Impact of browsing ungulates on plant cover and tree regeneration in windthrow areas

Wild ungulates are often considered a threat to natural forest regeneration in windthrow areas. We studied their impact on developing vegetation in windthrow clearings on the northern side of the Swiss Alps. Fifty pairs of exclosure and control plots were established seven years after the windthrow and the composition and percentage of vegetation cover recorded. At that time, vegetation cover, including regeneration of woody species, did not differ on the two types of plots. Three years later, total cover had increased by about 40% in both types of plots. Thus, browsing ungulates did not slow down the growth of plant cover. The ungulates had only mild effects on the development of some plant groups: tall forbs, such as <I>Epilobium angustifolium</I>, which ungulates prefer, were fewer in the unfenced control plots than in exclosures, although the frequency of the other favourite species like <I>Vaccinium myrtillus</I> were not influenced by ungulates. The numbers of seedlings and saplings of woody species had increased four-fold on both types of plots by the end of the study. Thus, browsing ungulates affected neither the development nor the survival of woody species. Only <I>Sorbus aucuparia</I>, a species that ungulates prefer, was 30% higher in the exclosures. Other preferred species, such as <I>Acer pseudoplatanus</I>, were not affected by browsing. Although ungulates are able to modify forest ecosystems and may significantly reduce vegetation on forest floors, in the windthrow areas the rapidly increasing plant biomass seemed to exceed their consumption needs and browsing capacity. The ungulates had access to more than ample food and could select the best. Therefore, our results provide no evidence that browsing ungulates threaten the natural regeneration of forest stands in windthrow gaps.