Abstract: Investigating the growth, biomass, and biomass allocation characteristics of forest plantations under different stand densities offers theoretical support for the sustainable management and high-quality development of plantations. We conducted field surveys and stem analysis of sample trees to explore the differences in growth process, biomass, and biomass allocation of 50-year-old Pinus tabuliformis plantations with stand densities of 600, 930, 1200, and 1650 trees·hm^-2. The results showed that: (1) The rapid growth period of the diameter at breast height (DBH) of Pinus tabuliformis was between 5 and 20 years old, and then entered a slow growth phase. Tree height had a rapid growth phase between 5 and 15 years old, followed by a slow growth stage. The ages at which DBH and tree height entered the slow growth phase varied among different stand densities. The lowest density (600 trees·hm^-2) delayed such transition, while the highest density (1650 trees·hm^-2) entered the slow growth phase earliest. The basal area growth remained fast before the age of 40 years, and continued to grow rapidly at 50 years for the density of 930 trees·hm^-2. (2) Aboveground biomass did not enter a slow growth phase at the age of 50. The growth was fastest at 930 trees·hm^-2 and slowest at 1650 trees·hm^-2 at the age of 50. (3) Aboveground biomass of individual trees ranged from 55.78 to 105.21 kg and decreased with increasing stand density. Across all stand densities, biomass allocation in various organs was in order of trunk > branch > needle. For cultivating large-diameter timber, the density of 600 trees·hm^-2 is recommended. The density should be adjusted at the age of 20 years. For carbon sequestration and ecological functions in water and soil conservation forests, biomass accumulation should be prioritized. In this situation, stand density should be adjusted to 930 trees·hm^-2 at around 40 years based on the basal area. In the actual tending and management of Pinus tabuliformis plantations, appropriate density regulation measures should be selected according to different silvicultural requirements.

Key words: stand density, forest growth regularity, Pinus tabuliformis plantation, loess region of western Shanxi Province