Chapter 12
Ecological Subregions of the United States



Alaska Range Humid Tayga - Tundra - Meadow

Two Sections have been delineated in this Province: These Sections are located in southern Alaska, partly bordering Canada. The area of these Sections is about 61,000 mi2 (158,000 km2).

Section M135A--Alaska Mountains

Geomorphology. This Section consists of steep, rugged mountain ridges separated by broad valleys. Elevation ranges from 1,640 ft (500 m) in valleys to greater than 13,125 ft (4,000 m) on mountain peaks. Mount McKinley is about 20,320 ft (6,200 m).

Lithology and Stratigraphy. The Section comprises fragments of deep ocean floor rock, as well as continental fragments of Peninsular, Kahiltna, and Wrangellia terranes. These are early Mesozoic to Cenozoic assemblages with very complex morphology.

Soil Taxa. The dominant soils are Aquepts, Orthents, Umbrepts, and Ochrepts, all having pergelic or cryic temperature regimes. About two-thirds of the area has no soil.

Potential Natural Vegetation. A substantial portion of the area is barren of vegetation. Where vegetation exists, alpine and moist tundra communities of prostrate plants predominate. Riparian spruce-hardwood forests occur infrequently at low elevations.

Fauna. Pigmy shrews are present in dry, forested habitats. Pikas are common in the alpine areas. Dall sheep occur throughout the mountainous areas of this Section. Gray wolves are abundant and wolverines are relatively common. This Section has relatively high brown bear densities for interior habitats. The Nelchina caribou herd ranges through this Section. Lake trout are commonly found in the deep, oligotrophic lakes in this Section.

Climate. Average annual precipitation ranges from 10 to 60 in (250 to 1,520 mm). Average annual temperature ranges from 22 to 33 oF (-6 to 1 oC). Freezing conditions may occur year around.

Water Characteristics. Extensive systems of valley glaciers occur at high elevations. Permafrost is discontinuous. Streams are swift and braided, often originate from glaciers, and carry heavy sediment loads. Lakes are more numerous in the southern portion of the area. Soils on lower slopes and in valleys over permafrost are typically poorly drained. Wetlands occupy 7 percent of the area.

Disturbance Regimes. Occurrence of wildfire is low. Snow avalanches are frequent in the winter.

Land Use. Human use of the area is minimal, mainly consisting of hunting and fishing.

Cultural Ecology. Tanaina and Ahtna Athabaskans historically roamed this Section.

Compiled by Alaska Region


Section M135B--Wrangell Mountains

Geomorphology. This Section, comprised of steep, rugged mountains of volcanic origin, is extensively covered by ice fields and glaciers. Elevation ranges from 1,970 to about 16,400 ft (600 to 5,000 m).

Lithology and Stratigraphy. This Section consists of island-arc volcaniclastic assemblages associated with other Cenozoic rocks. Portions are underlain by Wrangellia terrane.

Soil Taxa. Since much of the area consists of steep rocky slopes, ice fields, and glaciers, soils are infrequent and generally thin and stony. Principal soils include Lithic Cryorthents, Typic Cryorthents, Pergelic Cryochrepts, and Pergelic Cryumbrepts.

Potential Natural Vegetation. Most areas are barren of vegetation. Where vegetation occurs, alpine tundra communities of prostrate shrubs, forbs, grasses, and lichens predominate.

Fauna. Trumpeter swans nest in the river valleys, as do widgeons, lesser scaups, and greater scaups. Some of the best habitat for Dall sheep in Alaska occurs in this Section. Gray wolves are also abundant. Grayling occur in clear-water streams.

Climate. Average annual precipitation ranges from 10 to 60 in (250 to 1,525 mm). Average annual temperature ranges from 22 to 30 oF (-6 to -1 oC). Killing frost can occur any time of the year.

Surface Water Characteristics. Ice fields and glaciers are abundant throughout the area. Permafrost is discontinuous. Glacier streams radiate from the area. Lakes are few, and wetlands cover 7 percent of the area.

Disturbance Regimes. Wildfires are almost nonexistent. Snow avalanches are frequent in the winter.

Land Use. Some mining has been conducted in the past. Subsistence and recreational activities presently occur.

Cultural Ecology. Upper Tanana and Ahtna Athabaskans reside here.

Compiled by Alaska Region.