Changes in the Flora Composition of the Volga–Akhtuba Floodplain after Regulation of the Flow of Volga River

Abstract

Studies were carried out on four stationary transects laid in the Volga–Akhtuba floodplain by the Caspian expedition of Moscow State University in 1954—1955. The transects were reexamined in 1982 and in 2008–2013. The occurrence of the most common plant species in each of the three study periods was assessed. It was established that xerophytization and ruderalization of the flora occurred on all transects. The severity of these processes was not the same on different sections of the Volga–Akhtuba floodplain. They were most significant near the Volgograd hydroelectric power station and in places of valley narrowing. The main cause of vegetation xerophytization and ruderalization was the decrease in the height and duration of floods after regulation of the Volga flow, the high local pasture, and the recreational load. In the northern part of the floodplain, significant changes in the vegetation cover were made by invasions of adventitious species in natural phytocenoses: Fraxinus pennsylvanica, Bidens frondosa, Conyza canadensis, and Xanthium strumarium s. l.