Natural Resources
Conservation Service
Ecological site F220XY350AK
Subalpine Woodlands Gravelly Dry Slopes
Last updated: 6/21/2019
Accessed: 11/13/2024
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.
Figure 1. Mapped extent
Areas shown in blue indicate the maximum mapped extent of this ecological site. Other ecological sites likely occur within the highlighted areas. It is also possible for this ecological site to occur outside of highlighted areas if detailed soil survey has not been completed or recently updated.
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 Subalpine Mountain Hemlock Woodland (CES204.143) (NatureServe 2015)
Alaskan Vegetation Classification: Mountain Hemlock Dwarf Tree Scrub (Viereck et al. 1992)
Ecological site concept
Subalpine Dwarf Tree Scrub Gravelly Slopes ecological sites occur on linear to concave mountain slopes with severe exposure to wind (Viereck et al. 1992). The soils are gravelly Spodosols that are well-drained and very shallow to shallow, formed in colluvium over weathered residuum.
The reference vegetation on this ecological site is defined by stunted trees and dwarf shrubs. Mountain hemlock (Tsuga mertensiana (Bong.) Carrière) is the dominant tree on the site, and black crowberry (Empetrum nigrum L.) and bunchberry dogwood (Cornus canadensis L.) are the dominant dwarf shrubs. Commonly observed lichen species include star reindeer lichen (Cladina stellaris (Opiz) Brodo) and greygreen reindeer lichen (Cladina rangiferina (L.) Nyl.). The primary disturbance processes that maintain this plant community are exposure to cold temperatures, wind, avalanches, fungal pathogens, and blowdown (NatureServe 2018).
Associated sites
| R220XY349AK |
Subalpine Scrub Gravelly Dry Chutes Occurs on avalanche chutes in the subalpine life zone |
|---|---|
| F220XY205AK |
Subalpine Woodlands Gravelly Moist Slopes Occurs on a slightly higher landscape position |
Table 1. Dominant plant species
| Tree |
(1) Tsuga mertensiana |
|---|---|
| Shrub |
(1) Empetrum nigrum |
| Herbaceous |
(1) Cladina |
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