Common (Translated Scientific) Name: Yellow Mountain-heath - Mountain-avens species - Altai Fescue Alpine Tundra Division
Colloquial Name: Western North American Alpine Tundra
Hierarchy Level: Division
Type Concept: This division is found from the Alaskan mountain ranges down through the Cascade-Sierras of California and through the Rocky Mountains into northeastern Mexico. Vegetation physiognomy ranges from sparse cushion plants to dense turf, dwarf-shrublands and krummholz. Communities vary considerably in floristic composition over the range of this type. In the northern alpine, well-vegetated tundra is typically composed of Artemisia arctica, Carex microchaeta, Dryas integrifolia or Dryas octopetala, Festuca altaica, Polygonum viviparum, Salix reticulata, Silene acaulis, and some bryophytes, such as Aulacomnium turgidum and Hylocomium splendens, and lichens, such as Stereocaulon spp. or Flavocetraria nivalis.
The "typical" central and southern Rocky Mountain alpine tundra has a sparse to moderate cover dominated by Carex elynoides, Carex siccata, Carex scirpoidea, Carex nardina, Carex rupestris, Festuca brachyphylla, Festuca idahoensis, Geum rossii, Juncus drummondii, Kobresia myosuroides, Phlox pulvinata, or Trifolium dasyphyllum. Wind-exposed ridges and saddles have species such as Arenaria capillaris, Dryas integrifolia, Kobresia myosuroides, Luzula spicata, Minuartia obtusiloba, Oxytropis podocarpa, Paronychia pulvinata, Phlox pulvinata, Poa alpina, Potentilla nivea, Potentilla villosa, Saxifraga bronchialis, Silene acaulis, Trifolium dasyphyllum, and Trifolium parryi. Dwarf-shrubland dominates the coastal alpine and snowier sites in the other areas. Common heath species are Cassiope lycopodioides, Cassiope mertensiana, Cassiope tetragona, Empetrum nigrum, Harrimanella stelleriana, Luetkea pectinata, Phyllodoce aleutica, Phyllodoce empetriformis, and Phyllodoce glanduliflora. Scattered trees and patches of krummholz may occur at lower elevations, composed of Abies lasiocarpa, Picea glauca, or Tsuga mertensiana, depending upon the area. The drier alpine vegetation of the Great Basin ranges and Sierra Nevada may include lower elevation semi-desert species such as Carex filifolia, Poa fendleriana, Poa secunda, and Artemisia frigida. The alpine of northeastern Mexico is dominated by Potentilla leonina, Arenaria spp., and Thelesperma muelleri.
Environments are varied due to climatic and site variation. Wind and its effect on snow movement has a strong local effect, producing wind-scoured fell-fields, dry turf, snow accumulation heath communities, and short growing season snowbed sites. Fell-fields are typically free of snow during the winter as they are found on ridgetops, upper slopes and exposed saddles, whereas dry turf is found on gentle to moderate slopes, flat ridges, valleys, and basins where the soil has become relatively stabilized and the water supply is more-or-less constant. Dwarf-shrubland sites tend to be in level or concave areas with late-lying snow and subirrigation from surrounding slopes. The dominant disturbances are snow avalanche, soil creep and freeze-thaw action.
Diagnostic Characteristics: Low to dwarf-shrublands, tundra and sparse vegetation at and above upper timberline in the western North American Cordillera from the Aleutian Islands of Alaska to northern Mexico. There are many strong diagnostic species of this type as compared to other alpine floras. These include the graminoids Calamagrostis breweri, Carex elynoides, Carex helleri, Carex filifolia, Carex microchaeta, Carex rupestris, Festuca altaica, and Kobresia myosuroides; the dwarf-shrubs Cassiope mertensiana, Cassiope tetragona, Dryas integrifolia, Dryas octopetala, Phyllodoce empetriformis, Phyllodoce glanduliflora, Salix reticulata, Salix vestita; and forbs such as Artemisia arctica, Geum rossii, Phlox pulvinata, Potentilla nivea, Saxifraga bronchialis, Silene acaulis, and Trifolium dasyphyllum.
