Tests of different methods for measuring and estimating utilization rate of heather (Calluna vulgaris) by vertebrate herbivores.
In a field study at a hill sheep farm in the Tweedsmuir hills of SE Scotland the precision of 4 methods for measuring utilization rate of C. vulgaris was examined to determine which was most suitable for assessing when given stands are at risk of damage from overbrowsing. The 1st method was a direct measure of utilization rate measuring the percentage of shoots browsed (the 2nd method) in combination with the average amount removed from each browsed shoot. The percentage of shoots browsed gave almost as precise a measure of utilization rate (accuracy ±10%) as a more complex measure (for utilization rates <40%). Utilization rate was 0.67 times the percentage of shoots browsed. Measuring the percentage of shoots browsed was an appropriate method of determining utilization rate by sheep on moorland. Two other, more subjective, methods were less accurate. Both were visual estimates, one of percentage of canopy cover closely browsed and the other of percentage of shoots browsed. The latter was quick and might be useful for preliminary surveys. The results are discussed in relation to their applicability to other sites. Previously used methods were assessed in relation to current findings.