Effects of season and intensity of sheep grazing on tree regeneration in a British upland woodland

Abstract

This paper reports some effects of experimental alteration of season (summer, winter) and intensity of sheep grazing on tree regeneration, growth and browsing damage in an upland broadleaved woodland in Cumbria, UK. During the first 3 years of grazing treatments, seedling recruitment was primarily Betula pubescens, Sorbus aucuparia and Fraxinus excelsior. After 7 years of grazing treatments, seedlings and saplings of many species were numerous, with fewer seedlings in winter-grazed plots but a higher proportion of these were browsed. More seedlings had reached sapling stage in winter-grazed plots. Sapling numbers increased with decreasing grazing intensity, with lower proportions browsed at low grazing intensities. Within the first 3 years grazing treatments, recruitment of Betula pubescens seedlings was greater in grazed than ungrazed plots, and greater in winter-grazed than in summer-grazed plots. Browsing damage to these seedlings increased with grazing intensity in winter, and height increments were greatest in ungrazed plots. After 7 years, B. pubescens seedlings and saplings showed no significant treatment effects. After 3 years, recruitment of Sorbus aucuparia seedlings was greater in grazed than ungrazed plots, and greater in summer-grazed than winter-grazed plots. Fewer seedlings were browsed in low grazing intensity plots, and seedling height increments were greatest in ungrazed plots. After 7 years, more S. aucuparia seedlings were browsed in winter than summer, but saplings showed no treatment effects. After 3 years, recruitment of F. excelsior was greatest in low grazing intensity plots and smallest in medium grazing intensity plots. More seedlings were browsed at higher grazing intensities, but in summer-grazed plots height increments tended to be greatest in the most heavily grazed plots. After 7 years, F. excelsior seedlings were more numerous in summer-grazed plots but were not differentially browsed; sapling numbers were not affected by grazing treatments but browsing damage was very high in all except summer low grazing plots. The implications of the results are discussed in relation to woodland grazing management issues.