natural continental zones mainly in the northern hemisphere in arctic and subarctic zones. The few tundra zones in the southern hemisphere comprise small areas on islands near the antarctic. In the northern hemisphere the tundra zone is located between the zones of arctic wastelands in the north and the forest tundras to the south. It extends as a strip 300 to 500 km wide along the northern coast of Eurasia and North America.
The latitudes in which the tundra zones are located have a low annual radiation balance (in the northern part of the northern hemisphere 7–8 kcal/cu cm, and in the southern part up to 20 kcal/cu cm). From October to April the radiation balance is negative. The winter lasts eight to nine months, with 60 to 80 days of polar night during which radiation heat does not enter. In the tundra zone of the European USSR the mean January temperature is from –5° to – 10°C; in Northeastern Siberia and the Far East frosts of –50°C or lower have been recorded. The snow cover, which exists from October to June, is 50–70 cm deep in the European USSR and 20–40 cm deep in Eastern Siberia and Canada. Blizzards are frequent. The summer is short, with a prolonged polar day. Above-zero temperatures, sometimes as high as 10° to 15°C, are noted for two or three months; however, frosts are possible on any summer day. The vegetative period is 50 to 100 days. The summer is characterized by high relative air humidity, frequent fogs, and light rainfall. Precipitation is sparse: the plains have an annual rate of 150–350 mm, and the mountains up to 500 mm. The precipitation rate almost everywhere exceeds the evaporation rate, thereby promoting the formation of swamps and wet soils with concomitant processes of gleying.
The distinguishing features of tundra zones are treelessness, the prevalence of a sparse moss and lichen covering, severe swamping, wide distribution of permafrost, and brevity of the vegetative period. There is a predominance of flat lowlands. The mountains (Paikhoi, Byrranga, Koriak, the mountains of Baffin Island) are usually isolated massifs of medium elevation with traces of ancient glaciation. In the formation of tundra topography a large role was played by ancient glaciers, by the repeated transgressions of polar seas, and by modern permafrost processes, which cause the mosaic quality of the microtopography. Fossil ice, ice layers, and hydrolaccoliths are widespread. The depth of permafrost in northern Eastern Siberia reaches 600 m, in northern Alaska 300–400 m, and in northeastern Europe 20–60 m.
Severe climatic conditions in the tundra zones are the cause of the impoverished organic life. The vegetation includes only 200 to 300 species of flowering plants and about 800 species of mosses and lichens. The plant cover is often discontinuous; most characteristic are spreading forms of cushion plants, with roots located in the highest (best-heated) layers of the soil. The total volume of the phytomass is 10–12 quintals per hectare. In the south the phy-tomass volume is 25–30 quintals per hectare, and there is an annual increase of 5–7 quintals per hectare. In the river valleys, where woody vegetation grows, the phytomass increases to 500 quintals per hectare.
The animal world is unique. The willow grouse, alpine ptarmigan, reindeer, wolf, lemming, and arctic fox are characteristic. The musk ox is also encountered. Numerous aquatic birds nest in tundra zones during the summer. Mosquitoes and other bloodsucking insects are abundant. Invertebrates make up about 90 percent of the zoomass.
The principal occupations of the human population of the tundra zones are reindeer breeding, fishing, and hunting of fur and marine animals.
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.
Mil’kov, F. N. Prirodnye zony SSSR. Moscow, 1964.
V. A. MARKIN