Andorran high Pyrenees (Perafita Valley, Andorra): Serra Mijtana fen

(ENG) The Serra Mitjana (SM) fen (42º 28' 3'' N; 1º 34'58''E) is located at 2406 m above sea level (a.s.l.) in the Perafita Valley, southeast Andorra, eastern Pyrenees. This valley renges between 1400 and 2750 m a.s.l. and together with the adjacent Madriu and Claror valleys, it is included in the UNESCO World Heritage List in the category of Cultural Lanscape. Given its location in the southern basin of the eastern Pyrenees, the climate of this region is largely influenced by both Mediterranean and Oceanic conditions. The latter are favoured by the smooth topography of the French Pyrenees allowing the entrance of north and north-western Atlantic winds (Esteban et al. 2009). The geological substrate is mainly granodioritic and the geomorphology of the valley is the result of glacial and periglacial activity. SM fen was formed in a cirque glacier and it covers a surface of about 3.4 ha.The fen is situated in the alpine vegetation belt, above the current timberline in the Perafita Valley that oscillates between 2300 and 2400 m a.s.l. Extended alpine grasslands are dominated by acidophilous communities from the Caricetalia curvalue order. The main components are Nardus stricta L., Festuca airoides Lam.subsp. airoides and Festuca eskia Ramond ex DC. Subalpine forests below are mainly constituted by Pinusuncinata Mill. Ex Mirb. Woodlands with the occasional presence of Abies alba Mill. (Folch 1984). The presence of nitrofilous and ruderal plants from the Chenopodio-Taraxacetum pyrenaica alliance is explained by the current high grazing pressure.