Effects of excluding sheep from an alpine dwarf-herb community

Abstract

Background: The Festuca ovina–Alchemilla alpina–Silene acaulis dwarf-herb community is a rare component of the few and scattered calcareous grasslands found at high altitude in the Scottish Highlands. It contains nationally scarce and rare arctic-alpine species. The community is often heavily grazed and it has been suggested that it is a plagioclimax maintained by herbivores, principally sheep. Aim: Determine the role of sheep grazing in conserving the dwarf-herb community on Ben Lawers, Perthshire, Scotland. Methods: Sheep-proof cages were erected each spring from 1987 to 1996 and dismantled again each autumn. Species cover, the height of the vegetation, the amount of litter and the extent of bare ground were estimated every summer. Data were analysed by repeated measures analysis of variance. Results: Excluding sheep caused major shifts in the balance amongst species. Initially, graminoids and some forbs increased in cover, the vegetation increased in height and the amount of bare ground decreased. However this was followed by a decline in the cover of graminoids as bryophytes proliferated and litter accumulated. Conclusion: Sheep grazing is essential to the maintenance of the dwarf-herb community. Permanent removal of sheep might lead to the development of bryophyte-rich, tall-herb and/or scrub vegetation.