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C04 Cryomorphic Scrub, Herb & Cryptogam Vegetation Class

The U.S. National
Vegetation Classification
Type Concept Sentence: Tundra, alpine and tropical high montane habitats dominated by cryomorphic growth forms (including dwarf-shrubs, krummholz, associated herbs, lichens and mosses), with low height and open to closed canopy.
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Common (Translated Scientific) Name: Cryomorphic Scrub, Herb & Cryptogam Vegetation Class
Colloquial Name: Polar & High Montane Scrub, Grassland & Barrens
Hierarchy Level: Class
Type Concept: Shrubs and herbs with cryomorphic growth forms are dominant, including dwarf-shrub, caulirrosulate (páramo) or associated herbs. Nonvascular lichen and moss growth forms may also be dominant. The vegetation structure has irregular, horizontal spacing, is of low height, often much <1 m tall. Mesomorphic trees have <10% cover, and cryomorphic shrubs and herbs have the majority of cover compared to mesomorphic or xeromorphic growth forms. Climates include tropical high montane (alpine to nival) to polar tundra, with stands located above continuous forest line in altitude or latitude, and regular cold and/or freezing temperatures. Substrates are dry to wet, with varying degrees and depths of permafrost or cryic soils. Vegetation includes tundra, alpine, and tropical high montane types, such as páramo and puna, as well as polar barrens on rocky or gravelly soils.
Diagnostic Characteristics: Cryomorphic shrub, krummholz, herb, and nonvascular growth forms (including dwarf-shrubs, paramoid or associated herbs, lichens, mosses) have the majority of cover compared to mesomorphic or xeromorphic shrub and herb growth forms, and mesomorphic trees <10% cover. The vegetation structure is irregular horizontally, and of low height, often much <1 m tall.
Rationale for Nominal Species or Physiognomic Features:
Classification Comments: Our criteria would place a stand with 1% or more cover of cryomorphic shrubs and herbs, and 99% cover of nonvascular lichen and moss in this class, if stands lack mesomorphic vegetation (e.g., lichen tundra, typically foliose and fruticose lichens) (Viereck et al. 1992). Review is needed on the placement of páramo and puna in South America. Currently only super-páramo and higher elevation puna are placed here, as this class is restricted to the more strongly cryomorphic high montane forms of puna and páramos (e.g., in Venezuela there are stands dominated by cryomorphic growth forms but lack the typical grass cover). This is because lower elevation páramo and moist puna have mesomorphic grasses covering the ground (often exceeding 80% cover), whereas cryomorphic shrubs and herbs, although present and conspicuous, may be <20% cover. These lower elevation stands also lack any cryoturbation. Using these criteria, we would place these lower elevation stands in the mesomorphic "Tropical Montane Grassland & Shrubland" formation. On the other hand, we don't yet have a working set of "cryomorphic herbs" versus "mesomorphic herb" growth forms so it is hard to know how to weigh the presence of these mesomorphic herbs against the cryomorphic shrubs. Consistent placement of the subalpine and alpine zones across tropical, temperate and boreal regions is needed.
Similar NVC Types:
C02 Shrub & Herb Vegetation, note: "Distinguishing cryomorphic vegetation from mesomorphic vegetation can be a challenge in both arctic and alpine regions. Here we allow mesomorphic extensions into the cryomorphic climatic zone to be retained in the mesomorphic class (e.g., boreal mesomorphic tall willow shrublands along arctic drainages, or the tropics, lower elevation expressions of high montane pßramo and puna in South America)."
C03 Desert & Semi-Desert, note: "In high montane deserts, the xeromorphic desert growth forms will transition to cryomorphic growth forms. Review is needed to see where issues may arise between temperate alpine and dry deserts or tropical high montane puna and high deserts."
C06 Open Rock Vegetation, note: "This class is restricted to cryptogam-dominated sites associated with mesomorphic vegetation, as found in tropical, temperate and boreal vegetation regions."
Physiognomy and Structure: Growth Forms: Stands are dominated by cryomorphic growth forms, such as dwarf-shrub, caulirrosulate (páramo) and various associated herb growth forms (forb, graminoid), along with nonvascular lichen and moss growth forms. The various herb growth forms are not exclusive to the cryomorphic class, and more work is needed to assess whether additional herbaceous growth form types should be recognized that may be distinctive for this class (e.g., creeping or matted herb growth forms). In addition, lichens in this class may more commonly be foliose or fruticose (e.g., reindeer lichens), at least in Arctic tundra (Billings 2000).

Structure: Stands have open to closed irregular shrub or herb stem spacing; often a single low complex stratum, sometimes with prominent non-vegetated surfaces. There is <10% mesomorphic tree cover, and typically >10% shrub or herb cover (but sparse open cover between 1% and 10% may occur), and with a majority of that cover being cryomorphic shrub and/or herb growth form, as compared to mesomorphic or xeromorphic shrub and/or herb cover. Nonvascular growth forms may vary from 0 to 100%. At maturity, shrubs are typically <0.3 m, but occasionally as tall as 1 m, and herbs are typically <0.5 m.
Dynamics: Wind, grazing most common, insect.
Environmental Description: Climate:. Growing season is either very short, with snow cover persisting for most of the year, or growth is greatly restricted by freezing to near-freezing temperatures, such as the EDf climate zone of Köppen (cold continental climate without dry season).
Geographic Range: This type occurs in the Bailey (1989) Polar Domain, especially Tundra divisions, but also in the alpine elevations in other domains.
Omernik Ecoregions:
Plot Analysis Summary:
Confidence Level: Moderate
Confidence Level Comments:
Grank: GNR
Concept Lineage:
Obsolete Names:
Obsolete Parents:
Synonomy: = Arctic and Alpine Biomes (Quinn 2008)
Concept Author(s): Hierarchy Revisions Working Group, Federal Geographic Data Committee (Faber-Langendoen et al. 2014)
Author of Description: Hierarchy Revisions Working Group
Version Date: 17Oct2014
  • Bailey, R. G. 1989. Explanatory supplement to ecoregions map of the continents. Environmental Conservation 16:307-309 with separate map at 1:30,000,000. USDA Forest Service, Washington, DC.
  • 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.
  • 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.
  • Viereck, L. A., C. T. Dyrness, A. R. Batten, and K. J. Wenzlick. 1992. The Alaska vegetation classification. General Technical Report PNW-GTR286. USDA Forest Service, Pacific Northwest Research Station, Portland, OR. 278 pp.