Thinning Recommendations With Southern Pine Beetle Concerns

Thinning is defined as the mechanical removal of individual trees or entire rows of trees from a stand.  This allows the residual trees more space to continue their vigorous growth and health.  As the basal area of a stand increases beyond 100 ft²/acre the risk of southern pine beetle mortality increases.  Basal area is a measure of stocking and is defined as the cross-sectional area of tree boles on an unit area.  There are two types of thinning: pre-commercial and commercial.

1)Pre-commercial Thinning: Cutting in immature stands before trees reach their marketable size, usually less then 5 inches, is called pre-commercial thinning.  Generally pre-commercial thinning is not required if trees are planted at wider spacings (10' X 10' or greater).  At narrower spacings, pre-commercial thinning my be needed to allow additional space for the remaining trees to grow.  Trees may be thinned by using chainsaws or a row(s) can be removed with a bush-hog or drum chopper.  Pre-commercial thinning is a cost generator with no immediate income for the landowner.  However, it will improve the overall health of the stand when closely-spaced, young trees are competing with each other. 

2)Commercial Thinning: This thinning occurs much later when the canopy has closed and the trees are reaching pulpwood class, usually 12 to 15 years old.  The goal is to lower the basal area of the stand to 70 or 80 square feet per acre.  This prevents a reduction in the radial growth of the trees and helps to protect the stand from SPB infestations.  Additional thinnings should be conducted at older ages whenever  the basal area of the stand exceeds 100 to 120 ft²/acre or when the canopy closes, allowing additional space for crown expansion to maintain diameter growth of the remaining trees.

Care should be given any time that there is a mechanical entry into the stand.  More harm then good is often caused when residual trees are damaged during operations.