On the origin of birch forests on the Volga Upland

Spore-pollen and radiocarbon data were analyzed, resulting in the mapping of the main stages in the formation of birch forests and the forest-forming role of Betula sect. Albae on the Volga Upland. It has been established that birch appeared in the study area around 10 500 years BP as part of highly sparse tree communities of the cold ‘tundra-steppe’. The extent of birch stands within real pine-birch and birch cenoses was the greatest in the period 8000–6000 yrs. BP. In the last period of the Holocene (from 2500 yrs. BP onwards), high anthropogenic pressure has led to the formation of secondary forest types with birch. However, primary (native, pre-agricultural) forests with birch have also been preserved, especially in southern parts of the Volga Upland. These results are in good agreement with data for the adjacent territories (Cis-Urals, Central Russian Upland, southern spurs of the Volga Upland, Central Black Earth Region). Thus, based on the paleogeographic reconstructions and modern analysis of the distribution of birch communities, the modern groups of birch community associations native (primary) to the Volga Upland include: oak-birch forests (Betuleta nemorosa); paludal birch forests (Betuleta uliginosa); sub-steppe birch forests (Betuleta substepposa). The types to be recognized as secondary are feather-moss birch forests (Betuleta hylocomiosa); herbaceous birch forests (Betuleta herbosa), and the following associations: pine-birch forests with reed grass (Pinetum betuleto calamagrostidosobrachypodiosum); with round-leaved wintergreen (Pinetum betuleto pyroliosum rotundifoliae); with catsfoot (Pinetum betuleto antennariosum), with purple small-reed (Pinetum betuleto-calamagrostidosum canescens).