Level IV: (3b)Willamette River and Tributaries Gallery Forest
The Willamette River and Tributaries Gallery Forest ecoregion includes low-gradient, meandering river channels, oxbow lakes, and meander scars incised into the broad floodplains of the Willamette River and its tributaries. Elevation varies from 40 to 500 feet (12 to 150 m).
The region includes the historic floodplains of the Willamette River system, which rarely function today due to flood control dams in the upper basin that have reduced the frequency and volume of floods and contributed to the decline of the endemic, endangered Oregon chub. A small section, designated as the Willamette Floodplain, has been protected within the William L. Finley National Wildlife Refuge.
Historically, riparian gallery forests containing ash, black cottonwood, alder, and bigleaf maple grew on fertile, alluvial soils. Today, most of the forests have been replaced by agriculture and residential development.
The region covers 675 square miles (1,748 km2) in Oregon in a narrow band rarely more than 5 miles (8 km) wide that extends along nearly the entire length of the Willamette River and the lower reaches of the McKenzie, Long Tom, Santiam, Yamhill, Molalla, Clackamas, and Tualatin rivers, including the Tualatin River National Wildlife Refuge.