D4.1 - Niveau 3 : Bas-marais riches en bases, y compris les bas-marais eutrophes à hautes herbes, suintements et ruissellements calcaires
Wetlands and spring-mires, seasonally or permanently waterlogged, with a soligenous or topogenous base-rich, often calcareous water supply. Peat formation, when it occurs, depends on a permanently high watertable. Rich fens may be dominated by small or larger graminoids (Carex spp., Eleocharis spp., Juncus spp., Molinia caerulea, Phragmites australis, Schoenus spp., Sesleria spp.) or tall herbs (e.g. Eupatorium cannabinum). Where the water is base-rich but nutrient-poor, small sedges usually dominate the mire vegetation, together with a "brown moss" carpet. Hard-water spring mires (D4.1N) often contain tufa cones and other tufa deposits. Excluded is the water body of hard-water springs (C2.1); calcareous flushes of the alpine zone are a separate category (D4.2). Rich fens are exceptionally endowed with spectacular, specialised, strictly restricted species. They are among the habitats that have undergone the most serious decline. They are essentially extinct in several regions and gravely endangered in much of central and western Europe.