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Changes in forest cover in the center of the East European Plain (Central Russian Upland) from the end of the 19th century to the end of 20th century have been assessed. Over that period, forest cover has increased in the northern part of the studied territory and declined in the southern part. After the end of the 1990s and beginning of 2000s, increases in forest cover occurred within the subzones of mixed coniferous–broad-leaved forest, while in the southern regions it has hardly manifested at all. The fallow land overgrowth rate, without any anthropogenic interference, has been determined for the Central Russian Upland (from 10 to 50% of fallow area has been covered by forest vegetation over a period of 10 years), decreasing gradually in from west-northwest to east-southeast. Special attention is paid to the forests that grew on nonforested lands over a period of 150 years. This process occurs everywhere in the northern part of the Upland and along the river valleys in the southern part. The forest structure of newly formed forests is studied as well (deciduous, mixed, pine, and spruce). In the southern parts of the Central Russian Upland, the newly grown forests are mostly pine plantations. The analysis of the field data suggests that, in the Central Russian Upland, within the broadleaved forests subzone, fallows are usually overgrown with birch (Betula pendula), or, less frequently, with aspen (Populus tremula). On the western and southwestern slopes, the overgrowth occurs with broadleaved (Querqus robur and Acer platanoides), small-leaved (Populus tremula), and steppe species (Prunus spinosa, Malus praecox, and Pyrus pyraster). In the south, overgrown fallows are dominated by steppe or adventive species (Acer negundo).

The results of floristic studies on plankton in the Barents Sea performed from 2007 to 2018 are discussed in the paper. The findings of 16 species new to the indigenous flora were documented and their distribution in the Barents Sea and adjacent waters was analyzed. We also calculated statistical indicators (indices) that characterize the regularity and quantitative expression of their presence in certain sectors of the sea. The data obtained demonstrate the intensity and direction of invasion of Atlantic algal flora. The most intense and regular invasion is directed eastward from the southwestern border of the Barents Sea to its central part. No less stable, but a less intense vector of influence of Atlantic flora was found in the northwestern Barents Sea directed southward to the central and eastern parts of the sea. These processes are characterized from the historical aspect as the activation of florogenesis coincident in time and, most likely, caused by the current climatic situation in the region, mainly by the increased advection of Atlantic water. At least one adventive species has been discovered to be currently integrated into the succession system of the Barents Sea phytoplankton in the position of seasonal dominant.

The paper summarizes new and literature data on the species composition, trophic relationships, and population dynamics of phyllophagous lepidopterans dominant on woody plants in St. Petersburg and its environs (Russia). Most of these species have concealed larvae (e.g., leaf miners and leaf rollers), and some of them are invasive. The data were accumulated during approximately a hundred years of observations and field collections. Concealed species form the dominant group within the studied complex of phyllophagous moths in St. Petersburg and Leningrad Province (27 species from 13 families). Changes in the composition of dominant pests of the dog rose, bird cherry, elm, poplar, and other woody plants have been recorded. Outbreaks of some species, such as Phyllonorycter salicicolella (Gracillariidae), Archips rosana (Tortricidae), Leucoma salicis, Lymantria monacha, and Orgyia antiqua (Erebidae), were recorded during the XX century but since about 1980 the population density of these species has remained at a very low level. Another group of species, which includes Phyllonorycter populifoliella (Gracillariidae), Batrachedra praeangusta (Batrachedridae), Acleris bergmanniana, and Epinotia abbreviana (Tortricidae), demonstrated a sharp increase in population density in the 1990–2000s, a phenomenon which had not been observed before. The possible causes of such population dynamics are discussed. The dominant species of phyllophagous micro-lepidopterans, including some recent invaders (e.g., Cameraria ohridella and Phyllonorycter issikii, Gracillariidae) and adventive species (e.g., Ph. populifoliella and Ph. acerifoliella, Gracillariidae) pose a serious threat to woody plants in St. Petersburg and Leningrad Province.

