The saturated, periodically flooded edges of lakes are naturally colonised by Reed (Phmgmites australis) and tall sedges (for example, Carex elata). This stage of reed or tall sedge swamp is followed by moistureloving woody plants, such as Alnus glutinosa, Prunus padus and several Salix species, forming a wet woodland or carr. Shade-tolerant helophytes, for example ferns, Carex elongata or Calla palustris, dominate the ground layer (Figure 8.7).
Fens and straw meadows
Only if the environment is very poor in nutrients will a wood-free fen or low bog form naturally. In Central Europe, such plant associations mostly result when carrs have been cleared. In the long term they can only be preserved if mown once a year. Mowing has been practised in the autumn since the Middle Ages to obtain straw for farm animal bedding. Typical plant communities of wet straw-meadows are low sedge swamps, formed by shallow growing Carex species, such as Carex davalliana, C. flava, C. nigra or others, along with attractive flowering perennials. The construction of drainage ditches results in dryer types of straw meadows, characterised by the Purple Moor Grass (Molinia caerulea), again including visually attractive forbs.