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Discover ecoregions

What is an ecoregion?

“Ecoregion” is one of those fancy words that can be very confusing. A widely accepted definition of ecoregion is the one used by the World Wildlife Fund:

An ecological region, or ecoregion, is a large area of land or water that contains a geographically distinct assemblage of natural communities that:

  • share a large majority of their species and ecological dynamics
  • share similar environmental conditions
  • interact ecologically in ways that are critical for their long-term persistence

Put simply, an ecoregion is a large area defined by the range of species or environmental conditions present.

Oregon ecoregions

This ecoregions map source is Oregon Ag In The Classroom.

We have two ecoregions in Clackamas County

Clackamas County contains part of two major ecoregions: the Cascades ecoregion, and the Willamette Valley ecoregion.

For more information

More information is available on these pages:

Cascades ecoregion

Zone 4 is the Cascades ecoregion

The Cascades ecoregion covers parts 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.

Detailed view of the Cascades ecoregion (zone 4)

The mountainous region is underlain by volcanic rock that has been affected by alpine glaciations. The eastern part of the region contains active and dormant volcanoes in the Cascades Volcanic Arc, with elevations of up to 11,239 feet (3,426 m).

The western Cascades are older, lower, and dissected by numerous, steep-sided stream valleys. The region has a moist, temperate climate, which supports an extensive and highly productive coniferous forest that is intensively managed for logging, as well as recreational use. Subalpine meadows occur at higher elevations. (Source: Wikipedia)

The following table contains technical descriptions drawn from CEC Level III descriptions (document available below) produced for the EPA.

 TECHNICAL DESCRIPTIONWHAT IT MEANS
LOCATIONStretches from the central portion of western Washington, through the spine of Oregon, and includes a disjunct area around Mt. Shasta in northern California.Mainly covers the mountainous region from the middle of Washington State through the Oregon Cascade range.
CLIMATEThe ecoregion has a mild to severe mid-latitude climate, varying by elevation, with mostly dry warm summers and relatively mild to cool very wet winters. The mean annual temperature ranges from approximately -1°C to 11°C. The frost-free period ranges widely from 5 to 180 days depending on elevation and latitude. The mean annual precipitation is 1824 mm, ranging from 1150 mm to 3600 mm. Average temperatures range from 30°F to 52°F. Average annual precipitation is 72 inches, ranging from 45 inches to 142 inches a year.
VEGETATIONExtensive and highly productive coniferous forests. At lower elevations, Douglas-fir, western hemlock, western red cedar, big leaf maple, red alder. At higher elevations, Pacific silver fir, mountain hemlock, subalpine fir, noble fir, lodgepole pine. To the south, Shasta red fir, white fir. Subalpine meadows and rocky alpine zones occur at highest elevations.This region is known for producing a lot of trees! Trees with needle-like leaves dominate this landscape. Lower, warmer parts of this zone have Douglas fir, western hemlock, western red cedar, big leaf maple and red alder trees. Higher, colder elevations have Pacific silver fir, mountain hemlock, subalpine fir, noble fir, and lodgepole pine. At the highest elevations you'll find meadows and rocky landscapes.
HYDROLOGYMany intermittent and perennial streams in a dense drainage network; many alpine lakes; some large reservoirs at lower elevations. Water quality is high.Some streams in the Cascades ecoregion flow only part of the year, and some flow all year. There are many streams and at high elevations there are many lakes. Artificial lakes behind dams exist at lower elevations in the region. Water quality is good.
TERRAINThis mountainous ecoregion is underlain by Cenozoic volcanics and has been affected by alpine glaciations. It is characterized by steep ridges and river valleys in the west, a high plateau in the east, and both active and dormant volcanoes. Elevations range from about 250 meters upwards to 4,390 meters. Soils are mostly cryic and frigid temperature regimes, with some mesic at low elevations and in the south. Andisols and Inceptisols are common.The Oregon Cascades are composed of rocks as old as 3.5 million years. Glaciers in the highest regions have carved various small basins, valleys, and left behind steep peaks and ridges. Steep landscapes dominate the western side of the Cascades and a high plateau dominates the eastern slope. Active and dormant volcanoes are common. Elevations range from about 820 feet above sea level to 14,403 feet. Soils range from very cold soils churned by frost to medium-textured well-drained soils.
WILDLIFERoosevelt elk, black-tailed deer, black bear, mountain goats in the north, cougar, coyote, beaver, river otter, mountain quail, pileated woodpecker, northern goshawk, mountain chickadee, northern spotted owl, chinook salmon, steelhead trout, bull trout.Roosevelt elk, black-tailed deer, black bear, mountain goats in the north, cougar, coyote, beaver, river otter, mountain quail, pileated woodpecker, northern goshawk, mountain chickadee, northern spotted owl, chinook salmon, steelhead trout, bull trout.
LAND USE/HUMAN ACTIVITIESForestry, recreation, water supply for urban and agricultural areas in adjacent lowland ecoregions, a few areas of ranching and livestock grazing. Large areas are in public lands (national forests, national parks) and population density is relatively low. No cities occur in the region. Larger towns include Stevenson, Cascade Locks, and Oakridge.Forestry, recreation, water supply for urban and agricultural areas in adjacent lowland ecoregions, a few areas of ranching and livestock grazing. Large areas are in public lands (national forests, national parks) and population density is relatively low. No cities occur in the region. Larger towns include Stevenson, Cascade Locks, and Oakridge.

