With pre-commercial thinning, trees are removed prior to reaching merchantable size. The objective of pre-commercial thinning is to release trees in overstocked stands by reducing densities to prevent stagnation and increase the growth of remaining trees. With pre-commercial thinning, scattered trees throughout the timber stand are removed, creating larger openings in the forest canopy that will close as the surrounding trees grow. This thinning typically is not intended to establish regeneration (a new generation of young trees in the understory), although in certain cases it can.
Pre-commercial thinning, also known as Timber Stand Improvement, enhances the quality of growing timber, rather than harvesting and selling the timber.
Landowner objectives determine which trees are removed during pre-commercial thinning.
To enhance future timber production, undesirable species, poor-formed trees and slow-growing individuals are removed.
Depending on wildlife considerations, sometimes poor-formed or cull trees are left to provide wildlife habitat.
A common mistake in pre-commercial thinning is to leave too many trees in the residual stand. Generally, 40 to 60 percent of the trees are harvested during a thinning.
Several thinning operations may take place before the stand reaches maturity.