Willamette Valley (ecoregion)

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Willamette Valley
Eugene wetlands.jpg
Level III ecoregions, Pacific Northwest.gif
Willamette Valley ecoregion (3)
Ecology
Realm Nearctic
Biome Temperate broadleaf and mixed forests
Borders Cascades, Coast Range, Klamath Mountains and Puget lowland forests
Bird species177 [1]
Mammal species77 [1]
Geography
Area14,900 km2 (5,800 sq mi)
Country United States
States Washington and Oregon
Coordinates 44°48′N123°12′W / 44.8°N 123.2°W / 44.8; -123.2 Coordinates: 44°48′N123°12′W / 44.8°N 123.2°W / 44.8; -123.2
Conservation
Habitat loss65.679% [1]
Protected4.07% [1]

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 (96 to 152 cm), 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. [2] [3]

Contents

Setting

The ecoregion covers an area of 14,900 square kilometers (5,800 sq mi), [4] lying mostly in Oregon, with a small portion lying across the Columbia River in southern Washington. The ecoregion lies in the Willamette Valley, which runs from south to north between the Oregon Coast Range to the west and the Cascades Range to the east. The ecoregion is drained mostly by the Willamette River and its tributaries, which flows into the Columbia River straddled by Portland, Oregon.

Landscape and threats

Grove of Oregon white oaks near Hillsboro Oregon oak grove.jpg
Grove of Oregon white oaks near Hillsboro
Fall colors in Wilsonville Mixed forest Wilsonville.JPG
Fall colors in Wilsonville

Historically, the Willamette Valley forests were mostly an oak savanna, tall grasslands with scattered Oregon white 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 Oregon white oak savanna preserved at Mount Pisgah Arboretum in Eugene.

Level IV ecoregions

Level IV ecoregions in the Willamette Valley. (Full map). Level IV ecoregions, Willamette Valley.png
Level IV ecoregions in the Willamette Valley. (Full map).

The Willamette Valley ecoregion is made up of four Level IV ecoregions:

Portland/Vancouver Basin (3a)

The Portland/Vancouver Basin ecoregion (named for the cities of Portland and Vancouver) is a geological depression at the base of the Portland Hills fault-block. It contains the confluence of the Willamette and Columbia Rivers and is composed of deltaic sands and gravels deposited by Pleistocene floods, notably the Missoula Floods. Elevation varies from 0 to 300 feet (0 to 90 m), with buttes as high as 650 feet (200 m). Historically, the basin was characterized by Oregon white oak groves and Douglas-fir forests on the uplands; black cottonwood groves on riverbanks and islands; Oregon ash, red alder, and western redcedar in riparian areas; and prairie openings maintained by Native American burning, with camas, sedges, tufted hairgrass, fescue, and California oatgrass. Numerous wetlands, oxbow lakes, and ponds can still be found, but today the region is dominated by urban and suburban development, pastures, cropland, and tree farms. The climate is usually marine-influenced, but easterly winds from the Columbia River Gorge periodically bring continental temperature extremes. The region covers 305 square miles (790 km2) in Washington and 269 square miles (697 km2) in Oregon, including the northern and eastern suburbs of the Portland metropolitan area. It contains several National Wildlife Refuges within the Ridgefield National Wildlife Refuge Complex. [2] [3]

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. [2] [3]

Ankeny National Wildlife Refuge in the Prairie Terraces ecoregion Ankeny NWR 01339r.JPG
Ankeny National Wildlife Refuge in the Prairie Terraces ecoregion

Prairie Terraces (3c)

The Prairie Terraces ecoregion includes all terraces of the Willamette River upstream of the Portland/Vancouver Basin. It is dissected by low-gradient, meandering streams and rivers. Elevation varies from 160 to 500 feet (50 to 150 m). The region's broad fluvial terraces once supported oak savanna and prairies, featuring Oregon white oak, camas, sedges, tufted hairgrass, fescue, and California oatgrass. Wetter areas supported Oregon ash, Douglas-fir, bigleaf maple, black cottonwood, and an understory of poison-oak, hazel, and Indian plum, with some Ponderosa pine to the south. Today, only relict native prairie remains. The poorly drained soils derived from glacial lake deposits are extensively farmed for grass seed and small grains, as grasses tolerate poor drainage and poor rooting conditions better than other crops. Historically, seasonal wetlands and ponds were common, but many streams are now channelized, and the wetlands have been reclaimed for grain crops. In addition to agriculture, the Prairie Terraces have experienced the brunt of urban and suburban development along the Interstate 5 corridor. The region covers 1,971 square miles (5,105 km2) in Oregon along the length of the valley and includes the Baskett Slough and Ankeny national wildlife refuges. [2] [3]

