Investigating the Self‐Thinning Rule in Plantation Forests: Analyzing the Relationship Between the Basal Area and Height Growth in Southern China

The self-thinning rule in forest stands is fundamental to the development of density management strategies, as it determines the maximum stand density achievable for a given tree size. Accurate modeling of the maximum density line is crucial, but selecting representative data points for this purpose remains a challenge. Using 18 years of data from five <i>Cunninghamia lanceolata</i> plantations with varying initial planting densities, this study investigated whether relationships between mean tree basal area (<i>g</i>) and height (<i>H</i>) can reveal forest developmental stages and identify when stands begin self-thinning and reach maximum density. Our results showed a significant linear relationship (<i>p</i> < 0.05) between <i>g</i> and <i>H</i> after self-thinning was established, supporting the presence of self-regulatory growth mechanisms. These findings enabled the development of a novel sample selection method for constructing more accurate maximum density line models, outperforming traditional methods that rely on arbitrary thresholds. Additionally, we derived formulas to describe total stand basal area (<i>G</i> _1.0) during different growth stages, revealing positive correlations with mean height during early growth and negative correlations with mean diameter during self-thinning. This research advances the understanding of self-thinning dynamics and provides practical tools for improving density management in plantation forestry.