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Biomes and Regions of Northern Eurasia

The Arctic Environments

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Polar Deserts

In polar deserts, little solar radiation is available as a result of the polar night and the low position of the sun during the polar day, and much of the received radiation is reflected by snow and ice. Annual radiation budgets do not exceed 10 kcal cm^-2. The growing season is very short, six to eight weeks, and is characterized by low temperatures. Apart from temperature, two other factors are of great importance for the environments of polar deserts: snow cover and wind. Heavy snowfalls are typical of the Barents province while in the Siberian provinces snow cover is lower. Thus, at Franz Josef Land the depth of the snow pack in coastal areas averages 40-60 cm (Govorukha, 1970) while in the Siberian provinces it is less than 30 cm (Semenov, 1970). Winds are strong across the polar desert biome. Snow is often blown away from raised sites and exposed slopes and is deposited in depressions and on the lower parts of slopes. Snow cover has a very different effect on vegetation in polar deserts compared to tundra. In tundra, snow cover has an insulating, protective function. In polar deserts, gradually melting snow has an extremely negative effect on the development of vegetation because it reduces the short vegetative period further. Thus, at Franz Josef Land, the most favourable conditions for the growth of plants occur where snow forms a cover about 20 cm thick and disappears by the middle of June. Where snow cover is thicker, the development of sparse vegetation is hampered further and where snow cover reaches 1 m and melts away after the middle of July, vegetation does not develop at all (Aleksandrova, 1988). Fohn winds, which form due to the relatively high topography and deep fjords, such as at Severnaya Zemlya, are important local factors. Fohn winds account for the formation of the arctic tundra oases containing such species as Salix polaris (Safronova, 1976).

Soil-forming processes are to a great extent suppressed and soils of polar deserts are skeletal. Frost weathering is the main agent which creates cryogenic types of surfaces. Freeze-sorting of substartes is a typical feature. The extremely low rates of chemical and biochemical weathering produce very little clay material; however, if clay fraction is present, the surface is often broken into polygons by fission. A characteristic feature of the polar desert polygons is their small dimensions which vary between 10 cm and 50 cm in diameter (Aleksandrova, 1988; Matveeva, 1979). Continuous vegetation often occurs in the form of moss-lichen swards developing along a network of polygons. In contrast to those of the tundra, soils of polar deserts do not have a pronounced peat horizon and gleying takes place only in favourable habitats at the southern part of the zone (Chugunova, 1979).

Polar deserts are a realm of bare rocks, shattered bedrock, and gravel. Plants are distinguished by their scarcity and by a low number of species. Closed plant cover is limited in extent in zonal habitats and is absent from a significant part of the territory, particularly from the tops of hills and nunataks. Blue-green algae dominate the soil microflora (Novikova-Ivanova, 1972). Lichens are the most abundant plants, followed by mosses; the role of flowering plants is insignificant and there are no dwarf shrubs. At Franz Josef Land, 115 species and subspecies of lichens, 102 of mosses, and 57 of flowering plants are known (Aleksandrova, 1988). At Cape Chelyuskin, 136 species and subspecies of lichens (Piyn, 1979), 74 of mosses, and 59 of flowering plants (Safronova, 1979) have been identified. At the northern edge of the polar deserts flora is even poorer: at the Zemlya Aleksandry island there are only 24 species of flowering plants and on the northern islands of Severnaya Zemlya there not more than 17 species. Crustose lichens often form a crust on the ground while flowering plant cover ranges between 1 per cent and 6 per cent (Aleksandrova, 1988). Flowering plants grow individually and their root systems do not intermingle. Biomass is low: on the Bolshoy Lyakhovsky island it does not exceed 5 t ha^-1 (Rodin and Bazilevich, 1965). Species composition differs between the Barents and Siberian provinces. The majority of the Siberian and Siberian-American species occur only in the southern part of polar deserts and further north the predominance of circumpolar flora becomes stronger (Young, 1971). Detailed reviews of the flora of polar deserts are given by Aleksandrova (1980, 1988).

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