Download the U.S. EPA source document for the technical descriptions quoted above: CEC_LEVEL_III_Descriptions_US_May2010

Willamette Valley ecoregion

The Willamette Valley is an amazing place, with a rich geologic history, great soil, a moderate climate, and abundant water.

Zone 3 is the Willamette Valley ecoregion

The U.S. Environmental Protection Agency has designated the Willamette Valley ecoregion as a Level III ecoregion. It is slightly larger than the Willamette Valley for which it is named. The Willamette Valley ecoregion has less precipitation and lower elevations than neighboring mountainous ecoregions.

Willamette Valley ecoregion

Historically, the region contained 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. (Source: Wikipedia.)

The following table contains technical descriptions drawn from CEC Level III descriptions (document available below) produced for the EPA.

 TECHNICAL DESCRIPTIONWHAT IT MEANS
LOCATIONThe ecoregion covers an area of 14,900 square kilometers (5,800 sq mi), 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.Covers the Willamette Valley in Oregon and a small area in southern Washington State.
CLIMATEThe ecoregion has a Mediterranean-type climate, with warm, dry summers and mild, but wet winters. The mean annual temperature is approximately 10 to 13 degrees Centrigrade. The frost-free period ranges from 165 to 210 days. The mean annual precipitation is 1228 mm, ranging from 900 mm to 1600 mm in the mountainous foothills. Average temperatures range from 50°F to 55°F. The frost-free season is five to seven months long. Average annual precipitation is 48 inches, ranging from 35 to 63 inches.
VEGETATIONMosaic of oak savanna, oak woodlands, prairies, and Douglas-fir forests. Oregon white oak, Douglas-fir, madrone, some valley ponderosa pine are typical. Riparian areas with black cottonwood, oregon ash, bigleaf maple, Douglas-fir, western red cedar, and various shrubs. Almost all of the native prairies have been converted to other uses. The Willamette Valley is a very important crop-growing area. Clearing of forests have changed the composition of this landscape, with pockets of remnant forest still occurring scattered across the landscape. Many native prairies have been converted to farming and housing.
HYDROLOGYLarge rivers, numerous streams from adjacent mountainous regions. Numerous seasonal wetlands and ponds. A few reservoirs.Surface water is dominated by rivers and streams, plus seasonal wetlands and ponds.
TERRAINMostly a rolling, broad, lowland valley. Elevations range from about 6 m to over 600 m on higher peaks. Landforms consist of terraces and floodplains that are interlaced and surrounded by rolling hills. Relatively deep alluvium, colluvium, and glacio-lacustrine deposits overlie Miocene volcanic basalt and marine sandstone. Soils are productive, have a mesic temperature regime, and a variety of texture and moisture characteristics. Mollisols and Alfisols are typical in the valley with some Ultisols and Alfisols in the foothills.The Willamette Valley is a rolling, broad, lowland valley. Elevations are low, as is topographic relief in the valley. Landforms are old terraces and floodplains. Deep soils and gravels cap volcanic basalts and old ocean sediments. Soils are productive.
WILDLIFEBlack-tailed deer, red fox, coyote, racoon, striped skunk, beaver, Oregon and grey-tailed vole, red-tailed hawk, Cooper’s hawk, Canada geese, mallard and northern pintail ducks, great blue heron, white-breasted nuthatch, chipping sparrow, a variety of amphibians and reptiles.Black-tailed deer, red fox, coyote, racoon, striped skunk, beaver, Oregon and grey-tailed vole, red-tailed hawk, Cooper’s hawk, Canada geese, mallard and northern pintail ducks, great blue heron, white-breasted nuthatch, chipping sparrow, a variety of amphibians and reptiles.
LAND USE/HUMAN ACTIVITIESProductive soils and a temperate climate make it one of the most important agricultural areas in Oregon. Vegetables, fruits, nut orchards, nursery products, and grass seed production are typical. Vineyards and Christmas tree farms are common in the foothills. Some sheep and cattle grazing. Urban, suburban, and rural residential uses are spreading. It contains most of Oregon’s population, with larger cities including Portland, Gresham, Beaverton, Hillsboro, Salem, Albany, Corvallis, Eugene, and Springfield. Productive soils and a temperate climate make it one of the most important agricultural areas in Oregon. Vegetables, fruits, nut orchards, nursery products, and grass seed production are typical. Vineyards and Christmas tree farms are common in the foothills. Some sheep and cattle grazing. Urban, suburban, and rural residential uses are spreading. It contains most of Oregon’s population, with larger cities including Portland, Gresham, Beaverton, Hillsboro, Salem, Albany, Corvallis, Eugene, and Springfield.

Download the U.S. EPA source document for the technical descriptions quoted above: CEC_LEVEL_III_Descriptions_US_May2010