Riverbottom forests grow along the edges of rivers and streams. They depend on the spring floods to deposit silt and replenish the soil with nutrients. In return, their roots stabilize stream and riverbanks, helping to reduce erosion. Riverbottom forests are very diverse habitats with a large number of plant species. This makes them attractive to many different wildlife species as they provide a variety of food and shelter, and are close to water. Habitats located along waterways are also called riparian habitats: riverbottom forest is one type of riparian habitat.
Riverbottom forests can generally be divided into three sections: the channel shelf or riverbank, the floodplain, and the terrace.
The riverbank is the gently sloping area right next to the edge of a river, stream or creek. This area of the riverbottom forest is dominated by trees such as willow and cottonwood. Few shrub species dominate in the riverbank area because of yearly flooding and damage from spring ice breakup. Instead, this part of the forest has more grasses and annual wildflowers.
Above the riverbank is the relatively flat floodplain. This part of the forest is usually dominated by trees such as green ash, basswood, American elm, and Manitoba maple. The greatest variety of species is usually found on the floodplain. Here the plant community is dominated by flood-tolerant perennial species. Common shrub species include: American hazelnut, beaked hazelnut, downy arrowwood, and chokecherry. Many flowers and grasses, as well as woody and non-woody vines also exist in the floodplain.
The terrace lies above the floodplain, on the highest elevation within the riverbottom forest, farthest from the river. As this area is not flooded as often, this part of the forest is dominated by plants which prefer a drier habitat such as bur oak. Many of the plants found in the floodplain may also grow on the terrace.
Although these three sections of riverbottom forest have distinct characteristics, it is usually difficult to tell where the boundaries are between them. Dutch Elm Disease has killed many of the American elm trees causing a shift in the dominant tree species from elm to green ash.