Stepe plants spread to North along disturbed habitats. This process is contemporary. Disturbed habitats (waterside slopes, baidzharakhs, querries, ground roads, village streets) are good for studying of the recent processes - successions and fluctuations of vegetation, soil-forming processes, etc. The study of the disturbed habitats in Kolyma lowland (tundra, forest- tundra) showed that the process of reclamation of these distribution is a common schematic character under the conditions of dry and cold climate with not infrequent hot days in the summer period.

First these disturbed habitats are vegetated with plant of the nearly habitats and plant - erosiophylles (Tripleurospermum hookeri Sch.Bip = Matricaria phaeocephala (Rupr.) Stefanss., Descurainia sophiodes Fisch.ex Hook.) O. E. Schulz, Lactuca sibirica (L.) Maxim. = Mulgedium sibiricum (L.) Lessing and others, which are generally regarded as weeds or ruderals, serving as pioneers in this case. Then steppe plants appear on dry bulges of the disturbed habitats: Artemisia dracunculus L., Festuca lenensts Drob., Poa botryoides (Trin.ex Griseb.) Kom. etc. Soil similar to steppe ones are also formed: humus is accumulated but not peat, medium reaction is close to the control, the amount of calcium and magnium absorbed increases.

Stanislav V. Maximovich
Institut of Soil Science and Photosynthesis,
Academy of Sciences of Russia
Pushchino, Moscow District 142292
RUSSIA
Phone: 923-35-58
E-mail: gilichin@issp.serpukhov.su