Contributions to the plant ecology of the Oregon coastal sand dunes

Graduation date: 1966Sand dunes are found along the coasts of most of the large land\ud masses of the world. Because of their proximity to man and his\ud activities, the maritime sand dunes of Europe, particularly Germany,\ud France, Holland and Scandinavia, have the longest history of stabilization\ud activities and botanical investigation. There are coastal dune\ud areas, some of great extent, in Africa, tropical Asia, Australia, and\ud South America. In general, little published information is available\ud concerning these areas. Ecological studies of coastal dune vegetation\ud and environment have been most extensive in Great Britain, and\ud to a lesser extent, in North America.\ud Of the North American coastal dunes, those of the east coast\ud have received considerable attention while those of the west coast\ud have been largely neglected. Along the Oregon coast are found some\ud of the most extensive and best developed coastal sand dune areas in\ud North America. Occurring on some 225 km. of the state's 500 km. of ocean facing coastline, these areas are made up of a great variety\ud of dune landscape features and present unique conditions for the development\ud and maintenance of vegetation.\ud There are many places in this dune area where the strong,\ud constant winds have eroded the sand surface to or near the water\ud table resulting in a stabilized surface - the deflation plain - which\ud provides an excellent starting point for the development of vegetation.\ud After preliminary ground and air reconnaissance, 11 deflation plains\ud were selected for detailed study, ranging in location from Sand Lake\ud on the north to Tahkenitch Creek on the south. These deflation plains\ud and their location are described in detail.\ud Vegetation data (species and cover) were taken on a total of 134\ud sampling stands, each consisting of five meter-square quadrats for\ud herbaceous vegetation, and one 6 x 6 meter quadrat for shrub and\ud forest vegetation. The species and stand data we arranged on comparative\ud charts so as to bring together stands with mutually occurring\ud species. This resulted in the delineation of seven communities\ud with definite successional relationships. Primary succession begins\ud with one of four herbaceous communities: dry meadow, meadow,\ud rush meadow or marsh. Succession then proceeds to low shrub,\ud tall shrub and finally forest.\ud The dry meadow is dominated by three species: Lupinus\ud littoralis, Ammophila arenaria and Poa macrantha. The site is dry with no standing water at any time. Sand deposition and deflation\ud occur in varying degrees. The important species of the meadow are\ud Festuca rubra, Aira praecox, Hypochaeris radicata and Fragaria\ud chiloensis. The surface is dry except for short periods of standing\ud water during the winter months. There is no sand deposition. The\ud rush meadow is characterized by its dense growth of Trifolium\ud willdenovii and Juncus phaeocephalus. The site is low and moist,\ud with water standing on the surface during the winter months. The\ud marsh is found on areas which are quite damp-water stands on the\ud surface for around six months of the year, and is just below the\ud surface for the remainder of the time. It is made up of dense stands\ud of Carex obnupta and Potentilla anserina.\ud The low shrub community is an open stand of Salix hookeriana,\ud Gaultheria shallon, Vaccinium ovatum and Myrica californica. This\ud develops into a tall shrub stage which is frequently an impenetrable\ud thicket with increasing dominance of seedlings of Pinus contorta and\ud Picea sitchensis. Development of a forest of Pinus and Picea is very\ud rapid. If the area is free from disturbance long enough, the shorter\ud lived Pinus dies out, leaving a forest of Picea.\ud The deflation plains represent only part of the many aspects of\ud the total dune landscape still awaiting investigation. The increasing\ud importance of the Oregon coastal dunes to industry and recreation\ud make imperative the initiation of long term ecological studies