Abstract: Long-term monitoring of forest communities is helpful for understanding the construction mechanism and regeneration dynamics of forest communities. Based on the data from three community surveys of an 8hm² dynamic monitoring plot in the spruce (Picea schrenkiana) forest in Tianshan Mountains (2009, 2014, and 2019), we analyzed species composition, importance value, mortality rate, recruitment rate, and diameter at breast height (DBH) structure. The results showed that the living individuals of woody plants with DBH ≥1 cm decreased from 11835 (8 species, 8 genera, and 6 families) in 2009 to 10301 (6 species, 6 genera, and 5 families) in 2019, indicating no significant change in species composition. The total basal area, average DBH, and tree height increased with time, by 4.55 m²·hm^-2, 2.35 cm, and 2.27 m, respectively. The annual mortality rate and annual recruitment rate of individuals with DBH >1 cm were 3.41% and 0.65%, respectively. There was an inverted Jshaped DBH structure, with largeabundance of medium and small diameter (DBH ≤20 cm) individuals, accounting for 70.59%-78.74% of the total, showing a downward trend year by year. Meanwhile, the proportion of dead individuals in the small diameter class (DBH ≤10 cm) was the highest, with the proportions of 16.90% and 15.26% every five years, respectively. The proportion of individuals with tree height >10 m was large and relatively stable, increasing from 48.94% to 55.45%. Species composition and community structure of spruce forest did not change significantly within the 10 years. The high mortality rate and low recruitment rate in the community, especially the insufficient regeneration of dominant species, resulted in a slow regeneration. Our results are helpful for understanding the dynamics of species composition and structure of spruce forest in Tianshan Mountains, and provide scientific basis for the protection and sustainable management of spruce forest.

Key words: dynamic monitoring plot, spruce forest, mortality rate, recruitment rate, diameter at breast height (DBH).