Abstract

The effect of thinning has not been investigated previously in young even-aged Chinese fir [Cunninghamia lanceolata (Lamb.) Hook.] stands in Southern China. In long-term experiments, the effect of thinning on growth and yield of Chinese fir trees at five spacing levels was studied (2 × 3 m, 2 × 1.5 m, 2 × 1 m, 1 × 1.5 m and 1 × 1 m) thinned or left unthinned every 2 years from age 10. Trees in 2 × 3 m spaced unthinned plots were used as controls. Tree growth at the highest planting densities was lower in thinning treatments than in the control. The highest proportions of small, intermediate- and large stems were in plots with initial planting densities of 1 × 1 m, 1 × 1.5 m and 2 × 1 m, respectively. Merchantable volume increment after thinning showed no significant difference but increased with the initial planting density. The proportion of large-diameter trees and merchantable volume were highest in the controls. The total stand volume in thinning treatments increased with increasing initial planting density, but was lower than that of the control. Thinning Chinese fir stands with a planting density greater than 2 × 1 m could increase tree diameter but not merchantable volume. A stand density of less than 2 × 3 m is most profitable for increased tree growth and merchantable volume.

Key words: Diameter class distribution, thinning, Cunninghamia lanceolata (Lamb.) Hook., merchantable volume