Thinnings

Thinnings are intermediate cuttings made in immature stands to control stand density and redirect resources (light, water, and nutrients) to residual trees (Beck 1986). The primary objectives of thinning in central hardwoods are to:

• Increase the rate of diameter growth of the residuals so that the stand can be harvested at an earlier age.
• Concentrate growth on more desirable trees in order to produce a greater volume of high-quality and high-value products.
• Obtain income during the rotation.
• Salvage losses that would occur as a result of impending suppression and normal mortality (Hicks 1998).

Five thinning methods are commonly used in silvicultural systems: low thinning, crown thinning, selection thinning, mechanical thinning, and free thinning. Each thinning method has distinct characteristics, and foresters use different combinations of them to serve different kinds of landowner objectives. The age of a stand at the time of first thinning, the condition and species of trees in it, and the financial constraints of a landowner usually prove most decisive in selecting a thinning method. Several concepts should be understood before selecting a particular thinning method and intensity. First, response of any tree to release depends on several factors, including general tree health and vigor. Tree vigor, in turn, is related to factors such as site quality, stocking density, crown position, fire history, climatic stresses (drought, frost, ice), and insect and disease conditions. Therefore, knowing the various biotic controls on tree growth will help to understand the how thinning affects tree growth and stand volume production.

Second, there are several conceptual tools related to the use of thinning programs, including methods for assessing competition and vigor of individual trees, and models for determining the timing and intensity of thinnings (stocking guides and yield tables).

Finally, there are several financial considerations to understand before deciding on a particular thinning regime.

See also: Using Thinnings in Oak Management