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

Abstract

The Lanphere Dunes, part of the Humboldt Bay National Wildlife Refuge, has been the focus of foredune restoration efforts since the 1980s. Efforts have centred around removal of an invasive European beach grass species, Ammophila arenaria, introduced in the early 1900s to stabilize the dunes to protect landward communities from coastal flooding and storm surges. Despite effectively stabilizing the foredune, A. arenaria forms monotypic vegetation stands, with highly dense roots, rhizomes, and above-ground biomass that can lead to pronounced scarping of the seaward slope, alongshore steering of wind and sediment, a lack of landward transfer of sand, and a steeper, more peaked profile.Effective foredune restoration must consider the coupled interactions between dominant plant type and the geomorphic processes that influence dune form. A 5 ha reach of recently restored foredune was monitored biannually with terrestrial laser scanner and uncrewed aerial systems platforms between 2015 and 2021 to characterize the impacts of dynamic restoration on foredune form and resiliency. This reach included two control plots: (1) native, non-restored and (2) invasive, and three restored plots revegetated with native species: (3) a native grass (Elymus mollis), (4) a low-lying herb and subshrub assemblage, and (5) a mixture of the native grass, herbs, and subshrubs.After five growing seasons, restored plots exhibited distinct geomorphic and sediment budget differences. Natively vegetated plots recovered from extensive scarping 2 years faster than the invasive plot. Restored plots saw foredune height (0.5-0.7 m) and width increase, landward extension (1 m) while maintaining a similar seaward position, and positive lee-slope sediment budgets that exceeded both control plots (up to 0.015 m 3 m À2 month À1 ). These results suggest that the native vegetation plots allowed increased landward sand transport across the foredune, and increased the capacity of the foredune to recover more quickly following dune scarping.

Post‐wildfire coastal dunefield response using photogrammetry and satellite indices

“…Significant changes are described according to the drone surveys hardware and method's respective error (LoDs) by quantifying changes in derived point clouds. Similar to recent studies (Hilgendorf et al, 2021(Hilgendorf et al, , 2022Konlechner & Hilton, 2022;Walker et al, 2022), both vegetation and surfaces changes are of research interest as they show the post-fire ecogeomorphic response of landscapes and indicate stability, dynamism or transgression. Satellite indices are used to separate landcover types and to assess the 3D changes between pre-fire sandy active areas, and regions that were burnt or unburnt.…”

“…Disturbances are a key driver of aeolian erosion and landscape destabilisation as they remove or destroy stabilising vegetation and microbial soil crusts (Ravi et al, 2011) as well as decrease the threshold velocity for wind erosion (Ravi et al, 2009). The transition of coastal dunes from stabilised systems to fully active transgressive dunefields has been observed in some cases (Hesp, 2013) and is a continuing area of study (Fisher et al, 2021; Gao et al, 2020; Hesp & Walker, 2021; Hilgendorf et al, 2022). Fire has been suggested to be an initiator of a transgressive dune phase when paired with extreme weather or periods of atypical climate or climate change (Filion, 1984; Filion et al, 1991; Matthews & Seppälä, 2013).…”

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.…”

“…Over at least the past 30 years, more “dynamic” approaches to dune restoration have emerged that aim to re‐establish natural ecological and geomorphic disturbance processes (e.g., wind erosion, sand transport, burial), floral and faunal communities, and related morphodynamics to restore lost ecosystem form and function (e.g., Arens, Mulder, et al, 2013; Arens, Slings, et al, 2013; Bird et al, 2020; Darke et al, 2016; De Jong et al, 2014; Van der Meulen et al, 1989; Hesp & Hilton, 2013; Hilgendorf et al, 2022; Houston, 1991, 1997; Konlechner et al, 2015; Lithgow et al, 2013; Martínez & Psuty, 2004; Nordstrom, 2008; Ruessink et al, 2018; Walker et al, 2013, this volume). Substantial research suggests that a more dynamic dune landscape, wherein natural geomorphic and biotic processes are stimulated and restored, provides a more resilient ecosystem with favorable ecological conditions to support native plant communities.…”

Contemporary research in coastal dunes and aeolian processes

“…The increasing need for dune research on developed coasts was made explicit by Nordstrom (2004) in Beaches and dunes of developed coasts, and themes such as the restoration of coastal dunes have been the focus of dedicated textbooks, for example, Restoration of coastal dunes (Martínez et al, 2013). Examples of human interventions in coastal dunes in this special issue include the removal of invasive vegetation Hilgendorf et al, 2022;Konlechner & Hilton, 2022), engineered foredune notches (Nguyen et al, 2022), and intensely managed or constructed foredunes (Dickey et al, 2023;He et al, 2022;Sanromualdo-Collado et al, 2022;Walker et al, 2023).…”