This coastal forest system, primarily Sitka spruce and western hemlock, is an extension of the rainbelt forests so important along the Pacific coast. Timberline varies from about 1,000 ft. (300 m.) in the Yakataga area to 2,000 ft. (600 m.) near Prince William Sound, more than 500 ft. (150 m.) near Cook Inlet and on Afognak Island, and little more than sea level on Kodiak Island and farther west on the Alaska Peninsula.

West of Cook Inlet, Sitka spruce dominates within this forest and is the lone native conifer on Kodiak and Afognak Islands. Mountain hemlock begins to replace western hemlock in the Cook Inlet area. The deciduous hardwoods present are found primarily on stream floodplains.

This forest requires cool temperatures, high humidity, and abundant rainfall. Soil types and conditions vary greatly throughout the forest. This vegetation type generally occurs in areas where permafrost is absent.

This tall, relatively dense forest system primarily contains white spruce, locally mixed with large cottonwood and balsam poplar, found on level to nearly level floodplains, low river terraces, and more deeply thawed south-facing slopes. This forest type is generally not found at elevations higher than 1,000 ft. (300 m.). Both black cottonwood and balsam poplar quickly invade floodplains and grow rapidly. Alaska paper birch and quaking aspen are often conspicuous. These species are, in turn, replaced by white spruce in the successional process. Where this type occurs, a deep thawed layer overlies the permafrost which controls the depth of roots. Extensive stands of this timber type are found in the Susitna and Copper River valleys.

This is a fairly dense, mixed forest composed of white spruce, Alaska paper birch, quaking aspen, black cottonwood, and balsam poplar. Because of extensive burns during the past 100 years, large areas of this system are generally found on higher portions of the interior valleys in the Gulf of Alaska subregion, and on the more deeply thawed, well-drained southerly slopes at lower to mid-elevations and on bench lands in the Cook Inlet subregion. This timbered zone extends from sea level near Eklutna to more than 3,500 ft. (1,100 m.) in elevation in eastern portions of the region with the treeline descending east to west.

In the interior eastern highlands, soils supporting the dominant species are well-drained, shallow to moderately deep gravelly loams, and silt loams. Black spruce occupies sites with poor drainage. Such high water tables result from water catchment basins in uneven terrain and from the presence of permafrost, particularly on north-facing slopes. Pure stands of white spruce and mixed stands of black cottonwood and balsam poplar are likely to occur along streams. Combined stands, including these species and birch and aspen but excluding black spruce, are commonly found on well-drained, south-facing slopes. Hot, dry summers limit moisture on such sites and inhibit growth. Following fire, birch commonly invades on east- and west-facing slopes, with quaking aspen following willow stages on most south-facing slopes (Lutz 1956). These young trees and associated shrubs provide especially good moose browse for several years following fires.

This is a dense-to-open lowland forest of evergreen and deciduous trees, including pure stands of black spruce. It usually occurs on areas of shallow peat, glacial deposits, outwash plains, and on north-facing slopes. The upper valleys of the Copper and Susitna Rivers and on the Kenai Peninsula sustain extensive stands. Open forest stands with lichens provide excellent winter range for caribou. Willows and other brush species furnish shelter and browse for moose.

The dominant species in these dense-to-open deciduous brush systems range from dense willows along streams to dense alder above timberline. The type occurs between beach and forest, between treeline and alpine tundra, in avalanche paths through forests, on floodplains, and in old forest burn areas. Trees, such as quaking aspen, Alaska paper birch, and white spruce may be present but are widely scattered. The high brush system occupies a great variety of soils—from poorly drained with permafrost in low river valleys to well-drained shallow upland soils on moraines. It is also found on outwash and mountain slope soils with intermittent permafrost. A coastal alder thicket subsystem extends along the southern portion of the Alaska Peninsula and eastern Cook Inlet. Extensive portions of Kodiak Island support this plant type. Species composition varies considerably with location. Floodplain thickets comprise another subsystem that develops quickly on periodically flooded river and stream alluvium. Such stands may reach 20 ft. (six m.) in heiqht. In interior portions of the region, particularly along parts of the Susitna and Copper River valleys and in the Mentasta Mountains, a birch-alder-willow thicket type is found near timberline. Areas where fires are common frequently support this type. Thickets may be as high as five ft. (1.5 m.) to 15 ft. (five m.).

Many animals use this type for at least part of the year.

Dwarf shrubs usually dominate over a mat of sedges, mosses, and lichens. Ponds or standing water are often present in the peaty substrate. This type is found in wet, flat basins where conditions are frequently too moist for tree growth. Two different forms of this system, coastal muskegs and interior bogs, exist in Southcentral Alaska. In the coastal muskegs, western hemlock and Alaska cedar are commonly scattered over the drier portions of muskeg, with shrubs dominant on exposed and dry sites. Such associations are found on the Kenai Peninsula and in drainages bordering upper Cook Inlet. In the interior bogs of the boreal forest, trees are usually not found because conditions are too wet. Large localized patches of cottongrass tussocks may exist in such places. These bogs occur primarily in the Susitna and Copper River valleys.

Most of the larger mammals use this type only intermittently, but it is an important type for waterfowl.

This low-growing type usually forms a complete ground cover and is extremely productive during the growing season. Composition varies from almost continuous cottongrass, with a sparse growth of sedges and dwarf shrubs, to stands where dwarf shrubs dominate. This type is generally characterized by cottongrass tussocks. Underlying soils vary from wet, shallow, and loamy with thin peat layers on upper slopes to deep, wet, clayey soils with peat in the Copper River lowlands. This system is found primarily along the Denali Highway and in the eastern foothills of the Talkeetna Mountains.

Dominant vegetation is sedge and cottongrass, usually occurring as a mat rather than as tussocks. A few woody and herbaceous plants occur on drier sites above the water table. Rooted aquatic plants occur along shorelines and in shallow lakes. This type occupies tide flats and areas of little topographic relief near sea level.

Wet tundra occurs mainly on the Copper River delta and numerous smaller deltas of upper Cook Inlet. Soils in the latter area are primarily peat. Limited activity of soil organism due to cold temperatures reduces peat decomposition and there is little accumulation of vegetable matter.

This type is the most important waterfowl habitat and is a major nesting ground of the trumpeter swan, Olor buccinator, and the dusky Canada goose, Branta canadensis occidentalis. The latter nests only on the Copper River delta.

This type is composed mostly of low mat pIants, both herbaceous and shrubby, and is typically found on rock and rubble of mountains above 2,500 ft. (800 m.). It occurs on all the higher mountains of the Region, usually above the forest and brush systems. White mountain avens may cover entire ridges and slopes in the Alaska Range. Regeneration (plant growth) is often extremely slow following damage by fire, mechanical disturbance, or by over-grazing. Some lichens may require more than 60 years to fully recover.

Alpine tundra is of prime importance to Dall sheep and mountain goat in the Southcentral Region.