The ZSC Valle del medio Tagliamento is conventionally included among the sites belonging to the Alpine biogeographical region (mountainous part), although the area involved in the project lies in the continental region (plain part). The site actually develops partly on the pre-Alpine slopes that descend sharply towards the Tagliamento River and partly into the vast plain area that includes the gravelly riverbed and, in the westernmost area, the humid plain of Osoppo. The ZSC Valle del medio Tagliamento therefore presents many environments that are widely differentiated and characterized by significant naturalistic values. The altitudinal excursion goes from a minimum height of 158 mt asl (Tagliamento river bed) to a maximum of 1478 mt asl (Mount Cuar), with an average of 450 mt.