3.1 Environmental importance of floodplains

please provide general comments on section 3.1 here

Floodplains play an important role in flood risk management (see also section 3.4), by modifying the river discharge and protecting societies and economic activities from damages. Floodplains are also very heterogeneous habitats creating favourable conditions for many species and so have a high environmental value.

Floodplain water bodies

Under natural conditions, floodplains can contain a wide range of freshwater ecosystems including permanently flowing and temporal channels, oxbow lakes, spring brooks, tributaries and temporary wetlands. They are found along a gradient of decreasing hydrological connectivity from permanent to temporary links with the main channel of the river (Paillex, et al., 2007). The degree of hydrological connectivity influences major habitat components such as water physicochemical properties, its nutrient content, substrata and the morphology, which are the main drivers of biodiversity in floodplain freshwater ecosystems (Amoros, and Bornette, 2002). For example, studies on fish communities underlined the importance of diverse waterbodies in riverine landscapes for spawning and as nurseries, feeding and refuge areas (Aarts, et al., 2004), which can also support the re-settlement of the river after extreme disturbances.

Floodplain forests

The natural vegetation of floodplains in most European areas is dense riverside forest (Glaeser, and Wulf, 2009; Klimo, et al., 2001). Only a few areas such as open water, flood channels, silted up areas, and gravel banks are naturally non-wooded. The floodplain forests occur on nutrient rich soils, which have over time been deposited by rivers during flooding. They are among the richest and most complex forest ecosystems of Europe.

Rapidly growing softwoods such as willows and poplars are characteristic for floodplains near rivers with soil largely comprising sediment. Floodplain areas further away from rivers tend to have a lower water table and older soil, and therefore are often made up of hardwood tree species such as the English oak, ash or elm, but they also contain a high diversity of other tree species. While softwood forests annually experience between 60 and 180 inundation days, hardwood floodplain forests can be flooded between 1 and 60 days per year in the growing season. Because of their nutrient rich soils, a good water supply and diversely structured forest strata, old hardwood forests host one of the most species-rich and unique plant, bird or invertebrate communities of European forests (Scholz, et al., 2005).

Floodplain grasslands

Since centuries, floodplains have been used extensively for livestock feeding. Population growth and increased knowledge on flood-protection led to more intensive grazing and farming activities in floodplains during the Middle Age. Forests became more and more degraded and replaced by productive farmland and open extensive grassland. These man-made grasslands are characteristic of seasonally flooded areas and are characterized by a high diversity of grass and herbaceous species and regular management (EC 2008; Leyer, 2004). Such grasslands have small-scale relief features, including hollows and lower and higher areas with different flood return frequencies and different groundwater levels. Although floodplain grasslands cover most of the active floodplains in Western, Central and Eastern Europe, most of them are threatened by hydrological alterations, intensified and changing agricultural needs and changing policies (EC 2008; EEA 2015d).