Abstract. A vegetation survey of semi-permanent plots was performed in 1977–1980 and in 1997–1998 to study the floristic changes in a mixed deciduous forest situated in a region of intensive livestock breeding. Our aim was to test the hypothesis of allogenic succession in the forest ground vegetation caused by the emissions of the surrounding agricultural activities. During the last 20 years, a significant increase of nitrogen indicators and a decline of moisture indicators were observed. Results were consistent at the community, the plot and the species level. Nitrogen deposition and the lowering of the groundwater table are suggested as the driving forces behind the changes. The results are discussed in the context of current ecological theory concerning resource competition and community diversity.