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).