Rationale for Nominal Species or Physiognomic Features: One key species from each of the three main types was selected. Phyllodoce glanduliflora occurs over much of the range of this type, particularly in coastal mountains. Dryas octopetala is wide-ranging and could be used without Dryas integrifolia, but the latter often dominates where the former does not. Festuca altaica characterizes the boreal alpine, although other species could be used, e.g., Artemisia arctica or Salix reticulata.
Classification Comments: Subalpine meadows extend into the alpine but are mostly treated in 2.B.2.Na Western North American Grassland & Shrubland Division (D022); they contain species of both the alpine and subalpine but due to their lush herbaceous growth form, they are best treated there. It appears that graminoid meadows are part of this alpine division (D043) and there may be a need to address further what meadow vegetation should be included here.
Alpine in the subarctic region of Alaska (and presumably Yukon and Northwest Territories) is included in 4.B.2.Xa Arctic Tundra & Barrens Division (D044). There is considerable floristic similarity between subarctic alpine and boreal alpine of this division. This separation requires further assessment. Yukon combines arctic, subarctic alpine and boreal alpine at the zone level, with consideration to subzone distinction for the three regions (Flynn pers. comm. 2015). Although they lack the data to be certain of the relationship, the subarctic alpine occurs above subarctic woodland, so is more of an alpine entity than an arctic one. With that said, there are floristic similarities between arctic and alpine; e.g., even in Colorado, the alpine is considered to have about one-third species with arctic affinities.
It is somewhat debatable whether the alpine of Cerro Potosí should be included in this alpine division (D043) or combined with the zacatonal of southern Mexico. The species on this limestone mountain are mostly of a very southern distribution with only a few species providing a link to the flora of D043. However, it is considered that the alpine communities of Cerro Potosí have closer phytogeographic affinities to forb-dominated communities of the southern Rocky Mountains than with the grass-dominated, zacatonal vegetation.
Similar NVC Types:
D044 Arctic Tundra & Barrens, note:
D135 Caribbean-Mesoamerican Montane & High Montane Grassland & Shrubland, note: includes alpine grassland (zacatonal) that is closely related to the southern extent of this division.
D022 Western North American Grassland & Shrubland, note: "characterizes lower elevation grasslands and shrublands, some of which occur in and near the alpine of D043, e.g., high-montane grasslands, subalpine deciduous shrubland, avalanche tracks, and subalpine meadows."
D042 Eastern North American Alpine Tundra, note: "characterizes the alpine of eastern North America and includes eastern species such as Carex bigelowii, Kalmia angustifolia, Harrimanella hypnoides, and Diapensia lapponica, and Picea mariana and Abies balsamea compose the krummholz."
Physiognomy and Structure: The communities of this type are composed of sparse and open- to closed-canopy herbaceous stands, dominated by graminoids and/or perennial forbs, as well as dwarf-shrub stands, and near treeline, needle-leaved evergreen trees in krummholz form. Stands of low-statured forbs are often in cushion plant form or matted, flat to the ground in rosettes, and often densely haired and thickly cutinized. The low growth forms of alpine plants allows them to take advantage of the more favorable temperatures that occur near the ground. The height of krummholz is correlated with mean winter snow depth. Although some turf communities are extensive, the vegetation overall is a mosaic of small-patch plant communities.
Floristics: Communities vary considerably in floristic composition over the range of this type. Although species vary individually in their distribution, some floristic groups are evident. Many alpine tundra species also occur in the arctic tundra, e.g., Carex rupestris, Cassiope tetragona, Dryas integrifolia, Dryas octopetala, Kobresia myosuroides, Salix reticulata, the proportion becoming less southward, although about one-third of the Colorado alpine flora occurs in the arctic.
