The influence of vegetation pattern on the grazing of heather moorland by red deer and sheep. II. The impact on heather.
Red deer (Cervus elaphus) and Scottish Blackface sheep were grazed in a series of 10-day periods in plots of heather (Calluna vulgaris) moorland having a 20% coverage of grass distributed in either 1, 4 or 12 patches. Heather utilization was recorded following each 10-day period in permanent quadrats established in three heather zones that varied in their distance from the grass/heather interface. Shoots were examined in 6 cm diameter wire rings at 200 positions in each zone in each plot. Rates of heather utilization varied seasonally, and during autumn utilization by sheep increased whilst that of deer remained constant. Utilization was significantly higher at 0-5 cm from the patch edge than further away, particularly in plots with only one large patch of grass, where the length of patch edge was shortest. When overall utilization of heather was assessed there was no significant difference between the plots of different patch-size treatments. Differences in utilization between patch-size treatments and zones did not exactly match patterns in locations of grazing animals observed during daylight hours, the associated errors for both measures being quite high. The observed differences in impact in relation to distance from the grass patches are used to build a simple model of heather utilization under different patch-size treatments.