Intensity of red deer browsing on young rowans differs between freshly-felled and standing individuals

Abstract

Because red deer (Cervus elaphus) forage extensively on woody plants, browsing is a serious problem in forest stands especially in initial growth stages. In Slovakia, rowans (Sorbus aucuparia) are the most attractive tree species for red deer, and when present, they may serve to divert the attention of foraging red deer from commercial forest stands. In this study we compared the extent of herbivory by red deer on standing and freshly-felled rowans within a mixed conifer forest. We quantified the biomass of stem bark, branch bark and whole branches consumed by red deer on 60 rowans between 200 and 600 cm tall within young stands that regenerated after a large scale windstorm in the Tatra National Park, Northern Slovakia. We calculated the dry biomass of browsed branches using allometric relationships with branch diameter and browsed bark biomass from the product of the area of consumed bark and specific surface mass of bark. We found that the extent and intensity of browsing was much higher on felled than standing rowans. The number of patches of stripped bark on stems was twice as high (12 ± 6 bites/stem) on felled than on standing trees (6 ± 2 bites/stem). Similarly, red deer consumed more total biomass (i.e., bark stripping on both stem and branches and browsed whole branches) from felled (45 ± 41 g) than standing (28 ± 22 g) rowans. Red deer consumed more mass from stem bark than branches. Total browsed mass on trees (especially on felled ones) increased with their height. Based on our findings, we recommend cutting rowans after most trees exceed 500 cm in height and leaving them in the site. However, if rowans have been intensively damaged by browsing and the forage potential of the stem bark and branches is reduced, trees can be felled before they reach 500 cm. We concluded that cut timing and after-cut arrangement of rowans, and likely other non-commercial tree species attractive to red deer, may substantially mitigate red deer browsing on commercial tree species in young stands.