Fens are peatlands that formed from vegetation receiving a constant supply of base-rich groundwaters and therefore can be described as minerotrophic (fed by groundwater). Fen peats in Ireland have usually a relatively high pH. Fen peats are mineral rich, with a relatively high ash content (10–20%) and a relatively shallow peat depth (c. 2 m). The vegetation is generally species rich and largely contains tall herbs, rushes and grasses, with brown mosses a feature of the ground layer.

While a fen can be seen as a transitional ecosystem enroute to becoming a raised bog, they rarely progress in this natural direction due to human-induced influences, be it reclamation for agriculture, roadworks or landfilling. Natural fens are rare, as 97% of the country’s fens have been drained for agriculture. While fens of conservational importance still occur right across the country, their current extent is estimated at 20,180 ha (EPA, 2011).

previousPrevious - Mountain Blanket Bog
Next - Raised Bognext