Observations on bark-stripping by red deer in a Picea sitchensis forest in western Scotland over a 35-year period

The impact of bark-stripping by red deer on an 1825 ha plantation of Picea sitchensis is reported. Monitoring began in 1978 with initially 6500 trees at 37 sites; by 2014 only 10 sites remained due to felling. Sites became vulnerable to bark-stripping once the trees reached 7 years age, and from then until felling at age c. 45 years incidence rates averaged 1% of the trees damaged yearly. Intense damage at a site in a year (> 2% trees damaged) was often followed by intense damage next year, but on average 53% of sites were undamaged in a year. Many trees suffered repeat wounding, which reduced final impact by c. 30% compared to the theoretical impact calculated from annual damage and damage duration. The trees bark-stripped were on average smaller than plot mean girths once these means exceeded 20 cm; this had only minor effect on final impact since bark-stripped small trees had similar mortality to undamaged small trees. Most wounds (> 90%) were small (< 180 cm2) and healed quickly, so were unlikely to develop decay. Larger wounds never healed in less than 8 years, but the proportion healed increased progressively from 10 to 20 years after wounding.