Coastal dunes are wind-built ridges of sand that form wherever a beach is wide enough, dry enough, and exposed to onshore winds. They look simple, but they are among the most dynamic landforms on Earth, constantly reshaped by wind, waves, and the plants and organisms that colonize them. Far from being lifeless piles of sand, dunes support specialized ecosystems, buffer inland areas from storm surges, store carbon, and filter groundwater. Understanding how they form, what lives on and in them, and why they are increasingly threatened gives a fuller picture of one of the most underappreciated landscapes on any coastline.
How Wind Builds a Dune
Dune formation begins with sand supply. Waves deposit sediment on the beach, the sun and wind dry the surface grains, and once wind speeds exceed a threshold, those grains begin to bounce and roll inland. The precise wind speed needed to start moving sand varies with grain size and moisture, and researchers have found that simple threshold calculations often fail to predict when transport actually happens in the field, because surface moisture, salt crusts, and shell fragments all complicate things.1Sedimentology. Thresholds of aeolian sand transport: establishing suitable values The real world, in other words, is messier than equations suggest.
Once airborne, sand grains move in a characteristic bouncing motion called saltation. When those grains hit an obstacle on the beach, whether that is a piece of driftwood, a clump of seaweed, or a tuft of grass, they slow down and settle. Sand piles up, the pile itself becomes a larger obstacle, and the feedback loop begins. On beaches backed by cliffs or steep slopes, the dynamics get more complex. Measurements at one beach-to-clifftop system showed that sand transport rates actually dropped from the beach onto the lower slope of the climbing dune, but at the dune’s uppermost section, transport was roughly four times higher than on the flat beach at moderate wind speeds, because wind accelerates as it compresses over the dune crest.2Journal of Geophysical Research: Earth Surface. Airflow Dynamics and Aeolian Sand Transport Across a Beach‐Climbing Dune‐Clifftop Dune System That acceleration is why dune crests are such restless, shifting features.
The Grasses That Build Their Own Hills
If wind is the engine of dune formation, vegetation is the steering wheel. The classic example in Europe and eastern North America is marram grass (Ammophila arenaria and its close relative Ammophila breviligulata). Marram traps windblown sand among its stems, the sand buries the plant, and the plant responds by growing upward through the new layer. That fresh growth traps still more sand, creating a positive feedback loop that can build dunes meters high.3PubMed Central. Two sides of the coin: Feedback-driven landscape formation results in trade-off between establishment and resilience of marram grass
Burial is not just tolerated by these grasses; it actively stimulates their growth. In controlled experiments, burial in sand triggered faster shoot growth in marram grass, with the effect appearing within ten days at deeper burial levels. Both shoot and root mass increased when plants were moderately buried, and deeper burial drove especially strong root growth.4Botanica. Variation in Growth Response of Coastal Dune-Building Grass Species Ammophila Arenaria and Leymus Arenarius to Sand Burial That response is not limited to grasses, either. Virginia creeper, a woody vine found on some North American dunes, also grew larger when buried in sand regardless of whether it came from a coastal or an inland population.5Plant Ecology. Coastal provenance increases salt spray tolerance but not sand stress responses in the vine Parthenocissus quinquefolia Burial, for many dune plants, is not a stressor to survive but a signal to thrive.
The way marram grass interacts with airflow tells you a lot about why dune shape depends so heavily on vegetation density. When wind hits a patch of dense marram, it cannot penetrate the canopy easily, so sand is forced upward and carried above the grass in a “skimming flow.” In dense stands, up to 70% of total sand transport occurs above the canopy rather than through it. In sparser stands, nearly half the sand still moves through and among the stems.6Journal of Geophysical Research: Earth Surface. Skimming Flow and Sand Transport Within and Above Ammophila (Marram) Grass on a Foredune Dense vegetation, then, builds taller, steeper dunes because it forces sand higher and drops it on the crest, while sparse vegetation lets sand filter through, building lower, broader forms.
