Herbivores are constitutive elements of most terrestrial ecosystems. Understanding effects of herbivory on ecosystem dynamics is thus a major, albeit challenging task in community ecology. Effects of mammals on plant communities are typically explored by comparing plant densities or diversity in exclosure experiments. This might over-estimate long-term herbivore effects at community levels as early life stage mortality is driven by a multitude of factors. Addressing these challenges, we established a set of 100 pairs of ungulate exclosures and unfenced control plots (25 m²) in mixed montane forests in the Alps in 1989 covering a forest area of 90 km². Investigations ran until 2013. Analogous to the gap-maker–gap-filler approach, dynamically recording the height of the largest trees per tree species in paired plots with and without exclosures might allow for assessing herbivore impacts on those individuals with a high probability of attaining reproductive stages. We thus tested if recording maximum heights of regenerating trees would better reflect effects of ungulate herbivory on long-term dynamics of tree regeneration than recording of stem density, and if species dominance patterns would shift over time. For quantifying the effects of ungulate herbivory simultaneously at community and species level we used principle response curves (PRC). PRCs yielded traceable results both at community and species level. Trajectories of maximum heights yielded significant results contrary to trajectories of total stem density. Response patterns of tree species were not uniform over time: e.g., both Norway spruce and European larch switched in their response to fencing. Fencing explained about 3% of the variance of maximum tree heights after nine years but increased to about 10% after 24 years thus confirming the importance of long-term surveys. Maximum height dynamics of tree species, addressed in our study, can thus reflect local dominance of tree species via asymmetric plant competition. Such effects, both within and among forest patches, can accrue over time shaping forest structure and composition.

Different species-specific traits of woody plant species, feeding preferences of herbivores together with resulting effects on plant competition are expected to translate into different plant community structures and expressions of biodiversity. We studied the diversity of woody plant species (trees and shrubs) and structural diversity of forest trees, using a 30-year and an 18-year dataset of ungulate exclosure-control plot pairs in a mixed alpine forest community in Austria. We surveyed the tallest individuals per tree species and plot and analyzed the collective of top-height individuals per plot pair. Incidence data for exclosure and control plots were aggregated. Comparing species diversity and diversity of height classes on the plots throughout time, we calculated diversity profiles based on Hill numbers. Diversity of top height individuals and structural diversity, expressed by height classes, were two diversity aspects that differed between exclosures and control plots. Other diversity estimates of woody plant species showed huge variation without significant differences between plots. Height growth was significantly suppressed by ungulate herbivory. Effects of ungulate herbivores in forest ecosystems are highly complex and context-dependent and thus not reducible to simple top-down forces. Long-term surveys provide data that reflect “ultimate” effects of herbivory interacting with other drivers of community dynamics.

Increasing numbers of wild ungulates in human-dominated landscapes in Europe could lead to negative effects, such as damages to forests through browsing. To prevent those effects and, thus, mitigate wildlife-based conflicts while ensuring viable ungulate populations, sustainable management is required. Roe deer, as the most abundant cervid species in Europe, is primarily managed via hunting to decrease population densities through harvesting. Besides direct mortality, non-lethal effects of hunting activities further affect the spatial habitat selection for this species. Accordingly, the spatial distribution of hunting locations might influence game impact on forest vegetation. To examine these relationships in more detail, we linked the spatial distribution of hunting locations for roe deer with forest damage through browsing in 20 regions in Upper Austria. Consistent with our hypothesis, an avoidance of forests by hunters was found in regions with <20% forest cover and intolerable browsing impact. When hunters in certain regions, however, used forests according to their availability, game impact on forest vegetation was tolerable. Although forest damage by ungulates depends on numerous factors, we conclude that careful consideration of hunting locations might be an additional approach to reduce browsing intensity by roe deer, at least in regions with low forest cover.

Ungulate populations and browsing intensities following the reintroduction of lynx in the canton of St. Gallen: In the context of the project “Lynx resettlement north-east Switzerland” (LUNO), the Eurasian lynx (Lynx lynx L.) was reintroduced in the canton of St. Gallen from 2001. As a consequence of reduced roe deer (Capreolus capreolus L.) and Alpine chamois (Rupicapra rupicapra L.) population sizes, one goal was the reduction of browsing intensities in young forest stands. This study investigates interactions between the levels of this trophic cascade by means of data on lynx distribution, roe deer and chamois populations (hunting statistics and population estimations) as well as browsing intensities. The results have shown significantly reduced roe deer and chamois population sizes in the years after lynx reintroduction. The effect of lynx could have worked cumulatively with factors like hunting, weather conditions and diseases (chamois). Within the chamois population, the lynx probably affected primarily the forest chamois, although before and after the lynx presence other causal reasons have been responsible for population decreases. Furthermore, there was noted a significantly positive relationship between hunting statistics (as an indicator of local ungulate population sizes) and browsing intensities, although the size of local ungulate populations was one influencing factor among many more. The browsing intensity of silver fir (Abies alba Mill.) was significantly reduced after lynx reintroduction in the core area of lynx distribution. All results have shown significant correlations and suggest an indirect influence of lynx on browsing intensities of silver fir. However, causal connections should be analysed in further studies.

Wild ungulates are important drivers of the dynamics of many terrestrial ecosystems and impact biodiversity at different system levels