New discoveries about old-growth forests

PORTLAND, Ore. July 24, 2003. Scientists have long debated exactly how to define an old-growth forest. It is generally accepted that old-growth forests are ecosystems defined as forests with old trees and related structural attributes like large trees, large dead woody material on the forest floor, and horizontal and vertical canopy diversity.

But Tom Spies, an ecologist at the Forest Service's Pacific Northwest Research Station, says that as scientists study old-growth forests more closely, they are discovering that these forests contain many stages of forest development and that they differ widely in character with age, geographic location, and disturbance history. In examining the old-growth Douglas-fir along the Pacific coast, Spies and his colleagues shared these findings during a recent workshop:

Pacific coast old-growth forests are diverse regionally in both their structure and their development because of differences in climate, history, fire history, site productivity, and species composition.
Dominant trees have a wide range of ages in many old-growth forests.
Today's old-growth forests develop along multiple pathways, and disturbance continues to be a natural and important part of this development.
Centuries-old Douglas-fir trees can renew their crowns by growing new branches to replace damaged or broken branches (epicormic branch initiation).
In some old-growth forests fire suppression has resulted in an uncharacteristically high buildup of fuels, whereas in other old-growth forests fire suppression has had little or no impact on fuels because fuel loads are naturally high.
Today's old-growth forests developed from disturbances and under the climate conditions of the last millennium. The particular composition and structure of these old-growth forests may not occur again under modern climate and disturbance regimes.

"If we've learned anything in the last 30 years," Spies says, "it's that our understanding of ecosystems will change, just as our understanding of old-growth forests changed during the late 20th century. As we discover greater complexity in forests than we ever imagined, we will need to develop greater complexity in our cultural responses to forests as well."

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For a copy of the workshop findings go to http://sequoia.fsl.orst.edu/ccem/pdf/old-growth.pdf

Visit the PNW Research Station Web site at www.fs.fed.us/pnw

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