In the northern alpine, the more densely vegetated tundra is composed of dwarf willows, graminoids, and forbs with bryophytes and lichens. Common species of this tundra are Artemisia arctica, Carex microchaeta, Dryas integrifolia (limestone-influenced soils) or Dryas octopetala, Festuca altaica, Polygonum viviparum, Salix reticulata, Silene acaulis, and some bryophytes, such as Aulacomnium turgidum, Hylocomium splendens, and Polytrichum spp., and lichens, such as Stereocaulon spp. or Flavocetraria nivalis (= Cetraria nivalis).
Alpine "heath," composed of Cassiope tetragona and other ericaceous species, occupies sites of deeper snow. Windblown sites are sparsely vegetated with cushion or mat-forming species such as Dryas integrifolia, Oxytropis podocarpa, Potentilla nana, Saxifraga oppositifolia, Saxifraga tricuspidata, or Silene acaulis. On high alpine ridges with some snow cover, Silene acaulis dominates, with Artemisia arctica, Luzula spicata, Poa alpina, and Polytrichum spp. Scattered trees and patchy krummholz may occur at lower elevations, composed of species such as Abies lasiocarpa, Picea glauca, or Pinus contorta, depending upon the area.
The "typical" central and southern Rocky Mountain alpine tundra varies from sparse to moderate cover dominated by cushion plants to moderately dense to dense cover of low-growing, perennial graminoids and forbs that form a turf. Rhizomatous, sod-forming sedges are the dominant graminoids, and prostrate and mat-forming plants with thick rootstocks or taproots characterize the forbs. Dominant species include Artemisia arctica, Carex elynoides, Carex siccata, Carex scirpoidea, Carex nardina, Carex rupestris, Festuca brachyphylla, Festuca idahoensis, Geum rossii, Juncus drummondii, Kobresia myosuroides, Phlox pulvinata, and Trifolium dasyphyllum. The sparsely vegetated fell-field plants are cushioned or matted, frequently succulent, flat to the ground in rosettes, and often densely haired and thickly cutinized. Plant cover on fell-fields is 15-50%, while exposed rocks covered with crustose lichens make up the rest. They are usually found on wind-exposed ridges and saddles, within or adjacent to alpine dry turf. Common species include Arenaria capillaris, Geum rossii, Minuartia obtusiloba, Paronychia pulvinata, Phlox pulvinata, Potentilla nivea, Potentilla villosa, Saxifraga bronchialis, Silene acaulis, Trifolium dasyphyllum, and Trifolium parryi. The dwarf-shrubland "heath" of these southern areas is characterized by Cassiope mertensiana and Phyllodoce empetriformis or Phyllodoce glanduliflora. Dryas octopetala- and Dryas integrifolia-dominated communities occur on more windswept and drier sites than the heath communities. Dwarf willows, e.g., Salix nivalis or Salix reticulata, are often found with Dryas. Snowbed communities are often dominated by Carex subnigricans and Sibbaldia procumbens.
The drier alpine vegetation of the Great Basin ranges and Sierra Nevada may include lower elevation semi-desert species such as Carex filifolia, Poa fendleriana, Poa secunda, and Artemisia frigida. Other species specific to these mountains include Aquilegia pubescens, Carex congdonii, Calamagrostis breweri, Castilleja nana, Eriogonum gracilipes, Eriogonum incanum, Phlox covillei, Podistera nevadensis, and Carlquistia muirii (= Raillardiopsis muirii, = Raillardella muirii). Alpine dwarf-shrublands are dominated or codominated by Cassiope mertensiana, Ericameria discoidea, Kalmia microphylla, Polygonum shastense, Phyllodoce breweri, Ribes cereum, Salix arctica, and Vaccinium cespitosum.
In northeastern Mexico, the alpine of Cerro Potosí in Nuevo Leon is dominated by Potentilla leonina, Arenaria sp., and Bidens muelleri. Linum lewisii and Trisetum spicatum also occur here and link this alpine region to this type. Pinus hartwegii is the treeline species in this area.
