regenerated individuals have some deficiencies. Counting the number of rings (N_r) is destructive, while counting the number of whorls (N_w) lacks accuracy for many tree species including Korean pine (Pinus koraiensis). Further, the methods for growth stage division have not been uniformed. To accurately, efficiently, and non-destructively estimate the age of natural regeneration individuals of Korean pine, and divide growth stages of its regeneration layer reasonably, regeneration census including the root collar diameter and height of Korean pine (a total of 6831 individuals) was conducted in the primary mixed broadleaved-Korean pine forest in Lesser Khingan MountainsChangbai Mountains areas. Their ages were preliminarily estimated by traditional methods (counting the number of bud scars or whorls). Meanwhile, 153 regenerated individuals of Korean pine were destructively sampled by cutting base disk and counting N_r of the bottom section. Six calibration models between N_w and N_r were established. Method for growth stage division was proposed based on the biological characteristics of Korean pine and literature analysis (from 53 literatures). Results showed that directly using N_w as the age of regeneration individuals would underestimate age, while the calibrated N_w by the regression model (N_r=1.199N_w+2.962) was much closer to real age. According to the real age, height, and diameter at breast height (DBH) of regeneration individuals, the regeneration layer of Korean pine was divided into four stages, which were young seedlings (age ≤3 a), old seedlings (age >3 a and height <30 cm), small saplings (30 cm ≤ height <150 cm), and tall saplings (height≥150 cm and DBH <5 cm).

Key words: mixed broadleaved-Korean pine forest, regeneration layer, young seedling, old seedling, small sapling, tall sapling.