Old growth forest is a term that everyone has heard. It refers to forest
stands that have a large number of old trees. Defining the specifics of
what is an old growth forest is a much more complicated proposition. The
terms "primary forest" or "natural heritage forest" may be more appropriate
terms for management and study purposes because their definitions recognize
that forests are part of a dynamic system that are affected by natural
disturbances and regrowth.

The Minnesota Department of Natural Resources
http://www.dnr.state.mn.us/forests/oldgrowth/index.html  defines old growth
as follows: "Old-growth forests are natural forests that have developed
over a long period of time, generally at least 120 years (DNR definition
and consistent with definitions for the eastern United States), without
experiencing severe, stand-replacing disturbance--a fire, windstorm, or
logging. Old-growth forests may be dominated by species such as sugar
maple, white spruce, or white cedar that are capable of reproducing under a
shaded canopy. These old-growth forests can persist indefinitely.
Old-growth forest may also be dominated by species such as red pine, white
pine, or red oak that do not reproduce as well under shade and that require
disturbance to open the canopy. These old-growth forests will eventually be
replaced by the more shade tolerant tree species in the absence of
disturbance."

The attempt to define old growth is a mire of different viewpoints,
perspectives, motivations, terminology. A simple all-encompassing
definition doesn’t exist as the characteristics of an old growth forest
varies from locality to locality and from forest type to forest type.
Maurice Schwartz found ninety-eight separate definitions of old growth with
an internet search. The above definition has problems itself. Some forest
types are dominated by trees with a lifespan of less than 120 years. These
forests otherwise may have all of the characteristics of old growth but are
excluded by the time criteria stated above. The definition is also
ambiguous with respect to how much disturbance is severe disturbance.
Regulators want a strict definition that can be applied without compromise,
dynamicists want a definition based upon processes that are taking place in
the evolution of the forest, environmentalists want a more encompassing
definition to include areas peripheral to the oldest forest which are
essential to maintaining ecosystem integrity, lumbering interests want a
limited definition that says that very little forest is old growth because
of potential public opposition to timbering old growth forest.

Old Growth Forest can also be defined (after Frelich 2002): Forest that
meets a threshold determined by some political and (or) scientific process.
Often officials working for public land management agencies will propose a
threshold and then get feedback from elected officials and the public to
develop a final threshold. These thresholds can vary considerably and could
include one or more of the following: a minimum stand age; minimum age of
trees, either absolute age or relative to their potential maximum age;
minimum size of trees (either absolute or relative to maximum potential for
the site); stage of development and succession; and degree of naturalness,
such as the historic lack of logging.

Under many definitions an old growth forest that has suffered a fire,
blowdown, or other natural disturbance would cease to be old growth with
the loss of old trees. Lee Frelich (Sept 30, 2004, ENTS post) wrote: "There
is not and never will be a biological definition of old growth. Since old
growth is a human construct, it is what people say it is, and that varies
among political jurisdictions. However, if you want a simple inclusive
definition for outlining forests on the ground for preservation, then use
primary forests (forests that have not been logged). There is still some
subjectivity here, since in some regions all forests had at least some
selective cutting, and you still have to come up with a subjective
criterion for amount of human disturbance that disqualifies a stand from
the category of primary forest. Also, primary forest includes a stands
dominated by young early successional forest, old early successional
forest, young late successional forest, and old late successional forest."

"Primary forest or natural heritage forest: Forest with a continuous
heritage of natural disturbance and regeneration. In North America this
usually means that the forest was not cleared for agriculture or heavily
logged for timber by Native Americans or by European settlers. Historical
records and paleoecological evidence can often be used to establish the
existence of primary forest; in many parts of North America large-scale
logging is a recent phenomenon and stand ages greater than the dates of
first logging can be used to establish primary status." (Frelich and Reich,
2003)

"Primary old growth forests or natural heritage old growth forests are
primary forest stands that are in late stages of succession and
development... The natural-heritage criterion for delimiting old growth
makes it clear that natural disturbance is an integral part of the
old-growth ecosystem and ensures that old forest will continue to include
species in all stages of succession and development that have undergone
genetic selection by natural processes, rather than harvesting and
highgrading." (Frelich and Reich, 2003).

"The old-growth forest that blows down, whether 25%, 50%, or all of it, is
still primary forest and has the potential to recover to a developmental
stage with large old trees. Since all forests are created by disturbance,
this is part of the natural cycle. The most important function of reserved
old-growth forests is to see how they respond to and recover from
disturbance." (Lee Frelich, ENTS post Oct 2, 2004) 

The challenge is to refocus the debate over natural forests to "primary"
rather than "old growth", which is simply a snapshot in the life of the
primary (and autopoietic) forest. The danger in continuing to focus on "old
growth forests" is that as these forests undergo natural disturbance
policymakers could legally (and quite logically) take them out of
protection. (Gary Beluzo, ENTS post Oct. 3, 2004)

Most people are impressed by large old trees. They are more motivated to
visit and protect these stands of ancient forest. A relatively young, early
successional forest, may be a primary forest. Lee Frelich (ENTS post, Oct.
4, 2004) argues: "Most tree populations in the northeastern U.S. that have
not been logged go back 3000-5000 years. That usually interests most
people, especially when you tell them that the young post-disturbance
forest is carrying on a 5000 year heritage." An educational goal would be
to make people aware of the long history of these primary forests.

Can other plant communities can be called old growth or primary growth?
Yes, without any doubt,  a threshold for level of human disturbance that
disqualifies a community from being primary can be developed analogous 
to the criteria for primary forests. For example, a savanna that did not 
have the trees cut, was never plowed, and can be restored and maintained by 
prescribed fires would qualify.  Lee Frelich (ENTS Post Feb 10, 2004) wrote:
"Minnesota Department of Natural Resources recently switched to natural
community-based definition for forest and other vegetation. They used
ordinations including trees, shrubs and understory plants to separate
communities within each region of the state. The ordinations were based on
thousands of plots where all trees and plants were identified by Natural
Heritage Ecologists. Those plots that fell together in clusters in
multi-dimensional ordination space defined a natural community, and the
characteristics of those plots were used in the descriptions that have now
been published." 

The PA Bureau of Forestry,
http://www.dcnr.state.pa.us/forestry/oldgrowth/principles.aspx  has an
discussion of the term old growth: "Finally, it is also important to
include representatives of different ecosystems in old growth, not only the
typical hemlock-white pine or hemlock-beech associations of the well-known
Cook Forest and Heart's Content. It is for those reasons that places are
included in this tour such as Bear Meadows (a large ancient bog) and
Cranberry Swamp, giving visitors a broader vision of the varied components
of the entire macro-system. While it is true sometimes that "we can't see
the forest for the trees," it is just as true that we should not confuse
the forest with the trees. In other words, while we speak of old-growth
forests in terms of the major tree species found there, old-growth is
really a term describing entire ecosystems. The other plants and animals
who live within the tree-defined framework are vital to the whole."

Frelich, L. E. 2002. Forest dynamics and disturbance regimes, studies from
temperate evergreen-deciduous forests. Cambridge University Press,
Cambridge, U.K.

Frelich, L. E. and Reich, P. B. Environ. Rev. Vol. 11 (Suppl. 1), 2003.
Perspectives on development of definitions and values related to old-growth
forests.

-  Edward Frank, October 26, 2004