Ecological consequences of beaver activity at water-bodies in southern Karelia were assessed. Vegetation succession induced by beaver foraging and construction activity was studied; the effect of long-term forest flooding on invertebrate and small mammal fauna. Beaver foraging activity results in the loss of 23.2 to 92.1% of aspen, 3.0 to 26.5% of birch and nearly all willow from the riparian plant community. Beaver dam construction induces the formation of wetland communities of mixed categories, including Sphagnum communities getting overgrown with birch, sedge-Sphagnum, Sphagnum-cotton grass, and various dwarf shrub-Sphagnum communities dominated by one or another dwarf shrub species. Organic carbon and the total nitrogen content in the soils of former beaver ponds increases, whereas pH decreases (Sidorova and Fyodorov 2007). The abundance and species composition of invertebrate and small mammal fauna also change significantly within the drained pond area. The number of invertebrates at beaver ponds increases 2 – 2½ times. Expansion of the terrestrial invertebrate fauna goes along with increase in its species and age diversity. In some surveys, the abundance of small mammals dropped nearly 10 times – from 7.0 animals per trap-day in reference plots to 0.67 in abandoned beaver sites. In other surveys, the abundance of shrews and voles increased 2-2.5 times.

Keywords: Beaver activities, changes of riparian ecosystems, forest vegetation, community, small mammals, invertebrates, plant.