Saving the dynamic Dutch dunes

The Netherlands is famous for its canals, tulips and quaint towns with steep-gabled houses. Less iconic are the dramatic dunes that make up some two-thirds of the Dutch coastline.

Yet these rolling seaside hills are a defining aspect of the country's natural beauty and integral to human life, protecting land from sea and sheltering some of its most biodiverse habitats.

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"Seven hundred and fifty or more out of 1,500 natural plant species in the Netherlands occur in the coastal dunes," Bert van der Valk of the Netherlands Center for Coastal Research told DW. They are not only important nature conservation areas, he adds, but also "a natural resource for nature development, recreation and, in some cases, storage for drinking water."

The dunes are a draw for hikers and cyclists, and the swimmers who immerse themselves in these little patches of wilderness before plunging into the North Sea.

Throughout the year, they offer picturesque views, from bright flowers that bloom in spring and summer, to tans and yellows in fall, through to dark greens and browns of winter plants. A closer look reveals colorful lichens and rare treasures like the fen orchid.

What visitors may not fully sense as they enjoy this seasonally changing landscape, is that it shifts through other cycles, too. And that without protection, they could fall into a state of permanent disrepair.

A living landscape

Dunes are dynamic systems, pushed and pulled by the elements and the life cycles of the organisms they support.

They begin to form as sand is blown in from the sea and collects above the high-tide mark. Tiny, tough plants take root, trapping more sand, and decaying to enrich it with nutrients that allow other vegetation to grow. Gradually, roots bind the sand into more solid structures that can support a still greater diversity of life.

The youngest — or "embryo" — dunes are those closest to the sea. Rising in turn like waves, come bigger "white" dunes where hardy plants like marram grass and searocket colonize the moving sand, and, farthest inland, static "gray" dunes take their name from the hues of lichen and moss that grow between the bigger plants that anchor them in place. 

The Netherlands is home to around 17% of the gray dunes protected by the European Union's Natura 2000 network of conservation areas. Carline thistles and dune pansies dot the verges between open sand and gray dunes, butterflies and grasshoppers flit between the flowers, and birds like the ringed plover come to breed.

Where dunes collapse, hollows that sink below sea level, called "dune slacks," provide yet another habitat, supporting marsh plants and animals — newts, toads and dragonflies — that thrive in damp conditions.

The dunes also play a role in human systems, proving some 4 million people in the Netherlands with clean drinking water, which is filtered through the dunes to remove impurities.

Tangled up in weeds

But these ecosystems are delicate and the dunes are no longer as dynamic as they used to be.

"Over the last century, the situation has changed drastically," Ted Sluijter, a ranger with the Dutch Society for Nature Conservation, told DW. "It seems that mainly due to human intervention, the conditions have started to work in favor of rising [plant] growth."

Atmospheric nitrogen pollution from intensive farming, traffic and the gas industry has nourished plants that shouldn't be there — including exotic species, like black cherry — that are growing out of control. The warmer weather the Netherlands is increasingly experiencing — as the planet as a whole heats up — gives them an extra boost.

These weeds crowd out the dunes' natural diversity, fixing them in a final, unwanted stage of their evolution.

In the past, rabbits riddled the gray dunes with their labyrinthine warrens and nibbled away at plants, keeping them in check. But since the mid 20th century, rabbit numbers have been decimated, mainly by diseases like myxomatosis that were, like the invasive plant species, introduced by humans.

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Back in motion

Water companies and conservation groups are making a concerted effort to bring life and motion back to the Netherlands' coastline. A collaboration between the Dutch Society for Nature Conservation, water utility PWN and the Rijnland Water Authority, for example, has transformed the Voornes and Goeree dunes in South Holland.

The first step was to wrench unwanted trees from the dunes and hack out overgrown shrubs — carefully, though, to preserve certain plants and, for example, ants' nests. In some areas, sand was removed to get white dunes moving again and create new dune slacks.

Sluijter admits all this left a desolate-looking scene. But plants and animals have taken advantage of the new conditions and are bringing the sands rapidly back to life, restoring the Voorne and Goeree dune areas to vibrant mixed habitats of dune grasslands, marshy hollows and mixed woodland, where endangered species like the turtle dove and sand lizard are multiplying.

Forest management and water utilities elsewhere on the Dutch coast are making up for the loss of rabbits with sheep, goats, highland cattle and even European bison and Konik horses.

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Changing landscape in a changing climate

At the other end of the dune system, the government agency responsible for flood defense oversees a process whereby sand is dredged up from under the sea, and deposited on the foreshore to counter erosion by the rough North Sea.

Historically, the Rhine and Meuse rivers brought sand that replenished the coast from inland. But over the centuries, these waterways became intensely managed for human needs, and van der Valk says that without intervention, the coast would recede by an average of a meter each year.

"Dunes are natural boundaries between land and sea," van der Valk says, which is why people have made homes in the dunes for centuries, seeking protection from storms raging in from the ocean.

Now, dunes provide the only defense for 200 kilometers of Dutch coastline that are not protected by dikes. And that function is only becoming more important as the climate crisis makes the sea all the more capricious.

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"We have to be alert," van der Valk says, "to the effects of sea-level rise, and the effects of storms, which may be even more important for the Netherlands. We're monitoring this continuously."

With the low-lying Netherlands at greater risk of from the swelling oceans than most, only a careful confluence of natural and human processes can keep this unique coastline and all it shelters safe.