Willamette Valley Ponderosa Pine

Although it is more commonly associated with eastern Oregon, Ponderosa Pine has been growing in the Willamette Valley for thousands of years. Archeological research has recorded Ponderosa Pine pollen from 7,000 years ago in the Willamette Valley. Research has also shown that the Ponderosa Pine trees that grow in the Willamette Valley are genetically different from those that grow on the east side of the Cascades. It may be surprising to some that Native Willamette Valley Ponderosa Pine is found at lower elevations (generally less than 1000 feet) and on both very wet and very dry soils. A typical site has the heavy clay soils characteristic of both high winter water tables and severe summer drought conditions. Historical studies have shown that in 1850, Ponderosa Pine in the Willamette Valley was often found growing with Oregon white oak, and occasional Douglas Fir, in wide-open habitats called savannas, where the trees are widely spaced. Today, pine groves are often found associated with Oregon White Oak and poison oak.

Historically, stands of Ponderosa Pine were supported by frequent fires that prevented tree species such as Incense Cedar, Grand Fir and Douglas-Fir from outgrowing and shading out the pine seedlings, thus preventing their survival. These fires prevented what is called forest succession,
where one set of tree species succeeds another.

Since settlement of the Willamette Valley by
Euro-Americans in the 1850’s, fire has been suppressed, which has allowed forest succession to occur,
reducing the amount of surviving Ponderosa Pine.
Other causes for the decline of Ponderosa pine in the Willamette Valley include urban development and timber harvest.

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