How much ‘old growth’ forest is left in the U.S.?

As crazy as it sounds, no one really knows how much old growth is left in America’s forested regions, mainly because various agencies and scientists have different ideas about how to define the term. Generally speaking, “old growth” refers to forests containing trees often hundreds, sometimes thousands, of years old. But even when there is agreement on a specific definition, differences in the methods used to inventory remaining stands of old growth forest can produce major discrepancies. Or so complains the National Commission on Science for Sustainable Forestry (NCSSF) in its recent report, “Beyond Old Growth: Older Forests in a Changing World.” In 1991, for example, the U.S. Forest Service and the nonprofit Wilderness Society each released its own inventory of old-growth forests in the Pacific Northwest and northern California. They both used the Forest Service’s definition based on the number, age and density of large trees per acre, the characteristics of the forest canopy, the number of dead standing trees and fallen logs and other criteria. However, because each agency used different remote sensing techniques to glean data, the Forest Service came up with 4.3 million acres of old-growth and the Wilderness Society found only two million acres. The NCSSF also studied the data, and they concluded that 3.5 million acres (or six percent) of the region’s 56.8 million acres of forest qualified as old growth–that is, largely trees over 30 inches in diameter with complex forest canopies....