SELECTIVE FORAGING ON WOODY SPECIES BY THE BEAVER CASTOR FIBER, AND ITS IMPACT ON A RIPARIAN WILLOW FOREST

Beavers were re-introduced in the Biesbosch, The Netherlands, a wood dominated by willows Salix spp. Conservationists expected that herbivory by beavers would enhance succession to a mixed broad-leaved forest. Willows formed the staple food of the beavers, but they removed only 1.4% of the standing crop. rn the future, this might increase to 5%, which is roughly one-third of the regrowth of these willows. Non-willow species such as Alnus, Corylus, Fraxinus, Populus and Prunus were very uncommon in the Biesbosch, but they were positively selected by beavers away fr om the den and - in one year - away from the water. Beavers were possibly selecting complementary nutrients, choosing Corylus and Fraxinus for Na, and Prunus and Populus for p. Alternatively, they may have been eating a mixed diet as a strategy to avoid dietary deficiencies of whatever type. We conclude that the beavers will not enhance the succession to a more mixed forest, because they selectively remove non-willow tree species. In any case, we doubt whether such a succession would take place without restoration of a more natural water regime