EXPERIMENTAL REVEGETATION OF THE REGULATED LAKE ONTOJARVI IN NORTHERNFINLAND

Water level regulation causes large-scale ecological changes in the li ttoral areas of lakes in northern Finland. If the summertime water lev el is raised, intensive erosion processes. begin, causing a sudden dec line in shore vegetation. The need for shore protection is obvious in areas of high recreational value. At lake Ontojarvi, planting experime nts with littoral helophytes and bushes were carried out during the ye ars 1990-92. All the experiments were carried out in the eroded sandy areas, which were partly protected by mechanical barriers. Several pla nt species were planted on the shore which had been treated with diffe rent peat mixtures, etc. The frequencies of the different species were followed monthly. After the first summer, the average survival rates were about 45 % due to the drying of seedlings. A rapid decrease in th e survival rates took place during the high water level period in 1991 at which point only 20% of the planted individuals were alive. The be st results were obtained for the helophyte Carer rostrata Stokes, of w hich 30% had survived erosion. Tall willows (Salix phylicifolia L.) we re also erosion-resistant with a survival rate of 80%.