Patterns of invasive plant species distribution in the Upper Volga basin.
The patterns of invasive plant species distribution in the Upper Volga basin territory (including five administrative oblasts - Ivanovo, Kostroma, Vladimir, Yaroslavl, and Tver) are considered. The present flora of this district comprises 770 alien species, among which 135 are successfully naturalized in natural and seminatural communities and 32 (4.2%) are invasive plants. Only 24 invasive species (3.1%) are widespread in all Upper Volga regions, which is in concordance with a hypothetical model of invasion intensity by Di Castri. The majority (e.g., Bidens frondosa, Elodea canadensis, Epilobium adenocaulon, Juncus tenuis, and Impatiens glandulifera) have invaded waterbodies and riparian communities. Some species (e.g., Acer negundo, Amelanscier spicata, Fraxinus pennsylvanica, and Sambucus racemosa) are commonly recorded in different types of forest and shrub ecosystems; others are found in grasslands. Echinocystis lobata, Heracleum sosnowskyi, Hippophae rhamnoides, and Impatiens parviflora are the most aggressive and play the role of a transformer. The examples of local invasions are described. A potential invasive group comprises 26 alien species, which compete successfully with native species and tend to invade plant communities (e.g., Crataegus monogyna, Populus balsamifera, Parthenocissus inserta, and Reynoutria japonica).