How Much Old Growth Is There In Oregon's Forests?

Discussion of old growth is often confusing because of varying definitions having to do both with age and structural characteristics. Old growth forests are commonly thought to include: large trees, often with broken tops or signs of decay, a multi-layered canopy with trees of different sizes and ages, and heavy accumulations of wood, including standing dead trees (snags) and large logs on the ground. The age needed to attain old growth status varies among species and sites. For example, a stand of lodgepole pine is considered old at 100 years, while it may take a Douglas-fir forest 200 years or more to develop old growth characteristics.

Today many scientists use a more inclusive term, "late successional," to refer to older forests that have some, but not necessarily all, of the features of old growth. In western Oregon, forests with trees greater than about 21 inches in diameter and/or 100 years or more in age are often considered late successional. These forests may provide important wildlife habitat features, such as large trees or snags, needed by species that use mature forests.

Approximately 4.9 million acres in Oregon were classified as old growth forest, according to data published by the USDA Forest Service in 1993.This estimate was based largely on National Forest Plans using data classified between 1980 and 1992. Preliminary data from more recent inventories (1993-97) indicate that there are approximately 7.4 million acres of forest greater than 100 years in age, and 1.25 million acres of forests greater than 200 years in age on federal lands in Oregon.

In a subsequent study published in 1994 of forests in western Oregon, the USDA Forest Service estimated that there were about 2.14 million acres, 1.47 million (69%) were protected or severely restricted from timber harvest. Other data from recent satellite imagery indicate that there are about 1.4 million acres of forest in western Oregon with an average diameter of greater that 20 inches, and 700,000 acres of forest with an average diameter greater than 30 inches. Of these 2.1 million acres, 1.3 million are protected.

Most of the late successional and old growth forest in Oregon is on federal lands.

SOURCE: Oregon Forest Resources Institute, Forest Fact Book.