The Utilization of Blanket Bog Vegetation by Grazing Sheep

determined by the limits to stocking rates set by the need to provide sheep with a minimum tolerable level of winter nutrition. This leads to low levels of pasture utilisation, particularly during the summer growing period, and is associated with the poor cycle of nutrition which is basic to the problems of low levels of individual animal performance. Eadie & Maxwell (1974) have recently proposed grazing systems to improve animal production from hill land. These systems involve the use of a small area of improved pasture with the remaining unimproved hill. The improved area is enclosed and grazed during lactation and lamb growth and prior to and during mating, when high quality food has the most beneficial effect on individual sheep performance. The unimproved area is used during the rest of the year. In such grazing systems, the utilization of the unimproved bog vegetation is likely to be increased and the seasonal pattern of use substantially changed compared with a setstocked year round system of grazing. However, there must be a limit to this use since blanket bog vegetation appears to be vulnerable to overgrazing, particularly in combination with periodic burning (McVean & Lockie 1969). A prediction of the effects of these changes in grazing management on species composition and productivity of bog communities is not possible on present evidence. This study arose from the need to obtain further information. The results reported here concern the patterns and levels of utilization of the main bog species as affected by season of use and grazing pressure.