Abstract
The invasive ecosystem engineer Ammophila arenaria, native to Europe, was first introduced to California (USA) in 1896. More than a century later, it has come to dominate coastal foredune vegetation on the west coast of North America to the near exclusion of native species. A. arenaria builds a narrow, steep, peaked, and densely vegetated foredune, in contrast to the broad, more sparsely vegetated foredunes built by the native Elymus mollis. As such, it has modified dune processes by fixing the foredune and disrupting exchange of sediment between the beach, foredune, and dunefield. In the 1930s the congener A. breviligulata, native to the east coast and Great Lakes USA, was first introduced to Oregon, and has been displacing A. arenaria in southern Washington. Ammophila spp. have drastically reduced biodiversity, outcompeting native plant species, and displacing both invertebrate and vertebrate species. Restoration of west coast dunes through the removal of Ammophila began in the 1990s. Methods usually consist of one or a combination of manual digging, burning/herbicides, or excavation with heavy equipment. There are benefits and disadvantages to each method. Manual removal has proven most effective at restoring foredune form and process but is expensive. Excavation and herbicides may result in the loss of foredune morphology. Managers must articulate goals carefully before selecting restoration methods.
Highlights
An important ecosystem service of coastal dunes is their ability to ameliorate storminduced erosion through dissipation of wave energy and protection from flooding, protecting human infrastructure and natural resources [1,2]
The vegetation native to west coast dune systems includes the foredune community Elymus mollis herbaceous alliance dominated by the dune builder Elymus mollis Trin. subsp. mollis (American dune grass) (Figure 1), as well as the Abronia latifolia-Ambrosia chamissonis herbaceous alliance, a diverse, suffrutescent community characterized by variable but often moderate to low cover [9,10] (Figure 2)
Ammophila arenaria was found to exhibit two modes of spread at a barrier located in northern California, a linear, shore-parallel advance along the foredune characterized by exponential growth, and invasion from satellite populations in the more inland dunefield [52]
Summary
An important ecosystem service of coastal dunes is their ability to ameliorate storminduced erosion through dissipation of wave energy and protection from flooding, protecting human infrastructure and natural resources [1,2]. A. arenaria’s primary mode of spread is vegetative [18], with long distance dispersal via marine transport of dormant rhizomes [47,48]. It produces abundant viable seed, primarily in areas of fresh sand deposition, such as the foredune [9,49]. Ammophila arenaria was found to exhibit two modes of spread at a barrier located in northern California, a linear, shore-parallel advance along the foredune characterized by exponential growth, and invasion from satellite populations (some planted) in the more inland dunefield [52]. A. arenaria is capable of rapid spread, at one site the area occupied was shown to increase 574% in 50 years [52]
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