The share of anthropophytes in the tree stands of urban forests in Katowice (Silesian upland, S Poland)

Urban forests are an important element of nature in highly urbanised areas. Due to their specificity (e.g. fragmentation, disturbances, alien propagule pressure), they are particularly susceptible to the penetration of alien species. The aim of this study was to determine the share of alien species in the tree stand structure of urban forests in the city of Katowice (Upper Silesian Industrial Region). A total of 50 woody species were recorded in the analysed stands, including 31 native species and 19 of alien origin. The share of alien species in the stands of individual forests was significant, as they constituted from 15% to 44% of the total number. Among the 20 trees most frequently included in the stand, as many as six are species of alien origin (Robinia pseudoacacia L., Padus serotina (Ehrh.) Borkh., Acer negundo L., Quercus rubra L., Juglans regia L. and Fraxinus pennsylvanica Marshall). The most abundant species were Robinia pseudoacacia, Quercus rubra and Padus serotina. The local potential of alien woody species was determined using the index of their abundance in the understory; the highest value of the average abundance index was obtained by Padus serotina, Robinia pseudoacacia, Acer negundo and Quercus rubra. Most alien tree species were more likely to inhabit forest edges (ecotone zone).