Ammophila Breviligulata Research Articles

A novel hybrid beachgrass is invading U.S. Pacific Northwest dunes with potential ecosystem consequences

AbstractInvasive plants formed via hybridization, especially those that modify the structure and function of their ecosystems, are of particular concern given the potential for hybrid vigor. In the U.S. Pacific Northwest, two invasive, dune‐building beachgrasses, Ammophila arenaria (European beachgrass) and A. breviligulata (American beachgrass), have hybridized and formed a new beachgrass taxa (Ammophila arenaria × A. breviligulata), but little is known about its distribution, spread, and ecological consequences. Here, we report on surveys of the hybrid beachgrass conducted across a 250‐km range from Moclips, Washington to Pacific City, Oregon, in 2021 and 2022. We detected nearly 300 hybrid individuals, or an average of 8–14 hybrid individuals per km of surveyed foredune. The hybrid was more common at sites within southern Washington and northern Oregon where A. breviligulata is abundant (75%–90% cover) and A. arenaria is sparse and patchy. The hybrid displayed morphological traits such as shoot density and height that typically exceeded its parent species suggesting hybrid vigor. We measured an average growth rate of 30% over one year, with individuals growing faster at the leading edge of the foredune, nearest to the beach. We also found a positive relationship between hybrid abundance and A. arenaria abundance, suggesting that A. arenaria density may be a controlling factor for hybridization rate. The hybrid showed similar sand deposition and associated plant species richness patterns compared with its parent species, although longer term studies are needed. Finally, we found hybrid individuals within and near conservation habitat of two Endangered Species Act‐listed, threatened bird species, the western snowy plover (Charadrius alexandrinus nivosus) and the streaked horned lark (Eremophila alpestris strigata), a concern for conservation management. Documenting this emerging hybrid beachgrass provides insights into how hybridization affects the spread of novel species and the consequences for communities in which they invade.

Impact of invasive Carex kobomugi on the native dune community in a US mid-Atlantic coastal system

Dunes provide numerous ecosystem services including habitat for flora and fauna, coastal protection through mitigation of wind and wave energy, and as a barrier to storm flooding. Dune vegetation that inhabits these systems plays a vital role in building dunes and resisting erosion. In the United States, the Virginia coast is a transitional temperature zone for several dominant dune grasses, where the northern species, Ammophila breviligulata (C3) and the southern species, Uniola paniculata and Panicum amarum (both C4) overlap. At Back Bay National Wildlife Refuge (NWR), Virginia, warming temperatures are resulting in native species range shifts altering biotic interactions. Additionally, the invasive sedge, Carex kobomugi (C3) has become more prevalent in the region with unknown effects on the landscape. To understand the impact of Carex on the native plant community, we quantified species distribution and morphological traits of three dominant native species, A. breviligulata, Panicum, and Uniola as well as invasive Carex. We found that Carex was most dominant and exhibited similar individual traits when compared to native species. The suite of plant traits was unique in Carex, with less variation than in native species allowing for rapid nutrient acquisition and growth. These traits, combined with species distribution data suggest that Carex may limit Ammophila abundance. Similarly, presence of Carex had a negative effect on Panicum growth, but no discernible effect on Uniola. Success of Carex at Back Bay NWR may be indicative of the future spread of the species due to above and belowground morphological traits, which may give the invasive an advantage with climate warming.

An analysis of coastal sand dune management in Oregon (United States) from the 19th to the 21st century

The Drivers-Pressures-State-Impact-Response (DPSIR) framework was employed to understand the land use policies developed to manage coastal sand dunes and their consequences in Oregon, United States of America, during two contrasting periods: from the 19th to the late 20th century and from there to the early 21st century. A combination of historical data and scientific literature was used for this study. Dune destabilization became a socio-economic issue as Euro-Americans settled in Oregon in the 19th century. Ammophila arenaria and Ammophila breviligulata were widely used for stabilization. This led to a paradigm shift regarding dunes, at a time when their management was becoming more complex due to socio-natural factors. As non-native beachgrasses turned invasive causing the loss of biodiversity and habitats, their removal became the focus to restore the active dunes to support the natural processes of the ecosystem. However, the removal of these beachgrasses, particularly, Ammophila arenaria, results in low dune heights, increasing the risk of coastal flooding by reducing their effectiveness as a natural defense against sea-level rise and extreme storm surges. The reason for the contrasting dune management policies in Oregon since the 1930 s is that the management response to environmental impacts due to human drivers creates new drivers, pressures, and corresponding impacts, as shown in the DPSIR analysis. Thus, land use policies for managing coastal dunes in Oregon and other places must balance efforts to restore the native biodiversity while minimizing coastal flooding in a context of accelerating and continuous sea-level rise in the 21st century.

