Poor fen

Wide group of acidic (pH 3-5), minerotrophic mires, dominated by sedges and Sphagnum species. Poor fens occur in many different hydro-topographical situations and are typical components of the marginal lagg of raised bogs. In temperate Europe they also occur around mountain springs, in forest hollows, and in infertile fen-grassland complexes, but always on non-calcareous bedrock. Poor fens can also form the main type of usually small mire areas in weakly minerotrophic basins. Poor fens are the main transition type between D2.3a Quaking mires and D1.1 Raised bogs. Poor fens receive limited minerotrophic water input from upper catchments usually via non-distinct, diffuse flow paths. Poor fens can have unidirectional slope and lateral water flow but hummock-string patterning typical for D3.2 Aapa mires is missing.

Poor fens are characterized by continuous carpets of oligotrophic Sphagnum spp. combined with high abundance of sedges like Carex canescens, Carex echinata, Carex nigra, Carex lasiocarpa, Eriophorum scheuchzeri, Trichophorum cespitosum. Other abundant species are and Andromeda polifolia, Betula nana, Dactylorhiza maculata, Eriophorum vaginatum, Potentilla erecta, and Vaccinium oxycoccos. Also certain deep-rooted species more characteristic of D2.3a Quaking mires are frequent in poor fens, namely Eriophorum angustifolium, Carex rostrata and Menyanthes trifoliata. Ground layer is often dominated by Sphagnum angustifolium, Sphagnum fallax, Sphagnum flexuosum, Sphagnum papillosum and Sphagnum magellanicum, while other brown mosses can also be frequent, including Straminergon stramineum, Polytrichum commune and Warnstorfia fluitans. Higher degree of minerotrophic influence can be found only occasionally, as indicated by occurrence of e.g. Sphagnum subsecundum, Sphagnum obtusum or Sphagnum teres. In boreal zone, hummocks with Sphagnum fuscum, Polytrichum strictum, Calluna vulgaris and Empetrum nigrum are sometimes found in poor fens, with Salix spp., Rhamnus frangula, Betula pubescens or individual cranked pines (Pinus sylvestris).

Indicators of good quality:

Under natural conditions, water table is high also in summer and continuous carpets of mosses prevail with abundant sedges. Species diversity of vegetation is generally slightly higher than in D1.1 Raised bogs but clearly lower than in intermediate fens. In good hydrological condition there are no ditches that drain or disconnect water flow from the upper drainage area to the mire. Tree growth is limited to scattered individuals on hummocks or mire margins.

Synthesis of Red List assessment

Confidence in the assessment

Pressures and threats