| Résumé | Bogs are an integral part of the tundra terrain of the plains. In the tundra zone they occasionally occupy up to 70% of the area. Estimates are that bogs in Western Siberia occupy 6.1 million hectares. The main type of tundra bog, including polygonal bogs, occurs on flat undrained water divides, on the bottom of drained lakes, on terraces and in river valleys. The polygonal forms are due mainly to the effect of frost fracturing accompanied by cryogenic and geological processes such as thermokarst, formation of ice inclusions, etc. Different morphological varieties of polygonal bogs have been noted and types such as ridged- polygonal, concave-polygonal and flat-polygonal are well known. On this basis a typological classification has been developed for the tundra zone. Apart from polygonal bogs there are also bogs of uniform structure in the tundra such as grassy shrub-covered, shrub-covered and moss-covered etc. These types occur around lakes, in run-off depressions and on other terrain forms, and can be classified on the basis of occurrence and vegetation. Their vegetation is usually fairly uniform and is represented by several species of flowering plants and mosses. |
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