Crown Thinning

The crown-thinning method is defined by Smith (1986) as thinning that involves the removal of trees in the upper strata of the canopy to favor desirable trees in the same canopy range. In crown thinning, the focus is on the better trees (crop trees) that are to be provided with additional growing space and resources. As with all thinning methods, crown thinning is applied at the stand level where residual stocking targets are an important consideration. Crown thinning seems particularly applicable to fully stocked or overstocked mixed oak or mixed mesophytic hardwood stands on above-average sites. Although species such as northern red oak (Q. rubra L.) are capable of responding to release at age 50 and older, appropriate candidate stands of shade-intolerant species such as yellow-poplar and black cherry should be treated earlier than oaks. Care should be given to residual stand density, understory composition, and stem wounding of residual trees. Excessive thinning can induce epicormic branching of residuals or release undesirable midstory or understory species, or both. Sonderman and Rast (1988) recommend thinnings of moderate-to-light intensity in mixed oak stands in order to minimize branch-related defects that typically result from heavier thinnings in such stands. Residual stand density should be maintained at a level above the "B" line and below the "A" line defined by Gingrich (1967).