Understanding the Sand Dunes — Why the Sefton Dune System Matters

15 November 2025

How dunes form

Sand dunes form where sand is blown inland from the beach and trapped by vegetation. On the Sefton Coast, the process has been running for several thousand years — the youngest, most mobile dunes are at the seaward edge; the oldest, most stable dunes are furthest inland.

The key plant in dune formation is Marram Grass. It tolerates burial by sand and actually grows faster when covered — its roots bind the sand and its stems trap more. Without Marram, dune systems don't accumulate. With it, they can build to ten or fifteen metres in height.

The dune zones

Moving inland from the beach: the embryo dunes just above the high-tide mark are sparsely colonised by Sea Rocket and Prickly Saltwort. Behind them, the mobile yellow dunes — steep, unstable, dominated by Marram — are where the system is still building.

Further back, the fixed grey dunes are older and more stable. The Marram gives way to a richer plant community — Restharrow, Lady's Bedstraw, Sand Sedge, Hare's-foot Clover. These are the botanically interesting dunes and they hold most of the dune-specialist invertebrates.

In the hollows between ridges — the dune slacks — the water table reaches the surface in winter. These are the wettest part of the system and they hold some of the rarest species: Grass of Parnassus, Round-leaved Wintergreen, Marsh Helleborine, and the Natterjack Toad.

Why the system is changing

Two things are changing the dunes. At the seaward edge, erosion is taking the front face of the dunes back by a metre or more a year in some places. This is partly natural process, partly accelerated by sea level rise and changing wave patterns.

At the landward edge, the problem is different. Without disturbance, scrub — Sea Buckthorn and Creeping Willow in particular — invades the grey dunes and slacks and shades out the specialist plants. The fixed dunes are becoming scrub woodland in some sections, losing their open character and the species that depend on it.

Active management — scrub removal, cattle grazing, occasional heavy machinery — is required to maintain the open dune habitats. It's expensive, ongoing and unglamorous. The alternative is losing the habitat entirely.

What to look for when you visit

The botanically best areas are the fixed grey dunes and the wet slacks. Ainsdale NNR is the best site — Natural England runs guided walks in summer that are worth booking for their plant-identification value.

For invertebrates, the fixed dunes on sunny days in summer produce impressive diversity — look for mining bees and solitary wasps in bare sand patches, and several nationally scarce beetle species have been recorded in the dunes here.

Don't walk on the mobile dunes unnecessarily. Marram breaks under foot traffic and once the surface is broken, erosion accelerates. The paths exist for a reason.