Forests dominated by Abies nephrolepis in Mt. Doota–Mt. Cheongok (Gangwon-do, Korea) were investigated to characterize vegetation structure and temporal changes. Eighteen circular plots (400 m²) were established, and field surveys were conducted in 2019, 2021, and 2023 to collect tree census and vegetation data. Using these data, temporal changes in living-tree density and basal area, layer-specific importance values (I.V.), DBH-class distributions, tree status codes, sapling occurrence, and species diversity indices were analyzed. During the study period, living-tree density decreased by 15.3 trees/ha, whereas total basal area increased from 547.806 m²/ha in 2019 to 568.174 m²/ha in 2023 (+20.368 m²/ha), indicating continued diameter growth of surviving individuals. Layer-specific I.V. analysis showed minor changes in the tree layer (I.V. of A. nephrolepis, −0.36 percentage points; I.V. of Quercus mongolica, +0.16 percentage points), whereas I.V. shifts were observed for other major species and in the subtree layer. In the shrub layer, the mean I.V. of A. nephrolepis was 5.34%, and pronounced I.V. shifts were evident in the herb layer. DBH-class distributions indicated a unimodal pattern for A. nephrolepis concentrated in the 15–25 cm classes, and DBH-class changes were relatively large in the 15–30 cm range. Major deciduous broad-leaved species, including Q. mongolica, Betula ermanii, and Sorbus commixta, exhibited an inverse J-shaped distribution with individuals concentrated in the 6–15 cm classes. For tree status of A. nephrolepis, alive-standing trees decreased from 309.7 trees/ha to 304.2 trees/ha, and dead-standing trees decreased from 72.2 trees/ha to 63.9 trees/ha. Saplings in the 10–<50 cm height class decreased from 226.4 trees/ha in 2019 to 80.6 trees/ha in 2021, but increased to 100.0 trees/ha in 2023; saplings ≥50 cm remained above 100 trees/ha throughout the period (109.7 trees/ha in 2019, 131.9 trees/ha in 2021, and 133.3 trees/ha in 2023). The Shannon diversity index (H′) increased from 2.505 in 2019 to 2.569 in 2021 and 2.627 in 2023, with a mean value of 2.567. Overall, although no marked structural change in the overstory was detected during the study period, variation in understory composition and sapling dynamics suggests that repeated surveys on the same permanent plots and long-term monitoring are required to build a continuous dataset.