Invasions of bird-dispersed shrub species in specially protected natural reservations of Saint-Petersburg and Leningrad Region

The research deals with recent invasions of bird-dispersed shrubs in specially protected natural reservations of St.Petersburg and Leningrad Region. The results of bird-dispersed woody species inventory in 5 partial nature reserves and nature sanctuaries of the area (See Fig. 1), based upon the extensive phytocoenological research data of 2014-2018, are given (See Table 1). Out of the adventive shrub species listed, the two most aggressive invaders were chosen according to their constancy and abundance in natural forest communities. These are Lonicera nigra in Komarovskiy Bereg [Komarovo Coast] Nature Sanctuary and Amelanchier spicata in Lisinskiy [Lisino] Partial Nature Reserve. For this purpose, distributions of these species are traced along with different forest types they invade, paying attention to species constancy and projective cover in different layers of forest communities (See Tables 2 and 4). Values of intralandscape species activeness, based upon the proper relevé sets, were also calculated for both aboriginal and adventitious plant species from different community types in each study area (See Tables 3 and 5). Lonicera nigra has never been detected as an invader before. It is presumably dispersed by robins, thrushes, and warblers, also by means of barochory and secondary hydrochory. The latter is proved by the occurrence of the oldest shrubs in riverine Norway spruce and Scots pine forests on the Littorine terrace of the Gulf of Finland within Komarovo Coast Nature Sanctuary. The results of secondary bird dispersal of this species are observed in sorrel spruce forests where the untypical low shrub layer is being formed (See Fig. 2). These plants are remote form brooks or drainage channels (See Table 2). L. nigra acts as one of the most active species in the sanctuary forest coenofloras studied (See Table 3). Nevertheless, floristic composition of these forest communities remains yet unchanged in its main features. The invasion of L. nigra in the sanctuary area was first mentioned in literature by NN Tzvelev in 2000 but it took place much earlier, as the ancestral plant specimens were likely to grow in a transplant nursery near the present-day sanctuary north-eastern border in the early XX-th century. According to Komarov Botanical Institute Herbarium (LE) data, the secondary area of L. nigra in Russia is restricted to several findings in the Karelian Isthmus. Amelanchier spicata, the June berry, listed among the most aggressive plant invaders in European Russia, is dispersed by thrushes along roads in forests and then invades sorrel and horsetail-peatmoss spruce and pine forests on southern-boreal watersheds in Lisino Reserve, often as a gap-filling species. It is less common and abundant in secondary birch and aspen forests. In contrast to Lonicera nigra, it is infrequent and never abundant in riverine forests (See Table 4), the fact probably explained by difference in prevailing bird distributor species. A. spicata is never found in feathermoss pine forests on fluvial-glacial sand as well as in dwarfshrub-peatmoss pine bog forests. The invasion of this species in the reserve area probably took place after 1984-1987 when the species was not registered in forest communities of the area according to the author’s personal observations. In 2017, the activeness of A. spicata is low in all the forest types it inhabits, being compared to that of the dominant aboriginal species (See Table 5). As follows from the correlation analysis results, no one of the discussed invaders affects the projective cover of any of the native plant species in both protected areas significantly. Speaking of Amelanchier spicata, it is in fact far less aggressive than in the more southern areas of Central and Southern Russia where the species transforms forest communities actively and affects aboriginal field- and ground-layer plants negatively, even as far as to the extinction of some of the latter, as it is well-known from the literature on the subject. We are just at the beginning of the invasion process in the forests of the Russian North-West yet. The invasion of both species studied is likely to be connected with the climate change processes. The research reveals that a neglected adventive species, persisting long within a given area, may also suddenly become an aggressive invader (the case of Lonicera nigra). The invasion of adventive shrubs into the paludified forest communities, including those of the boreal peatmoss spruce forests which served as etalons of floristic stability quite recently, is also alarming.