Grazing and mowing as management tools on dunes

Published source details Hewett D.G. (1985) Grazing and mowing as management tools on dunes. Vegetatio (now Plant Ecology), 441-447.
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Summary

This paper describes the first results of the effect of sheep grazing and mowing of coastal duneland vegetation as management techniques at a nature reserve on the island of Anglesey, North Wales. Aims of the experiments included the control of and achieving a decrease in, the frequency of false oat-grass Arrhenatherum elatius, a common and competitive tussock-forming species at the locality, and to reduce the height of the vegetation to encourage a more diverse plant community.

Study area: The experiments were undertaken at Newborough Warren NNR on the island of Anglesey, north-west Wales. Habitats include mobile marram Ammophila arenaria dunes through to dune slack. Well vegetated, stable grassland areas were experimentally managed by grazing or mowing.

Grazing experiment: The grazing experiment comprised 9.7 ha divided into two blocks, each of 16, 0.3 ha paddocks. There were two intensities of grazing: 1 or 2 sheep/paddock. The effect of grazing in different seasons was examined by dividing the year into thirds: January to April, May to August and September to December. There were also two ungrazed controls in each block. In each paddock 12, 2 x 2 m quadrats were systematically spaced. A record of all vascular plant species and visual estimates of cover were made during 1982.

Mowing experiment: Plots were mown to more-or-less ground level, either once (May), twice (May and July), three (May, July and September) or five times (May, June, July, August and September). Again vascular plant species and estimates of cover were made.

Overall trends: Analysis indicated the variability of the habitat, e.g. the blocks were somewhat different and thus the author urges that a cautious interpretation of results should be made. Despite this, some trends were apparent: the average numbers of plant species per plot, and bird’s-foot trefoil Lotus corniculatus increased under grazing or mowing; false oat-grass A.elatius declined. This suggests a desirable trend towards the increased presence of small herbs. Other species did not show clear-cut changes.

All the grazed treatments had higher average numbers of species than the ungrazed controls. There was little difference between time of year at the lower grazing levels except perhaps for those grazed from January to August. The largest average number of species was for plots grazed for two thirds of the year at the higher grazing level, especially grazed January to August and August to April. Those grazed for the whole year had values between the plots grazed for one third and two thirds of a year. It became clear that the highest grazing level was too heavy for optimum numbers of species.

Arrhenatherum declined in abundance in the most heavily grazed paddocks and mowing killed tussocks, but it still survived in the sward.

Conclusions and discussion: Both methods appear to provide practical means of maintaining a short turf on stable dune grassland, but there were indications that longer-term effects of mowing may not be beneficial to the vascular plant flora. Whilst grazing produced more subtle changes, the husbandry and control of livestock requires considerable expenditure in terms of manpower and fencing, which may limit its use.

Consideration of these management regimes on the vertebrate and invertebrate fauna is not reported, but the author acknowledges that there are some obvious effects which should be taken into consideration if contemplating such management.

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