The early effects of excluding sheep from high-level grasslands in the north Pennines.
The effects of exclosure for 7 years on the botanical composition of 3 high-altitude Pennine grasslands were assessed by using vertical-pomi-quadrat analysis and measuring herbage yield. One site, Knock Fell, at 2450 ft alt., was on limestone soil and carried Agrosto-Festucetum rich in species ; the other 2 sites, Little Dun Fell at 2750 ft alt. and Hard Hill at 2250 ft alt., were on more acidic soils with Festuceta poor in species. At all sites, bryophytes, lichens and flowering plants other than grasses decreased in the absence of grazing. Nardus stricta and Juncus squarrosus, which are unpalatable to sheep, also declined markedly, but Deschampsia flexuosa increased notably. The number of species fell most (83-67 spp.) on Knock Fell, but the frequencies of Agrostis tenuis[Agrostis capillaris], D. cespitosa, Festuca rubra and Achillea millefolium increased. The standing crops after 7 years and after 1 season of exclosure were compared by harvesting with hand shears in Aug. The difference was least at Little Dun Fell, where it was only 18 g DM/m2. Hard Hill was intermediate. On Knock Fell the 7-year crop was 218 g/m2 whereas the 1-season crop was 123 g/m2. This increase was produced mainly by fine-leaved grasses. A further cut at soil-level showed that the layer of stubble and litter was greater after 7 years of exclosure than in the grazed sward. The largest increase was on Little Dun Fell, where the slowest rate of decomposition would be expected. The effect of exclosure on the rare species of Pennine grasslands depends on their position in the succession; some can exist only where grazing restricts their potential competitors, whereas others may be excluded by grazing. F. s.-R.B.