The coastal alpine is dominated by dwarf-shrub species, including Cassiope lycopodioides (Haida Gwaii), Cassiope mertensiana, Cassiope tetragona, Empetrum nigrum, Harrimanella stelleriana, Luetkea pectinata, Phyllodoce aleutica, Phyllodoce empetriformis, and Phyllodoce glanduliflora. Ericaceous species typically dominate, but sites dominated by Salix arctica, Salix nivalis, and Salix reticulata occur. Scattered tall shrubs and dwarf trees may also be present.
At the highest elevations of this division, conditions are too harsh for most vascular plants, often a combination of a short snow-free period and limited soil development (i.e., mostly rocky substrates), and the vegetation is dominated by lichens.
Dynamics: The dominant natural disturbances in this type are snow avalanche, soil creep and freeze-thaw action. Wind and insolation also impact strongly on vegetation development. Small mammals can be important in modifying the soil of meadows.
Environmental Description: This alpine division occurs at and above the upper treeline in the mountains of the Western Cordillera. These alpine areas can be extensive where the mountain ranges have considerable, contiguous area above treeline, but many alpine areas are isolated on individual mountain peaks. The elevation of upper treeline varies considerably from north to south, as low as 100 m elevation in Alaska to over 3500 m in northern Mexico. The treeline elevation is lower in wet maritime climates as compared to more continental climates at the same latitude. The heavy, deep snow of maritime areas limits the length of the growing season. Alpine vegetation is controlled by snow retention, wind desiccation, soil depth, permafrost, cryoturbation, solifluction, and a short growing season. Wind exposure has a strong impact on the type of vegetation in alpine areas. Ridgetops, windward upper slopes and exposed saddles can have little snow during the winter, due to wind-scouring. Level or concave areas and leeward slopes will have deeper snow, and in some areas the snow will not melt in most summers. Areas with late snowmelt will be composed of species adapted to a very short growing season; some of these species can initiate growth under the snow, and some are capable of surviving even when there are years of continuous snow cover.
Climate: This division combines high-elevation, temperate and boreal climates, including maritime and continental expressions. The high elevations result in long cold snowy winters and a very short growing season. The precipitation regime varies considerably. In the south and along the coast, it is strongly seasonal with most precipitation falling in the winter months as snow, and little precipitation in the summers. In many northern interior areas, the opposite is the case; higher precipitation occurs during the summer months. A high snowpack characterizes this environment. The higher cover of vegetation of this division occurs on slopes and depressions where snow lingers, the soil has become relatively stabilized, and the water supply is more-or-less constant. In high-snow areas, it is common for patches of snow to persist all summer.
Soils/substrate: Soils are typically shallow, well-drained, and stony, and can be subject to colluviation, solifluction, and cryoturbation; permafrost can occur, especially in northern areas. Substrates are variable across fell-fields, alpine turf and dwarf-shrub vegetation. Fell-field sites are generally shallow, stony, low in organic matter, and poorly developed with wind deflation (erosion) often resulting in a gravelly pavement. Alpine turf sites have deeper, more developed soils, although they may have moderately high cover of cobbles and boulders present. The dwarf-shrubland soils have become relatively stabilized, are moist but well-drained, strongly acidic, and often have substantial peat layers. Subirrigation from snowmelt can be an important source of moisture, especially as soils are often shallow in depth and with rock fragments. Rock, ice and late-persisting snow characterize considerable portions of the landscape adjacent to this type.
Biogeography: Latitude, elevation, and degree of continentality impact the development of vegetation in this division. The species vary considerably over the range of latitude, although, e.g., Trisetum spicatum occurs over most of the range of alpine from Mexico to Alaska. There are groups of species that occur within certain latitudinal bands. Alpine also forms elevational zones, where the low alpine zone has higher plant cover overall, has krummholz, and has species of the subalpine, e.g., subalpine meadows. Conversely, the highest alpine zone is sparsely vegetated, with more rock, ice and snow patches, and a prevalence of lichen communities on the rock. Maritime alpine is dominated by heath vegetation; whereas alpine under more of a continental influence has a greater graminoid and forb component, as well as dwarf-shrubs such as Dryas spp. or Salix spp. The heath communities are restricted to sites of deep snow.
