Vegetation changes in sown grassland in the UK after nine years of extensive grazing management

The effect of extensive grazing management with sheep on vegetation change in sown pastures (initially containing Lolium perenne and Trifolium repens) in the uplands of Scotland was investigated from 1990-1999. One treatment was representative of current more intensive management systems; it was fertilized, and maintained at a sward surface height of 4 cm. Two treatments were unfertilized and were maintained at sward surface heights of 4 cm or 8 cm; the ewe numbers carried on these treatments averaged 74% and 44%, respectively, of those on the fertilized treatment. In all treatments the sheep were Scottish Blackface ewes. Their single lambs also grazed from May until weaning in mid-August. Over 9 years there were only small changes in species composition in the unfertilized treatments. The changes were primarily shifts in abundance of the species present initially, with only a few additions or losses of species. L. perenne made a similar contribution to cover in both the 8 cm and fertilized swards. The highest content of T repens Was in unfertilized swards and the least was in the 4 cm fertilized swards. This study demonstrates that the contribution of the sown species to sward composition remains high in grazed upland swards that are more extensively managed for nearly ten years. Since there was little overall change in species composition, it could be difficult to achieve increased plant biodiversity in these systems simply by removing fertiliser and reducing grazing intensity.