Hardwood floodplain forests (Ficario-Ulmetum, Syn.: Querco-Ulmetum), being amongst the most endangered plant communities in Germany, have been selected as ‘Plant community of the year 2021’ by the Floristisch-soziologische Arbeitsgemeinschaft. Hardwood floodplain forests are temperate lowland broad-leaved forest ecosystems typical of extensive river valleys. In Central Europe, stands represent biodiversity hotspots for woody species (as habitats for rare tree species such as Ulmus laevis and Populus nigra), but also host numerous fungi and animal species typical of floodplains. Since floodplains have been subject to river regulation activities for centuries, to date less than 10% of the former natural area of floodplain forests remained. Current threats are overexploitation, cultivation of non-native tree species, floodplain construction projects accompanied by drainage, eutrophication, invasive species, and outbreaks of elm and ash dieback by fungi infections and climate change. River flooding constitutes an important abiotic site factor, which in turn is responsible for site-specific disturbance processes such as ice drift, sedimentation or erosion. Remnants of near-natural hardwood floodplain forests are of outstanding conservation value and deserve protection within large-scale nature reserves in riverine landscapes. Successful restoration requires to reestablish the flooding regime, as a precondition for the reintroduction of important plant, fungi, and animal species originating from appropriate donor populations.