General information

Provisional. A provisional ecological site description has undergone quality control and quality assurance review. It contains a working state and transition model and enough information to identify the ecological site.

MLRA notes

Major Land Resource Area (MLRA): 222X–Southern Alaska Coastal Mountains

This area is in the Southern Alaska Region and includes the higher elevations of the Coast, St. Elias, Chugach, and Kenai Mountains. The area makes up about 26,335 square miles. The terrain consists of steep, rugged, high-relief mountains. Glaciers and ice fields make up about 54 percent of the area. Unglaciated portions of the area are deeply incised with narrow to broad valleys. Flood plains and stream terraces on valley floors rapidly give rise to steep alluvial fans and mountain footslopes. Elevation ranges from sea level at the base of tidewater glaciers and ice fields to 18,008 feet at the summit of Mt. St. Elias (USDA 2006).

During the Pleistocene epoch, the area was covered with glacial ice. As the glacial ice melted, sediments were deposited by the melting ice. However, most of the original glacial deposits have eroded away or have been buried by colluvium and slope alluvium, which covers more than 90 percent of the present unglaciated landscape. The remaining glacial and glaciofluvial deposits and recent fluvial deposits are generally restricted to the bottoms of the larger valleys. Paleozoic, Mesozoic, and Lower Tertiary stratified sedimentary rocks, and occasionally Paleozoic intrusive rocks, underlie much of the area and are exposed on steep mountain slopes and ridges (USDA 2006).

Miscellaneous (non-soil) areas make up more than 90 percent of this MLRA. The most common miscellaneous areas are rock outcrop, rubble land, avalanche chutes, and glaciers. The dominant soil orders in this area are Spodosols and Histosols. The soils in the area have a cryic soil temperature regime or a subgelic soil temperature class, a udic or aquic soil moisture regime, and mixed or amorphic mineralogy (USDA 2006).

Alpine plant communities characterize the vegetation in this area. Alpine vegetation consists of a variety of dwarf scrub and herbaceous communities. Low willow scrub is common in drainages. Lichens, scattered herbs, and dwarf shrubs dominate bedrock exposures and very shallow soils. In general, there is little or no plant growth at elevations above about 7,500 feet (USDA 2006). At lower elevations, subalpine vegetation consists of a variety of mountain hemlock and tall scrub communities. These subalpine plant communities typically occur at elevations between 1500 to 3000 feet (Boggs et al. 2010, Carstensen 2007, Jaques 1983; Martin et al. 1995) and are associated with the Alexander Archipelago-Gulf of Alaska Coast area (MLRA 220X).

The area is almost entirely undeveloped wild land. Remote wild-land recreation is the principal land use in this area. The rugged, high mountains, extensive glaciers and ice fields, and wilderness qualities of the area attract visitors from around the world. Small rural communities along the road system are the only permanent settlements. Part of the Wrangell-St. Elias Bay National Park and Preserve, the Glacier Bay National Park and Preserve, the Misty Fjords National Monument, the Chugach National Forest, and the Tongass National Forest are in this MLRA.

Classification relationships

National Vegetation Classification – Ecological Systems: Alaskan Pacific Maritime Alpine Dwarf Shrubland (CES204.310) (NatureServe 2015)

Biophysical Settings: Alaskan Pacific Maritime Herbaceous Dwarf Shrubland (BpS 7816430) (LANDFIRE 2009)

Ecological site concept

This alpine site occurs on moist and rocky soils on protected mountain slopes. The alpine is characterized as having very short growing seasons, cold temperatures, and high winds. The soils are somewhat poorly to moderately well drained with bedrock typically occurring within 20 inches. Protected slopes are prone to deep and persistent snowpack and occur on concave shaped slopes or colder northerly slopes. When compared to adjacent slopes in more exposed positions, the deeper snowpack results in comparatively warmer winter soil temperatures and a shorter growing season. These protected positions support a unique assemblage of highly adapted alpine vegetation, which is markedly different from plant communities on more protected positions of these mountain slopes.

The reference plant community is ericaceous dwarf scrub. Species diversity can be high with a diverse range of shrub, graminoid, and forb species. The most abundant shrub species are Alaska bellheather and partridgefoot. Other common species in late season snow beds include western moss heather, yellow mountainheath, and narcissus anemone (Jaques 1983).

Associated sites

Similar sites

Table 1. Dominant plant species