The 20th century dynamics of the species composition of alien plants in the southern Arkhangelsk region

The article concerns changes in the composition and distribution of alien vascular plant species in the vegetation cover of the Ustya and Kokshenga rivers interfluve (middle taiga of the Arkhangelsk region) in the 20th - early 21st centuries. The article compares the data of own studies (1992-2024) and the flora data by A.I. Perfil’ev (1925). It was found that the current list of alien plants includes 56 species belonging to 22 families and five life forms. Representatives of the Asteraceae, Fabaceae, and Rosaceae families predominate; among the life forms, annual and perennial grasses are most widely represented. According to their natural ranges, more than a half of alien species come from the southern and western regions of Europe, the Mediterranean, Asia Minor, and the Caucasus. The main ways of alien species penetration into the middle taiga area are, first of all, intentional introduction and subsequent spread of plants from plantations, as well as unintentional distribution along railways, highways and as a result of the transportation of agricultural products. Changes in the composition of alien species over almost a century have showed a significant increase in taxonomic diversity. The total number of species has become almost one and a half times larger, and the number of families increased by 36%. The number of aliens from North America increased threefold, and plants from East and South Asia have appeared. In terms of penetration and spread, transport routes, especially railways, have acquired greater importance. More than 30% of alien species grow now in natural communities (secondary forests, meadows and overgrown fallow lands), which is twice as much as at the beginning of the 20th century. Other species grow in disturbed communities, along roadsides and field edges, as well as in old settlements. At present 16 species of alien plants identified within the studied area are on the lists of invasive species according to the Black Books of the Central Russia and neighboring regions. Therefore they are of a real threat to the biodiversity of natural communities.