How Dune Soils Change Over Thousands of Years
A freshly formed dune is almost pure quartz sand, often mixed with shell fragments that make it strongly alkaline. Over time, rain leaches the calcium carbonate from those shells, soil organisms move in, and the chemistry shifts dramatically. A two-million-year dune chronosequence in southwestern Australia shows the full arc: young dunes (under about 6,500 years old) are alkaline and carbonate-rich. By the time dunes reach a few hundred thousand years, they are yellow, decalcified sands with iron oxide coatings on the grains. After two million years of weathering, even the iron is gone, leaving bleached white quartz several meters deep.7Ecosystems. Soil Development and Nutrient Availability Along a 2 Million-Year Coastal Dune Chronosequence Under Species-Rich Mediterranean Shrubland in Southwestern Australia
The nutrient story follows a predictable pattern. Nitrogen builds up quickly as bacteria and organic matter accumulate, peaking in intermediate-aged dunes and then declining. Phosphorus, by contrast, drops continuously because it is locked in minerals that slowly dissolve and wash away with no geological mechanism to replace them. After two million years, phosphorus levels in those Australian dunes are among the lowest of any soils on Earth.7Ecosystems. Soil Development and Nutrient Availability Along a 2 Million-Year Coastal Dune Chronosequence Under Species-Rich Mediterranean Shrubland in Southwestern Australia That shift from nitrogen-poor young soils to phosphorus-starved ancient ones reshapes which plants can survive at each stage.
The pH of the soil matters, too. On younger, calcareous dunes, phosphorus exists in insoluble forms that plants struggle to access on their own, so species that partner with mycorrhizal fungi tend to dominate, because the fungi help scavenge scarce nutrients. On older, acidified dunes where grasses have encroached, phosphorus becomes more available in organic and weakly bound forms, and the plant community shifts toward species that release their own root chemicals to dissolve nutrients instead of relying on fungal partners.8Ecosphere. Resilience in coastal dune grasslands: pH and soil organic matter effects on P nutrition, plant strategies, and soil communities
Biological Soil Crusts and Invisible Ecosystems
Before shrubs and grasses colonize bare sand, a less visible community often arrives first. Biological soil crusts, thin living layers of cyanobacteria, algae, mosses, and fungi, form on stabilized sand surfaces. These crusts act as ecosystem engineers by binding loose grains together, reducing wind erosion, and beginning the slow process of building actual soil.9PubMed. Biological Soil Crusts from Coastal Dunes at the Baltic Sea: Cyanobacterial and Algal Biodiversity and Related Soil Properties
As these crusts develop and mature, they measurably increase the organic matter and moisture content of the sand beneath them. Carbon, nitrogen, and phosphorus all accumulate as crust organisms grow and begin cycling nutrients.10PubMed Central. Successional Development of the Phototrophic Community in Biological Soil Crusts on Coastal and Inland Dunes These crusts are essentially bootstrapping soil formation on what was recently a sterile surface. They are fragile, though. Foot traffic, vehicle tires, or even sustained trampling by animals can destroy them in seconds, undoing years of slow biological accumulation.
Dune Slacks and Their Waterlogged Diversity
Between parallel dune ridges, the land surface sometimes dips low enough to intersect the water table, creating seasonally flooded depressions called dune slacks. These are among the most biodiverse habitats in any dune system, supporting orchids, mosses, rare sedges, and amphibians that could not survive on the dry ridges above.
What drives slack communities is hydrology, particularly the depth and seasonal timing of the water table. In field studies of multiple dune slacks, the maximum water level and spring mean water level showed the strongest correlation with vegetation composition.11Ecological Indicators. Five-year carry-over effects in dune slack vegetation response to hydrology Species sort themselves along fine elevation gradients within a single slack, so that even a few centimeters of difference in ground height can separate one plant community from another. In slacks with substantial topographic variation, hydrology significantly shaped community composition, while more uniform slacks supported less diverse assemblages.12Journal of Vegetation Science. Fine‐scale hydrological niche segregation in coastal dune slacks
Management turns out to be critical for keeping slacks functional. In northwest England, slacks receiving active management like winter grazing, regular mowing, and scrub removal maintained significantly higher soil moisture than unmanaged or lightly managed slacks.13PubMed Central. Plant diversity and community composition in managed humid coastal dune slacks in NW England Without intervention, shrubs and trees invade, draw down the water table, and shade out the light-demanding species that make slacks special.
Animals That Have Made Dunes Home
Dune animals face harsh conditions: extreme surface temperatures, desiccation, sand instability, and limited food. The species that persist have evolved specific solutions. Among the most conspicuous dune insects in the Mediterranean are darkling beetles (family Tenebrionidae), which show adaptations including elongated legs that lift their bodies above scorching sand surfaces, a sealed cavity beneath the wing covers that reduces water loss, and finely tuned daily and seasonal activity patterns that shift in response to temperature.14Fragmenta entomologica. Adaptations of tenebrionid beetles to Mediterranean sand dune environments and the impact of climate change Many of these beetles are nocturnal, emerging to forage only after the sand cools.
