Species: Ammophila arenaria

Synecology: <br><br>Native habitat. Ammophila arenaria is native to the British Isles and the coasts of the Baltic and North seas from 30 to 63 degrees north latitude. It grows most vigorously on mobile and semi-fixed dunes of varying chemical and physical make-up. However, all of the substrates share instability, free drainage, low organic material content, and a homogeneous soil profile (Huiskes 1979a). <br><br>European beachgrass plays an important role in the process of dune formation. Young plants become established along the upper beach, often in the lee of driftwood or other beach plant species. As the grass grows taller, wind is deflected upward over the plant. An equilibrium is established between the growth of A. arenaria and sand deposition. The plant causes the wind to slow and sand particles to be deposited. Sand deposition stimulates growth of A. arenaria, which in turn encourages more sand deposition. Too much sand deposition slows growth; too little causes senescence. Thus, sand dune formation is largely determined by the interaction of A. arenaria and wind. Added protection from the wind and sand deposition results in the pattern of new growth to the lee of the existing tussocks (Willis et al. 1959a, 1959b). <br><br>In native habitats, A. arenaria alone makes up the foredune plant community. It also occupies dunes further inland where sand is actively moving. This community is known as "Pure Ammophiletum." As dunes become stabilized by this species, however, other species are able to take hold. This process creates a "Mixed Ammophiletum" community. This mosaic community is typically found on the lee slopes of dunes, mostly on inland, less active slip faces. Occasionally it is found in sheltered areas near the sea. It is an open community with only a moderate amount of bare sand. Since the sand supply is reduced by the fully colonized foredune, the vigor of A. arenaria generally declines in the "Mixed Ammophiletum" community (Willis et al. 1959a, 1959b). <br><br>Non-native habitat. A. arenaria has been introduced to stabilize sand on the west coast of the United States since the early 1900's (Knudson 1917, Barbour and Johnson 1977, Crook 1979a, 1979b). When planted on disturbed dunes or bare sand, it has initiated dune formation in the manner described above. Rhizome fragments washed along the shore may become buried on the beach, initiating the formation of foredunes (Wiedemann et al. 1974). However, the topography and composition of the foredunes differ from those formed by plant species native to the West Coast (Barbour and Johnson 1977). <br><br>A. arenaria has escaped and become naturalized north of San Francisco (Barbour and Johnson 1977) and forms extensive stands as far south as Vandenberg Air Force Base, San Luis Obispo county. Before the introduction of European beachgrass, foredunes in northern California were dominated by Elymus. The foredunes were low and rose above the beach with a gentle slope. Inland from the foredune was a series of dune ridges and swales aligned roughly perpendicular to the coast in the direction of the prevailing onshore winds. <br><br>Currently, where dominated by A. arenaria, the foredune topography has changed to a steep slope, and the orientation of the dunes is parallel to the coast. In addition to topographical alterations, A. arenaria replaces the native foredune vegetation, greatly reducing species diversity (Barbour and Johnson 1977). <br><br>In Oregon, Crook (1979a, 1979b) reports that prior to the introduction of European beachgrass there were no foredunes along the coast. Since its introduction in 1910 near Coos Bay and in 1935 on the Clatsop Plains, A. arenaria has created a foredune and colonized portions of the deflation plains. In addition, it occupies the hummock dunes, the fields of vegetated sand dune mounds occurring inland from the foredune, and the deflation plain. The foredune, as a recent geomorphological feature, has greatly reduced sand supplies to the interior moving dunes and led to their decline (Crook 1979a, 1979b, Bruce 1983). It has recently been determined that A. breviligulata, native to the dunes of the East Coast and Great Lakes and introduced to Washington and Oregon, is actually more prevalent than A. arenaria in Washington (Wiedemann 1988). <br><br>Competitive relations: <br><br>A study of Pacific Coast beach vegetation (Barbour et al. 1976) revealed that A. arenaria exerts more control over community competition than any other beach dominant. The upper beach and foredune along much of northern California's coast were formerly dominated by Elymus mollis (Barbour and Johnson 1977). Research on Elymus and Ammophila ssp. has shown several morphological and physiological differences that may explain A. arenaria's competitive advantage. <br><br>A. arenaria's adaptation to sand accretion is well known. Ranwell (1959) reports that it can survive 100 cm of sand deposition per year, whereas Elymus mollis can only tolerate 30 cm per year. Increased human disturbance and therefore sand dune destabilization, along the coastline favors A. arenaria (Barbour and Johnson 1977). <br><br>At Point Reyes, California, Barbour (1977) found that A. arenaria had twice the root density of Elymus at every depth measured from 1-5 m. Differences in root systems may provide A. arenaria greater resistance to drought and more efficient means of tapping soil moisture. In addition, the leaves of A. arenaria inroll during dry periods reducing water loss through transpiration (Huiskes 1979a). <br><br>Radioactive carbon studies suggest that Ammophila ssp. may have a higher photosynthetic rate than E. mollis during the September to May wet season (Barbour 1977). <br><br>In contrast, Elymus mollis is able to withstand tidal inundation and is tolerant of a wider range of soil salt concentrations. A. arenaria cannot tolerate salt concentrations greater than 1.5-2.0 percent, whereas E. mollis can withstand concentrations of 12 percent or more (Huiskes 1979a).