Pirjo Hellemaa The Development of Coastal Dunes And Their Vegation in Finland University of Helsinki Department of Geography © Pirjo Hellemaa Aerial photos: © Maanmittauslaitos, lupa nro 51/MML/08 ISBN 951-45-8665-4 (PDF version) ISBN 951-45-8664-6 (HTML version) Helsingin yliopiston verkkojulkaisut, 1999 2 Abstract Hellemaa, Pirjo (1998). The development of coastal dunes and their vegetation in Finland. Fennia 176: 1, pp. Helsinki. ISSN 0015-0010. 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 exam- ined in a case study of samples collected at Yyteri. The coastal dunes of Finland were formed in connection with glaciofluvial for- mations 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. Par- allel foredune ridges are formed on very gently sloping, prograding beaches con- sisting 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 in- creases, 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 sur- faces 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 ero- sion. If the trampling is not too heavy and continuous, however, it may create new 3 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. Pirjo Hellemaa, Department of Geography, P.O. Box 4, FIN-00014 University of Helsinki, Finland. MS. received 8th September, 1997 (revised 19th January, 1998). 4 Contents ABSTRACT 3 INTRODUCTION 9 Background and purpose 9 Coastal dune chronology in relation to climate and sea level 9 Coastal morphodynamics 12 Successional zonation 14 Review of the literature 15 Terminology and definitions 16 METHODS 19 THE COASTAL DUNE FIELDS STUDIED 24 Coasts of the Gulf of Finland 24 1. Hyypiä, Virolahti (4 ha) 24 Coasts of the Hanko Peninsula 24 2. Lappohja (7 ha) 25 3. Syndalen (2 ha) 25 4. Henriksberg 25 5. Vedagrundet 26 6. Kolaviken, Hanko (6 ha) 27 7. Tulliniemi, Hanko (17 ha) 27 Coasts of the southwestern archipelago 29 8. Padva, Tenhola (6 ha) 29 Coasts of the Bothnian Sea 31 9. Yyterinsannat, Pori (100 ha) 31 5 10. The Herrainpäivät area, Yyteri, Pori (25 ha) 40 11. The Karhuluoto area, Yyteri, Pori (15 ha) 41 Coasts of the Quark 43 12. Storsanden, Monäs (50 ha) 44 13. Tisskärssanden, Vexala (10 ha) 46 14. Storsand and Lillsand, Pietarsaari (14 ha) 46 Coasts of the Vattaja Cape, Lohtaja (500 ha) 47 15. The Karhi dune field 47 16. The Vattaja dune field 50 17. The bathing beach of Vattaja 53 Coasts of the Bothnian Bay 53 18. Hietasärkät, Kalajoki (85 ha) 53 19. Letto, Kalajoki (35 ha) 60 20. Yrjänä, Tauvo 61 21. Haikaranhietikko, Tauvo ( 30 ha) 62 22. Ulkonokanhietikko, Tauvo (180 ha) 64 23. Koppana, Oulunsalo (15 ha) 66 24. Pajuperä, Hailuoto (23 ha) 67 25. Marjaniemi, Hailuoto (27 ha) 70 26. Virpiniemi, Haukipudas 71 27. Röyttänhieta, Simo 71 28. Tiironhiekka, Simo 71 FACTORS AFFECTING THE DEVELOPMENT OF COASTAL DUNE FIELDS72 Climate 72 The sea 76 Sand 82 Availability of sand 82 Grain-size parameters and topography 83 6 Chemical characteristics of the material 93 Water repellency of the sand surface 95 Vegetation cover 98 Dune plants 98 Effect of plant species on the dune topography 100 Statistical analysis of the vegetation cover 102 Changes caused by man and animals 109 THE GEOMORPHOLOGICAL AND ECOLOGICAL SUCCESSION 112 The beach zone 112 Cut-and-built terraces 114 Beaches 114 Berms veneered with aeolian sand 114 Foredunes 115 Dune slacks 116 Intermediate dunes 117 Deflation surfaces and hummock dunes 118 Dry deflation surfaces 119 Damp deflation surfaces 120 Hummock dunes 121 Forest edge ecotones 121 Old dunes 122 Successional sequence 123 DIFFERENCES BETWEEN AREAS 126 NEED FOR CONSERVATION 128 CONCLUSIONS AND SUMMARY 131 7 EPILOGUE, GEOECOLOGICAL INTERRELATIONSHIPS 136 ACKNOWLEDGEMENTS 138 REFERENCES 139 APPENDIX 1. 153 APPENDIX 2. 154 8 Introduction Background and purpose Sand accumulated by swash drifts with the wind on open beaches and piles up around vegetation patches and other obstacles. At the same time the plants are able to take nutrients from the beach. The flora of the dune fields is adapted to the poor surroundings, but in time the rain water washes the soil and the plant debris in- creases the amount of organic material, leading to an ecological succession. When sand brought by the waves welds onto the prograding beach, the plant communities form successive zones parallel to the shoreline. The geomorphological develop- ment of the shore depends on this succession. In a dune landscape the geomor- phological processes are gradually impeded by plant biomass production (Van Der Meulen 1990). Both geomorphological and pedological processes are active and easy to detect on coastal dune fields. The active coastal dune fields of Finland are located between the swash zone ecotone and the forest edge ecotone. The effect of waves during storms reaches far beyond the actual beach and can cause great changes to sandy beaches at an ex- ceptional speed. On the other hand, there can be periods, perhaps decades, of quiet evolution between the more severe storms. The coasts of Finland are characterized by a rapidly advancing shoreline, brackish water, a microtidal environment, a humid climate with moderate winds and long, severe winters. The aeolian sand, which originates from glaciofluvial sediments washed by the waves, is usually very infertile and acid because of the acidic nature of the bedrock, and this poor environment can support only a small number of species. There is only about 1300 ha of the open dune landscapes on the coasts of Finland remaining, and this area is continuously diminishing because of building and rapid invasion by pine forest. On these grounds one can very well speak of a threatened environment. This work treats the coastal dune fields in Finland in their entirety, from the shoreline morphodynamics to the effectively stabilizing forest cover. The aim is to explain the evolution of these coasts during the present century and the most im- portant factors affecting it. Topic of investigation is thus the geomorphological and the ecological succession of these areas and variations in this succession. Coastal dune chronology in relation to climate and sea level The wind has been shaping the sand dunes on the Finnish coasts since the begin- ning of the Holocene Epoch. Most of these dunes were formed in a periglacial en- vironment (Aartolahti 1980: 81) and are now stabilized far away from the present coastline. They often have parabolic outlines and they are higher than the dunes on the present coasts. This older phase of dune formation ended about 8000 BP, when 9 the climate was becoming warmer (Eronen & Olander 1990: 60) and more humid (Korhola 1992: 84, 1995), favouring plant growth. According to Stetler and Gay- lord (1996) the interaction between climate and aeolian activity is sensitive even to small changes in precipitation. During the Atlantic stage (8000–5000 BP) the fine sand was mainly shaped into low beach ridges (Aartolahti 1973: 47; Hellemaa 1980: 92).