Leader Browsing by Red and Roe Deer on Young Sitka Spruce Trees in Western Scotland I. Damage Rates and the Influence of Habitat Factors

Abstract

Leader browsing was monitored for several years on some 2000 trees at 14 sites in Glenbranter Forest, Argyll. We recorded trees individually to obtain cumulative totals for browsing and other damage, and to relate incidence to height and state (i.e. whether the trees had single or multiple leaders, old or new leaders). Rates of leader browsing peaked in late winter and also for a few weeks during the spring flush of growth; they were least from mid June to September. Incidence was closely related to height, trees from 30 to 50 cm tall suffering the most damage, while trees taller than 80 cm rarely incurred leader browsing. Annual rates of leader browsing were greatest in the second and third year after planting but varied considerably among sites. Newly established crops were no more damaged than second-rotation restocked crops. Multiple regression showed that the incidence of leader browsing was significantly negatively related to the density of trees <60 cm tall and to percentage cover of ericoid plants, and significantly positively related to deer presence, as measured by the accumulation of pellet groups of both deer species. Individual trees were browsed two to three times on average before reaching a safe height, but a few trees experienced up to eight leader browsings. In recovery from browsing, trees often produced several leaders; we found that trees with multiple leaders or new leaders were more susceptible to leader browsing than trees with single or old leaders. So once a tree has been browsed the likelihood of future browsing is increased.