The goal of this study was to evaluate to what extent wild ungulates (fallow deer) can contribute to the maintenance of semi-natural calcareous grasslands, which are a threatened habitat type (natura 2000 code *6210). In a ten-year exclosure experiment we tested the effects of ungulate foraging using three treatments: (A) control with combined foraging of herded sheep and wild fallow deer, (B) sheep exclosure with only deer foraging and (C) total exclosure with no foraging. Treatments not grazed by sheep (B, C) were characterized by significantly declining species numbers, litter accumulation and shrub encroachment. Despite high population densities, the effect of fallow deer alone (B) was weak: Succession of woody species was only partly inhibited, while annuals, short-growing and rosette-building plant species were strongly suppressed by litter accumulation. Only the combination of sheep and fallow deer foraging preserved vegetation structure and species richness and led to a promotion of target species. Synthesis and applications: We conclude that we need to continue the traditional land-use forms such as sheep grazing in order to maintain calcareous grasslands. However, we should also raise our awareness for wild animals and analyse more in depth their potential contribution to the conservation management of open habitats.

In 2011, an exclosure experiment was set up at ten different sites throughout a former quarry area. It comprised the following treatments: A) a control without exclusion of animals, which was regularly grazed by herded sheep and wild fallow deer as described above. B) a sheep exclosure, which was only temporarily enclosed for up to five days during the sheep grazing in May/June by a wooden fence of about 1 m height, leading to full access for wild fallow dear all year round. C) a total exclosure excluding fallow deer and sheep by a fence of about 2 m height. Effects of other animals such as rabbits or hares can be disregarded since they are not abundant in the area and have access to all treatments. Within each of the 30 site by treatment combinations, a permanently marked 3 x 3 m plot for vegetation sampling was established.

Vegetation was sampled between mid-May and mid-June every two years since the setup of the experiment in 2011 until 2021. We recorded all vascular plants to species level and measured abundance by visual cover estimates following a modified Braun-Blanquet scale. We also visually estimated covers of litter, stones and open soil as well as covers of vegetation in general, woody species, Poaceae, Cyperaceae, Fabaceae, other herbs and bryophytes. By measuring at several parts of the plot we recorded the average vegetation height, maximum vegetation height and maximum height of woody species. Green biomass and litter were sampled only in 2017, 2019 and 2021 within five frames of 0.1 m² per plot. The samples were dried at 70° for 24 hours before weighing.

In order to examine changes in species composition between the treatments, we extracted the following plant functional traits from the LEDA-Traitbase, an internet database of life-history traits of the Northwest European flora (Kleyer et al., 2008): leaf distribution, life-form, life cycle, age of first flowering, seed mass and seed bank type and, additionally, plant strategy types after Grime et al. (2007). For each of these traits we calculated cover weighted means for each plot.