Environmental variation as a key process of co-existence in flood-meadows

QuestionHow does the species composition and functional structure of flood-meadows change over time during a period with strong variations in flooding frequency and height? LocationFlood-meadows at the northern Upper Rhine, Germany. MethodsFrom 1998 to 2004 annually, and again in 2008, species composition and above-ground biomass were studied in 46 permanent plots located along a flooding gradient ranging from frequently flooded Magnocaricion to rarely flooded Arrhenaterion meadows. The plots were situated in the functional floodplain (natural) and in the fossil floodplain on the land side of high winter levees (anthropogenic altered). Temporal variation of the functional structure was analysed based on community-weighted mean traits. ResultsProductivity and functional structure varied markedly over the study period and between the functional and fossil floodplain. During the study period two contrasting extreme events occurred: a summer flood in 1999 and a drought period after 2003. After the flood in 1999, species composition and functional structure of the studied flood-meadows shifted towards the species composition of wetter sites. Flooding reduced species richness in the functional floodplain, but not in the fossil floodplain. ConclusionsFlood-meadows in the Upper Rhine fully recover from extreme disturbance events within a time frame of less than 10yr. Environmental fluctuations and disturbances, enabling the co-existence of species with contrasting ecological requirements are a key factor for the preservation of plant biodiversity in flood-meadows.