Managing heathland with sheep: the flock as a mower
Purple heathland remains open only if something eats the encroaching vegetation. On many Dutch sandy soils, that something is still a sheep.
Heathland is a cultural landscape. Without management, woodland takes over and species that depend on open, nutrient-poor ground disappear. Sheep keep young trees short, maintain variation in the vegetation and carry seeds in their wool. Their dung feeds dung beetles. Alterra described how shepherded flocks — accompanied by a shepherd — are used mainly to maintain restored heathland, not to eliminate heavily overgrown purple moor-grass in a single season. Land managers choose breeds suited to sandy terrain: Veluwe, Drenthe and Kempen heath sheep. On the Brabantse Wal, Kempen sheep suppress purple moor-grass that grows in response to nitrogen and can become highly flammable.
Grazing is not a control you can simply turn up indefinitely. Excessive year-round pressure can destroy nectar plants. Too little grazing, or grazing at the wrong time, can also change the vegetation. The effect depends on the terrain, the season and the animals. Mechanical mowing is an alternative, but it lacks the dung and seed dispersal. The shepherd determines where the grazing pressure falls. The heathland determines whether it works.
When you see a flock, look at what is not growing tall. That is the management at work. Current access rules for the terrain are set by the land manager; a flock is not an invitation to walk straight through the enclosure.
A fresh perspective
Sheep spread seeds in their wool; the flock is therefore also a travelling seed bank.
Compare a grazed heath with a fenced exclosure beside it: the difference in shrub height is the work of the sheep.