Assessment of growth parameters in Pinus sylvestris L. stands: Five-year results of precommercial thinning

Abstract

Determining the optimal intensities for precommercial thinning (PCT) in Pinus sylvestris stands, which hold significant ecological and economic value in Türkiye, is crucial for enhancing growth performance and ensuring well-formed stems. This study investigates the effects of various PCT intensities on the growth parameters of young, naturally regenerated stands located in the Western Black Sea and Central Anatolia regions of Türkiye. A total of 24 experimental plots (4 PCT intensities × 3 replications × 2 sites) were established in thicket-stage stands, and four PCT treatments were applied: T1 (classic), T2 (0.75–1.0 m spacing), T3 (1.5–2.0 m spacing), and a control (unthinned). Diameter at breast height, height, total basal area, and total volume were measured at the end of each growing season for five consecutive years. The results indicated that PCT intensity had a significant effect (p < 0.05) on all measured growth parameters. Both DBH and height increments were positively correlated with increased PCT intensity, with the greatest gains observed in the T1 and T3 PCT treatments. In particular, the relative increment values increased in parallel with the rise in PCT intensity in all measured growth parameters. In conclusion, leaving around 3000–3500 stems per hectare during PCT provides the best outcomes in terms of growth and stand structure. The findings suggest that PCT interventions should be performed on a 3–5 year cycle to maximize growth potential and maintain forest health.