BA — What in the world is that basal area?

This table shows the number of trees by 1-inch diameter with the associated BA. Due to space issues, the complete chart could not be put into the magazine. We apologize for the inconvenience of our magazine readers.

Landowners go to forestry meetings and they keep hearing a term used ... “basal area” and they wonder, “What in the world is Basal Area?”

Basal Area, or BA, is a common term used to describe the average amount of an area, commonly an acre, which is occupied by tree stems. In other words, how much of the area of one acre is taken up in trees.

One way to describe what this looks like is to take a very sharp knife and slice off all the trees at DBH. Oh, there’s another term foresters use. DBH is Diameter at Breast Height, which is a standard measure of 4.5 feet above the ground line. DBH is where you measure the diameter of a tree. Now, with all the trees sliced off at 4.5 feet, you have a lot of saucers or flat surfaces of the trees. The surface of these tree slices have an area in square feet.

One acre has 43,560 square feet (208.71 feet x 208.71 feet). The basal area of the tree stems is the amount of square feet of wood on one acre or say 80 square feet of wood in 43,560 square feet. The area of the tree stems is calculated to determine the square feet of the tree stems. Mathematically it looks like this:

Basal Area = pi x ((DBH)/4) x 144

Basal Area = 0.005454 x (DBH)

The number 0.005454 is known as the “foresters constant,” which converts the measured inches into square feet. Table 1 below illustrates the square feet of basal area per tree for several DBH classes. Table 2 can serve as a guide to assist landowners when estimating trees per acre from certain basal area measurements.

Basal area is a useful tool for understanding forest-wildlife habitat relationships and making timber harvest decisions. The higher the basal area number, the thicker the stand and therefore the thicker the canopy.

Normally, a basal area number higher than 100, would need a thinning operation. Generally, timber stan