tundra(redirected from Polar Grassland)
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tundra(tŭn`drə), treeless plains of N North America and N Eurasia, lying principally along the Arctic Circle, on the coasts and islands of the Arctic Ocean, and to the north of the coniferous forest belt. The tundra area is widest in N Siberia on the Kara Sea and reaches as far south as 60° N at the neck of the Kamchatka peninsula. Although sometimes called the Arctic steppe and situated mainly within the Arctic Circle, it reaches southward into the Scandinavian, Timan, and Ural mts. For most of the year the mean monthly temperature is below the freezing point; winters are long and severe. The summers are short and relatively warm, but even in July the mean monthly temperature does not rise above 50°F; (10°C;). Although high temperatures may be reached during a summer day, the subsoil is perpetually frozen. During summer, sedges, mosses, and lichens appear in abundance, along with some flowering plants. Among the few large animal species found in the tundra are the caribou, the arctic fox, the snowshoe rabbit, and occasionally the polar bear. Precipitation is spread evenly during the year and is slight, varying from 8 to 12 in. (20–30 cm). Evaporation is low, and much of the flat ground in areas of poor drainage becomes swampy during the summer months. Because there are very few species of flora and fauna, the destruction of the tundra is a simple process. The elimination of a single species or the disruption of the permanently frozen subsoil (permafrost) may severely damage this fragile ecosystem. Russia's tundra supports a small human population mostly consisting of the Nensty (Samoyedes) and the Komi. Eskimos inhabit the North American tundra.
See E. Bowen, Grasslands and Tundra (1985).
An area supporting some vegetation beyond the northern limit of trees, between the upper limit of trees and the lower limit of perennial snow on mountains, and on the fringes of the Antarctic continent and its neighboring islands. The term is of Lapp or Russian origin, signifying treeless plains of northern regions. Biologists, and particularly plant ecologists, sometimes use the term tundra in the sense of the vegetation of the tundra landscape. Tundra has distinctive characteristics as a kind of landscape and as a biotic community, but these are expressed with great differences according to the geographic region.
Characteristically tundra has gentle topographic relief, and the cover consists of perennial plants a few inches to a few feet or a little more in height. The general appearance during the growing season is that of a grassy sward in the wetter areas, a matted spongy turf on mesic sites, and a thin or sparsely tufted lawn or lichen heath on dry sites. In winter, snow mantles most of the surface. By far, most tundra occurs where the mean annual temperature is below the freezing point of water, and perennial frost (permafrost) accumulates in the ground below the depth of annual thaw and to depths at least as great as 1600 ft (500 m).
a type of vegetation characteristic of the arctic region, bounded on the south by forests and on the north by arctic wastelands. The tundra is associated with a cold climate and with cold soils, under which lies, as a rule, permafrost. Mountain tundras are encountered in Scandinavia, the Ural region, Siberia, Alaska, and northern Canada.
Perennial plants predominate in the tundra: mosses, lichens, herbaceous hemicryptophytes and chamaephytes (cespitóse, rhi-zomatous, cushion, semicushion, rosette, and semirosette plants), deciduous chamaephytic dwarf shrubs (for example, Salix polaris), dwarf evergreen shrubs (Empetrum hermaphrodi-tum and Ledum decumbens), and deciduous low-growing nano-phanerophytic shrubs (Betula nana, Betula exilis, and Salix lanata). Annuals (Koenigia islándica) and bulbous geophytes (Lloydia serótina) are rare. The tundra is characterized by poly-dominance (there are several dominant species belonging to various life-forms in each plant community) and mosaic structure. The latter is a result of the cryogenic microtopography, represented by hillocks and small hollows. Often the dense plant cover is interrupted by spots of bare ground.
Subarctic tundras (northern and southern) occupy a large part of the tundra zone of the northern hemisphere. At their northern boundaries they are replaced by arctic tundras, where there are no scrub thickets but where arcto-alpine shrubs (Salix polaris, Dryas octopetala), mosses, lichens, and grasses play a major role. In the eastern part of European USSR and in Western Siberia, southern tundras are characterized by large dwarf-birch tundras, with a marked stratum of dwarf birch (Betula nana) and an admixture of willow. Toward the north, the stratum of shrubs becomes sparse, and the shrubs decrease in height. Mosses, dwarf shrubs, trailing shrubs, and sedge (Carex ensifolia ssp. arctisibirica) are common, and there is a significant admixture of Dryas. In Eastern Siberia, where the climate is more continental, the large dwarf-birch tundras are replaced by small dwarf-birch tundras, with a different species of birch (Betula exilis) predominating. In Chukotka and Alaska hummock tundras with cotton grass (Eriophorum vaginatum) and sedge (Carex lugens) predominate; there are hypnum and sphagnum mosses, with an admixture of low shrubs, which diminishes to the north. In the subarctic tundras of Canada and Greenland there is a predominance of eri-coid shrubs (for example, Vaccinium uliginosum ssp. microphyl-lum and Cassiope tetrágono).
Tundras serve as pastures for reindeer, hunting lands, and sources of berries (cloudberry, bog whortleberry, crowberry). It is possible to raise vegetables in the open ground, and methods have been developed for creating high-yield meadows on tundra sites.
REFERENCESGorodkov, B. N. Rastitel’nost’ tundrovoi zony SSSR. Moscow-Leningrad, 1935.
Sochava, V. B., and B. N. Gorodkov. “Arkticheskie pustyni i tun-dry.” In Rastitel’nyi pokrov SSSR: Poiasnitel’nyi tekst k “Geobo-tanicheskoi karte SSSR” (m. 1:4,000,000), [part] 1. Moscow-Leningrad, 1956.
Tikhomirov, B. A. “Dinamicheskie iavleniia v rastitel’nosti piatnis-tykhtundr Arktiki.” Botanicheskii zhurnal, 1957, vol. 42, no. 11.
Aleksandrova, V. D. “Printsipy zonal’nogo deleniia rastitel’nosti Arktiki.” Botanicheskii zhurnal, 1971, vol. 56, no. 1.
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Knapp, R. Die Vegetation von Nord-und Mittelamerika und der Hawaii-Inseln. Jena, 1965.
Walter, H. Die Vegetation der Erde in ôkologischer Betrachtung, vol. 2: Die gemassigten undarktischen Zonen. Jena, 1968.
V. D. ALEKSANDROVA