Alien plants in forest communities of the Middle Volga Region: dissemination and degree of naturalization

In forest communities of the Middle Volga forest-steppe zone (within Penza, Samara and Ulyanovsk Regions) there are 60 alien species of vascular plants. 25 species of adventives (42%) have naturalized in forests, 7 species are epecophytes (Cotoneaster lucidus , Oenothera biennis, O. rubricaulis, and O. villosa, Populus suaveolens, Ulmus minor, Xanthoxalis stricta) and 18 species are agriophytes (Acer negundo, Amelanchier spicata, Bidens frondosa, Caragana arborescens, Conyza canadensis, Echinocystis lobata, Heracleum sosnowskyi, Impatiens parviflora, Fraxinus lanceolata, F. pennsylvanica, Lonicera tatarica, Lupinus polyphyllus, Malus domestica, Parthenocissus inserta, Salix euxina, Sambucus racemosa, S. sibirica, Ulmus pumila). Transformer-types are arboreal - Acer negundo, Fraxinus lanceolata, F. pennsylvanica, Parthenocissus inserta, Ulmus pumila, as well as herbaceous plants - Bidens frondosa, Conyza canadensis, Echinocystis lobata, Heracleum sosnowskyi, Impatiens parviflora. The introduction of alien trees and shrubs in the forest can lead to dense thickets, disrupt underbrush resumption and main forest-forming species growth, as well as negatively affect the herbaceous layer. Most vulnerable to the introduction of adventive plants are roadsides and the places where forests are close to human settlements. The introduction of alien plants in forest communities is the result of ornithochory (33; 54%), anemochory (11 species; 18%), anthropochory (8 species; 13%) or a combination of various ways of introduction.