The class Alnetea glutinosae comprises alder swamp forests and willow scrub occurring in habitats with a permanently high water table. Dominant species include Alnus glutinosa, Salix aurita and S. cinerea. The herb layer is formed of wetland plants such as tall sedges and grasses, while typical forest species are absent. In waterlogged sites litter decomposition is impeded and fen-like conditions begin to form.