The goal of this study was to investigate whether or not beavers Castor fiber albicus improve the quality of their food plants by dam construction, resulting in periodic flooding associated with the deposition of mud and nutrients on their feeding grounds. For this, food selection of beavers was studied in relation to plant chemicals in the Spessart mountains (central Germany). The concentrations of the preferred plant chemicals were compared between individuals of the same plant species growing in areas that were flooded periodically and areas that were edaphically dry. Plants eaten by beavers contained higher concentrations of nitrogen and lower concentrations of neutral detergent fibre and hemicellulose than neighbouring plants that were not eaten. Neither nitrogen concentrations nor neutral detergent fibre contents differed significantly between plants from the dry and wet sites. Thus, beaver activities did not improve the chemical quality of their food plants.