Nitrogen addition and fungal symbiosis alter early dune plant succession.

Anthropogenic nitrogen (N) enrichment can have complex effects on plant communities. In low-nutrient, primary successional systems such as sand dunes, N enrichment may alter the trajectory of plant community assembly or the dominance of foundational, ecosystem-engineering plants. Predicting the consequences of N enrichment may be complicated by plant interactions with microbial symbionts because increases in a limiting resource, such as N, could alter the costs and benefits of symbiosis. To evaluate the direct and interactive effects of microbial symbiosis and N addition on plant succession, we established a long-term field experiment in Michigan, USA, manipulating the presence of the symbiotic fungal endophyte Epichloë amarillans in Ammophila breviligulata, a dominant ecosystem-engineering dune grass species. From 2016 to 2020, we implemented N fertilization treatments (control, low, high) in a subset of the long-term experiment. N addition suppressed the accumulation of plant diversity over time mainly by reducing species richness of colonizing plants. However, this suppression occurred only when the endophyte was present in Ammophila. Although Epichloë enhanced Ammophila tiller density over time, N addition did not strongly interact with Epichloë symbiosis to influence vegetative growth of Ammophila. Instead, N addition directly altered plant community composition by increasing the abundance of efficient colonizers, especially C4 grasses. In conclusion, hidden microbial symbionts can alter the consequences of N enrichment on plant primary succession.

Evaluation of soil heavy metals pollution and the phytoremediation potential of copper-nickel mine tailings ponds.

Heavy metal pollution in soils caused by mining has led to major environmental problems around the globe and seriously threatens the ecological environment. The assessment of heavy metal pollution and the local phytoremediation potential of contaminated sites is an important prerequisite for phytoremediation. Therefore, the purpose of this study was to understand the characteristics of heavy metal pollution around a copper-nickel mine tailings pond and screen local plant species that could be potentially suitable for phytoremediation. The results showed that Cd, Cu, Ni, and Cr in the soil around the tailings pond were at the heavy pollution level, Mn and Pb pollution was moderate, and Zn and As pollution was light; The positive matrix factorization (PMF) model results showed that the contributions made by industrial pollution to Cu and Ni were 62.5% and 66.5%, respectively, atmospheric sedimentation and agricultural pollution contributions to Cr and Cd were 44.6% and 42.8%, respectively, the traffic pollution contribution to Pb was 41.2%, and the contributions made by natural pollution sources to Mn, Zn, and As were 54.5%, 47.9%, and 40.0% respectively. The maximum accumulation values for Cu, Ni, Cr, Cd, and As in 10 plants were 53.77, 102.67, 91.10, 1.16 and 7.23 mg/kg, respectively, which exceeded the normal content of heavy metals in plants. Ammophila breviligulata Fernald had the highest comprehensive extraction coefficient (CEI) and comprehensive stability coefficient (CSI) at 0.81 and 0.83, respectively. These results indicate that the heavy metal pollution in the soil around the copper nickel mine tailings pond investigated in this study is serious and may affect the normal growth of plants. Ammophila breviligulata Fernald has a strong comprehensive remediation capacity and can be used as a remediation plant species for multiple metal compound pollution sites.

