Effect of microsites, logs and ungulate browsing on Picea abies regeneration in a mountain forest

Abstract

Browsing by ungulates is often reported as one of the major hazards for tree regeneration, e.g. in sites disturbed by windthrow and bark beetles. As tree regeneration in mountain forests is typically concentrated on suitable microsite types, the question arises how browsing is distributed in snag stands (e.g. in standing dead Norway spruce stands), i.e. if browsing is reduced or even impeded in some microsites. Furthermore, we wanted to determine whether logs could be considered as obstacles for ungulates, and thus whether they could protect tree regeneration. The distribution of Picea abies saplings and the impact of browsing were investigated in snag stands on the Gandberg in the Swiss Alps. The frequency of microsite types was assessed along 128 m× 10 m long lines on four elevational levels. Around these lines, in 2 m wide strip transects the height and shoot lengths of P. abies saplings were measured, and the microsite type on which they occurred was noted together with the distance to the next log, and damage due to browsing. Microsite types had a large influence on the abundance of P. abies saplings on the snag stands in the Gandberg mountain forests, i.e. the following microsite types had, in comparison to their occurrence, disproportionately many P. abies saplings: coarse woody debris, roots and boulders covered with mosses on the subalpine level, and on the montane level Polytrichum and Hylocomium cushions, and moss covered by Rubus idaeus. In contrast, sites with ferns, grasses and dense Rubus cover were poorly regenerated. Browsing was higher on the montane than on the subalpine level, regardless of the microsite types and the proximity of logs. Shrubs and logs did not reduce the browsing intensity. In contrast, more Picea saplings were browsed close or under logs than far away from logs on the montane level. Hence, logs cannot be considered as obstacles for chamois in these snag stands.