Overgrown dunes
Large areas of the dunes of Schiermonnikoog are overgrown with shrubs. Reasons for this are:
- the blowing in of fertilizing substances, which make trees and shrubs grow faster
- the decline of the number of rabbits, due to viral diseases. The small number of rabbits left cannot eat all sprouting trees.
- the planting of forest in the beginning of the last century. In the lee of the forest new shrubs can grow.
- withering of dune valleys. In valleys that are flooded every winter shrubs cannot thrive.
Many nice views of the dunes have disappeared in the last decades due to this growing thick with bushes and trees. Rare plant and animal species that are characteristic for an open dune landscape disappear.
Natuurmonumenten opens up the dunes on several places, e.g. by cutting sods and by mowing. Cattle and ponies also contribute.
Cutting sods
By cutting sods we remove the upper layer of ground, which contains remnants of plants and nutritious soil. After this, bare sand remains. Shortly after this the landscape looks like a lunar landscape. But the ground still contains seeds of plants, waiting patiently till they get a change to grow. These rare pioneer plants don’t make a chance in a closed turf. They are small, but often have beautiful flowers, like fairy flax (white with yellow) and seaside centaury (deep pink).
Mowing
Every autumn Natuurmonumenten mows the dune valleys. If this isn’t done on a regular basis, the valleys will get overgrown with willows and birches. Rare plants like orchids and grass-of-Parnassus would disappear. Not the whole valley is mowed; mostly a stroke is left undisturbed. This is important for wintering caterpillars and other insects.
Thanks to this mowing regime the valleys on the island are in an excellent condition. The most flowery valleys are the valley near the northern lighthouse and the Hertenbosvallei. The verges next to the bicycle paths are also full of flowers, thanks to the mowing regime.
Grazers
In the dunes large animals roam, like cows, horses, goats, and sheep. All of them are vegetarians, who love to eat grass and young trees. They keep the dunes of the island open. In the open dune landscape special flowers can grow that would otherwise loose the competition with fast growing grasses and shrubs. And it is advantageous for walkers as well. The grazers eat dense and prickly shrubs, so that in the grazed areas walking is often more pleasant than elsewhere in the dunes.