Geographic Range: This type occurs above upper timberline in the mountains of the western North American Cordillera, including the Brooks and Alaska ranges in Alaska, the MacKenzie Mountains of Yukon and western Northwest Territories, from there southward in the Coast, Cascade and Rocky Mountain ranges and the Sierra Nevada, culminating in the Sierra Madres of Mexico and Guatemala.
Nations: CA, MX, US
States/Provinces: AB, AK, AZ, BC, CA, CO, ID, MT, MXNU, NM, NT, NV, OR, UT, WA, WY, YT
|US Forest Service Ecoregions (2007)|
Confidence Level: Moderate
Confidence Level Comments:
Synonomy: ? AM Alpine Meadow (Ecosystems Working Group 1998) [Mapping unit for British Columbia alpine meadow vegetation used in broad ecosystem inventory.]
< AT Alpine Tundra (Ecosystems Working Group 1998) [Mapping unit for British Columbia alpine vegetation used in broad ecosystem inventory.]
> Alpine Tundra Zone (Pojar and Stewart 1991) [Describes alpine vegetation of British Columbia; unit precedes Coastal, Boreal and Interior alpine zones of BC.]
< Alpine vegetation of North America (Billings 2000) [Describes alpine vegetation of all of North America, whereas this type is for the western cordillera.]
> Boreal Altai Fescue Alpine Zone (MacKenzie 2005) [Describes boreal alpine vegetation of British Columbia - applicable to alpine of YT and NT.]
> Coastal Mountain-heather Alpine Zone (MacKenzie 2005) [Describes coastal mountain alpine vegetation of British Columbia - somewhat applicable to alpine of adjacent states (AK, WA).]
> Interior Mountain-heather Alpine Zone (MacKenzie 2005) [Describes continental temperate alpine vegetation of British Columbia; applicable to alpine vegetation of adjacent states/provinces (AB, ID, MT)]
Concept Author(s): W.D. Billings (2000)
Author of Description: D. Meidinger
Acknowledgements: G. Kittel, K.A. Schulz
Version Date: 29Oct2015
- Billings, W. D. 2000. Alpine vegetation of North America. Pages 537-572 in: M. G. Barbour and W. D. Billings, editors. North American terrestrial vegetation. Second edition. Cambridge University Press, New York. 434 pp.
- Ecosystems Working Group. 1998. Standards for broad terrestrial ecosystem classification and mapping for British Columbia. Prepared by the Ecosystems Working Group, Terrestrial Ecosystem Task Force, Resources Inventory Committee, for the Province of British Columbia. 174 pp. plus appendices. [http://srmwww.gov.bc.ca/risc/pubs/teecolo/tem/indextem.htm]
- Faber-Langendoen, D., J. Drake, S. Gawler, M. Hall, C. Josse, G. Kittel, S. Menard, C. Nordman, M. Pyne, M. Reid, L. Sneddon, K. Schulz, J. Teague, M. Russo, K. Snow, and P. Comer, editors. 2010-2019a. Divisions, Macrogroups and Groups for the Revised U.S. National Vegetation Classification. NatureServe, Arlington, VA. plus appendices. [in preparation]
- MacKenzie, W. 2005. Biogeoclimatic ecosystem classification of the alpine areas in British Columbia. Botanical Electronic News 344. ISSN 1188-603X.
- Pojar, J., and A. C. Stewart. 1991. Alpine tundra zone. Pages 263-274 in: D. Meidinger and J. Pojar, editors. Ecosystems of British Columbia. British Columbia Ministry of Forests Special Report Series 6. Province of British Columbia, Victoria.