Trends, over 14 years, in the ground cover on an unimproved western hill grazed by sheep, and associated trends in animal performance

Abstract

The frequency of individual plant species at ground level and the species composition of the unimproved vegetation on a western hill farm, stocked with Scottish Blackface sheep, were monitored from 1995 to 2008. Performance criteria of the flock that relied totally, or almost totally, on this vegetation for sustenance from 1994 to 2011 were evaluated. The frequency of vegetation increased over time (from 65% to 82% of the surface area; P < 0.05), with a corresponding decline in the frequency of bare soil, thus reducing vulnerability to soil erosion. This increased incidence of vegetation cover reflected increases in 'other forbs' (P < 0.01), heather (P < 0.05) and grass (P < 0.08). A significant change (P < 0.05) also occurred in the species composition of the vegetation, reflecting an increase in the proportions of 'other forbs' (P < 0.05) and heather (P = 0.14), and a decline in the proportion of sedges (P = 0.14). A similar pattern occurred in the two main habitats: blanket bog and wet heath. Annual stocking rate (ewes per hectare, based on actual ewe grazing days) on the unimproved hill grazing averaged 0.9 (0.13 livestock units) per hectare prior to 1999 and 0.78 (0.11 livestock units) per hectare subsequently. There was no trend in weight gain of replacement females while confined to the unimproved hill area between weaning (14 weeks old) and first joining at 18 months of age. A negative trend (P < 0.01) occurred in the pre-weaning growth rate of lambs on the hill. The average number of lambs reared per ewe joined (reflecting fertility, litter size and ewe/lamb mortality) was 1.0, and this showed no evidence of change over time. The study flock performed 10% to > 60% better, depending on the variable, than similar flocks in the National Farm Survey at comparable stocking rates. A well-defined rational management system can sustain a productive sheep enterprise on unimproved hill land without negative consequences for the frequency or composition of the vegetation.