The European beaver (Castor fiber) is well known to cut down trees for food, a behavior driven by multiple preferences. These preferences were assessed at selected study sites in the Donau-Auen National Park. The distance to the nearest waterbody proved being the most important factor. The nearer a tree was to the water, the higher was the chance to be cut down by the beaver, thereby supporting the 'central-place-foraging' - theory. In addition, a selection for thicker trees and certain species

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... was shown. Populus sp. (poplar), Cornus sp. (dogwood) and Salix sp. (willow) were favored over other species. In addition, the influence of this selective foraging behavior on the riparian forest was investigated. No change in tree composition at the selected areas due to beavers browsing was detected. However, the composition of shrubs changed significantly. In the shrub layer species richness and density of shrubs was increased in areas with higher beaver-activity. The intensity of beaver feeding activity on trees was positively related to shrub density. Furthermore, it was experimentally tested if the beaver uses neophytes like Acer negundo (box elder), Ailanthus altissima (tree of heaven) and Robinia pseudoacacia (black locust) to show a possible interaction between beaver activity and their fast spreading. As predicted, the beaver avoided these new species, with A. negundo being the most commonly consumed among them. The beaver is an important keystone-species in the Donau-Auen National Park. Its presence enhances the biodiversity, but also supports invasive neophytes through the removal of native woody plants.