No. 26. Coastal Dunes and Beaches

Christopher B. Chappell, David H. Johnson, and Jimmy Kagan

Geographic Distribution. This habitat occurs primarily along the outer coast from southern Washington (Copalis Beach, Grays Harbor) south to northern California. It occurs in all coastal Oregon counties, most abundantly in Tillamook County and between Florence and Reedsport. In Washington it occurs mainly in Grays Harbor and Pacific counties, and sporadically along the inland marine waters of Clallam, San Juan, Skagit, and Island counties. It also occurs in British Columbia.

Physical Setting. This habitat occurs primarily in wet, mild outer coastal climates. Precipitation, almost always rain, typically averages >80 inches (203 cm) annually. Summers are relatively dry, but fog is common. Elevation is at and very near sea level, only extending as high as the highest dunes. Topography is mildly to strongly undulating in the form of mostly north-south trending dune ridges and troughs. Soils, when present, are always sandy and are underlain by deep deposits of sand, thereby creating edaphically dry sites. Soils are also very poor in nutrients and organic matter. These dunes, spits, and berms are derived from sand carried by longshore drift and wind erosion. Dunes consist of several types that differ in their physical form, including foredunes, transverse dunes, parabola dunes, and retention ridges ²²⁰. Outlier examples away from the outer coast in the northern Puget Trough are small in extent, occur in a drier climate, and mainly occur in the form of sand spits and berms as opposed to dunes.

Landscape Setting. This habitat occurs in a natural mosaic with Westside Lowland Conifer-Hardwood Forest, Westside Riparian-Wetlands, and Herbaceous Wetlands. Forests adjacent to this habitat are found on stabilized dunes and are dominated by shore pine (Pinus contorta var. contorta) and Sitka spruce (Picea sitchensis). Wooded, shrubby, and herbaceous wetlands occur in seasonally flooded deflation plains or dune troughs. Hooker’s willow (Salix hookeriana) and slough sedge (Carex obnupta) are the 2 most characteristic species in these wetlands. This habitat is in a mosaic with the Urban habitat, as coastal areas have been developed extensively for tourism and low-density residential uses. Recreation is a major land use and includes the use of off-road vehicles. In southern Washington and northern Oregon, the wetlands are often converted to agriculture for cranberries.

Structure. This habitat consists of a variable mosaic of structures ranging from open sand with sparse herbaceous vegetation to dense shrublands. Trees are typically absent but may be scattered. Unstabilized sand may have very little vegetation or open short grasslands or forb-dominated communities, though these are now relatively uncommon and local. Medium-tall grasslands, typically closed, are a major component in the current landscape. Tall broadleaf evergreen shrubs, typically dense, are also a significant component of the mosaic.

Composition. Where they are vegetated, unstabilized dunes or strand are typically dominated or co-dominated by American dunegrass (Leymus mollis), dune bluegrass (Poa macrantha), or Chinook lupine (Lupinus littoralis). Red fescue (Festuca rubra) was once a major dominant on more stabilized dunes but has been largely replaced by European beachgrass (Ammophila arenaria), an introduced species that is now the most common dune grass. Many forb species are largely confined to herb-dominated dunes  or strand and may take on local importance.

Tall shrublands are dominated primarily by salal (Gaultheria shallon) and evergreen huckleberry (Vaccinium ovatum), but may also have prominent amounts of hairy manzanita (Arctostaphylos columbiana), kinnikinnick (Arctostaphylos uva-ursi), bush lupine (Lupinus arboreus), or California wax-myrtle (Myrica califorica). Coyotebrush (Baccharis pilularis) is abundant in southern Oregon. Both Scot’s broom (Cytisus scoparius) and gorse (Ulex europaeus) are exotic shrubs that dominate disturbed areas. Scattered trees are mainly shore pine (Pinus contorta var. contorta), or, less commonly, Sitka spruce (Picea sitchensis).

Other Classifications and Key References. Franklin and Dryness ⁸⁸ called this habitat sand dune and strand communities. The Oregon Gap II Project ¹²⁶ and Oregon Vegetation Landscape-Level Cover Types ¹²⁷ would crosswalk with coastal dunes habitat. This habitat is not well represented by the Washington Gap project: it takes up small percentages of several types in the Sitka spruce zone, including conifer forest, hardwood forests, and coastline, sandy beaches, and rocky islands. Other references describe this habitat ^{8, 42, 137, 219, 220}.

Natural Disturbance Regime. Erosion and deposition of sand are the primary natural processes controlling this habitat. Sand is deposited initially on beaches, and then moved into dunes through wind erosion ²²⁰. Wind also maintains unstabilized dune areas. Major winter storm events may result in blowouts that create holes in existing stabilized or unstabilized dunes, creating new areas of sand deposition.

Succession and Stand Dynamics. The different structural variants of the mosaic within this habitat are primarily stages in succession from freshly deposited sand to completely stabilized shrub-dominated dunes ²²⁰. Unstabilized sand, such as foredunes with little European beachgrass, has the most open and herbaceous vegetation. Closing of the vegetation typically results in stabilization of the sand. Recently stabilized dunes are now primarily dominated by European beachgrass. Given more time without a major disturbance, shrubs and/or trees colonize the grasslands. Shrublands are sometimes an intermediate stage in succession toward forests. Pine woodlands are another very common intermediate stage. Eventually, pine woodlands are colonized by Sitka spruce or Douglas-fir and become mixed pine-spruce or pine-Douglas-fir forests. Any one of these stages can be set back to sand by a blowout or reburial by dunes, and a cyclic successional sequence is common in many areas ⁴².

Effects of Management and Anthropogenic Impacts. European beachgrass has been extensively planted for stabilization purposes and has also spread widely on its own. Unstabilized sand is now a relatively rare condition primarily because of the introduction of this species. The physical forms of dunes also have been altered by beachgrass ^{55, 56}. Forests are probably forming at a greater rate than they did in the past because of increased stabilization. Exotic species, especially sweet vernalgrass (Anthoxanthum odoratum) and common velvetgrass (Holcus lanatus), are now a nearly ubiquitous component of herb-dominated communities. The spread of such species may be related to past livestock grazing in many areas ⁴². Scot’s broom and gorse are aggressive exotic shrub invaders that were planted for stabilization and have spread widely. Since both are legumes, they result in major nitrogen increases where they establish. Off-road vehicle use has resulted in complete destruction of native herbaceous communities in some areas ²²⁰. Trampling is a potential threat in herbaceous communities ^{42, 220}.

Status and Trends. This habitat covers a relatively limited area and major expanses of it have been converted to other uses. The vast majority of herbaceous vegetation that remains is in poor condition, being dominated by exotic species. Current trends are probably decreasing in both extent and condition because of continued development in coastal areas and continuing expansion of exotic species into the few remaining native-dominated areas. Six of 11 plant associations currently listed in the National Vegetation Classification representing this habitat are considered imperiled or critically imperiled ¹⁰.