Natural Resources
Conservation Service
Ecological site R220XY361AK
Subalpine Shrub Dry Flood Plain
Last updated: 3/10/2025
Accessed: 03/31/2025
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): 220X–Alexander Archipelago-Gulf of Alaska Coast
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, 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).
While both alpine and subalpine plant communities characterize the vegetation in this area, most of the unglaciated terrain in this region is in the true alpine zone. 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).
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
USFS Ecoregion Province: Marine Mountains (M240), Forest-Meadow High (M242b) (Bailey 2007)
U.S. EPA Level III Ecoregion: Pacific Coastal Mountains (119) (Gallant et al. 2010)
National Vegetation Classification – Ecological Systems: Alaskan Pacific Maritime Alpine Floodplain (CES204.161) (NatureServe 2015)
Biophysical Settings: Alaskan Pacific Maritime Alpine Floodplain (BpS 7716760) (LANDFIRE 2009)
Alaska Natural Heritage Program Landcover Class: Low-Tall Shrub: Willow Shrubland (Boggs et al. 2016)
Alaskan Vegetation Classification: Tall Alder-Willow Shrub, Mesic Sedge-Grass Meadow Tundra, Sedge-Willow Tundra (Viereck et al. 1992)
Ecological site concept
This site occurs on the flood plain of low-order, glacially fed streams at high elevations. Unvegetated gravel bars are common directly adjacent to the active stream channel. As distance from the stream channel increases, the flood plain becomes more vegetated. This site floods frequently (greater than 50 times in 100 years) to occasionally (5 to 50 times in 100 years). When flooded, soils are saturated. However, as flooding subsides, these soils drain and are dry for much of the growing season. As a result, the soils are considered somewhat poorly to moderately well drained. Flooding results in a patchwork of highly diverse vegetation that includes forb meadow, low shrub, and tall shrub communities.
The reference community is open tall scrub. Sitka alder and feltleaf willow are the dominant tall shrub species. Common understory species include netleaf willow, sprouting leaf willow, dwarf fireweed, and Nootka lupine (Landfire 2009).
Associated sites
| R220XY362AK |
Subalpine Sedge Wet Flood Plain Occurs on similar flood plains but on wetter, organic-rich soils. |
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Similar sites
| R220XY362AK |
Subalpine Sedge Wet Flood Plain Both sites occur on high elevation flood plain, however R220XY362AK occurs on wetter soils that have more wetland indicator species and fewer shrubs. |
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Table 1. Dominant plant species
| Tree |
Not specified |
|---|---|
| Shrub |
(1) Alnus viridis ssp. sinuata |
| Herbaceous |
(1) Chamerion latifolium |
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Ecosystem states
State 1 submodel, plant communities
| 1.1A | - | High-velocity flood |
|---|---|---|
| 1.2A | - | Flood recovery |