The biogeography of various aquatic species deemed glacial relicts that are found in Lake Sommen is likely related to a different geography during the early history of the lake. One theory claims that aquatic species were transferred from the Baltic Ice Lake through a natural lock system in connection with a temporary advance of the ice-front during the Younger Dryas.[3] On land, the unusual occurrence of dwarf birch near Sund is also judged to be a leftover from a cold geological past.[4]
^Hellgren, George (1960). "Något om växtligheten i Ydre". In Filén, Thure (ed.). Ydre-Boken (in Swedish). Linköping. pp. 86–91.{{cite book}}: CS1 maint: location missing publisher (link)