Kathie Durbin offers the following set of characteristics that indicate an old growth forest. Her description was published by the National Forest Service's Pacific Northwest Forest and Range Experiment Station in 1981.

[There are] four key structural characteristics of old growth: large, live trees 175 to 750 years of age and even older; standing dead trees called snags; logs fallen to the forest floor; and logs lying in streams. © 1996. Durbin, K. Oregon. In R. Kirk (Ed.), The Enduring Forests. Seattle: The Mountaineers, p. 62.

You may want to see another set of criteria for recognizing a temperate rain forest and learn more about the climate of the Olympic National Park of Washington.

The Douglas Fir
Douglas-fir, our most famous tree, thrives throughout the mountainous far west from Central British Columbia into Mexico and from the Pacific Ocean east as far as Colorado. Close relatives live in California, Mexico, China, Taiwan, and Japan. The trees can be very old and, on the coast, very large. Reliable statistics are not nearly so dramatic as those in folklore and fuzzy memories, but even careful figures indicate that Douglas-fir often live 750 years and the oldest may reach 1,300 years of age, with heights reaching 315 feet and trunk diameters as great as 14 feet. © 1996. Edwards, Y. British Columbia. In R. Kirk (Ed.), The Enduring Forests. Seattle: The Mountaineers, p. 116.

Understanding What Old Growth Is
Old-growth Douglas-fir like that of the central Cascades, if lost, will not regrow to this stage within the lifetime of our great, great, great, great, great, great, great grandchildren. © 1996. Durbin, K. Oregon. In R. Kirk (Ed.), The Enduring Forests. Seattle: The Mountaineers, p. 61.

Microclimates in the Forest Microclimates are climatic pockets where conditions differ from the overall climate of a larger surrounding area. Microclimates often occur where there is a special "lay of the land" or a distinctive vegetative cover. Left: Large cedars in the Hoh Rainforest of Washington. Photo: Ed Shay

Left: Large redwoods in Henry Cowell Redwoods State Park.  The person stands 5'11" tall.  Photo: Courtesy of Stephanie Stockman

Tall trees become winners; sunlight is strongest at the top of the forest, and by using its energy trees are the most successful earthbound invaders of the atmosphere. They create their own climate, quite different from that outside the forest. They cool warm air, tame winds, and pump water from the soil. They hold winter snowfalls aloft to be melted, delay the spring melting of accumulated snow on the forest floor, and turn fogs into local rain. © 1996. Edwards, Y. British Columbia. In R. Kirk (Ed.), The Enduring Forests. Seattle: The Mountaineers, p. 110.

Elevation and Latitude Affect Plant Life
Ecologists no longer use his (C. Hart Merriam) terminology, but the pattern he first called attention to remains: vegetation varies with both elevation and latitude. This phenomena is now expressed in the concept of zones, which are defined locally for each region or mountain complex. © 1996. Sawyer, J. O., Jr. Northern California. In R. Kirk (Ed.), The Enduring Forests. Seattle: The Mountaineers, p. 38.

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