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Wetland Plants and Plant Communities of Minnesota and Wisconsin

VII. FLOODPLAIN FORESTS


Floodplain forests are wetlands dominated by mature, deciduous hardwood trees growing on alluvial soils associated with riverine systems. The soils are inundated during flood events, but are usually somewhat well-drained for much of the growing season (Shaw and Fredine 1971). The most characteristic feature of floodplains is the alluvial soil that is constantly being deposited in some locations and eroded away in others. Floodplain forests typically include the northern and southern wet- mesic hardwood forest associations described by Curtis (1971). Dominant hardwoods include silver maple, green ash, river birch, eastern cottonwood, American elm, and black willow. The herbaceous groundlayer is commonly composed of jewelweed and nettles. The shrub layer is typically sparse to lacking because of frequent flooding.

Floodplain forests have a great diversity of plant and animal species because they serve as migration corridors. Some of the many species of wildlife that inhabit floodplain forests are wood duck, barred owl, herons, egrets, and a variety of songbirds. Pools within the forest may provide habitat for amphibians and invertebrates, while adjoining areas of open sand may provide habitat for reptiles. During high water periods, these forests even provide habitat for fish.

Floodplain forests are extremely important for floodwater storage. Diking of floodplain forests to allow development or agricultural use can aggravate both upstream and downstream flooding impacts.

Floodplain forest in April
April
Floodplain forest in August
August
Two seasonal views of a floodplain forest at approximately the same location. The first photograph shows high water conditions during spring flooding; the second photograph shows low water levels during late summer.

VEGETATION: The floodplain forest shown by the two photographs is dominated by silver maple (Acer saccharinum) with a groundlayer dominated by wood nettle (Laportea canadensis) and honewort (Cryptotaenia canadensis). Also present are green ash (Fraxinus pennsylvanica), American elm (Ulmus americana), eastern cottonwood (Populus deltoides), riverbank grape (Vitis riparia), a sedge (Carex grayi), jewelweed (Impatiens capensis), stinging nettle (Urtica dioica), clearweed (Pilea pumila) and goldenglow (Rudbeckia laciniata).

SOILS: A complex composed of a Mollic Udifluvent (a young soil formed in alluvium) and Bremer silty clay loam (Typic Argiaquolls), a poorly-drained soil also formed in alluvium. Bremer silty clay loam occupies slightly higher elevations (one to three feet in height) while the Mollic Udifluvent occupies drainageways and depressions. Landscape position is the floor of a deep valley within the Paleozoic Plateau of southeastern Minnesota.

HYDROLOGY: Adjacent to the Cannon River and inundated during spring flood events and heavy summer rainfall events.

LOCATION: Cannon River, Goodhue County, Minnesota.

SPECIES ACCOUNT:

Silver Maple (Acer saccharinum L.)
Green Ash (Fraxinus pennsylvanica Marsh.)
American Elm (Ulmus americana L.)
Black Willow (Salix nigra Marsh.)
Eastern Cottonwood (Populus deltoides Marsh.)
River Birch (Betula nigra L.)
Box Elder (Acer negundo L.)
River-bank Grape (Vitis riparia Michx.)
Stinging Nettle (Urtica dioica L.)
Cardinal Flower (Lobelia cardinalis L.)


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