Intraspecific competition in common coastal dune grasses overshadows facilitation on the dune face

Restoration of degraded dunes through revegetation of native dune building species is critical to preserve multiple ecosystem services (i.e., coastal protection, habitat). As dunes exhibit high levels of abiotic stress, it is likely that facilitative interactions among plants occur, reducing stress caused by harsh abiotic conditions, and benefiting restoration efforts. The research was to determine how plant spatial arrangement (clumped vs. dispersed) at the dune slope affects the growth of two dominant dune grasses along the United States Atlantic coast, Ammophila breviligulata (American beachgrass) and Uniola paniculata (sea oats). We determined the local distribution and density of each species through field surveys to inform a manipulative study of planting arrangement and to assess plant growth and survival under different spatial arrangements. Planting arrangement did not influence the survival of U. paniculata, but dispersed plantings had a positive effect on growth parameters (height, stem number, ramet number), compared to the clumped arrangement. No plantings of A. breviligulata survived by the end of the second season, regardless of planting arrangement. Clumped arrangements did not improve growth of U. paniculata or growth and survival of A. breviligulata over the two growing seasons studied; thus, creating clumped arrangements may not be necessary for revegetation efforts. However, observing natural spatial patterns and using this information to guide restoration planting may be beneficial as climate change may impact revegetation results due to increased abiotic stress. Further research focusing on biotic interactions and density of plantings at multiple locations along dunes will contribute to dune restoration planning.

Epichloë Increases Root Fungal Endophyte Richness and Alters Root Fungal Endophyte Composition in a Changing World.

Plants harbor a variety of fungal symbionts both above- and belowground, yet little is known about how these fungi interact within hosts, especially in a world where resource availability is changing due to human activities. Systemic vertically transmitted endophytes such as Epichloë spp. may have particularly strong effects on the diversity and composition of later-colonizing symbionts such as root fungal endophytes, especially in primary successional systems. We made use of a long-term field experiment in Great Lakes sand dunes to test whether Epichloë colonization of the dune-building grass, Ammophila breviligulata, could alter fungal root endophyte species richness or community composition in host plants. We also tested whether nitrogen addition intensified the effects of Epichlöe on the root endophyte community. We found that Epichloë increased richness of root endophytes in Ammophila by 17% overall, but only shifted community composition of root endophytes under nitrogen-enriched conditions. These results indicate that Epichlöe acts as a key species within Ammophila, changing richness and composition of the root mycobiome and integrating above- and belowground mycobiome interactions. Further, effects of Epichloë on root endophyte communities were enhanced by N addition, indicating that this fungal species may become even more important in future environments.

Sand supply and dune grass species density affect foredune shape along the US Central Atlantic Coast

AbstractCoastal foredunes form via biophysical feedbacks between sand accretion and burial‐tolerant vegetation and can protect coastlines from hazards such as extreme storms and sea level rise. Predicting how coastal dunes, and the services they provide, will change in the future requires an understanding of the relative roles of the physical and ecological processes that shape their structure and function. Here we assess the relative roles of sand supply, beach morphology, and vegetation in determining foredune morphology, and its change, along a 300‐km stretch of the US Central Atlantic coast. In particular, we used the spatial variability inherent in beaches and dunes of this region to determine the relative importance of shoreline change rate (SCR; a proxy for sand supply to the beach), beach morphology, and grass density of four widespread dune grasses (Uniola paniculata, Ammophila breviligulata, Panicum amarum, and Spartina patens) to foredune morphology metrics (height, width, and aspect ratio) along the North Carolina Outer Banks barrier islands. Foredune morphology and change metrics are correlated with three main factors: multidecadal SCR (1997–2016), beach slope, and dune grass density and species identity. Multidecadal SCR and beach width explained the most variation in, and were positively correlated with, foredune height and width, and were negatively correlated with foredune aspect ratio (height divided by width). In addition, grass density and changes in grass density contributed significantly to foredune morphology change. We found a positive relationship between change in A. breviligulata density and foredune width, which aligns with previous studies on the US Atlantic and Pacific Northwest coasts. Our results demonstrate the interactive roles of beach sand supply and dune grass functional morphology in dune building processes on highly vulnerable coastlines.

Comparative genomics of the plant-growth promoting bacterium Sphingobium sp. strain AEW4 isolated from the rhizosphere of the beachgrass Ammophila breviligulata

