BA/ac measures basal area per acre. In what units?

• A. Square feet
• B. Square meters
• C. Acres
• D. Cubic feet

Answer: (A)

Basal area per acre is about the cross-sectional area of all tree stems at breast height divided by land area. That cross-sectional area is an area quantity, so the unit is square units, and because the land area is expressed in acres in this context, the standard expression is square feet of cross-sectional area per acre of land (ft^2/acre). That’s why square feet is the correct basis here.

To connect the idea, basal area for a stand is calculated by summing pi*(DBH/2)^2 for all trees, giving a total area in square units; when you divide by one acre of land, you end up with ft^2/acre. The other options don’t fit: cubic feet would be volume, not area; acres is just land area without the cross-sectional aspect; square meters would be the metric analogue (ft^2/acre corresponds to m^2/ha, not a direct per-acre metric).