The Influence of Wild Ungulates on Forest Regeneration in an Alpine National Park

Browsing of wild ungulates can have profound effects on the structure and composition of forests. In the Swiss National Park, the density of wild ungulates including red deer (Cervus elaphus), ibex (Capra ibex), and chamois (Rupicapra rupicapra) is exceptionally high due to strict protection and the absence of large predators. We examined count data of larch (Larix decidua), cembra pine (Pinus cembra), spruce (Picea abies), upright mountain pine (Pinus mugo subsp. uncinata), and mountain ash (Sorbus aucuparia) of four sampling years between 1991 and 2021 and modelled how different topographic and location factors affected the probability of browsing on saplings of larch, cembra pine, and spruce. Despite the high density of wild ungulates, the numbers of saplings and young trees increased over the past 30 years. The probability of browsing on saplings was highest for larch at a height of 10 - 40 cm and increased with increasing elevation. In our study area, open grasslands are mainly located above the tree line, which might explain the positive correlation between elevation and the probability of browsing. Other factors like exposition and slope, available food resources and disturbance by humans did not have clear effects on the probability of browsing.

Automated summary

Browsing by wild ungulates has significant effects on forest structure and composition. In the Swiss National Park, the high density of red deer, ibex, and chamois is attributed to strict protection and absence of large predators. Analysis of count data from 1991 to 2021 reveals an increase in saplings and young trees despite the presence of wild ungulates. Browsing probability is highest for larch saplings at a height of 10-40 cm and increases with elevation.