BackgroundThe genus Sphingobium within the class Alpha-proteobacteria contains a small number of plant-growth promoting rhizobacteria (PGPR), although it is mostly comprised of organisms that play an important role in biodegradation and bioremediation in sediments and sandy soils. A Sphingobium sp. isolate was obtained from the rhizosphere of the beachgrass Ammophila breviligulata with a variety of plant growth-promoting properties and designated as Sphingobium sp. strain AEW4.ResultsAnalysis of the 16S rRNA gene as well as full genome nucleotide and amino acid identities revealed that this isolate is most similar to Sphingobium xenophagum and Sphingobium hydrophobicum. Comparative genomics analyses indicate that the genome of strain AEW4 contains unique features that explain its relationship with a plant host as a PGPR, including pathways involved in monosaccharide utilization, fermentation pathways, iron sequestration, and resistance to osmotic stress. Many of these unique features are not broadly distributed across the genus. In addition, pathways involved in the metabolism of salicylate and catechol, phenyl acetate degradation, and DNA repair were also identified in this organism but not in most closely related organisms.ConclusionThe genome of Sphingobium sp. strain AEW4 contains a number of distinctive features that are crucial to explain its role as a plant-growth promoting rhizobacterium, and comparative genomics analyses support its classification as a relevant Sphingobium strain involved in plant growth promotion of beachgrass and other plants.

Whole plant traits of coastal dune vegetation and implications for interactions with dune dynamics

AbstractCoastal dunes are important protective features against sea level rise and coastal storms. Interactions between dune plant aboveground structures and sediment trapping that allow for dune building and maintenance are well established. More recently, studies documenting belowground biomass for promoting erosion resistance in dominant dune species have been conducted, yet a knowledge gap remains regarding species‐specific characterization of whole plants, specifically with respect to roots, rhizomes, and belowground stems. Our objective was to quantify above‐ and belowground traits of four dominant dune grasses to document the potential for species‐specific effects on dune growth, maintenance, and erosion resistance. We examined above‐ and belowground traits among four prominent dune grasses of the Atlantic and Gulf Coasts of North America: Ammophila breviligulata, Panicum amarum, Spartina patens, and Uniola paniculata. Whole plant samples of each species were collected from the foredune at the US Army Engineer Research and Development Center's Field Research Facility in Duck, North Carolina, USA, and quantified for several above‐ and belowground traits (e.g., stem height, rhizome number and length, root surface area by diameter class, root tensile strength, and mycorrhizal percent infection). Belowground factors known to impact important dune processes, such as rhizome length, mycorrhizal percent infection, and root traits, differed substantially among species. When visualized in multivariate space, all species significantly differed in suites of above‐ and belowground traits. When considering belowground only, Ammophila and Spartina were similar, despite differences in biomass allocation. Species separated along axes related to mycorrhizal association, biomass allocation, and root construction. The four co‐occurring dune grass species were dissimilar in suites of plant traits. Belowground trait differences were driven by those describing root construction, biomass allocation, and mycorrhizal infection. Dissimilarity in above‐ and belowground suites of traits may demonstrate different approaches for surviving the dune environment. Incorporating belowground traits into modeling will enhance predictions of dune response to climate change through interactions between vegetation and dune dynamics that facilitate coastal resistance and resilience.

Spatial Diversity in Bacterial Communities across Barren and Vegetated, Native and Invasive, Coastal Dune Microhabitats

The microbial community composition of coastal dunes can vary across environmental gradients, with the potential to impact erosion and deposition processes. In coastal foredunes, invasive plant species establishment can create and alter environmental gradients, thereby altering microbial communities and other ecogeomorphic processes with implications for storm response and management and conservation efforts. However, the mechanisms of these processes are poorly understood. To understand how changing microbial communities can alter these ecogeomorphic dynamics, one must first understand how soil microbial communities vary as a result of invasion. Towards this goal, bacterial communities were assessed spatially along foredune microhabitats, specifically in barren foredune toe and blowout microhabitats and in surrounding vegetated monocultures of native Ammophila breviligulata and invasive Carex kobomugi. Across dune microhabitats, microbial composition was more dissimilar in barren dune toe and blowout microhabitats than among the two plant species, but it did not appear that it would favor the establishment of one plant species over the other. However, the subtle differences between the microbial community composition of two species could ultimately aid in the success of the invasive species by reducing the proportions of bacterial genera associated exclusively with A. breviligulata. These results suggest that arrival time may be crucial in fostering microbiomes that would further the continued establishment and spread of either plant species.

