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 Mesic Herbaceous Meadow (CES204.163), Alaskan Pacific Maritime Alder-Salmonberry Shrubland (CES204.152) (NatureServe 2015)

Biophysical Settings: Alaskan Pacific Maritime Mesic Herbaceous Meadow (BpS 7816530), Alaskan Pacific Maritime Subalpine Alder-Salmonberry Shrubland (BpS 7816520) (LANDFIRE 2009)

Alaska Natural Heritage Program Landcover Class: Herbaceous (Mesic): Alpine and Subalpine Mesic Herbaceous, Low-Tall Shrub: Alder-Salmonberry (Boggs et al. 2016)

Alaskan Vegetation Classification: Mesic Sedge-Grass Meadow Tundra, Mesic Sedge-Herb Meadow Tundra, Closed Tall Alder Shrub (Viereck et al. 1992)

Ecological site concept

Subalpine Mosaic Gravelly Slopes ecological sites occur on subalpine mountain slopes on creep landforms (Boggs et al. 2016). The soils are well-drained, shallow, and stony, formed in colluvium, residuum, or glacial till (Viereck et al. 1992; Boggs et al. 2008; LANDFIRE 2009; Boggs et al. 2016; NatureServe 2018).

The reference vegetation on this ecological site is defined by a mosaic of tall shrubs and herbaceous vegetation. The tall shrub component of the mosaic is primarily composed of Sitka alder (Alnus viridis (Chaix) DC. ssp. sinuata (Regel) Á. Löve & D. Löve) and salmonberry (Rubus spectabilis Pursh). The herbaceous meadow component is very diverse, with no single dominant species. Commonly reported species include beauverd spiraea (Spiraea stevenii (C.K. Schneid.) Rydb.), spreading woodfern (Dryopteris expansa (C. Presl) Fraser-Jenkins & Jermy), and bluejoint (Calamagrostis canadensis (Michx.) P. Beauv.) (Viereck et al. 1992; Boggs et al 2016). Snow avalanche, freeze-thaw action, and soil creep are the primary disturbance regimes of Subalpine Mosaic Gravelly Slopes (LANDFIRE 2009; Boggs et al. 2016).

Associated sites

Similar sites

Table 1. Dominant plant species