The effects of controlled sheep grazing on the dynamics of upland Agrostis-Festuca grassland

Published source details Hulme P.D., Pakeman R.J., Torvell L., Fisher J.M, & Gordon I.J. (1999) The effects of controlled sheep grazing on the dynamics of upland Agrostis-Festuca grassland. Journal of Applied Ecology, 36.
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Summary

Common bent Agrostis capillaris–sheeps fescue Festuca ovina-dominated communities are widespread in the uplands of Great Britain. They are agriculturally productive in terms of providing grazing for livestock, mostly sheep. However, little is known about how to manage this community for specific goals. Vegetation response was examined in this plant community to different sheep grazing management regimes at two sites in Scotland. One site had a substantial presence of moorland species, the other was characterized by a more productive vegetation. Management consisted of maintaining sward heights of 3, 4.5 or 6 cm during the growing season, or complete exclusion of grazing stock. The experiment was duplicated at two sites to represent different parts of the spectrum covered by this vegetation community.

Study sites: The study was undertaken at two Scottish sites:

Cleish - located at 240–250 m on the Cleish Hills of Fife (National Grid Reference NT080936; 56°08'N 3°29'W), on a freely drained brown earth soil. The site had previously been used in grazing studies during which it had been managed by grazing cattle and sheep at moderate, characteristic levels (20–35%).

Kirkton - located at 410–445 m on the Scottish Agricultural College's Kirkton Farm near Crianlarich, Perthshire (NGR NN360310; 56°27'N 4°39'W), on a podsolic gley with a patchy, peaty top and frequent protruding boulders. Prior to 1989, the site had been grazed by sheep for short periods equivalent to a year-round stocking rate of 0.7 ewes/ha.

At each site, six plots of 0.3 ha, in two blocks of three plots, were fenced. In order to describe the effects of no grazing, two 5 × 5 m exclosure cages were sited in each plot to prevent livestock grazing. The grazing treatments commenced at Cleish on 2 August 1989, and at Kirkton on 11 May 1990. Thus differences between the vegetation recorded in 1989 and that in 1990 reflect only a part of a year's treatment. Herbage mass was also assessed but, due to difficulties assessing where litter and shoot material graded into soil or root material, respectively, estimates were highly variable between years and observers. This measure was therefore not considered further.

Treatments: Three treatments were imposed randomly within each block (i.e. sward heights maintained between 3–3.5 cm, 4.5–5 cm and 6–6.5 cm). This was achieved by stocking plots with predominantly Scottish Blackface wether sheep during the growing season (May–October). Treatment heights were maintained by approximately weekly measurements of sward surface height and adjusting animal numbers as necessary. Forty random measurements of sward surface height were taken per plot using a HFRO sward stick.

Vegetation: Floristic composition was recorded annually in June from 1989 to 1995, except in 1994. The Cleish site was recorded during the first 2 weeks of June, and at Kirkton in the following two weeks. Floristic composition was estimated by recording contact with an inclined point quadrat. Twenty quadrat positions were sited in a grid pattern at regular intervals along four or five transects (depending on plot shape). The data used in all analyses were percentage ground cover of each species.

Changes in plant species composition were small over the 7 years duration of the experiment, with few species colonising or lost. Changes were largely as a result of shifts in abundance of the dominant species.

Maintenance of a shorter sward height (3-3.5 or 4.5-5 cm) during the growing season resulted in spread of matgrass Nardus stricta where present. Where matgrass was absent, the sward developed a higher content of the mosses Hypnum jutlandicum and Rhytidiadelphus squarrosus.

Removal of sheep grazing resulted in an increase of cover of grazing-intolerant species, such as wavy hair-grass Deschampsia flexuosa and purple moor-grass Molinia caerulea, and in the cover of dwarf shrub species e.g. heather Calluna vulgaris, where present.

The two sites differed in the treatment that resulted in the smallest change in species composition. At the more productive site (Cleish), maintenance of the sward at 4.5 cm resulted in the smallest overall change in species composition. At the less productive site (Kirton), grazing the sward to 6 cm resulted in the smallest shift in vegetation composition. Grazing at this height appeared to prevent the spread of both purple moor-grass and matgrass.

Conclusions: This Scottish study demonstrates that sustainable sheep grazing regimes for upland Agrostis–Festuca grasslands in the region need to take into account both initial vegetation composition, specifically the presence of species capable of replacing A. capillaris and F.ovina and of achieving dominance, and the overall productivity of the site.

Note: If using or referring to this published study, please read and quote the original paper. The original paper can be viewed at:http://www.blackwell-synergy.com/doi/full/10.1046/j.1365-2664.1999.00452.x