Plant Succession on the Sand Dunes of the Oregon Coast

Parabolic sand dune succession was studied on 48 plots within a 150—mile section of the Oregon coastline. The sand dune communities were described and related to their successional sequence. Both plot and plotless techniques were used to obtain data for frequency, density, cover, and dominance. Successional stages of upland areas of coastal sand dune were represented by nine communities of plants which ranged from scattered, pioneer, herbaceous plants on barren, shifting sand to the near—climax, physical—biological system–the dune forest. The stands included a pioneer stage consisting of herbaceous plants which appeared early on the unstabilized dunes. A second community made up of many annual and some perennial herbaceous plants emerged on protected, lee slopes along the edges of dunes supporting pioneer communities. The third community located on somewhat stabilized sand was produced by a merging of some of the more hardy herbaceous plants from the second community, and the appearance of some shrubs also found in the following community. The fourth community was located on sites of stabilized sand and consisted mainly of shrubs. The remaining five communities, containing trees and shrubs on stabilized sand, were Pinus contorta—shrub; Pinus—Picea—shrub; Picea sitchensis—shrub; Picea—Tsuga—shrub; and Tsuga heterophylla—shrub. Many of the dominant species gradually declined as the succession proceeded from one community to another and other dominants appeared. The most notable exception to this progression occurred in the herbaceous community along the lee edges of the initial dunes, where the vegetational changes were much more abrupt.