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S12 Temperate to Polar Alpine & Tundra Vegetation Subclass

The U.S. National
Vegetation Classification
Type Concept Sentence: Alpine dwarf-shrublands, krummholz, forb meadows, grasslands, and cryptogam barrens occurring above treeline in temperate and boreal regions around the globe, predominantly in North America and Eurasia, with more isolated occurrences in the Southern Hemisphere. Polar tundra is dominated by dwarf-shrubs, cushion shrubs, sedges and grasses, mosses and lichens, and is found in the high latitudes north of 60°N in the Arctic region and south of 50°S in the Antarctic region, in permafrost soils that range from dry to seasonally saturated.
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Common (Translated Scientific) Name: Temperate to Polar Alpine & Tundra Vegetation Subclass
Colloquial Name: Temperate to Polar Alpine & Tundra Vegetation
Hierarchy Level: Subclass
Type Concept: Temperate to Polar Alpine & Tundra Vegetation occurs above treeline in temperate and boreal regions, predominantly in North America and Eurasia, with more isolated occurrences in the Southern Hemisphere. Creeping, matted and low upright dwarf-shrubs may occur, along with alpine grasses and forbs. The ground layer density varies from densely vegetated to open, rocky, rubbly, or frost-sorted habitats, and includes fell-field, boulderfield, tundra, heath and meadow. Bryophyte and lichen cover also varies considerably. Treeline varies depending on latitudinal shifts in climate, moisture, and type of mountain range, including its size and degree of isolation; for example, from 1650 m in the Andean steppe of Argentina to 3300-3600 m in the Himalayas, Southern Rocky Mountains and Californian Sierra Nevada to 2300 m in the Lesotho Plateau of South Africa.
Diagnostic Characteristics: Alpine dwarf-shrublands, forb meadows and grasslands occurring above treeline in temperate and boreal regions. Vegetation is dominated by graminoids, low creeping or matted dwarf-shrubs, and perennial forbs, often in cushion or rosette form, as well as cryptogams. Polar tundra growth forms are varied and often with complex patterns of dominance by dwarf-shrubs, sedges and grasses, mosses and lichens. In many tundra areas, the deep layers of the soil are permanently frozen, and only the surface layer is thawed and becomes biologically active during the summer.
Rationale for Nominal Species or Physiognomic Features:
Classification Comments: This type excludes very sparse alpine semi-desert vegetation, where the alpine regions grade into high-elevation deserts. Soils show cryogenic features. Alpine and tundra scree and talus, along with fell-fields and barrens are placed here because they contain cryomorphic vegetation similar to other vegetation in this class. Snowbank vegetation, which can be seasonally saturated, with wetland-like conditions, is tentatively included here.

Placement of alpine vegetation in arctic and subarctic regions is under review. In those regions, the vegetation is beyond the latitudinal limits of trees. If alpine vegetation exists in those regions, then the subclass should include Arctic or Subarctic in the name.

The High Arctic is often bare not because it is "rock" but because of the climate (cold and wind) and cryomorphic processes, hence it fits here. In true polar deserts, even cryptogams are sparse, and total cover is 0-3% (Quinn 2008).

We include "wet tundra" (tundra on saturated, somewhat peaty soils) with dry to mesic tundra. Arctic wet meadows and marshes are treated with temperate and boreal wet meadows and marshes under 2.C.4 Temperate to Polar Freshwater Marsh, Wet Meadow & Shrubland Formation (F013).

Alpine tundra of most Eurasian and North American mountains is similar to that of the Arctic tundra but with a richer flora (Quinn 2008).
Similar NVC Types:
Physiognomy and Structure: Alpine vegetation includes creeping and matted dwarf-shrubs, and occasional trees may occur, along with alpine grasses and forbs, including cushion forms of dwarf-shrubs and forbs. The ground layer varies from densely vegetated to open, rocky, rubbly or frost-sorted habitats (Whittaker 1975, Quinn 2008). Polar tundra exists on the treeless arctic plains; the vegetation growth forms are varied and often with complex patterns of dominance by dwarf-shrubs, sedges and grasses, mosses and lichens (Whittaker 1975). The Low Arctic region typically contains continuous vegetation cover (80-100%), except in rocky places, and contains the typical mix of dwarf-shrubs, sedges and grasses, mosses and lichens. Tundra also occurs in the High Arctic, and plants are primarily lichens and mosses with scattered herbs. It includes polar desert or barrens on rock substrates, where even cryptogams are sparse, and total cover is 1-3% (Quinn 2008).

Alpine tundra of most Eurasian and North American mountains is similar to that of the Arctic but with a richer flora (Quinn 2008).
Floristics:
Dynamics: No Data Available
Environmental Description: Alpine vegetation occurs above the treeline. Treeline varies depending on latitude and the "mountain mass" (i.e., large mountain masses retain more heat and tend to have higher treeline elevations, whereas smaller and more isolated mountain masses tend to have lower treeline elevations). In addition to elevation, exposure to wind is a key factor in the type of vegetation; in snowy regions, it impacts on the depth and duration of snow cover and, hence, protection of the vegetation, length of growing season, and soil moisture conditions.

Climate: For alpine vegetation, the "tundra" climate of high altitudes does not necessarily correspond to that of high latitudes (i.e., Arctic tundra). Although both regions have low mean annual temperature and short growing seasons, and experience a seasonal change in sun angle (high in the summer, low in the winter), the light regimes are quite different. Alpine regions never experience 24 hours of day or night; day length varies with latitude. And although permafrost occurs on high mountains, it does not produce the kinds of landforms found in the Arctic because few flat sites are available. Conversely, avalanches and rockslides are common in alpine regions, but do not occur in the Arctic (Quinn 2008). Some alpine regions can have very deep snow (several meters), whereas the Arctic generally has low snow cover.

