Changes in the composition of Carex bigelowii-Racomitrium lanuginosum moss heath on Glas Maol, Scotland, in response to sheep grazing and snow fencing

Distant to the fence the composition of the Carex-Racomitrium heath changed little over 12 years of monitoring. Agrostis increased and C. bigelowii declined, both changes being significant but much smaller than adjacent to the fence. Also Polytrichum alpinum increased significantly and some lichens declined. For Racomitrium there was a fall of only 2.5% from its initial cover of 40% in 1990. Since the dung counts showed only a negligible reduction in sheep usage between plots at 13-15 and 43-45 m from the fence, the trends in composition recorded at positions 19-20 and 39-40 m from the fence apply to the extensive moss heath used by the dotterel on Glas Maol. These birds still nest in the distant zone, and we judge that the condition of the Carex-Racomitrium heath will remain satisfactory for them unless sheep usage increases by 25% or more. However, the ongoing loss of lichens and the sparsity of Vaccinium myrtillus imply that the current level of sheep grazing has appreciably modified this community from its former pristine condition.