Immigration of Acer negundo L. (Aceraceae) into the floodplain forests of the northwest of Orenburg oblast.
Acer negundo L., the invasive tree species of North American origin, is naturalizing in the floodplain forests of Orenburg oblast. Now A. negundo has created an extensive secondary range on the territory of Orenburg oblast and occupies an area of more than 20 000 ha. On the right and left sides of the Tok River in Krasnogvardeysky and Grachevsky districts in the northwest of Orenburg oblast, four test areas of 20×2000 m were laid, and inside each test area, 40 sample plots of 20×50 m were laid. Nine tree species were considered; the data of records were recalculated per 1 ha. In tree communities of the floodplain of the River Tok, an absolute dominance of A. negundo, which in abundance exceeded all other floodplain tree species (281.13 and 383.25 specimens/ha), was noted. The share of invasive species in the floodplain forests of this area on average was 66.39%. The performed calculation of natural renewal of woody vegetation showed the considerable superiority of undergrowth of A. negundo (130 833.50 and 178 831.50 specimens/ha). Naturalization of A. negundo in floodplains of Orenburg oblast influenced negatively the height, development, and renewal of local forest-forming species, leading to irreversible consequences of degeneration of the floodplain forests.