The effects of plant structure and flow properties on the physical response of coastal dune plants to wind and wave run-up

Vegetation is an important feature of coastal dunes and is often managed to stabilize restored dunes and provide coastal protection. Despite a high investment in planting and management efforts, little is known about how vegetation is affected by wind and wave run-up. The objectives of this study were to 1) investigate the lift forces and drag moments experienced by coastal dune vegetation from wind and wave run-up and 2) relate them to flow properties and plant morphology. Panicum amarum, Ammophila breviligulata, A. arenaria and Cakile maritima were subjected to laboratory wind and wave run-up conditions. Measurements were taken of fluid velocity, run-up depth, Reynolds number, and plant biophysical properties. The plant lift and drag responses were recorded with the use of a novel sensor designed to address the complexities induced by the flexibility and morphology of real vegetation under varying conditions. Regression analysis was used to describe the relationships between plant response and plant structure and flow properties. Experiments showed that wind induced a constant lift force and drag moment on plants over time, whereas run-up induced plant response was time-dependent. Plant height (R2 = 0.64, p < 0.001) and number of leaves (R2 = 0.67, p = 0.30) were the most important predictors of drag moment from wind and run-up experiments, respectively. Plant drag coefficients from wind (5.0 × 10−4 to 3.6 × 10−2) and run-up (2.7 × 10−3 to 1.7) were negatively correlated with flow turbulence, indicating that coastal dune plants likely have biophysical adaptations to the induced forces, such as a propensity for streamlining. In particular, our data suggests that tall and thin dune grasses are best adapted and used on the dune crest and fronts to mitigate wind energy, while low shrubby plants are best used on the backbeach or dune toe to reduce run-up energy. Our study provides valuable information on the ability of dune vegetation to interrupt flow, such that modelers and managers can better understand how to best protect coastlines.

Vegetation effects on coastal foredune initiation: Wind tunnel experiments and field validation for three dune-building plants

As the land-sea interface, foredunes buffer upland habitats with plants acting as ecosystem engineers shaping topography, and thereby affecting storm response and recovery. However, many ecogeomorphic feedbacks in coastal foredune formation and recovery remain uncertain in this dynamic environment. We carried out a series of wind tunnel experiments testing how the morphology, density, and configuration of three foredune pioneer dune building plant species influence the most basic stage of dune initiation — nebkha formation around individual plants. We established monocultures of native Ammophila breviligulata and Panicum amarum and invasive Carex kobomugi in 1 m × 1 m planter boxes of sand to simulate approximate natural and managed densities and planting configurations on the US Mid-Atlantic coast. We subjected each box to constant 8.25 m/s wind for 30 min in a moveable-bed unilateral-flow wind tunnel with an unvegetated upwind sand bed. We quantified resulting topography with sub-millimeter precision and related it to plant morphology, density, and configuration. Plant morphology, density, and configuration all influenced the resulting topography. Larger plants produced larger nebkha with greater relief, height, and sand volume. However, nebkha area, height, and planform shape varied among species, and taller plants did not necessarily produce taller nebkha. The erect grasses, Ammophila and Panicum, produced more elongated, high-relief nebkha compared to the low-lying Carex, which produced lower and more symmetrical equant nebkha. A staggered planting configuration produced greater net sediment accumulation than non-staggered. We validated these results against high-resolution field topographies of foredune nebkha and found strong agreement between the datasets. Our results provide species-specific parameters useful in designing foredune plantings and beach management and can be used to parameterize vegetation in models of foredune evolution associated with different plant species. By first understanding the underlying ecogeomorphic feedbacks involved in nebkha formation, we can more effectively scale up to forecast coastal foredune evolution and recovery.

Spatial extent and severity of all‐terrain vehicles use on coastal sand dune vegetation

