fen

Wikipedia:

A fen is one of the four main types of wetland, and is usually fed by mineral-rich surface water or groundwater. Fens are characterised by their water chemistry, which is neutral or alkaline, with relatively high dissolved mineral levels but few other plant nutrients. They are usually dominated by grasses and sedges, and typically have brown mosses in genera including Scorpidium or Drepanocladus. They frequently have a high diversity of other plant species including carnvivorous plants such as Pinguicula. They may also occur along large lakes and rivers where seasonal changes in water level maintain wet soils with few woody plants. The distribution of individual species of plants is often closely connected to water regimes and nutrient concentrations

Fens have a characteristic set of plant species, which sometimes provide the best indicators of environmental conditions. For example, fen indicator species in New York include Carex flava, Cladium mariscoides, Potentilla fruticosa, Pogonia ophioglossoides and Parnassia glauca

Fens are distinguished from bogs, which are acidic, low in minerals, and usually dominated by sedges and shrubs, along with abundant mosses in the genus Sphagnum

Fens have been damaged in the past by land drainage, and also by peat cutting. Some are now being carefully restored with modern management methods. The principal challenges are to restore natural water flow regimes, to maintain the quality of water, and to prevent invasion by woody plants.

Etymology

The word "fen" is derived from Old English fenn. from Proto-Germanic *fanja. Cognates include Gothic (fani), Old Frisian (fenne), Dutch (veen, ven) and German (Fenn(e), Venn, Vehn, Feen, Fehn).

Fen vegetation

Carr is the northern European equivalent of the wooded swamp of the south-eastern United States, also known in the United Kingdom as Wet woodland. It is a fen overgrown with generally small trees of species such as willow (Salix spp.) or alder (Alnus spp.). In general, fens may change in composition as peat accumulates. A list of species found in a fen can therefore cover a range of species from those remaining from the earlier stage in the successional development to the pioneers of the succeeding stage.

Where streams of base-rich water run through bog, these are often lined by strips of fen, separating "islands" of rain-fed bog.

Temporary flooding by beavers can have negative effects on fens.