Resumen
River channels are regulated in various ways and the fertile soils of valleys are occupied for agricultural purposes, accompanied by human settlements. In many places on the floodplains, gravel or sand is mined and former pits fill with water. The consequences are changes in water relations, changes in land use and land cover. Natural riparian ecosystems gradually disappear. In addition, river valleys are susceptible places for the spread of invasive plant species. In the section of the Upper Odra Valley discussed in this article, all of the aforementioned factors have played roles in shaping modern habitats. The present study shows the impact of human-induced changes on the transformation of the plant cover of the Upper Odra Floodplain. In designated transects, we studied land use changes from 1910 to the present day and examined plant species diversity. The results show that the more heavily transformed floodplain adjacent to the channelized channel has a higher level of species diversity than agricultural areas located along a section of the river with a natural channel course. Most of the river valleys are colonized by geographically invasive alien species, such as Reynoutria japonica, Reynoutria sachalenesis and Impatiens glandulifera, which have contributed to the fact that all of the species typical of the ash, poplar and willow riparian forests characteristic of this habitat type have retreated, which is the main reason for the very low biodiversity.