The most invasive tree and shrub species in Polish forests.
More than 200 alien woody plant species can be found in Polish forests. A considerable part of them was introduced into the forest environment intentionally, whereas a relatively small group of taxa has found its way there as a result of spontaneous migrations from cultivated land outside the forests. The majority of the alien trees and shrubs is rarely found, has not settled permanently and does not pose a significant threat to forest biological diversity. Approximately 10% of the above-mentioned number of species can be treated as invasive plants, including: Acer negundo, Amelanchier lamarckii, A. spicata, Aronia × prunifolia, Celtis occidentalis, Clematis vitalba, Cornus sericea, Cotoneaster lucidus, Fraxinus pennsylvanica, Prunus serotina, Quercus cerris, Quercus rubra, Robinia pseudoacacia and Spiraea tomentosa. Based on the field observations, the dynamic trends of the species and indicated factors that contribute to their spread in forest areas in Poland, are characterized.