Johannessen, Carl L. , William A. Davenport, Artimus Millet, Steven McWilliams. The Vegetation of the Willamette Valley. Annals of the Association of American Geographers 61 (2), 286-302. 1971.

The vegetation of the Willamette Valley, Oregon, has been modified by man for centuries. Thc earliest white men described the vegetation as extensive prairies maintained by annual fires set by Indians. The cessation of burning in the 1850s allowed expansion of forest lands on the margins of the former prairies. Today some of these forest lands have completed a cycle of growth, logging, and regrowth. Much of the former prairie is now in large-scale grain and grass seed production and is still burned annually. The pasture lands of the Valley are still maintained as open lands with widely scattered oaks. KEY WORDS: historical vegetation, Indian burning, prairies, vegetation change, Willamette Valley.

The vegetation of the Willamette Valley, Oregon, has changed significantly under human influence. The Indians of this area, at the time of contact with white settlers, set prairie fires annually, which created a prairie/open woodlands complex. The new settlers, who increased rapidly in the mid-nineteenth century, forced the Indians to leave. Their practice of annual burning was temporarily discontinued. White settlers brought modifications of the habitat with their livestock and cropping, and more recently, forestry systems...

The fire-tolerant, widely-spaced oak, fir, or pine seeded the so-called openings to form thickets that have grown to dense woodlands and forest. Firs now dominate these woodlands, because the firs are able to continue vertical growth and reach light more effectively than the broadleaf trees. A complete cycle has occurred in some locations. Mature 70 to 100-year-old fir trees have been harvested from formerly open prairie and parkland, and now new crops of seedlings
have invaded the logged-over areas...

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