Effects of grazing by free-ranging cattle on vegetation dynamics in a continental north-west European heathland

1. Abandonment and eutrophication are major threats to traditional pastoral landscapes and their wildlife in Europe. Social and economical developments have rendered traditional pastoralism impracticable. More knowledge is needed about the effects of grazing with free-ranging herbivores, which is increasingly used as a substitute for the traditional herding system. 2. We studied the effects of free-ranging cattle on the recovery of Calluna heather, tree encroachment and plant species richness in six habitats in a grass-rich Dutch heathland during a 10-year period. The habitats differed in soil fertility, initial heather-grass ratio and developmental stage of Calluna. 3. Despite preferential grass defoliation, cattle grazing neither reduced grass cover in grass heath nor prevented grass invasion in heather. Grass invasion failed only in a nitrogen-poor turf-stripped Calluna heath. Grazing induced a substantial Calluna recovery in grass heaths on podzolic soils, but its recovery failed in grass heath on a phosphorus-rich medieval arable field. As a consequence, the grass-heather mosaics generated by free-ranging cattle were restricted to habitats of intermediate soil fertility. 4. Grazing did not prevent encroachment by pine and birch. Removal by the site manager prevented conversion of 10-20% of the open heathland to forest. 5. During the first 5 years, grazing induced a significant increase in species richness in all habitats. During the second 5 years, species richness stabilized in grass heath and heather-grass mosaics and it declined in the pioneer Calluna heaths. 6. We found indications of various nutrient-mediated grazing effects on the competitive balance between grass and woody pioneers. These suggest that nutrient-mediated feedback might be an important explanatory mechanism for the described vegetation mosaic cycling in heathlands. 7. Free-ranging grazing did not remove the high atmospheric nutrient inputs of the whole area. Substantial amounts of nutrients were redistributed from the grass lawns to the forest. 8. Free-ranging grazing combined with tree cutting appeared to be a suitable management regime for the maintenance of species-rich open heathlands with dynamic grass-heather mosaics. 9. Without tree cutting, free-ranging grazing would have created dynamic tree-grass-heather mosaics in open heathland. Wood-pasture landscapes are fundamentally different from the open heather-dominated heathlands produced by the traditional sedentary farming system. Integrated grazing of heathland, nutrient-rich farmland and forests accelerates this change. Alternative grazing regimes are discussed.