Increase of alien and C4 plant species in annual river bank vegetation of the River Rhine

Recent and historic releves of the annual river bank vegetation (Polygono brittingeri-Chenopodictum rubri, Chenopodium rubrum subassociation) of the middle and lower River Rhine (Germany) were evaluated with regard to their representation of alien and C, plant species. The releves evaluated covered a period of more than 50 years from the second half of the 20,h to the beginning of the 21(st) century. There was a distinct increase in the proportion of alien and C, plant species: The mean percentage of post-1492 aliens (neophytes) increased from 9.9% in 1964 to 27.5% in 2002. In the same period, the mean percentage of C-4 plants increased from 4.4% to 11.5%. In 1998 - 2002 99 alien plant species were recorded in the annual sand and gravel bank vegetation of the study area. Possible reasons for the increase of alien and C, plants may include increased trade activities and increased temperatures due to global climate change.