Valley Foothills (3d)

The Valley Foothills ecoregion is a transitional zone between the agricultural Willamette Valley and the more heavily forested Cascade and Coast ranges. It contains rolling foothills with medium gradient, sinuous streams, and a few buttes and low mountains, rising to an elevation of approximately 1,500 feet (457 m). The region receives less rainfall than its more mountainous neighbors, and consequently the potential natural vegetation is distinct. The eastern foothills are wetter than those that lie on the western side of the valley in the lee of the Coast Range. Historically, the drier areas supported Oregon white oak and madrone woodlands and prairies, with California oatgrass, fescue, blue wildrye, brodiaea, and other prairie forbs; while the moister areas supported Douglas-fir forests, with sword fern, oceanspray, hazel, baldhip rose, poison oak, and wild blackberry. Today, the valley foothills are characterized by rural residential development, pastures, timberland, vineyards, Christmas tree farms, and orchards. The largest of the Willamette Valley subregions, it covers 2,415 square miles (6,255 km2) in Oregon and 112 square miles (290 km2) in Washington. [2] [3]

See also

Related Research Articles

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The Northern California coastal forests are a temperate coniferous forests ecoregion of coastal Northern California and southwestern Oregon.

<span class="mw-page-title-main">William L. Finley National Wildlife Refuge</span>

William L. Finley National Wildlife Refuge is a natural area in the Willamette Valley in Oregon, United States. It was created to provide wintering habitat for dusky Canada geese. Unlike other Canada geese, dusky Canada geese have limited summer and winter ranges. They nest on Alaska's Copper River Delta and winter almost exclusively in the Willamette Valley. Habitat loss, predation, and hunting have caused a decrease in population.

<span class="mw-page-title-main">Ankeny National Wildlife Refuge</span>

Ankeny National Wildlife Refuge is located in the fertile Willamette Valley of northwestern Oregon, 12 miles (19 km) south of Salem. The valley was once a rich mix of wildlife habitats. Valley wetlands were once extensive, with meandering stream channels and vast seasonal marshes. Today, the valley is a mix of farmland and growing cities, with few areas remaining for wildlife.

<span class="mw-page-title-main">Baskett Slough National Wildlife Refuge</span>

Baskett Slough National Wildlife Refuge is in northwestern Oregon, 10 miles (16 km) west of Salem in Polk County. The Refuge consists of 1,173 acres (4.75 km²) of cropland, which provide forage for wintering geese, 300 acres (1.2 km²) of forests, 550 acres (2.2 km²) of grasslands, and 500 acres (2.0 km²) of shallow water seasonal wetlands and 35 acres (0.14 km²) of permanent open water. In 1965, Baskett Slough National Wildlife Refuge was created to help ensure some of the original habitat remained for species preservation. The refuge is managed by the U.S. Fish and Wildlife Service, an agency of the U.S. Department of the Interior.

<span class="mw-page-title-main">Johnson Creek (Willamette River tributary)</span> Creek in Oregon, USA

Johnson Creek is a 25-mile (40 km) tributary of the Willamette River in the Portland metropolitan area of the U.S. state of Oregon. Part of the drainage basin of the Columbia River, its catchment consists of 54 square miles (140 km2) of mostly urban land occupied by about 180,000 people as of 2012. Passing through the cities of Gresham, Portland, and Milwaukie, the creek flows generally west from the foothills of the Cascade Range through sediments deposited by glacial floods on a substrate of basalt. Though polluted, it is free-flowing along its main stem and provides habitat for salmon and other migrating fish.

<span class="mw-page-title-main">Balch Creek</span> Tributary of Willamette River

Balch Creek is a 3.5-mile (5.6 km) tributary of the Willamette River in the U.S. state of Oregon. Beginning at the crest of the Tualatin Mountains, the creek flows generally east down a canyon along Northwest Cornell Road in unincorporated Multnomah County and through the Macleay Park section of Forest Park, a large municipal park in Portland. At the lower end of the park, the stream enters a pipe and remains underground until reaching the river. Danford Balch, after whom the creek is named, settled a land claim along the creek in the mid-19th century. After murdering his son-in-law, he became the first person legally hanged in Oregon.

