Natural Resources
Conservation Service
Ecological site R220XY361AK
Subalpine Shrub Dry Flood Plain
Last updated: 6/20/2019
Accessed: 11/21/2024
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
The Southern Alaska Coastal Mountains (MLRA 222) encompasses the Pacific Border Ranges and Coast Mountains physiographic provinces (Wahrhaftig 1965). Spanning approximately 26,355 square miles, the elevation ranges from sea level at the base of glaciers and ice fields to 18,008 feet at Mt. St. Elias. The MLRA was covered by glacial ice during the Pleistocene epoch, a time period spanning from 2.6 million to 11,700 years ago. During interglacial periods glacial extent was reduced, leaving behind various glacial deposits. Over time these deposits have been eroded or buried by colluvium and slope alluvium, which now covers more than 90 percent of the unglaciated landscape. 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-NRCS 2006).
This landscape lies in the true alpine zone where glacial ice is, and has been, the dominant ground cover. Glacial ice encompassed all the MLRA during the Late Wisconsinan glaciation, 25,000 – 21, 000 years ago (Kauffman et al. 2011). Changes in climatic conditions following this period resulted in the recession of some glaciers and slowly exposed new surfaces for inhabitation by terrestrial ecosystems. Pioneer plant communities began to establish on the new substrate within the first 30 years and consisted mostly of evergreen, herbaceous dwarf shrubs with some pockets of low shrubs. These communities quickly transitioned to tall shrubs within 100 years of deglaciation. By approximately 13,000 years ago, four stable plant communities emerged across the non-glaciated landscape – ericaceous dwarf shrub, low shrub, tall shrub, and herbaceous communities – and form the present-day ecosystems (Boggs et al. 2010).
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
Subalpine Scrub Gravelly Drainageway ecological sites occur on low order streams in high-elevations (LANDFIRE 2009; NatureServe 2018). The soils are formed in alluvium and are a mixture of silt, sand, gravel, and cobbles (Boggs et al. 2008).
The reference vegetation on this ecological site is defined by tall shrubs. Sitka alder (Alnus viridis (Chaix) DC. ssp. sinuata (Regel) Á. Löve & D. Löve) and feltleaf willow (Salix alaxensis (Andersson) Coville) are the dominant species. Flooding is the primary disturbance factor of Subalpine Scrub Gravelly Drainageways (LANDFIRE 2009; NatureServe 2018).
Associated sites
R220XY358AK |
Subalpine Scrub Gravelly Dry Slopes Occur adjacent to R222XY361AK on a higher landscape positions |
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R222XY360AK |
Alpine Herbaceous Wet Organic Depressions Occur at the headwaters of and within riparian zones associated with R222XY361AK |
Similar sites
R220XY358AK |
Subalpine Scrub Gravelly Dry Slopes The tall shrub component of the mosaic is similarly dominated by Sitka alder, but the site occurs on creep landforms |
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R220XY349AK |
Subalpine Scrub Gravelly Dry Chutes The site is similarly dominated by Sitka alder, but dwarf shrubs and herbs are prominent ground covers |
Table 1. Dominant plant species
Tree |
Not specified |
---|---|
Shrub |
(1) Alnus viridis ssp. sinuata |
Herbaceous |
Not specified |
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