Dwarf-shrub heaths are manifold complexes of plant communities distributed circumpolarly within the Low Arctic, penetrating into the High Arctic, and abundant worldwide in mountain alpine and subalpine regions. The term heathland, initially used for the wide open landscapes deforested by humans in England, now refers to ecosystems characterized by evergreen xeric (dry habitat) and mesic (intermediate moisture habitat) plants, dominated by representatives of certain plant families (Ericaceae, Empetraceae, and Diapensiaceae in the Arctic), and a preference for acid soils low in nutrients, although heathland may also occur in calcareous soils. In the Low Arctic, heath-dominated communities occur between snow-poor dry tundra and mesic shrub and tussock tundra of complex environmental gradient occupying well-drained soils of river terraces, slopes, and uplands where winter snow is at least 20-30 cm deep.
Most heathland soils are usually podzolized, although the true podzols decrease northward due to the lower summer temperatures and the small extent of percolation, resulting in a weakly stratified soil profile. Characteristic evergreen heath plants are Ledum palustre subsp. decumbens (Labrador tea), Rhododendron lapponicum, Loiseleuria procumbens (alpine azalea), Phyllodoce caerulea (purple or mountain heather), Cassiope tetragona, Andromeda polifo-lia (bog rosemary), Vaccinium vitis-idaea subsp. minus (mountain cranberry), Diapensia lapponica, and Empetrum nigrum (crowberry), although deciduous-leaved dwarf shrubs and low shrubs are also abundant (bog bilberry or Vaccinium uliginosum subsp. microphyllum, black bearberry or Arctostaphylos alpina, A. rubra, birch Betula nana, and some willows). The cryptogamic floor of mosses, algae, and lichens is also well developed. The most common lichens include Cetraria cucullata, C. nivalis, Cladina rangiferina, C. stellaris, C. mitis, Cladonia sylvatica, Dactylina arctica, Thamnolia vermicularis, etc. and the mosses Dicranum elongatum, Aulacomnium turgidum, A. palustre, Rhacomitrium lanuginosum, Hylocomium splendens, Tomenthypnum nitens, etc.
Dwarf-shrub-lichen heaths are one of the major reindeer and snow sheep pastures, including in winter, due to the relatively thin snow cower. Reindeer grazing strongly influences the condition of fruticose lichen cover, although dwarf shrubs are also significant forage especially in late winter and early spring. Summertime grazing is especially disastrous for the fruticose lichens because of their high sensitivity to trampling when dry. In the ground layer, overgrazing leads to increase of the lichen Stereocaulon paschale and to decrease of poorly trample-resistant and slowly recovering Cladina species. Trampling has usually increased grasses (Calamagrostis lapponica, Festuca ovina, Arctagrostis latifolia, etc.) and sedges (e.g., Carex bigelowii), whereas dwarf-shrubs Betula nana, Empetrum nigrum, Vaccinium vitis-idaea subsp. minus, etc. may have decreased in the most efficiently grazed areas. Extreme overgrazing results in establishment of grassland instead of heathland.
South of the tundra zone, dwarf-shrub heaths of nearly the same species composition are abundant in north alpine and subalpine environments combining with tall shrub and birch thickets, especially in Fennoscandia and the Kola Peninsula, and in the amphi-Beringian area. In well-drained snow-rich habitats where snow lies up to July, Cassiope tetragona dominates, with an admixture of prostrate willows (Salix reticulata, S. herbacea, S. polaris), and numerous lichens and mosses. The southernmost portion of the High Arctic is first and foremost characterized by a circumpolar occurrence of Cassiope tetragona dominated heaths (absent or very rare in the Arctic only between southern Svalbard and the polar Urals) with an admixture of ground-hugging willows (Salix arctica, S. pulchra, S. reptans) and Betula nana, and prostrate Dryas species. It is much more rare and less prominent in alkaline areas than on acidic substrates.
See also Cassiope Heaths; Empetrum Heaths; Lichen
Aleksandrova, V.D., The Arctic and Antarctic: Their Division into Geobotanical Areas, Cambridge and New York: Cambridge University Press, 1980 Chapin III, F.S. & Ch. Körner (editors), Arctic and Alpine Biodiversity: Patterns, Causes, and Ecosystem Consequences, New York: Springer, 1995
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Elvebakk, A., "Bioclimatic Delimitation and Subdivision of the Arctic." In The Species Concept in the High North—A Panarctic Flora Initiative, edited by I. Nordal & V.Yu. Razzhivin, Oslo: Norwegian Academy of Science and Letters, 1999, pp. 81-112 Haapasaari, M., "The oligotrophic heath vegetation of northern Fennoscandia and its zonation." Acta Botanica Fennica, 135(1988): 1-219 Oksanen, L. & R. Virtanen, "Topographic, altitudinal and regional patterns in continental and suboceanic heath vegetation of northern Fennoscandia." Acta Botanica Fennica, 153(1995): 1-80 Virtanen, R., L. Oksanen, & V. Razzhivin, "Topographic and regional patterns of tundra heath vegetation from northern Fennoscandia to the Taimyr Peninsula." Acta Botanica Fennica, 167(1999): 29-83
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