The utilization of blanket bog vegetation by grazing sheep.
Three areas of bog in western Scotland were grazed at monthly intervals at the times of the year when sheep would graze these areas in hill sheep production systems which incorporate areas of improved pasture. Three stocking rates were used at each site. The lowest stocking rate (1.5 ha/sheep) was equivalent to local practice and results in the utilization of 10-15% of the annual dry matter production. The intermediate and high stocking rates were approximately 2 and 3 times as great, respectively. The seasonal pattern of use of various bog species was estimated by visual scoring of permanently sited quadrats and by examination of cuticle fragments in faeces.During May-July grazing was confined mainly to Molinia caerulea, Trichophorum caespitosum and scattered plants of Deschampsia flexuosa, Agrostis canina and Carex species. Calluna vulgaris, Eriophorum vaginatum and E. angustifolium were hardly eaten. As the year advanced, the grazing of the first group of species decreased and that of the second group increased. During January-March Calluna vulgaris and Eriophorum vaginatum formed the basis of the diet.The patterns of utilization are considered in relation to seasonal patterns of availability and digestibility of the species in vitro. Stocking rate had little effect on utilization where preferred species, e.g. Trichophorum caespitosum and Molinia caerulea, were in short supply and utilization was high. Where preferred species, e.g. Calluna vulgaris and Eriophorum vaginatum, were plentiful stocking rate had a large effect.The results are discussed in relation to systems of sheep farming and the nature of vegetation mosaics in hill land.