AbstractQuestionsIncreases in all‐terrain vehicle (ATV) use on dunes raises concerns about an ecosystem vital for coastal protection. We asked: with distance from trails, what are the effects of ATV use on (a) total, native, and non‐native plant species richness and (b) presence and cover of the dune‐stabilising plant Ammophila breviligulata? Specifically, how do (a) and (b) differ (1) between regions with and without ATV use; (2) with deeper ruts and increased distance from the ATV trail; and (3) between pioneer and shrub zones of dunes in each region?LocationMiscou Island and Kouchibouguac National Park, New Brunswick, Canada.MethodsWe assessed ATV effects by conducting field vegetation surveys in a region with (Miscou Island) and without (Kouchibouguac National Park) ATV use. Line transects were used to capture gradients of effects across the dune community via plots evenly placed to measure trail effects (on the trail), close‐edge effects (edge of the trail), and distant‐edge effects (every 5 m up to 25 m away from trail), in pioneer and shrub zones of dunes.ResultsAll‐terrain vehicle rut depth was associated with a decrease in total and native species on the trails and on the edge of trails, and with a slight increase in non‐native species beyond the trail edge. We also found a rut depth threshold of approximately 50 cm, beyond which was an abrupt decline across all species. Where ATV activity occurred, there was also a decrease of A. breviligulata in presence and cover, non‐native species increased in the pioneer zone, and the shrub zone had fewer native species.ConclusionsAll‐terrain vehicle use plays a major role in the vegetation changes observed on coastal dunes. A management plan that recognises the specific effects caused by ATV use on dune vegetation will help preserve dunes, enabling more cost‐effective coastal protection than engineered interventions.

Determining How Soil Amendments Enhance the Recovery of Ammophila breviligulata Following Dune Die-Off Events in Coastal New England

ABSTRACT Moore, G.E.; Burdick, D.M., and Payne, A.R., 2020. Determining how soil amendments enhance the recovery of Ammophila breviligulata following dune die-off events in coastal New England. Jou...

Effects of white-tailed deer (Odocoileus virginianus) exclusion on plant recovery in overwash fans after a severe coastal storm.

We documented the impacts of an abundant deer population on dune vegetation recovering from severe storm surge on a barrier island through use of permanent plots and a repeated measures analysis. Three years after landfall of the storm, vegetation cover was dominated by American beachgrass, Ammophila breviligulata, though we observed 12 plant species among plots surveyed. We documented significantly greater vegetation cover in fenced than unfenced plots in overwash fans in two consecutive years. The difference in species richness between fenced and unfenced plots was significant, though richness was consistently low (≤4 species per plot) and we did not detect a statistically significant difference between years. Both deer trampling and foraging effects were captured in this study, though separation between these effects was not possible. Because trampling effects are often exacerbated on sandy soils, trampling and foraging effects should be isolated and investigated in future assessments of deer impacts on coastal vegetation. Managing deer to lower abundance may enhance coastal resilience if vegetation is allowed to recover unimpeded by foraging and trampling, though a better understanding of the precise nature of deer impacts on dune vegetation is necessary.

Testing for loss of Epichloë and non-epichloid symbionts under altered rainfall regimes.

Microbial symbionts can buffer plant hosts from environmental change. Therefore, understanding how global change factors alter the associations between hosts and their microbial symbionts may improve predictions of future changes in host population dynamics and microbial diversity. Here, we investigated how one global change factor, precipitation, affected the maintenance or loss of symbiotic fungal endophytes in a C3 grass host. Specifically, we examined the distinct responses of Epichloë (vertically transmitted and systemic) and non-epichloid endophytes (typically horizontally transmitted and localized) by considering (1) how precipitation altered associations with Epichloë and non-epichloid endophytic taxa across host ontogeny, and (2) interactive effects of water availability and Epichloë on early seedling life history stages. We manipulated the presence of Epichloë amarillans in American beachgrass (Ammophila breviligulata) in a multiyear field experiment that imposed three precipitation regimes (ambient or ±30% rainfall). In laboratory assays, we investigated the interactive effects of water availability and Epichloë on seed viability and germination. Reduced precipitation decreased the incidence of Epichloë in leaves in the final sampling period, but had no effect on associations with non-epichloid taxa. Epichloë reduced the incidence of non-epichloid endophytes, including systemic p-endophytes, in seeds. Laboratory assays suggested that association with Epichloë is likely maintained, in part, due to increased seed viability and germination regardless of water availability. Our study empirically demonstrates several pathways for plant symbionts to be lost or maintained across host ontogeny and suggests that reductions in precipitation can drive the loss of a plant's microbial symbionts.

