The beaver: an ecosystem engineer
provide structural shelter for organisms that require it.
Sediments settle to the bottom of this still water. Years after the beaver vacate the pond, the dam may break, draining an area of rich soil that gives rise to a meadow, usually consisting of different vegetation than surrounding areas.
Beavers also dig canals, which can extend hundreds of metres into surrounding forest. These allow the beaver to float cut wood to the safety of the pond.
Now let's consider some of the particular wildlife species that are affected by beaver activity.
Beaver ponds are the principle breeding ground of pileated woodpeckers (Dryocopus pileatus), which excavate large holes in the standing dead tress. Wood ducks (Aix sponsa) are also particularly attracted to these sites, as are many waterfowl. Canada geese (Branta canadensis) will nest on abandoned beaver lodges. Other birds attracted to beaver ponds include herons, kingfishers, swallows and nuthatches. Ospreys (Pandion haliaetus) favour the dead tops of trees in beaver ponds for their nest sites.
Certain reptiles are attracted to beaver ponds. Turtles like slow-moving water, use floating logs for sun-basking, and hibernate under logs and lodges. Some lizard and snake species prefer the early successional woodland species associated with beaver, however some woodland snakes that prefer cool, moist, late-successional forests are negatively impacted by beaver activity.
The ponds create an environment favourable for most species of frogs, as well as the red-spotted newt (Notophthalmus viridescens). Salamanders, however, are more likely to be found near streams without beaver impoundments.
Beaver activity dramatically influences the populations of invertebrates in streams. Fast-moving streams are dominated by lotic insect larvae including blackflies, caddisflies, mayflies and stoneflies. After beaver dam a river, these invertebrates are replaced by lentic (slow-water) species: leeches, dragonflies, mussels, tube worms, aquatic beetles and large aquatic bugs. However on slow-moving rivers dominated by continuous stretches of beaver impoundments, the dams themselves may provide the only fast-moving water for lotic organisms like blackfly larvae.
These relationships demonstrate the key role beaver play in aquatic ecosystems and adjoining forests. By altering water movement and woodland structure, they create wetlands, enhancing the diversity of plants and wildlife and providing habitats for endangered species. In this role they are more influential than many other species.
For more information:
Beaver Ecology (PDF) from New Jersey School of Conservation
Beavers: Wetlands and Wildlife
Ecology of the Beaver from Ecology.Info