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The impact of sheep grazing on bilberry moorland - BD0102

Bilberry moorland is a nationally scarce vegetation type but little is known about the factors maintaining it or bringing about its development. Effects of livestock grazing on bilberry and its inter-relationships with other moorland dominants are poorly understood, and the herbivore densities that maintain or deplete bilberry stands are not quantified.

As a step towards obtaining this knowledge a grazing experiment was set up in the Ashop Valley in 1990 financed by the Joseph Nickerson Heather Improvement Trust (Welch 1993). Winter, summer and year-round sheep grazing were compared in their impact on the cover and height of bilberry at two nearby sites. One was dominated by bilberry, the other had scattered patches of heather but bilberry cover was still high (69%). At each site an exclosure was erected, sections of the fencing being movable so that protection could be alternated between winter-grazed and summer-grazed plots. The open plots received grazing from the sheep normally present around the sites, and amounts of usage were assessed by pellet-group counts.

After three years it has become obvious that blaeberry experiences a short April peak in usage when new growth appears, and also a marked autumn peak in usage at these sites. This was somewhat unexpected, but is possibly explained by the intermediate position of bilberry in the sheep's preference rankings. In summer the sheep prefer to graze grasses, but as these senesce they turn to dwarf shrubs; heather seems to be less attractive than bilberry and is used later in the winter once most of the bilberry shoots have been bitten.

It would therefore be useful to find out if this usage pattern occurs at other sites in the Peak District. Also bilberry declined in cover at both sites from summer 1990 to summer 1993, at one site being replaced by heather, so it would be very desirable to see if this is a permanent trend or a fluctuation brought about by weather sequences viz. late-spring frosts which appeared to damage bilberry in 1991, and mild winters in 1991-92 and 1992-93, which may have lessened grazing impact on heather, allowing it to spread at the expense of bilberry.
1 To compare the effects of year-round, summer and winter grazing on bilberry.

2 To assess whether bilberry is being replaced by heather at an existing site in the Ashop Valley in the North Peak ESA, and to record the levels of shoot utilisation experienced by the two species.

3 To judge the implications of this for the estimated tolerance levels of utilisation that are the basis of the present ESA policies on sheep stocking rates.

4 To provide estimates of tolerable stocking densities so that existing stands of bilberry can be conserved.

5 To show if the pattern of grazing experienced at the two Ashop Valley sites is more general.
Time-Scale and Cost
From: 1994

To: 1996

Cost: £9,000
Contractor / Funded Organisations
Natural Environment Research Council
Fields of Study
Environmental Stewardship