How a bare beach becomes woodland

Sand dunes are one of the few British habitats where you can watch the whole process of ecological succession laid out in front of you, ridge by ridge. It starts with bare sand at the top of the beach and ends, many decades later, with scrub and woodland a few hundred metres inland. Because dune systems build in ridges roughly parallel to the shore, walking inland is a bit like walking through time. The plants and animals you meet change as the sand becomes more stable, richer in nutrients and less salty.

The key thing to grasp is the difference between succession and zoning. Succession is the slow change over time. Zoning is what you see in space: the neat bands of vegetation from strandline to woodland. On most dune systems, both are happening at once. New sand is still being trapped at the seaward edge while the older, inland dunes have already moved on to heath, scrub or woodland.

The zones you'll walk through

Most UK dune systems, from Studland to Braunton Burrows to the machair of the Outer Hebrides, show the same basic sequence.

• Strandline: the debris line at the top of the beach, where seaweed, cuttlefish bone and driftwood collect. Salty, disturbed and often rich in invertebrates.
• Embryo dunes: low hummocks of sand held together by sand couch and sea rocket. Fragile and easily trampled.
• Yellow dunes: the taller foredunes dominated by marram grass. Sand is still mobile here, and the ground feels soft and pale.
• Grey dunes: fixed, older dunes with a darker, mossier surface and a thin skin of soil. This is where dune grassland really develops.
• Dune slacks: damp hollows between ridges, sometimes flooded in winter, often home to orchids and amphibians.
• Dune scrub and woodland: the final stage, with sea buckthorn, willow, hawthorn, birch and occasionally pine.

The plants doing the heavy lifting

Marram grass is the chief dune builder. It grows up through fresh sand as it is buried, sending out long underground stems that knit the surface together. Sand sedge does something similar with rhizomes that can travel remarkable distances, while sea couch holds the earliest hummocks in place.

Once the sand settles, finer plants move in. On grey dunes look for sheep's fescue, red fescue, lady's bedstraw, wild thyme, kidney vetch and bird's-foot trefoil, often with a mat of lichens such as Cladonia species between them. These plants add organic matter, and as leaf litter accumulates, the soil slowly gains nutrients and holds water. That opens the door for scrub, which in turn shelters tree seedlings. Sea buckthorn is a common culprit for rapid scrub spread, and many reserves now manage it carefully to keep the open dune grassland that rare species depend on.

Insects, lizards and the birds that follow

Each zone supports its own cast. Bare and yellow dunes, with their warm open sand, suit burrowing insects: solitary wasps and bees, tiger beetles and the occasional sand lizard, which needs bare sand for egg-laying. Dune slacks are strongholds for natterjack toads in a handful of English and Scottish sites.

Grey dune grassland is butterfly country. Look for grayling, common blue, dark green fritillary and the day-flying six-spot burnet moth, whose caterpillars feed on kidney vetch. The birdlife shifts with the habitat too. Ringed plover and little tern nest on bare sand and shingle near the seaward edge, skylark and meadow pipit favour open fixed dune grassland, and stonechat, whitethroat and linnet take to the scrub. In winter, snow buntings and twite arrive to feed on seeds in the strandline and dune edge.

Beachcombing the strandline

The strandline is the beachcomber's zone, and it is best searched on a falling tide, ideally after a spell of onshore wind or a storm. Walk the highest line of debris rather than the hard sand near the water's edge.

• Eggcases: mermaid's purses from rays and skates, and whelk eggcases. Records of these are genuinely useful to marine conservation projects.
• Cuttlefish bone: the chalky internal shell, often washed up in quantity.
• Sea beans and driftwood: tropical seeds and worked timber that can travel enormous distances.
• Sea glass and pottery: pretty, but please leave the best pieces for the next person.

Handle anything living gently and put it back where you found it, and leave shells that are still occupied. Check local byelaws before collecting: on Sites of Special Scientific Interest and nature reserves, taking anything at all usually needs permission. Watch where you put your hands and feet in dry dune grassland, as adders bask there.

Reading the dunes on your next visit

Timing makes a big difference. Late spring and early summer are best for dune slacks and orchids, midsummer for butterflies, and autumn and winter storms for strandline treasure. Whatever the season, stick to boardwalks and worn paths where they exist; dune vegetation is easily damaged and slow to recover. Keep dogs on leads between March and September, when ground-nesting birds are vulnerable.

Finally, look for clues about which way the system is moving. A steep, cliff-like foredune usually means erosion; fresh embryo hummocks mean the dunes are still growing. Patches of dense scrub spreading across open grassland suggest over-stabilisation, which is why so much dune management today is about restoring bare sand and grazing. Once you can read those signals, a walk along the coast becomes far more than a walk.