Birds, too, depend on dune systems, though their requirements often conflict with vegetation succession. The Western Snowy Plover, a federally threatened shorebird along the U.S. Pacific coast, nests on open, sparsely vegetated sand. When invasive grasses convert those open flats to dense, tall ridges, the plover’s nesting habitat disappears.15Ecosphere. Non‐target effects of invasive species management: beachgrass, birds, and bulldozers in coastal dunes That tension between bare-sand species and vegetation-dependent species runs through all dune management decisions.
What Grows Below Matters as Much as What Grows Above
A dune plant’s survival strategy is often hidden underground. When researchers measured whole-plant traits across species on a foredune, they found that belowground characteristics like rhizome length, root construction, and the degree of mycorrhizal fungal colonization varied enormously among species growing side by side.16Ecosphere. Whole plant traits of coastal dune vegetation and implications for interactions with dune dynamics Some species invest in long, spreading rhizomes that stitch sand together over wide areas. Others put their energy into dense, deep root systems or into partnerships with soil fungi. Two plants can look superficially similar above ground but use completely different underground strategies to hold on in the same shifting environment.
The practical implication for dune management is that planting a single species, even a highly effective sand-trapper like marram grass, produces a structurally simple dune. A more diverse planting that includes species with different root strategies and mycorrhizal relationships is likely to create a more resilient landform, one that responds better to variable conditions of burial, drought, and salt spray.
Dunes as Storm Barriers
One of the main reasons governments invest in dune protection is flood defense. A well-vegetated dune ridge absorbs wave energy during storms, sacrificing sand from its seaward face to dissipate force and prevent water from flooding inland areas. The value of that plant cover was tested systematically in wave-flume experiments that simulated mild, moderate, and intense storms hitting dune profiles with varying vegetation densities. Vegetation reduced erosion of the dune face across all wave conditions, all profile types, and all erosion modes tested. During the strongest storms, vegetated dunes resisted overwash entirely, preventing erosion of the landward side of the dune that would otherwise occur.17Coastal Engineering. Response of vegetated dune–beach systems to storm conditions That finding held regardless of whether the beach in front of the dune had a pronounced berm or a flat profile.
The storm-barrier function is particularly relevant because it is self-renewing in ways that seawalls and riprap are not. After a storm erodes the seaward face, wind rebuilds it if sand supply and vegetation remain intact. A concrete wall, once damaged, requires engineered repair. This self-healing quality is why dune-based coastal defense is increasingly described as a nature-based solution, one that can be cheaper over decades even though it demands ongoing stewardship rather than one-time construction.
Sea-Level Rise and Faster-Than-Expected Retreat
Climate change threatens dune systems from multiple angles. Rising sea levels push the shoreline landward, narrowing the beach that supplies sand. More frequent and intense winter storms erode dune faces faster than calm periods can rebuild them. And warming temperatures can shift which plant species survive.
The retreat rates already being measured in some locations are worrying. Along the north coast of southwest England, dune systems are showing “dune roll-over,” where sand is stripped from the seaward face and deposited on the crest or landward side. Observed retreat rates in these embayed settings have been two to three times larger than what simple sea-level-rise models predict.18Marine Geology. Coastal dune dynamics in embayed settings with sea-level rise – Examples from the exposed and macrotidal north coast of SW England The researchers suggested that increased winter storminess, rather than sea-level rise alone, may be driving the excess retreat. For coastal managers, the implication is that planning based purely on projected sea-level curves underestimates how fast dunes may move.
Invasive Grasses and the Paradox of Too Much Vegetation
Not all dune vegetation is beneficial. On the Pacific coast of North America, two introduced species of beachgrass, European marram grass and American beachgrass, have spread aggressively and fundamentally altered dune geomorphology. These invasive grasses converted naturally open, low-lying dune systems with sparse native plant cover into tall, densely vegetated ridges.15Ecosphere. Non‐target effects of invasive species management: beachgrass, birds, and bulldozers in coastal dunes The irony is that the same sand-trapping ability that makes marram grass useful for coastal defense in its native Europe makes it destructive when introduced to systems that evolved without it.
