Ammophila Invasion Ecology and Dune Restoration on the West Coast of North America

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.

Assessing performance of a “nature‐based” foredune restoration project, Oceano Dunes, California, USA

“…to enhance aeolian processes and promote more dynamic ecosystem form and function. This is often accompanied by replanting of native dune species (e.g., Arens & Geelen, 2006; Arens et al, 2004; Conery et al, 2020; Darke et al, 2016; Hesp & Hilton, 2013; Hilgendorf et al, 2022, this volume; Hilton et al, 2009; Kollmann et al, 2011; Nordstrom et al, 2002; Nordstrom, 2008; Pickart et al, 2021; Pickart, 2013, 2021; Roze & Lemauviel, 2004; van Boxel et al, 1997; van der Meulen et al, 2008; Walker et al, 2013). The second approach involves revegetation to re‐establish dunes in areas where they have been removed or destroyed, intentionally or unintentionally, using plants to stimulate aeolian deposition and dune development, as is the case for this study.…”

“…As a result, many artificially stabilized dunes have dysfunctional ecological regimes that do not experience sufficient disturbance cycles and geomorphic processes required to maintain dune ecosystem structure and function. This results in significant ecological impacts, such as demise of specialized habitats for endemic and endangered species, declines in early successional floral species, and corresponding loss of species richness and diversity (e.g., Arens et al, 2004; Grootjans et al, 2002; Hilton et al, 2005; Lithgow et al, 2013; Martínez et al, 2006, 2013; Maun, 2009; Nordstrom, 1990, 2008; Nordstrom & Jackson, 2021; Pickart, 2013, 2021).…”

“…Such activities often occur without comprehensive understanding of, or planning for, the longer-term impacts on related ecosystem services provided by coastal dunes, including recreation and tourism, specialized habitat for endangered or endemic species, groundwater recharge, and protection from coastal erosion, flooding and sea-level rise, amongst others (Barbier et al, 2011;Martínez et al, 2008). In many cases, beach-dune systems have been so intensively used or modified that their form and function are decoupled from natural geomorphic and biotic processes and rendered either inactive or, with respect to dunes, obliterated (e.g., Arens et al, 2004;Hesp & Hilton, 2013;Hilton et al, 2005Hilton et al, , 2009Lithgow et al, 2013;Martínez et al, 2006Martínez et al, , 2013Maun, 2009;Nordstrom, 1990Nordstrom, , 2008Nordstrom & Jackson, 2021;Pickart, 2013Pickart, , 2021. Instead, what exists often reflects the outcomes of human interventions to maintain the system in some preferred state, such as a flat, stable, sandy beach free from debris, vegetation, topography, and geomorphic change that is not only accessible, but also aesthetically "pleasing" and/or functionally suitable for human use.…”

Dynamic restoration and the impact of native versus invasive vegetation on coastal foredune morphodynamics, Lanphere Dunes, California, USA

“…The property is managed by the United States Fish and Wildlife Service and the study area encompasses 350 m of protected established foredune. Foredunes within the Humboldt Bay region have a history of restoration efforts, primarily focusing on the removal of invasive species (Pickart, 1988(Pickart, , 2013(Pickart, , 2021Pickart & Hesp, 2019;Pickart & Sawyer, 1998;Pickart et al, 2021). This project is part of a larger coastal vulnerability assessment and serves as a demonstration site for methods to improve landform resilience to coastal erosion and sea level rise.…”

Effects of invasive Rosa rugosa on Baltic coastal dune communities depend on dune age

“…Those that are capable of creating ecological niches for new species of plants and animals are called invasive ecosystem engineers or transformers (Richardson et al 2000;Fei et al 2014). Amongst them are species associated with coastal ecosystems, for example, Ammophila arenaria, invasive in North America (Pickart 2021), Lupinus nootkatensis, invasive in Iceland (Vetter et al 2018) and Senecio inaequidens, invasive in Europe (Van De Walle et al 2022). By stabilising the ground surface and producing substantial amounts of organic matter, these invaders accelerate the soil formation process.…”