The influence of vegetation pattern on the grazing of heather moorland by red deer and sheep. I. The location of animals on grass/heather mosaics.
A study site comprising six 2.5 ha plots of heather (Calluna vulgaris) moorland which could be viewed from afar was created in NE Scotland. Each plot contained 20% by area of Agrostis/Festuca grassland, distributed in either 1 large, 4 medium or 12 small patches. The plots were grazed by groups of sheep or red deer (Cervus elaphus) in series of 10-day periods; in each period the activities and locations of all individuals were recorded at 30 min intervals during daylight hours on several days. In one experiment in early summer sheep and deer were compared at equivalent stocking rates, and in a second experiment in late summer sheep were compared at two stocking rates. Sheep grazed for longer than deer (53% cf. 37% of daylight time), both species spending more time grazing in the late afternoon and evening than earlier in the day. Typical group size (groups being defined as animals within 30 m of others) was greater in sheep than in deer. Sheep were seen in smaller groups when the grass patch number increased, but in deer group size was unaffected by vegetational pattern. The distribution of grass patches significantly affected the grazing time spent on heather by sheep but not by deer. In plots with one large grass patch sheep foraged on heather for only 9% of their grazing time (cf. 40% for deer), but in plots with 12 small grass patches the proportions of grazing time spent on heather were 43% for sheep and 48% for deer. On the heather the densities of grazing sheep and deer were higher in a zone 0-5 m from the edge of grass patches than further away, and densities were higher at the edge of large patches than at the edge of small patches. It is concluded that a simple ratio of grass:heather in a moorland may not be a good predictor of heather utilization because increased fragmentation of the available grass encourages grazers, and sheep in particular, to graze heather more.