Distribution of an Invasive Species of Heracleum sosnowskyi Manden. (Apiaceae) in Leningrad oblast

In Leningrad oblast, Heracleum sosnowskyi hogweed prefers well-developed fertile light and medium loamy sod-podzolic and sod-carbonate soils; it is practically absent in swamps and wetlands and in territories occupied by spruce forests, as well as pine forests with infertile thin soils on sandy and rocky substrates. The most favorable hydrothermal, orographic, hydrological, soil, and ecological conditions for the development and spread of Sosnowsky's hogweed are observed in the western, agriculturally developed areas (Slantsevsky, Kingisepp, Lomonosov, Volosovsky, Gatchina) with dismembered hilly relief, cultivated fields occupying 7-13% of their territory, and fallow lands. To the south, east, and north of the area, the conditions for development and spreading of hogweed become markedly worse, which is caused mainly toward the south and east by the flat low character of relief, its waterlogging, the spread of spruce and pine forests that are mostly unfavorable for hogweed, and thin and poor soils on rocky substrates, especially to the north on the Karelian Isthmus and in the Podporozhsky district in the northeast.