Silvicultural responses of two spruce plantations to midrotation commercial thinning in New Brunswick

Abstract

A midrotation commercial thinning experiment conducted in two independent spruce plantations compared several tree selection strategies as both early (age 19 or 24 years) single and double (again at age 30 or 34 years) entries over a 16 year period. A delayed (age 30 or 32 years) single-entry thinning and unthinned portions of the plantations served as references for the other treatments. With the exception of 50% systematic row thinnings, removal intensities were held relatively constant at about 40% of stand basal area. All of the thinning treatments satisfied the objectives of focusing diameter and volume growth on a reduced number of stems and making merchantable volume available during the rotation. Early single-entry thinning allowed 30–50 m3/ha to be harvested, increasing quadratic mean diameter and mean merchantable volume per stem at the end of the observation period by 10% and 24%, respectively, over unthinned stands. A second thinning removed an additional 48–64 m3/ha and increased diameter and volume gains to 25% and 71%, respectively. Only marginal differences were observed between the tree-selection strategies, and there were no overall gross total or gross merchantable volume gains or losses associated any of the thinning treatments relative to the unthinned plantations.