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Lisha Kill Forest Preserve
Niskayuna, NY
Bob Leverett
leads the way into an Ancient Forest
Lisha Kill Forest Preserve, Niskayuna, NY

PHOTO: DYarrow 12/1/01

Defining Old Growth
Words to Describe Ancient Forests

prepared by David Yarrow, June 2002

A significant confusion exists over the status, terms and definitions for old growth forests. When the first conference on eastern old growth forests was held early in the 1990s, over 40 scientists debated definitions for a full day and couldn’t come to an agreement. Similarly, in 1989, when the 23 National Forests east of the Mississippi were required to include old growth forests in their Forest Plan, each came up with a different definition, with even the minimum age for old growth varying from 90 to 150 years. Despite this confusing complexity, certain elements of a definition of old growth forests have emerged from all this discussion and policy.

One aspect of this confusion is that a variety of words are used to describe ancient forests. These terms aren’t synonyms; each has a slightly different nuance or emphasis. Some are common in popular culture, while others were developed by individual authors or groups of researchers, and thus have a more precise, technical definition.

  • Ancient: A general, non-technical term for forests that contain significant populations of trees that are old for their species. A numerical value for ancient varies with each species: a pitch pine is old at 90 years, while a hemlock or oak reaches maturity only at 150 years, and commonly live for four or five centuries.
  • Virgin: This word suggests an ancient forest with no human disturbances. This pristine forest is the rarest of all, since most forests had minor to significant—even catastrophic—amounts of modification by man, including selective logging, firewood cutting, thinning, turpentining, charcoaling, fire, or grazing. Ecologists continue to debate whether disturbance by native Americans is an exception to this restrictive disturbance criteria.
  • Primeval: This term refers to forests that express a quality that is pristine in prehistoric, geologic sense—regressing to a time before humans and civilization created any disturbance. Primeval is virgin, but with an even more ancient character, implying an atmosphere or mood as much as physical conditions.
  • Original (Pre-settlement): This term is similar to virgin, and refers to forests displaying characteristics typical of conditions before Europeans discovered America and began to settle, clear and farm the land 400 years ago.
  • First: Some writers refer to uncut virgin and pre-settlement forests as first forests, to distinguish them from second and third growth forests that have regrown from cut over forests.
  • Old-growth: The most general term for ancient forests, old growth has acquired a somewhat technical definition with a lengthy list of criteria. These characteristics are detailed below.
  • Climax: This term is based on technical definitions of ecology, which sees that land undergoes a series of successive changes over many decades as it goes from open field to fully forested. Initially, land is covered by fast growing, sun-loving trees, but in later stages, shade tolerant, slow growing species become dominant, forming a high canopy above understory plants. “Climax” refers to the last stage of these successional transformations.
  • Secondary Old Growth: This phrase refers to forests that were disturbed—even clear cut—but have regenerated to a fully forested state, with old trees and understory. Nearly all forests in the eastern U.S. were cut, so most forests today are second and third growth. A small percent of these re-grown forests have acquired many or most characteristics of an ancient forest, and thus can qualify as old growth. Generally, secondary old growth forests have re-grown undisturbed for at least the minimum years required to meet old growth age criteria.
  • The debate over old growth definitions is driven in part by the different constituencies involved. Conventional forestry is motivated by economics, and sees trees as commodities for harvest, whereas most enthusiastic proponents of old growth develop their concepts using science and ecology. To a commercial forestry perspective, an old growth forest is over-mature, and overdue for timber harvest. To an ecologist, a forest is not a crop of trees for harvest, but a stable, self-sustaining community of living organisms that includes not only trees, but other lesser plants, animals, insects, micro-organisms, and even geological factors. While the economic views of commercial forestry predominated, in the last two decades, the values of science have acquired recognition and status in the society and public policy.



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