The distribution and phytocenotic association of Parthenocissus vitacea and Vinca minor on the territory of the Bryansk oblast has been studied. An assessment of the distribution of invasive species is performed on a grid basis. Vinca minor is registered in 19 cells on the territory of the oblast, which is 4.9% of the total number of cells and 11.9% of the surveyed cells; Parthenocissus vitacea is registered in 50 cells, which is 12.8% of the total number of cells and 31.2% of the surveyed cells. The invasive status of Parthenocissus vitacea and Vinca minor is category 3: an adventive species whose invasions into natural and seminatural habitats in the region at the moment are rare and, as a rule, confined to the outskirts of populated areas, abandoned parks, and old plantings. The indices of successful invasion in forest communities is the formation of syntaxonomically valid variants of the communities of Corylo avellanae-Pinetum sylvestris Bulokhov et Solomeshch 2003 with depleted cenoflora. Invasive species change the phytosphere and reliably decrease the indices of α and β diversity, the structural indices of communities. The invasion of Parthenocissus vitacea and Vinca minor is successful due to active vegetative reproduction, allelopathic effects on native species, and decreasing illumination of the ground cover. The introduction of invasive species into complex pine forests blocks demutational changes of endogenous succession during the restoration of broad-leaved forests: they simplify the structure of communities and reduce the intensity of the mosaic. Parthenocissus vitacea and Vinca minor can exhibit signs of an edificator, a community builder, and a violent and transformer type. There has been only one case of a radical transformation of the natural community, registered on the territory of the Lyubin Khutor nature monument (Novozybkovskii district, Bryansk oblast).

The data on the distribution of Canadian pondweed (Elodea canadensis), an invasive aquatic plant native to North America, in the Republic of Bashkortostan are presented. This species has widely expanded in Bashkortostan and poses a threat to the Southern Ural ecosystems. Canadian pondweed is naturalized in waters of this region and occurs in various aquatic vegetation types; it often replaces native species and forms monodominant communities of the Elodeetum canadensis association. The species is present in many other aquatic communities, including 32 associations and six unions of the Lemnetea and Potametea classes of aquatic vegetation. A map of the secondary range of Elodea canadensis on the territory of Bashkortostan is charted.

In 2018, all the three species of the weevil genus Otiorhynchus Germ.: O. albidus Stierlin, O. asphaltinus Germar, and O. rotundus Marseul, first recorded from St. Petersburg in 2017, were present at approximately the same densities on Syringa vulgaris L. and S. josikaea Jack. in the places where they occurred in 2017.

The relative competitiveness of adventive plants in herbaceous communities of the Western Caucasus is analyzed using a simple mathematical model, Sa = Na(S/N), where N and S are the numbers of vascular plant species on 15-m2 and 0.5-m2 plots, respectively, and Na and Sa are the numbers of adventive plant species on 15-m2 and 0.5-m2 plots, respectively. The model is based on two assumptions: (1) stochastic character of the processes of species immigration and extinction occurring on the area of plant communities, and (2) ecological equivalence of indigenous and adventive species. If adventive species of a herbaceous community are characterized by a higher or lower competitiveness as compared with indigenous species, then one should expect the actual number of these species on 0.5-m2 plots to be higher or lower as compared with the number calculated using this model. The communities of low-mountain and mid-mountain near-riverbed shoals, forest glades, steppe meadows, annual crop fields, fallow lands, and the herbaceous layer of low-mountain forest communities are chosen as the objects of this study. The results show different competitiveness of adventive plants in different herbaceous communities of the Western Caucasus.

On the basis of the deductive approach of floristic classification of plants, five derivative communities formed by adventive species, Solidago gigantea, Asclepias syriaca, Aster × salignus, Sorbaria sorbifolia, and Spiraea alba, are determined. The ecological and floristic characteristics of the communities are given.