The ecological consequences extend beyond physical dune shape. Several native plant species have declined as the invasive grasses outcompete them, and the loss of open sand habitat has directly reduced populations of the Western Snowy Plover. Restoration projects that remove invasive beachgrass to recover open habitat have to navigate this tradeoff carefully: the bulldozers and herbicides used to eliminate the grass can themselves disturb nesting birds and remaining native vegetation if poorly timed.
Restoring Dunes That Have Been Damaged
Dune restoration typically combines physical sand trapping with revegetation. Sand fences, brush barriers, and other structures slow wind and encourage sand to accumulate, rebuilding lost volume. Once enough sand has gathered, native dune grasses and shrubs are planted to stabilize it biologically. On the U.S. Atlantic coast, a restoration on Tybee Island, Georgia, showed that newly planted dune vegetation had a survivorship rate of nearly 97%. Those plants on average doubled in both percent cover and height within 14 months, reaching levels equivalent to a nearby natural reference dune.19Ecological Restoration. Plant Growth and Sand Movement in a Coastal Dune Restoration on Tybee Island, USA
Planting density turned out to be a key variable. Sand accretion increased with higher planting density, while bare plots gained almost no sand at all. Interestingly, though, the growth rate of individual plants decreased at higher densities, suggesting that competition among plants eventually limits the benefit of packing them in tighter.19Ecological Restoration. Plant Growth and Sand Movement in a Coastal Dune Restoration on Tybee Island, USA Restoration managers have to balance maximizing sand capture against the long-term vigor of the plant community.
Cost matters for these projects, which often cover large stretches of shoreline. In southern California, researchers tested a low-cost approach using small wooden “shims” placed in the sand alongside fencing. Plots with shims accumulated significantly more sand and supported more plants than plots with fencing alone or with seed only, suggesting that simple, inexpensive structural additions can meaningfully boost restoration outcomes.20Journal of Coastal Research. Nature-Based Solutions to Restore Coastal Sand Dunes in Southern California
Carbon Storage in Coastal Dune Habitats
Dunes are rarely mentioned alongside forests or peatlands as carbon stores, but they do accumulate soil carbon, and the amounts vary dramatically with habitat type. Along the Italian Adriatic coast, researchers quantified carbon stocks across four types of dune habitat within the Natura 2000 conservation network. Wooded dunes held significantly higher soil carbon density than mobile dunes, embryonic dunes, or fixed herbaceous dunes, and their greater total area meant they accounted for the bulk of carbon storage. Across all Adriatic dune Natura 2000 sites, the estimated sequestration rate was about 5,000 tonnes of CO₂ equivalent per year.21Applied Geography. The role of Italian coastal dunes as carbon sinks and diversity sources. A multi-service perspective
There is a trade-off, though. The wooded dunes that stored the most carbon supported fewer plant species than the open, fixed dunes, which were the richest in both total species count and specialist dune plants. Those species-rich fixed dunes survive only in small remnant patches along the Adriatic, making them highly endangered despite their relatively modest carbon stocks.21Applied Geography. The role of Italian coastal dunes as carbon sinks and diversity sources. A multi-service perspective Conservation policy that optimizes purely for carbon would favor letting dunes succeed toward dense woodland, but doing so would sacrifice exactly the open-dune habitats that harbor the most biodiversity. Managing for both goals requires maintaining a mosaic of dune stages rather than pushing all sites toward a single climax state.
Salt Spray and Local Adaptation
One of the less obvious stressors on dune plants is salt spray. Onshore winds carry fine droplets of seawater that coat leaves and can damage plant tissue through osmotic stress and direct toxicity. Coastal populations of some species have evolved measurably higher tolerance to this challenge. When researchers compared Virginia creeper vines collected from coastal dunes with those from inland habitats, the coastal individuals showed higher tolerance to foliar salt spray whether grown from cuttings or from seed. Coastal-origin seedlings also regrew thicker leaves after defoliation caused by salt exposure.5Plant Ecology. Coastal provenance increases salt spray tolerance but not sand stress responses in the vine Parthenocissus quinquefolia
That finding has practical significance for restoration. If coastal plant populations are genetically better adapted to the specific stresses of the dune environment, using locally sourced seed or cuttings should improve project outcomes compared to importing stock from inland nurseries. The difference was provenance-specific for salt tolerance but not for sand burial, where all populations responded similarly, suggesting that local adaptation is a patchy, trait-by-trait phenomenon rather than a blanket advantage across all dune stresses.