Browsing by deer on naturally regenerating Scots pine ( Pinus sylvestris L.) and its effects on sapling growth

Abstract

Browsing by deer has been identified as an important factor in preventing the regeneration of Scots pine ( Pinus sylvestris) woodland. In this 4-year study, we monitored use by red deer ( Cervus elaphus) and roe deer ( Capreolus capreolus) and the incidence and severity of browsing to individual saplings across a range of Caledonian pinewood sites in the Highlands of Scotland and related sapling growth to browsing history and site characteristics. Browsing incidence during winter increased with use (as indexed by dung counts) by red deer, but not roe deer, and increased with sapling height and the apparency of the sapling. The form of these relationships was influenced by the characteristics of the ground vegetation. In contrast, browsing during summer increased with use by roe deer, but not red deer, and was most frequent on saplings of around 1 m tall. In both winter and summer, saplings showing a history of previous browsing were more likely to be browsed, than saplings of the same height with little or no browsing history. The length of the leading shoot varied with aspect, soil type and the sapling’s height. Annual variation in shoot length was considerably greater than variation between sites. Saplings with a history of previous browsing showed some degree of compensatory growth, with an increased leader length, but decreased basal diameter increment. The severity of browsing had a significant effect on leader length, but much less of an effect than browsing to the leader itself. The severity of browsing had very little effect on basal diameter increment. This study demonstrates the complexity of factors influencing the suppression of natural regeneration by deer, and we recommend combining further field studies with simulation modelling to allow predictions to be made of the conditions under which regeneration is likely to be successful in the presence of deer.