The effect of adventive dominants (Erigeron annuus, Solidago canadensis, Ambrosia artemisiifolia, Asclepias syriaca, etc.) on the composition and species richness of fallow plant communities (Belaya River basin, Western Caucasus) are analyzed. The results show that (1) adventive dominants have light effects on the composition of fallow communities; (2) communities with more abundant adventive dominants are characterized by lower community species richness on the plots of 0.5 and 15 m2 as a whole, and a lesser number of native species and higher number of adventive ones; and (3) communities with more abundant adventive dominants are characterized by a lower average frequency of native and adventive species on the plots of 0.5 m2. However, the relations between all these characteristics are poor.

The floristic composition of plant communities dominated by Carex acuta in the northern Volga-Akhtuba floodplain has been analyzed over the period from 1928 to 2009. It has been shown that, in 2008 to 2009, some hygrophytes disappeared from these phytocenoses; simultaneously, their composition was enriched with mesophytes and adventive species. Ramenskii’s ecological scales have indicated a decrease in water supply to habitats of the communities studied.

The data on the species composition of the alien flora and the groups of adventive species according to the time, the way of their transfer, and the degree of naturalization are presented. Rare and newly revealed species are recorded. The degree of flora adventization in protected natural territories and of urban floras is evaluated. The plants of the basin that are included in the list of quarantine species and the Black Book of the flora of Central Russia are distinguished.

The adventive fraction of the Middle Ural flora is represented by 328 species of vascular plants from 198 genera and 51 families. Most of the adventive plants are nonaggressive and form the group of epecophytes (41%); all these plants have been accidentally introduced into the Middle Ural flora (xenophytes). Ephemerophytes occupy second place in the number of species (27%). More than half of this group (60%) is represented by ergasiophytes. The maximum diversity of ephemerophytes is observed in the urban flora (26%) and along railways (23%). Colonophytes form a group of similar size (26%), and most of these species are introduced plants. Agriophytes (18 species, or 6%) represent the most aggressive group. Among them, 78% belong to xenophytes and 22% are ergasiophytes. Thirteen agriophyte species represent alien plants: Heracleum sosnowskyi, Artemisia absinthium, Conyza canadensis, Impatiens grandulifera, Bunias orientalis, Chenopodium album, Convolvulus arvensis, Echinocystis lobata, Hippophae rhamnoides, Elodea canadensis, Epilobium adenocaulon, Epilobium pseudorubescens, and Amelanchier spicata. Thus, alien plants are a minor component of the adventive flora of the Middle Urals (4%).

The results of the study on naturalization of adventive plants in Magadan region are given. The list of adventive flora of the region consists of 292 species and includes 22 pseudoaboriginals. Ergasiophygophytes include 42% of ephemerophytes, 34% of colonophytes, 16% of epoecophytes and 8% of agriophytes. Xenophytes consist of 15% of ephemerophytes, 40% of colonophytes, 26% of epoecophytes and 19% of agriophytes. Unintentionally introduced species have greater potential to naturalization. Pseudoaboriginal xenophytes have greater part of epoecophytes than other xenophytes. Sixteen percent of adventive species spread to natural ecotopes.

In the territory of the Vyatka-Kama Cis-Urals, 22 species of alien macrophytes are recorded. They compose 6.5% of the number of known macrophyte species known for the region. Most of them do not play an active role in formation of vegetative communities and constitute a part of aquatic communities as accompanying elements (Amaranthus retroflexus, Chenopodium glaucum, C. rubrum, Xanthium strumarium, Epilobium pseudorubescens, Juncus gerardii, Senecio vulgaris, Typha laxmannii, Mimulus guttatus, Butomus junceus, Scirpus tabernaemontani, and Zannichellia repens). They grow in secondary and open natural ecotones and do not pose a serious threat to aquatic ecosystems in the region because of their low activity in aquatic communities. Among alien species of macrophytes, invasive species are encountered. Some of them (Najas major, Vallisneria spiralis, Phragmites altissimus, Juncus tenuis, and Echinochloa crusgalli) have become a constant part of secondary biotope communities but pose a threat to indigenous macrophyte species only in specific biotopes where ecological conditions differ significantly from normal ones. Other species (Elodea canadensis, Epilobium adenocaulon, Impatiens glandulifera, Mentha longifolia, and Lemna gibba) have successfully naturalized in natural ecosystems or have been penetrating into them. The overwhelming majority of alien macrophyte species within the region are plants which do not refer to aquatic plants: hygrophytes (ten species or 45.5%) and hygromesophytes (three species or 13.6%). Only five species (22.7%) belong to hydrophytes and four species are helophytes (18.2%). Six species of alien macrophytes are characterized by transcontinental (North America) drift, 12 species (54.5%) are characterized by transzonal drift, and four species (18.2%) have been introduced from adjacent natural zones.

