Structure and dynamics of alien flora of the railroads in the forest-steppe zone of Middle Volga Region

The following paper is a result of many-year-observations of the railways flora in the Middle Volga Region. Observations were carried out on the territory of several entities with different configurations of the railway network and the intensity of its operation. The cited data characterize the foreign component as a two-level dynamic system consisting of a core and a fluctuating outer belt. The core is represented by American and Eurasian invasive species that are firmly established in the natural plant communities and capable of prolonged growth in one place. External fluctuating belt consists of naturalized alien species and permanently or occasionally presents in the composition of ruderal vegetation, capable of changing their numbers, depending on the living conditions and the operation of the railways. Structurally alien flora is formed under the influence of extreme living conditions that is reflected in the predominance of annual herbaceous plants xerophytic spectrum, as well as the cosmopolitan weed. The taxonomic structure shows impoverishment of the species composition, low values of the species occupancy rate, but at the same time the generic fillability of the families shows relatively high indices. In general, foreign component flora characterized by considerable resistance to extreme environmental conditions, is capable of long-term existence in a certain area, with a tendency to settling in adjacent territories characterizing similar habitat conditions.