Dunes and Sandy Habitats

Sand that stays put, mostly

Sand dunes are hills of loose sand built by wind. They sit behind some of the larger sandy beaches on Cornwall’s Atlantic coast, and a few cover considerable areas. To the casual visitor they can look like empty scrubland. In fact they are an unusual, specialized habitat, and one that is easily damaged.

How dunes form

Dunes need three things: a plentiful supply of sand, a wind strong enough to move it, and something to stop it. On a wide beach, sand dries out at low tide and is blown inland. Anything that slows the wind, such as a piece of driftwood or a clump of seaweed along the strandline, causes the sand to drop and build up in a small heap.

Pioneer plants then colonize these heaps. Hardy grasses and other salt-tolerant plants can survive being buried and sprayed with salt, and as sand builds up around them, they grow upward through it. Their roots and stems bind the sand together and let the dune grow taller and more stable.

Over time, a dune system often develops in bands running away from the sea:

• Embryo dunes close to the beach, small and new, with few plants.
• Fore dunes or yellow dunes, taller, where sand is still moving and marram grass is common.
• Fixed or grey dunes further inland, where plant cover is thicker and the surface is more stable.
• Dune slacks, damp hollows between ridges where the water table is close to the surface.

The names reflect color: bare sand looks yellow, while older, more vegetated ground looks grayer as plant material and organic matter accumulate.

The role of marram grass

Marram grass is the best-known dune plant. It is well adapted to the harsh conditions: it has tough, rolled leaves that reduce water loss and an extensive network of roots and underground stems. Burial by blown sand actually stimulates growth. In effect, marram is the engineer of the dune system, trapping sand and holding it in place.

This is also why damage to marram is serious. When plants are worn away, the wind finds the bare sand and scoops it out. This can create a blowout, a hollow that can grow over time and may spread, eating into the dune.

Life in the dunes

Despite appearing harsh, dunes can be rich in life. The shifting conditions create many different microhabitats in a small space.

• Plants. Besides grasses, dunes can support low-growing flowering plants that thrive in lime-rich sand, helped in some places by crushed shell in the sand. Dune slacks, being damp, may hold a different community altogether.
• Insects. Warm, sheltered sand suits many insects, including bees, wasps, beetles and butterflies. Some burrow into bare sand to nest.
• Reptiles and amphibians. Sunny, sheltered dune areas can be home to lizards, and damp slacks can attract amphibians in some locations.
• Birds. Ground-nesting birds may use quiet parts of dune and beach, and their eggs and chicks are very hard to see. Seasonal signs asking visitors to keep clear are intended to protect them.
• Small mammals. Rabbits are often a feature of dunes, and their grazing can help keep grass short, which some plants rely on.

Because specific species vary from one dune system to another, local information boards are the best guide to what lives where.

Why walkers are asked to stay on paths

Signs asking visitors to keep to marked routes are common in dune areas, and the reasoning is simple.

1. Trampling kills plants. Marram and other dune plants are tough against wind but not against repeated footsteps, which crush stems and expose roots.
2. Bare sand erodes quickly. Once plant cover is gone, wind can lift sand away rapidly, and a worn track can turn into a blowout.
3. Nesting and burrowing wildlife can be disturbed. Eggs and burrows may be invisible, and a single misplaced step can destroy them.
4. Concentrating footfall protects the rest. A few well-made paths take the wear so that the surrounding area can recover.

The effect is cumulative: one person’s footsteps do little, but thousands of walkers each choosing their own route can strip a slope.

Dunes and the coast as a whole

Dunes also act as a natural buffer. A healthy dune system can absorb wave energy in storms and releases sand back to the beach, which helps the shoreline adjust. They are part of a moving balance between wind, waves and tides. Storms can cut into the front of a dune, and in time sand may build up again, although a damaged dune recovers more slowly.

Beyond the dunes, the sandy ground may merge into coastal heathland or grassland, with its own wildflowers. Dunes are only one of the settings among the Cornish beaches, and they fit into a much broader coastal picture.

Visiting dunes responsibly

• Stay on marked paths and boardwalks, and follow any seasonal closures.
• Do not slide down or play on steep dune faces, which damages plants and can collapse.
• Keep dogs under control or on a lead where signs ask, especially during nesting season.
• Do not light fires or barbecues in dune areas, since dry grass burns readily and fire can destroy the habitat.
• Take all litter home.
• Be aware that soft sand can hide hazards such as old fence posts or holes, and that paths may shift after storms.

A habitat in motion

Dunes show that even something as simple as sand can form a living landscape. They are never entirely still, and they depend on a delicate partnership between plants and wind. A little care from visitors helps them keep shifting in a healthy way.