Invasion of the Ash-Leaved Maple (Acer negundo L.) in the Buzulukskiy Bor National Park

The invasion of Acer negundo L. into floodplain forests with the dominance of Alnus glutinosa (L.) Gaertn. has been studied in the Buzulukskiy Bor National Park located in the Orenburg region. In this region, this invasive species is observed in various forest stands. According to the current data, it occupies over 20 000 hectares or ~5% of the total forest area and is actively naturalizing in natural floodplain forests. A. negundo is included into the “black list” of Orenburg and neighboring regions and in the “black hundred” of invasive species of Russia. This work was arranged on two bands of sample plots located on the right and left banks of the Borovka River that flows through the protected area (65 plots in total, each 20 × 50 m in size). The woody phytocenoses of the Borovka River floodplains are formed mainly by Alnus glutinosa, Salix alba L., Acer negundo, and Populus nigra L. For the entire studied area, the dominant species is A. glutinosa (100% occurrence), whose average number reaches 545 per ha (80.4% of the total number of trees) and significantly exceeds the total number of trees of other species. The average number of A. negundo trees is 34 per ha (66.2% occurrence); this invasive species takes the third place among tree species after S. alba (46 per ha, 63.1% occurrence). Another 11 tree species have been classified as species of low importance for the floodplain communities of the Borovka River. According to the obtained data, the dense and mature riparian forest formed mainly by A. glutinosa with the admixture of S. alba and P. nigra is able to maintain the balance of its species diversity, and both the invasion and the degree of dominance of A. negundo do not exceed the value of a secondary species with a 5% share in phytocoenoses on average (for some sample plots, the maximum share of this species reaches 17–20%). A. negundo invasion into floodplain forests of the Buzulukskiy Bor National Park causes undesirable floristic pollution of this protected area.