page_title: Willamette Valley (ecoregion)
section_title: Landscape and threats
hierarchical_section_title: Willamette Valley (ecoregion) / Landscape and threats
caption_attribution_description: English: Forest in fall colors in w:Wilsonville, Oregon, USA
context_page_description: The Willamette Valley ecoregion is a Level III ecoregion designated by the United States Environmental Protection Agency in the U.S. states of Oregon and Washington. Slightly larger than the Willamette Valley for which it is named, the ecoregion contains fluvial terraces and floodplains of the Willamette River system, scattered hills, buttes, and adjacent foothills. It is distinguished from the neighboring Coast Range, Cascades, and Klamath Mountains ecoregions by lower precipitation, lower elevation, less relief, and a different mosaic of vegetation. Mean annual rainfall is 37 to 60 inches, and summers are generally dry. Historically, the region was covered by rolling prairies, oak savanna, coniferous forests, extensive wetlands, and deciduous riparian forests. Today, it contains the bulk of Oregon's population, industry, commerce, and agriculture. Productive soils and a temperate climate make it one of the most important agricultural areas in Oregon.
context_section_description: Historically, the Willamette Valley forests were mostly an oak savanna, tall grasslands with scattered Garry oaks (Quercus garryana), and groves of coast Douglas-fir (Pseudotsuga menziesii subsp. menziesii). The river floodplains contained extensive wetlands, stands of willow, alder, and cottonwood, and gallery forests.
  This landscape was maintained by the Native American inhabitants of the valley who set frequent fires which encouraged the open grasslands and killed young trees. The American settlers of the region, since the 19th century, suppressed fires and converted much of the valley to agriculture, which has caused much of the former grassland and savanna to revert to closed-canopy forest.
  Less than one-tenth of one percent of the original savanna vegetation remains. The remaining enclaves include a section of Garry oak savanna preserved at Mount Pisgah Arboretum in Eugene.
caption: Fall colors in Wilsonville
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