Issue 9

What Do Foresters Mean By...?

Basal Area Retention

Basal area is the cross-sectional area (in square feet) of the base of the tree measured at breast height (4.5 feet above the ground). For example, the basal area of a tree that measures 14 inches in diameter at breast height (d.b.h.) is about 1 square foot.

Basal area can also refer to the sum of the basal areas of the individual trees within an acre of forest. For example, a well-stocked hardwood stand might have a basal area of 100 to 120 square feet per acre.

When foresters talk about 50 percent basal area retention, they mean that half the basal area represented by the standing trees will be cut, the other half retained. In the case above, this would mean cutting out 50 to 60 square feet per acre. This rarely means just going in and cutting half the trees in an area. Depending on the goal of the treatment, this could mean cutting out small diameter trees, large diameter trees, or a combination.

For the intermediate stand treatment on the Bankhead National Forest covered in the following article, basal area retention was calculated in terms of residual square feet (square feet per acre retained) rather than by percent. For the regeneration studies in Jackson County, AL the researchers reduced basal area by a gradient of percentages, leaving a residual basal area of 0, 25, 50, 75, or 100 percent.

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