Proposing an efficient indicator of grazer distribution on heterogeneous hill vegetation

Abstract

Irish and UK uplands and peatlands are of international importance but are under threat from several factors, including heavy grazing pressure. Sheep preferentially graze patches of acid grassland with short dense swards, sometimes referred to as 'grazing lawns', and have been implicated in damage to uplands. The aim of this study was to increase our understanding of resource selection by grazers to further inform the design and implementation of conservation strategies. Grazing lawn frequency and habitat condition were mapped and GPS collars were used to track Scottish Blackface sheep on a hill farm in Ireland. Weighted compositional analysis (multivariate analysis of variance) was used to test for random use of different categories of grazing lawn frequency and habitat condition. Grazing lawn frequency was spatially uneven and habitat condition ranged from undamaged to very severely damaged areas. Typically, selection of differing categories of habitat condition was not significant (P>0.05), although the highest selection rank was consistently for the 'moderate-undamaged' category. Sheep most selected 1 ha grid squares containing numerous/extensive grazing lawns (P<0.05) day, night and year-round. As a simple, efficient indicator of hill use by sheep, which would be a valuable input in models predicting grazing impact on hill vegetation, the mapping of grazing lawn frequency is suggested.