Elucidating Coastal Foredune Ecomorphodynamics in the U.S. Pacific Northwest via Bayesian Networks

AbstractAs sea level rise and possible changes in storminess threaten coastal communities and infrastructure, the capacity for foredunes to provide protection depends on their geomorphology, which is determined by interactions between physical beach processes and vegetation. Here we use descriptive Bayesian network analyses to examine how sediment supply, beach characteristics, and two species of beachgrass (Ammophila arenaria and Ammophila breviligulata) alter foredune morphology and patterns of sand accretion on U.S. Pacific Northwest foredunes. We show that sediment supply and beach type primarily determine foredune morphology. Beachgrass density also influences foredune shape, but its effects differ among species: increasing density of A. arenaria was associated with steeper sloping dunes, whereas increasing density of A. breviligulata was associated with wider, more shallow sloping dunes. An examination of the change in foredune morphology over a 2‐year period found sand accretion was most strongly influenced by species‐specific patterns of vegetation growth and beach type. Specifically, A. breviligulata exhibited more lateral growth, resulting in greater sand accretion at the seaward margin of the foredune. In contrast, A. arenaria exhibited little lateral growth, resulting in comparatively more sand accretion near the foredune crest. Consequently, growth form‐generated sand accretion patterns resulted in steep, narrow A. arenaria‐dominated foredunes and shallow‐sloping, wider A. breviligulata‐dominated foredunes. These results illustrate that vegetation density and patterns of growth influence foredune morphology and its changes over time.

Species-Specific Functional Morphology of Four US Atlantic Coast Dune Grasses: Biogeographic Implications for Dune Shape and Coastal Protection

Coastal dunes arise from feedbacks between vegetation and sediment supply. Species-specific differences in plant functional morphology affect sand capture and dune shape. In this study, we build on research showing a relationship between dune grass species and dune geomorphology on the US central Atlantic Coast. This study seeks to determine the ways in which four co-occurring dune grass species (Ammophila breviligulata, Panicum amarum, Spartina patens, Uniola paniculata) differ in their functional morphology and sand accretion. We surveyed the biogeography, functional morphology, and associated change in sand elevation of the four dune grass species along a 320-kilometer distance across the Outer Banks. We found that A. breviligulata had dense and clumped shoots, which correlated with the greatest sand accretion. Coupled with fast lateral spread, it tends to build tall and wide foredunes. Uniola paniculata had fewer but taller shoots and was associated with ~42% lower sand accretion. Coupled with slow lateral spread, it tends to build steeper and narrower dunes. Panicum amarum had similar shoot densities and associated sand accretion to U. paniculata despite its shorter shoots, suggesting that shoot density is more important than morphology. Finally, we hypothesize, given the distributions of the grass species, that foredunes may be taller and wider and have better coastal protection properties in the north where A. breviligulata is dominant. If under a warming climate A. breviligulata experiences a range shift to the north, as appears to be occurring with U. paniculata, changes in grass dominance and foredune morphology could make for more vulnerable coastlines.

Investigating dune‐building feedback at the plant level: Insights from a multispecies field experiment

AbstractCoastal foredunes provide the first line of defense against rising sea levels and storm surge and for this reason there is increasing interest in understanding and modeling foredune formation and post‐storm recovery. However, there is limited observational data available to provide empirical guidance for the development of model parameterizations. To provide guidance for improved representation of dune grass growth in models, we conducted a two‐year multi‐species transplant experiment on Hog Island, VA, U.S.A. and measured the dependence of plant growth on elevation and distance from the shoreline, as well as the relationship between plant growth and sand accumulation. We tracked total leaf growth (length) and aboveground leaf length and found that Ammophila breviligulata (American beachgrass) and Uniola paniculata (sea oats) grew more than Spartina patens (saltmeadow cordgrass) by a factor of 15% (though not statistically significant) and 45%, respectively. Our results also suggest a range of basal/frontal area ratios (an important model parameter) from 0.5‐1 and a strong correlation between transplant growth and total sand deposition for all species at the scale of two years, but not over shorter temporal scales. Distance from the shoreline and elevation had no effect on transplant growth rate but did have an effect on survival. Based on transplant survival, the seaward limit of vegetation at the end of the experiment was approximately 30 m from the MHWL and at an elevation of 1.43 m, corresponding to inundation less than 7.5% of the time according to total water level calculations. Results from this experiment provide evidence for the dune‐building capacity of all three species, suggesting S. patens is not a maintainer species, as previously thought, but rather a moderate dune builder even though its growth is less stimulated by sand deposition than A. breviligulata and U. paniculata. © 2019 John Wiley &amp; Sons, Ltd.