135 Coastal Trough Humid Tayga Province

Cook Inlet-Susitna lowland, Copper River lowland, 15,700 mi2 (40,700 km2)


Land-surface form.--This province includes smooth and irregular plains surrounded by high mountains. Cook Inlet is level to rolling, with areas of ground moraine and stagnant ice topography, drumlin fields, eskers, and outwash plains. Most of the lowland is less than 500 ft (150 m) above sea level, with a local relief of 50-250 ft (15-80 m). The Copper River lowland is a broad basin of rolling to hilly moraines and nearly level alluvial plains on the site of a Pleistocene glacial lake. With an altitude of 1,000-2,000 ft (300-600 m), it is trenched by the Copper River and its tributaries, which form steep-walled canyons 100-500 ft (30-150 m) deep.

Climate.--Although the climate is subarctic, it is less severe than the interior of Alaska, because the region is sheltered by the Alaska Range to the north. Proximity to the Gulf of Alaska makes the climate transitional to the marine climates to the south. Average annual temperatures range from 32 to 39F (0 to 4C), with a winter average of about 5F (-15C) and summer maximums of about 64F (18C). Average annual precipitation ranges from 10 to 18 in (260 to 460 mm). Annual snowfall averages from 4 to 10 in (100 to 260 mm).

Vegetation.--Throughout the Cook Inlet lowlands, lowland spruce-hardwood forests are abundant. Bottom land spruce-poplar forest adjoins the larger river drainages, along with thickets of alder and willow. Wet tundra communities exist along the Cook Inlet coastline. The Copper River lowland is characterized by black spruce forest interspersed with large areas of brushy tundra. White spruce forests occur on southfacing gravelly moraines, and cottonwood-tall bush communities are common on large floodplains.

Soils.--Spodosols are the principal upland soils in the Cook Inlet. Inceptisols are dominant in the Copper River lowland.

Fauna.--The diversity of habitats in this province supports a large variety of species. Muskrats and red foxes abound, moose flourish in lowland areas, and Dall sheep are frequently seen in the uplands. Black bear populations are dense throughout the region.

Trumpeter swans nest here, and tundra swans are present during migration.

King, sockeye, and silver salmon are common or abundant.