Anoka Ecosystems:
Willow Swamp
Unlike willows often seen growing thick along rivers and streams in sand, this willow community grows on peat and muck soils in moist depressions. Willow swamps are seasonally flooded and may consist of a mixture of wetland trees, shrubs and emergent vegetation, especially sedges.
In terms of species composition, willow swamps are actually much closer to wet meadows and wet prairies than to alder swamps. A variety of willows dominate this community including Bebbs willow, pussy willow, and slender willow. Also, autumn willow and shining willow are species of willow which can be found exclusively in willow swamps. Some beneficial wildlife shrubs exist here as well including speckled alder, bog birch, red-osier dogwood and poison sumac. Quaking aspen and paper birch are also sometimes found in willow swamps, but never more than 30% of the canopy. The understory is much like wet meadows, having blue-joint, lake sedge and tussock sedge, as well as ground covers such as northern marsh fern and spotted touch-me-not.
Historically, these ecosystems were common along the flatter areas of the Anoka sandplain, but most of these areas have been drained and converted for agricultural use during the drought of the 1930's. Today, undisturbed willow swamps are very uncommon, but disturbed willow swamps are gradually becoming more common. For example, many willow swamps have invaded wet prairies and wet meadows as natural fires have been suppressed. Other willow swamps have developed following the abandonment of croplands which had previously been wetlands. These are called disturbed, though, and are not true willow swamps as the understory lacks the native plants and often has a continuous cover of the aggressive invasive species reed canary-grass.
Sources:
"Minnesota's Native Vegetation: A Key to Natural Communities"
Version 1.5 Minnesota Department of Natural Resources, Natural Heritage
Program, 1993.
Wovcha, D., B. Delaney, and G. Nordquist. Minnesota's St. Croix Valley and Anoka Sandplain: A Guide to Native Habitats. MInneapolis: University of Minnesota Press, 1995.
