Chapter 26
Ecological Subregions of the United States

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Pacific Coastal Mountains Forest - Meadow

Three Sections have been delineated in this Province:

These Sections are located in southern and southeastern Alaska and partly border the Gulf of Alaska. The area of these Sections is about 40,000 mi2 (103,600 km2).

Section M244A--Chugach-St. Elias Mountains

Geomorphology. The Kenai, Chugach, and St. Elias Mountains form a rugged, crescent-shaped barrier along the coast of the Gulf of Alaska. High segments of the mountains are dominated by extremely rugged east-trending ridges. The entire range is heavily glaciated, and the topography is characterized by horns, aretes, cirques, and U-shaped valleys. The south coast is deeply indented by fjords and sounds, and the ridges extend southward as chains of islands. Elevation ranges from 330 to greater than 14,750 ft (100 to more than 4,500 m).

Lithology and Stratigraphy. This Section consists of Chugach terrane composed of near-shore oceanic rock of late Mesozoic age. The mountains are composed of chiefly metamorphosed slate and graywacke that have pronounced vertical cleavage that strikes parallel to the trend of the ridges. A belt of Paleozoic and Mesozoic schist, greenstone, chert, and limestone lies along the north edge of the mountains. All these rocks are cut by granitic intrusions.

Soil Taxa. Where not covered by glaciers, ice fields, and rock outcrops, soils have developed from glacial till and colluvium. Dominant soils are Lithic Cryorthents, Andic Cryumbrepts, Pergelic Cryumbrepts, Typic Cryumbrepts, Typic Haplocryods, Andic Humicryods, Humic Cryorthods, and Humic Lithic Cryorthods.

Potential Natural Vegetation. Most of the Section is either barren, ice-covered, or mantled with alpine tundra heath meadows. Some spruce-hardwood forests occur along the largest rivers.

Fauna. The alpine tundra vegetation in this Section provides habitat for a limited number of species. Surfbirds and rosy finches are uncommon breeders in this Section. Mountain goats utilize these high elevation habitats during the summer.

Climate. Average annual precipitation ranges from 12 to 160 in (300 to 4,060 mm). Average annual temperature ranges from 24 to 40 oF (-4 to 4 oC), depending on elevation and aspect. Killing frosts can occur any month of the year.

Surface Water Characteristics. Streams are short and swift, and headwater in glaciers. Lakes lie in ice-carved basins. Wetlands occupy less than 3 percent of the area.

Disturbance Regimes. Wildfire occurrence is low, whereas snow and rock avalanches are common.

Land Use. Permanent settlements are rare. Past mining perturbations are still detectable.

Cultural Ecology. Historic residents include Tanaina and Ahtna Athabaskans; Alutiiq Eskimos; Eyaks; and Tlingits.

Compiled by Alaska Region.

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Section M244B--Lynn Canal

Geomorphology. The area is dominated by rugged glaciated mountains with deep V-shaped and U-shaped valleys. Many of the bays have narrow borders of hilly moraines, with short flat-bottomed valleys at the head. Most slopes throughout the Section are steep. Elevation ranges from sea level to over 14,750 ft (4,500 m).

Lithology and Stratigraphy. The area consists of continental fragments of the Craig subterrane, composed of northwest-trending belts of Triassic to Mesozoic sedimentary, volcanic, and crystalline schist, gneiss, and granitic rocks.

Soil Taxa. Where not covered by glaciers, ice fields, and rock outcrops, soils have developed from glacial till and colluvium. Dominant soils are Lithic Cryorthents, Typic Cryumbrepts, Typic Haplocryods, Humic Cryorthods, and Humic Lithic Cryorthods.

Potential Natural Vegetation. Since the Section is partially modified by polar air masses, the prevailing vegetation is quite diverse. Forest vegetation dominated by western hemlock and Sitka spruce predominate in the low-lying areas up to 300 m in elevation. Mixed conifer, black cottonwood, and lodgepole pine forest types occur on drier inland sites. Low-growing alpine tundra vegetation of sedges and mosses prevails on sites above tree line.

Fauna. Bald eagles and marbled murrelets nest in forested areas. Red-breasted sapsuckers, Pacific-slope flycatchers, golden-crowned kinglets, and red and white-winged crossbills are common breeders. Blue grouse are found throughout the area. Northern water shrews are commonly present. Porcupines, river otters, and mink are found throughout the Section. Mountain goats occupy habitats from alpine to forested slopes. Sitka black-tailed deer occur throughout the Section. Moose live in habitats associated with the major river systems. Brown bears, black bears, and gray wolves occur in low numbers. Boreal toads occur in this Section. King salmon are associated with the major, mainland rivers. Pink salmon are the most numerous of the salmon species. Dolly varden are the most widely distributed resident fish.

Climate. Average annual precipitation ranges from 30 to 120 in (760 to 3,050 mm). Average annual temperature ranges from 33 to 41 oF (1 to 5 oC). The growing season is from May 15 to September 30. At higher elevations, killing frost can occur at any time of the year.

Surface Water Characteristics. Streams are short and swift and headwater in glaciers. Lakes lie in ice-carved basins. Wetlands occupy less than 3 percent of the area.

Disturbance Regimes. Due to the general steepness of the terrain, landslides and avalanches are common.

Land Use. Several small communities occur in this Section. Subsistence and recreational activities are the major land uses.

Cultural Ecology. This Section historically has been occupied by Tlingit Indians.

Compiled by Alaska Region.

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Section M244C--Boundary Range

Geomorphology. The area is dominated by rugged glacier-covered mountains or glaciated mountains with deep V-shaped and U-shaped valleys that straddle the international boundary with Canada. Most slopes throughout the Section are steep. Elevation ranges from sea level to over 9,840 ft (3,000 m).

Lithology and Stratigraphy. The Boundary Ranges are underlain mostly by massive granitic and gneissic rocks of the Coast Range batholith; a belt of schist and phyllite along its western margin and magmatized roof pendants within the batholith give a strong westwardly grain to the topography. Small fragments of the Taku terrane occur at the extreme western portions.

Soil Taxa. Where not covered by glaciers, ice fields, and rock outcrops, the soils have developed from glacial till and colluvium. Dominant soils are Lithic Cryorthents and Humic Lithic Cryorthods.

Potential Natural Vegetation. Most of the area is either barren, ice-covered, or covered by alpine heath meadows. Forest vegetation of hemlock and spruce occurs along river corridors within mountain passes.

Fauna. The alpine tundra vegetation in this Section provides habitat for a limited number of species. Mountain goats utilize these high elevation habitats during the summer.

Climate. Average annual precipitation ranges from 40 to 100 in (1,020 to 2,540 mm). Average annual temperature ranges from 39 to 43 oF (4 to 6 oC). Killing frost can occur at any time of the year.

Surface Water Characteristics. Streams are steep and fast flowing. A few small lakes lie in rock basins on valley floors and in mountainside hollows in the ice-free portions. Wetlands occupy less than 3 percent of the area.

Disturbance Regimes. Snow avalanches create large-scale vegetation disturbances. Wildfire is of little consequence.

Land Use. Human settlements and uses of the area are few.

Cultural Ecology. Historically this Section has been occupied by Tlingit Indians.

Compiled by Alaska Region.

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