Persistence of Carex bigelowii–Racomitrium lanuginosum moss heath under sheep grazing in the Grampian Mountains, Scotland

Carex bigelowii–Racomitrium lanuginosum moss heath has been monitored on the summit of Glas Maol, Grampian Mountains, Scotland since 1990 to assess the impact of herbivores and snow-lie. This vegetation community has high conservation value in Britain, being near-natural and the habitat of some rare arctic-alpine birds. In recent decades, it has decreased in extent in British uplands, and changed in composition due to declining Racomitrium cover, with the main drivers believed to be heavy grazing and nitrogen deposition. Permanent plots were established for the monitoring, laid out at fixed distances from a ski corridor built in 1986. Sheep grazing was assessed by pellet-group counts, and botanical composition by point-quadrat analysis. Monitoring was in summer annually between 1990 and 1996, but less frequently since. The moss heath was found to retain its main characteristics from 1990 to 2008/09, with Carex bigelowii Torr. ex Schwein dominant and Racomitrium lanuginosum (Hedw.) Brid. having much cover. There was a small but significant increase in grasses, and lichens declined, but the community remained species-poor. Some ground experienced increased grazing pressure and suffered a temporary decline of Racomitrium, but recovery followed despite continuing substantial grazing. The species experiencing greatest change was Dicranum fuscescens Turner, which first increased but later lost most of its cover; its relationships to Racomitrium lanuginosum are discussed.