Classification, composition and conservation status of fen habitats in NW Navarra, Spain

The study of 16 mire sites in Northwestern Navarra (Northern Spain) has proved the diversity of these habitats in Navarra. Among them, just one (Xuriain) is genuinely ombrogenic, while minerogenic sites are the most abundant. Their occurrence is determined mainly by geological contacts between water retaining and non-permeable rocks. Chemical water analyses show mostly acid pH (4.2 – 5.8), low conductivity, and low Ca2+ and Mg2+ contents.
Only four of the studied sites (Arxuri, Belate, Baltsagorrieta and Gesaleta) may be considered as true peat mires, bearing peat deposits over 1 m deep. The rest of sites are designed as para-peaty habitats, with essentially mineral deposits with peat absent or punctual. Anyway, trophic conditions and vegetation allow mires in Navarra to be assigned to fen forms.
The flora is composed of 432 cormophytic and bryophytic taxa. 43 phytocoenosis have been recognized, down to community, variant or association level, most of them typical of mires; Narthecium ossifragum and Sphagnum auriculatum community, Erico tetralicis-Sphagnetum papillosi and Eriophoro angustifolii-Sphagnetum rubelli are the most outstanding novelties.
Conservation status is varied, ranging from well preserved sites to deeply modified and altered ones. Main threats are caused by cattle managing. The existence of two pristine peat mires must be noted (Baltsagorrieta and Gesaleta).