The blacklist of Bryansk oblast flora including 100 adventive species is compiled. Plants from this blacklist are divided into four groups based on the classification recommended for keeping Black Books.

The saturation of herbaceous communities with adventive species in the Northern Caucasus has been estimated using as an indicator the number of such species in 0.5-m2 plots. Among factors accounting for variation in the test parameter, consideration has been given to the coverage of the herbaceous layer, the species richness of communities (in 0.5-m2 plots), and the numbers of adventive and indigenous species (in 15-m2 plots). The field data have been processes by methods of ordinary and multivariate regression analysis. The results show that variation in saturation with adventive species between small areas of herbaceous communities largely depends on the number of such species in larger areas, their species-holding capacity, and the level of completeness of communities.

The results of analysis of adventive species of the Crassulaceae family from different regions of the Earth are presented. The highest number of alien and naturalized species of Crassulaceae is found in Australia (approximately 50 species). Most of these species grow in New Zealand, North America, and Europe. There are known cases of wild Crassulaceae in Eastern Europe. The following species of Crassulaceae were identified in this region as adventive: Phedimus spurious, Ph. crenatus, Ph. stoloniferus, Sedum reflexum, S. forsterianum, S. lineare, S. sexangulare (wild in western regions of Eastern Europe and naturalized in Izhevsk and others), Hylotelephium erythrostictum, Aizopsis hybrida, A. kamtschatica, Sempervivum tectorum, and others. Data on naturalization of Sedum album L. and Hylotelephium spectabile appeared recently. Our studies showed that, at present, Sedum reflexum is most actively naturalized in Eastern Europe and the Caucasus. Most adventive Crassulaceae can be considered as neophytes or colonophytes (rarely ephemerophytes).

The results of the study of adventive species of Caprifoliaceae Juss. S.L. on the territory of the Northwest European part of Russia are presented. At present, 6 wild and 16 adventive species from this family are found on the territory of St. Petersburg and Leningrad oblast. An analysis of adventive species according to the degree of naturalization from appearance of self-sowings around plantings (first stage of naturalization) until entering the natural plant communities (last stage) is carried out.

Eight species of Heteroptera, including one adventive species (Elasmostethus sp.) and one aquatic species (Callicorixa producta), were found on Dolgii Island (the southern tundra subzone). Among the seven indigenous species, six are Holarctic; the distribution of five species is confined to tundra landscapes, and five species are predators. The phytophagous Chlamydatus acanthioides and Nysius groenlandicus are associated with the most humid and the best drained parts of the inland landscape, respectively. The predatory species of the family Saldidae, Chiloxanthus arcticus, Ch. stellatus, Salda littoralis, and Calacanthia trybomi, show specific patterns of distribution among the biotopes with different levels of humidity and salinity. The biotopic preferences of Chiloxanthus species vary significantly within their ranges. The northward expansion of Heteroptera appears to be limited by the mean July isotherm of +3°C.

Data on an adventive species new to the flora of the Republic of Mordovia, Rosa glauca Pourr., are given. Several locations of the species were discovered in Romodanovskiy district. One cenopopulation of R. glauca was registered on a steppe slope together with several rare plant species—Adonis vernalis L. and Iris aphylla L.