Appendix 3 Manipulation of sheep grazing patterns on upland moors and the effects on vegetation




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Appendix 3


Manipulation of sheep grazing patterns on upland moors and the effects on vegetation
Project BD 1216.

Sixth BGS Research Conference, British Grassland Society, Reading

2000

Manipulation of sheep grazing patterns on upland moors and the effects on vegetation

S.L. HETHERINGTON

ADAS Pwllpeiran, Cwmystywth, Aberystwyth, Ceredigion SY23 4AB.

INTRODUCTION

The lower stocking rates associated with the introduction of ESA prescriptions for the management of semi-natural rough grazing has acted to maintain existing heather (Calluna vulgaris), but has not prevented localised over-grazing and concomitant under-grazing of less desirable species (ADAS, 1998). Species such as mat grass (Nardus stricta) are avoided by sheep when the grazing pressure is reduced (Armstrong & Milne, 1995), which may give these species a competitive advantage over dwarf shrub heath species such as heather. It is known that the pattern of sheep grazing can be modified during the summer months by the strategic use of feed blocks (Davies & Griffiths, 2000). However, sheep tend to graze heather and other dwarf shrubs during the autumn and winter (Welch, 1984) when more palatable grasses are not available to meet their metabolic requirements. The aim of this project is to determine whether feed blocks can be used to promote the establishment of a more balanced mosaic of dwarf shrub and grass-dominated vegetation on moorland.



METHODS

The study sites were located in the Cambrian Mountains ESA. Sites were selected on a basis that the farms possessed an ESA agreement that imposed stocking rates on an enclosed moorland management unit covered with mosaics of heather, mat grass and bilberry (Vaccinium myrtillus). Each site was grazed by Welsh Mountain ewes at stocking rates set by the ESA prescriptions designated to the individual sites.

Six 50 m diameter areas of mat grass-bilberry dominated vegetation were identified. On three of these, a feeding block was placed at the centre during April/May and October/November for a period of six weeks, and the remaining three had no feeding block. Within each area, baseline quantitative assessments were made of the occurrence of mat grass, bilberry, heather, purple moor-grass (Molinia caerulea) and other species in 4 m2 quadrats. The occurrence of bare ground, sheep droppings, vegetation height, and level of grazing on each of the named species was also quantified for each quadrat.

RESULTS

The mean frequency of key species in the 50 m2 experimental areas was very similar with no significant differences observed between feed block and non feed block sites when analysed with a split-plot ANOVA model. The presence of feed blocks (F+) led to a general increase in grazing on the key species sampled, particularly for graminoids, but only a significant increase in grazing frequency was observed for Nardus (Figure 1).

There was no relationship between the number of total cells grazed per quadrat and the distance of that quadrat from the feeding block (P>0.05). In areas where feed blocks were present, there was a significant decline in the occurrence of sheep dung with increasing distance from the feed block (P<0.05). For example, within 5 m of the feed block dung occurrence exceeded 60% of cells, where as 30 m away from the feed block this decreased to less than 13 %.
Fig. 1. The proportion of key species grazed in areas with (+F) and without feed blocks (-F).

In areas where feed blocks were present, analysis of the average height of mat grass in the sward following a summer of unmanipulated grazing showed that there was a significant relationship with distance from the central point (Table 1), However, in areas where feed blocks were absent there was no relationship.



Table 1. Summary statistics for the relationships between the distance from the centre in areas and the height of mat grass with and without feed blocks at their centre.




With feed blocks

Without feed blocks

r2

0.591

0.002

P

0.043

0.900

CONCLUSIONS

Although this project is on going, it is possible to conclude that:



  • The use of feed blocks can result in an increased intensity in grazing of unpalatable grasses resulting in a reduction in the biomass of these grasses above ground;

  • Associated with this increase in grazing there is an increase in nutrient supply to these areas, which could potentially affect future vegetation composition and grazing levels.

ACKNOWLEDGEMENTS

The author wishes to acknowledge the financial support of the Ministry of Agriculture, Fisheries and Food.



REFERENCES

ADAS. 1998 Effect of stocking rates and vegetation management practices on the regeneration of Calluna and dwarf shrub heath communities. Unpublished report to MAFF Countryside Management Division.

ARMSTRONG H.M. and MILNE J.A. (1995) The effects of grazing on vegetation species composition. In: Thompson D.B.A., Hester A.J.H., and Usher M.B. (eds) Heaths and Moorlands: Cultural Landscapes. Edinburgh: .HMSO.

DAVIES O.D. and GRIFFITHS J.B. (2000) The strategic use of feed blocks to manage sheep grazing in the uplands. In: Rook J.A. (ed) BGS Occassional Symposium No 34, 67-72.



WELCH D. (1984) Studies in the grazing of heather moorland in north-east Scotland. 1. Site descriptions and patterns of utilisation. Journal of Applied Ecology, 21, 179-195.


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