Plants that grow in and beside water have to be prepared for marked and rapid changes in their living conditions. They must be able to tolerate living under water without drowning, and getting totally dried out without whithering. Many swamp plants are well adapted to these kinds of changes.
Lysekloster was the largest agricultural property in the country when it was phased out during the Reformation in 1537. In its prime this cloister encompassed two-thirds of all the farms in Os. The monks introduced and cultivated new plant species and it was probably they who stocked the waters with fish not indigenous to the area. This legacy from the Middle Ages has left a lasting mark.
In Sanddalen and Helldalsåsen the building of houses has increased dramatically. Where there eariery was grazing land, hundreds of families now live. Not far away, lies Rambjøra as an oasis in the built up area.