The effects of controlled sheep grazing on the dynamics of upland Agrostis-Festuca grassland.
Agrostis capillaris-Festuca ovina plant communities are widespread in the uplands of Great Britain. They are agriculturally productive but little is known about how to manage this community for specific goals. Vegetation trajectories were examined in this plant community under different sheep grazing management regimes at two sites in Scotland. One site had a substantial presence of moorland species, the other was characterized by a more productive vegetation. Management consisted of maintaining sward heights of 3, 4.5 or 6 cm during the growing season, or complete exclusion of grazing stock. Changes in species composition were small over the 7 years of the experiment and few species invaded or were lost. The observed changes were largely as a result of shifts in abundance of the dominant species. Maintenance of sward height at low levels (3 or 4.5 cm) during the growing season resulted in the spread of Nardus stricta where present. Where N. stricta was absent, the sward developed a higher content of mosses, specifically Hypnum jutlandicum and Rhytidiadelphus squarrosus. Removal of grazing resulted in an increase of cover of grazing-intolerant species, such as Deschampsia flexuosa and Molinia caerulea, and in the cover of dwarf shrub species where present. The two sites differed in the treatment that resulted in the smallest change in species composition. At the more productive site, maintenance of the sward at 4.5 cm resulted in the smallest overall change in species composition. At the less productive site, grazing the sward to 6 cm resulted in the smallest shift in vegetation composition. Grazing at this height appeared to prevent the spread of both M. caerulea and N. stricta. It is suggested that sustainable grazing regimes for upland Agrostis-Festuca grasslands need to take into account both the initial composition of the vegetation, specifically the presence of species capable of replacing A. capillaris and F. ovina, and of achieving dominance, and the overall productivity of the site.