Cooperating dune grasses make climate-resilient dunes easier to realize
NIOZ Royal Netherlands Institute for Sea ResearchDutch dikes are world-famous, but we have also been building dunes for centuries. The first artificial dunes (so-called “drift dikes”) were already constructed in the 15th century. More recently, near Petten around 30 million square metres of sand was used to form the Hondsbossche Dunes. These artificial dunes are starting to resemble natural dunes, but important differences remain (see figure below).
Natural dunes are resilient
Artificial dunes function like a dike: they often consist of a single high, robust dune that keeps seawater out. But if such a dune is breached, there is hardly any protection behind it. Natural dunes are wider and made up of countless smaller dunes. A single natural dune is therefore more vulnerable than an artificial dune, but all those dunes together provide strong protection. Above all, natural dunes are resilient: they can recover after a storm and keep up with a rising sea level. Properties that are especially valuable in a changing climate.
4000 dune grass patches
Using aerial photographs and elevation models, Paul Berghuis and colleagues tracked the development of a young, unmanaged dune landscape at De Hors (Texel). Berghuis: “We studied how more than 4000 dune grass patches – with a size of multiple square meters – formed a 12-hectare dune landscape over ten years. This showed that dune formation is mainly determined by how patches are positioned relative to each other, while the size of the individual patch is of less importance.” (see figure below).
Capturing sand twice as efficiently
The analyses also reveal a clear tipping point: “Neighboring patches can already cooperate when the distance between them becomes less than 4.5 meters. The system then abruptly shifts from isolated sand traps to functionally connected groups.” That makes a big difference: “Within these groups, sand is captured and retained up to twice as efficiently, accelerating dune growth. Strikingly, dune grass only needs to cover a small fraction of the ground surface to build a large dune quickly.”
Useful for dune restoration
According to Berghuis, these new insights are very useful for dune restoration. “By planting dune grass strategically, we can reach the tipping point for cooperation between patches sooner. That means we can build natural dune landscapes with relatively few plants and at lower cost.” Working with nature thus becomes a more attractive option: “The idea is simple: by planting strategically, we give dune formation an easy start. After that, natural processes take over. In this way, we work together with nature to build resilient, future-proof dune landscapes.”
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Images: Tom Kisjes