During 8 years the changes of diversity and composition of herbaceous species in fenced and unfenced plots were studied in order to evaluate the impact of ungulate herbivory on the ground vegetation. In 1990 pairs of fenced and unfenced plots were established in newly thinned beech and mixed beech-oak forests in the Forest District of the city of Lübeck (Northern Germany). Relevés according to the method of Braun-Blanquet were conducted in 1990 to 1992, 1996 and 1997. Roe deer (Capreolus capreolus) is clearly the most abundant ungulate in the study area. Results of the reaction of woody plants in the experiment are presented by Kriebitzsch et al. (2000). Total number of species, mean species richness (Tab. 1) and mean species diversity showed opposite trends with decreasing numbers inside and increasing numbers outside the exclosures. The number of immigrant species is significantly lower in protected plots compared with the unfenced ones (Tab. 2). Mean cover of herbaceous species decreased more rapidly inside than outside exclosures (Tab. 1). Exclusion of ungulates resulted in significantly decreasing graminoid richness and cover. In contrast, there were no significant differences between fenced and unfenced plots in the trend of species richness and cover of preferentially grazed species on the one hand and never or rarely grazed species on the other (Tab. 1 and 3). The study indicates that the given intensity of ungulate herbivory results in a greater species diversity of herbaceous plants as it is documented by the trends on unfenced plots. This may be especially due to a change in competition with tree regeneration, which generally increased in cover percentage inside the exclosures (Fig. 2). In future work the experimental design should allow for a more powerfull separation of main factors influencing the diversity and composition of vascular plants in forests such as light, nutrients and moisture.