Bark stripping damage by red deer in a Sitka spruce forest in Western Scotland. I. Incidence

Abstract

Bark stripping was monitored over a seven-year period on 240 permanent plots in Glenbranter Forest, Argyll. Sharp seasonal variation in incidence was found, rates being greatest in winter (December–March) and least in summer. There was very little damage in high-canopy ** forest (>44 years of age) or at the establishment stage (0–8 years). although 0.6 per cent y −1 of these younger trees were frayed. Trees aged 9–14, 15–28 and 29–44 years had mean rates of damage of 0.6, 1.0 and 0.5 per cent y −1 respectively. Norway spruce, only present in the pole and high-canopy stages, was more severely damaged than Sitka spruce. The incidence of bark stripping was patchy, the trees found damaged in the 3-month observation periods often being near neighbours. Over 2-year periods 74 per cent of the plots received no damage, but on 2 per cent of the plots >10 per cent of the trees were bark stripped. At such ‘hot-spots’ the intensity of damage was usually much lower in the preceding and following periods. However, individual trees suffered repeated bark stripping more often than would be expected by chance although the likelihood of repeated damage declined as time after the initial wounding increased. The trees damaged were quite variable in girth; their size was average on plots with mean girth of 20–40 cm, significantly bigger than average when mean girth was < 20 cm, and smaller than average above 40 cm mean girth. Rates of damage were not related to the number of red deer pellet groups deposited on 15×5 m plots; most dung occurred on vegetated plots yet bark stripping was commonest on plots without vegetation. But when plots within each forest stage were classified according to their position, most damage was found in the spatial zone with most dung (edge in thicket and high-canopy forest, interior in pre-thicket and polestage forest).