sentences:  Of this total, 2.4 million acres (90 percent) are classified as timberland.Timberland is defined as land growing at least 20 cubic feet (or the equivalent of twenty-four 2" x 4" x 8' framing studs) of wood on every acre each year with the potential of harvesting it.Examples of areas not classified as timberland include federal and state park land, Christmas tree farms, and forests set aside for scientific study.