Sand dunes are moving landscapes that we keep trying to stop

What follows is an argument about sand dune ecology, and about where the received version of it stops being true.

Movement is the habitat

A healthy dune system contains a gradient from bare mobile sand at the front to fixed grassland behind. Many of the rarest species — specialist invertebrates, orchids, natterjack toads in some systems — depend on the early, bare stages. A dune system that has stopped moving loses those stages first.

The sequence has names because each stage is a distinct habitat — embryo dunes forming around a strandline, yellow dune held by marram, grey dune with its lichens and mosses, dune heath behind — and every one of them depends on new bare sand still arriving at the front.

Stabilisation had unintended effects

Extensive planting of marram and pine through the twentieth century was intended to prevent sand blow onto farmland and roads. It worked, and it converted dynamic systems into fixed, scrubby, species-poor ones. Much current dune conservation is undoing that deliberately.

Planting was not the only cause, since sand supply itself fell where coasts were defended and channels dredged, and grazing pressure collapsed when rabbit populations crashed, so several unrelated changes pushed the same way at once.

Nitrogen accelerates it

Atmospheric nitrogen deposition fertilises dune grassland, which favours coarse grasses and scrub over the specialists. This happens regardless of local management and is a diffuse pressure that is difficult to address on site.

It is one reason dune systems have fixed faster than historical rates would suggest. The two pressures compound, because a mobile dune keeps burying and resetting its vegetation while a fixed one accumulates everything that lands on it, so stabilisation and deposition together drive change far faster than either would alone.

Restoration means making a mess

Notching foredunes, removing scrub, and creating bare sand patches are all standard techniques now. They look destructive and are unpopular with visitors who expect conservation to mean planting things. Explaining the reasoning publicly is a substantial part of running these projects.

Getting it right is technical rather than merely bold, since a notch has to be cut in the right place and at the right size for the prevailing wind: too small and it closes over within a season, too large and it opens a blowout nobody intended.

Visiting without damage

Sticking to paths in fixed dune grassland protects fragile ground; walking on bare mobile sand does very little harm. That inverts the usual instinct and is worth knowing.

On the ground, dogs and ground-nesting birds are the main seasonal conflict on dune systems. It is also why access is deliberately funnelled through a few fenced or boarded paths, because a fresh line worn through fixed dune grassland exposes sand that the wind then enlarges, and a footpath can become a blowout without anybody meaning it to.

The wet hollows are the richest part

Dune slacks are the low ground between ridges where the water table sits at or near the surface for part of the year. Seasonal flooding there suppresses scrub and maintains the bare, damp, lime-rich conditions that orchids, rare sedges and amphibians such as the natterjack toad depend on. Slacks are therefore vulnerable to anything that lowers groundwater — abstraction from the dune aquifer, drainage of the farmland behind, or the extra water drawn up by a pine plantation planted on the system itself.

Restoration frequently means scraping slacks back down to the water table, which produces the raw bare hollows that visitors occasionally report as vandalism.

The takeaway

A dune that has stopped moving is a dune that is dying, however green it looks.

Go slowly enough to notice, and most of this stops being advice and starts being obvious.