Chapter 9
Ecological Subregions of the United States



Coastal Trough Humid Tayga

Two Sections have been delineated in this Province:

The area of these Sections, which are located in south-central Alaska, is about 15,700 mi2 (40,700 km2).

Section 135A--Cook Inlet Lowlands

Geomorphology. A level-to-rolling surface derived mainly through glacial events (ground moraine, drumlin fields, eskers, and outwash plains). Elevation ranges from sea level to 500 ft (150 m).

Lithology and Stratigraphy. Alluvial fan and uplifted continental shelf deposits of Tertiary age dominate.

Soil Taxa. Soils are fairly diverse and include Haplocryands, Andic Haplocryods, and Andic Humicryods. Sphagnic Borofibrists, Terric Borosaprists, and Typic Borohemists occur in poorly drained depressions.

Potential Natural Vegetation. Lowland black spruce forests are abundant. Bottomland spruce-poplar forests are adjacent to larger river drainages, along with thickets of alder and willow. Some wet tundra communities exist along the Cook Inlet coastline.

Fauna. The diversity of habitats in this Section results in the presence of a large number of species. Trumpeter swans nest in the Kenai Peninsula. During migration, tundra swans occur throughout the Section. The Cook Inlet Lowlands are within the range of the pigmy shrew and northern water shrew in Alaska. Muskrats and red foxes are abundant in the northern portion of this Section. Red squirrels are abundant on the Kenai Peninsula. Moose are numerous in the lowland portions and Dall sheep are frequently seen in the uplands. Caribou were extirpated on the Kenai Peninsula about 1913 and were reintroduced in the mid 1960's. Black bear populations are dense throughout the Section. King, sockeye, and silver salmon are common to abundant. Wood frogs have been reported here. Dolly Varden and white fish occur in fresh waters throughout the Section.

Climate. Average annual precipitation ranges from 12 to 32 in (300 to 810 mm). Average annual temperature ranges from 27 to 37 oF (-3 to 3 oC). The growing season extends from approximately May 10 to September 30. Average freeze-free period is 110 to 150 days.

Surface Water Characteristics. Numerous small lakes and depressional bogs occur in areas of stagnant ice topography and on ground moraines. The Section is generally free of permafrost. Wetlands occupy over 25 percent of the area.

Disturbance Regimes. Wildfire occurrence is low.

Land Use. This section is heavily populated, and substantially affected by agriculture, urban development, petroleum extraction, and human recreation.

Cultural Ecology. Historically occupied by Tanaina Athabaskans, a variety of cultures now reside in this heavily developed section.

Compiled by Alaska Region.


Section 135B--Copper River Basin

Geomorphology. The area is a broad basin of rolling-to-hilly moraines and nearly level alluvial plains that occupy the site of a Pleistocene glacial lake. Most rivers originate from glaciers located in the surrounding mountains. Elevation ranges from 1,380 to 2,950 ft (420 to 900 m).

Lithology and Stratigraphy. Post-accreted deposits of Tertiary and Quaternary age predominate (e.g., alluvial fan and upland basin fill).

Soil Taxa. Most soils are Aquepts, formed in pergelic temperature and aquic moisture regimes. Specifically, Histic Pergelic Cryaquepts, Aquic Cryochrepts, Typic Cryochrepts, Pergelic Cryaquolls, and Typic Cryoborolls predominate. Soils generally formed in clayey to silty glaciolacustrine sediments over gravelly glacial drift.

Potential Natural Vegetation. Open black spruce forests interspersed with large areas of brushy tundra characterize this Section. White spruce forests occur on south-facing, gravelly moraines, whereas cottonwood-tall bush communities are found on large floodplains.

Fauna. Ruffed grouse occur throughout the low elevation, forested habitats. The range of the Nelchina caribou herd encompasses this Section. For interior habitats, relatively high populations of black and brown bears live here. A comparatively high density of wolverines also occurs in this Section. Sockeye salmon is the major anadromous fish present; minor numbers of king salmon also occur. Arctic grayling and burbot are found in the lakes and streams throughout this Section.

Climate. Average annual precipitation ranges from 10 to 20 in (250 to 500 mm). Average annual temperature ranges from 26 to 30 oF (-3 to -1 oC). The growing season consists of approximately 10 weeks of frost-free days during the summer.

Surface Water Characteristics. The overall drainage pattern is poorly defined, except for lower stretches of larger rivers. Permafrost is discontinuous over the area and thaw lakes are numerous. Morainal and abandoned melt-water channel lakes are frequent. Soils above permafrost are wet or moist throughout the summer. Wetlands occupy 36 percent of the area.

Disturbance Regimes. Flooding is probably the most important naturally-occurring disturbance in the area. Wildfire frequency is low.

Land Use. The area is used primarily for subsistence and recreational hunting and fishing.

Cultural Ecology. Ahtna Athabaskans reside in this Section.

Compiled by Alaska Region.