Ground cover change on fallow fields of Kargopol district of Arkhangelsk region

The paper analyses old cultivated herbaceous vegetation deposits located in the middle taiga subzone of Arkhangelsk region (Kargopol district), which are characterized by extremely fertile sod podsol on the carbonate moraine base. While carrying out the research, ancient deposits (15-130 years old; sample plots - 27) no longer used for agricultural purposes were investigated. Conventional geobotanic description techniques were applied. The research revealed occurrences of the herbal phytocenosis rotation (secondary succession) with specific succession in transition stages. The change was observed in the old cultivated herbaceous vegetation deposits for a significant period of time (over 100 years). In the early stages, meadow grass grows intensively, and agricultural species used in the crop rotation survive up to 40 years. Simultaneously, Gramineae - Asteraceae - Rosaceae - Le-guminosae association is formed, its composition includes the largest number of weed species and forbs composed of meadow grass. Then, an abrupt phytocenosis change takes place after 40 year term of rotation. This conclusion is proven by the analysis of phytocenosis similarities. At this stage, Rosaceae - Leguminosae association including forest grass species and the moss lichen sublevel are formed. The canopy predominantly consists of the shade tolerant species. Furthermore, when the stand canopy closed (60 years later), the native forest species started to dominate in the ground cover. The forest conditions began to stabilize. However, the obtained results showed that meadow grass species invade dominating ground cover.