<span class="mw-page-title-main">Coast Range (EPA ecoregion)</span> Coastal ecoregion in the Western United States

The Coast Range ecoregion is a Level III ecoregion designated by the Environmental Protection Agency (EPA) in the U.S. states of Washington, Oregon, and California. It stretches along the Pacific Coast from the tip of the Olympic Peninsula in the north to the San Francisco Bay in the south, including Grays Harbor, Willapa Bay, and the Long Beach Peninsula in Washington, the entire length of the Oregon Coast, and the Northern California Coast. Named for the Coast Range mountains, it encompasses the lower elevations of the Olympic Mountains, the Oregon Coast Range, the Californian North Coast Ranges, and surrounding lowlands.

<span class="mw-page-title-main">Cascades (ecoregion)</span> Temperate coniferous forests ecoregion of the United States

The Cascades ecoregion is a Level III ecoregion designated by the United States Environmental Protection Agency (EPA) in the U.S. states of Washington, Oregon, and California. Somewhat smaller than the Cascade mountain range for which it is named, the ecoregion extends north to Snoqualmie Pass, near Seattle, and south to Hayden Pass, near the Oregon-California border, including the peaks and western slopes of most of the High Cascades. A discontiguous section is located on Mount Shasta in California.

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<span class="mw-page-title-main">Blue Mountains (ecoregion)</span> Temperate coniferous forests ecoregion of the United States

The Blue Mountains ecoregion is a Level III ecoregion designated by the United States Environmental Protection Agency (EPA) in the Pacific Northwest, mainly in the state of Oregon, with small areas over the state border in Idaho and southeastern Washington. It is also contiguous with the World Wildlife Fund's Blue Mountain forests ecoregion.

<span class="mw-page-title-main">Columbia Plateau (ecoregion)</span> Xeric shrubland ecoregion.of Canada and the United States

The Columbia Plateau ecoregion is a Level III ecoregion designated by the United States Environmental Protection Agency (EPA) encompassing approximately 32,100 square miles (83,139 km2) of land within the U.S. states of Washington, Oregon, and Idaho. The ecoregion extends across a wide swath of the Columbia River Basin from The Dalles, Oregon to Lewiston, Idaho to Okanogan, Washington near the Canada–US border. It includes nearly 500 miles (800 km) of the Columbia River, as well as the lower reaches of major tributaries such as the Snake and Yakima rivers and the associated drainage basins. It is named for the Columbia River Plateau, a flood basalt plateau formed by the Columbia River Basalt Group during the late Miocene and early Pliocene. The arid sagebrush steppe and grasslands of the region are flanked by moister, predominantly forested, mountainous ecoregions on all sides. The underlying basalt is up to 2 miles (3 km) thick and partially covered by thick loess deposits. Where precipitation amounts are sufficient, the deep loess soils have been extensively cultivated for wheat. Water from the Columbia River is subject to resource allocation debates involving fisheries, navigation, hydropower, recreation, and irrigation, and the Columbia Basin Project has dramatically converted much of the region to agricultural use.

<span class="mw-page-title-main">Snake River Plain (ecoregion)</span>

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<span class="mw-page-title-main">Willamette Valley</span> Valley in the Pacific Northwest region of the United States

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<span class="mw-page-title-main">Mississippi Alluvial Plain (ecoregion)</span> Ecoregion in the southern United States

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<span class="mw-page-title-main">Arkansas Valley (ecoregion)</span>

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References

  1. 1 2 3 4 Hoekstra, J. M.; Molnar, J. L.; Jennings, M.; Revenga, C.; Spalding, M. D.; Boucher, T. M.; Robertson, J. C.; Heibel, T. J.; Ellison, K. (2010). Molnar, J. L. (ed.). The Atlas of Global Conservation: Changes, Challenges, and Opportunities to Make a Difference . University of California Press. ISBN   978-0-520-26256-0.
  2. 1 2 3 4 5 PD-icon.svg This article incorporates public domain material from Thorson, TD; Bryce, SA; Lammers, DA; et al. Ecoregions of Oregon (PDF). United States Geological Survey. (color poster with map, descriptive text, summary tables, and photographs; with a Reverse side ).
  3. 1 2 3 4 5 PD-icon.svg This article incorporates public domain material from Pater, D; Bryce, SA; Kagan, J; et al. Ecoregions of Western Washington and Oregon (PDF). United States Geological Survey. (color poster with map, descriptive text, summary tables, and photographs; with a Reverse side ).
  4. "Willamette Valley forests". Terrestrial Ecoregions. World Wildlife Fund.