The development of coastal dunes and their vegetation in Finland

Abstract

The area of open coastal dune landscapes remaining in Finland is only about 1300 ha and is continuously diminishing. The development of coastal dune fields in the area from Virolahti to Hailuoto is studied here from the literature, maps, aerial photographs and vegetation transect analyses. Grain-size parameters, pH and Ca, K, Mg and P concentrations are determined from sand samples, and the amounts of water and organic material and the water repellency of the dune sand were examined in a case study of samples collected at Yyteri.

The coastal dunes of Finland were formed in connection with glaciofluvial formations uplifted from the Baltic. The median grain-size of the aeolian material varies in the range 0.15-0.56 mm from one area to another, the coarsest material being found in hummock dunes lying on deflation surfaces and in transgressive dunes and the finest in parallel dune ridges. The grain-size of the material in a beach, which controls its steepness, sediment supply and moisture content, is also the most important factor affecting its topography and ecological succession. Parallel foredune ridges are formed on very gently sloping, prograding beaches consisting of fine material. The highest foredunes border on the beaches in places where the sediment budget is in balance and the shoreline remains unchanged for a long period of time. A dune cliff may be formed by marine erosion. When the beach slopes steeply and consists of coarser material, the foredune is replaced by a low berm built by a combination of waves and wind action. The speed and manner of growth of the dune-forming plants will affect the dune forms and dimensions.

Leymus arenarius binds 0.5-8 m high foredunes on the coasts of Finland, while behind these the ecological and geomorphological succession is determined mainly by pedological processes. Distally to the foredune (pH >6) Leymus becomes sterile (pH <5.9) and the amount of hydrophobic organic material in the soil increases. The dunes become lower as a result of water erosion and deflation, a process that may be enhanced by easily erodible material, storms and trampling. Deschampsia flexuosa on the stabilizing surfaces replaces the Festuca species that thrive on the bare sand. As the amount of phosphorus decreases and the acidity of the soil increases, the dry meadows (pH 5.5-5.7) change into Empetrum heaths (pH 5.2-5.4). Salix repens and Juncus balticus grow on moist surfaces. The occurrence of plant communities on the open dune shores depends on the soil moisture content and geographical location as well as the succession. The southern flora of the Hanko Peninsula differs most clearly from that of other coasts examined. The ecological succession can be prevented by sand movement.

Only very few dune coasts in Finland are in a natural state. Wide deflation surfaces and transgressive dunes were formed at the beginning of this century as a consequence of grazing, and now the forest is invading the coastal dune meadows and heaths. The vegetation cover around tourist attractions is being destroyed by heavy trampling, which leads to impoverishment of the vegetation and causes erosion. If the trampling is not too heavy and continuous, however, it may create new habitats for the threatened pioneer species. The vegetation cover of old dunes should be protected, as their bare sand surfaces are especially vulnerable to water erosion. In addition to building, trampling and forest invasion, the dune coasts are being threatened by eutrophicating air and water pollutants.