The size–growth relationship (SGR) quantifies growth partitioning among different sized trees in a stand and helps to elucidate stand growth dynamics during stand development. SGR strongly correlates with stand density, stand age, and drought severity. This study focused on larch (Larix principis-rupprechtii (Mayr)) forests with different stand ages (17–19 years, 20–29 years, 30–39 years, and 40–46 years) and stand densities (300–1400 trees·ha⁻¹ and 1400–3300 trees·ha⁻¹) as the research subjects. Employing a linear mixed model, we aimed to quantify the effects of stand density, stand age, and drought index on SGR. The results revealed that the Gini coefficient had a significant variation between high-density and low-density larch stands (p < 0.01). Stand age, stand density, and drought index exerted varying degrees of influence on the growth dominance coefficient (GD) and SGR of larch forests. In stands aged less than 39 years, a pronounced growth advantage of large trees over small trees was evident (typically SGR > 1 and GD > 0), indicating a positive growth dominance stage where large trees dominated. Compared to high-density stands, low-density stands exhibited a notably greater positive growth dominance. After 40 years, the growth stage transitioned to a relatively symmetric stage (SGR approximately equal to 1), with a discernible shift towards a reverse growth dominance stage (GD < 0). Compared to stand density and stand age, the drought index had a more influential effect on SGR. As drought severity increased, SGR increased, amplifying the growth advantage of large trees over small ones. The findings underscored the significance of adjusting stand density and optimizing tree size structure to enhance larch resilience against the warming and drying effects.

Our study aimed to assess the impacts of varying forest gap sizes on the density, growth, and spatial patterns of seedlings and saplings in spruce (Picea asperata) forests in the Saihanba region, Hebei Province, China. Twenty-four forest gaps were surveyed and categorized into six classes based on the gap size. A one-way ANOVA was used to compare differences in the density, height, and ground diameter of seedlings and saplings among six gap classes. Ripley’s K function was used to explore the spatial patterns of regeneration establishment in each class. The findings of our study indicated that the forest gap size did not significantly influence the density of seedlings or the ground diameter growth of saplings, whereas it significantly influenced the height growth of saplings. In smaller gaps, natural regeneration occurred primarily in the gap edges. As the gap size increased, the natural generation began to shift from the edge areas to the gap centers. Large forest gaps had the highest percentages of random distribution patterns across all spatial scales. Aggregated distributions were observed at distances less than 1 m in all gap size classes, whereas uniform distributions tended to occur in the small gaps at distances of 2–4 m. Our findings indicated that larger forest gaps, ranging from 60 to 120 m², were more conducive to spruce regeneration. The results can inform the development of targeted strategies for understory afforestation and the artificial promotion of natural regeneration in spruce forests.