Temperatures in the Arctic and Antarctic vary with the season, which has periods of 24-hour light (summer) and dark (winter). The number of days with those extremes varies with latitude, ranging from 1 day at the Arctic and Antarctic circles (66½°N and S latitude) to 6 months at the poles. Temperatures vary both with latitude and degree of continentality. Mean temperatures of the warmest summer months vary considerably but generally average between 4.5° and 13°C. In the winter, they average from -20° to -30°C. Annual precipitation, which often falls as snow, is typically <25 cm, but some localities may have as much as 50 cm.

Soil/substrate/hydrology: Most alpine soils are regularly disturbed by freezing, erosion and downslope slides, and contain a mix of rocks and fine particles (Quinn 2008). Three major types of soils occur in the alpine regions: (1) Poorly developed rocky or stony soils (or Entisols) are sometimes called Lithosols when formed on bare rock of slopes and ridges and Regosols when formed on unconsolidated rock-like talus, scree, or rubble (soil orders from Soil Survey Staff (1999)) [see Brady and Weil (2002) for comparison of U.S. soil orders with Canadian and FAO systems]. Both types are shallow, dry and azonal. (2) Alpine turf and meadow soils (or Inceptisols) are up to 75 cm deep and exhibit distinct horizons; and (3) bog soils (Histosols) are found in depressions or where seepage saturates the ground to a depth of 1 m or more (Quinn 2008).

In many polar tundra areas, the deep layers of the soil are permanently frozen (permafrost), and only the surface layer is thawed and becomes biologically active during the summer (Whittaker 1975). Soils may be dry to seasonally saturated. Permafrost is ground that is permanently frozen, and is widespread in the Arctic, covering large parts of Canada and Russia. It is discontinuous in the Boreal Forest & Woodland region to the south. It can extend down more than 600 m, depending on mean annual temperature, type of soil and rock, proximity to the ocean and topography. In the summer, only the soil surface may thaw, up to 20-60 cm. On slopes, the thawed soil may begin to move, a process called solifluction (Quinn 2008). Permafrost also creates specific landscape features collectively called patterned ground, forming circles, polygons, nets, hummocks, steps or stripes (Quinn 2008).
Geographic Range: Temperate to Polar Alpine & Tundra Vegetation occurs above treeline in temperate and boreal regions around the globe, predominantly in North America and Eurasia, with more isolated occurrences in the Southern Hemisphere. Polar tundra is dominated by complex patterns of dominance by dwarf-shrubs, sedges and grasses, mosses and lichens, and is found in the high latitudes north of 60°N in the Arctic region and south of 50°S in the Antarctic region, where climatic conditions exclude tree and tall-shrub growth forms.
Nations:
States/Provinces:
Omernik Ecoregions:
Plot Analysis Summary:
Confidence Level: High
Confidence Level Comments:
Grank: GNR
Greasons:
Name:Database Code:Classification Code:
Class 4 Polar & High Montane Scrub, Grassland & Barrens C04 4
Subclass 4.B Temperate to Polar Alpine & Tundra Vegetation S12 4.B
Formation 4.B.2 Polar Tundra & Barrens F031 4.B.2
Formation 4.B.1 Temperate & Boreal Alpine Tundra F037 4.B.1
Concept Lineage: 4.C merged into 4.B (S12) (DFL 7-12)
Predecessors:
Obsolete Names:
Obsolete Parents:
Synonomy: >< Alpine grassland: biome-type 15 (Whittaker 1975)
>< Alpine shrubland: biome-type 14 (Whittaker 1975)
< Arctic and Antarctic Tundra (Quinn 2008) [The author includes both lithomorphic and cryomorphic vegetation in the Polar High Arctic semi-desert description as well as wet tundras.]
= Low Arctic Tundra (Bliss 2000) [Bliss includes both dry and wet tundra in his description.]
= Mid-latitude Alpine Tundra (Quinn 2008) [Approximately equivalent. Quinn includes alpine scree and talus in her concept.]
Concept Author(s): Hierarchy Revisions Working Group, Federal Geographic Data Committee (Faber-Langendoen et al. 2014)
Author of Description: D. Faber-Langendoen
Acknowledgements: Chris Lea
Version Date: 17Oct2014
References:
  • Bliss, L. C. 2000. Arctic tundra and polar desert biome. Pages 1-40 in: M. G. Barbour and W. D. Billings, editors. North American terrestrial vegetation. Second edition. Cambridge University Press, New York.
  • Brady, N. C., and R. R. Weil. 2002. The nature and properties of soils. Thirteenth edition. Prentice Hall, Upper Saddle River, NJ.
  • Faber-Langendoen, D., T. Keeler-Wolf, D. Meidinger, C. Josse, A. Weakley, D. Tart, G. Navarro, B. Hoagland, S. Ponomarenko, J.-P. Saucier, G. Fults, and E. Helmer. 2015c. Classification and description of world formation types. General Technical Report RMRS-GTR-000. USDA Forest Service, Rocky Mountain Research Station, Fort Collins, CO.
  • Quinn, J. A. 2008. Arctic and alpine biomes. Greenwood Press, Westport, CT.
  • Soil Survey Staff. 1999. Soil taxonomy: A basic system of soil classification for making and interpreting soil surveys. Second edition. USDA Natural Resources Conservation Service, Washington, DC.
  • Whittaker, R. H. 1975. Communities and ecosystems. Second edition. Macmillan Publishing Co., New York. 387 pp.